RF-spectrum opportunities for cognitive radio networks operating over GSM channels

In this paper we characterize the radio frequency (RF) spectrum opportunities available in a common GSM (Global System for Mobile Communications) channel to support the operation of a cognitive radio network (CRN). In a first step, we describe the technical details involved to sample the channel using a Software Defined Radio (SDR) device. Adopting a simple Energy-based detector, we identify the two energy regions where the GSM system is active or inactive. Based on the output of the detector, we show that the distribution of the durations of busy and idle periods are approximated by geometric distributions. Finally, we validate a theoretical model for the distribution of the service time. The validation results indicate that the service time can be successfully represented by a discrete Generalized Pareto (dGP) distribution, which is confirmed by the Kolmogorov-Smirnov test. Because the throughput of the CRN is represented by the inverse of the service time, the proposed analysis provides an upper bound for the networks' throughput, indicating the maximum throughput that can be attained when a single SU transmits over a GSM cellular channel. The results presented in the paper are validated with real data, confirming the accuracy of the proposed service time model.