Throughput enhancements in point-to-multipoint cognitive systems

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 an exponential 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.