Understanding LTE with MATLAB an overview

By:

Houman Zarrinkoub PhD.

Motivations • Why LTE?

• Delivers global broadband mobile communications for 21st 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) 1.92 Mb/s

HSDPA (Rel 5) 14 Mb/s

HSPA+ (Rel 6) 84 Mb/s

WiMAX (802.16e) 26 Mb/s

LTE (Rel 8) 300 Mb/s

WiMAX (802.16m) 303 Mb/s

LTE-Advanced (Rel 10) 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

Downlink

Uplink

eNB

UE

UE

= User Equipment

= Mobile unit

eNB

= eNodeB

= enhanced Node

Base station

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 time-

multiplexed

H(f)

(0,0)

Fc(DL)

Uplink (UL)

Operating band

Downlink (DL)

Operating band

Fc(UL)

H(f)

(0,0) Downlink (DL) &

Uplink (UL)

Operating band

Fc(UL)=Fc(DL)

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

Multicast/Broadcast

Mode of transmission

Unicast

Mode of transmission

Traffic

channel

Control

channels

Traffic

channel

Control

channel

L2/L1

Control

channels

LTE time framing

LTE frequency structure

Chanel

Bandwidths

(MHz)

Number of

Resource

Blocks

Transmission

Bandwidths

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

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

LTE time-frequency paradigm Resource grid

LTE Multi-antenna transmission

frequency

time

space

OFDM

symbol 2

OFDM

symbol 1

OFDM

symbol 3

Subcarrier 2

Subcarrier 1

Subcarrier 3

Antenna port 1

Antenna port 2

Antenna port 3

…

…

…

Multiple resource grids on each antenna port

…

X

Resource grid on

Antenna port 1

Resource grid on

Antenna port 2

Resource grid on

Antenna port 3

Resource grid on

Antenna port 4

LTE Downlink transmission modes Depend on MIMO techniques used

LTE transmission modes Description

Mode 1 Single-antenna transmission

Mode 2 Transmit diversity

Mode 3 Open-loop codebook-based precoding

Mode 4 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

Tx Rx ω1

ω2

ω3

ω4

+

Maximum Ratio Combining

Receive diversity

Transmission Mode 1 (SIMO):

Receive Diversity

Transmit diversity x1

x2

x3

x4

…

…

-x*2

x1

-x*4

x3

…

…

Transmit

Diversity

Combiner

h11

h12 h21

h22

Transmission Mode 2:

Transmit Diversity

𝑌

𝑥1

𝑥2

𝑦1

𝑦2

𝑌 =ℎ11 ℎ12

ℎ21 ℎ22𝑋

𝑋

Spatial multiplexing

Transmission Mode 4:

Closed-loop Spatial Multiplexing

UE1

MU-MIMO

UE2 eNB

UE3

UE4

MU=MIMO pair

MU=MIMO pair

Transmission Mode 5:

Multi-user MIMO

Rx

ω1

ω2

ω3

ω4

Beamforming

Transmission Mode 7:

UE-specific beamforming

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

Mode

…

System model: Transmitter

Mode …

𝑥 𝑦

𝑥1

𝑥2

𝑥3

𝑥4

𝑦1

𝑦2

𝑦3

𝑦4

+

+

+

+

𝑛1

𝑛2

𝑛3

𝑛4

MIMO channel

AWGN channel

𝑥 (1) , 𝑥 (2) , ⋯ , 𝑥 (𝑛) 𝑦 (1) , 𝑦 (2) , ⋯ , 𝑦 (𝑛)

System model: MIMO fading channel

Mode

…

System model: Receiver

Mode …

Overview of chapter 9 Simulation

Simulation acceleration techniques

MATLAB to C

User’s Code

GPU

processing

Parallel

Computing

Better MATLAB

code

System objects MATLAB test

cases: • LTE PDCCH

processing chain

• Turbo coding

algorithm

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