Opportunistic Relaying in Wireless Ad Hoc Networks With Controllable Delay–Throughput Tradeoffs

Driven by the fact that communication devices have become increasingly pervasive and have grown much faster than the infrastructure relay support, a specific wireless setup, which consists of a large number of source and destination nodes and a relatively small number of relays, has drawn significant attention recently. One of the notable works concentrating on this setup is the two-hop opportunistic relaying (THOR) scheme proposed by Cui et al. By connecting the receivers to the best transmitters for each hop individually, THOR maintains a linearly scalable network with affordable overhead. Notwithstanding the appealing implementation simplicity, THOR can suffer from communication and decoding delay, rendering it difficult to support delay-sensitive applications. The objective of this paper is to explore the possibility of achieving a controllable delay-throughput tradeoff without sacrificing linear throughput scaling. We begin with an opportunistic pair scheduling (OPS) scheme by restricting the relays to schedule only matched source-destination (S-D) pairs. This scheme is found to maintain throughput linearity and to reduce the end-to-end delay to the minimum as well. In particular, it is shown that OPS achieves a throughput scaling of Θ(-W_-1(-n^-1/m^-1)) for Nakagami fading with the corresponding fading parameter m > 1, taking integer values and a throughput of Θ(log n) under Rayleigh fading. To achieve a different throughput-delay tradeoff in a controlled manner, we then develop this scheme further into a general L-scheduling scheme, which captures THOR and OPS as two extreme cases. By adjusting design parameter L, the desired tradeoff can be achieved, catering to applications with diverse delay and throughput requirements. Simulation results validate our theoretic findings and demonstrate the flexibility of the proposed schemes.