协同通信与AF和DF中继协议

1、AbstractNowadays, 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.

2、 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

3、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 ma

4、ke 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 senderIn th

5、is 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

6、 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 wo

7、rk are mentioned at the end of the thesis.59 / 59文档可自由编辑Table of ContentsAbstractTable of containsList of figuresList of abbreviations and Symbols1 Introduction.91.1 Background.91.2 Objectives.91.3 Approaches.91.4 Thesis outline.102 Literature Review.122.1 Overview.122.2 Spatial diversity technology

8、.132.3 Basic Model for Wireless.132.3.1 SISO system.132.3.2 MIMO system.142.3.3 Cooperative model.142.4 Cooperative schemes.152.4.1 Amplify-and-forward method.162.4.2 Decode-and-forward method.162.4.3 Coded cooperation.173 Simulation and Analyses of AF.213.1 Overview.213.2 Maximum likelihood method.

9、213.3 Simulation and Analysis.213.3.1 The whole procedure and analysis.213.3.2 Simulation.243.4 Summary.264 Simulation and Analysis of DF.274.1 Overview.274.2 Quantization method.274.3 Convolutional Code and Viterbi decode.274.3.1 Convolutional code.284.3.2 Viterbi decode.284.4 Simulation and analys

10、is.284.4.1 The whole procedure and analysis.294.4.2 Simulation.304.5 Performance comparison between AF and DF .314.6 Main challenges.324.7 Summary.335 Conclusions and future work.345.1 Conclusion.345.2 Prospect.345.3 Future work.35Reference.36Appendix A Thesis specification.37Appendix B Logbook Summ

11、ary Signature.40Appendix C MATLAB programs.41C.1 Amplify-and-Forward Protocol.41C.2 Decode-and Forward protocol.42C.3 Rayleigh channel.45List of FiguresFigure 2.1 virtual MIMO system .13Figure 2.2 Cooperative communication .14Figure 2.3 MIMO system.15Figure 2.4 Cooperative model.16Figure 2.5 Relay a

12、mplify model.17Figure 2.6 Decoded and forward model.18Figure 2.7 Coded cooperative model.19Figure 2.8 Coded cooperation data allocation.20Figure 2.9 Four cases in coded cooperative.20Figure 3.1 first time slot in AF method.23Figure 3.2 Second time slot in AF method .24Figure 3.3 AF protocol BER diag

13、ram .26Figure 4.1 (n,k,m) convolutional encoder.29Figure 4.2 first time slot of DF.30Figure 4.3 Second time slot.30Figure 4.4 DF protocol BER diagram.32Figure 4.5 DF whole procedures.32Figure 4.6 performance compared between AF and DF.33List of Abbreviations and SymbolsMIMOMultiple input multiple ou

14、tputSISOSingle input single outputAFAmplify-and-ForwardDFDecode-and-ForwardCCCoded CooperationBERBit error rateQPSKQuadrature phase-shift keyingi.i.dindependently and identically distributionMLMaximum likelihoodSNRSignal noise-ratio1 Introduction1.1 BackgroundWireless communication is, recently, the

15、 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 oth

16、er 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 so

17、rts 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 fading11. To solve these problems, cooperative communication is one of t

18、he 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 limit

19、ation 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 addit

20、ional antennas but achieves the gain of MIMO system8.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

21、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 fo

22、cused 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 ObjectivesThe purpose of this project is to analyse the advantages of cooperative co

23、mmunication 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 th

24、e three cooperative protocols that antennas obeyAF ( amplifyand- 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 ApproachesFirstly, analyzing the concept of coope

25、rative 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 thei

26、r performance.1.4 Thesis outlineThis 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 ab

27、out 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 Review2.1 OverviewTo overcome the lack of multiple antennas limited by size or hardware com

28、plexity, 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 th

29、e 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.

30、 Figure 2.1 virtual MIMO systemTo 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 communic

31、ation 2.2 Spatial diversity technologyCooperative 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 rec

32、eive many formats about this signal. In this way, it can increase the signal-to-noise ratio(SNR) at the receiver which result in recovering the source signal better. There are three common diversity technologies: time diversity, frequency diversity and spatial diversity. Spatial technology is to bui

33、ld many relays to retransmit the signal which creates additional channels in space. The cooperative communication applies the spatial diversity technology mainly4. 2.3 Basic Model for Wireless 2.3.1 Single input and single output (SISO) systemSingle input and single output is the tradition model whi

34、ch both transmitter and receiver have one antenna to send or receive signal. In this way, the information is transmitted by electromagnetism wave in the air. Due to the effect of multiple path fading, the destination is hard to recover the source signal from receiver signal. 2.3.2 Multiple input and

35、 multiple output(MIMO) systemAs the name said, MIMO allows both the source and destination to have multiple antennas to send and receive signal9. Due to the effect of multiple path fading, the quality of signal will be decreased. However, by building additional ways between source and destination, m

36、ore information will be transmitted at the same time and for the destination many formats of source signal will be received so that MIMO can greatly improve the spectrum utilization and channel capacity without increasing the bandwidth. But more antennas mean more communication devices in both sourc

37、e and destination. It has to cost a lot to build enormous system to support the multiplexing technology9. Figure 2.3 MIMO system2.3.3 Cooperative modelThe basic cooperative model is the source-relay-destination model. Here we defined the cooperative antenna as relay. This model is naturally represen

38、ted by the graph below 3. Here we set the source-to-relay channel gain to H1, noise is N1; the gain of source-to-destination to H2, noise is N2; the gain of relay-to-destination to H3, noise is N3. At the first time slot, the source sent the source signal X1 to the relay and destination:Y2=H1*X1+N1Y

39、3=H2*X1+N2At the second time slot, the relay takes some measures to process the received signal Y2, we set the process to C: X2=C*Y2. Then, the relay retransmitted the X2 to the destination: Y4=H3*X2+N3. As a result, at the destination Y4 and Y3 are received:Y3=H2*X1+N2Y4=C*H3*H1*X1+C*H3*N1+N2The de

40、stinations task is recovering X1 from Y3 and Y4.2.4 Cooperative schemesAlthough the spatial diversity technology can increase the rate of successful packet receipt and the receiver SNR, during the signal transmitting through the channel (Rayleigh fading channel), the signal still suffer from the fad

41、ing like noise. Due to the negative effect of Rayleigh fading, the signal density and phase will be changed. To weakened this effect, the relay node need to take some cooperative coding strategies.2.4.1 Amplify-and-forward method (AF)In practical, during the signal transmitted in channel, one of the

42、 fading problems is amplitude fading, which may lead to packets loss and power efficiency decreasing 4. Amplify-and-forward method is quite simple. After the relay received the signal from source, the relay just amplifies the signal and retransmits it to the destination. Although the noise part is amplified as well, the destination can have gain of diversity8. However, the amplify coefficient should meet the constraint of power. Here, we set the power of source sending signal to P, the power of noise between source and relay is n1.