Cognitive Networks Achieve Throughput Scaling of a Homogeneous Network

TL;DR

This paper demonstrates that cognitive networks can achieve the same throughput scaling as primary networks with minimal loss, using modified routing protocols and percolation theory, even when secondary users are denser.

Contribution

It introduces new multihop routing protocols for cognitive users that preserve primary network throughput and proves simultaneous throughput scaling using percolation theory.

Findings

Both networks achieve the same throughput scaling as standalone networks.

Primary network throughput is only slightly reduced by secondary users.

Secondary users can communicate at nearly optimal rates with minimal outage.

Abstract

We study two distinct, but overlapping, networks that operate at the same time, space, and frequency. The first network consists of $n$ randomly distributed \emph{primary users}, which form either an ad hoc network, or an infrastructure-supported ad hoc network with $l$ additional base stations. The second network consists of $m$ randomly distributed, ad hoc secondary users or cognitive users. The primary users have priority access to the spectrum and do not need to change their communication protocol in the presence of secondary users. The secondary users, however, need to adjust their protocol based on knowledge about the locations of the primary nodes to bring little loss to the primary network's throughput. By introducing preservation regions around primary receivers and avoidance regions around primary base stations, we propose two modified multihop routing protocols for the cognitive users. Base on percolation theory, we show that when the secondary network is denser than the primary network, both networks can simultaneously achieve the same throughput scaling law as a stand-alone network. Furthermore, the primary network 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 all secondary source-destination pairs can communicate at a rate of order $m^{-1/2-\delta}$.