Introduction

Over the past few years, an increasingly diverse and ever-changing wireless spectrum has created a need for cognitive radio networks. Such networks leverage spectrum sensing and information from each layer in the protocol stack to overcome spectrum diversity by adapting all layers (e.g., the MAC and PHY) on the fly. By doing so, cognitive radios can achieve the greatest level of performance, given the current networking conditions. For example, in areas where access to the spectrum is highly contended, the radio can switch from using a carrier sense multiple access (CSMA) MAC protocol, to a time division multiple access protocol that reduces overhead in accessing the spectrum to increase capacity and reduce collisions. Despite the increased recent activity in cognitive radio networks, supporting the development of protocols at the MAC and PHY layers, as well as cross-layer optimizations for such networks, has been extremely challenging. Commodity wireless hardware does not facilitate such development, because the majority of MAC functionality is placed on the network interface (NIC) hardware, where programmability is limited and access to the software that runs on the NIC is often restricted.

The limited programmability of wireless NICs makes Software-Defined Radios (SDRs) an attractive alternative for building cognitive radio network protocols. SDRs implement the majority of functionality, including the physical and link layers, in software running on commodity hardware, making all layers of the protocol stack easy to modify.