Throughput Analysis of Primary and Secondary Networks in a Shared IEEE 802.11 System

TL;DR

This paper provides an analytical framework for understanding how primary and secondary networks coexist in IEEE 802.11 systems, focusing on spectrum sensing, channel capture, and throughput impacts, validated through simulations.

Contribution

It introduces a novel analytical model combining transmission slots and physical time slots to evaluate primary and secondary throughput in shared IEEE 802.11 networks.

Findings

Secondary network's spectrum sensing minimally affects primary throughput.

Increasing secondary contention window size has limited impact on primary protection.

Analytical results closely match extensive NS2 simulations.

Abstract

In this paper, we analyze the coexistence of a primary and a secondary (cognitive) network when both networks use the IEEE 802.11 based distributed coordination function for medium access control. Specifically, we consider the problem of channel capture by a secondary network that uses spectrum sensing to determine the availability of the channel, and its impact on the primary throughput. We integrate the notion of transmission slots in Bianchi's Markov model with the physical time slots, to derive the transmission probability of the secondary network as a function of its scan duration. This is used to obtain analytical expressions for the throughput achievable by the primary and secondary networks. Our analysis considers both saturated and unsaturated networks. By performing a numerical search, the secondary network parameters are selected to maximize its throughput for a given level of protection of the primary network throughput. The theoretical expressions are validated using extensive simulations carried out in the Network Simulator 2. Our results provide critical insights into the performance and robustness of different schemes for medium access by the secondary network. In particular, we find that the channel captures by the secondary network does not significantly impact the primary throughput, and that simply increasing the secondary contention window size is only marginally inferior to silent-period based methods in terms of its throughput performance.