Channel-adaptive relaying in mobile ad hoc networks with fading
Michael R. Souryal, Nader Moayeri · 2005
This paper describes an approach for relaying in multihop networks that adapts to the time-varying channel and exploits spatial diversity to mitigate multipath fading. Ignored in some performance analyses, fading arises from multipath propagation and causes fluctuations in the signal strength in mo- bile networks, adversely affecting communication performance. Our approach uses limited cross-layer interactions between the physical, link and routing layers to provide adaptivity to both large and small-scale channel effects and to achieve spatial diversity gain without the use of multiple antennas. The routing layer uses long-term measurements of link quality in the form of the average signal-to-noise ratio (SNR) to opportunistically select next-hop relays on a hop-by-hop basis. Small-scale variations are overcome at the MAC layer through efficient multicast polling of multiple next-hop candidate relays prior to data transmission. A performance analysis for networks employing geographic routing and an IEEE 802.11-based MAC (i) demonstrates significant improvements in network capacity and end-to-end delay achieved with these channel-adaptive techniques in Rayleigh and Ricean fading environments, (ii) shows that most of the small-scale diversity gain is obtained through the use of only two next-hop relay choices, and (iii) assesses the practical limit of the short- term adaptive component in terms of maximum node velocity.