Performance models for wireless spectrum shared by wideband and narrowband sources

This work examines the blocking performance of narrow-band (NB) and wideband (WB) sources that access a shared pool of wireless channels. The NB sources utilize a single channel, whereas WB sources access simultaneously a larger group of channels. This system is analyzed in the context of maximizing the utilization of spectrum that is allocated to the WB system by allowing NB sources random access to the same spectrum. The performance measure to be controlled is the blocking experienced by WB sources. A queueing model of this system is proposed that allows evaluation of the impact of NB sources on WB performance. Assuming Poisson arrival process models and negative exponential distributions for the channel holding times, the dependence of the blocking probability of the WB source is derived as a function of the NB utilization factor. In an uncontrolled NB access scheme, the WB blocking is lower bounded by the blocking probability experienced by NB sources. The performance improvement afforded by adding extra NB channels and by controlling the access rates of the NB source for finite population WB sources is presented. The analysis presented here provides an assessment of some of the emerging paradigms for adaptive spectrum allocation. Of particular interest are the criteria under which spectrum agile, cognitive and software radios functioning in an opportunistic fashion can access unused spectrum allocated to a primary system without adversely affecting the performance of the primary system