On the achievable rate region of gaussian cognitive multiple access channel

We consider the communication scenario where multiple cognitive users wish to communicate to the same receiver through AWGN channels, in the presence of primary transmission. The cognitive users are assumed to have the side information about the primary transmission. The achievable rate region of cognitive users is formulated under the constraint that the rate of primary transmission is not changed as if no cognitive users existed. Moreover, the maximum achievable sum-rate point of the rate region is characterized