Degrees of freedom of the bursty MIMO X channel without feedback

We investigate the degrees of freedom (DoF) of the symmetric bursty MIMO X channel without feedback, where the presence of the two cross links is governed by a Bernoulli pc random state. The sum DoF is characterized for most of the antenna-burstiness configurations, except the case where pc > 0.5 and the ratio of the number of transmit and receive antennas is between 2/3 and 3/2. When pc ≤ 0.5, the sum DoF of the bursty MIMO X channel is equal to that of the interference channel, and hence cross-link messaging does not help. When pc > 0.5, cross-link messaging is necessary, and we showed that simple interference alignment schemes suffice to achieve the sum DoF. For the case where the characterization of DoF remains open, we propose a combination of Han-Kobayashi coding and interference alignment that achieves higher DoF than interference alignment alone. This is in sharp contrast to the non-bursty case where interference alignment alone is DoF-optimal.