Distributed Cellular-Systems Oriented Relay Selection Techniques

In recent years, cooperative communication has gained widespread concern due toits advantage of overcoming channel fading, enhancing reliability, expanding coverageand improving the spectrum efficiency. The prerequisite for cooperative transmission isthe selection of appropriate cooperative relays. Since cooperative transmission willbring additional system overhead, if cooperation cannot provide cooperative gain, awaste of resources may result. It has been demonstrated that, if the relay nodes are notappropriately chosen, cooperative transmissions may not always outperformnon-cooperation transmissions. Hence, optimization of cooperative relays, which is thefocus of this thesis, is vital to cooperative communication.Most existing related work only focused on relay selection at a single end, i.e., userequipment (UE) end or based station end. Moreover, UEs are usually involved in thecomputation of relay selection and have to feed the channel state information back tothe base station. This results in a big burden and high complexity for UEs. Motivated bythe drawbacks, we proposed a novel two-step relay selection algorithm which is basedon time-frequency-synchronization and channel energy constraints. In the proposedalgorithm, both cooperative UEs and base stations can be determined simultaneously.As a result, the optimal multi-point multiple-UE transmission pair is selected for thedesired UE. Moreover, since the computation burden is mainly undertaken by the basestation, the complexity of the UEs is greatly reduced. Simulation results verify thevalidity of the time-frequency constraint criterion. And the effectiveness and superiorityof the short-time average channel energy criterion is also demonstrated in thesimulations.