Understanding LTE with MATLAB an overview By: Houman Zarrinkoub PhD.
Motivations Why LTE? Delivers global broadband mobile communications for 21 st century Features innovative new air interface technologies OFDMA, MIMO, Fast link adaptations Achieves remarkable performance Basis of 4G wireless technology Has staying power for even 5G technologies and beyond Every communications engineer should know something about it My favorite reason: Puts Fourier analysis and in general Math back in telecommunications
Motivations Why LTE with MATLAB? Underlying transmission technologies has deep mathematical roots Dynamic nature of LTE transceiver system is best understood and revealed through simulation MATLAB provides a natural language and environment for mathematical modeling and simulation Area of author s expertise
Overview of chapter 1 Introduction
Evolution of wireless standards * *Although ETSI the European standardization body started GSM, later ETSI and other standard bodies formed 3GPP and 3G and 4G standards were developed globally by 3GPP. For a while a standard body known as 3GPP2 competed with 3GPP and developed North American 3G CDMA standards based on IS-95 but 3GPP2 finally dissolved in 2005
LTE Requirements Improved system capacity and coverage High peak data rates Low latency (both User-plane and Control-plane) Reduced operating costs Multi-antenna support Flexible bandwidth operations Seamless integration with existing systems (3G, WiFi, etc.)
Evolution of LTE LTE (Release 8) was completed in 2008 LTE (Release 9) released in 2009 with minor modifications to Rel. 8 LTE-Advanced = LTE-A = LTE Release 10 A maximum peak data rate of 1 Gbps approved by the ITU as an IMT-Advanced technology
History of peak data rates Technology Theoretical peak data rate (at low mobility) WCDMA (UMTS) HSDPA (Rel 5) HSPA+ (Rel 6) WiMAX (802.16e) LTE (Rel 8) WiMAX (802.16m) LTE-Advanced (Rel 10) 1.92 Mb/s 14 Mb/s 84 Mb/s 26 Mb/s 300 Mb/s 303 Mb/s 1 Gb/s
LTE enabling technologies Air interface Downlink: OFDMA Uplink: SC-FDMA Multi-antenna (MIMO) techniques Defining multiple transmission modes Link adaptation Adaptive modulation & coding Adaptive precoding Adaptive MIMO (ranks or number of layers) Flexible bandwidth allocation Computationally efficient Turbo Coding
LTE Downlink transmitter processing chain
Organization of the book Chapter 2: Overview of the LTE Physical Layer Chapter 3: MATLAB for Communications System Design Chapter 4: Modulation and Coding Chapter 5: OFDM Chapter 6: MIMO Chapter 7: Link Adaptation Chapter 8: System-Level Specification Chapter 9: Simulation Chapter 10: Prototyping as C/C++ Code Chapter 11: Summary
Overview of chapter 2 LTE physical layer specification
Uplink and Downlink nomenclature enb = enodeb = enhanced Node Base station enb Downlink Uplink UE UE = User Equipment = Mobile unit
FDD & TDD FDD: Frequency Division Duplex frequency bands are paired simultaneous transmission on two frequencies (one for downlink and the other for uplink) TDD: Time Division Duplex frequency bands are unpaired uplink and downlink transmissions share the same channel and carrier frequency The transmissions in uplink and downlink directions are timemultiplexed H(f) (0,0) H(f) F c (UL) Uplink (UL) Operating band F c (UL)=F c (DL) (0,0) Downlink (DL) & Uplink (UL) Operating band F c (DL) Downlink (DL) Operating band
Data transfer Hierarchy Logical channels connect Layer 3 (IP RRC) to Layer 2 (MAC) Transport channels connect layer 2 (MAC) to Layer 1 (PHY) Physical channels constitute the signal to be transmitted
Mapping Downlink channels Traffic channel Control channels Control channel Traffic channel L2/L1 Control channels Unicast Mode of transmission Multicast/Broadcast Mode of transmission
LTE time framing
LTE frequency structure OFDM subcarrier spacing = 15 khz Number of subcarriers per resource block = 12 resource block = unit of frequency scheduling = 12 x 15 = 180 khz Transmission bandwidth = a multiple of number of resource blocks Chanel Number of Transmission Bandwidths Resource Bandwidths (MHz) Blocks 1.4 6 6 x 12 x 15 khz = 1.080 MHz 3 15 15 x 12 x 15 khz = 2.7 MHz 5 25 25 x 12 x 15 khz = 4.5 MHz 10 50 50 x 12 x 15 khz = 9.0 MHz 15 75 75 x 12 x 15 khz = 13.5 MHz 20 100 100 x 12 x 15 khz = 18.0 MHz
LTE time-frequency paradigm Resource grid
LTE Multi-antenna transmission space Subcarrier 3 Subcarrier 2 frequency Antenna port 2 Antenna port 3 Subcarrier 1 Antenna port 1 time OFDM symbol 1 OFDM symbol 2 OFDM symbol 3
Multiple resource grids on each antenna port Resource grid on Antenna port 4 X Resource grid on Antenna port 3 Resource grid on Antenna port 2 Resource grid on Antenna port 1
LTE Downlink transmission modes Depend on MIMO techniques used LTE transmission modes Description Mode 1 Mode 2 Mode 3 Mode 4 Single-antenna transmission Transmit diversity Open-loop codebook-based precoding Closed-loop codebook-based precoding Mode 5 Multi-user-MIMO version of transmission mode 4 Mode 6 Single-layer special case of closed-loop codebook-based precoding Mode 7 Release-8 non-codebook-based precoding supporting only single-layer based on beamforming Mode 8 Release-9 non-codebook-based precoding supporting up to two layers. Mode 9 Release-10 non-codebook-based precoding supporting up to eight layers
Transmission Mode 1 (SIMO): Receive Diversity Receive diversity Tx ω 1 Rx ω 2 + ω 3 Maximum Ratio Combining ω 4
Transmission Mode 2: Transmit Diversity x 1 x 2 Transmit diversity h 11 x 3 -x * 2 x 4 h 21 h 22 h 12 Transmit Diversity Combiner x 1 -x * 4 x 3
Transmission Mode 4: Closed-loop Spatial Multiplexing Spatial multiplexing x 1 y 1 X x 2 y 2 Y Y = h 11 h 12 h 21 h 22 X
Transmission Mode 5: Multi-user MIMO MU-MIMO UE 3 UE 4 MU=MIMO pair UE 1 enb UE 2 MU=MIMO pair
Transmission Mode 7: UE-specific beamforming Beamforming Rx ω 1 ω 2 ω 3 ω 4
Overview of chapter 3 MATLAB for Communications System Design
From specification to implementation Elaborate specifications in a model as a blue-print for implementation Introduce innovative proprietary algorithms Assess system-level performance Accelerate simulation for large data sets Fill gaps from computer model to implementation
Where does MATLAB fit? MATLAB and Communications System Toolbox for algorithm and system design MATLAB and Simulink for dynamic & large scale simulations Accelerate simulation with a variety of options in MATLAB Connect system design to implementation with C and HDL code generation
Overview of chapter 4 Modulation and coding
Description & MATLAB programs for: LTE Modulation schemes Scrambling/descrambling Turbo coding Early-termination algorithms Rate matching Transport block processing
Overview of chapter 5 OFDM
Description & MATLAB programs for: Fading channel models OFDM and frequency-domain equalization Resource grid content OFDM transmitter & receiver Transmission mode 1 (SISO, SIMO)
Overview of chapter 6 MIMO
Description & MATLAB programs for: MIMO Fading channel models MIMO channel estimation MIMO receivers (ZF, MMSE, SD) MIMO techniques: Transmit diversity (TD) spatial multiplexing (SM) Transmission modes 2 (TD), 3 (open-loop SM) & 4 (closed-loop SM)
Overview of chapter 7 Link Adaptations
Description & MATLAB programs for: Channel Quality Estimation (CQI) Precoder Matrix Estimation (PMI) Rank Estimation (RI) Adaptive modulation and coding based on CQI Adaptive precoding based on PMI Adaptive MIMO based on RI
Overview of chapter 8 System-level specifications
System model: Transmitter Mode Mode
System model: MIMO fading channel n 1 x 1 + y 1 x 2 + n 2 y 2 x (1), x (2),, x (n) x x 3 + n 3 y 3 y y (1), y (2),, y (n) x 4 + n 4 y 4 MIMO channel AWGN channel
System model: Receiver Mode Mode
Overview of chapter 9 Simulation
Simulation acceleration techniques Better MATLAB code User s Code System objects MATLAB to C MATLAB test cases: LTE PDCCH processing chain Turbo coding algorithm Parallel Computing GPU processing
Overview of chapter 10 Prototyping as C/C++ Code
From MATLAB to C MATLAB test cases: LTE PDCCH processing chain Adaptive modulation CSR interpolation Equalization OFDM & FFT implementation
Overview of chapter 11 Summary