LTE Doc.

CELLULAR / MOBILE TELECOMMUNICATIONS

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 was a 3G or as some would call it a 3.99G technology, but with further additions the technology fulfilled the requirements for a 4G standard. In this form it was referred to 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 timeapprox

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

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

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


LTE MIMO

TDD & FDD

Frame & subframe


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.

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 onth e same frequency shifted by 90° which are

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

Click on the link for a QAM tutorial

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 compartmentalise 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 uplink

For 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.

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


LTE MIMO

TDD & FDD

Frame & subframe


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 utilises 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 systemThe transmitter and receiver have more than one antenna and using the processing power available at either end of the link, they are able to utilise 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 utilises 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 optimise 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 beamforming 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.

LTE FDD, TDD, TD-LTE Duplex Schemes- information, overview, or tutorial about the LTE TDD and LTE FDD duplex schemes used with LTE and including TD-LTE.IN THIS SECTION

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

LTE has been defined to accommodate both paired spectrum for Frequency Division Duplex, FDD and unpaired spectrum for Time Division Duplex, TDD operation. It is anticipated that both LTE TDD and LTE FDD will be widely deployed as each form of the LTE standard has its own advantages and disadvantages and decisions can be made about which format to adopt dependent upon the particular application.

LTE FDD using the paired spectrum is anticipated to form the migration path for the current 3G services being used around the globe, most of which use FDD paired spectrum. However there has been an additional emphasis on including TDD LTE using unpaired spectrum. TDD LTE which is also known as TD-LTE is seen as providing the evolution or upgrade path for TD-SCDMA.

In view of the increased level of importance being placed upon LTE TDD or TD-LTE, it is planned that user equipments will be designed to accommodate both FDD and TDD modes. With TDD having an increased level of importance placed upon it, it means that TDD operations will be able to benefit from the economies of scale that were previously only open to FDD operations.

Duplex schemesIt is essential that any cellular communications system must be able to transmit in both directions simultaneously. This enables conversations to be made, with either end being able to talk and listen as required. Additionally when exchanging data it is necessary to be able to undertake virtually simultaneous or completely simultaneous communications in both directions.

It is necessary to be able to specify the different direction of transmission so that it is possible to easily identify in which direction the transmission is being made. There are a variety of differences between the two links ranging from the amount of data carried to the transmission format, and the channels implemented. The two links are defined:

Uplink: the transmission from the UE or user equipment to the eNodeB or base station.

Downlink the transmission from the eNodeB or base station to the UE or user equipment.

Uplink and downlink transmission directionsIn order to be able to be able to transmit in both directions, a user equipment or base station must have a duplex scheme. There are two forms of duplex that are commonly used, namely FDD, frequency division duplex and TDD time division duplex..

Note on TDD and FDD duplex schemes:In order for radio communications systems to be able to communicate in both directions it is necessary to have what

is termed a duplex scheme. A duplex scheme provides a way of organizing the transmitter and receiver so that they

can transmit and receive. There are several methods that can be adopted. For applications including wireless and

cellular telecommunications, where it is required that the transmitter and receiver are able to operate simultaneously,

two schemes are in use. One known as FDD or frequency division duplex uses two channels, one for transmit and

the other for receiver. Another scheme known as TDD, time division duplex uses one frequency, but allocates

different time slots for transmission and reception.

Click on the link for more information on TDD FDD duplex schemes

Both FDD and TDD have their own advantages and disadvantages. Accordingly they may be used for different applications, or where the bias of the communications is different.

Advantages / disadvantages of LTE TDD and LTE FDD for cellular communicationsThere are a number of the advantages and disadvantages of TDD and FDD that are of particular interest to mobile or cellular telecommunications operators. These are naturally reflected into LTE.

COMPARISON OF TDD LTE AND FDD LTE DUPLEX FORMATS

PARAMETER LTE-TDD LTE-FDD

Paired spectrum

Does not require paired spectrum as both transmit and receive occur on the same channel

Requires paired spectrum with sufficient frequency separation to allow simultaneous transmission and reception

Hardware cost Lower cost as no diplexer is needed to isolate the transmitter and receiver. As cost of the UEs is of major importance because of the vast numbers that are produced, this is a key aspect.

Diplexer is needed and cost is higher.

Channel reciprocity

Channel propagation is the same in both directions which enables transmit and receive to use on set of parameters

Channel characteristics different in both directions as a result of the use of different frequencies

UL / DL asymmetry

It is possible to dynamically change the UL and DL capacity ratio to match demand

UL / DL capacity determined by frequency allocation set out by the regulatory authorities. It is therefore not possible to make dynamic changes to match capacity. Regulatory changes would normally be required and capacity is normally allocated so that it is the same in either direction.

Guard period / guard band

Guard period required to ensure uplink and downlink transmissions do not clash. Large guard period will limit capacity. Larger guard period normally required if distances are increased to accommodate larger propagation times.

Guard band required to provide sufficient isolation between uplink and downlink. Large guard band does not impact capacity.

Discontinuous transmission

Discontinuous transmission is required to allow both uplink and downlink transmissions. This can degrade the performance of the RF power amplifier in the transmitter.

Continuous transmission is required.

Cross slot interference

Base stations need to be synchronised with respect to the uplink and downlink transmission times. If neighbouring base stations use different uplink and downlink assignments and share the same channel, then interference may occur between cells.

Not applicable

LTE TDD / TD-LTE and TD-SCDMAApart from the technical reasons and advantages for using LTE TDD / TD-LTE, there are market drivers as well. With TD-SCDMA now well established in China, there needs to be a 3.9G and later a 4G successor to the technology. With unpaired spectrum allocated for TD-SCDMA as well as UMTS TDD, it is natural to see many operators wanting an upgrade path for their technologies to benefit from the vastly increased speeds and improved facilities of LTE. Accordingly there is a considerable interest in the development of LTE TDD, which is also known in China as TD-LTE.

With the considerable interest from the supporters of TD-SCDMA, a number of features to make the mode of operation of TD-LTE more of an upgrade path for TD-SCDMA have been incorporated. One example of this is the subframe structure that has been adopted within LTE TDD / TD-LTE.

While both LTE TDD (TD-LTE) and LTE FDD will be widely used, it is anticipated that LTE FDD will be the more widespread, although LTE TDD has a number of significant advantages, especially in terms of higher spectrum efficiency that can be used by many operators. It is also anticipated that phones will be able to operate using either the LTE FDD or LTE-TDD (TD-LTE) modes. In this way the LTE UEs or user equipments will be dual standard phones, and able to operate in countries regardless of the flavour of LTE that is used - the main problem will then be the frequency bands that the phone can cover.

LTE 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


LTE MIMO

TDD & FDD

Frame & subframe


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

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 Stot.

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

UPLINK-DOWNLINK

CONFIGURATION

DOWNLINK TO UPLINK SWITCH

PERIODICITY

SUBFRAME NUMBER

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)

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


LTE MIMO

TDD & FDD

Frame & subframe


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 channels

The 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.

LTE Frequency Bands & Spectrum Allocations- a summary and tables of the LTE frequency band spectrum allocations for 3G & 4G LTE - TDD and FDD.IN THIS SECTION

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

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 allocations

There is 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

28 703 - 748 758 - 803 45 55 10

29 n/a 717 - 728 11

FDD LTE BANDS & FREQUENCIES

LTE BAND

NUMBER

UPLINK(MHZ)

DOWNLINK(MHZ)

WIDTH OF

BAND (MHZ)

DUPLEX SPACING (MHZ)

BAND GAP

(MHZ)

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. . . . . . . . .

Additional information on LTE frequency bands.

LTE UE Category & Class Definitions- LTE utilises UE or User Equipment categories or classes to define the performance specifications an enable base stations to be able to communicate effectively with them knowing their performance levels. Some like LTE Cat 3, LTE Cat 4 and LTE Cat 0 are widely quoted and used. Other like LTE Cat 7 and LTE Cat 8 are much newer.LTE TUTORIAL INCLUDES

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

In the same way that a variety of other systems adopted different categories for the handsets or user equipments, 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 rationale

The LTE 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 9 different LTE UE categories that are defined. As can be seen in the table below, the different LTE 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 CATEGORIES

LTE UE CATEGORY

LINK 1 2 3 4 5 6 7 8

Downlink 10 50 100 150 300 300 300 1200

Uplink 5 25 50 50 75 50 150 600

It can be seen that the headline data rates for category 8 exceed the requiremetns for IMT-Advanced by a considerable margin.

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 1 - 5

LTE CATEGORY

PARAMETER LTE CAT 1 LTE CAT 2 LTE CAT 3 LTE CAT 4 LTE 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

UL AND DL PARAMETERS FOR LTE UE CATEGORIES 6, 7, 8

LTE CATEGORY

PARAMETER LTE CAT 6 LTE CAT 7 LTE CAT 8

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

299 552 299 552 1 200 000

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

TBD TBD TBD

Total number of soft channel bits

3 667 200 TBD TBD

Maximum number of supported layers for spatial multiplexing in DL

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

TBD TBD TBD

Support for 64-QAM in UL No Yes, up to RAN 4

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 LTE 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 LTE CAT 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 Cat 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.

LTE SAE System Architecture Evolution

- information, overview, or tutorial about the basics of the 3G LTE SAE, system architecture evolution and the LTE NetworkIN THIS SECTION

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

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 grater 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 optimised 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 CoreAs 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.

LTE SON Self Organizing Networks- LTE, Long Term Evolution and the requirements for LTE SON, Self Organising Networks

IN THIS SECTION

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

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 organising networks.

Accordingly LTE can be seen as one of the major drivers behind the self-organising 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 development

The 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 SONAlthough 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 organise 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.

Voice over LTE - VoLTE Tutorial- operation of Voice over LTE VoLTE system for providing a unified format of voice traffic on LTE, and other systems including CSFB, and SV-LTE.IN THIS SECTION

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

The Voice over LTE, VoLTE scheme was devised as a result of operators seeking a standardised 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 standardHowever 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 Voice

When 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 standardised 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 a 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 VoLTEAs 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- it is necessary with VoLTE to ensure that calls can be handed over to legacy systems in a seamless manner - SRVCC, Single radio Voice Call Continuity system ensures that this can be achieved.LTE TUTORIAL INCLUDES

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

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 performanceOne 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 he 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.

LTE-M, LTE Machine to Machine, M2M- with the Internet of Things, IoT, and Machine to Machine, M2M communications becoming more widespread, there has been a growing need for a version of LTE that meets the needs of low power, low data rate and long battery life..LTE TUTORIAL INCLUDES

LTE Introduction


LTE MIMO

TDD & FDD

Frame & subframe


Bands and spectrum

UE categories

SAE architecture

LTE SON

VoLTE

SRVCC

LTE-M

LTE-U / LAA

Security

See also

4G LTE Advanced

The 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.

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


LTE MIMO

TDD & FDD

Frame & subframe


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-LAAIn 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 basicsThe 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-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


LTE MIMO

TDD & FDD

Frame & subframe


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 background

There 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-LAAIn 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 basicsThe 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.

Cellular Telecommunications & Cell Phone Technology- articles and information on the basics of cellular telecommunications and cell phone or mobile phone technology

Key details and essential information about mobile phone or cellular telecommunications technology ranging from the most ercent developments in 5G mobile technology to some of the older established systems including the 2G GSM system that is still widely used.

Most popular cellular telecommunications tutorials

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Basic cellular concepts

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UMB, Ultra Mobile Broadband

UMTS / W-CDMA Tutorial

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