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 is 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 (DFT) are developed that perform well for such networks. For multiple-access channels (K=T, R=1) with equal transmitter powers the strategies achieve the feedback sum-rate capacity if the powers are beyond some threshold. For the same channels with fixed transmitter powers and large K, the achievable sum-rate is approximately (log log K)/2 larger than the sum-rate capacity without feedback. For broadcast channels (T=1, K=R) with strong symmetries, the strategies achieve a monotonically increasing sum-rate with K. For interference channels (K=T=R) with strong interference, the strategies significantly enlarge the no-feedback capacity region by "correlation routing."