Cooperative Communication Adds Bandwidth Flexibility to Fixed Multiplexing Radio Networks

Many are the known advantages of cooperative communication in radio networking. One example is the ability to improve the radio channel capacity thanks to the spatial diversity provided by a cooperating node, i.e., the relay. Another advantage is the reduced latency of the automatic retransmission request (ARQ) protocols that make use of neighboring collaborating nodes. In this poster presentation, the use of cooperative communications is investigated in the context of fixed multiplexing and applied to a time-division multiple access (TDMA) system. In conventional TDMA solutions, the radio channel is divided into time slots, and every source node is reserved one slot for transmission in every time frame. An example of TDMA system is the GSM digital cellular system. It is demonstrated that the use of cooperative communications has the desirable property of alleviating one of the main drawbacks of TDMA, i.e., the lack of flexible bandwidth allocation when supporting variable bit rate traffic flows. The conditions under which the use of cooperative communications in TDMA yields asymptotically optimal throughput (i.e., that of perfect statistical multiplexing) are shown. These conditions include a bad signal quality on the source-destination channel and a good signal quality on the channel between the cooperating nodes. Potential throughput gains are quantified by means of simple flow equations that take into account varying channel quality conditions. Finally, with the support of simulation results, it is shown that besides the added bandwidth flexibility and throughput gains, the use of cooperative communications in TDMA systems may yield improved network latency when compared to TDMA without cooperation.