Research On Cooperative Communication Based On Network Coding

The inherent multipath fading nature of wireless channel is one of the mainfactors which block the channel capacity enhancement and QoS amelioration. MIMOand cooperative communication are two main schemes to suppress channel fadingand improve transmission reliability, but the severe demand of MIMO technologymakes it hard to practise for small-scale mobile terminals. On the other hand, thereis not necessity for cooperative communication to deploy multiple antennas in mobileterminal, but cooperate with each other to convey data, which makes it be a practicalapproach for MIMO. With whom to cooperate, how to cooperate and the e?ect ofcooperation are three key problems for cooperative communication which have tobe resolved. The nature of network coding is to allow intermediate relaying nodes toforward the mixed data received from di?erent incoming channels, which necessitatesto enhance the capacity of intermediate nodes. The most important feature ofnetwork coding is its capacity to substantially improve network throughput andtransmission e?ciency, so the combination between network coding and cooperativecommunication can improve cooperative system performance further.Applying network coding as a powerfully cooperative scheme, this dissertationinvestigates intensively cooperative communication mechanism based on networkcoding. The main contributions are expressed as follows:1. For multi-user cooperative communication system, when the channel conditionbetween user nodes are not perfect, a cooperative scheme based on networkcoding is proposed and compared with the traditional decode-and-forward.When the number of user node is 2 and the basic ?eld is GF(2), the systemoutage probabilities in closed-form for these forward protocols are derived andwe prove that the two forward schemes can both achieve a diversity order of 2.When the number of user node is 3 and the basic ?eld is GF(2) or GF(4), thesystem outage probabilities in closed-form for these forward protocols are alsoderived, and we prove that when the basic ?eld is GF(2), then the decode-and-forward scheme can achieve a diversity order of 3, but network coding schemecan only obtain a diversity order of 2. However, when the ?eld is GF(4) andthe channels between user nodes are perfect, network coding strategy can geta diversity order of 4. The results of numerical simulation further shows thatthe scheme based on opportunistic network coding outperforms the traditionaltransmission schemes. 2. For one-way cooperative communication system, when the channel conditionbetween users and relaying node are not perfect, a cooperative scheme basedon (deterministic or opportunistic) network coding are proposed and comparedwith traditional decode-and-forward relaying scheme. When there is only onerelaying node, the system outage probabilities for those schemes are derivedand used to prove that all forward schemes can obtain a diversity gain withorder 2. When the number of relay node is 2 and the basic ?eld is GF(2),the system outage probabilities for those schemes are also derived, but inthis case, network coding strategy can only achieve a diversity order of 2 butnot 3. However, when the ?eld is GF(4), network coding scheme can alsoobtain a diversity order of 3 which indicates that the basic ?eld can in?uencethe performance of network coding cooperation. The results of numericalsimulation indicate that the outage performance of network coding scheme isslightly worse than that of decode-and-forward scheme.3. For two-way cooperative communication system with multiple pairs of usernodes, when the arrival process of packets generated by user node is accordingto binomial distribution, we propose the relaying scheme based on opportunis-tic network coding and study the package delay and power consumption inrelaying node from network layer. Under steady state, the average packagedelivering delay and power consumption in closed-form are derived. The opti-mization problem for minimizing power consumption is further proposed andthe optimal result is obtained when the bu?er size is equal to 1 and the arrivalrate of packets from uses is a constant.4. For two-way cooperative communication system with two pairs of user nodes,we study the relaying scheme based on analogy network coding and derive theupper and lower bound of system outage probability. Numerical results showthat these bounds approach closely with each other when relaying node liesexactly between the middle of two users.