Adaptive modulation in ad hoc DS/CDMA packet radio networks

This paper investigates the benefit of adaptive modulation based on channel state information (CSI) in DS/CDMA multihop packet radio networks. By exploiting varying channel conditions on different links, adaptive modulation can be used in ad hoc networks to provide upper layers with higher capacity links over which to route traffic. Performance is evaluated in terms of the information efficiency, a new progress-related measure for multihop networks. Three types of adaptivity are analyzed, differing in the level of CSI available: (i) full knowledge of the SIR at the receiver, (ii) knowledge of only the signal attenuation due to fading, and (iii) knowledge of only the slow fading component of the signal attenuation. The effect on performance of imperfect channel information is also investigated. Sample results are given for interference-limited networks experiencing fourth-power path loss with distance, Rayleigh fading, and lognormal shadowing.