Cyclostationary Signature Detection in Multipath Rayleigh Fading Environments

Abstract

Cognitive radio-based Open Spectrum systems offer a solution to the issue of spectrum scarcity by allowing wireless networks to dynamically access spectrum while coordinating to co-exist and avoid the creation of harmful interference. However, before a practical open spectrum system may be implemented, a number of significant technical and policy challenges must be overcome. One such technical challenge is the distributed coordination of operating frequencies and bandwidths between co-existing systems. Cyclostationary signatures have been shown to be a powerful tool in overcoming this challenge. A cyclostationary signature is a unique identifier or watermark which may be embedded in the physical properties of a communications signal. Such signatures may be used to aid peer devices in performing a number of critical tasks, including signal detection, classification and frequency acquisition. A key limitation of cyclostationary signatures when implemented in orthogonal frequency division multiplex (OFDM)-based systems is the sensitivity exhibited in time-variant multipath Rayleigh fading environments. Although OFDM-based systems offer robust performance under multipath conditions, detection of cyclostationary signatures can be severely degraded. As signature detection is adversely affected, the ability of Open Spectrum Systems to coordinate and coexist is seriously undermined. This paper therefore presents techniques for effectively over-coming the issue of multipath Rayleigh fading in the detection of cyclostationary signatures for Open Spectrum systems. Approaches for the generation and detection of signatures in OFDM-based waveforms are outlined and improvements in detection performance are illustrated using simulation results.