Symmetric Feedback Capacity of the Gaussian Interference Channel to within One Bit
Changho Suh David Tse
Proceedings of the IEEE International Symposium on Information Theory, Seoul, South Korea, June 2009

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.