Patrick Mitran - Prof. University of Waterloo, Canada Communication systems
Date: - Location: Eurecom
Cognitive radio is perhaps an overly broad term used to describe a variety of recent communications technologies. In this talk, we first look at some of the definitions of cognitive radio and then settle on the notion of prioritized spectrum sharing. We look at some of the problems typically associated with interference mitigation and argue for the need of a band manager. Given the presence of a band manager, we present some of our recent results on interference mitigation in cognitive radio with respect to scheduling. First, we determine interference scaling laws for arbitrary primary and secondary network topology. In the second part, we consider the coexistence of collocated primary and secondary point-to-multipoint systems such as cellular systems that simultaneously access the same spectrum. In particular, we analyze the number of users and sum-rate of the secondary system as a function of the maximum impact it is allowed to have on the primary system when simultaneous transmissions are treated as interference. As a base reference, we compare to channel sharing via time division (TD). We find that provided the secondary system is given sufficient channel state information, the impact of the interference to the primary system on its sum-rate can be mitigated by judicious choice of the active secondary nodes and quantify the improvement that is realized. This quantification is achieved by a key lemma on the sum of low order statistics of a random variable. We also analyze the more symmetric case when both primary and secondary networks are given sufficient channel state information to selectively activate nodes.
