Approximate Ergodic Capacity of a Class of Fading Two-User Two-Hop Networks.

The fading AWGN two-user two-hop network is considered where the channel coefficients are independent and identically distributed (i.i.d.) according to a continuous distribution and vary over time. For a broad class of channel distributions, the ergodic sum capacity is characterized to within a constant number of bits/second/hertz, independent of the signal-to-noise ratio. The achievability follows from the analysis of an interference neutralization scheme where the relays are partitioned into M pairs, and interference is neutralized separately by each pair of relays. When M=1, the proposed ergodic interference neutralization characterizes the ergodic sum capacity to within 4 bits/sec/Hz for i.i.d. uniform phase fading and approximately 4.7 bits/sec/Hz for i.i.d. Rayleigh fading. It is further shown that this gap can be tightened to 4\log\pi-4 bits/sec/Hz (approximately 2.6) for i.i.d. uniform phase fading and 4\-4\log (3\pi/8) bits/sec/Hz (approximately 3.1) for i.i.d. Rayleigh fading in the limit of large M. ref refid="fn1"/ id="fn1" asterisk="no"paraThroughout this paper, log(.) denotes the logarithm of base two.para [ABSTRACT FROM AUTHOR]