LTE System Overview Training

Slide 0Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
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Course Code
www.huawei.com
LTE System Overview
LTE System Overview
LTE System Overview
Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
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Objectives
Upon completion of this course, you will be able to:
Describe LTE development and features
Outline LTE network architecture
Explain LTE key technologies
Describe LTE deployment
LTE System Overview
LTE System Overview
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Contents
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Contents
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Contents
LTE System Overview
LTE System Overview
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~20ms
LTE is the next step in the evolution of 3GPP Radio Interfaces to deliver “Global Mobile Broadband”.
3G-WCDMA in R99/R4
LTE System Overview
LTE System Overview
Confidential Information of Huawei. No Spreading Without Permission
3GPP set up LTE study item for feasibility in December, 2004, and set up LTE work item for standards in September, 2006,
The first version of LTE commercial protocols were released in 3GPP R8 at the end of 2009, in which 36.XXX are the main protocols.
Requirements of LTE
Peak data rate:100 Mbps DL/ 50 Mbps UL within 20 MHz bandwidth
Up to 200 active users in a cell (5 MHz)
Less than 5 ms user-plane latency
Mobility
Supported for high performance for 15 ~ 120 km/h
Supported up to 350 km/h or even up to 500 km/h
Coverage
Performance should be met for 5 km cells with slight degradation for 30 km cells. Up to 100 km cells not precluded
Enhanced multimedia broadcast multicast service (E-MBMS)
Spectrum flexibility:1.25 ~ 20 MHz
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Drivers for LTE
There are at least three major key drivers for LTE mobile broadband networks:
Demand for higher data-rates
New spectrum allocation
LTE System Overview
LTE System Overview
Market opportunities:
Premium VOD/MOD Services
Consumer Electronics
Business Applications for Vertical Markets
Increased data throughput & spectral efficiency
DL target: average user throughput per MHz to be 3-4 times greater than HSDPA Rel.6 (instantaneous downlink peak data-rate 100Mb/s within 20 MHz downlink allocation – 5bps/Hz)
UL target: average user throughput per MHz to be 2-3 times greater than HSUPA Rel.6 (instantaneous uplink peak data-rate 50Mb/s within 20 MHz downlink allocation – 2.5bps/Hz)
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Contents
LTE System Overview
LTE System Overview
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LTE System Overview
LTE System Overview
Simplified/Flat architecture:
UMTS RNC “removed”
eNodeB connected directly to the Evolved Packet Core (EPC)
The E-UTRAN only transfers PS service in which the voice is transferred by VOIP.
S1 interface connects eNB and EPC (Evolved Packet Core) and functions like Iu-PS.
X2 interface conntets eNB and other eNB and functions like Iur.
eNB
UE authentication.
Mobility management.
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Contents
LTE System Overview
LTE System Overview
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3GPP defines many bands for LTE.
LTE System Overview
LTE System Overview
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LTE Channel Bandwidths
LTE must support the international wireless market and regional spectrum regulations and spectrum availability. To this end the specifications include variable channel bandwidths selectable from 1.4 to 20 MHz, with subcarrier spacing of 15 kHz.
NRB is the number of resource blocks
Channel bandwidth BWChannel [MHz]
The smallest amount of resource that can be allocated in the uplink or downlink is called a resource block (RB). An RB is 180 kHz wide and lasts for one 0.5 ms timeslot. For standard LTE, an RB comprises 12 subcarriers at a 15 kHz spacing,
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Contents
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MIMO: Multiple input multiple output
64QAM
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Multiple access technology in the downlink: OFDM and OFDMA
OFDMA is used as multiple access technology in downlink. OFDMA is a variant of orthogonal frequency division multiplexing (OFDM), a digital multi-carrier modulation scheme.
OFDM signal represented in frequency and time
LTE System Overview
LTE System Overview
OFDMA is a variant of orthogonal frequency division multiplexing (OFDM). OFDM makes use of a large number of closely spaced orthogonal subcarriers that are transmitted in parallel. Each subcarrier is modulated with a conventional modulation scheme (such as QPSK, 16QAM, or 64QAM) at a low symbol rate. The combination of hundreds or thousands of subcarriers enables data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
The diagram in the slide illustrates the key features of an OFDM signal in frequency and time. In the frequency domain, multiple adjacent tones or subcarriers are each independently modulated with data. Then in the time domain, guard intervals are inserted between each of the symbols to prevent inter-symbol interference at the receiver caused by multi-path delay spread in the radio channel.
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Multiple access technology in the downlink: OFDM and OFDMA (cont.)
OFMDA incorporates elements of time division multiple access (TDMA).
LTE System Overview
LTE System Overview
With standard OFDM, very narrow UE-specific transmissions can suffer from narrowband fading and interference. That is why for the downlink 3GPP chose OFDMA, which incorporates elements of time division multiple access (TDMA). OFDMA allows subsets of the subcarriers to be allocated dynamically among the different users on the channel, as shown in Figure 7. The result is a more robust system with increased capacity. This is due to the trunking efficiency of multiplexing low rate users and the ability to schedule users by frequency, which provides resistance to multi-path fading.
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The key technologies of IFFT and FFT are separately used in the transmitter and the receiver, IFFT modulates the parallel data to different sub-carriers, and implements the transmission from frequency domain to time domain, and FFT has the inverse procedure
Adding Cyclic Prefix is to avoid the inter-carrier interference, and insure the orthogonality of the different sub-carriers
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Multiple access technology in the uplink: SC-FDMA
The high peak-to-average ratio (PAR) associated with OFDM led 3GPP to look for a different transmission scheme for the LTE uplink.
SC-FDMA is used in uplink as multiple access technology.
LTE System Overview
LTE System Overview
With standard OFDM, very narrow UE-specific transmissions can suffer from narrowband fading and interference. That is why for the downlink 3GPP chose OFDMA, which incorporates elements of time division multiple access (TDMA). OFDMA allows subsets of the subcarriers to be allocated dynamically among the different users on the channel, as shown in Figure 7. The result is a more robust system with increased capacity. This is due to the trunking efficiency of multiplexing low rate users and the ability to schedule users by frequency, which provides resistance to multi-path fading.
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LTE System Overview
LTE System Overview
A graphical comparison of OFDMA and SC-FDMA as shown in the slide is helpful in understanding the differences between these two modulation schemes. For clarity this example uses only four (M) subcarriers over two symbol periods with the payload data represented by quadrature phase shift keying (QPSK) modulation. As described earlier, real LTE signals are allocated in units of 12 adjacent subcarriers.
Visually, the OFDMA signal is clearly multi-carrier with one data symbol per subcarrier, but the SC-FDMA signal appears to be more like a single-carrier (hence the “SC” in the SC-FDMA name) with each data symbol being represented by one wide signal. Note that OFDMA and SC-FDMA symbol lengths are the same at 66.7 μs; however, the SC-FDMA symbol contains M “sub-symbols” that represent the modulating data. It is the parallel transmission of multiple symbols that creates the undesirable high PAR of OFDMA. By transmitting the M data symbols in series at M times the rate, the SC-FDMA occupied bandwidth is the same as multi-carrier OFDMA. But, crucially, the PAR is the same as that used for the original data symbols. Adding together many narrow-band QPSK waveforms in OFDMA will always create higher peaks than would be seen in the wider-bandwidth, single-carrier QPSK waveform of SC-FDMA. As the number of subcarriers M increases, the PAR of OFDMA with random modulating data approaches Gaussian noise statistics but, regardless of the value of M, the SC-FDMA PAR remains the same as that used for the original data symbols.
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Wireless Channel
In wireless communications, MIMO refers to a wireless channel with multiple inputs and multiple outputs.
In a MIMO system, there are N*M signal paths from the transmit antennas and the receive antennas, and the signals on these paths are not identical.
MIMO uses space multiplexing to increase the data rate.
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Wireless Channel
Here 2*2 MIMO is used as a example.
With MIMO system, the multiplexing gain is obtained with independent data streams on different antennas. For example 2*2 MIMO can double the peak data rate if compared with non-MIMO system.
Whether MIMO is applicable is related to channel condition. Only when the channel conditions are good, two parallel data streams can be carried in different transmitters. This is dual-stream case. Otherwise only one data stream is carried even though two transmitters are used. This is single-stream case. Receiver will feedback channel information to transmitter. Transmitter will decide whether space multiplexing can be used.
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LTE Multiple Antenna Scheme
In downlink LTE can use 2*2 or higher order MIMO to increase date rate.
In uplink MU-MIMO (multi-user MIMO) can be used to double uplink capacity.
With MU-MIMO the uplink peak data rate of single user can not be doubled.
LTE System Overview
LTE System Overview
The baseline configuration of the UE has one transmitter. This configuration was chosen to save cost and battery power, and with this configuration the system can support MU-MIMO—that is, two different UE transmitting in the same frequency and time to the eNB. This configuration has the potential to double uplink capacity (in ideal conditions) without incurring extra cost to the UE.
An optional configuration of the UE is a second transmit antenna, which allows the possibility of uplink Tx diversity and SU-MIMO (single-user MIMO). The latter offers the possibility of increased data rates depending on the channel conditions.
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AMC, Adaptive Modulation and Coding
the radio-link data rate is controlled by adjusting the modulation scheme and/or the channel coding rate
DL/UL modulations: QPSK, 16QAM, and 64QAM
LTE System Overview
LTE System Overview
Transmit power control can be seen as one type of link adaptation and used in WCDMA and CDMA system, that is the adjustment of transmission parameters, in this case the transmit power, to adapt to differences and variations in the instantaneous channel conditions to maintain the received Eb/N0 at a desired level. This results in a basically constant data rate, regardless of the channel variations.
Actually, even in case of typical ‘constant-rate’ services such as voice and video, (short-term) variations in the data rate are often not an issue, as long as the average data rate remains constant, assuming averaging over some relatively short time interval. In such cases, that is when a constant data rate is not required, an alternative to transmit power control is link adaptation by means of dynamic rate control.
Instead, with rate control in LTE system, the data rate is dynamically adjusted to compensate for the varying channel conditions. In situations with advantageous channel conditions, the data rate is increased and vice versa.
Rate control in principle implies that the power amplifier is always transmitting at full power and therefore efficiently utilized.
In case of advantageous radio-link conditions, the Eb/N0 at the receiver is high and the main limitation of the data rate is the bandwidth of the radio link. Hence, in such situations higher-order modulation, for example 16QAM or 64QAM, together with a high code rate is appropriate. Similarly, in case of poor radio-link conditions, QPSK and low-rate coding is used.
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Contents
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Contents
3.1 LTE Protocol Stacks
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LTE System Overview
LTE System Overview
The eNB hosts the following functions:
Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of user data stream;
Selection of an MME at UE attachment when no routing to an MME can be determined from the information provided by the UE;
Routing of User Plane data towards Serving Gateway;
Scheduling and transmission of paging messages (originated from the MME);
Scheduling and transmission of broadcast information (originated from the MME or O&M);
Measurement and measurement reporting configuration for mobility and scheduling;
The MME hosts the following functions (see 3GPP TS 23.401 [17]):
NAS signalling;
Inter CN node signalling for mobility between 3GPP access networks;
Idle mode UE Reachability (including control and execution of paging retransmission);
Tracking Area list management (for UE in idle and active mode);
PDN GW and Serving GW selection;
MME selection for handovers with MME change;
SGSN selection for handovers to 2G or 3G 3GPP access networks;
Roaming;
Authentication;
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LTE System Overview
LTE System Overview
Mobility anchoring for inter-3GPP mobility;
E-UTRAN idle mode downlink packet buffering and initiation of network triggered service request procedure;
Lawful Interception;
Transport level packet marking in the uplink and the downlink;
Accounting on user and QCI granularity for inter-operator charging;
UL and DL charging per UE, PDN, and QCI.
The PDN Gateway (P-GW) hosts the following functions:
Per-user based packet filtering (by e.g. deep packet inspection);
Lawful Interception;
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The radio interface described in this specification covers the interface between the User Equipment (UE) and the network. The radio interface is composed of the Layer 1, 2 and 3.
The physical layer offers a transport channel to MAC. The transport channel is characterized by how the information is transferred over the radio interface. MAC offers different logical channels to the Radio Link Control (RLC) sub-layer of Layer 2. A logical channel is characterized by the type of information transferred.
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LTE System Overview
LTE System Overview
In the user-plane, where PDCP, RLC and MAC sublayers (terminated in eNB on the network side) perform the functions for the user plane such as header compression, ciphering, scheduling, ARQ and HARQ;
In the control plane, where:
PDCP sublayer (terminated in eNB on the network side) performs the functions listed for the control plane in subclause 6, e.g. ciphering and integrity protection;
RLC and MAC sublayers (terminated in eNB on the network side) perform the same functions as for the user plane;
RRC (terminated in eNB on the network side) performs the functions:
Broadcast;
Paging;
UE measurement reporting and control.
NAS control protocol (terminated in MME on the network side) performs among other things:
EPS bearer management;
eNB
PHY
UE
PHY
MAC
RLC
MAC
PDCP
PDCP
RLC
eNB
PHY
UE
PHY
MAC
RLC
MAC
MME
RLC
NAS
NAS
RRC
RRC
PDCP
PDCP
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Physical Downlink Control Channel (PDCCH)
Physical Hybrid ARQ Indicator Channel (PHICH)
Physical Downlink Shared Channel (PDSCH)
Physical Multicast Channel (PMCH)
LTE System Overview
LTE System Overview
UL physical signals
Reference signal (RS)
QPSK, 16-QAM, and 64-QAM
But it will be addressed in the future release
Multi-user collaborative MIMO supported
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Physical layer transport channels offer information transfer to medium access control (MAC) and higher layers
DL
A transport channel is defined by how and with what characteristics the information is transmitted over the radio interface.
Following the notation from HSPA, which has been inherited for LTE, data on a transport channel is organized into transport blocks. In each Transmission Time Interval (TTI), at most one transport block of a certain size is transmitted over the radio interface in absence of spatial multiplexing. In case of spatial multiplexing (‘MIMO’), there can be up to two transport blocks per TTI.
Associated with each transport block is a Transport Format (TF), specifying how the transport block is to be transmitted over the radio interface. The transport format includes information about the transport-block size, the modulation scheme, and the antenna mapping. Together with the resource assignment, the resulting code rate can be derived from the transport format. By varying the transport format, the MAC layer can thus realize different data rates. Rate control is therefore also known as transport-format selection.
Broadcast Channel (BCH) has a fixed transport format, provided by the specifications. It is used for transmission of the information on the BCCH logical channel.
Paging Channel (PCH) is used for transmission of paging information on the PCCH logical channel. The PCH supports discontinuous reception (DRX) to allow the mobile terminal to save battery power by sleeping and waking up to receive the PCH only at predefined time instants..
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Physical layer transport channels offer information transfer to medium access control (MAC) and higher layers
DL
Downlink Shared Channel (DL-SCH) is the transport channel used for transmission of downlink data in LTE. It supports LTE features such as dynamic rate adaptation and channel-dependent scheduling in the time and frequency domains, hybrid ARQ, and spatial multiplexing. It also supports DRX to reduce mobile-terminal power consumption while still providing an always on experience, similar to the CPC mechanism in HSPA. The DL-SCH TTI is 1 ms.
Multicast Channel (MCH) is used to support MBMS. It is characterized by a semi-static transport format and semi-static scheduling. In case of multi-cell transmission using MBSFN, the scheduling and transport format configuration is coordinated among the cells involved in the MBSFN transmission.
Uplink Shared Channel (UL-SCH) is the uplink counterpart to the DL-SCH.
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Control Channels: Control-plane information
Broadcast Control Channel (BCCH)
Paging Control Channel (PCCH)
Dedicated Control Channel (DCCH)
Common Control Channel (CCCH)
Traffic Channels: User-plane information
Dedicated Traffic Channel (DTCH): transmission of all uplink and non-MBMS downlink user data
Multicast Traffic Channel (MTCH): transmission of MBMS services
LTE System Overview
LTE System Overview
A logical channel is defined by the type of information it carries and are generally classified into control channels, used for transmission of control and configuration information necessary for operating an LTE system, and traffic channels, used for the user data. The set of logical-channel types specified for LTE includes:
Broadcast Control Channel (BCCH), used for transmission of system control information from the network to all mobile terminals in a cell. Prior to accessing the system, a mobile terminal needs to read the information transmitted on the BCCH to find out how the system is configured, for example the bandwidth of the system.
Paging Control Channel (PCCH), used for paging of mobile terminals whose location on cell level is not known to the network and the paging message therefore needs to be transmitted in multiple cells.
Dedicated Control Channel (DCCH), used for transmission of control information to/from a mobile terminal. This channel is used for individual configuration of mobile terminals such as different handover messages.
Multicast Control Channel (MCCH), used for transmission of control information required for reception of the MTCH, see below.
Dedicated Traffic Channel (DTCH), used for transmission of user data to/from a mobile terminal. This is the logical channel type used for transmission of all uplink and non-MBMS downlink user data.
Multicast Traffic Channel (MTCH), used for downlink transmission of MBMS services.
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FDD
10 subframes are available for DL in each 10 ms interval
10 subframes are available for UL in each 10 ms interval
TDD
a subframe is either allocated to DL or UL transmission
Subframe 0 and subframe 5 are always allocated for DL transmission.
In case of FDD, that is operation in paired spectrum, all subframes of a carrier are either used for downlink transmission (a downlink carrier) or uplink transmission (an uplink carrier).
On the other hand, in case of operation with TDD in unpaired spectrum the first and sixth subframe of each frame (subframe 0 and 5) are always assigned for downlink transmission while the remaining subframes can be flexibly assigned to be used for either downlink or uplink transmission. The reason for the predefined assignment of the first and sixth subframe for downlink transmission is that these subframes include the LTE synchronization signals. The synchronization signals are transmitted on the downlink of each cell and are intended to be used for initial cell search as well as for neighbor-cell search.
As the subframe assignment needs to be the same for neighbor cells in order to avoid severe interference between downlink and uplink transmissions between the cells, the downlink/uplink asymmetry cannot vary dynamically.
To provide consistent and exact timing definitions, different time intervals within the LTE radio access specification can be expressed as multiples of a basic time unit Ts =1/30720000.1 The time intervals outlined in Figure 16.1 can thus also be expressed as Tframe =307200 · Ts and Tsubframe =30720 · Ts.
Each 1 ms subframe consists of two equally sized slots of length Tslot =0.5 ms (15360 · Ts).
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In the frequency domain the downlink subcarriers are grouped into resource blocks, where each resource block consists of 12 consecutive subcarriers3 corresponding to a nominal resource-block bandwidth of 180 kHz. In addition, there is an unused DC-subcarrier in the center of the downlink spectrum. The reason why the DC-subcarrier is not used for any transmission is that it may coincide with the local-oscillator frequency at the base-station transmitter and/or mobile-terminal receiver. As a consequence, it may be subject to un-proportionally high interference, for example, due to local-oscillator leakage.
Downlink scheduling is carried out on a subframe (1 ms) basis. Thus, as a downlink resource block is defined as a number of subcarriers during one 0.5 ms slot, the downlink resource-block assignment is always carried out in terms of pairs of resource blocks, where each pair consists of two, in the time domain, consecutive resource blocks within a subframe.
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For 10 MHz system, the data will be doubled.
For the LTE downlink, the OFDM subcarrier spacing has been chosen to f =15 kHz. Assuming an FFT-based transmitter/receiver implementation, this corresponds to a sampling rate fs =15000 ·NFFT, where NFFT is the FFT size. The time unit Ts defined in the previous section can thus be seen as the sampling time of an FFT-based transmitter/receiver implementation with NFFT =2048.
In practice, an FFT-based transmitter/receiver implementation with NFFT =2048 and a corresponding sampling rate fs =30.72MHz is suitable for the wider LTE transmission bandwidths, such as bandwidths in the order of 15MHz and above. However, for smaller transmission bandwidths, a smaller FFT size and a correspondingly lower sampling rate can very well be used. As an example, for transmission bandwidths in the order of 5 MHz, an FFT size NFFT =512 and a corresponding sampling rate fs =7.68MHz may be sufficient.
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Contents
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The E2E LTE solution, showing the eUTRAN position within network/architecture.
Terminal
E-UTRAN
EPC
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eNB
eNB
FE/GE
FE/GE
FE/GE
eNB
Co-transmission with legacy 2G/3G
LTE System Overview
LTE System Overview
IPv4 IPv6 HW ready
QoS: DSCP marking, Traffic shaping, congestion control, flow control, etc
Transport security: IPSec
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Modularization
Using BBU plus RRU and RFU leads to a flexible configuration for Distributed and Macro.
Multimode
uniNodeB series.
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Investment protection while evolving from GSM/UMTS to LTE
Radio units for GSM/UMTS and LTE are inter-changeable in the same frequency band
Baseband boards in multi-mode BBU are inter-changeable between GSM/UMTS and LTE
LTE Card
LTE (100M/50M)
Same band
Different band
Same band
Different band
GSM/HSPA(+)/LTE RRU
LTE RRU
GSM/HSPA(+)/LTE RFU
LTE RFU
LTE Card
BBU
RRU
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GSM&UMTS operator
UMTS roll out will reduce GSM expansion investment at hot spot
Operator issue New business ALL IP service
GSM for Voice
UMTS&LTE operator
LTE for mobile broadband
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Summary
Support for both FDD and TDD.
Flexible spectrum allocation (1.4 ~ 20 MHz).
IP-based flat network architecture
Multicarrier-based radio air interface
ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer
LTE System Overview
LTE System Overview
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Thank you
M
internet
eNB

LTE System Overview Training

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