On the Feedback Capacity of the Fully Connected K-User Interference Channel

The symmetric K-user interference channel with fully connected topology is considered, in which 1) each receiver suffers interference from all other (K-1) transmitters, and 2) each transmitter has causal and noiseless feedback from its respective receiver. The number of generalized degrees of freedom (ssr GDoF) is characterized in terms of α, where the interference-to-noise ratio (ssr INR) is given by ssr INR = ssr SNR^α. It is shown that the per-user ssr GDoF of this network is the same as that of the two-user interference channel with feedback, except for α = 1, for which existence of feedback does not help in terms of ssr GDoF. The coding scheme proposed for this network, termed cooperative interference alignment, is based on two key ingredients, namely, interference alignment and interference decoding. Moreover, an approximate characterization is provided for the symmetric feedback capacity of the network, when the ssr SNR and ssr INR are far apart from each other.