Research On Relay Selection Scheme Based On Location Information In Cooperative Communications

As a novel network architecture of future wireless communication systems, cooperative communication network has broad research and application prospects, and relay selection is one of the research hotspots. This thesis focuses on cellular mobile network and wireless sensor network respectively, based on location information of user equipments or sensor nodes, and gives a comprehensive and intensive study on the relay selection scheme in the cooperative communications.This thesis first derives the optimal location of a single AF relay in the three nodes line network under equal power allocation scheme, which is on the midpoint between the source and the destination. Based on the conclusion above, a centralized Location-Matched AF Relay Selection (LMRS) scheme is proposed for the cellular mobile network. By gathering the location information of user equipments at the base station (BS), BS selects the relay whose actual location is best matched the optimal location for the user to cooperate. In the multi-user system, BS will allocate relay for each user according to the worst-link-first rule. The bit error rate (BER) performance analysis and simulation results show that LMRS scheme achieves the same performance level as selecting the relay with best channels, and can effectively improve the communication quality of cell edge users compared with direct transmission.The distributed opportunistic relay scheme is modified for the wireless sensor network in this thesis. Based on the AF relay's optimal location conclusion and the location information of sensor nodes, the distributed Location-Aware AF Relay Selection (LARS) scheme is proposed. It aims to reduce the number of contending relays through dividing the contending zones. The potential relay will start its timer to contend to send FLAG packet when it satisfies both the contending zone and the channel quality conditions. The collision probability and outage probability performance analysis and simulation results show that LARS scheme decreases the number of contending relays and collision probability, and achieves the sub-optimal outage probability performance.Furthermore, in order to improve the network lifetime performance of LARS scheme, the Energy-Equilibrium Enhanced LARS (ELARS) scheme is proposed. The node's channel state information and residual energy level are both considered when setting the initial value of timer at relay. It is balanced between these two factors by altering the adjustment factor. The simulation results show that ELARS scheme with optimal adjustment factor not only maintains the outage performance but also extends the network lifetime, and meanwhile the collision probability keeps the same lower level as the LARS scheme's one.