Enabling synchronous directional channel access on SDRs for spectrum sharing applications

Abstract

Ubiquitous wireless small-cell deployment requires a fundamental rethink of interference management within the cell, between cells, and with overlaying macrocells. One mean to increase spectral efficiency in these scenarios is through simultaneous directional transmissions and receptions, wherein the antenna directions can be selected such that the overall interference is minimized, or some other cost function is satisfied. To realistically evaluate the performance of these beamsteering techniques, network simulators or testbeds are often required. Nevertheless, a capable testbed that covers sufficient small-cell operational aspects and incorporates directional antennas has yet to be found in the literature. In this paper we present WARP-TDMAC, a software-defined radio framework to enable the prototyping of directionality-based spectrum sharing schemes for small cells. WARP-TDMAC integrates compact pattern-reconfigurable antennas with a high performance 802.11 physical layer and uses a time division multiple access (TDMA) based medium access control (MAC) scheme for antenna direction scheduling. We characterize the synchronization and temporal/spatial scheduling capabilities of this testbed through several example MAC schemes that would have been difficult to realize without our cross-layer framework. The empirical results show that appropriate use of directionality can result in higher network sum rates in dense small-cell deployments, but further investigation is required to find an effective solution for this highly complex operational environment.