Capacity Analysis of Multicast Network in Spectrum Sharing Systems

In this paper, we consider the capacity of a multicast network, where a single-antenna secondary base station (SBS) utilizes the spectrum licensed to primary users (PUs) to broadcast the same information to multiple secondary users (SUs) with a single-antenna simultaneously, when the interference received by PUs is less than a predefined threshold. Based on extreme value theory, we first derive the average capacity of the multicast/unicast schemes in the case that perfect channel station information from the SBS to the PUs (interference CSI) is known at the SBS. Due to limited cooperation between the SBS and the PUs, perfect interference CSI is not always available at the SBS. Thus, we also analyze the average capacity of the above-mentiontd schemes in the case of imperfect interference CSI at the SBS. The analytical and simulated results reveal that when interference CSI is perfectly available at the SBS, and the SBS transmit power P is sufficiently larger than the interference temperature threshold Q , the average capacity of the multicast scheme scales as Θ(Q) similar to a previously known scaling law in the non-spectrum sharing multicast systems, while the average capacity of the unicast scheme scales as Θ(log (1 + P (log(NQ)-log log NQ))) in the case of Q ≪ P ≪ NQ or Θ(log (1 + (N-1)Q)) in the case of P ≫ NQ, where N denotes the number of SU. If perfect interference CSI is not available at the SBS, the average capacity of the multicast and unicast schemes will be respectively scaled by the factors λ/(λ+1) and |(λ-1)/λ|, compared to that of perfect interference CSI available at the SBS, where 1/λ denotes the mean of interference CSI estimation error.