  We consider the communication scenario where multiple cognitive users wish to
communicate to the same receiver, in the presence of primary transmission. The
cognitive transmitters are assumed to have the side information about the
primary transmission. The capacity region of cognitive users is formulated
under the constraint that the capacity of primary transmission is not changed
as if no cognitive users exist. Moreover, the maximum sum-rate point of the
capacity region is characterized, by optimally allocating the power of each
cognitive user to transmit its own information.
