The Design Of ARQ Protocol In Cooperative Networks

Cooperative Communication has drawn extensively attention by many researchers in recent years due to its novel way of achieving spatial diversity. Automatic Repeat-reQuest (ARQ) Protocol is another effective link layer technology often used to combat channel fading, where an error detection code is always attached in packets for error detection. In this thesis, we mainly focus on the design of cooperative ARQ protocol in wireless relay networks. Except for the basic three-node model, there are two other important relay networks: multi-relay networks and user cooperation networks. The main work of this thesis is to design Cooperative ARQ protocol based on decode-and-forward mode in such two networks.First in multi-relay networks, many relays are available to be used to help source's transmission to destination. It is well-known that decode-and-forward mode will suffer from diversity order loss problem due to possible deep fading of the source-relay channel. This problem is even more substantial in multi-relay networks, because many available relays might not be able to join in the assistance of source's transmission. We notice that in multi-relay networks equipped with ARQ protocol, this diversity-loss problem can be ameliorated.The Cooperative ARQ protocol is often made up of two phases. In the first phase, source will broadcast packet to all the relays and destination. If destination request retransmission, all the relays which can decode source's packet (termed as decoding-relay) in the first phase will take charge of retransmission till the destination can decode source's packet correctly or ARQ process is expired. However, it is possible that (1) channel between decoding-relay and destination is really poor; (2) the number of decoding-relay (compared to the total number of relays) is very small. Only relays which become decoding-relays after source's broadcasting get involved into the whole ARQ process is not efficient. Hence, during the decoding-relay' retransmitting source's packet other undecoding relay can overhear this packet retransmitting and have extra chance to decode source's packet and join in the next possible retransmission. We term this proposed ARQ protocol as updatable ARQ protocol, which can extract much more spatial diversity compared current cooperative ARQ protocol in multi-relay networks.The second part of this thesis investigates the relay-assisted ARQ protocol in user cooperation networks, where two users have been grouped into cooperative pairs. We will design fairness-aware cooperative ARQ protocol in such networks, which can guarantee fairness between two users. By fairness, we have two meanings. One is delay issue, which is that two users should enjoy similar average delay performance. The other is relay power, which is that the power each user consumed by providing relay service to the other should be the same.Users in one cooperative pair will request its cooperative partner to get involved into its ARQ process whenever its original transmission is failed. If without careful design, this protocol might cause serious delay and power consumption unfairness between users in one cooperative pair, when the two users have different packet arrival rates or different downlink channel condition. However, few of works has taken into consideration of these fairness issues of the ARQ protocol in the cooperative system. According to the statistical channel condition and packet arrival rates information, we divide the total power of each user into two parts. One part is for transmission their own packets and the other part is for transmission its partner's packets. We can allocate each user's two parts of power to minimize the packet loss ratio of users in constraint of either kind of fairness issue. In this way, the proposed fairness-ware ARQ protocol can work to guarantee either delay fairness or relay power fairness, according to application requirement.