Cognitive Networks Achieve Throughput Scaling of a Homogeneous Network

摘要

We study two distinct, but overlapping, networks that operate at the sametime, space, and frequency. The first network consists of $n$ randomlydistributed \emph{primary users}, which form either an ad hoc network, or aninfrastructure-supported ad hoc network with $l$ additional base stations. Thesecond network consists of $m$ randomly distributed, ad hoc secondary users orcognitive users. The primary users have priority access to the spectrum and donot need to change their communication protocol in the presence of secondaryusers. The secondary users, however, need to adjust their protocol based onknowledge about the locations of the primary nodes to bring little loss to theprimary network's throughput. By introducing preservation regions aroundprimary receivers and avoidance regions around primary base stations, wepropose two modified multihop routing protocols for the cognitive users. Baseon percolation theory, we show that when the secondary network is denser thanthe primary network, both networks can simultaneously achieve the samethroughput scaling law as a stand-alone network. Furthermore, the primarynetwork throughput is subject to only a vanishingly fractional loss.Specifically, for the ad hoc and the infrastructure-supported primary models,the primary network achieves sum throughputs of order $n^{1/2}$ and$\max\{n^{1/2},l\}$, respectively. For both primary network models, for any$\delta>0$, the secondary network can achieve sum throughput of order$m^{1/2-\delta}$ with an arbitrarily small fraction of outage. Thus, almost allsecondary source-destination pairs can communicate at a rate of order$m^{-1/2-\delta}$.