Approximate Capacity Region of the MAC-IC-MAC

An approximate capacity region is established of a class of interfering multiple access channels consisting of two multiple-access channels (MACs), each with an arbitrary number of users, with interference from one of the transmitters of one MAC to the receiver of the other MAC, which we refer to henceforth as the MAC-IC-MAC. It is shown that, for the semi-deterministic MAC-IC-MAC, single-user coding at the non-interfering transmitters in each MAC and superposition coding at the interfering transmitter of each MAC achieves a rate region that is within a quantifiable gap of the capacity region, thereby generalizing the result by Telatar and Tse for the 2-user semi-deterministic interference channel. Next, with an explicit coding scheme, we establish an approximate capacity region that is within a one-bit gap of the capacity region for the Gaussian MAC-IC-MAC, thereby extending the work by Etkin et al for the two-user Gaussian interference channel. The symmetric generalized degrees of freedom (GDoF) of the symmetric Gaussian MAC-IC-MAC with more than one user per cell, which is a function of the interference strength (the ratio of INR to SNR at high SNR, both expressed in dB) and the numbers of users in each cell, is V-shaped with flat shoulders. An analysis based on the deterministic method shows that, when interference is sufficiently weak or strong, the non-interfering transmitters are not mere sharers of the degrees of freedom with the interfering transmitters. They instead also utilize power levels that cannot be accessed by interfering transmitters (due to the restriction of superposition coding), thereby improving the symmetric sum GDoF to up to one degree of freedom per cell under a range of SINR exponent levels. Time sharing between interfering and non-interfering transmitters is suboptimal.