On the capacity of the MIMO cognitive interference channel

The cognitive interference channel is a variation of the classical interference channel in which one of the transmitters, the cognitive transmitter, has full and a priori knowledge of the message of the other user, the primary user. This additional knowledge is termed cognition and idealizes the cognitive transmitter learning the messages of the primary user by overhearing its transmissions over a wireless channel. This paper studies the multiple-input multiple-output cognitive interference channel and derives inner and outer bounds for the capacity of this channel model as well as approximate characterizations of the capacity region. In particular, it is shown that capacity can be achieved to within an additive gap which depends on the number of antennas at the cognitive decoder and to within a constant multiplicative factor of two.