On the Generalized Degrees on Freedom Region of the MIMO Interference Channel with No CSIT

The generalized degrees of freedom region (GDoF) of the multiple-input multiple-output (MIMO) interference channel (IC) is studied under the "no CSIT" assumption under which there is perfect channel state information (CSI) at the receivers and no CSI at the transmitters (CSIT). In the very weak interference regime, where the ratio of channel gains (in dB) of the interfering and direct links, alpha, is <= 0.5, the GDoF regions are characterized for the two classes of the MIMO ICs defined by (a) M-1 - N-1 > M-2 >= N-2 and (b) M-1 - N-1 > N-2 > M-2 (where M-i is the number of antennas at transmitter i and N-i is the number of antennas at receiver i, i is an element of {1,2}). In particular, inner-bounds are obtained by developing CSI-independent coding schemes using which it is shown that for each of the two classes a significant portion of the perfect-CSIT GDoF region can be achieved even without CSIT. Furthermore, tight outer-bounds to the no-CSIT GDoF regions are obtained that simultaneously account for the interference encountered by both the receivers. These bounds are thus fundamentally different from those derived in earlier works which deal with the case of alpha = 1, i.e., the degrees of freedom (DoF) regions. Interestingly, it is found that the loss of DoFs due to lack of CSIT is much less pronounced for the alpha <= 1/2 than it is for alpha = 1.