  In this paper we introduce the two-user asynchronous cognitive multiple
access channel (ACMAC). This channel model includes two transmitters, an
uninformed one, and an informed one which knows prior to the beginning of a
transmission the message which the uninformed transmitter is about to send. We
assume that the channel from the uninformed transmitter to the receiver suffers
a fixed but unknown delay. We further introduce a modified model, referred to
as the asynchronous codeword cognitive multiple access channel (ACC-MAC), which
differs from the ACMAC in that the informed user knows the signal that is to be
transmitted by the other user, rather than the message that it is about to
transmit. We state inner and outer bounds on the ACMAC and the ACC-MAC capacity
regions, and we specialize the results to the Gaussian case. Further, we
characterize the capacity regions of these channels in terms of multi-letter
expressions. Finally, we provide an example which instantiates the difference
between message side-information and codeword side-information.
