Long Term Evolution Technology training Part 1 1

Long Term Evolution Technology training (Part 1) 1

Outline • • 2 LTE and SAE overview LTE radio interface architecture LTE radio access architecture LTE multiple antenna techniques

Part 1 LTE/SAE OVERVIEW 3

Mobile broadband (3 GPP) Release Standardized Commercial Major features 3 GPP R 99 1999 2000 • Bearer services • 64 kbit/s CS • 384 kbit/s PS • Location services • Call services: compatible with GSM 3 GPP R 5 2002 2006 • IP Multimedia Subsystem (IMS) • IPv 6, IP transport in UTRAN • Improvements in GERAN • HSDPA 3 GPP R 6 2004 2007 • Multimedia broadcast and multicast • Improvements in IMS • HSUPA • Fractional DPCH 3 GPP R 7 2008 • Enhanced L 2 • 64 QAM , MIMO • Vo. IP over HSPA • CPC - continuous packet connectivity • FRLC - Flexible RLC 3 GPP R 8 2008 2010 • DC-HSPA+ (Dual Cell HSPA+) • HSUPA 16 QAM 3 GPP R 8 (LTE) 2008 2010 • New air interface (OFDM/SC-FDMA) • New core network 4 • • 3 G continues to evolve Standardized through 3 GPP 3 G gracefully evolves into 4 G – starting from R 7 and R 8 Date rates – – – • R 99: 0. 4 Mbps UL, 0. 4 Mbps DL R 5: 0. 4 Mbps UL, 14 Mbps DL R 6: 5. 7 Mbps UL, 14 Mbps DL R 7: 11 Mbps UL, 28 Mbps DL R 8: 50 Mbps UL on LTE, 160 Mbps DL on LTE, 42 Mbps DL on HSPA Two branches of the standards – – HSPA : Gradual performance improvements at lower incremental costs LTE: revolutionary changes with significant performance improvements (higher cost, first step towards IMT advanced)

LTE Releases Release 3 GPP R 8 (LTE) 3 GPP R 9 (LTE) 3 GPP R 10 (LTE) LTE Advanced • • • 5 Standardized 2008 Commercial 2010 Major features • Multi antenna support • Channel dependent scheduling • Bandwidth flexibility • ICIC (Intercell Interference Coordination) • Hybrid ARQ • FDD + TDD support 2009 • Dual layer beam forming • Network based UE positioning • MBSFN (Multicast/Broadcast Single Frequency Network) 2010 • Multi antenna extension • Relaying • Carrier aggregation • Heterogeneous networks (Het. Net’s) LTE – has an “evolution path” of its own Evolution is towards IMT-Advanced (LTE advanced) LTE advanced – spectral efficiency 30 bps/Hz (DL), 15 bps/Hz (UL) Note: This presentation focuses on R 8 features

LTE requirements • • Outlined in 3 GPP TR 29. 913 Seven different areas – – – – • Capabilities System performance Deployment related aspects Architecture and migration Radio resource management Complexity, and General aspects Capabilities – – – 6 DL data rate > 100 Mbps in 20 MHz UL data rate > 50 Mbps in 20 MHz Rate scales linearly with spectrum Latency user plane: 5 ms (transmission of small packet from UE to edge of RAN) Latency control plane: transmission time from camped state – 100 ms, transmission time from dormant state 50 ms Support for 200 mobiles in 5 MHz, 400 mobiles in more than 5 MHz • System performance – – – – Baseline is HSPA Rel. 6 Throughput specified at 5% and 50% Maximum performance for low mobility users (0 -15 km/h) High performance up to 120 km/h Maximum supported speed 500 km/h Cell range up to 100 km Spectral efficiency for broadcast 1 b/s/Hz Throughput requirements relative to baseline Performance measure DL target relative to base line UL target relative to baseline Average throughput per MHz 3 -4 times 2 -3 times Cell edge user throughput per MHz 2 -3 times Spectrum efficiency (bit/sec/Hz) 3 -4 times 2 -3 times

LTE requirements (2) • • Deployment related aspects – LTE may be deployed as standalone or together with WCDMA/HSPA and/or GSM/GPRS – Full mobility between different RANs – Handover interruption time targets specified Spectrum flexibility – Both paired and unpaired bands – IMT 2000 bands (co-existence with WCDMA and GSM) – Channel bandwidth from 1. 4 -20 MHz Handover interruption time Non-real time services (ms) Real time services (ms) LTE to WCDMA 500 300 LTE to GSM 500 300 LTE duplexing options 7

LTE requirements (3) • Architecture and migration – Single RAN architecture – RAN is fully packet based with support for real time conversational class – RAN architecture should minimize “single points” of failure – RAN should simplify and reduce number of interfaces – Radio Network Layer and Transport Network Layer interaction should not be precluded in interest of performance – Qo. S support should be provided for various types of traffic 8 • Radio resource management – Support for enhanced end to end Qo. S – Support for load sharing between different radio access technologies (RATs) • Complexity – LTE should be less complex than WCDMA/HSPA

SAE design targets • • • SAE – Service Architecture Evolution SAE = core network Requirements placed into seven categories – – – – • 9 High level and operational aspects Basic capabilities Multi-access and seamless mobility Man-machine interface aspects Performance requirements for Evolved 3 GPP system Security and privacy Charging aspects SAE requirements mainly non access related (highlighted ones have impact on RAN)

Basic principles – Air interface • • Downlink OFDM = Orthogonal Frequency Division Multiplexing OFDM = Parallel transmission on multiple carriers Advantages of OFDM – – • High PAPR and lower power amplifier efficiency Uplink DFTS-OFDM (SC-FDMA) DFTS = DFT spread OFDM SC-FDMA = Single carrier FDMA Advantages (all critical for UL) – – – Avoid intra-cell interference Robust with respect to multi-path propagation and channel dispersion Disadvantage of OFDM – • • • Signal has single carrier properties Low PAPR Similar hardware as OFDM Reduced PA cost Efficient power consumption Disadvantage – Equalizer needed (not critical from UL) UL modulation 10 DL modulation

Basic principles – Air interface • Shared channel transmission – Only PS support – No CS services • Fast channel dependent scheduling – Adaptation in time – Adaptation in frequency – Adaptation in code Scheduler takes the advantage of timefrequency variations of the channel • Hybrid ARQ with soft combining – Chain combining – Incremental redundancy 11 ARQ reduces required Eb/No One shared channel simplifies the overall signaling

Basic principles – air interface • MIMO support – MIMO = Multiple Input Multiple Output – Use of multiple TX / RX antennas – Three ways of utilizing MIMO Outline of spatial multiplexing idea • RX diversity/TX diversity • Beam forming • Spatial multiplexing (MIMO with space time coding) – MIMO transmission in Rayleigh fading environment increases theoretical capacity by a factor equal to number of independent TX RX paths – As a minimum LTE mobiles have two antennas (possibly four) 12 Note: Rayleigh fading de-correlates the paths and provides multiple uncorrelated channels

Basic principles – air interface • • • ICIC – Inter-cell interference coordination LTE affected by inter-cell interference (more than HSDPA) In LTE interference avoidance becomes scheduling problem By managing resources across multiple cells inter-cell interference may be reduced Standard supports exchange of interference indicators between the cells One possible implementation of ICIC. Cell edge implements N=3. Cell interior implements N=1. 13

SAE-Architecture • SAE – flat architecture – – • Single element simplifies RAN No single point of failure Core network provides two planes – – • LTE Network layout RAN consist of single elements: e. Node B – – • Core network, RAN User plane (through SGSN) Control plane (through MME) Interfaces – – S 1 -UP (e. Node B to SGSN) S 1 -CP (e. Node B to MME) X 2 between two e. Node Bs (required for handover) Uu (UE to e. Node B) SAE = System Architecture Evaluation 14 UE – user equipment (i. e. mobile) e. Node B – base station SGSN – Support GPRS Serving Node GGSN – Gateway GPRS Serving Node MME – Mobility Management Entity PCRF - Policy and Charging Rules function

LTE protocol-control plane NAS RRC PDCP RLC MAC 15 – Non Access Stratum – Radio Resource Control – Packet Data Convergence Protocol – Radio Link Control – Medium Access Control S 1 -AP – S 1 Application SCTP – Stream Control Transmission Prot. IP – Internet Protocol Note: LTE control plane is almost the same as WCDMA (PDCP did not exist in WCDMA control plane)

LTE protocol- user plane PDCP – Packet Data Convergence Protocol GTP-U - GPRS Tunneling Protocol RLC – Radio Link Control MAC – Medium Access Control Note: LTE user plane is identical to UMTS PS side. There is no CS in LTE – user plane is simplified. 16

LTE protocol – X 2 • Connects all e. Node. B’s that are supporting end user active mobility (handover) Supports both user plane and control plane Control plane – signaling required for handover execution User plane – packet forwarding during handover • • • Control plane GTP-U: GPRS tunneling protocol STCP: Stream Transmission Control Protocol 17 User plane

Channel structure • Channels – defined on Uu • Logical channels – Formed by RLC – Characterized by type of information • Transport channels – Formed by MAC – Characterized by how the data are organized • Physical channels – Formed by PHY – Consist of a group of assignable radio resource elements 18 Uu interface Note: LTE defines same types of channels as WCDMA/HSPA

LTE - channel mapping 19

Logical channels • BCCH – Broadcast Control CH – System information sent to all UEs • PCCH – Paging Control CH – Paging information when addressing UE • CCCH – Common Control CH – Access information during call establishment • DCCH – Dedicated Control CH – User specific signaling and control • DTCH – Dedicated Traffic CH – User data • MCCH – Multicast Control CH – Signaling for multi-cast • MTCH – Multicast Traffic CH – Multicast data Red – common, green – shared, blue - dedicated 20 LTE Channels

Transport channels • BCH – Broadcast CH – Transport for BCCH • PCH – Paging CH – Transport for PCH • DL-SCH – Downlink Shared CH – Transport of user data and signaling. Used by many logical channels • MCH – Multicast channel – Used for multicast transmission • UL-SCH – Uplink Shared CH – Transport for user data and signaling • RACH – Random Access CH – Used for UE’s accessing the network Red – common, green – shared 21 LTE Channels

PHY Channels • PDSCH – Physical DL Shared CH – • Uni-cast transmission and paging PBCH – Physical Broadcast CH – • Broadcast information necessary for accessing the network PMCH – Physical Multicast Channel – • Data and signaling for multicast PDCCH – Physical Downlink Control CH – • Carries mainly scheduling information PHICH – Physical Hybrid ARQ Indicator – • Reports status of Hybrid ARQ PCIFIC – Physical Control Format Indicator – • Information required by UE so that PDSCH can be demodulated (format of PDSCH) PUSCH – Physical Uplink Shared Channel – • Uplink user data and signaling PUCCH – Physical Uplink Control Channel – • Reports Hybrid ARQ acknowledgements PRACH – Physical Random Access Channel – 22 Used for random access Red – common, green – shared LTE Channels

Time domain structure • Two time domain structures – Type 1: used for FDD transmission (may be full duplex or half duplex) – Type 2: used for TDD transmission • Both Type 1 and Type 2 are based on 10 ms radio frame Radio frame : Type 1 Radio frame : Type 2 23

TDD frame configurations • • Different configurations allow balancing between DL and UL capacity Allocation is semi-static Adjacent cells have same allocation Transition DL->UL happens in the second subframe of each halfframe Note: TDD frame structure allows coexistence between LTE TDD and TD-SCDMA 24

Allocatable resources • LTE – radio resource = “time-frequency chunk” Resource Block (RB) = 12 carriers in one TS (12*15 KHz x 0. 5 ms) • • 25 Time domain ü 1 frame = 10 sub-frames ü 1 subframe = 2 slots ü 1 slot = 7 (or 6) OFDM symbols Frequency domain ü 1 OFDM carrier = 15 KHz Note: In LTE resource management is along three dimensions: Time, Frequency, Code

Bandwidth flexibility • • • LTE supports deployment from 6 RBs to 110 RBs in 1 RB increments 6 RBs = 6 x 12 x 15 KHz = 1080 KHz -> 1. 4 MHz (with guard band) 110 RBs = 110 X 12 X 15 KHz = 19800 KHz -> 20 MHz (with guard band) Typical deployment channel bandwidths: 1. 4, 3, 5, 10, 15, 20 MHz Straight forward to support other channel bandwidths (due to OFDM) • UE needs to support up to the largest bandwidth (i. e. 20 MHz) 26

UE States • UE may be in three states – Detached: not connected to the network – Idle: attached to the network but not active – Connected: attached and active • Note: Both the UE states and UE tracking are simpler than in UMTS UE tracking – Detached state: UE position unknown – Idle state: UE position know with the Tracking Area (TA) resolution – Connected: UE location known to the e. Node. B resolution 27

3 GPP Specifications • All 3 GPP specs are available at http: //www. 3 gpp. org – – – RAN 1 RAN 2 RAN 3 RAN 4 RAN 5 36. 2 xx series 36. 3 xx series 36. 4 xx series 36. 1 xx series 36. 5 xx series Example specs organization 28 PHY layer Layers 2 and 3 S 1 and X 2 interfaces Core performance requirements Terminal conformance testing

Section review 1. What are 3 GPP broadband cellular technologies? 2. What releases of 3 GPP standard contains LTE? 3. What were target DL and UL throughputs for LTE? 4. What does SAE stand for? 5. What are components of the CS part of the LTE core network? 6. What is the access scheme used on the DL? 7. What is the role of fast scheduler on LTE DL? 8. What is the smallest allocateable resource in LTE DL? 29 9. What is Radio Block (RB)? 10. What are spectrum bandwidth deployment options for LTE? 11. How many radio blocks are in 20 MHz deployment? 12. Does LTE support TDD deployment? 13. What are three UE States supported by LTE?

Part 2 LTE RADIO ACCESS 30

Overview • • • 31 Overview of OFDM/OFDMA LTE Downlink transmission Overview of DFTS-OFDM LTE Uplink transmission Multi-antenna transmission

Single carrier transmission • • • Data are used to modulate amplitude/phase (frequency) of a single carrier Higher data rate results in wider bandwidth Over larger bandwidths ( > 20 KHz), wireless channel is frequency selective As a result of frequency selectivity the received signal is severely distorted Channel equalization needed Complexity of equalizer increases rapidly with the signal bandwidth requirements Transmission of single carrier in mobile terrestrial environment 32 Note: over small portion of the signal spectrum, fading may be seen as flat

Multi-carrier transmission • • • Channel fading over smaller frequency bands – flat (no need for equalizer) Divide high rate input data stream into many low rate parallel streams At the receiver – aggregate low data rate streams Signal for each stream experiences flat fading 33

FDM versus OFDM • • OFDMA minimizes separation between carriers Carriers are selected so that they are orthogonal over symbol interval Carrier orthogonality leads to frequency domain spacing Df=1/T, where T is the symbol time In LTE carrier spacing is 15 KHz and useful part of the symbol is 66. 7 microsec Note: orthogonality between carriers in time domain allows closer spacing in frequency domain. 34 FDM versus OFDM

OFDM transmitter/receiver • • • 35 Practically OFDM TX/RX is implemented using IFFT/FFT Use of the IFFT/FFT at the baseband means that there is no need for separate oscillators for each of the OFDM carriers FFT (IFFT) hardware is readily available – TX/RX implementation is simple

Guard time • • 36 Duration of the OFDM symbol is chosen to be much longer than the multi-path delay spread Long symbols imply low rate on individual OFDM carriers In multipath environment long symbol minimizes the effect of channel delay spread To make sure that there is no ISI between OFDM symbols – guard time is inserted OFDM symbols without guard time OFDM symbols with guard time

Cyclic prefix • • 37 Guard time eliminates ISI between OFDM symbols Multipath propagation degrades orthogonality between carriers within an OFDMS symbol To regain the orthogonality between subcarriers – cyclic prefix is used Cyclic prefix fills in the guard time between the OFDM symbols

Block diagram of full OFDM TX/RX • • 38 LTE supports numerous AMC schemes AMC adds additional level of adaptation to the RF channel Size of CP depends on the amount of dispersion in the channel Two CP are used: normal (4. 7 us) and extended (16. 7 us)

OFDMA time-frequency scheduling • • Minimum allocateable resource in LTE is Resource Block pair Resource block pair is 12 carriers wide in frequency domain and lasts for two time slots (1 ms) Depending on the length of cyclic prefix RB pair may have 14 or 12 OFDM symbols PHY channels consist of certain number of allocated RB pairs Overhead channels are typically in a predetermined location in time frequency domain Within a RB different AMC scheme may be used Allocation of the radio block is done by scheduler at e. Node B 39

Part 3 LTE DOWNLINK TRANSMISSION 40

LTE OFDM Parameter Bandwidth (MHz) Value 1. 4 3 5 10 Frame /subframe duration 10/1 ms Subcarrier spacing 15 KHz Useful symbol part 66. 7 us 15 20 FFT size 128 256 512 1024 1536 2048 Resource blocks 6 15 25 50 75 100 Number of used subcarriers 72 180 300 600 900 1200 Cyclic prefix length Normal: 5. 1 us for first symbol in a slot and 4. 7 us for other symbols , Extended: 16. 7 us OFDM symbols /slot 7 (normal CP), 6 (extended CP) Error coding 1/3 convolutional (signaling); 1/3 turbo (data) 41 Basic timing unit: Ts = 1/(2048 x 15000) ~ 23. 552 ns

Detailed time domain structure Need for two different CP: 1. To accommodate environments with large channel dispersion 2. To accommodate MBSFN (Multi. Cast Broadcast Single Frequency Network) transmission In case of MBSFN it may be beneficial to have mixture of sub -frames with normal CP and extended CP. Extended CP is used for MBSFN sub-frames TCP: 160 Ts (5. 1 us) for first symbol, 144 Ts (4. 7 us) for other six symbols TCP-e: 512 Ts (16. 7 us) for all symbols 42

Exercise – OFDM data rate capability at the PHY Case 1. Case 2. Normal CP (no MIMO) Resource block: 12 carriers x 14 OFDM symbols = 168 resource elements Each resource element carries one modulation symbol For 64 QAM: 1 symbol = 6 bits Number of bits per subframe = 168 x 6 = 1008 bits/subframe Raw PHY data rate = 1008/1 ms = 1, 008, 000 bits/sec/resource block (180 KHz) For 20 MHz, Raw PHY data rate = 100 RB x 1, 008, 000 bits/sec/RB = 100. 8 Mbps Extended CP (no MIMO) Resource block: 12 carriers x 12 OFDM symbols = 144 resource elements Each resource element carries one modulation symbol For 64 QAM: 1 symbol = 6 bits Number of bits per subframe = 144 x 6 = 864 bits/subframe Raw PHY data rate = 864/1 ms = 864, 000 bits/sec/resource block (180 KHz) For 20 MHz, Raw PHY data rate = 100 RB x 864, 000 bits/sec/RB = 86. 4 Mbps Note: with the use of MIMO the rates are increased 43

Downlink reference signals • • • For coherent demodulation – terminal needs channel estimate for each subcarrier Reference signals – used for channel estimation There are three type of reference signals 1. Cell specific DL reference signals – – Every DL subframe Across entire DL bandwidth 2. UE specific DL reference signals – – Sent only on DL-SCH Intended for individual UE’s 3. MBSFN reference signals – Support multicast/broadcast Note: Reference signals are staggered in time and frequency. This allows UE to perform 2 -D complex interpolation of channel timefrequency response 44

Cell specific reference signals Two port TX • • • DL transmission may use up to four antennas Each antenna port has its own pattern of reference signals Reference signals are transmitted at higher power in multi -antenna case Reference signals introduce overhead • – – – • 4. 8% for 1 antenna port 9. 5% for 2 antenna ports 14. 3 % for 4 antenna ports Four port TX Reference symbols vary from position to position and from cell to cell – cell specific 2 dimensional sequence Period of the sequence is one frame • One port TX 45

Cell specific reference signals (2) • • There are 504 different Reference Sequences (RS) They are linked to PHY-layer cell identities The sequence may be shifted in frequency domain – 6 possible shifts Each shift is associated with 84 different cell identities (6 x 84 = 504) Shifts are introduced to avoid collision between RS of adjacent cells In case of multiple antenna ports – only three shifts are useful For a given PHY Cell ID - sequence is the same regardless of the bandwidth used – UE can demodulate middle RBs in the same way for all channel bandwidths Shifts for single port transmission 46

UE Specific RS • • • UE specific RS – used for beam forming Provided in addition to cell specific RS Sent over resource block allocated for DL-SCH (applicable only for data transmission) Note: additional reference signals increase overhead. One of the most beneficial use of beam forming is at the cell edge – improves SNR 47

PHY channels supporting DL TX • SCH – allows mobile to synchronize to the DL TX during acquisition PBCH – used to broadcast static portion of the BCCH PDSCH – carries user information and signaling from upper layers of protocol stack PDCCH – channel used by MAC scheduler to configure L 1/L 2 and assign resources (DL scheduling and UL grants) PCFICH – explains to the UE the format of the DL transmission PHICH – support for HARQ on the uplink PUCCH – support for HARQ on the downlink • • • 48 Channels required for DL transmission

Summary of PHY DL channels L 1/L 2 signaling L 1/L 2 Control Coding scheme PHY Channel Modulation CFI (Channel format Indicator) Block code R=1/16 PCFICH QPSK HI (HARQ information) Repetition 1/3 PHICH BPSK DCI (Downlink control Information) Convolutional 1/3 with rate matching PDCCH QPSK Services to upper layers 49 Transport channel Coding scheme PHY Channel Modulation DL-SCH Turbo 1/3 PDSCH QPSK, 16 -QAM, 64 -QAM BCH Convolutional 1/3 PBCH QPSK PCH Turbo 1/3 PDSCH QPSK MCH Turbo 1/3 PMCH QPSK, 16 -QAM, 64 -QAM

Downlink L 1/L 2 signaling • • Signaling that supports DL transmission Originates at L 1/L 2 (no higher layer data or messaging) Consists of • – – • Scheduling assignments and associated information required for demodulation and decoding of DL-SCH Uplink scheduling grants for UL-SCH HARQ acknowledgements Power control commands L 1/L 2 signaling is transmitting in first 1 -3 symbols of a subframe – control region Size of control region may vary dynamically – always whole number of OFDM symbols (1, 2, 3) Signaling – beginning of the subframe • • – – 50 Reduces delay for scheduled mobiles Improves power consumption for non-scheduled mobiles Three different PHY channel types 1. 2. 3. PCFIC (PHY Control Format Indicator Channel) PHICH (PHY – Hybrid ARQ Channel) PDCCH (PHY Downlink Control Channel)

PCFICH • • PCFICH – PHY Channel Format Indicator Channel Indicates to UE the size of the control region (1, 2 or 3 OFDM symbols) PCFICH value may be 1, 2 or 3 (0 is reserved for future use) Decoding of PCFICH is essential for UE operation – – – Encoded with 1/16 repetition code Uses QPSK modulation Mapped to the first symbol of each subframe 16 resource elements in 4 groups of 4 (RE Groups) Location of the resource elements depends on cell identity Processing of PCFICH 51 Note: REGs of the PCFICH are spread in frequency domain to achieve frequency diversity

PHICH • • PHICH = PHY Hybrid-ARQ Indicator Channel HARQ acknowledgements for UL-SCH transmission As many PHICH channels as the number of UEs in the cell A set of PHICH channels is multiplexed on the same resource elements (8 normal CP, 4 extended CP) Transmitted in the first OFDM symbol of the subframe Occupies 3 resource element groups (REGs) = 12 resource elements (RE) PHICH response comes 4 sub-frames after PU-SCH Processing of PHICH 52

PDCCH • • PDCCH = Physical Downlink Control Channel Used for – – – • • 53 DL scheduling assignments UL scheduling grants Power control commands PDCCH message occupies 1, 2, 4 or 8 Control Channel Elements (CCEs) CCE = 9 Resource Element groups (REGs) = 36 Resource Elements (REs) One PDCCH carrier one message with a specific Downlink Control Information (DCI) Multiple UE-s scheduled simultaneously -> Multiple PDCCH transmissions in a subframe

PDCCH DCIs • • 54 PDCCH carrier Downlink Control Information (DCI) Multiple DCI formats are defined based on type of information DCI formats of PDCCH Format Purpose Content # of bits (FDD) 0 UL PUSCH grant RB assignment, MCS, hopping flag, NDI, cyclic shift of DM-RS, CQI, … 44 1 DL PDSCH grant for single code word Resource allocation header, RB allocation, MCS, HARQ PID, … 55 1 A Compact DL PDSCH grant of single code word Similar to format 1, but with smaller flexibility 44 1 A RACH initiated by PDCCH order Localized/distributed VRB assignment flag, preamble index, PRACH message mask index 44 1 B Compact DL PDSCH grant with pre -coding information Similar to 1, but with distributed VRB flag, reduced RB allocation flexibility, transmit PMI and pre-coding 49 1 C Very compact DL PDSCH grant Reduced payload for improved coverage, always uses QPSK on associated PDSCH, restricted RB assignment, No HARQ, … 31 1 D Compact DL PDSCH grant with pre -coding information and power offset Same as 1, but with reduced RB allocation flexibility and addition of distributed VRB transmission flag. Transmit PMI information for pre -coding, DL power offset 49 2 MIMO DL grant Same as 1, but for MIMO transmission 76 2 A Compact MIMO DL grant Same as 1 A, but for MIMO transmission 68 3 2 -bit UL power control TPC for 14 UEs plus 16 bit CRC 44 3 A 1 -bit UL power control TPC for 28 UEs plus 16 bit CRC 44

PDSCH • • • DL-SCH = DL Shared channel Used for user data coming from upper layers (both signaling and payload) Optimized for low latency and high data rate Individual steps in the processing chain operate on data blocks – enables parallel processing Many different adaptation modes – – 55 Modulation Coding Transport block size Antenna mapping (TX diversity, beam forming, spatial multiplexing)

Time/Frequency location of PBCH and SS - FDD • PBCH = Physical Broadcast Channel – • SS = Synchronization Signal – – – 56 Used for BCH transport channel Note: PBCH and SS use innermost part of the spectrum. This way the system acquisition is the same regardless of deployed bandwidth P-SS = Primary Synchronization Signal S-SS = Secondary Synchronization Signal SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity

Time/Frequency location of PBCH and SS - TDD • PBCH = Physical Broadcast Channel – • SS = Synchronization Signal – – – 57 Note: The position of the P-SS is different in TDD and FDD. By acquiring P-SS, the UE already knows if the system is FDD or TDD. Used for BCH transport channel P-SS = Primary Synchronization Signal S-SS = Secondary Synchronization Signal SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity

Synchronization Channel (SCH) • • • SCH – first channel acquired by UE Based on SCH, UE determines e. Node B PHY cell identity 504 possible PHY layer cell IDs 168 groups with 3 identities per group SCH consist of 2 signals – – • • • PSS (Primary Synchronization Signal) SSS (Secondary Synchronization Signal) 3 possible PSS sequences: NID(2) = 0, 1, 2 168 possible SSS sequences: NID(1) = 0, 1, …, 167 Cell ID: NIDcell = 3* NID(1) + NID(2) For FDD (frame type 1) • PSS is transmitted on OFDM symbol 7 in the first time slot of subframe 0 and 5 • SSS is transmitted on OFDM symbol 6 in the first time slot of subframe 0 and 5 For TDD (frame type 2) • PSS is transmitted on OFDM symbol 3 in the first time slot of subframe 1 and 6 • SSS is transmitted on OFDM symbol 6 in the first time slot of subframe 0 and 5 58

PBCH • • • PBCH = PHY Broadcast Channel PBCH provides PHY channel for static part of Broadcast Control Channel (BCCH) BCCH carriers RRC System Information (SI) messages SI messages carry System Information Blocks (SIBs) SI-M is a special SI that carrier Master Information Block (MIB) In LTE BCCH is split into two parts – – 59 Primary broadcast: Carriers MIB and provides UE with fast access to vital system broadcast information. Primary broadcast is mapped to PBCH Dynamic broadcast: Carries all SIBs that contain quasi-static information on system operating parameters. Dynamic broadcast is mapped to PDSCH Mapping of the BCCH information

PCH • • • PCH = Paging Channel Transmitted over PDSCH (messages), PDCCH (paging indicator) LTE support DRX (UE sleeps between paging occasions) – – • LTE defines DRX cycle UE is assigned to P-RNTI (Paging – Radio Network Temporary Identifier) P-RNTI is set on PDCCH UE that finds set P-RNTI reads PCH on PDSCH to determine if it is being paged DRX cycle compromise – Long cycle: good battery life, higher paging delay – Short cycle: faster paging response, shorter UE battery life DRX and paging 60 Mapping of PCCH

Section review 1. Explain the main idea behind OFDM? 2. How is OFDMA different from FDMA? 3. What is the role of cyclic prefix (CP) in OFDM? 4. What are DL reference signals? 5. How are cell specific reference signals linked to cell’s physical identity? 6. What is the role of PCFICH? 7. What is the role of PHICH? 8. What is the channel used for user data and higher layer signaling? 61 9. What is SCH? 10. What portion of the time-frequency resources is occupied by SCH? 11. What is the duration of LTE frame? 12. How many subframe are in LTE frame? 13. What is the time duration of one LTE time slot?

DFTS-OFDM • • DFTS-OFDM = DFT Spread OFDM Also known as s Single Carrier FDMA (SC-FDMA) Used on RL of LTE Advantages: – – – • Lower PAPR than OFDM (4 d. B for QPSK and 2 d. B for 16 -QAM) Orthogonality between the users in the same cell Low complexity TX/RX due to DFT/FFT Disadvantage: – – Needs an equalizer at the Node B RX Need for some synchronization in time domain Outline of the DFTS-OFDM 62 Note: In DFTS-OFDM, M < N

DFTS-OFDM TX/RX chain Note: the TX/RX of DFTS-OFDM is almost the same as OFDM. The DFT precoding / decoding and equalization are done in software 63

Uplink user multiplexing • Two ways of mapping the output of the DFT – Consecutive carriers: Localized DTFS-OFDM – Distributed carriers: Distributed DTFS-OFDM • Distributed OFDM has benefit of frequency diversity Note 1: Mapping between output of the OFDM and carriers is performed by MAC scheduler Note 2: Spectrum bandwidth may be allocated in dynamic fashion Localized DFTS-OFDM 64 Distributed DFTS-OFDM

Uplink frame format Need for two different CP: 1. To accommodate environments with large channel dispersion 2. To accommodate MBSFN (Multi. Cast Broadcast Single Frequency Network) transmission Note: UL and DL frame formats are identical TCP: 160 Ts (5. 1 us) for first symbol, 144 Ts (4. 7 us) for other six symbols TCP-e: 512 Ts (16. 7 us) for all symbols 65

PHY channels supporting UL TX • • • PRACH – initial random access and UL timing alignment PUSCH – channel used for transmission of user data and upper layer signaling PUCCH – uplink control channel used for scheduling requests for synchronized UEs PDCCH – uplink scheduling grants PHICH – HARQ feedback channel supporting UL transmission 66

Uplink reference signals (1) • • Used for uplink channel estimation Two types of sequences – Data demodulation Reference Signal (DM-RS) – Sounding Reference Signal (SRS) • DM-RS – Sent on each slot transmission to help demodulate data – Occupies center part of the slot transmission (symbols 4) in both transmission slots – Use same bandwidth as the UL data (multiples of 12 carrier RBs) – Properties of DM-RS sequences • • 67 Small power variations in frequency domain Small power variations in time domain

Uplink reference signals (2) • SRS – Allow network to estimate channel quality across entire band – Used by MAC scheduler to perform frequency dependent scheduling – Optional implementation – UE can be configured to send SRS sequence at time intervals from 2 ms to 160 ms – Two modes of operation • • 68 Wideband SRS – UE send the sequence across the entire spectrum Hopping SRS – UE sends narrowband sequence that hops across different parts of the spectrum

PUSCH • • PUSCH = PHY Shared channel PUSCH carries UL-SCH (user data/higher layer signaling) During data transmission L 1/L 2 signaling also mapped o PUSCH – preserve single carrier TX Resources allocated to the UE on per subframe basis Allocation is done in PRB (12 carriers by 1 ms) Modulation used may be QPSK, 16 -QAM or 64 QAM (optional) Allocated PRBs may be hopped from subframe to subframe Two modes of hopping – – • Intra subframe and inter subframe Only inter subframe Hopping may be on the basis of explicit grants from Node B or following predefined cellspecific mirroring patterns 69 Example: 2 UE’s, 10 MHz (50 RB) Note: Frequency hopping provides frequency diversity and interference averaging for the UL transmission

PUCCH • • PUCCH = PHY Uplink Control Channel Used for L 1/L 2 signaling – – – • • Used only when there is no scheduled PUSCH transmission (single carrier TX) Uses PRBs at the very end of the allocated channel bandwidth – – • • Scheduling request ACK/NACK/DTX for DL-SCH transmission Feedback on DL channel quality (CQI/PMI/RI) Increases frequency diversity Allows scheduling of larger resource “chunks” for uplink transmission Number of PRBs is configured by the network in a semi-static manner Bandwidth of a single resource block in a subframe is shared by several UE’s – – 70 Economical use of allocated resources Reduces signaling overhead Note: PUCCH performs frequency hopping between two slots of a subframe

PUCCH formats PUCCH format Modulation Purpose Bits/subframe 1 On/off keying Scheduling requests N/A 1 a BPSK ACK/NACK for SIMO 1 1 b QPSK ACK/NACK for MIMO 2 2 QPSK CQI/PMI/RI 20 2 a QPSK+BPSK CQI/PMI/RI+ACK/NACK for SIMO 21 2 b QPSK+QPSK CQI/PMI/RI+ACK/NACK for MIMO 22 Note 1: There are 2 formats: Format 1 (1, 1 a and 1 b) and Format 2 (2, 2 a and 2 b) Note 2: PUCCH power offset depends on the PUCCH format 71

PUCCH – Format 1 • • Small in size (1 or 2 bits) Used for – – • DL HARQ ACK/NACK for MIMO/SIMO Scheduling request • By using different cyclic shifts and different covers sequences, multiple users may be multiplexed on the same PUCCH resource Typically there are 6 shifts and 3 cover sequences – 18 UE’s per PUCHH resource Note: Format 1 is repeated in two corresponding slots in the subframe 72

PUCCH – Format 2 • Larger in size (20, 21 or 22 bits) − − • 10 bits for CQI report 2 bits for ACK/NACK Used for – DL HARQ ACK/NACK for MIMO/SIMO – Scheduling request – CQI/PMI and RI information • • By using different cyclic shifts of the CAZAC sequence multiple UE’s may be multiplexed on one PUCCH resource Format 1 and 2 share the same basic format Note: for Format 2, both CQI report and ACK/NACK information are sent 73 Processing of CQI report

PRACH • • PRACH = PHY Random Access Channel Physical channel used in support of random access In LTE initial access is handled only on PHY, all the signaling is sent through UL-SCH (PUSCH) PRACH carries one of 64 preambles Available preambles are signaled in SIB-2 UE selects a preamble based on the amount of data it needs to send on UL-SCH (this way Node B knows how to reserve resources) PRACH preamble is sent over PRACH time frequency resource – – 74 Occupies middle 1. 08 MHz of spectrum Same spectrum regardless of total LTE bandwidth PRACH access subframe may occur every 1, 2, 5, 10 or 20 ms (20 ms – optional, only in synchronized networks) Subframe allowed for access – signaled on SIB-2, paremeter PRACH_Configuration index UL time frequency resources for PRACH

Section review 1. Why is OFDM not suitable for UL transmission? 2. What is PAPR? 3. What is DFTS-OFDM? 4. What are two types of UL reference signals? 5. Why is there need for sounding reference signals? 6. How often can a mobile configured to send SRS signals? 7. What is PUSCH? 8. What is PUCCH? 9. What are PUCCH formats? 75 10. What information is carried on PUCCH? 11. What is PRACH? 12. How does UE learn what preamble sequences are available for PRACH?

Part 3 MULTIPLE ANTENNA TECHNIQUES 76

Multi antenna configuration • • LTE uses of multiple antennas at both communication ends LTE standard requires support for Downlink MIMO – 4 antennas at the e. Node. B – 2 antennas at the UE • Multiple antennas may be used in three principle ways – Reception/transmission diversity – Beam forming – Spatial multiplexing (MIMO antenna processing) • Downlink MIMO – TX diversity – Beam forming or SDMA – Spatial multiplexing • Uplink MIMO – Multi user MIMO (SDMA) 77 Uplink MIMO Note: UL MU MIMO avoids use of multiple PAs at the UE

DL transmit diversity • Two implementations – Cyclic Delay Diversity (CDD) – Space-Time Transmit Diversity (STTD) • CDD – Multiple antenna elements are used to introduce additional versions of the signal that are cyclically delayed – UE perceives these signals as additional multi-paths – Assuming low correlations between TX antennas –created “multi-paths” fade independently – source of diversity • CDD TX diversity STTD – Uses Space-Frequency Block Codes – Special encoding (SFBC) makes the channel matrix unitary (full rank) – Reference symbols are used to estimate and invert channel matrix SFBC TX diversity 78

TX Diversity - CDD • • • OFDM is robust with respect to multi-path propagation (within CP interval) CDD simulates multi-path propagation No modification in RX signal processing – UE ‘sees’ single antenna transmission in dispersive environment Note: Extension of CDD to more than 2 antennas is straightforward. Each antenna has its own cyclic delay. 79 Processing in case of 2 antenna CDD TX diversity

TX Diversity – 2 TX SFBC • Data sent to different antenna are encoded using SFBC – 2 symbols at the time for 2 antennas TX diversity – Open loop SFBC in case of 2 TX diversity Note 1: UE needs to have good estimate of the channel – estimate obtained using PHY reference sequences 80

TX Diversity – 4 TX SFBC • Data sent to different antenna are encoded using SFBC – 4 symbols at the time for 4 antennas TX diversity – TX diversity operates on a resource element group (REG) – Open loop SFBC in case of 4 TX diversity Note 1: 4 TX SFBC diversity may be seen as two 2 TX SFBC diversity transmissions multiplexed in time 81

Spatial multiplexing • Capacity benefit of SM MIMO Basic idea: fading channel provides uncorrelated parallel paths for data transmission Example: 2 by 2 Spectral efficiency (bps/Hz) NT NR 12. 00 10. 00 8. 00 C/W (1, 1) 6. 00 C/W (1, 2) 4. 00 C/W (2, 2) 2. 00 0 82 - number of TX antennas - number of RX antennas 5 S/N (d. B) 10 15

Spatial multiplexing in LTE • Two types – Open loop (used high speed scenarios) • Large delay Cyclic Delay Diversity (CDD) – Closed loop (used in low speed scenarios) • Mobile provides channel feedback to e. Node B Feedback Closed loop spatial multiplexing Open loop spatial multiplexing PMI (Pre-coded matrix indicator) PMI feedback from UE based on instantaneous channel state No feedback from UE. Fixed pre-coding at e. Node B implementing cyclic delay diversity (CDD) CQI (Channel quality indicator) Separate CQI for each code word Aggregate CQI (one value) RI (Rank indicator) Based on the rank of estimated channel matrix (indicates number of spatial channels) Based on the rank of estimated channel matrix when SFBCs are used 83 Closed loop spatial multiplexing

Code word – layer mapping • • LTE uses either 1 or 2 code words Code words are mapped onto layers – 1 layer for 1 codeword – 2, 3 or 4 layers for 2 code words • Mapping between code-words and layers Number of modulation symbols in each layer is the same – Accomplished through numerous transportblock formats and sizes • Through a pre-coding matrix the layers are mapped onto the antennas – There is a set of pre-defined pre-coded matrices – Through PMI, UE recommends to e. Node. B which pre-coded matrix to use – e. Node. B may not follow UE’s recommendation – informs UE about precoding matrix through explicit signaling 84 Note: layers are mapped to antennas one symbol at the time

Antenna configurations 85 Transmission modes Description Comments 1 Single antenna (Port 0) Used for SISO and SIMO transmission 2 Transmit diversity Used in low SNR and high mobility 3 Open loop spatial multiplexing (large delay CDD) Beneficial in high SNR and rich multipath environment 4 Closed loop spatial multiplexing (Rank 2, 3 or 4) Beneficial in high SNR and rich multipath environment 5 Multi-user MIMO Beneficial in high SNR environment for interference reduction 6 Closed loop Rank = 1 Beneficial in low SNR environments 7 Single antenna port (Port 5) Used for beam forming of antenna arrays

SIMO/MIMO mode selection Note: Detection of the environment type and best use of MIMO/SIMO is one of the tasks for scheduler – major differentiating factor between different equipment vendors 86

Section review 1. 2. 3. 4. 5. 6. 7. What is MIMO? What is receive diversity? What is transmit diversity? What is beam forming? What is SDMA? What is spatial multiplexing? How much is capacity of link increased using spatial multiplexing? 8. What is CQI? 9. What is RI? 10. How is RI used by the scheduler? 87 11. What is the main idea behind SFBC? 12. What is CDD? 13. Explain the main idea behind CDD?