On the Throughput-Delay Tradeoff in the Diamond Relay Networks

Diamond relay channel has recently been attracting considerable attention in wireless ad hoc networks. In some previous discussions, a cooperative mode named SRP (spatial reused pattern) has been proposed and the corresponding capacity or the maximum transmit rate was studied in the case of AWGN channel. However, for the wireless time-varying and fading channel, opportunistic scheduling scheme may be useful to improve the whole throughput performance by efficiently using the rather good links. To do so, we first review the capacity in the SRP mode in the half-duplex case with the assumption that channel side information is known to all the nodes and then we put forward a new strategy in which buffers are employed by both relay nodes. By efficiently utilizing the rather good links, the throughput is greatly improved at the cost of the queuing delay. Furthermore, we quantitatively analyze and evaluate the average queuing delay based on finite state fading channel model and the G/G/l queuing model. The tradeoff between the throughput and the additional queuing delay is also discussed. Finally, to realize our developed strategy, we presented two criteria used to characterize the reasonable thresholds and an algorithm on the adjustment of the predefined thresholds to realize the tradeoff.