Welcome to

Welcome to

Simulation of communication systems (DT001A)

[email protected] and [email protected]

A project course about MATLAB with SIMULINK and Communications Blockset

MATLAB = Matrix Laboratory.Tool for numerical calculation and visualization. Commonly used for simulation of the communication system physical layer, signal and image processing research, etc.

SIMULINK: Toolbox in Matlabthat allows graphical data-flow oriented programming.

Aim of the course To prepare the student for thesis project and work in the

area of telecommunciations development and research. To give experience of performance analysis of communication

systems and algorithms, at the physical layer and datalink layer.

To give experience of simulation tools such as MATLAB and SIMULINK.

This may include modelling and simulation of traffic sources, channel models, modulation schemes, error coding schemes, equalizers, algorithms and protocols.

A real-world project is studied within an application area such as cellular communications, modems for broadband access, wireless networks, short-range communication, digital TV transmission, IP-TV or IP-telephony.

Prerequisites Computer Networks A 7.5 ECTS credits or similar Computer Engineering B, Wireless Internet access (most

important!) Computer Engineering AB-level, 30 ECTS credits TCP/IP networking Mathematical statistics Programming

Other helpful courses: Transform theory, 7.5 ECTS credits. Electrical engineering A, Analog electronics or Circuit theory Electrical Engineering B, Telecommunications, 7.5 ECTS credits. Electrical engineering B, Signals and systems, 7.5 ECTS credits. Markov processes/Queueing theory

Litterature

Matlab and Simulink documentation will be provided electronically.

Please repeat physical layer issues and datalink layer issues in basic books in Computer Networks and Wireless Internet Access.

Requirements

All lectures and supervision lessons are mandatory. You are expected to devote 20 hours/week to this

course, for example in L209. Quzzes (multiple choice tests): At least 70% correct

answers. Lab: About 20 hours of work. Homework problem. Oral presentations. Project

Requirements on the project Review at least one research paper, and describe some standard and

some existing simulation model. Simulate a communications standard, or check the simulations made

in a research paper. At least modify an existing simulation model, for exampel a Simulink

or Matlab demo, or build a model of your own (more difficult) Produce some plots for several parameter cases, showing for

example BER, bit rate or delay as function of at least two different parameters, for example SNR, facing model, modulation scheme, etc.

The simulation results should be stable (the plots smooth and not jerky), i.e simulate sufficiently long simulation time, or take the average of sufficiently large number of simulations.

Draw some interesting conclusions from this.

Grading is based on

Keeping deadlines.

Quzzes.

Showing good understanding when andwering questions from teachers and other students about your presentations.

Extent of own code.

Research relevance.

Own new results or conclusions.

Time plan and deadlines (prel) Week 44-45   - Introduction lectures - Start lab: Intro to Simulink. (About 20 hours of work)    - Electronic quizzes in webct

- Choose a standard and en existing model to simulate Week 46   - Assignment 1 (homework problem).

- Conclude lab (demonstrate to teachers) Week 47-48   - Present chapter 2 for class: Theory study – present a standard and review a research paper - Present chapter 3 for class: Model – present an existing

simulation model

Week 49-50   - Demonstrate chapter 1 to teachers: Introduction (goal of your project)

- Demonstrate chapter 4: Modifications to an existing simulation model, or a new model that you have built.

Week 51-02   - Demonstrate some simulation results to teachers. Week 03  - Final report and project presentations, incl chapter 5:

Results, and chapter 6: Conclusions.

”IMRaD” report disposition

Use MIUN template for technical reports.

Abstract Table of contents. 1. Introduction 2. Theory study (describe a standard and review a research

paper) 3. Existing simulation model 4. Modifications to the simulation model/own simulation model 5. Simulation results 6. Conclusions List of sources Appendix: Simulation code

Assignment 1: Theory repetition The first assignment consists of old exam problems in

Computer Networks A, Wireless Internet access B and Telecommunications B.

Deadline: At the supervision lesson week 45. Be

prepared to present your answers on the whiteboard.

12

MATLAB

MATLAB = Matrix Laboratory.Tool for numerical calculation and visualization. Commonly used for simulation of the communication system physical layer, signal and image processing research, etc.

13

Command window

Workspace

Commandhistory

This is how MATLAB looks like

14

More MATLAB windows

Figure window

M-file editor

Array editor

15

How to get help in MATLAB?help functionsname

Shows unformatted text

doc funktionsnamn

Shows HTML documentation in a browser

SIMULINK

SIMULINK: Toolbox in Matlabthat allows graphical data-flow oriented programming.

Repetition of some basic concepts Frequency spectrum Digitalisation, source coding Error coding Modulation Multiple-access methods Base-band model Distorsion, noise Signal-to-noise ratio Bit-error ratio Statistics

Repetition of some basic concepts

Digitalization

PCM = Pulse Code Modulation = Digital transmission of analogue signals

SamplerAD-converter

with seerial output

011011010001...

DA-converter

Anti aliasing-filter

Interpolationfilter

Number exemples from PSTN = the public telephone network

300-3400Hzband pass

filter. Stopseverything

over 4000Hz.

8000sampelsper sec

8 bit per sampeli.e. 64000 bpsper phone call

28 = 256voltage levels

0

1

Microphone Loudspeaker

Aliasing

Quantization noice

Digital transmission

Distorsion

Effect of attenuation, distortion, and noise on transmitted signal.

Point-to-point communication

Mikrofon Högtalare

Source coding Source decodingDigitalizatingcompression

0110 0110

Error management Error control.

0100010

Bitfel

0110010

Flow control Flow control

Modulation Demodulation

0110010NACKACK

Layer6

Layer2

Layer1

Layer7

Digital modulation methods

Binary signal

ASK = Amplitude Shift Keying (AM)

FSK = Frequency Shift Keying (FM)

PSK = Phase Shift Keying (PSK)

0 0.005 0.01-2

0

2000

0 0.005 0.01-2

0

2001

0 0.005 0.01-2

0

2011

0 0.005 0.01-2

0

2010

0 0.005 0.01-2

0

2100

0 0.005 0.01-2

0

2101

0 0.005 0.01-2

0

2111

0 0.005 0.01-2

0

2110

8QAM example:Below you find eight symbols used for a so called 8QAM modem (QAM=Quadrature Amplitude Modulation). The symbols in the first row represent the messages 000, 001, 011 and 010 respectively (from left to right). The second row representents 100, 101, 111 and 110.

a) The signal below is transmitted from the modulator. What bit sequency is transmitted?

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-2

0

2

Tid [sekunder]

Sp

än

nin

g [V

olt]

Modulatorns utsignal

b) The time axis is graded in seconds. What is the symbol rate in baud or symbols/s?

c) What is the bit rate in bit/s?

Example 2 cont.

Bit rate vs baud rate

Bit rate in bit/s:

Where M is the number of symbols and fs is the symbol rate in baud or symbols/s.

2logb Sf f M

Bit and baud rate comparison

ModulationModulation UnitsUnits BitsBits/symbol/symbol Baud rateBaud rate Bit Rate

ASK, FSK, 2-PSKASK, FSK, 2-PSK Bit 1 N N

4-PSK, 4-QAM4-PSK, 4-QAM Dibit 2 N 2N

8-PSK, 8-QAM8-PSK, 8-QAM Tribit 3 N 3N

16-QAM16-QAM Quadbit 4 N 4N

32-QAM32-QAM Pentabit 5 N 5N

64-QAM64-QAM Hexabit 6 N 6N

128-QAM128-QAM Septabit 7 N 7N

256-QAM256-QAM Octabit 8 N 8N

Figure 5.14 The 4-QAM and 8-QAM constellations

Q (Quadrature phase)

I (Inphase)

Q (Quadrature phase)

I (Inphase)

Sine wave example

I

5 Volt

л/2 radians = 90º

Complex representation

Inphase and quadrature phase signal Sine wave as reference (inphase) signal:

Cosine wave as reference (inphase) signal:

( ) ( )sin(2 ) ( ) cos(2 ).c cs t I t f t Q t f t

( ) ( ) cos(2 ) ( )sin(2 ).c cu t I t f t Q t f t

Complex baseband representation

C = I+jQ

Amplitude:

Phase:

RF signal (physical bandpass signal, if a cosine is reference signal):

2 2C I Q I

jQ

C|C|

Arg C

arctan , if 0arg( )

arctan , if 0

QI

II jQQ

II

( ) cos(2 arg ).cs t C f t C

Equivalent baseband signal

( ) ( )sin(2 ) ( ) cos(2 ).c cs t I t f t jQ t f t

Figure 5.11 The 4-PSK characteristics

Figure 5.12 The 8-PSK characteristics

Figure 5.16 16-QAM constellations

Spectrum of ASK, PSK and QAM signal

Figure 3.9 Three harmonics

Figure 3.10 Adding first three harmonics

Example: Square Wave  

Square wave with frequency fo

Component 1:

Component 5:

Component 3:

.

.

.

.

.

.

...}5cos5

13cos

3

1{cos

4)( ttt

Ats ooo

tA

ts o

cos4

)(1

tA

ts o

3cos3

4)(3

tA

ts o

5cos5

4)(5

Figure 3.11 Frequency spectrum comparison

Filtering the Signal Filtering is equivalent to cutting all the frequiencies outside the band of the

filter

High pass

INPUTS1(f)

H(f)

H(f)

OUTPUT S2(f)= H(f)*S1(f)

Low pass

INPUTS1(f)

H(f)

H(f)

f

OUTPUT S2(f)= H(f)*S1(f)

Band pass

INPUTS1(f)

H(f)

H(f)

OUTPUT S2(f)= H(f)*S1(f)

• Types of filters– Low pass

– Band pass

– High pass

f

f

Figure 6.4 FDM (Frequency division multiplex)

Figure 6.5 FDM demultiplexing example

Figure 6.19 Time division multiplex (TDM) in the american telephone network

Multiple access = channel access Several transmitters sharing the same physical medium, for

example wireless network, bus network or bus network.Based on

A physical layer multiplexing scheme A data link layer MAC protocol (medium access control) that avoids

collisions, etc.

Examples: TDMA (time division multiple-access) based on TDM FDMA (time division multiple-access) based on FDM CDMA based on spread spectrum multiplexing CSMA (carrier sense multiple-access) based on packet switching =

statistical multiplexing

Cellular telephony generations

1G: (E.g. NMT 1981) Analog, FDMA circuit switched.

2G: (E.g. GSM 1991) Digital, FDMA+TDMA, 8 timeslots, circuit switched.

2.5G: (GPRS) Packet switched = statistical multiplexing. The old circuit switched infrastructure is kept.

3G: (e.g. WCDMA) FDMA + CDMA (= spread spectrum).

4G: (E.g. 3gpp LTE) All-IP. OFDM or similar.

Spread spectrum

DS-CDMA = Direct Sequence Code DivisionMultiple Access

Chip sequencies

Figure 13.15 Encoding rules

Figure 13.16 CDMA multiplexer

Figure 13.17 CDMA demultiplexer

Figure 9.1 Discrete Multi Tone (DMT)

Essentially the same thing as OFDMUsed in ADSL modems

Figure 9.2 ADSL Bandwidth division

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-1

0

1

Sub

carr

ier

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-1

0

1

Sub

carr

ier

20 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

-1

0

1

Sub

carr

ier

3

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-1

0

1

Sub

carr

ier

4

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-5

0

5

Sum

sig

nal

Time [ms]

OFDM modulation

A simple example:4 sub-carriers

8 PSK

-1.5 -1 -0.5 0 0.5 1 1.5-1.5

-1

-0.5

0

0.5

1

1.5

000

001

010

011

100

101

110

111

The 8PSK constellation

cos

-sin

{ { { { { {30 k=1 k=31 k=4 k=2k=0

OFDM symbol 1 OFDM symbol 2

0 0 0 1 0 0 0 1 0 0 1 0 1 1 1 0 0 0 0 1 0 0 0 0kk k == =

< >E5F1442443144444444444444424444444444444443 14444444444444244444444444443

Technical data for DAB and DVB-T DAB DVB-T

Adopted 1995 1997

Coverage in parts of: Canada, Europe, Australia Europe and Australia

Net bit rate R per frequency channel:

576 - 1152 kbit/s 4.98 - 31.67 Mbit/s

Channel separation B: 1.712 MHz 8 MHz

Link level spectrum efficiency R/B:

0.34 - 0.67 bit/s/Hz 0.62 - 4.0 bit/s/Hz

Freq. range of today’s receivers:

174 – 240 MHz , 1452 – 1492 MHz.

470 - 862 MHz

Maximum speed: About 200 - 600 km/h 36 - 163 km/h

Number of OFDM sub-carriers:

1536, 384, 192 or 768. The 2K mode: 1705 The 8K mode: 6817

Sub-carrier modulation: DQPSK QAM, 16QAM or 64QAM

Inner Forward Error Correction Coding (FEC):

Convolutional coding with code rates 1/4, 3/8 or 1/2.

Convolutional coding with code rates 1/2, 2/3, 3/4, 5/6 or 7/8.

Outer FEC: None RS(204,188,t=8)

Time (outer) interleaving: Convolutional interleaving of depth 384 ms.

Convolutional interleaving of depth 0.6 - 3.5 ms.

Orthogonal Frequency Division Multiplex (OFDM)Summary of advantages Can easily adapt to severe channel conditions without complex equalization Robust against narrow-band co-channel interference Robust against Intersymbol interference (ISI) and fading caused by

multipath propagation High spectral efficiency Efficient implementation using FFT Low sensitivity to time synchronization errors Tuned sub-channel receiver filters are not required (unlike conventional

FDM) Facilitates Single Frequency Networks, i.e. transmitter macrodiversity.

Summary of disadvantages Sensitive to Doppler shift. Sensitive to frequency synchronization problems. Inefficient transmitter power consumption, due to linear power amplifier

requirement.

Bit error rate (BER) = Bit error probability = Pb

Packet error rate (PER) = Packet error probability for packet length N bits:Pp = 1 – (1-Pb)N

Error-correcting codes (ECC), also known as Forward-error correcting codes (FCC)

A block code converts a fixed length of K data bits to a fixed length N codeword, where N > K.

A convolutions code inserts redundant bits into the bit-stream. Code rate ¾ means that for every 3 information bit, totally 4 are transferred, i.e. every forth of the transferred bits is redundant.

Bit rates

Gross bit rate = Transmission rate. Symbol rate = Baud rate ≤ Gross bit rate In spread spectrum: Chip rate ≥ Bit rate ≥

Symbol rate. In FEC: Net bit rate = Information rate =

Useful bit rate ≤ Code rate * Gross bit rate Maximum throughput ≤ Net bit rate Goodput ≤ Throughput

Nyquist formula Gives the gross bit rate,without taking noise into

consideration: Symbol rate < Bandwidth*2 Bit rate < Bandwidth * 2log M

The above can be reached for line coding (base band transmission) and so called single-sideband modulation. Howeverm in practice most digital modulation methods give: Symbol rate = Bandwidth

Signal to noise ratios S/N= SNR = Signal-to-noise ratio. Often same thing as

C/N=CNR = Carrier-to-noise ratio SNR in dB = 10 log10 (S/N)

S/I = SIR = Signal-to-interference ratio. Often the same thing as C/I=CIR = Carrier-to-interference ratio. I is the cross-talk power.

CINR = C/(I+N) = Carrier-to-noise and interference ratio Eb/N0 = Bit-energy (Power in watt divided by bitrate)

divided by Noise density (in Watt per Hertz) Es/N0 = Symbol-energy (Power in Watt divided by

bitrate) divided by Noise density (in Watt per Hertz)

Shannon-Heartly formula

Gives the channel capacity, i.e. the maximum information rate (useful bit rate) excluding bit error rate.

I=B * 2log (1+C/N)

Some statistical distributions

Gaussian noise

Time

Voltage

Gaussian = Normal distributionProbability density funciton

Additive White Gaussian Noise (AWGN) channel White noise = wideband (unfiltered) noise

with constant noise density in Watt/Hertz Pink noise = lowpass-filtered noise. Additive = linear mixing.

+Signal

Noise source

Noisy signal

Channel Noise

Info

Error Rate Calculation

Tx

Rx

Error Rate Calculation

BSC

Binary SymmetricChannel

BernoulliBinary

Bernoulli BinaryGenerator

0

Display

0 1 0 1 1 0 1 0 0 1 0

Bernoulli distribution

Random sequence of independent 0:s and 1:s.

Exponential distribution

Commonly used for time between phone calls and length of phonecalls. Simple model for calcuclation and simulation, but does not reflect data traffic bursty nature.

More commons distributions

Poisson distribution Rectangular distribution Discrete distributions, for example the

distribution of a dice