Feedback Strategies for White Gaussian Interference Networks

A white Gaussian interference network is a channel with T transmitters and R receivers where the received symbols are linear combinations of the transmitted symbols and white Gaussian noise. This paper considers the case where K messages are transmitted through the network in a point-to-point manner, i.e., each message is encoded by exactly one transmitter and is destined for exactly one receiver. 

It is further assumed that feedback available so that each transmitter sees the outputs of the receivers to which it is sending messages. Communication strategies based on the discrete Fourier transform are developed that perform well for such networks. For multiple-access channels (K=T, R=1) with equal transmitter powers the strategies achieve the sum-rate capacity if the signal-to-noise ratio (SNR) is large enough. For the same channels with a fixed SNR and large K the sum-rate is approximately (log log K)/2 larger than the sum-rate capacity without feedback. 

For broadcast channels (T=1, K=R) the strat gies achieve a monotonically increasing sum-rate with K when the channels have strong symmetries. For interference channels (K=T=R) the strategies significantly enlarge the no-feedback capacity region, especially for very strong interference. For this last case, the strategies use the interference to their advantage by ``correlation routing.''