Research On Capacity Optimizaiton Techniques In Wireless Relaying Communication Systems

With the increasing dependence and demand for wireless communicaitons, future communication systems are envisioned to meet the requirements of higher speed, larger capacity, wider coverage and lower cost. Relay communication technology, which can expand communication coverage, improve edge user rate and balance network load, has become an important technology in LTE-A systems. However, due to the half-duplex constraint of relay node, the relay transmission needs to consume double the resources compared to the traditional direct transmission, which will bring capacity loss to wireless relaying communication systems. Therefore, it is of great theoretical and practical significance for us to design effective scheme to enhance the capacity of existing relaying communication systems in combination of new technologies.Aiming to improve the capacity of existing wireless relay communication systems and combining new technologies such as MIMO, OFDM and two way relay, this dissertation first begins with the capacity optimization in system layer including relay network deployment and OFDM resource reuse. Then the research turns to linear processing in multiuser MIMO relay systems as an evolution transmission scheme in link layer. Finally the last study lies in network coding scheme design for revolutionary two way relay communication links. The major work and contributions of this dissertation consist in:First of all, this dessertation investigate the relay network deployment problem. The power optimizaiton for link model with AF and DF relays is first studied. Then we focus on the relay network deployment in macro cell scenario and explore the affection to system performance by relay transmission protocol, relay number, relay location and relay power. Finally combined with the cost analysis, a relay deployment optimization design is given in ordder to achieve the requirements of system capacity and coverage expansion. The analysis also reflects the relationship between system capacity improvement and coverage expansion.Second, the problem to enhance the spectrum efficiency of OFDM relay networks is addressed. In order to make the resource utilization more efficient, we select sectored relay cell to design two resource reuse scheme, i.e. full reuse interference coordination scheme based on power varying and user grouping and parial reuse interference coordination scheme based on user binding. The results show that they can mitigate intra-sector interference and increase system throughput compared to full reuse scheme.Third, in multi-user MIMO relay system, the transmission of multi-antenna node processing have a significant impact on system capacity and reliability, while linear processing can reduce the realization complexity and the processing delay. Based on the uplink multi-access relay channel and the downlink broadcast relay channel respectively, iterative algorithms are derived to compute the achievable sum rates. In addition, several optimal or suboptimal linear processing schemes for both uplink and downlink scenarios are proposed according to optimization derivation. The results show that all the proposed schemes can achieve higher data rates than the single user MIMO relay system.Fourth, the problems for network coding in two way MIMO relay systems are addressed considering2-phase two way relay protocol and3-phase two way cooperatvie relay protocol. Based on minimum mean square error criterion, the optimal network coding schemes are derived for the above two scenarios. Furthermore, we also propose a suboptimal closed-form solution for2-phase scenario which can effectively reduce the complexity. The study also shows that, regardless of2-phase or3-phase two-way relay communication scheme can effectively solve the capacity loss problems brought by the traditional one-way relay system and thus achieve a good tradeoff of efficiency and reliability.Finally, conclusions and future work are summarized in the end of this dissertation.