Queuing analyses and statistically bounded delay control for two-hop green wireless relay transmissions

Although the wireless relay transmission has been recognized as one of the effective approaches in extending the coverage area and improving the network capacity, the delay control over the two-hop wireless channels toward end users' QoS satisfaction is still challenging in green wireless network designs. In this paper, we propose the QoS-driven delay control schemes over two-hop wireless relay links to statistically upper bound the total queuing delay for the decode-and-forward relay transmissions. Specifically, we first conduct asymptotic queuing-delay analyses for the relay transmissions. Then, we show that an efficient approach for statistical delay guarantees is to make the exponentially decaying speed of the complementary cumulative distribution functions of the queueing delay at both hops identical. We further derive that this target needs to be attained through asymmetric resource allocations over the two hops. Motivated by this fact, we formulate two optimization problems aiming at satisfying the specified delay-bound violation probability for the relay transmission, while minimizing the power consumption toward green wireless networking. One framework is for the frequency-division duplex relay mode and the other is for time-division duplex relay mode. In the frequency-division duplex relay mode, the source and relay nodes use a different transmit power. For the time-division duplex relay mode, the source and relay nodes use time-slots with different length but with the same instantaneous power. We solve for the optimal solutions for both of the aforementioned frameworks. Also conducted is a set of simulation results to show the impact of the QoS requirements, traffic load, and position of the relay node on the resource allocation over wireless relay links.