Sum-Rate Results in Point-to-Multipoint Cognitive Networks: Effect of Path Loss

We consider simultaneous operation of primary and secondary point-to-multipoint networks in the same frequency band when interference in treated as noise. The variations in channel and interference gains are characterized by path loss and multipath fading. Scaling laws for the primary and secondary sum-rates are derived when the scaling is in terms of the number of primary users. In order to maintain a quality of service requirement for the primary system and simultaneously obtain positive sum-rate for the secondary, a scheduling strategy can be applied to activate users in each network based on their interference gains only. Interestingly, using this strategy, the scaling laws for sum-rates are independent of the path loss consideration of the channel, i.e., the primary and secondary networks can achieve the same asymptotic sum-rates as shown in when only multipath fading is considered. Consequently, while the primary network is protected, we can obtain significant improvement in the asymptotic secondary sum-rate compared to that achievable under channel sharing via time division (TD).