Abstract

Spectrum sharing between cellular and ad-hoc networks is studied in this work. Weak signals and strong interferences at the cell-edge area usually cause severe performance degradation. To improve the cell-edge users’ performance quality while keeping high spectrum efficiency, in this paper, we propose a cooperative spectrum sharing scheme. In the proposed scheme, the ad-hoc users can actively employ cooperative diversity techniques to improve the cellular network downlink throughput. As a reward, a fraction of the cellular network spectrum is released to the ad-hoc network for its own data transmission. To determine the optimal spectrum allocation, we maximize the ad-hoc transmission capacity subject to the constraints on the outage probability of the ad-hoc network and on the throughput improvement ratio of the cellular network. Both the transmission capacity of the ad-hoc network and the average throughput of the cellular network are analyzed using the stochastic geometry theory. Numerical and simulation results are provided to validate our analytical results. They demonstrate that our proposed scheme can effectively facilitate ad-hoc transmissions while moderately improving the cellular network performance.

Introduction

Cognitive spectrum sharing was recently studied to accommodate growing demands for wireless broadband access, which can alleviate the problem of under-utilization of licensed spectrum. Spectrum sharing techniques can be generally classified into three categories: interweave, underlay, and overlay [1]. For the interweave spectrum sharing, the secondary system can opportunistically access spectrum holes. For the spectrum underlay, secondary users (SUs) transmit simultaneously with primary users (PUs) under the constraint that interference caused by the SUs on the PUs must be below a certain threshold. For the spectrum overlay, SUs actively help primary data transmission in exchange for a spectrum access in time domain [2], spatial domain [3], or frequency domain [4]. The locations of SUs are usually fixed or restricted into a small area without suffering interference from other concurrent transmissions. It is nontrivial to extend the cooperative spectrum sharing to the secondary ad-hoc networks, as the topology changes frequently and the interference suffers from uncertainties caused by both random user locations and channel fadings.