Contents Abstract 1 Introduction 1.1 1.2 1.3 Introduction to cooperative relay networks 1.1.1 The relay protocols 1.1.2 Advantages of Cooperative Diversity Relaying Networks Introduction to Network Coding 1.2.1 Non-Binary and Binary Network Coding 1.2.2 Advantages of Network Coding 1.2.3 Weaknesses of Network Coding 11 Cooperative Diversity Relaying Networks using network coding 13 System models 15 2.1 Traditional Relay Multiple-Wireless Networks 16 2.2 Single Relay Networks using Network Coding 20 2.3 Multiple-Relay Networks using Network Coding 22 Outage Probability Calculations 24 3.1 Mutual Information 24 3.2 Outage Probability Definition 25 3.3 Outage Probability of Multiple-Relay Networks 27 3.3.1 Traditional Decode-and-Forward relaying 27 3.3.2 Selection Decode-and-Forward relaying 29 3.4 Outage Probability of Single Relay Networks using Network coding 32 3.5 Outage Probability of Multiple-Relay Networks using Network Coding 36 Conclusions and Future Works 42 iii Bibliography 43 iv List of Figures 1.1 Frequency Diversity 1.2 Space Diversity 1.3 Cooperative relay network 1.4 An example of Network Coding 1.5 An example of Non-linear Network Coding 1.6 An example of linear Network Coding 1.7 The butterfly network 10 1.8 The weakness of Network Coding 12 2.1 A traditional single relay network 19 2.2 A traditional multiple-relay network 19 2.3 Network coding in single relay network 20 2.4 Multiple-relay network using network coding 22 3.1 The direct link between the input and the output 25 3.2 Outage probability of a direct link 27 3.3 Outage Probability of fixed and selection DF relay 32 3.4 The degraded system model of a single relay network based on NC 34 3.5 The degraded system model of a single relay network based on NC 35 3.6 Outage probability of the single relay network with and without network coding 36 3.7 Link s1 r1 is in outage 39 3.8 Outage probability of relay networks with different scenarios 41 v Abstract In communication, Cooperative Diversity Relaying refers to devices communicating with one another with the help of relays in order to increase the performance of the network However, in one timeslot, the relay only transmits the signal of one source Therefore, Network Coding is introduced to improve the throughput of the network Combining Cooperative Relay Network and Network Coding should be studied to achieve significant benefits and overcome some weakness In this thesis, we consider the effect of Network Coding on Cooperative Relay Network We propose to use Selection Decode-and-Forward instead of Traditional Decode-and-Forward protocol at the relay We also use the instantaneous channel gains to calculate the outage probability of the proposal system model The rest of the thesis is organized as follows In Chapter II, the system model of a multiple-relay network is described The outage probability is calculated in Chapter III Finally, the conclusions and the future works are drawn in Section IV Chapter Introduction 1.1 Introduction to cooperative relay networks The sharp increase in the number of mobile subscribers which needs large bandwidth for multimedia applications anywhere and anytime requires the network service providers to optimize and develop the current technologies in order to ensure that the Quality of Services (QoS) is always satisfied Diversity scheme are used to improve the reliability of a message signal by transmitting multiple version of the same signal over different communication channels Because of time-varying channel conditions, the diversity plays an important role in combating fading and co-channel interference Diversity techniques are divided into the following types: time diversity, frequency diversity, space diversity, polarization diversity, muiltiuser diversity! [1] • Time diversity: The transmitter sends the same data at different time instants or a redundant error correcting code is added into the messages before transmitting Repetition coding is one of the most popular types of time diversity • Frequency diversity: The signal transmitted by using different frequency channels on a single antenna At the destination, it requires the number of receivers as the number of frequencies used at the transmitter It therefore requires more spectrum usage Transmitter Transmitted signal antenna Receiver Recovered signal antenna Transmitter Receiver Figure 1.1: Frequency Diversity • Spatial diversity The signal is transmitted over different path by using several antennas at the transmitter in order to allow multiusers to share a spectrum and avoid co-channel interference Figure 1.2: Space Diversity • Polarization diversity: The same messages are transmitted and received by using antennas with different polarization A diversity combining technique designed to combine the multiple received signals at the destination is used in this case • Multiuser diversity: In this technique, the transmitter and receiver rely on the quality of the link between the transmitter and each receiver in order to selects the best partner In recent years, MIMO (multi-input multi-output) technology based on spatial diversity and spatial diversity has attracted attention in wireless communication because it greatly improves the reliability, the throughput and the transmission rate without additional bandwidth nor requiring higher transmitter power However, this technique requires both the transmitter and the receiver to have multi-antennas, and all channels must be independent In practice, users not often achieve full-rank MIMO because they either not have multiple-antennas installed on a small-size devices, or the propagation environment cannot support MIMO, for example, there is not enough scattering Even if the users have enough antennas, full-rank MIMO is not guaranteed because the links between several antenna elements are often correlated To overcome the limitations in diversity gain MIMO, a new communication paradigm which uses an intermediate node to generate independent channel between the user and the base station was introduced The intermediate node often called relay node receives the signal transmitted from the user and forward it to the base station And this paradigm is called Cooperative Diversity Relaying Network 1.1.1 The relay protocols A key aspect of the cooperative communication process is the processing of the signal received from the source node carried out by the relay These different processing schemes depend on the protocols of the relays which can be generally categorized into fixed relaying schemes, selection relaying protocol (adaptive relaying schemes) and incremental relaying protocol In Fixed relaying protocols, the relay either amplifies what it receives, or fully decodes, re-encodes, and re-transmits the source message These fixed relaying options are called amplify-and-forward (AF) and decode-and-forward (DF), respectively Amplify and Forward is the protocol in which the relay receives the signal form the source and amplifies it before forwarding to the destination While, Decode-and-Forward relay decodes and re-encodes the received message before sends it to the destination Note that the decoded signal at the relay may be incorrect If an incorrect signal is forwarded to the destination, the decoding at the destination is meaningless [2] Therefore, sometimes the relay must be silent because it can not detect the presence of the signal or the signal quality is not good enough for the relay to decode fully the messages Selection relaying (SR) protocol is designed to overcome the shortcomings of DF relaying when the measured SNR at the relay falls below a threshold that the relay becomes unable to decode the message, the source simply continues its direct transmission to the destination using repetition coding or other more powerful codes In incremental relaying (IR) protocol, the relay only transmits upon a neg4 ative feedback from the destination Fixed relaying makes inefficient use of relay channel resources when operating at high rates because the relays repeat all the time, and under good transmission conditions this is un-necessarily In IR networks, the destination sends a one-bit ACK to the source and the relay if it can successfully decode message from the source, otherwise it sends a NACK to signal it fails to decode the message Only when the relay receives a NACK and if it is able to decode the source message, it will forward the message to the destination by employing AF relaying The destination receiver then uses maximum ratio combining (MRC) of the signal from the source and the relay to build up its receive SNR until it can successfully decode the message This is equivalent to using the well known repetition coding technique to combat deep fading situations 1.1.2 Advantages of Cooperative Diversity Relaying Networks Cooperative Diversity Relaying refers to devices communicating with one another with the help of relays in order to increase the performance of the network [3] Thereby, the relay channel can be considered as an auxiliary channel to the direct channel between the source and destination Figure 1.3 shows a network model using M relays The operation of this model can be divided into M + time slots In the first time slot, the source sends its messages to the relays and the destination using the broadcast method The relay i relies on the defined protocol to receive and process the source message before retransmitting it to the destination in timeslot i The presence of the signal is decided at the destination by comparing the measured SNR with a threshold R1 R2 Direct link S Broadcast mode RM D Broadcast mode Figure 1.3: Cooperative relay network The operation of each relay is independent of the others, so that there is no correlation among all channels We will show that the diversity gain and the robustness of this system model is increased significantly It is clear that the destination can not decode a source’s messages if and only if all links connecting the M relays and that source to the destination are in outage Assuming that the outage probabilities of these links are the same, and denoted by p Then the probability of system outage event is pout = pM +1 In [4], the diversity gain is defined as D, − log P SN R→∞ log SN R lim (1.1) in which P is the outage probability, SN R is the signal to noise ratio Then D= − log P M +1 ≈M +1 SN R→∞ log SN R lim (1.2) Equation 1.2 indicates that the user can guarantee the maximum diversity which is equal the number of the relays plus the direct link, i.e being the minimum cut at each source It means that the limitation of MIMO technique ... 19 2.2 A traditional multiple -relay network 19 2.3 Network coding in single relay network 20 2.4 Multiple -relay network using network coding ... transmission delay and more bandwidth consumption [8] So that, in general case, we cannot conclude which better linear or non-linear network coding In this thesis, we only concentrate on binary network. .. repetition coding or other more powerful codes In this thesis, we only consider the relay using selection Decode-and-Forward protocol in Time-Division mode 2.1 Traditional Relay Multiple-Wireless Networks