Symmetric Feedback Capacity of the Gaussian Interference Channel to Within One Bit

We characterize the symmetric capacity of the two-user Gaussian interference channel with feedback to within 1 bit/s/Hz. The result makes use of a deterministic model to provide insights into the Gaussian channel. We derive a new outer bound to show that a proposed scheme can achieve the symmetric capacity to within one bit for all channel parameters. One consequence of the result is that feedback provides unbounded gain, i.e., the gain becomes arbitrarily large for certain channel parameters. It is a surprising result because feedback has been so far known to provide no gain in memoryless point-to-point channels and only power gain (bounded gain) in the multiple access channels. The gain comes from using feedback to fully exploit the side information provided by the broadcast nature of the wireless medium.