BTRS: Buffer-Threshold Based Relay Selection Scheme for Cooperative Wireless Networks

Buffer-equipped relay selection schemes in cooperative communication offer evident performance gains in terms of the outage probability and throughput. However, it brings in the increased delay which can be reduced by increasing the selection probability of relay-to-destination links. In this paper, a controlling parameter, termed as the buffer limit, is proposed for the buffer occupancy, which modifies the selection of the corresponding (transmitting and receiving) links of the relay and also has its impact on the average delay and throughput. The probability of selecting the transmitting and receiving channels is directly controlled by reallocating the weights of links considering the buffer limit. A link having the largest weight is activated, and the corresponding relay is chosen for transmission or reception. We evaluate the outage probability, average end-to-end queuing delay, and average throughput using Markov modeling of the status of the buffers at relays. Analytical findings are studied for various values of the buffer limit and confirmed by means of the Monte Carlo simulations. The proposed scheme works as the max-weight relay selection scheme when the buffer limit is set to 1/2 of the buffer size. The suggested scheme is compared with the existing schemes. The outage probability is traded with the average end-to-end queuing delay or the average throughput by adjusting the values of the buffer limit.