Limits on Cognitive Communications in the Wide-band Regime

This paper studies cognitive communication, where a cognitive transmit-receive pair utilizes an existing (occupied) wide-band spectrum for communication. The cognitive transmitter is assumed to have perfect knowledge on the signal levels of all the legitimate transmitters in the system and must cause negligible interference at all legitimate receivers. The goal of this research is to determine fundamental limits on communication in this setting. In particular, it is shown that communication with a minimum energy per bit arbitrarily close to that of a wide-band interference-free additive white Gaussian noise channel is possible using a pulse-position modulation scheme for the cognitive user in the wide-band limit.