  The capacity region of the interference channel in which one transmitter
non-causally knows the message of the other, termed the cognitive interference
channel, has remained open since its inception in 2005. A number of subtly
differing achievable rate regions and outer bounds have been derived, some of
which are tight under specific conditions. In this work we present a new
unified inner bound for the discrete memoryless cognitive interference channel.
We show explicitly how it encompasses all known discrete memoryless achievable
rate regions as special cases. The presented achievable region was recently
used in deriving the capacity region of the general deterministic cognitive
interference channel, and thus also the linear high-SNR deterministic
approximation of the Gaussian cognitive interference channel. The high-SNR
deterministic approximation was then used to obtain the capacity of the
Gaussian cognitive interference channel to within 1.87 bits.
