On Design of Opportunistic Spectrum Access in the Presence of Reactive Primary Users

TL;DR

This paper develops an optimal opportunistic spectrum access strategy for secondary users in cognitive radio networks, accounting for reactive primary users whose behavior depends on past secondary user actions, and balances throughput with primary user protection.

Contribution

It models reactive primary user behavior using a 4-state Markov chain and formulates the OSA design as a POMDP, introducing a novel long-term PU throughput constraint for better protection.

Findings

Optimal OSA policy structure under LPUT constraint derived

Proposed suboptimal policy offers lower complexity

Numerical results reveal tradeoffs between SU throughput and PU protection

Abstract

Opportunistic spectrum access (OSA) is a key technique enabling the secondary users (SUs) in a cognitive radio (CR) network to transmit over the "spectrum holes" unoccupied by the primary users (PUs). In this paper, we focus on the OSA design in the presence of reactive PUs, where PU's access probability in a given channel is related to SU's past access decisions. We model the channel occupancy of the reactive PU as a 4-state discrete-time Markov chain. We formulate the optimal OSA design for SU throughput maximization as a constrained finite-horizon partially observable Markov decision process (POMDP) problem. We solve this problem by first considering the conventional short-term conditional collision probability (SCCP) constraint. We then adopt a long-term PU throughput (LPUT) constraint to effectively protect the reactive PU transmission. We derive the structure of the optimal OSA policy under the LPUT constraint and propose a suboptimal policy with lower complexity. Numerical results are provided to validate the proposed studies, which reveal some interesting new tradeoffs between SU throughput maximization and PU transmission protection in a practical interaction scenario.