Compact and simple diversity methods for mitigating severe fading

Recently, measured channel responses for wireless links in airframes, busses and helicopter environments have demonstrated that frequency-selective fading can be more severe than predicted by the Rayleigh channel model. The work herein investigates simple diversity methods as a means to mitigate such fading which is referred to as exhibiting hyper-Rayleigh behavior. In particular, the work presents the gains achieved by utilizing selection diversity for two spatially separated antennas and by simple phasing of a two-element array. The key results are that: (1) severe fades are well-mitigated in selection diversity even if elements are spaced less than the lambda/2 typically assumed for statistically independent paths; and (2) even coarse phasing (increments of 45deg) of elements mitigates severe fades. The motivation for this work is to develop diversity strategies that are suitable for use by low-energy wireless sensor nodes that may be deployed in such severe environments; that is, the methods should be computationally simple, physically compact, and require minimum DC power to implement.