3 g lte long term evolution tutorial

3G LTE Long Term Evolution Tutorial & Basics- developed by 3GPP, LTE, Long Term Evolution is the successor to 3G UMTS and HSPA providing much higher data download speeds and setting the foundations for 4G LTE Advanced. Discover more about LTE basics in this tutorial.

IN THIS SECTION

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

LTE, Long Term Evolution, the successor to UMTS and HSPA is now being deployed and is the way forwards for high speed cellular services.

In its first forms it is a 3G or as some would call it a 3.99G technology, but with further additions the technology can be migrated to a full 4G standard and here it is known as LTE Advanced.

There has been a rapid increase in the use of data carried by cellular services, and this increase will only become larger in what has been termed the "data explosion". To cater for this and the increased demands for increased data transmission speeds and lower latency, further development of cellular technology have been required.

The UMTS cellular technology upgrade has been dubbed LTE - Long Term Evolution. The idea is that 3G LTE will enable much higher speeds to be achieved along with much lower packet latency (a growing requirement for many services these days), and that 3GPP LTE will enable cellular communications services to move forward to meet the needs for cellular technology to 2017 and well beyond.

Many operators have not yet upgraded their basic 3G networks, and 3GPP LTE is seen as the next logical step for many operators, who will leapfrog straight from basic 3G straight to LTE as this will avoid providing several stages of upgrade. The use of LTE will also provide the data capabilities that will be required for many years and until the full launch of the full 4G standards known as LTE Advanced.

3G LTE evolutionAlthough there are major step changes between LTE and its 3G predecessors, it is nevertheless looked upon as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different form of radio interface, using OFDMA / SC-FDMA instead of CDMA, there are many similarities with the earlier forms of 3G architecture and there is scope for much re-use.

In determining what is LTE and how does it differ from other cellular systems, a quick look at the specifications for the system can provide many answers. LTE can be seen for provide a further evolution of functionality, increased speeds and general improved performance.

WCDMA(UMTS)

HSPAHSDPA / HSUPA

HSPA+ LTE

Max downlink speedbps

384 k 14 M 28 M 100M

Max uplink speedbps

128 k 5.7 M 11 M 50 M

Latencyround trip time

150 ms 100 ms 50ms (max) ~10 ms

WCDMA(UMTS)

HSPAHSDPA / HSUPA

HSPA+ LTE

approx

3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8

Approx years of initial roll out 2003 / 4 2005 / 6 HSDPA2007 / 8 HSUPA

2008 / 9 2009 / 10

Access methodology CDMA CDMA CDMA OFDMA / SC-FDMA

In addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. Originally there was also no basic provision for voice, although Voice over LTE, VoLTE was added was chosen by GSMA as the standard for this. In the interim, techniques including circuit switched fallback, CSFB are expected to be used

LTE basics:- specification overviewIt is worth summarizing the key parameters of the 3G LTE specification. In view of the fact that there are a number of differences between the operation of the uplink and downlink, these naturally differ in the performance they can offer.

LTE BASIC SPECIFICATIONS

PARAMETER DETAILS

Peak downlink speed64QAM(Mbps)

100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO)

Peak uplink speeds(Mbps)

50 (QPSK), 57 (16QAM), 86 (64QAM)

Data type All packet switched data (voice and data). No circuit switched.

Channel bandwidths(MHz)

1.4,   3,   5,   10,   15,   20

Duplex schemes FDD and TDD

Mobility 0 - 15 km/h (optimised),15 - 120 km/h (high performance)

Latency Idle to active less than 100msSmall packets ~10 ms

LTE BASIC SPECIFICATIONS

PARAMETER DETAILS

Spectral efficiency Downlink:   3 - 4 times Rel 6 HSDPAUplink:   2 -3 x Rel 6 HSUPA

Access schemes OFDMA (Downlink)SC-FDMA (Uplink)

Modulation types supported QPSK,   16QAM,   64QAM (Uplink and downlink)

These highlight specifications give an overall view of the performance that LTE will offer. It meets the requirements of industry for high data download speeds as well as reduced latency - a factor important for many applications from VoIP to gaming and interactive use of data. It also provides significant improvements in the use of the available spectrum.

Main LTE technologiesLTE has introduced a number of new technologies when compared to the previous cellular systems. They enable LTE to be able to operate more efficiently with respect to the use of spectrum, and also to provide the much higher data rates that are being required.

OFDM (Orthogonal Frequency Division Multiplex):   OFDM technology has been incorporated into LTE because it enables high data bandwidths to be transmitted efficiently while still providing a high degree of resilience to reflections and interference. The access schemes differ between the uplink and downlink: OFDMA (Orthogonal Frequency Division Multiple Access is used in the downlink; while SC-FDMA(Single Carrier - Frequency Division Multiple Access) is used in the uplink. SC-FDMA is used in view of the fact that its peak to average power ratio is small and the more constant power enables high RF power amplifier efficiency in the mobile handsets - an important factor for battery power equipment. Read more about LTE OFDM / OFDMA / SCFMDA

MIMO (Multiple Input Multiple Output):   One of the main problems that previous telecommunications systems has encountered is that of multiple signals arising from the many reflections that are encountered. By using MIMO, these additional signal paths can be used to advantage and are able to be used to increase the throughput.

When using MIMO, it is necessary to use multiple antennas to enable the different paths to be distinguished. Accordingly schemes using 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used. While it is relatively easy to add further antennas to a base station, the same is not true of mobile handsets, where the dimensions of the user equipment limit the number of antennas which should be place at least a half wavelength apart. Read more about LTE MIMO

SAE (System Architecture Evolution):   With the very high data rate and low latency requirements for 3G LTE, it is necessary to evolve the system architecture to enable the improved performance to be achieved. One change is that a number of the functions previously handled by the core network have been transferred out to the periphery. Essentially this provides a much "flatter" form of network architecture. In this way latency times can be reduced and data can be routed more directly to its destination. Read more about LTE SAE

A fuller description of what LTE is and the how the associated technologies work is all addressed in much greater detail in the following pages of this tutorial.

LTE OFDM, OFDMA SC-FDMA & Modulation- LTE, Long term Evolution uses the modulation format, OFDM - orthogonal frequency division multiplex, adapted to provide a mulple access scheme using OFDMA and SC-FDMA.

LTE TUTORIAL INCLUDES

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

One of the key elements of LTE is the use of OFDM, Orthogonal Frequency Division Multiplex, as the signal bearer and the associated access schemes, OFDMA (Orthogonal Frequency Division Multiplex) and SC-FDMA (Single Frequency Division Multiple Access).

OFDM is used in a number of other of systems from WLAN, WiMAX to broadcast technologies including DVB and DAB. OFDM has many advantages including its robustness to multipath fading and interference. In addition to this, even though, it may appear to be a particularly complicated form of modulation, it lends itself to digital signal processing techniques.

In view of its advantages, the use of ODFM and the associated access technologies, OFDMA and SC-FDMA are natural choices for the new LTE cellular standard.

LTE modulation & OFDM basicsThe use of OFDM is a natural choice for LTE. While the basic concepts of OFDM are used, it has naturally been tailored to meet the exact requirements for LTE. However its use of multiple carrier each carrying a low data rate remains the same.

Note on OFDM:

Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced

carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other,

but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split

across all the carriers to give resilience against selective fading from multi-path effects..

Click on the link for an OFDM tutorial

The actual implementation of the technology will be different between the downlink (i.e. from base station to mobile) and the uplink (i.e. mobile to the base station) as a result of the different requirements between the two directions and the equipment at either end. However OFDM was chosen as the signal bearer format because it is very resilient to interference. Also in recent years a considerable level of experience has been gained in its use from the various forms of broadcasting that use it along with Wi-Fi and WiMAX. OFDM is also a modulation format that is very suitable for carrying high data rates - one of the key requirements for LTE.

In addition to this, OFDM can be used in both FDD and TDD formats. This becomes an additional advantage.

s

LTE channel bandwidths and characteristicsOne of the key parameters associated with the use of OFDM within LTE is the choice of bandwidth. The available bandwidth influences a variety of decisions including the number of carriers that can be accommodated in the OFDM signal and in turn this influences elements including the symbol length and so forth.

LTE defines a number of channel bandwidths. Obviously the greater the bandwidth, the greater the channel capacity.

The channel bandwidths that have been chosen for LTE are:

1. 1.4 MHz2. 3 MHz3. 5 MHz4. 10 MHz5. 15 MHz6. 20 MHz

In addition to this the subcarriers spacing is 15 kHz, i.e. the LTE subcarriers are spaced 15 kHz apart from each other. To maintain orthogonality, this gives a symbol rate of 1 / 15 kHz = of 66.7 µs.

Each subcarrier is able to carry data at a maximum rate of 15 ksps (kilosymbols per second). This gives a 20 MHz bandwidth system a raw symbol rate of 18 Msps. In turn this is able to provide a raw data rate of 108 Mbps as each symbol using 64QAM is able to represent six bits.

It may appear that these rates do not align with the headline figures given in the LTE specifications. The reason for this is that actual peak data rates are derived by first subtracting the coding and control overheads. Then there are gains arising from elements such as the spatial multiplexing, etc.

LTE OFDM cyclic prefix, CPOne of the primary reasons for using OFDM as a modulation format within LTE (and many other wireless systems for that matter) is its resilience to multipath delays and spread. However it is still necessary to implement methods of adding resilience to the system. This helps overcome the inter-symbol interference (ISI) that results from this.

In areas where inter-symbol interference is expected, it can be avoided by inserting a guard period into the timing at the beginning of each data symbol. It is then possible to copy a section from the end of the symbol to the beginning. This is known as the cyclic prefix, CP. The receiver can then sample the waveform at the optimum time and avoid any inter-symbol interference caused by reflections that are delayed by times up to the length of the cyclic prefix, CP.

The length of the cyclic prefix, CP is important. If it is not long enough then it will not counteract the multipath reflection delay spread. If it is too long, then it will reduce the data throughput capacity. For

LTE, the standard length of the cyclic prefix has been chosen to be 4.69 µs. This enables the system to accommodate path variations of up to 1.4 km. With the symbol length in LTE set to 66.7 µs.

The symbol length is defined by the fact that for OFDM systems the symbol length is equal to the reciprocal of the carrier spacing so that orthogonality is achieved. With a carrier spacing of 15 kHz, this gives the symbol length of 66.7 µs.

LTE OFDMA in the downlinkThe OFDM signal used in LTE comprises a maximum of 2048 different sub-carriers having a spacing of 15 kHz. Although it is mandatory for the mobiles to have capability to be able to receive all 2048 sub-carriers, not all need to be transmitted by the base station which only needs to be able to support the transmission of 72 sub-carriers. In this way all mobiles will be able to talk to any base station.

Within the OFDM signal it is possible to choose between three types of modulation for the LTE signal:

1. QPSK (= 4QAM)   2 bits per symbol2. 16QAM   4 bits per symbol3. 64QAM   6 bits per symbol

Note on QAM, Quadrature Amplitude Modualtion:

Quadrature amplitude modulation, QAM is widely sued for data transmission as it enables better elvels of spectral

efficiency than other forms of modulation. QAM uses two carriers on the same frequency shifted by 90° which are

modulated by two data streams - I or Inphase and Q - Quadrature elements.

The exact LTE modulation format is chosen depending upon the prevailing conditions. The lower forms of modulation, (QPSK) do not require such a large signal to noise ratio but are not able to send the data as fast. Only when there is a sufficient signal to noise ratio can the higher order modulation format be used.

Downlink carriers and resource blocksIn the downlink, the subcarriers are split into resource blocks. This enables the system to be able to compartmentalize the data across standard numbers of subcarriers.

Resource blocks comprise 12 subcarriers, regardless of the overall LTE signal bandwidth. They also cover one slot in the time frame. This means that different LTE signal bandwidths will have different numbers of resource blocks.

Channel bandwidth(MHz)

1.4 3 5 10 15 20

Number of resource blocks 6 15 25 50 75 100

LTE SC-FDMA in the uplinkFor the LTE uplink, a different concept is used for the access technique. Although still using a form of OFDMA technology, the implementation is called Single Carrier Frequency Division Multiple Access (SC-FDMA).

One of the key parameters that affects all mobiles is that of battery life. Even though battery performance is improving all the time, it is still necessary to ensure that the mobiles use as little battery power as possible. With the RF power amplifier that transmits the radio frequency signal via the antenna to the base station being the highest power item within the mobile, it is necessary that it operates in as efficient mode as possible. This can be significantly affected by the form of radio frequency modulation and signal format. Signals that have a high peak to average ratio and require linear amplification do not lend themselves to the use of efficient RF power amplifiers. As a result it is necessary to employ a mode of transmission that has as near a constant power level when operating. Unfortunately OFDM has a high peak to average ratio. While this is not a problem for the base station where power is not a particular problem, it is unacceptable for the mobile. As a result, LTE uses a modulation scheme known as SC-FDMA - Single Carrier Frequency Division Multiplex which is a hybrid format. This combines the low peak to average ratio offered by single-carrier systems with the multipath interference resilience and flexible subcarrier frequency allocation that OFDM provides.

By Ian Poole

LTE MIMO: Multiple Input Multiple Output Tutorial- MIMO is used within LTE to provide better signal performance and / or higher data rates by the use of the radio path reflections that exist.

IN THIS SECTION

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

MIMO, Multiple Input Multiple Output is another of the LTE major technology innovations used to improve the performance of the system. This technology provides LTE with the ability to further improve its data throughput and spectral efficiency above that obtained by the use of OFDM.

Although MIMO adds complexity to the system in terms of processing and the number of antennas required, it enables far high data rates to be achieved along with much improved spectral efficiency. As a result, MIMO has been included as an integral part of LTE.

LTE MIMO basicsThe basic concept of MIMO utilizes the multipath signal propagation that is present in all terrestrial communications. Rather than providing interference, these paths can be used to advantage.

General Outline of MIMO system

The transmitter and receiver have more than one antenna and using the processing power available at either end of the link, they are able to utilize the different paths that exist between the two entities to provide improvements in data rate of signal to noise.

Note on MIMO:

Two major limitations in communications channels can be multipath interference, and the data throughput limitations

as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a

transmitter and receiver to significantly improve the data throughput available on a given channel with its defined

bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal

processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby

increasing the data capacity of a channel.

Click on the link for a MIMO tutorial

MIMO is being used increasingly in many high data rate technologies including Wi-Fi and other wireless and cellular technologies to provide improved levels of efficiency. Essentially MIMO employs multiple antennas on the receiver and transmitter to utilise the multi-path effects that always exist to transmit additional data, rather than causing interference.

LTE MIMOThe use of MIMO technology has been introduced successively over the different releases of the LTE standards.

MIMO has been a cornerstone of the LTE standard, but initially, in releases 8 and 9 multiple transmit antennas on the UE was not supported because in the interested of power reduction, only a single RF power amplifier was assumed to be available.

It was in Rel. 10 that a number of new schemes were introduced. Closed loop spatial multiplexing for SU-MIMO as well as multiple antennas on the UE.

LTE MIMO modesThere are several ways in which MIMO is implemented in LTE. These vary according to the equipment used, the channel function and the equipment involved in the link.

Single antenna:   This is the form of wireless transmission used on most basic wireless links. A single data stream is transmitted on one antenna and received by one or more antennas. It may also be referred to as SISO: Single In Single Out or SIMO Single In Multiple Out dependent upon the antennas used. SIMO is also called receive diversity.

Transmit diversity:   This form of LTE MIMO scheme utilizes the transmission of the same information stream from multiple antennas. LTE supports two or four for this technique.. The information is coded differently using Space Frequency Block Codes. This mode provides an improvement in signal quality at reception and does not improve the data rate. Accordingly this form of LTE MIMO is used on the Common Channels as well as the Control and Broadcast channels.

Open loop spatial multiplexing:   This form of MIMO used within the LTE system involves sending two information streams which can be transmitted over two or more antennas. However there is no feedback from the UE although a TRI, Transmit Rank Indicator transmitted from the UE can be used by the base station to determine the number of spatial layers.

Close loop spatial multiplexing :   This form of LTE MIMO is similar to the open loop version, but as the name indicates it has feedback incorporated to close the loop. A PMI, Pre-coding Matrix Indicator is fed back from the UE to the base station. This enables the transmitter to pre-code the data to optimize the transmission and enable the receiver to more easily separate the different data streams.

Closed loop with pre-coding:   This is another form of LTE MIMO, but where a single code word is transmitted over a single spatial layer. This can be sued as a fall-back mode for closed loop spatial multiplexing and it may also be associated with beam forming as well.

Multi-User MIMO, MU-MIMO:   This form of LTE MIMO enables the system to target different spatial streams to different users.

Beam-forming:   This is the most complex of the MIMO modes and it is likely to use linear arrays that will enable the antenna to focus on a particular area. This will reduce interference, and increase capacity as the particular UE will have a beam formed in their particular direction. In this a single code word is transmitted over a single spatial layer. A dedicated reference signal is used for an additional port. The terminal estimates the channel quality from the common reference signals on the antennas.

There is a growing number of LTE frequency bands that are being designated as possibilities for use with LTE. Many of the LTE frequency bands are already in use for other cellular systems, whereas other LTE bands are new and being introduced as other users are re-allocated spectrum elsewhere.

FDD and TDD LTE frequency bandsFDD spectrum requires pair bands, one of the uplink and one for the downlink, and TDD requires a single band as uplink and downlink are on the same frequency but time separated . As a result, there are different LTE band allocations for TDD and FDD. In some cases these bands may overlap, and it is therefore feasible, although unlikely that both TDD and FDD transmissions could be present on a particular LTE frequency band.

The greater likelihood is that a single UE or mobile will need to detect whether a TDD or FDD transmission should be made on a given band. UEs that roam may encounter both types on the same band. They will therefore need to detect what type of transmission is being made on that particular LTE band in its current location.

The different LTE frequency allocations or LTE frequency bands are allocated numbers. Currently the LTE bands between 1 & 22 are for paired spectrum, i.e. FDD, and LTE bands between 33 & 41 are for unpaired spectrum, i.e. TDD.

LTE frequency band definitions

FDD LTE frequency band allocationsThere are a large number of allocations or radio spectrum that has been reserved for FDD, frequency division duplex, LTE use.

The FDD LTE frequency bands are paired to allow simultaneous transmission on two frequencies. The bands also have a sufficient separation to enable the transmitted signals not to unduly impair the receiver performance. If the signals are too close then the receiver may be "blocked" and the sensitivity impaired. The separation must be sufficient to enable the roll-off of the antenna filtering to give sufficient attenuation of the transmitted signal within the receive band.

FDD LTE BANDS & FREQUENCIES

LTE BAND

NUMBER

UPLINK(MHZ)

DOWNLINK(MHZ)

WIDTH OF

BAND (MHZ)

DUPLEX SPACING (MHZ)

BAND GAP

(MHZ)

1 1920 - 1980 2110 - 2170 60 190 130

2 1850 - 1910 1930 - 1990 60 80 20

3 1710 - 1785 1805 -1880 75 95 20

4 1710 - 1755 2110 - 2155 45 400 355

5 824 - 849 869 - 894 25 45 20

6 830 - 840 875 - 885 10 35 25

7 2500 - 2570 2620 - 2690 70 120 50

8 880 - 915 925 - 960 35 45 10

9 1749.9 - 1784.9 1844.9 - 1879.9 35 95 60

10 1710 - 1770 2110 - 2170 60 400 340

11 1427.9 - 1452.9 1475.9 - 1500.9 20 48 28

12 698 - 716 728 - 746 18 30 12

13 777 - 787 746 - 756 10 -31 41

14 788 - 798 758 - 768 10 -30 40

15 1900 - 1920 2600 - 2620 20 700 680

16 2010 - 2025 2585 - 2600 15 575 560

17 704 - 716 734 - 746 12 30 18

18 815 - 830 860 - 875 15 45 30

19 830 - 845 875 - 890 15 45 30

20 832 - 862 791 - 821 30 -41 71

21 1447.9 - 1462.9 1495.5 - 1510.9 15 48 33

22 3410 - 3500 3510 - 3600 90 100 10

23 2000 - 2020 2180 - 2200 20 180 160

24 1625.5 - 1660.5 1525 - 1559 34 -101.5 135.5

25 1850 - 1915 1930 - 1995 65 80 15

26 814 - 849 859 - 894 30 / 40 10

27 807 - 824 852 - 869 17 45 28

FDD LTE BANDS & FREQUENCIES

LTE BAND

NUMBER

UPLINK(MHZ)

DOWNLINK(MHZ)

WIDTH OF

BAND (MHZ)

DUPLEX SPACING (MHZ)

BAND GAP

(MHZ)

28 703 - 748 758 - 803 45 55 10

29 n/a 717 - 728 11

30 2305 - 2315 2350 - 2360 10 45 35

31 452.5 - 457.5 462.5 - 467.5 5 10 5

TDD LTE frequency band allocationsWith the interest in TDD LTE, there are several unpaired frequency allocations that are being prepared for LTR TDD use. The TDD LTE bands are unpaired because the uplink and downlink share the same frequency, being time multiplexed.

TDD LTE BANDS & FREQUENCIES

LTE BANDNUMBER

ALLOCATION (MHZ) WIDTH OF BAND (MHZ)

33 1900 - 1920 20

34 2010 - 2025 15

35 1850 - 1910 60

36 1930 - 1990 60

37 1910 - 1930 20

38 2570 - 2620 50

39 1880 - 1920 40

40 2300 - 2400 100

41 2496 - 2690 194

42 3400 - 3600 200

43 3600 - 3800 200

44 703 - 803 100

There are regular additions to the LTE frequency bands / LTE spectrum allocations as a result of negotiations at the ITU regulatory meetings. These LTE allocations are resulting in part from the digital dividend, and also from the pressure caused by the ever growing need for mobile communications. Many of the new LTE spectrum allocations are relatively small, often 10 - 20MHz in bandwidth, and this is a cause for concern. With LTE-Advanced needing bandwidths of 100 MHz, channel aggregation over a wide set of frequencies many be needed, and this has been recognised as a significant technological problem. . . . . . . . .

In the same way that a variety of other systems adopted different categories for the handsets or user equipment, so too there are 3G LTE UE categories. These LTE categories define the standards to which a particular handset, dongle or other equipment will operate.

LTE UE category rationaleThe LTE UE categories or UE classes are needed to ensure that the base station, or eNodeB, eNB can communicate correctly with the user equipment. By relaying the LTE UE category information to the base station, it is able to determine the performance of the UE and communicate with it accordingly.

As the LTE category defines the overall performance and the capabilities of the UE, it is possible for the eNB to communicate using capabilities that it knows the UE possesses. Accordingly the eNB will not communicate beyond the performance of the UE.

LTE UE category definitionsthere are five different LTE UE categories that are defined. As can be seen in the table below, the different LTE UE categories have a wide range in the supported parameters and performance. LTE category 1, for example does not support MIMO, but LTE UE category five supports 4x4 MIMO.

It is also worth noting that UE class 1 does not offer the performance offered by that of the highest performance HSPA category. Additionally all LTE UE categories are capable of receiving transmissions from up to four antenna ports.

A summary of the different LTE UE category parameters is given in the tables below.

HEADLINE DATA RATES FOR LTE UE CATEGORIES

CATEGORY

LINK 1 2 3 4 5

Downlink 10 50 100 150 300

Uplink 5 25 50 50 75

While the headline rates for the different LTE UE categories or UE classes show the maximum data rates achievable, it is worth looking in further detail at the underlying performance characteristics.

UL AND DL PARAMETERS FOR LTE UE CATEGORIES

CATEGORY

PARAMETER CAT 1 CAT 2 CAT 3 CAT 4 CAT 5

Max number of DL-SCH transport block bits received in a TTI

10 296 51 024 102 048 150 752 302 752

Max number of bits of a DL-SCH block received in a TTI

10 296 51 024 75 376 75 376 151 376

Total number of soft channel bits

250 368 1 237 248 1 237 248 1 827 072 3 667 200

Maximum number of supported layers for spatial multiplexing in DL

1 2 2 2 4

Max number of bits of an UL-SCH transport block received in a TTI

5 160 25 456 51 024 51 024 75 376

Support for 64-QAM in UL No No No No Yes

From this it can be seen that the peak downlink data rate for a Category 5 UE using 4x4 MIMO is approximately 300 Mbps, and 150 Mbps for a Category 4 UE using 2x2 MIMO. Also in the Uplink, LTE UE category 5 provides a peak data rate of 75 Mbps using 64-QAM.

Note:    DL-SCH = Downlink shared channel    UL-SCH = Uplink shared channel    TTI = Transmission Time Interval

LTE Category 0With the considerable level of development being undertaken into the Internet of Things, IoT and general machine to machine, M2M communications, there has been a growing need to develop an LTE category focussed on these applications. Here, much lower data rates are needed, often only in short bursts and an accompanying requirement is for the remote device or machine to be able to draw only low levels of current.

To enable the requirements of these devices to be met using LTE, and new LTE category was developed. Referred to as LTE Category 0, or simply Cat 0, this new category has a reduced performance requirement that meets the needs of many machines while significantly reducing complexity and current consumption. Whilst Category 0 offered a reduced specification, it still complied with the LTE system requirements.

LTE CATEGORY 0 PERFORMANCE SUMMARY

PARAMETER CATEGORY 0 PERFORMANCE

Peak downlink rate 1 Mbps

Peak uplink rate 1 Mbps

Max number of downlink spatial layers 1

Number of UE RF chains 1

Duplex mode Half duplex

UE receive bandwidth 20 MHz

Maximum UE transmit power 23 dBm

The new LTE Category 0 was introduced in Rel 12 of the 3GPP standards. And it is being advanced in further releases.

One major advantage of LTE Category 0 is that the modem complexity is considerably reduced when compared to other LTE Categories. It is expected that the modem complexity for a Cat 0 modem will be around 50% that of a Category 1 modem.

LTE UE category summaryIn the same way that category information is used for virtually all cellular systems from GPRS onwards, so the LTE UE category information is of great importance. While users may not be particularly aware of the category of their UE, it will match the performance an allow the eNB to communicate effectively with all the UEs that are connected to it.

Along with 3G LTE - Long Term Evolution that applies more to the radio access technology of the cellular telecommunications system, there is also an evolution of the core network. Known as SAE - System Architecture Evolution. This new architecture has been developed to provide a considerably higher level of performance that is in line with the requirements of LTE.

As a result it is anticipated that operators will commence introducing hardware conforming to the new System Architecture Evolution standards so that the anticipated data levels can be handled when 3G LTE is introduced.

The new SAE, System Architecture Evolution has also been developed so that it is fully compatible with LTE Advanced, the new 4G technology. Therefore when LTE Advanced is introduced, the network will be able to handle the further data increases with little change.

Reason for SAE System Architecture EvolutionThe SAE System Architecture Evolution offers many advantages over previous topologies and systems used for cellular core networks. As a result it is anticipated that it will be wide adopted by the cellular operators.

SAE System Architecture Evolution will offer a number of key advantages:

1. Improved data capacity:   With 3G LTE offering data download rates of 100 Mbps, and the focus of the system being on mobile broadband, it will be necessary for the network to be able to handle much greater levels of data. To achieve this it is necessary to adopt a system architecture that lends itself to much greater levels of data transfer.

2. All IP architecture:   When 3G was first developed, voice was still carried as circuit switched data. Since then there has been a relentless move to IP data. Accordingly the new SAE, System Architecture Evolution schemes have adopted an all IP network configuration.

3. Reduced latency:   With increased levels of interaction being required and much faster responses, the new SAE concepts have been evolved to ensure that the levels of latency have been reduced to around 10 ms. This will ensure that applications using 3G LTE will be sufficiently responsive.

4. Reduced OPEX and CAPEX:   A key element for any operator is to reduce costs. It is therefore essential that any new design reduces both the capital expenditure (CAPEX)and the operational expenditure (OPEX). The new flat architecture used for SAE System Architecture Evolution means that only two node types are used. In addition to this a high level of automatic configuration is introduced and this reduces the set-up and commissioning time.

SAE System Architecture Evolution basicsThe new SAE network is based upon the GSM / WCDMA core networks to enable simplified operations and easy deployment. Despite this, the SAE network brings in some major changes, and allows far more efficient and effect transfer of data.

There are several common principles used in the development of the LTE SAE network:

a common gateway node and anchor point for all technologies.

an optimized architecture for the user plane with only two node types.

an all IP based system with IP based protocols used on all interfaces.

a split in the control / user plane between the MME, mobility management entity and the gateway.

a radio access network / core network functional split similar to that used on WCDMA / HSPA.

integration of non-3GPP access technologies (e.g. cdma2000, WiMAX, etc) using client as well as network based mobile-IP.

The main element of the LTE SAE network is what is termed the Evolved Packet Core or EPC. This connects to the eNodeBs as shown in the diagram below.

LTE SAE Evolved Packet Core

As seen within the diagram, the LTE SAE Evolved Packet Core, EPC consists of four main elements as listed below:

Mobility Management Entity, MME:   The MME is the main control node for the LTE SAE access network, handling a number of features:

o Idle mode UE tracking

o Bearer activation / de-activation

o Choice of SGW for a UE

o Intra-LTE handover involving core network node location

o Interacting with HSS to authenticate user on attachment and implements roaming restrictions

o It acts as a termination for the Non-Access Stratum (NAS)

o Provides temporary identities for UEs

o The SAE MME acts the termination point for ciphering protection for NAS signaling. As part of this it also handles the security key management. Accordingly the MME is the point at which lawful interception of signalling may be made.

o Paging procedure

o The S3 interface terminates in the MME thereby providing the control plane function for mobility between LTE and 2G/3G access networks.

o The SAE MME also terminates the S6a interface for the home HSS for roaming UEs.

It can therefore be seen that the SAE MME provides a considerable level of overall control functionality.

Serving Gateway, SGW:   The Serving Gateway, SGW, is a data plane element within the LTE SAE. Its main purpose is to manage the user plane mobility and it also acts as the main border between the Radio Access Network, RAN and the core network. The SGW also maintains the data paths between the eNodeBs and the PDN Gateways. In this way the SGW forms a interface for the data packet network at the E-UTRAN.

Also when UEs move across areas served by different eNodeBs, the SGW serves as a mobility anchor ensuring that the data path is maintained.

PDN Gateway, PGW:   The LTE SAE PDN gateway provides connectivity for the UE to external packet data networks, fulfilling the function of entry and exit point for UE data. The UE may have connectivity with more than one PGW for accessing multiple PDNs.

Policy and Charging Rules Function, PCRF:   This is the generic name for the entity within the LTE SAE EPC which detects the service flow, enforces charging policy. For applications that require dynamic policy or charging control, a network element entitled the Applications Function, AF is used. 

LTE SAE PCRF Interfaces

LTE SAE Distributed intelligenceIn order that requirements for increased data capacity and reduced latency can be met, along with the move to an all-IP network, it is necessary to adopt a new approach to the network structure.

For 3G UMTS / WCDMA the UTRAN (UMTS Terrestrial Radio Access Network, comprising the Node B's or basestations and Radio Network Controllers) employed low levels of autonomy. The Node Bs were connected in a star formation to the Radio Network Controllers (RNCs) which carried out the majority of the management of the radio resource. In turn the RNCs connected to the core network and connect in turn to the Core Network.

To provide the required functionality within LTE SAE, the basic system architecture sees the removal of a layer of management. The RNC is removed and the radio resource management is devolved to the base-stations. The new style base-stations are called eNodeBs or eNBs.

The eNBs are connected directly to the core network gateway via a newly defined "S1 interface". In addition to this the new eNBs also connect to adjacent eNBs in a mesh via an "X2 interface". This provides a much greater level of direct interconnectivity. It also enables many calls to be routed very directly as a large number of calls and connections are to other mobiles in the same or adjacent cells. The new structure allows many calls to be routed far more directly and with only minimum interaction with the core network.

In addition to the new Layer 1 and Layer 2 functionality, eNBs handle several other functions. This includes the radio resource control including admission control, load balancing and radio mobility control including handover decisions for the mobile or user equipment (UE).

The additional levels of flexibility and functionality given to the new eNBs mean that they are more complex than the UMTS and previous generations of base-station. However the new 3G LTE SAE network structure enables far higher levels of performance. In addition to this their flexibility enables them to be updated to handle new upgrades to the system including the transition from 3G LTE to 4G LTE Advanced.

The new System Architecture Evolution, SAE for LTE provides a new approach for the core network, enabling far higher levels of data to be transported to enable it to support the much higher data rates that will be possible with LTE. In addition to this, other features that enable the CAPEX and OPEX to be reduced when compared to existing systems, thereby enabling higher levels of efficiency to be achieved.

With LTE requiring smaller cell sizes to enable the much greater levels of data traffic to be handled, there networks have become considerably more complicated and trying to plan and manage the network centrally is not as viable. Coupled with the need to reduce costs by reducing manual input, there has been a growing impetus to implement self-organizing networks.

Accordingly LTE can be seen as one of the major drivers behind the self-organizing network, SON philosophy.

Accordingly 3GPP developed many of the requirements for LTE SON to sit alongside the basic functionality of LTE. As a result the standards for LTE SON are embedded within the 3GPP standards.

LTE SON developmentThe term SON came into frequent use after the term was adopted by the Next Generation Mobile Networks, NGMN alliance. The idea came about as result of the need within LTE to be able to deploy many more cells. Femtocells and other microcells are an integral part of the LTE deployment strategy. With revenue per bit falling, costs for deployment must be kept to a minimum as well as ensuring the network is operating to its greatest efficiency.

3GPP, the Third Generation Partnership Programme has created the standards for SON and as they are generally first to be deployed with LTE, they are often referred to as LTE SON.

While 3GPP has generated the standards, they have been based upon long term objectives for a 'SON-enabled broadband mobile network' set out by the NGMN.

NGMN has defined the necessary use cases, measurements, procedures and open interfaces to ensure that multivendor offerings are available. 3GPP has incorporated these aspirations into useable standards.

Major elements of LTE SON ( SELF ORGANIZING NETWORK )Although LTE SON self-optimising networks is one of the major drivers for the generic SON technology, the basic requirements remain the same whatever the technology to which it will be applied.

The main elements of SON include:

Self configuration:   The aim for the self configuration aspects of LTE SON is to enable new base stations to become essentially "Plug and Play" items. They should need as little manual intervention in the configuration process as possible. Not only will they be able to organize the RF aspects, but also configure the backhaul as well.

Self optimisation:   Once the system has been set up, LTE SON capabilities will enable the base station to optimise the operational characteristics to best meet the needs of the overall network.

Self-healing:   Another major feature of LTE SON is to enable the network to self-heal. It will do this by changing the characteristics of the network to mask the problem until it is fixed. For example, the boundaries of adjacent cells can be increased by changing antenna directions and increasing power levels, etc..

Typically an LTE SON system is a software package with relevant options that is incorporated into an operator's network.

Note on SON, Self Organizing Networks:

SON mainly came out of the requirements of LTE and the more complicated networks that will arise. However the

concepts behind SON can be applied at any network enabling its efficiency to be increased while keeping costs low.

Accordingly, it is being used increasingly to reduce operational and capital expenditure by adding software to the

network to enable it to organise and run itself.

Click on the link for further information about Self Organising Networks, SON

LTE SON and 3GPP standardsLTE Son has been standardised in the various 3GPP standards. It was first incorporated into 3GPP release 8, and further functionality has been progressively added in the further releases of the standards.

One of the major aims of the 3GPP standardization is the support of SON features is to ensure that multi-vendor network environments operate correctly with LTE SON. As a result, 3GPP has defined a set of LTE SON use cases and the associated SON functions.

As the functionality of LTE advances, the LTE SON standardisation effectively track the LTE network evolution stages. In this way SON will be applicable to the LTE networks.

The Voice over LTE, VoLTE scheme was devised as a result of operators seeking a standardized system for transferring traffic for voice over LTE.

Originally LTE was seen as a completely IP cellular system just for carrying data, and operators would be able to carry voice either by reverting to 2G / 3G systems or by using VoIP in one form or another.

From around 2014 Phones like this iPhone6 incorporated VoLTE as standard

However it was seen that this would lead to fragmentation and incompatibility not allowing all phones to communicate with each other and this would reduce voice traffic. Additionally SMS services are still widely used, often proving a means of set-up for other applications.

Even though revenue from voice calls and SMS is falling, a format for voice over LTE and messaging, it was as necessary to have a viable and standardized scheme to provide the voice and SMS services to protect this revenue.

Options for LTE VoiceWhen looking at the options for ways of carrying voice over the LTE system, a number of possible solutions were investigated. A number of alliances were set up to promote different ways of providing the service. A number of systems were prosed as outlined below:

CSFB, Circuit Switched Fall Back:   The circuit switched fall-back, CSFB option for providing voice over LTE has been standardized under 3GPP specification 23.272. Essentially LTE CSFB uses a variety of processes and network elements to enable the circuit to fall back to the 2G or 3G connection (GSM, UMTS, CDMA2000 1x) before a circuit switched call is initiated.

The specification also allows for SMS to be carried as this is essential for very many set-up procedures for cellular telecommunications. To achieve this the handset uses an interface known as SGs which allows messages to be sent over an LTE channel.

SV-LTE - Simultaneous Voice LTE:   SV-LTE allows packet switched LTE services to run simultaneously with a circuit switched voice service. SV-LTE facility provides the facilities of CSFB at the same time as running a packet switched data service. It has the disadvantage that it requires two radios to run at the same time within the handset which has a serious impact on battery life which is already a major issue.

VoLGA, Voice over LTE via GAN:   The VoLGA standard was based on the existing 3GPP Generic Access Network (GAN) standard, and the aim was to enable LTE users to receive a consistent set of voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks. For mobile operators, the aim of VoLGA was to provide a low-cost and low-risk approach for bringing their primary revenue generating services (voice and SMS) onto the new LTE network deployments.

One Voice / later called Voice over LTE, VoLTE:   The Voice over LTE, VoLTE scheme for providing voice over an LTE system utilises IMS enabling it to become part of a rich media solution. It was the option chosen by the GSMA for use on LTE and is the standardised method for providing SMS and voice over LTE.

Voice over LTE, VoLTE formationOriginally the concept for an SMS and voice system over LTE using IMS had been opposed by many operators because of the complexity of IMS. They had seen it as far too expensive and burdensome to introduce and maintain.

However, the One Voice profile for Voice over LTE was developed by collaboration between over forty operators including: AT&T, Verizon Wireless, Nokia and Alcatel-Lucent.

At the 2010 GSMA Mobile World Congress, GSMA announced that they were supporting the One Voice solution to provide Voice over LTE.

To achieve a workable system, a cut down variant of IMS was used. It was felt that his would be acceptable to operators while still providing the functionality required.

The VoLTE system is based on the IMS MMTel concepts that were previously in existence. It has been specified in the GSMA profile IR 92.

Voice over LTE, VoLTE basicsVoLTE, Voice over LTE is an IMS-based specification. Adopting this approach, it enables the system to be integrated with the suite of applications that will become available on LTE.

Note on IMS:

The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem, IMS is an architectural framework

for delivering Internet Protocol, IP multimedia services. It enables a variety of services to be run seemlessly

rather than having several disparate applications operating concurrently.

Click for an IMS tutorial

In order that IMS was implemented in fashion that would be acceptable to operators, a cut down version was defined. This not only reduced the number of entities required in the IMS network, but it also simplified the interconnectivity - focussing on the elements required for VoLTE.

Reduced IMS network for VoLTE

As can be seen there are several entities within the reduced IMS network used for VoLTE:

IP-CAN IP, Connectivity Access Network:   This consists of the EUTRAN and the MME.

P-CSCF, Proxy Call State Control Function:   The P-CSCF is the user to network proxy. In this respect all SIP signalling to and from the user runs via the P-CSCF whether in the home or a visited network.

I-CSCF, Interrogating Call State Control Function:   The I-CSCF is used for forwarding an initial SIP request to the S-CSCF. When the initiator does not know which S-CSCF should receive the request.

S-CSCF, Serving Call State Control Function:   The S-CSCF undertakes a variety of actions within the overall system, and it has a number of interfaces to enable it to communicate with other entities within the overall system.

AS, Application Server:   It is the application server that handles the voice as an application.

HSS, Home Subscriber Server:   The IMS HSS or home subscriber server is the main subscriber database used within IMS. The IMS HSS provides details of the subscribers to the other entities within the IMS network, enabling users to be granted access or not dependent upon their status.

The IMS calls for VoLTE are processed by the subscriber's S-CSCF in the home network. The connection to the S-CSCF is via the P-CSCF. Dependent upon the network in use and overall location within a network, the P-CSCF will vary, and a key element in the enablement of voice calling capability is the discovery of the P-CSCF.

An additional requirement for VoLTE enabled networks is to have a means to handing back to circuit switched legacy networks in a seamless manner, while only having one transmitting radio in the handset to preserve battery life. A system known as SRVCC - Single Radio Voice Call Continuity is required for this. Read more about SRVCC - Single Radio-Voice Call Continuity

VoLTE codecsAs with any digital voice system, a codec must be used. The VoLTE codec is that specified by 3GPP and is the adaptive multi-rate, AMR codec that is used in many other cellular systems from GSM through UMTS and now to LTE. The AMR-wideband codec may also be used.

The used of the AMR codec for VoLTE also provides advantages in terms of interoperability with legacy systems. No transcoders are needed as most legacy systems now are moving towards the AMR codec.

In addition to this, support for dual tone multi-frequency, DTMF signalling is also mandatory as this is widely used for many forms of signalling over analogue telephone lines.

VoLTE IP versionsWith the update from IPv4 to IPv6, the version of IP used in any system is of importance.

VoLTE devices are required to operate in dual stack mode catering for both IPv4 and IPv6.

If the IMS application profile assigns and IPv6 address, then the device is required to prefer that address and also to specifically use it during the P-CSCF discovery phase.

One of the issues with voice over IP type calls is the overhead resulting from the IP header. To overcome this issue VoLTE requires that IP header compression is used along with RoHC, Robust Header Compression, protocol for voice data packet headers.

SRVCC - Single Radio Voice call Continuity is a level of functionality that is required within VoLTE systems to enable the packet domain calls on LTE to be handed over to legacy circuit switched voice systems like GSM, UMTS and CDMA 1x in a seamless manner.

As LTE systems deploy VoLTE coverage will be limited and it is anticipated that it will be many years before complete LTE coverage will be available.

As a result it is necessary for operators to have a system whereby this complicated handover can be accommodated in a seamless fashion. This scheme needs to be in place as soon as they start to deploy VoLTE.

What is SRVCC?SRVCC, Single radio Voice Call Continuity, is a scheme that enables Inter Radio Access Technology, Inter RAT handover as well as a handover from packet data to circuit switched data voice calls.

By using SRVCC operators are able to make the handovers while maintaining existing quality of service, QoS and also ensuring that call continuity meets the critical requirements for emergency calls.

Some ideas for handover require that the handset has two active radios to facilitate handover. This is not ideal because it requires additional circuitry to enable the two radios to be active simultaneously and it also adds considerably to battery drain.

The SRVCC requires only a single active radio in the handset and requires some upgrades to the supporting network infrastructure.

SRVCC network architectureThe concept for SRVCC was originally included in the 3GPP specification Release 8. Since then it has evolved to take account of the various issues and changing requirements. As a result GSMA recommends that 3GPP Rel 10 or later is implemented as this ensures a considerably lower level of voice interruption and dropped calls.

The network upgrades required to the cellular network are needed in both the LTE network and that of the legacy network or networks. SRVCC requires that software upgrades are required to the MSS - Mobile SoftSwitch subsystem in the legacy MSC - Mobile Switching Centre, the IMS subsystem and the LTE/EPC subsystem. No upgrades are required for the radio access network of the legacy system, meaning that the majority of the legacy system remains unaffected.

The upgrades required for the MSC are normally relatively easy to manage. The MSC is normally centrally located and not dispersed around the network, and this makes upgrades easier to manage. If they are not easily accessible then a new dedicated MSC can be used that has been upgraded to handles the SRVCC requirements.

How SRVCC worksThe SRVCC implementation controls the transfer of calls in both directions.

LTE to legacy network handoverHandover from LTE to the legacy network is required when the user moves out of the LTE coverage area. Using SRVCC, the handover is undertaken in two stages.

Radio Access Technology transfer:   The handover for the radio access network and this is a well-established protocol that is in use for transfers from 3G to 2G for example.

Session transfer:   The session transfer is the new element that is required for SRVCC. It is required to move the access control and voice media anchoring from the Evolved Packet Core, EPC of the packet switched LTE network to the legacy circuit switched network.

During the handover process the CSCF within the IMS architecture maintains the control of the whole operation.

Voice handover using SRVCC on LTEThe SRVCC handover process takes place in a number of steps:

1. The handover process is initiated by a request for session transfer from the IMS CSCF.2. The IMS CSCF responds simultaneously with two commands, one to the LTE network, and

the other to the legacy network.3. the LTE network receives a radio Access Network handover execution command through the

MME and LTE RAN. This instructs the user device to prepare to move to a circuit switched network for the voice call.

4. The destination legacy circuit switched network receives a session transfer response preparing it to accept the call from the LTE network.

5. After all the commands have been executed and acknowledged the call is switched to the legacy network with the IMS CSCF still in control of the call.

Legacy network to LTEWhen returning a call to the LTE network much of the same functionality is again used.

To ensure the VoLTE device is able to return to the LTE RAN from the legacy RAN, there are two options the legacy RAN can implement to provide a swift and effective return:

Allow LTE information to be broadcast on the legacy RAN so the LTE device is able to perform the cell reselection more easily.

Simultaneously release the connection to the user device and redirect it to the LTE RAN.

SRVCC interruption performance

One of the key issues with VoLTE and SRVCC is the interruption time when handing over from an LTE RAN to a legacy RAN.

The key methodology behind reducing the time is to simultaneous perform the redirections of RAN and session. In this way the user experience is maintained and the actual interruption time is not unduly noticeable.

It has been found that the session redirection is the faster of the two handovers, and therefore it is necessary for the overall handover methodology to accommodate the fact that there are difference between the two.

By Ian Poole

M2MThe Internet of Things, IoT and machine to machine, M2M communications are growing rapidly.

LTE, the Long Term Evolution cellular system is well placed to carry a lot of the traffic for machine to machine communications.

The issue is that LTE is a complex system capable of carrying high data rates.

To overcome this issue a "variant" of LTE, often referred to as LTE-M has been developed for LTE M2M communications.

LTE-M key issuesThere are several requirements for LTE M2M applications if the cellular system is to be viable in these scenarios:

Wide spectrum of devices:   Any LTE machine to machine system must be able to support a wide variety of different types of devices. These may range from smart meters to vending machines and automotive fleet management to security and medical devices. These different devices have many differing requirements, so any LTE-M system needs to be able to be flexible.

Low cost of devices:   Most M2M devices need to be small and fit into equipment that is very cost sensitive. With many low cost M2M systems already available, LTE-M needs to provide the benefits of a cellular system, but at low cost.

Long battery life :   Many M2M devices will need to be left unattended for long periods of time in areas where there may be no power supply. Maintaining batteries is a costly business and therefore any devices should be able to have a time between battery changes of up to ten years. This means that the LTE-M system must be capable of draining very little battery power.

Enhanced coverage :   LTE-M applications will need to operate within a variety of locations - not just where reception is good. They will need to operate within buildings, often in positions where there is little access and where reception may be poor. Accordingly LTE-M must be able to operate under all conditions.

Large volumes - low data rates:   As it is anticipated that volumes of remote devices will be enormous, the LTE-M must be structured so that the networks are be able to accommodate vast numbers of connected devices that may only require small amounts of data to be carried, often in short peaks but with low data rates.

Rel 12 updates for LTE-MA number of updates were introduced in 3GPP Rel 12 to accommodate LTE-M requirements.

These updates mean that the cost of a low cost M2M modem could be 40 to 50% that of a regular LTE devices, making them comparable with EGPRS ones.

To accommodate these requirements a new a new UE category has been implemented LTE Category 0. These categories define the broad capabilities of the device so that the base station is able to communicate properly. Read more about LTE UE categories.

These low cost LTE-M, M2M modems have limited capability and are:

Antennas:   There is the capability for only one receive antenna compared to two receive antennas for other device categories.

Transport Block Size:   There is a restriction on the transport block size These low cost LTE-M devices are allowed to send or receive up to 1000 bits of unicast data per sub-frame. This reduces the maximum data rate to 1 Mbps in both the uplink and the downlink.

Duplex:   Half duplex FDD devices are supported as an optional feature - this provides cost savings because it enables RF switches and duplexers that are needed for the full performance modems to be removed. It also means there is no need for a second phase locked loop for the frequency conversion, although having only one PLL means that switching times between receive and transmit are longer.

LTE-M features planned for Rel 13There are several features that are being proposed and prepared for the next release of the 3GPP standards in terms of LTE M2M capabilities. These include some of the following capabilities:

Reduce bandwidth to 1.4 MHz for uplink and downlink

Reduce transmit power to 20dBm

Reduce support for downlink transmission modes

Relax the requirements that require high levels of processing, e.g. downlink modulation scheme, reduce downlink HARQ timeline

It should be stated that these last points for Rel 13 are currently only proposals and are not implemented.

With a number of cellular style M2M wireless communication systems like LoRa and SIGFOX being deployed, LTE needs its own M2M capability to ensure that it is able to compete with these growing standards. Otherwise LTE may not be suitable for carrying this form of low data rate date from devices that require long battery life, etc. LTE-M is the cellular operators' answer to this.

By Ian Poole

LTE-U Unlicensed, LTE-LAA- LTE-U (LTE-Unlicensed), or as it is also known LTE-LAA (LTE-License Assisted Access) utilises unlicensed spectrum, typically in the 5GHz band to provide additional radio spectrum.

LTE TUTORIAL INCLUDES

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

LTE networks are carrying an increasing amount of data. Although cells can be made smaller to help accommodate this, it is not the complete solution and more spectrum is needed.

One approach is to use unlicensed spectrum alongside the licensed bands. Known in 3GPP as LTE-LAA - LTE License Assisted Access or more generally as LTE U - LTE Unlicensed, it enables access to unlicensed spectrum especially in the 5GHz ISM band.

LTE-U backgroundThere is a considerable amount of unlicensed spectrum available around the globe. These bands are used globally to provide unlicensed access for short range radio transmissions. These bands, called ISM - Industrial, Scientific and Medical bands are allocated in different parts of the spectrum and are used for a wide variety of applications including microwave ovens, Wi-Fi, Bluetooth, and much more.

The frequency band of most interest for LTE-U, Unlicensed / LTE-LAA, License Assisted Access is the 5GHz band. Here there are several hundred MHz of spectrum bandwidth available, although the exact bands available depend upon the country in question.

5GHz bands for LTE-U / LTE-LAA

In addition to the basic frequency limits, the use of the 5GHz bands for applications such as LTE-U or LTE-LAA carries some regulatory requirements.

One of the main requirements for access to these frequencies is that of being able to coexist with other users of the band - a method of Clear Channel Assessment, CCA, or Listen Before Talk, LBT is required. This often means that instantaneous access may not always be available when LTE-U is being implemented.

Another requirements is that there are different power levels allowed dependent upon the country and the area of the band being used. Typically between 5150 and 5350 MHz there is a maximum power limit of 200 mW and operation is restricted to indoor use only, and the upper frequencies often allow power levels up to 1 W.

LTE-U / LTE-LAA basics

The use of LTE-U (Unlicensed) / LTE-LAA (License Assisted Access) was first introduced in Rel13 of the 3GPP standards. Essentially, LTE-U is built upon the carrier aggregation capability of LTE-Advanced that has been deployed since around 2013. Essentially Carrier aggregation seeks to increase the overall bandwidth available to a user equipment by enabling it to use more than one channel, either in the same band, or within another band.

There are several ways in which LTE-U can be deployed:

Downlink only:   This is the most basic form of LTE-U and it is similar in approach to some of the first LTE carrier aggregation deployments. In this the primary cell link is always located in the licensed spectrum bands.

Also when operating in this mode, the LTE eNodeB performs most of the necessary operations to ensure reliable operation is maintained and interference is not caused to other users by ensuring the channel is free.

Uplink and downlink:   Full TDD LTE-U operation with the user equipment having an uplink and downlink connection in the unlicensed spectrum requires the inclusion of more features. 

FDD / TDD aggregation:   LTE-CA allows the use of carrier aggregation mixes between FDD and TDD. This provides for much greater levels of flexibility when selecting the band to be used with in unlicensed spectrum for LTE-LAA operation.

LTE-U relies on the existing core network for the backhaul, and other capabilities like security and authentication. As such no changes are needed to the core network. Some changes are needed to the base station so that it can accommodate the new frequencies and also incorporate the capabilities required to ensure proper sharing of the unlicensed frequencies. In addition to this, the handsets or UEs will need to have the new LTE-U / LTE-LAA capability incorporated into them so they can access LTE on these additional frequencies.

LTE-U / Wi-Fi coexistenceOne of the great fears that many have is that the use of LTE-U will swamp the 5GHz unlicensed band and that Wi-Fi using these frequencies will suffer along with other users.

The LTE-U system is being designed to overcome this issue and using an listen before transmit, LBT solution, all users should be able to coexist without any undue levels of interference.

There will be cases where LTE-U operation and Wi-Fi use different channels and under these circumstances there will be only minimal levels of interference.

It is also possible to run LTE-U and Wi-Fi on the same channel. Under these circumstances both are able to operate, although with a lower data throughput. It is also possible to place a "fairness" algorithm into the eNodeB to ensure that the Wi-Fi signal is not unduly degraded and is still able to support a good data thro0ughput.

LTE Security- overview, about the basics of LTE security including the techniques used for LTE authentication, ciphering, encryption, and identity protection.

IN THIS SECTION

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

LTE security is an issue that is of paramount importance. It is necessary to ensure that LTE security measures provide the level of security required without impacting the user as this could drive users away.

Nevertheless with the level of sophistication of security attacks growing, it is necessary to ensure that LTE security allows users to operate freely and without fear of attack from hackers. Additionally the network must also be organised in such a way that it is secure against a variety of attacks.

LTE security basicsWhen developing the LTE security elements there were several main requirements that were borne in mind:

LTE security had to provide at least the same level of security that was provided by 3G services.

The LTE security measures should not affect user convenience.

The LTE security measures taken should provide defence from attacks from the Internet.

The security functions provided by LTE should not affect the transition from existing 3G services to LTE.

The USIM currently used for 3G services should still be used.

To ensure these requirements for LTE security are met, it has been necessary to add further measures into all areas of the system from the UE through to the core network.

The main changes that have been required to implement the required level of LTE security are summarised below:

A new hierarchical key system has been introduced in which keys can be changed for different purposes.

The LTE security functions for the Non-Access Stratum, NAS, and Access Stratum, AS have been separated. The NAS functions are those functions for which the processing is accomplished between the core network and the mobile terminal or UE. The AS functions encompass the communications between the network edge, i.e. the Evolved Node B, eNB and the UE.

The concept of forward security has been introduced for LTE security.

LTE security functions have been introduced between the existing 3G network and the LTE network.

LTE USIMOne of the key elements within the security of GSM, UMTS and now LTE was the concept of the subscriber identity module, SIM. This card carried the identity of the subscriber in an encrypted fashion and this could allow the subscriber to keep their identity while transferring or upgrading phones.

With the transition form 2G - GSM to 3G - UMTS, the idea of the SIM was upgraded and a USIM - UMTS Subscriber Identity Module, was used. This gave more functionality, had a larger memory, etc.

For LTE, only the USIM may be used - the older SIM cards are not compatible and may not be used.

By Ian Poole

4G LTE Advanced Tutorial- overview, information, tutorial about the basics of LTE Advanced, the 4G technology being called IMT Advanced being developed under 3GPP.

IN THIS SECTION

LTE Advanced Tutorial

Carrier Aggregation

Coordinated Multipoint - CoMP

LTE Relay

LTE D2D

LTE HetNet

See also

3G LTE

With the standards definitions now available for LTE, the Long Term Evolution of the 3G services, eyes are now turning towards the next development, that of the truly 4G technology named IMT Advanced. The new technology being developed under the auspices of 3GPP to meet these requirements is often termed LTE Advanced.

In order that the cellular telecommunications technology is able to keep pace with technologies that may compete, it is necessary to ensure that new cellular technologies are being formulated and developed. This is the reasoning behind starting the development of the new LTE Advanced systems, proving the technology and developing the LTE Advanced standards.

In order that the correct solution is adopted for the 4G system, the ITU-R (International Telecommunications Union - Radiocommunications sector) has started its evaluation process to develop the recommendations for the terrestrial components of the IMT Advanced radio interface. One of the main competitors for this is the LTE Advanced solution.

One of the key milestones is October 2010 when the ITU-R decides the framework and key characteristics for the IMT Advanced standard. Before this, the ITU-R will undertake the evaluation of the various proposed radio interface technologies of which LTE Advanced is a major contender.

Key milestones for ITU-R IMT Advanced evaluationThe ITU-R has set a number of milestones to ensure that the evaluation of IMT Advanced technologies occurs in a timely fashion. A summary of the main milestones is given below and this defines many of the overall timescales for the development of IMT Advanced and in this case LTE Advanced as one of the main technologies to be evaluated.

KEY MILESTONES ON THE DEVELOPMENT OF 4G LTE-ADVANCED

MILESTONE DATE

Issue invitation to propose Radio Interface Technologies. March 2008

ITU date for cut-off for submission of proposed Radio Interface Technologies.

October 2009

Cutoff date for evaluation report to ITU. June 2010

Decision on framework of key characteristics of IMT Advanced Radio Interface Technologies.

October 2010

Completion of development of radio interface specification recommendations.

February 2011

LTE Advanced development historyWith 3G technology established, it was obvious that the rate of development of cellular technology should not slow. As a result initial ideas for the development of a new 4G system started to be investigated. In one early investigation which took place on 25 December 2006 with information released to the press on 9 February 2007, NTT DoCoMo detailed information about trials in which they were able to send data at speeds up to approximately 5 Gbit/s in the downlink within a 100MHz bandwidth to a mobile station moving at 10km/h. The scheme used several technologies to achieve this including variable spreading factor spread orthogonal frequency division multiplex, MIMO, multiple input multiple output, and maximum likelihood detection. Details of these new 4G trials were passed to 3GPP for their consideration

In 2008 3GPP held two workshops on IMT Advanced, where the "Requirements for Further Advancements for E-UTRA" were gathered. The resulting Technical Report 36.913 was then published in June 2008 and submitted to the ITU-R defining the LTE-Advanced system as their proposal for IMT-Advanced.

The development of LTE Advanced / IMT Advanced can be seen to follow and evolution from the 3G services that were developed using UMTS / W-CDMA technology.

COMPARISON OF LTE-A WITH OTHER CELLULAR TECHNOLOGIES

WCDMA

(UMTS)

HSPAHSDPA / HSUPA

HSPA+ LTE LTE ADVANCED (IMT ADVANCED)

Max downlink speedbps

384 k 14 M 28 M 100M 1G

Max uplink speedbps

128 k 5.7 M 11 M 50 M 500 M

Latencyround trip timeapprox

150 ms 100 ms 50ms (max)

~10 ms less than 5 ms

3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8 Rel 10

Approx years of initial roll out

2003 / 4 2005 / 6 HSDPA2007 / 8 HSUPA

2008 / 9 2009 / 10 2014 / 15

Access methodology CDMA CDMA CDMA OFDMA / SC-FDMA

OFDMA / SC-FDMA

LTE Advanced is not the only candidate technology. WiMAX is also there, offering very high data rates and high levels of mobility. However it now seems less likely that WiMAX will be adopted as the 4G technology, with LTE Advanced appearing to be better positioned.

LTE Advanced key featuresWith work starting on LTE Advanced, a number of key requirements and key features are coming to light. Although not fixed yet in the specifications, there are many high level aims for the new LTE Advanced specification. These will need to be verified and much work remains to be undertaken in the specifications before these are all fixed. Currently some of the main headline aims for LTE Advanced can be seen below:

1. Peak data rates: downlink - 1 Gbps; uplink - 500 Mbps.2. Spectrum efficiency: 3 times greater than LTE.3. Peak spectrum efficiency: downlink - 30 bps/Hz; uplink - 15 bps/Hz.4. Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation

where non-contiguous spectrum needs to be used.5. Latency: from Idle to Connected in less than 50 ms and then shorter than 5 ms one way for

individual packet transmission.6. Cell edge user throughput to be twice that of LTE.7. Average user throughput to be 3 times that of LTE.

8. Mobility: Same as that in LTE9. Compatibility: LTE Advanced shall be capable of interworking with LTE and 3GPP legacy

systems.

These are many of the development aims for LTE Advanced. Their actual figures and the actual implementation of them will need to be worked out during the specification stage of the system.

LTE Advanced technologiesThere are a number of key technologies that will enable LTE Advanced to achieve the high data throughput rates that are required. MIMO and OFDM are two of the base technologies that will be enablers. Along with these there are a number of other techniques and technologies that will be employed.

Orthogonal Frequency Division Multiplex, OFDM   OFDM forms the basis of the radio bearer. Along with it there is OFDMA (Orthogonal Frequency Division Multiple Access) along with SC-FDMA (Single Channel Orthogonal Frequency Division Multiple Access). These will be used in a hybrid format. However the basis for all of these access schemes is OFDM.

Note on OFDM:

Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of

close spaced carriers that are modulated with low rate data. Normally these signals would be expected to

interfere with each other, but by making the signals orthogonal to each other there is no mutual interference.

The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-

path effects..

Click on the link for an OFDM tutorial

Multiple Input Multiple Output, MIMO:   One of the other key enablers for LTE Advanced that is common to LTE is MIMO. This scheme is also used by many other technologies including WiMAX and Wi-Fi - 802.11n. MIMO - Multiple Input Multiple Output enables the data rates achieved to be increased beyond what the basic radio bearer would normally allow.

Note on MIMO:

Two major limitations in communications channels can be multipath interference, and the data throughput

limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist

between a transmitter and receiver to significantly improve the data throughput available on a given channel

with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some

complex digital signal processing, MIMO technology enables the system to set up multiple data streams on

the same channel, thereby increasing the data capacity of a channel.

Click on the link for a MIMO tutorial

For LTE Advanced, the use of MIMO is likely to involve further and more advanced techniques including the use of additional antennas in the matrix to enable additional paths to be used, although as the number of antennas increases, the overhead increases and the return per additional path is less.

In additional to the numbers of antennas increasing, it is likely that techniques such as beamforming may be used to enable the antenna coverage to be focused where it is needed.

Carrier Aggregation, CA:   As many operators do not have sufficient contiguous spectrum to provide the required bandwidths for the very high data rates, a scheme known as carrier aggregation has been developed. Using this technology operators are able to utilise multiple channels either in the same bands or different areas of the spectrum to provide the required bandwidth. Read more about Carrier Aggregation, CA

Coordinated Multipoint :   One of the key issues with many cellular systems is that of poor performance at the cell edges. Interference from adjacent cells along with poor signal quality lead to a reduction in data rates. For LTE-Advanced a scheme known as coordinated multipoint has been introduced. Read more aboutCoordinated Multipoint, CoMP

LTE Relaying:   LTE relaying is a scheme that enables signals to be forwarded by remote stations from a main base station to improve coverage. Read more about LTE Relaying

Device to Device, D2D:   LTE D2D is a facility that has been requested by a number of users, in particular the emergency services. It enables fast swift access via direct communication - a facility that is essential for the emergency services when they may be on the scene of an incident. Read more about Device to Device communications

With data rates rising well above what was previously available, it will be necessary to ensure that the core network is updated to meet the increasing requirements. It is therefore necessary to further improve the system architecture.

These and other technologies will be used with LTE Advanced to provide the very high data rates that are being sought along with the other performance characteristics that are needed. . . . . . . . . . .

By Ian Poole

LTE CA: Carrier Aggregation Tutorial- 4G LTE Advanced CA, carrier aggregation or channel aggregation enables multiple LTE carriers to be used together to provide the high data rates required for 4G LTE Advanced.

4G LTE ADVANCED INCLUDES:

LTE Advanced Tutorial

Carrier Aggregation

Coordinated Multipoint - CoMP

LTE Relay

LTE D2D

LTE HetNet

See also

3G LTE

LTE Advanced offers considerably higher data rates than even the initial releases of LTE. While the spectrum usage efficiency has been improved, this alone cannot provide the required data rates that are being headlined for 4G LTE Advanced.

To achieve these very high data rates it is necessary to increase the transmission bandwidths over those that can be supported by a single carrier or channel. The method being proposed is termed carrier aggregation, CA, or sometimes channel aggregation. Using LTE Advanced carrier aggregation, it is possible to utilise more than one carrier and in this way increase the overall transmission bandwidth.

These channels or carriers may be in contiguous elements of the spectrum, or they may be in different bands.

Spectrum availability is a key issue for 4G LTE. In many areas only small bands are available, often as small as 10 MHz. As a result carrier aggregation over more than one band is contained within the specification, although it does present some technical challenges.

Carrier aggregation is supported by both formats of LTE, namely the FDD and TDD variants. This ensures that both FDD LTE and TDD LTE are able to meet the high data throughput requirements placed upon them.

LTE carrier aggregation basicsThe target figures for data throughput in the downlink is 1 Gbps for 4G LTE Advanced. Even with the improvements in spectral efficiency it is not possible to provide the required headline data throughput rates within the maximum 20 MHz channel. The only way to achieve the higher data rates is to increase the overall bandwidth used. IMT Advanced sets the upper limit at 100 MHz, but with an expectation of 40 MHz being used for minimum performance. For the future it is possible the top limit of 100 MHz could be extended.

It is well understood that spectrum is a valuable commodity, and it takes time to re-assign it from one use to another in view - the cost of forcing users to move is huge as new equipment needs to be bought. Accordingly as sections of the spectrum fall out of use, they can be re-assigned. This leads to significant levels of fragmentation.

To an LTE terminal, each component carrier appears as an LTE carrier, while an LTE-Advanced terminal can exploit the total aggregated bandwidth.

RF aspects of carrier aggregationThere are a number of ways in which LTE carriers can be aggregated:

Types of LTE carrier aggregation

Intra-band:   This form of carrier aggregation uses a single band. There are two main formats for this type of carrier aggregation:

o Contiguous:    The Intra-band contiguous carrier aggregation is the easiest form of LTE carrier aggregation to implement. Here the carriers are adjacent to each other.

Contiguous aggregation of two uplink component carriers

The aggregated channel can be considered by the terminal as a single enlarged channel from the RF viewpoint. In this instance, only one transceiver is required within the terminal or UE, whereas more are required where the channels are not adjacent. However as the RF bandwidth increases it is necessary to ensure that the UE in particular is able to operate over such a wide bandwidth without a reduction in performance. Although the performance requirements are the same for the base station, the space, power consumption, and cost requirements are considerably less stringent, allowing greater flexibility in the design. Additionally for the base station, multi-carrier operation, even if non-aggregated, is already a requirement in many instances, requiring little or no change to the RF elements of the design. Software upgrades would naturally be required to cater for the additional capability.

o Non-contiguous:    Non-contiguous intra-band carrier aggregation is somewhat more complicated than the instance where adjacent carriers are used. No longer can the multi-carrier signal be treated as a single signal and therefore two transceivers are required. This adds significant complexity, particularly to the UE where space, power and cost are prime considerations.

Inter-band non-contiguous:   This form of carrier aggregation uses different bands. It will be of particular use because of the fragmentation of bands - some of which are only 10 MHz wide. For the UE it requires the use of multiple transceivers within the single item, with the

usual impact on cost, performance and power. In addition to this there are also additional complexities resulting from the requirements to reduce intermodulation and cross modulation from the two transceivers

The current standards allow for up to five 20 MHz carriers to be aggregated, although in practice two or three is likely to be the practical limit. These aggregated carriers can be transmitted in parallel to or from the same terminal, thereby enabling a much higher throughput to be obtained.

Carrier aggregation bandwidthsWhen aggregating carriers for an LTE signal, there are several definitions required for the bandwidth of the combined channels. As there as several bandwidths that need to be described, it is necessary to define them to reduce confusion.

LTE Carrier Aggregation Bandwidth Definitions for Intra-Band Case

LTE carrier aggregation bandwidth classesThere is a total of six different carrier aggregation, CA bandwidth classes which are being defined.

CARRIER AGGREGATIONBANDWIDTH CLASS

AGGREGATED TRANSMISSION

BW CONFIGURATION

NUMBER OF COMPONENT CARRIERS

A ≤100 1

B ≤100 2

C 100 - 200 2

NB: classes D, E, & F are in the study phase.

LTE aggregated carriersWhen carriers are aggregated, each carrier is referred to as a component carrier. There are two categories:

Primary component carrier:   This is the main carrier in any group. There will be a primary downlink carrier and an associated uplink primary component carrier.

Secondary component carrier:   There may be one or more secondary component carriers.

There is no definition of which carrier should be used as a primary component carrier - different terminals may use different carriers. The configuration of the primary component carrier is terminal specific and will be determined according to the loading on the various carriers as well as other relevant parameters.

In addition to this the association between the downlink primary carrier and the corresponding uplink primary component carrier is cell specific. Again there are no definitions of how this must be organised. The information is signalled to the terminal of user equipment as part of the overall signalling between the terminal and the base station.

Carrier aggregation cross carrier schedulingWhen LTE carrier aggregation is used, it is necessary to be able to schedule the data across the carriers and to inform the terminal of the DCI rates for the different component carriers. This information may be implicit, or it may be explicit dependent upon whether cross carrier scheduling is used.

Enabling of the cross carrier scheduling is achieved individually via the RRC signalling on a per component carrier basis or a per terminal basis.

When no cross carrier scheduling is arranged, the downlink scheduling assignments achieved on a per carrier basis, i.e. they are valid for the component carrier on which they were transmitted.

For the uplink, an association is created between one downlink component carrier and an uplink component carrier. In this way when uplink grants are sent the terminal or UE will know to which uplink component carrier they apply.

Where cross carrier scheduling is active, the PDSCH on the downlink or the PUSCH on the uplink is transmitted on an associate component carrier other than the PDCCH, the carrier indicator in the PDCCH provides the information about the component carrier used for the PDSCH or PUSCH.

It is necessary to be able to indicate to which component carrier in any aggregation scheme a grant relates. To facilitate this, component carriers are numbered. The primary component carrier is numbered zero, for all instances, and the different secondary component carriers are assigned a unique number through the UE specific RRC signalling. This means that even if the terminal or user equipment and the base station, eNodeB may have different understandings of the component carrier numbering during reconfiguration, transmissions on the primary component carrier can be scheduled.

4G LTE CoMP, Coordinated Multipoint Tutorial- 4G LTE Advanced CoMP, coordinated multipoint is used to send and receive data to and from a UE from several points to ensure the optimum performance is achieved even at cell edges.

4G LTE ADVANCED INCLUDES:

LTE Advanced Tutorial

Carrier Aggregation

Coordinated Multipoint - CoMP

LTE Relay

LTE D2D

LTE HetNet

See also

3G LTE

LTE CoMP or Coordinated Multipoint is a facility that is being developed for LTE Advanced - many of the facilities are still under development and may change as the standards define the different elements of CoMP more specifically.

LTE Coordinated Multipoint is essentially a range of different techniques that enable the dynamic coordination of transmission and reception over a variety of different base stations. The aim is to improve overall quality for the user as well as improving the utilisation of the network.

Essentially, LTE Advanced CoMP turns the inter-cell interference, ICI, into useful signal, especially at the cell borders where performance may be degraded.

Over the years the importance of inter-cell interference, ICI has been recognised, and various techniques used from the days of GSM to mitigate its effects. Here interference averaging techniques such as frequency hopping were utilised. However as technology has advanced, much tighter and more effective methods of combating and utilising the interference have gained support.

LTE CoMP and 3GPPThe concepts for Coordinated Multipoint, CoMP, have been the focus of many studies by 3GPP for LTE-Advanced as well as the IEEE for their WiMAX, 802.16 standards. For 3GPP there are studies that have focussed on the techniques involved, but no conclusion has been reached regarding the full implementation of the scheme. However basic concepts have been established and these are described below.

CoMP has not been included in Rel.10 of the 3GPP standards, but as work is on-going, CoMP is likely to reach a greater level of consensus. When this occurs it will be included in future releases of the standards.

Despite the fact that Rel.10 does not provide any specific support for CoMP, some schemes can be implemented in LTE Rel.10 networks in a proprietary manner. This may enable a simpler upgrade when standardisation is finally agreed.

LTE CoMP - the advantagesAlthough LTE Advanced CoMP, Coordinated Multipoint is a complex set of techniques, it brings many advantages to the user as well as the network operator.

Makes better utilisation of network:   By providing connections to several base stations at once, using CoMP, data can be passed through least loaded base stations for better resource utilisation.

Provides enhanced reception performance:   Using several cell sites for each connection means that overall reception will be improved and the number of dropped calls should be reduced.

Multiple site reception increases received power:   The joint reception from multiple base stations or sites using LTE Coordinated Multipoint techniques enables the overall received power at the handset to be increased.

Interference reduction:   By using specialised combining techniques it is possible to utilise the interference constructively rather than destructively, thereby reducing interference levels.

What is LTE CoMP? - the basicsCoordinated multipoint transmission and reception actually refers to a wide range of techniques that enable dynamic coordination or transmission and reception with multiple geographically separated eNBs. Its aim is to enhance the overall system performance, utilise the resources more effectively and improve the end user service quality.

One of the key parameters for LTE as a whole, and in particular 4G LTE Advanced is the high data rates that are achievable. These data rates are relatively easy to maintain close to the base station, but as distances increase they become more difficult to maintain.

Obviously the cell edges are the most challenging. Not only is the signal lower in strength because of the distance from the base station (eNB), but also interference levels from neighbouring eNBs are likely to be higher as the UE will be closer to them.

4G LTE CoMP, Coordinated Multipoint requires close coordination between a number of geographically separated eNBs. They dynamically coordinate to provide joint scheduling and transmissions as well as proving joint processing of the received signals. In this way a UE at the edge of a cell is able to be served by two or more eNBs to improve signals reception / transmission and increase throughput particularly under cell edge conditions.

Concept of LTE Advanced CoMP - Coordinated Multipoint

In essence, 4G LTE CoMP, Coordinated Multipoint falls into two major categories:

Joint processing:   Joint processing occurs where there is coordination between multiple entities - base stations - that are simultaneously transmitting or receiving to or from UEs.

Coordinated scheduling or beamforming:   This often referred to as CS/CB (coordinated scheduling / coordinated beamforming) is a form of coordination where a UE is transmitting with a single transmission or reception point - base station. However the communication is made with an exchange of control among several coordinated entities.

To achieve either of these modes, highly detailed feedback is required on the channel properties in a fast manner so that the changes can be made. The other requirement is for very close coordination between the eNBs to facilitate the combination of data or fast switching of the cells.

The techniques used for coordinated multipoint, CoMP are very different for the uplink and downlink. This results from the fact that the eNBs are in a network, connected to other eNBs, whereas the handsets or UEs are individual elements.

Downlink LTE CoMPThe downlink LTE CoMP requires dynamic coordination amongst several geographically separated eNBs transmitting to the UE. The two formats of coordinated multipoint can be divided for the downlink:

Joint processing schemes for transmitting in the downlink :   Using this element of LTE CoMP, data is transmitted to the UE simultaneously from a number of different eNBs. The aim is to improve the received signal quality and strength. It may also have the aim of actively cancelling interference from transmissions that are intended for other UEs.

This form of coordinated multipoint places a high demand onto the backhaul network because the data to be transmitted to the UE needs to be sent to each eNB that will be transmitting it to the UE. This may easily double or triple the amount of data in the network dependent upon how many eNBs will be sending the data. In addition to this, joint processing data needs to be sent between all eNBs involved in the CoMP area.

Coordinated scheduling and or beamforming:   Using this concept, data to a single UE is transmitted from one eNB. The scheduling decisions as well as any beams are coordinated to control the interference that may be generated.

The advantage of this approach is that the requirements for coordination across the backhaul network are considerably reduced for two reasons:

o UE data does not need to be transmitted from multiple eNBs, and therefore only needs to be directed to one eNB.

o Only scheduling decisions and details of beams needs to be coordinated between multiple eNBs.

Uplink LTE CoMP

Joint reception and processing:   The basic concept behind this format is to utilise antennas at different sites. By coordinating between the different eNBs it is possible to form a virtual antenna array. The signals received by the eNBs are then combined and processed to produce the final output signal. This technique allows for signals that are very low in strength, or masked by interference in some areas to be receiving with few errors.

The main disadvantage with this technique is that large amounts of data need to be transferred between the eNBs for it to operate.

Coordinated scheduling:   This scheme operates by coordinating the scheduling decisions amongst the ENBs to minimise interference.

As in the case of the downlink, this format provides a much reduced load in the backhaul network because only the scheduling data needs to be transferred between the different eNBs that are coordinating with each other.

Overall requirements for LTE CoMPOne of the key requirements for LTE is that it should be able to provide a very low level of latency. The additional processing required for multiple site reception and transmission could add significantly to any delays. This could result from the need for the additional processing as well as the communication between the different sites.

To overcome this, it is anticipated that the different sites may be connected together in a form of centralised RAN, or C-RAN.

By Ian Poole

4G LTE Advanced Relay- 4G LTE Advanced relay technology, how LTE relaying works and details about relay nodes, RNs.

4G LTE ADVANCED INCLUDES:

LTE Advanced Tutorial

Carrier Aggregation

Coordinated Multipoint - CoMP

LTE Relay

LTE D2D

LTE HetNet

See also

3G LTE

Relaying is one of the features being proposed for the 4G LTE Advanced system. The aim of LTE relaying is to enhance both coverage and capacity.

The idea of relays is not new, but LTE relays and LTE relaying is being considered to ensure that the optimum performance is achieved to enable the expectations of the users to be met while still keeping OPEX within the budgeted bounds.

Need for LTE relay technologyOne of the main drivers for the use of LTE is the high data rates that can be achieved. However all technologies suffer from reduced data rates at the cell edge where signal levels are lower and interference levels are typically higher.

The use of technologies such as MIMO, OFDM and advanced error correction techniques improve throughput under many conditions, but do not fully mitigate the problems experienced at the cell edge.

As cell edge performance is becoming more critical, with some of the technologies being pushed towards their limits, it is necessary to look at solutions that will enhance performance at the cell edge for a comparatively low cost. One solution that is being investigated and proposed is that of the use of LTE relays.

LTE relay basicsLTE relaying is different to the use of a repeater which re-broadcasts the signal. A relay will actually receive, demodulates and decodes the data, apply any error correction, etc to it and then re-transmitting a new signal. In this way, the signal quality is enhanced with an LTE relay, rather than suffering degradation from a reduced signal to noise ratio when using a repeater.

For an LTE relay, the UEs communicate with the relay node, which in turn communicates with a donor eNB.

Relay nodes can optionally support higher layer functionality, for example decode user data from the donor eNB and re-encode the data before transmission to the UE.

The LTE relay is a fixed relay - infrastructure without a wired backhaul connection, that relays messages between the base station (BS) and mobile stations (MSs) through multihop communication.

There are a number of scenarios where LTE relay will be advantageous.

Increase network density:   LTE relay nodes can be deployed very easily in situations where the aim is to increase network capacity by increasing the number of eNBs to ensure good signal levels are received by all users. LTE relays are easy to install as they require no separate backhaul and they are small enabling them to be installed in many convenient areas, e.g. on street lamps, on walls, etc.

LTE relay used to increase network density

Network coverage extension :   LTE relays can be used as a convenient method of filling small holes in coverage. With no need to install a complete base station, the relay can be

quickly installed so that it fills in the coverage blackspot.

LTE relay coverage extension - filling in coverage hole

Additionally LTE relay nodes may be sued to increase the coverage outside main area. With suitable high gain antennas and also if antenna for the link to the donor eNB is placed in a suitable location it will be able to maintain good communications and provide the required coverage extension.

LTE relay coverage extension - extending coverage

It can be noted that relay nodes may be cascaded to provide considerable extensions of the coverage.

Rapid network roll-out:   Without the need to install backhaul, or possibly install large masts, LTE relays can provide a very easy method of extending coverage during the early roll-out of a network. More traditional eNBs may be installed later as the traffic volumes increase.

LTE relay to provide fast rollout & deployment

LTE relaying full & half duplexLTE relay nodes can operate in one of two scenarios:

Half-Duplex:   A half-duplex system provides communication in both directions, but not simultaneously - the transmissions must be time multiplexed. For LTE relay, this requires careful scheduling. It requires that the RN coordinates its resource allocation with the UEs in the uplink and the assigned donor eNB in the downlink. This can be achieved using static pre-assigned solutions, or more dynamic ones requiring more intelligence and communication for greater flexibility and optimisation.

Full Duplex:   For full duplex, the systems are able to transmit and receive at the same time. For LTE relay nodes this is often on the same frequency. The relay nodes will receive the signal, process it and then transmit it on the same frequency with a small delay, although this will be small when compared to the frame duration. To achieve full duplex, there must be good isolation between the transmit and receive antennas.

When considering full or half duplex systems for LTE relay nodes, there is a trade-off between performance and the relay node cost. The receiver performance is critical, and also the antenna isolation must be reasonably high to allow the simultaneous transmission and reception when only one channel is used.

LTE relay typesThere is a number of different types of LTE relay node that can be used. However before defining the relay node types, it is necessary to look at the different modes of operation.

One important feature or characteristic of an LTE relay node is the carrier frequency it operates on. There are two methods of operation:

Inband:   An LTE relay node is said to be "Inband" if the link between the base station and the relay node are on the same carrier frequency as the link between the LTE relay node and the user equipment, UE, i.e. the BS-RN link and the BS-UE link are on the same carrier frequency.

Outband:   For Outband LTE relay nodes, RNs, the BS-RN link operates of a different carrier frequency to that of the RN-UE link.

For the LTE relay nodes themselves there are two basic types that are being proposed, although there are subdivisions within these basic types:

Type 1 LTE relay nodes:  These LTE relays control their cells with their own identity including the transmission of their own synchronisation channels and reference symbols. Type 1 relays appear as if they are a Release 8 eNB to Release 8 UEs. This ensures backwards compatibility. The basic Type 1 LTE relay provides half duplex with Inband transmissions.

There are two further sub-types within this category:

o Type 1.a:    These LTE relay nodes are outband RNs which have the same properties as the basic Type 1 relay nodes, but they can transmit and receive at the same time, i.e. full duplex.

o Type 1.b:    This form of LTE relay node is an inband form. They have a sufficient isolation between the antennas used for the BS-RN and the RN-UE links. This isolation can be achieved by antenna spacing and directivity as well as specialised digital signal processing techniques, although there are cost impacts of doing this. The performance of these RNs is anticipated to be similar to that of femtocells.

Type 2 LTE relay nodes:  These LTE relaying nodes do not have their own cell identity and look just like the main cell. Any UE in range is not able to distinguish a relay from the main eNB within the cell. Control information can be transmitted from the eNB and user data from the LTE relay.

LTE RELAY CLASS CELL ID DUPLEX FORMAT

Type 1 Yes Inband half duplex

Type 1.a Yes Outband full duplex

Type 1.b Yes Inband full duplex

Type 2 No Inband full duplex

Summary of Relay Classifications & Features in 3GPP Rel.10

There is still much work to be undertaken on LTE relaying. The exact manner of LTE relays is to be included in Release 10 of the 3GPP standards and specifications.

By Ian Poole

4G LTE Device to Device, D2D- 4G LTE Advanced device to device, D2D communication for high data rate local direct communications using LTE devices.

4G LTE ADVANCED INCLUDES:

LTE Advanced Tutorial

Carrier Aggregation

Coordinated Multipoint - CoMP

LTE Relay

LTE D2D

LTE HetNet

See also

3G LTE

One of the schemes that is being researched and considered for 4G LTE Advanced is the concept of Device to Device communications.

This form of communication using the LTE system is used where direct communications are needed within a small area.

LTE D2D communications is a peer to peer link which does not use the cellular network infrastructure, but enables LTE based devices to communicate directly with one another when they are in close proximity.

One of the particular applications where LTE device to device communications is for the emergency services. With proprietary systems like TETRA being expensive to maintain because of the separate infrastructure required, the LTE is becoming increasingly attractive as a result of cost, and performance. The main issue is that of reliability.

LTE device to device communication is also being investigated for applications where peer discovery is required for commercial applications in the presence of network support.

LTE D2D was a feature that appeared in LTE REl 12.

Benefits of D2D communicationsDirect communications between devices can provide several benefits to users in various applications where the devices are in close proximity:

Data rates:   Devices may be remote from cellular infrastructure and may therefore not be able to support high data rate transmission that may be required

Reliable communications:   LTE Device to Device can be sued to communicate locally between devices to provide high reliability communications especially if the LTE network has failed for any reason - even as a result of the disaster.

Instant communications:   As the D2D communications does not rely on the network infrastructure the devices could be used for instant communications between a set number of devices in the same way that walkie-talkies are used. This is particularly applicable to t e way communications may be used by the emergency services.

Use of licensed spectrum:   Unlike other deveice to device systems including Wi-Fi, Bluetooth, etc, LTE would use licensed spectrum and this would enable the frequencies to be used to be less subject to interference, thereby allowing more reliable communications.

Interference reduction:   By not having to communicate directly with a base station, fewer links are required (i.e. essentially only between devices) and this has an impact of the amount of data being transmitted within a given spectrum allocation. This reduces the overall level of interference.

Power saving :   Using device to device communication provides energy saving for a variety of reasons. One major area is that if the two0 devices are in close proximity then lower transmission power levels are required.

LTE D2D basics4G LTE device to device, D2D would enable the direct link of a device, user equipment UE, etc to another device using the cellular spectrum. This could allow large volumes of media or other data to be transferred from one device to another over short distances and using a direct connection.. This form of device to device transfer would enable the data to be transferred without the need to run it via the cellular network itself, thereby avoiding problems with overloading the network.

Other examples of direct communication include Wi-Fi Direct, Bluetooth, etc. Networks can be formed in many ways.

LTE device to device, D2D concept

The D2D system would operate in a manner where devices within a locality would be able to provide direct communications rather than transmitting via the network. The cellular infrastructure, if present, may assist with issues like peer discovery, synchronisation, and the provision of identity and security information.

LTE D2D issuesThe addition of the LTE D2D or device to device communication capability impacts the whole of the network and is therefore not a trivial addition, Issues like authorisation and authentication are currently handled by the network and the overall LTE system would need to be extended to accommodate device to device to communication without the essential presence of the network.

Another issue would be that of direct communication between devices that are under subscriptions with different operators, although this is unlikely to occur in the event of public service or emergency services.

By Ian Poole

LTE Advanced Heterogeneous Networks, HetNet- LTE heterogeneous network, HetNet technology, how LTE HetNets work and details about their operation and deployment..

4G LTE ADVANCED INCLUDES:

LTE Advanced Tutorial

Carrier Aggregation

Coordinated Multipoint - CoMP

LTE Relay

LTE D2D

LTE HetNet

See also

3G LTE

LTE heterogeneous networks, HetNet are fast becoming a reality.

Within LTE and LTE Advanced, operators see the need to very significantly increase the data capacity of all areas of the network while also reducing the costs as cost per bit rates are falling.

Whilst LTE HetNet technology is starting to be defined, many operators are seeking to utilise the concepts to ensure that the delivery of service to the users meets expectations under the very varying conditions and scenarios that users are placing on the networks.

LTE heterogeneous network basicsTo achieve this LTE and LTE Advanced operators need to adopt a variety of approaches to meet the needs of a host of scenarios that will occur within the network.

Different types of user will need use the network in different places and for different applications. Coupled to this operators introducing LTE and LTE Advanced networks will have many legacy systems available. In any LTE heterogeneous network it will be necessary to accommodate other radio access technologies including HSPA, UMTS and even EDGE and GPRS. In addition to this other technologies including Wi-Fi also need to be accommodated.

These solutions for LTE heterogeneous networks need to incorporate not only the radio access network solutions, but also the core network as well. In this way a truly heterogeneous network can become functional.

To ensure the best use is made of the available capabilities, all the various elements need to be operated in a manner that is truly seamless to the user. The user should be given the best experience using the best available technology at any given time. The performance and hence the user experience should also be very much the same whatever the location and whatever the application.

Note on Heterogeneous Networks, HetNet:

The concept of the Heterogeneous Network or HetNet has arisen out of the need for cellular telecommunications

operators to be able to operate networks consisting of a variety of radio access technologies, formats of cells and

many other aspects, and combining them to operate in a seamless fashion.

Click on the link for further information about Heterogeneous Networks, HetNet

LTE HetNet featuresThere are a number of features for LTE that can be incorporated into an LTE heterogeneous network above and beyond some of what may be termed the basic wireless heterogeneous network techniques..Although they could conceivably be used with other forms of wireless heterogeneous network, they are currently found in LTE.

Carrier aggregation:   With spectrum allocated for 4G networks, operators often find they have a variety of small bands that they have to piece together to provide the required overall bandwidth needed for 4G LTE. Making these bands work seamlessly is a key element of the LTE heterogeneous network operation.

Coordinated multipoint:   In order to provide the proper coverage at the cell edges, signal from two or more base stations may be needed. Again, providing the same level of service regardless of network technology and areas within the cell can prove to be challenging. Adopting a heterogeneous network approach can assist in providing he same service quality regardless of the position within the cell, and the possibly differing cell and backhaul technologies used for the different base stations.

Heterogeneous networks are now an established concept within LTE networks. The requirement to provide a better level of coverage and performance in a greater variety of situations means that a greater variety of techniques is required. Making all the different technologies from radio access networks to base station technologies and backhaul paths all come together needs careful planning. Early cellular systems had a far more standard approach, where base stations were characterised by the mast and antennas. Now a much greater variety of approaches is needed.

By Ian Poole

LTE Physical, Logical and Transport Channels- overview, information, tutorial about the physical, logical, control and transport channels used within 3GPP, 3G LTE and the LTE channel mapping.

IN THIS SECTION

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

In order that data can be transported across the LTE radio interface, various "channels" are used. These are used to segregate the different types of data and allow them to be transported across the radio access network in an orderly fashion.

Effectively the different channels provide interfaces to the higher layers within the LTE protocol structure and enable an orderly and defined segregation of the data.

3G LTE channel typesThere are three categories into which the various data channels may be grouped.

Physical channels:   These are transmission channels that carry user data and control messages.

Transport channels:   The physical layer transport channels offer information transfer to Medium Access Control (MAC) and higher layers.

Logical channels:   Provide services for the Medium Access Control (MAC) layer within the LTE protocol structure.

3G LTE physical channelsThe LTE physical channels vary between the uplink and the downlink as each has different requirements and operates in a different manner.

Downlink:

o Physical Broadcast Channel (PBCH):    This physical channel carries system information for UEs requiring to access the network. It only carries what is termed Master Information Block, MIB, messages. The modulation scheme is always QPSK and the information bits are coded and rate matched - the bits are then scrambled using a scrambling sequence specific to the cell to prevent confusion with data from other cells.

The MIB message on the PBCH is mapped onto the central 72 subcarriers or six central resource blocks regardless of the overall system bandwidth. A PBCH

message is repeated every 40 ms, i.e. one TTI of PBCH includes four radio frames.

The PBCH transmissions has 14 information bits, 10 spare bits, and 16 CRC bits.

o Physical Control Format Indicator Channel (PCFICH) :    As the name implies the PCFICH informs the UE about the format of the signal being received. It indicates the number of OFDM symbols used for the PDCCHs, whether 1, 2, or 3. The information within the PCFICH is essential because the UE does not have prior information about the size of the control region.

A PCFICH is transmitted on the first symbol of every sub-frame and carries a Control Format Indicator, CFI, field. The CFI contains a 32 bit code word that represents 1, 2, or 3. CFI 4 is reserved for possible future use.

The PCFICH uses 32,2 block coding which results in a 1/16 coding rate, and it always uses QPSK modulation to ensure robust reception.

o Physical Downlink Control Channel (PDCCH) :    The main purpose of this physical channel is to carry mainly scheduling information of different types:

Downlink resource scheduling

Uplink power control instructions

Uplink resource grant

Indication for paging or system information

The PDCCH contains a message known as the Downlink Control Information, DCI which carries the control information for a particular UE or group of UEs. The DCI format has several different types which are defined with different sizes. The different format types include: Type 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3, 3A, and 4.

o Physical Hybrid ARQ Indicator Channel (PHICH) :    As the name implies, this channel is used to report the Hybrid ARQ status. It carries the HARQ ACK/NACK signal indicating whether a transport block has been correctly received. The HARQ indicator is 1 bit long - "0" indicates ACK, and "1" indicates NACK.

The PHICH is transmitted within the control region of the subframe and is typically only transmitted within the first symbol. If the radio link is poor, then the PHICH is extended to a number symbols for robustness.

Uplink:

o Physical Uplink Control Channel (PUCCH) :    The Physical Uplink Control Channel, PUCCH provides the various control signalling requirements. There are a number of different PUCCH formats defined to enable the channel to carry the required information in the most efficient format for the particular scenario encountered. It includes the ability to carry SRs, Scheduling Requests.

The basic formats are summarised below:

PUCCH FORMAT

UPLINK CONTROL INFORMATION MODULATION SCHEME

BITS PER SUB-FRAME

NOTES

Format 1 SR N/A N/A

Format 1a 1 bit HARQ ACK/NACK with or without SR

BPSK 1

Format 1b 2 bit HARQ ACK/NACK with or without SR

QPSK 2

Format 2 CQI/PMI or RI QPSK 20

Format 2a CQI/PMI or RI and 1 bit HARQ ACK/NACK

QPSK + BPSK 21

Format 2b CQI/PMI or RI and 2 bit HARQ ACK/NACK

QPSK + BPSK 22

Format 3 Provides support for carrier aggregation.

o Physical Uplink Shared Channel (PUSCH) :    This physical channel found on the LTE uplink is the Uplink counterpart of PDSCH

o Physical Random Access Channel (PRACH) :    This uplink physical channel is used for random access functions. This is the only non-synchronised transmission that the UE can make within LTE. The downlink and uplink propagation delays are unknown when PRACH is used and therefore it cannot be synchronised.

The PRACH instance is made up from two sequences: a cyclic prefix and a guard period. The preamble sequence may be repeated to enable the eNodeB to decode the preamble when link conditions are poor.

LTE transport channelsThe LTE transport channels vary between the uplink and the downlink as each has different requirements and operates in a different manner. Physical layer transport channels offer information transfer to medium access control (MAC) and higher layers.

Downlink:

o Broadcast Channel (BCH) :    The LTE transport channel maps to Broadcast Control Channel (BCCH)

o Downlink Shared Channel (DL-SCH) :    This transport channel is the main channel for downlink data transfer. It is used by many logical channels.

o Paging Channel (PCH) :    To convey the PCCH

o Multicast Channel (MCH) :    This transport channel is used to transmit MCCH information to set up multicast transmissions.

Uplink:

o Uplink Shared Channel (UL-SCH) :    This transport channel is the main channel for uplink data transfer. It is used by many logical channels.

o Random Access Channel (RACH) :    This is used for random access requirements.

LTE logical channelsThe logical channels cover the data carried over the radio interface. The Service Access Point, SAP between MAC sublayer and the RLC sublayer provides the logical channel.

Control channels: these LTE control channels carry the control plane information:

o Broadcast Control Channel (BCCH) :    This control channel provides system information to all mobile terminals connected to the eNodeB.

o Paging Control Channel (PCCH) :    This control channel is used for paging information when searching a unit on a network.

o Common Control Channel (CCCH) :    This channel is used for random access information, e.g. for actions including setting up a connection.

o Multicast Control Channel (MCCH) :    This control channel is used for Information needed for multicast reception.

o Dedicated Control Channel (DCCH) :    This control channel is used for carrying user-specific control information, e.g. for controlling actions including power control, handover, etc..

Traffic channels:These LTE traffic channels carry the user-plane data:

o Dedicated Traffic Channel (DTCH) :    This traffic channel is used for the transmission of user data.

o Multicast Traffic Channel (MTCH) :    This channel is used for the transmission of multicast data.

It will be seen that many of the LTE channels bear similarities to those sued in previous generations of mobile telecommunications.

TE Frame and Subframe Structure- information, overview, or tutorial about the LTE frame and subframe structure including LTE Type 1 and LTE Type 2 frames.

IN THIS SECTION

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

In order that the 3G LTE system can maintain synchronisation and the system is able to manage the different types of information that need to be carried between the base-station or eNodeB and the User Equipment, UE, 3G LTE system has a defined LTE frame and subframe structure for the E-UTRA or Evolved UMTS Terrestrial Radio Access, i.e. the air interface for 3G LTE.

The frame structures for LTE differ between the Time Division Duplex, TDD and the Frequency Division Duplex, FDD modes as there are different requirements on segregating the transmitted data.

There are two types of LTE frame structure:

1. Type 1:   used for the LTE FDD mode systems.

2. Type 2:   used for the LTE TDD systems.

Type 1 LTE Frame StructureThe basic type 1 LTE frame has an overall length of 10 ms. This is then divided into a total of 20 individual slots. LTE Subframes then consist of two slots - in other words there are ten LTE subframes within a frame.

Type 1 LTE Frame Structure ( 10ms )

Type 2 LTE Frame StructureThe frame structure for the type 2 frames used on LTE TDD is somewhat different. The 10 ms frame comprises two half frames, each 5 ms long. The LTE half-frames are further split into five subframes, each 1ms long.

Type 2 LTE Frame Structure(shown for 5ms switch point periodicity).

The subframes may be divided into standard subframes of special subframes. The special subframes consist of three fields;

DwPTS - Downlink Pilot Time Slot

GP - Guard Period

UpPTS - Uplink Pilot Time Slot.

These three fields are also used within TD-SCDMA and they have been carried over into LTE TDD (TD-LTE) and thereby help the upgrade path. The fields are individually configurable in terms of length, although the total length of all three together must be 1ms.

LTE TDD / TD-LTE subframe allocationsOne of the advantages of using LTE TDD is that it is possible to dynamically change the up and downlink balance and characteristics to meet the load conditions. In order that this can be achieved in an ordered fashion, a number of standard configurations have been set within the LTE standards.

A total of seven up / downlink configurations have been set, and these use either 5 ms or 10 ms switch periodicities. In the case of the 5ms switch point periodicity, a special subframe exists in both half frames. In the case of the 10 ms periodicity, the special subframe exists in the first half frame only. It can be seen from the table below that the subframes 0 and 5 as well as DwPTS are always reserved for the downlink. It can also be seen that UpPTS and the subframe immediately following the special subframe are always reserved for the uplink transmission.

UPLINK-DOWNLINK

CONFIGURATION

DOWNLINK TO UPLINK SWITCH

PERIODICITY

SUBFRAME NUMBER

0 1 2 3 4 5 6 7 8 9

0 5 ms D S U U U D S U U U

1 5 ms D S U U D D S U U D

2 5 ms D S U D D D S U D D

3 10 ms D S U U U D D D D D

4 10 ms D S U U D D D D D D

5 10 ms D S U D D D D D D D

6 5 ms D S U U U D S U U D

Where:    D is a subframe for downlink transmission    S is a "special" subframe used for a guard time    U is a subframe for uplink transmission

Uplink / Downlink subframe configurations for LTE TDD (TD-LTE)

By Ian Poole

LTE Frequency Band Notes- additional notes and information about the LTE frequency bands.

IN THIS SECTION

LTE Introduction

OFDM, OFDMA, SC-FDMA

LTE MIMO

TDD & FDD

Frame & subframe

Physical logical & transport channels

Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

There are many different bands that are being allocated for use with LTE. These bands are defined on the previous page.

On this page, additional notes and information are given about these different LTE bands.

LTE bands overviewThe number of bands allocated for use has increased as the pressure increases on spectrum.

It has not been possible for all LTE band allocations to be the same across the globe because of the different regulatory positions in different countries. It has not been possible to gain global allocations.

In some cases bands appear to overlap. This is because of the different levels of availability around the globe.

This means that roaming with LTE may have some limitations as not all handsets or UEs will be able to access the same frequencies.

Notes accompanying LTE band tabulationsThere are a few notes that can give some background to the LTE bands defined in the table on the previous page.

LTE Band 1:   This is one of the paired bands that was defined for the 3G UTRA and 3GPP rel 99.

LTE Band 4:   This LTE band was introduced as a new band for the Americas at the World (Administrative) Radio Conference, WRC-2000. This international conference is where international spectrum allocations are agreed. The downlink of band 4 overlaps with the downlink for Band 1. This facilitates roaming.

LTE Band 9:   This band overlaps with Band 3 but has different band limits and it is also only intended for use in Japan. This enables roaming to be achieved more easily, and many terminals are defined such that that are dual band 3 + 9

LTE Band 10:   This band is an extension to Band 4 and may not be available everywhere. It provides an increase from 45 MHz bandwidth (paired) to 60 MHz paired.

LTE Band 11:   This "1500 MHz" band is identified by 3GPP as a Japanese band, but it is allocated globally to the mobile service on a "co-primary basis".

LTE Band 12:   This band was previously used for broadcasting and has been released as a result of the "Digital Dividend."

LTE Band 13:   This band was previously used for broadcasting and has been released as a result of the "Digital Dividend." The duplex configuration is reversed from the standard, having the uplink higher in frequency than the downlink.

LTE Band 14:   This band was previously used for broadcasting and has been released as a result of the "Digital Dividend." The duplex configuration is reversed from the standard, having the uplink higher in frequency than the downlink.

LTE Band 15:   This LTE band has been defined by ETSI for use in Europe, but this has not been adopted by 3GPP. This band combines two nominally TDD bands to provide one FDD band.

LTE Band 16:   This LTE band has been defined by ETSI for use in Europe, but this has not been adopted by 3GPP. This band combines two nominally TDD bands to provide one FDD band.

LTE Band 17:   This band was previously used for broadcasting and has been released as a result of the "Digital Dividend."

LTE Band 20:   The duplex configuration is reversed from the standard, having the uplink higher in frequency than the downlink.

LTE Band 21:   This "1500 MHz" band is identified by 3GPP as a Japanese band, but it is allocated globally to the mobile service on a "co-primary basis".

LTE Band 24:   The duplex configuration is reversed from the standard, having the uplink higher in frequency than the downlink.

LTE Band 33:   This was one of the bands defined for unpaired spectrum in Rel 99 of the 3GPP specifications.

LTE Band 34:   This was one of the bands defined for unpaired spectrum in Rel 99 of the 3GPP specifications.

LTE Band 38:   This band is in the centre band spacing between the uplink and downlink pairs of LTE band 7.

Although 3GPP can defined bands for use in LTE or any other mobile service, the actual allocations are made on an international basis by the ITU are World radio Conferences, and then the individual country administrations can allocate spectrum use in their own countries. 3GPP has no legal basis, and can only work with the various country administrations.

Frequency bands may be allocated on a primary and secondary basis. Primary users have the first access to a band, secondary users, in general, may use the band provided they do not cause interference to the primary users.

LTE and LTE Advance Concept and Question

What is PUCCH Mixed Mode in LTE and PUCCH Format Types in LTE

What are different PUCCH formats and PUCCH Mixed Mode in LTE?

We should know what all PUCCH formats are available in LTE or LTE-A, before exploring PUCCH Mixed Mode.

Basically PUCCH formats are of two types Format 1 and Format 2 (Format 3 is introduced in LTE advance release 10, which uses modulation scheme QPSK and number of bits used as 48 per subframe).

PUCCH Format 1 (Rel 8):

Format Type Control Information Modulation Scheme No. of bits / Subframe

1 SR (Scheduling Request) Not Applicable Not Applicable

1a HARQ ACK/NACK BPSK 1 bit

1b HARQ ACK/NACK (for MIMO)

QPSK 2 bits

PUCCH Format 2:

Format Type Control Information Modulation Scheme No. of bits / Subframe

2 CSI (Channel State Info.) QPSK 20 bits

2a CSI+HARQ ACK/NACK QPSK+BPSK 21 bits

2b CSI+HARQ ACK/NACK (for MIMO)

QPSK + BPSK 22 bits

Location of PUCCH resources are on the edge of bandwidth allocated. To provide frequency diversity, PUCCH frequency resources are frequency hopping on the slot boundary (mentioned in below figure).

Mapping of modulation symbols for the physical uplink control channel

Why the location of PUCCH resources are on the edge of bandwidth? Here is the answer, to assign the contiguous RBs to single terminal for PUSCH data transmission along with increased frequency diversity experience by control signaling.  

You might be thinking that what could be the maximum value of m. The value of m depends on the number of UEs in the eNB or Macro eNB coverage area. To control more UEs, more control signaling with more PUCCH RBs would be required and hence value of m will be more.  Maximum value of m could be equivalent to the maximum number of RBs (in case of 10MHz bandwidth, it is 50), but it is not practical.

Now how do we derive the value of m?

Index m is derived from higher layer parameter, Refer 36.211 section 5.4.3 ( N1_PUCCH, N_RB_SC, N_UL_RB, N2_RB, c, Ncs, delta_pucch_shift) for Format 1.

Index m is derived from higher layer parameter, Refer 36.211 section 5.4.3 (N2_PUCCH, N_RB_SC, N_UL_RB) for Format 2. 

Where,

N1_PUCCH is Resource index for PUCCH formats 1/1a/1b.

N_RB_SC is Resource block size in the frequency domain, expressed as a number of subcarriers.

N_UL_RB is Uplink bandwidth configuration, expressed in multiples of N_RB_SC.

N2_RB is Bandwidth available for use by PUCCH formats 2/2a/2b, expressed in multiples of N_RB_SC.

Ncs is Number of cyclic shifts used for PUCCH formats 1/1a/1b in a resource block with a mix of formats 1/1a/1b and 2/2a/2b.

N2_PUCCH is Resource index for PUCCH formats 2/2a/2b.

You can explore more about the calculation of m here   .

So, what is PUCCH Mixed Mode? In my view, PUCCH mixed mode occurs,  if same resource block is shared between two or more UEs to transmit the PUCCH format 1 by first (or second ) UE and the PUCCH format 2 by second (or first) UE.

The actual meaning of PUCCH Mixed Mode is some UE are transmitting either SR or HARQ ACK/NACK in the same resource block whiles other transmitting CQI/PMI/RI with or without HARQ ACK/NACK in the same resource block.

To enable PUCCH mixed mode, Ncs parameter value should not be set as 0 (should be in between 1..7) and resource index parameter should be same for both UE profile configuration. Also, at most one resource block in each slot can support mix of format 1 and 2 (Example: m=0 in slot 1 and m=0 in slot 2 of subframe, in above figure).   

What is the benefit of using this PUCCH Mixed Mode in LTE?

It would not be suffice to allocate different RBs for different format type for smaller cell bandwidth (Example 1.4MHz, out of 6 RBs 2 RBs will be used for PUCCH for different formats). To minimize this overhead , it would be preferred to mix the format 1 and format 2 in same resource block. However to achieve this some phase rotation are used for guard to separate ACK/NACK and CQI , hence the efficiency in this mixed  mode is slightly lower.

Questions are welcome.

Posted by Abhishek Kumar   at 11:36 5 comments:   Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest

Labels: LTE, LTE advance, PUCCH, PUCCH Formats types, PUCCH MIXED MODE, Resource allocation

F r i d a y , 1 2 J u l y 2 0 1 3

What is Rank Indicaton in LTE

Rank Indication is one of the important input to eNB , in selection of the transmission layer in downlink data transmission. Even though the system is configured in transmission mode 3 (or open loop spatial multiplexing) for a particular UE and if the same UE report the Rank Indication value 1 to eNB, eNB will start sending the data in Tx diversity mode to UE . If UE report Rank Indication 2 , eNB will start sending the downlink data in MIMO mode (Transmission Mode 3).

Why we need this RI in LTE concept? When UE experience bad SNR and it would be difficult (error prone) to decode transmitted downlink data  it gives early warning to eNB by stating Rank Indication value as 1. When UE experience good SNR it pass this information to eNB by indicating rank value as 2.

Because of this reason, you might have observed that some time data transmitted by eNB is in Tx diversity mode, though MIMO was configured and hence you may have observed less downlink throughput than expected one.

However, it is not necessary that eNB will always change the transmission mode based on RI value, it could be implementation specific decision.  Questions are welcome.

Posted by Abhishek Kumar   at 11:16 1 comment:   Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest

Labels: LTE, LTE advance, Rank Indicator

T h u r s d a y , 1 1 J u l y 2 0 1 3

What is CQI PMI RI in LTE?

Well, we had discussed about uplink channel state information Difference between SRS and DMRS by reference signals (SRS and DMRS). Now to achieve 1Gbps or more downlink speed

in LTE with effective resource utilization of full bandwidth available,  CQI PMI RI and many more parameter play very important role. So what are CQI, PMI and RI in LTE?

CQI (Channel Quality Indicator), reported by UE to eNB. UE indicates modulation scheme and coding scheme to eNB , if used I would be able to demodulate and decode the transmitted downlink  data with maximum block error rate 10%. To predict the downlink channel condition, CQI feedback by the UE is an input. CQI reporting can be based on PMI and RI. Higher the CQI value (from 0 to 15) reported by UE, higher the modulation scheme (from QPSK to 64QAM ) and higher the coding rate will be used by eNB to achieve higher efficiency.

PMI (Precoding Matrix Indicator), UE indicates to eNB , which precoding matrix should be used for downlink transmission which is determined by RI.

RI (Rank Indicator), UE indicates to eNB, the number of layers that should be used for downlink transmission to the UE.

RI and PMI can be configured to support MIMO operation (closed loop and open loop spatial multiplexing). These both transmission modes use precoding from a well defined codebook (the lookup table of cross coupling factors used for precoding shared between UE and eNB) to form the transmission layers. In case of transmit diversity PMI and RI need not to be reported to eNB.

In wideband CQI reporting UE report one wideband CQI for the full system bandwidth region.  However, UE can also report CQI value for sub band also.

Now, what about periodicity of CQI, PMI and RI and its values. Yes these can be periodic and aperiodic .

eNB configure type of CQI reporting by RRC signaling. Aperiodic reporting is on request based (by eNB ), which always go with PUSCH.

Periodic CQI reporting can go on both PUCCH and PUSCH (along with data).  The minimum periodicity could be 2 ms. Periodicity are defined in 36.213 for different values of CQI-PMI-ConfigIndex (Table 7.2.2-1A for FDD). The range of CQI-PMI-ConfigIndex is 0 to 1023. Also the periodicity of RI is based on riconfig-index (Table 7.2.2-1B for FDD) and periodicity of CQI-PMI. The range of riconfig-index is 0 to 1023.

Example: From Table 7.2.2-1A of 36.213, for the value of CQI-PMI-ConfigIndex “17” the periodicity of CQI reporting is 20 ms (say X).  From Table 7.2.2-1B of 36.213, for the value of riconfig-index “483” the Y is 8 and the periodicity of RI will be 8 times of X (20ms) =160ms.

What about if CQI/PMI/RI collides with either ACK/NACK or SR on the same subframe? If CQI/PMI/RI collides with positive SR the CQI/PMI/RI will be dropped. If CQI/PMI/RI collides with ACK/NACK and simultaneousACKNACKandCQI is false CQI/PMI/RI will be dropped otherwise CQI/PMI/RI will be multiplexed with ACK/NACK.

It is only the eNB which decide the time and frequency on which UE can transmit the CQI, PMI and RI.  Questions are welcome.

Posted by Abhishek Kumar   at 12:17

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Labels: CQI, CSI, LTE, PMI, RI

W e d n e s d a y , 1 0 J u l y 2 0 1 3

Difference between SRS and DMRS

There are two types of reference signals used in LTE uplink, to estimate uplink channel quality. Which allow eNB to take smart decisions for resource allocation for uplink transmission, link adaptation and to decode transmitted data from UE .

So to take first smart decision by eNB Sounding Reference Signal  (SRS) is being used. SRS is being transmitted by UE on the last symbol of subframe (in which subframe will come to know later). This SRS report the channel quality of over all bandwidth and using this information eNB assign the resource (to UE for uplink transmission )has better channel quality comparing to  other bandwidth  region.

So is SRS optional in LTE? Yes. SRS is configurable and infact we do not need SRS at all in case eNB assign all resource block or full bandwidth or have no choice.

Now on the basis of configuration and node wise there are two types of SRS (refer 36.211), cell specific (Common SRS) and UE specific (Dedicated SRS).  eNB notify UE about the configuration of SRS parameter by RRC messages.

There are two types of SRS on the basis of periodicity. Periodic and Aperiodic (In Rel. 10 LTE Advance). The minimum periodicity of SRS is 2ms (1ms=1subframe) and the maximum is 320ms (it is even more than 320ms which is reserved according to specs 36.213).

Now you might be thinking what if all UEs transmit the SRS with same interval and periodicity or in other words how eNB distinguish the UE specific SRS in case of overlapped SRS transmission. Well in that case using transmission_comb and cyclic shift parameters present in RRC Connection setup and RRC Connection Reconfiguration, eNB distinguish and decode different UE specific SRS.

Demodulation reference signal (DMRS) in uplink transmission is used for channel estimation and for coherent demodulation which comes along with PUSCH and PUCCH. If DMRS is bad or by some reason not decoded properly by base station , PUSCH or PUCCH will be not decoded as well. Hence DMRS is not optional like SRS.

DMRS only state channel quality of frequency region in which PUSCH or PUCCH is being transmitted. So what about positioning of DMRS in resource grid, is this fixed ? Answer is Yes and No both. So, when DMRS sent by UE with PUCCH, position of reference signal vary according to PUCCH format indicator. But in case of PUSCH it is always the center symbol of a slot (3rd symbol of slot0 and 10th symbol of slot1).

To support a large number of UEs (User terminal), a large number of DMRS sequences needed and it is achieved by cyclic shifts of a base sequence. As we know in LTE -Advance we will have concept of MIMO in uplink as well, hence DMRS have to enhance for MIMO transmission and each UE will use different DMRS sequences.

DMRS is always mapped to PUSCH in multiple of 12 sub-carriers , however  DMRS mapped to PUCCH  is always in terms of 12 sub-carriers only.

The only similarity in between SRS and DMRS is both uses Constant Amplitude Zero Autocorrelation (CAZAC) sequences.

You may observe less throughput in case of SRS enabled data transmission , because to report SRS during  uplink data transmission , eNB schedule some RBs to UE which could have been used for actual data.

Guys you may have multiple questions roaming in your mind , so please post those question here.  We will try to learn and explore more.

> What if SRS and CQI coincide on the same subframe? Well in that case a UE shall not transmit SRS whenever SRS and PUCCH format 2/2a/2b transmissions (CQI, CQI with 1 or 2 bit HARQ ACK/NACK) happen to coincide in the same subframe [3GPP 36.213 Section 8.2]. Having said that, does it mean L2 scheduler will not schedule SRS and CQI on the same subframe ?

T u e s d a y , 2 3 S e p t e m b e r 2 0 1 4

Positioning Reference Signal PRS LTEPositioning Reference Signal (PRS) is taken into consideration in one of the LTE release 9 features to determine the location of User Equipment (UE) based on radio access network information. Now you might be thinking that what is the necessity of PRS, if we have a GPS technology already built in smartphones and in other cellular equipment. Just think of it (GPS may not be accurate always and GPS services may not be available all around the geographical areas , also the accuracy of functioning GPS depends on money you have paid for the services and the quality of GPS device). The end user application of this PRS feature could be supporting location based services which can be navigation (direction to hotel etc.), emergency call etc.

Process of finding UE location using PRS:

The overall process of finding UE locations are based on three major steps.

Step 1. UE receive PRS from cells (Reference cell and Neighbor cells)

Step 2. Based on received PRS, UE may measure observed time difference of arrival (OTDA) and report RSTD (mentioned in my previous article of LTE UE Measurement RSRP RSSI RSRQ RSTD) to cell.

Step 3. Based on UE reported reference signal time difference (RSTD), eNodeB may calculate the longitude and latitude of the UE (which can be based on any specific algorithm, not standardized).

Positioning Reference Signal is transmitted in downlink subframes (as per higher layer configuration, discussed later in this article) on antenna port 6. The PRS should not be sent on resource element used for PBCH, PSS or SSS. The PRS sequence will be generated on the basis of slot number, OFDM symbol number, cell ID, normal CP or extended CP.

Position of PRS in terms of OFDM symbol (Resource Element):

If both MBSFN (Multicast Broadcast Single Frequency Network) and normal downlink subframes are configured for PRS, the OFDM symbol configured for PRS uses the same cyclic prefix as subframe 0.

If only MBSFN subframe is configured for PRS, the OFDM symbol configured for PRS will use extended cyclic prefix.

The starting position of PRS OFDM symbol in a subframe will be identical to those in a subframe in which all OFDM symbols have the same CP length as PRS OFDM symbols; iff the subframe is configured for PRS transmission (PRS subframe configuration explained below). For more detail of mapping PRS resource element into resource grid, please refer 3GPP 36.211 section 6.10.4.2 for both normal CP and extended CP.

PRS subframe configuration (PRS periodicity, PRS subframe, PRS Configuration Index, Number of Consecutive PRS subframe):

From specs 36.211 of release 9, the configurations of PRS subframe are explained below where:

Nprs is number of consecutive downlink subframe with PRS (Configured by higher layers may be 1,2,4 or 6 subframes)

Iprs is the PRS Configuration Index (can be any value between 0-2399, values 2400 to 4095 are reserved)

Tprs is the periodicity of PRS in terms of subframes. This could be one value among 160, 320, 640 or 1280 depending on configuration of Iprs.

Dprs is the delta PRS subframe offset (can be Iprs, Iprs-160, Iprs-480 or Iprs-1120), depending on Iprs configuration index.

Please refer below table for composed values of Iprs, Tprs, Dprs:

Now take one example to understand the PRS subframe configuration:

Suppose the Nprs is configured by higher layers is 2 and Iprs is configured as 160. Hence from the above table the value of Dprs will be 0. The PRS instances for the first DL subframe of Nprs shall satisfy below formula:

(10*Nf+ ceiling_func_of Ns/2-Dprs) mod Tprs=0 --------Equation 1

Where Nf is system frame number and Ns is slot number.

Hence put the values of Tprs and Dprs in the above equation:

(10*Nf+ ceiling_func_of Ns/2-0) mod 320=0------------Equation 2

Hence for all the values of Nf and Ns which satisfy the Equation 2, will be the first downlink subframe which carry PRS. Hence Equation 2 satisfied for Nf value 32 and Ns (slot) value 0 (that is subframe #0). Hence the first subframe which carries PRS will be subframe 0 of system frame 32 and subframe 1 of system frame 32 (becauseNprs is configured as 2 from higher layer for accuracy of consecutive PRS).

Questions are welcome.

Posted by Abhishek Kumar   at 09:39 No comments:  

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Labels: lte blog, MBSFN, Positioning Reference Signal, PRS LTE, PRS Subframe

F r i d a y , 1 9 S e p t e m b e r 2 0 1 4

LTE 4G SmartphonesCompany Model Specification Category Speed

(DL-UL)Release date(Tentative)

Apple iPhone6 Detailed Specifications Cat4 150Mbps-50Mbps

September 2014

iPhone6 Plus

Detailed Specifications Cat4 150Mbps-50Mbps

September 2014

iPhone5c Detailed Specifications Cat3 100Mbps-NA

September 2013

iPhone5s Detailed Specifications Cat3 100Mbps-NA

September 2013

iPhone5 Detailed Specifications Cat3 100Mbps September 2012

Samsung Galaxy Note3

Know More Cat4 150Mbps- February 2014

Neo 50Mbps

Galaxy Note3

Know More Cat4 150Mbps-50Mbps

September 2013

Galaxy Express2

Know More Cat3 100Mbps-50Mbps

October 2013

Galaxy Golden

Know More Cat3 100Mbps-50Mbps

November 2013

Galaxy Mega 2

Know More Cat4 150Mbps-50Mbps

September 2014

Motorola PHOTON Q

spec NA NA August 2012

MOTO G 4G

spec NA NA June 2014

Nokia Lumia 635

Know your LTE Phone Cat3 100Mbps-50Mbps

June 2014

Lumia 930

Know your LTE Phone Cat4 150Mbps-50Mbps

July 2014

Lumia 1320

Know your LTE Phone Cat3 100Mbps-50Mbps

January 2014

Lumia 1520

Know your LTE Phone Cat4 150Mbps-50Mbps

November 2013

Lumia 1020

Know your LTE Phone Cat3 100Mbps-50Mbps

July 2013

Lumia 925

Know your LTE Phone Cat3 100Mbps-50Mbps

June 2013

LG LG D722K 4G spec Cat4 150Mbps-50Mbps

NA

LG G3 4G spec Cat4 150Mbps-50Mbps

June 2014

LG Pro 2 4G spec Cat4 150Mbps-50Mbps

April 2014

LG G Flex 4G spec Cat4 150Mbps-50Mbps

November 2013

LG nexus 5

4G spec Cat4 150Mbps-50Mbps

November 2013

Posted by Abhishek Kumar   at 12:29 No comments:  

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Labels: LTE 4G mobile

W e d n e s d a y , 1 7 S e p t e m b e r 2 0 1 4

LTE UE Measurement RSRP RSSI RSRQ RSTDIn LTE or any other cellular radio network, UE report some sort of signal to base station for various decision making. It could be used for better downlink scheduling (using CSI), uplink scheduling (using SRS), cell selection , handover, cell reselection , calculation of uplink and downlink path loss for power control, multipath propagation, Uplink interference and for location based services.

All of these achieved by parameter called RSRP, RSSI, RSRQ and RSTD.

RSRP:

RSRP Reference Signal Received Power is the average power received by UE from a single cell specific reference signal resource element spread over the full bandwidth. It is calculated by UE for cell selection, handover, cell reselection and for path loss calculation for power control. The power measurement is the energy of the OFDMA symbol excluding the energy of the cyclic prefix. The measurement of RSRP may be based on energy of reference signal transmitted by antenna port 1 or 1 and 2. UE comes to know which antenna port can be used for measurement, when it decodes SIB3.

The range of RSRP reported by UE are between -140 dBm to -44dBm (-140dBm <RSRP<= -44dBm). For each 1dBm difference from -140dBm, UE report an integer value (ranging 0 to 97) to base station. Example:

Value 0 reported when UE measure RSRP less than -140dBm (RSRP< -140dBm).

Value 1 reported when UE measure RSRP between -140dBm to -139dBm (-140dBm<=RSRP<-139dBm)

Value 97 reported when UE measure RSRP greater than and equal to -44dBm (RSRP>= -44dBm).

RSSI:

RSSI Receive Signal Strength Indicator is the total received signal power from all sources (power of each resource elements) which includes thermal noise also, unlikely to the RSRP. RSSI is never reported by UE to base station but it is the input to calculate the RSRQ.

RSRQ:

RSRQ Reference signal received quality is also used for cell selection, reselection and handover, only when RSRP is not sufficient for making decision. RSRQ is mathematically defined as (N*RSRP)/RSSI, where N is the number of Resource blocks of the LTE carrier RSSI measurement bandwidth. To calculate RSRQ, the numerator and

denominator are made over the same set of RBs (like for 5MHz, RSRP and RSSI calculation will be done on 25RBs only at a time). Since calculation of RSRQ uses RSSI, it enables the combined reporting of signal strength and interference. Range of RSRQ varies from -19.5dB to -3dB (integer value ranges from 0 to 34 ). For each .5dB variation UE report an integer value in RRC message.

Example:

Value 0 reported by UE to base station when RSRQ measured less than -19.5dBm (RSRQ<-19.5dB).

Value 1 reported by UE to base station when RSRQ measured between -19.5 to -19 (-19.5<=RSRQ<-19dB).

Value 34 reported when RSRQ measured greater than equal to -3dB (RSRQ>=-3dB).

Integer value of RSRP and RSRQ reported by UE is included in RRC message (measurement report of serving cell) shown below:

Measurement of RSRP, RSSI and RSRQ from different antenna port are shown below:

RSTD:

RSTD (reference 3gpp 36.133 and 36.214) reference signal time difference measure the subframe timing difference of reference cell and neighbor cell. RSTD used for location based services and introduced in LTE release 9 . RSTD measurement done by UE and it uses the power received in positioning reference signal (PRS) transmitted by eNodeB. PRS is also introduced in LTE release 9.

Questions are welcome.

Posted by Abhishek Kumar   at 20:59 1 comment:  

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Labels: LTE, PRS, RSRP, RSRQ, RSSI, RSTD, UE Measurement

T h u r s d a y , 4 S e p t e m b e r 2 0 1 4

Downlink Assignment Index (DAI)DAI (Downlink Assignment Index) is an index, which is communicated to UE by eNB to prevent ACK/NACK reporting errors due to HARQ ACK/NAK bundling procedure performed by the UE. To understand how DAI works we need to learn how ACK/NAK reporting used to happen in LTE TDD.

In LTE TDD, UE can send single ACK/NAK of multiple PDSCH sub frame in one bit for each code word CW0 and CW1.

UE perform AND logical operation on each code word CW0 and CW1 (CRC Passed/Failed) of each PDSCH received and report the result in two bits (00, 01, 10, 11) on specific uplink subframe. Below is the table which shows that which all PDSCH subframes need to be bundled for reporting ACK/NAK on which Uplink subframe for each TDD UL DL configurations (Mentioned only for config 1 and config 2 in green color).

For Example:

UL/DL Configuration 1:

We can see that the k value for 2nd subframe (Uplink) are 7,6 (according to Table 10.1.3.1-1 of specs 36.213 ) hence on this uplink subframe the ACK/NAK of 5th and 6th  subframe (PDSCH, shown in green) which could be bundled and will be reported on 2nd uplink subframe.

For 3rd uplink subframe the number of bundled subframe would be 1 (for 9th DL subframe of previous radio frame).

UL/DL Configuration 2:

According to above table, on uplink subframe 2nd, HARQ ACK/NAK   of DL subframe 4, 5, 8 and 6 of previous radio frame can be bundled.

In the same manner, on 7th Uplink subframe,  bundled HARQ ACK/NAK can go for 9th DL subframe of previous radio frame and 0,3rd  and 1st  DL subframe of current radio frame.

So DAI (Downlink Assignment Index), will ensure that number of HARQ bundled and reported by the UE is exactly for same number of PDSCH/PDCCH subframe received by the UE. Now consider a situation where eNB schedule two subsequent subframe to the UE, but UE misses the first transmission in the first subframe and successfully decodes the second subframe. The UE would transmit one ACK only for second transmission but eNB will interpret that, both transmission is successfully decoded by UE. To prevent such errors DAI will play important role.

In UE log , you can see what DAI is communicated to UE in DCI Information and you can also check how many subframes are bundled and transmitted on PUCCH or PUSCH in TDD ACK NAK report. If there is a mismatch there will be chance of DAI mismatch.

Example: Suppose for TDD UL/DL configuration 1, the maximum number of Downlink subframe could be bundled either 1 or 2 or 0 (in case no PDSCH or PDCCH scheduled to UE), hence DAI values can be either 1 or 2 or 4 (according to Table 7.3-X: Value of Downlink Assignment Index of specs 36.213), can be seen in LTE DCI information of UE log.

For more information on DAI Mismatch please refer section 7.3 of 3GPP specs 36.213.

Note: This DAI field (2 bits) is present only in TDD operating mode. Above explanation of DAI value only applicable for TDD UL/DL config other than 0. In UL DL config 0 , this DAI field used as an uplink index to signal for which uplink subframe(s) the grant is valid.

Please share if you like this post helpful and add more information in comment section.

Thanks for visiting. Questions are welcome.

Posted by Abhishek Kumar   at 12:35 1 comment:  

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Labels: DAI lte tdd, DAI Mismatch tdd, Downlink Assignment Index LTE TDD, HARQ ACK NACK LTE TDD, LTE, LTE advance

M o n d a y , 2 8 O c t o b e r 2 0 1 3

KMIMO LTEKMIMO is a parameter which is being used in bit collection , selection and transmission of downlink data (specifically to calculate size of a partition which is used for storing a transport block). It  is equal to  2, if UE is configured to receive PDSCH transmissions based on transmission mode 3, 4 or 8, as defined in section 7.1 of 3GPP 36.213, 1 otherwise.Also in other words , it represents maximum number of transport blocks that may be transmitted to the UE in a single TTI (Transmission Time Interval or 1ms or 1 subframe time). 

Questions are welcome.

Posted by Abhishek Kumar   at 10:31 1 comment:  

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Labels: KMIMO LTE, lte question, transmission modes, TTI

T h u r s d a y , 3 O c t o b e r 2 0 1 3

CQI/PMI and RI on same subframe, SRS and PUCCH format 1/1a/1b 2/2a/2b on same subframe, SR and CQI/PMI on same subframe

If SRS and PUCCH format 2/2a/2b messages coincide in same subframe, UE shall not transmit SRS.If SRS and PUCCH format 1/1a/1b (ACK/NACK and/or +SR) coincide in same subframe, UE shall transmit SRS iff simultaneousSRSACKNACK is true. If SRS and PUSCH RARG (Random Access Response Grant) coincide in same subframe SRS will be dropped.If SRS and retransmission of same transport block (as a part of contention based Random access procedure),  coincide in the same subframe SRS will be dropped.

If SR and CQI/PMI/RI coincide in same sub-frame, CQI/PMI/RI will be dropped only if UE send SR (which is triggered by BSR) otherwise CQI/PMI/RI will be reported by UE on the same subframe.

If CQI/PMI and RI is configured on same subframe and coincide, MAC will schedule RI on that subframe   and hence UE will report RI on that subframe instead of CQI/PMI (One possible reason could be Periodicity of RI is always greater than equal to CQI/PMI. Which means eNB will have RI input less frequent than CQI/PMI input from UE, hence priority is given to RI).(Example: Configure the higher layer parameter cqipmiconfigindex and riconfigindex in a way such that CQI/PMI and RI coincide on same subframe and verify the reporting using UE logs as well as FAPI interface . cqipmiconfigindex=17 and riconfigindex=483 could be one valid configuration to simulate this scenario,  according to Table 7.2.2-1A and Table 7.2.2-1B of 36.213).

Please share if you find this is useful information.Questions are welcome.