协同通信与AF和DF中继协议模板.doc

Abstract

Nowadays, there is a trend for communication system that the whole network system is becoming dynamic so that there are always having devices should be embedded and removed. Conventional wired communication, due to the complexity of cabling, does not adapt to the modern communication system. Wireless technique has been used widely because devices can be connected by electromagnetism wave without cabling. However, low transmitting reliablity because of inter-interference between electromagnetism waves is the key problem of wireless communication. Based on this, this thesis investigates one of the technique called cooperative communication and it cooperative protocols.

Cooperative communication is a virtual multiple-input multiple-output(MIMO) system. To increase the reliability of signal transmitted without increasing the amount of communication devices, this technology tries to make each antennas have one or more partners that assist them to transmit the signal. In wireless network, the devices not only transmit their own signal but also assist their “partner” to transmit their signal for saving the cost of installation of additional antennas at both receiver and sender

In this thesis, we focus on introducing three main protocols in cooperative communication: Amplify-and –Forward(AF), Decode-and-Forward(DF) and Coded Cooperation(CC). The performance and mathematical equations of AF and DF are analysed , and then MATLAB programs were created to simulate the performance of these two protocols.
About the three protocols, the main procedures are also introduced. The performance comparison for AF and DF in different signal-to-noise(SNR) are demonstrated. The result presents that the DF protocols has better performance than AF. Finally, some recommendations and future work are mentioned at the end of the thesis.
Table of Contents
Abstract
Table of contains
List of figures
List of abbreviations and Symbols
1 Introduction..................................................................................................................................9
1.1 Background.......................................................................................................................9
1.2 Objectives.........................................................................................................................9
1.3 Approaches.......................................................................................................................9
1.4 Thesis outline....................................................................................................................10
2 Literature Review.......................................................................................................................12
2.1 Overview...........................................................................................................................12
2.2 Spatial diversity technology..............................................................................................13
2.3 Basic Model for Wireless...................................................................................................13
2.3.1 SISO system............................................................................................................13
2.3.2 MIMO system.........................................................................................................14
2.3.3 Cooperative model.................................................................................................14
2.4 Cooperative schemes........................................................................................................15
2.4.1 Amplify-and-forward method................................................................................16
2.4.2 Decode-and-forward method................................................................................16
2.4.3 Coded cooperation.................................................................................................17
3 Simulation and Analyses of AF..................................................................................................21
3.1 Overview...........................................................................................................................21
3.2 Maximum likelihood method............................................................................................21
3.3 Simulation and Analysis.....................................................................................................21
3.3.1 The whole procedure and analysis.........................................................................21
3.3.2 Simulation..............................................................................................................24
3.4 Summary...........................................................................................................................26
4 Simulation and Analysis of DF...................................................................................................27
4.1 Overview..........................................................................................................................27
4.2 Quantization method.......................................................................................................27
4.3 Convolutional Code and Viterbi decode..........................................................................27
4.3.1 Convolutional code...............................................................................................28
4.3.2 Viterbi decode.......................................................................................................28
4.4 Simulation and analysis....................................................................................................28
4.4.1 The whole procedure and analysis........................................................................29
4.4.2 Simulation..............................................................................................................30
4.5 Performance comparison between AF and DF ................................................................31
4.6 Main challenges................................................................................................................32
4.7 Summary...........................................................................................................................33
5 Conclusions and future work.....................................................................................................34
5.1 Conclusion.........................................................................................................................34
5.2 Prospect............................................................................................................................34
5.3 Future work.......................................................................................................................35

Reference...................................................................................................................36
Appendix A Thesis specification..................................................................................37
Appendix B Logbook Summary Signature....................................................................40
Appendix C MATLAB programs....................................................................................41
C.1 Amplify-and-Forward Protocol……………………………………………………………….........……41
C.2 Decode-and –Forward protocol……………………………………………………..................……42
C.3 Rayleigh channel………………………………………………………......................................…..45

List of Figures

Figure 2.1 virtual MIMO system ………………………………………………………………………............….….…..13
Figure 2.2 Cooperative communication ………………………………………………………………………….....……14
Figure 2.3 MIMO system…………………………………………………………………………………………….......……..15
Figure 2.4 Cooperative model…………………………………………………………………………………….......……..16
Figure 2.5 Relay amplify model………………………………………………………………………………………...……..17
Figure 2.6 Decoded and forward model…………………………………………………………………………..……….18
Figure 2.7 Coded cooperative model…………………………………….........………………………………...........19
Figure 2.8 Coded cooperation data allocation…………………………………………………………..………...…….20
Figure 2.9 Four cases in coded cooperative……………………………………………………………......……………20
Figure 3.1 first time slot in AF method………………………………………………………………..…......…....…….23
Figure 3.2 Second time slot in AF method ………………………………………………………………….……………..24
Figure 3.3 AF protocol BER diagram ……………………………………………………………………………………..…..26
Figure 4.1 (n,k,m) convolutional encoder…………………………..……………………………………………....…….29
Figure 4.2 first time slot of DF…………………………………………………………………………………………………….30
Figure 4.3 Second time slot…………………………………….........…………………………………………………….…..30
Figure 4.4 DF protocol BER diagram……………………………………………………………………………………….....32
Figure 4.5 DF whole procedures……………………………..………………………………………………………...……..32
Figure 4.6 performance compared between AF and DF…….....................………………………….………33

List of Abbreviations and Symbols

MIMO
Multiple input multiple output
SISO
Single input single output
AF
Amplify-and-Forward
DF
Decode-and-Forward
CC
Coded Cooperation
BER
Bit error rate
QPSK
Quadrature phase-shift keying
i.i.d
independently and identically distribution
ML
Maximum likelihood
SNR
Signal –noise-ratio

1 Introduction

1.1 Background

Wireless communication is, recently, the fastest improving segment and most widely used way of the communication industry. For utilizing the broadcast property of electromagnetism wave, the information can be transmitted in wireless environment, which saves much cost for cabling and makes the change of network structure easily. On the other hand, as wireless technique is used more widely, there are also many problems appearing. For example, the wireless signal can be affected a lot by the transmitting medium and interfered with other signal and the destination will receive not only the direct wave but also some extra waves. These sorts of wave signal will generate and form the received signal at the destination, which will result in sharply differing with the original signal so that decreases the quality of signal and reliability. This is called multipath fading[11]. To solve these problems, cooperative communication is one of the methods.

Cooperative communication technique is a method based on MIMO(multiple-input multiple-output)system. MIMO system is a model that installing more than one antennas in both the sender and receiver, which achieve one signal is transmitted by different channels. In practical, due to the limitation of size, power waste and hardware, it is hard to install a lot of antennas in one communication device so that MIMO technique is hard to utilize in practical directly. Thus, cooperative communication is a model that builds a virtual MIMO system among existing antennas instead of building additional antennas but achieves the gain of MIMO system[8].

Compared with traditional transmitting method, cooperative communication builds a cooperative work relationship between each antenna which means each antenna will have a helper to assist them to transmit signal and these helper antennas will take some measures to optimize the quality of signal. Therefore, at the destination, lots of signals will be received so that receiver can have gain of diversity. Some protocols describe what functions these antennas apply for optimizing signal. In this report, some explanations and literature reviews focused on amplify and forward protocol, decoded and forward protocol and coded cooperative protocol are demonstrated. Otherwise, simulation result for amplify and forward and decoded and forward protocol is made.

1.2 Objectives

The purpose of this project is to analyse the advantages of cooperative communication by analysis of three main cooperative protocols. In this half year, this project can have a conclusion about three objectives:
1. Trying to understand the concept of cooperative communication and its working system models. Research for how the signal delivered through nodes.
2. Finding the three cooperative protocols that antennas obey—AF ( amplify—and-- forward), DF (decode- and- forward) and CC (coded cooperation) protocols and how they works.
3. Use the MATLAB to simulate the performance of AF and DF and do a comparison about them.

1.3 Approaches

Firstly, analyzing the concept of cooperative communication and finding the fundamental protocols about it. Secondly, finding the important described equations and the used coefficients. Finally, use MATLAB to simulate the procedures of AF and DF and try to get the BER( bit error rate)-SNR(signal-Noise ratio) diagram and compare the their performance.

1.4 Thesis outline
This report includes five parts: first part introduce the background of cooperative communication. Second part explains several literature reviews about wireless, diversity technology, MIMO and cooperative protocols. Third and forth parts demonstrate the simulation about AF and DF and get the result diagram. Additional, the forth part also includes the performance comparison between AF and DF. Last part makes a conclusion and the future work about the project.

2 Literature Review

2.1 Overview
To overcome the lack of multiple antennas limited by size or hardware complexity, cooperative communication is proposed. Cooperative communication can be understood a virtual multiple input multiple output(MIMO) system between source and destination.
In another words, the cooperative communication build a cooperative relationship among existing antennas. For utilizing the broadcast property of electromagnetism wave, not only the destination, there are also some other antennas receive the source signal. Instead of discarding this signal, this relationship asks these antennas to take some measures to process this signal and retransmit it to the appointed destination.

Figure 2.1 virtual MIMO system

To decrease the bit error rate and recover the source signal well, there are three common protocols for the helper antennas applying: amplify and forward(AF) protocol, decoded and forward (DF) protocol and coded cooperative(CC) protocol.

Figure 2.2 Cooperative communication

2.2 Spatial diversity technology

Cooperative communication utilizes the spatial diversity technology. Diversity is an idea that transmitting a signal through many independent channels, it is described in [1]. When source sends one signal in different independent channels, the destination will receive many formats about this signal. In this way, it can increase the signal-to-noise ratio(SNR) at the receiver whic