On the capacity of the cognitive Z-interference channel

We study the cognitive interference channel (CIC) with two transmitters and two receivers, in which the cognitive transmitter non-causally knows the message and codeword of the primary transmitter. We first introduce a discrete memoryless more capable CIC, which is an extension to the more capable broadcast channel (BC). Using superposition coding, an inner bound and an outer bound on its capacity region are proposed. These bounds are then applied to the Gaussian cognitive Z-interference channel (GCZIC), in which only the primary receiver suffers interference. Upon showing that jointly Gaussian distribution maximizes these bounds for the GCZIC, we evaluate them for the GCZIC. The evaluated outer bound appears to be the best outer bound to date on the capacity of the GCZIC in strong interference. More importantly, this outer bound coincides with the inner bound for |a| ≥ √(1+P₁). Thus, we establish the capacity of the GCZIC in this range and show that superposition encoding at the cognitive transmitter and successive decoding at the primary receiver are capacity-achieving.