In this work, spectrum sensing for cognitive radios is considered in the presence of Primary Users (PU) using frequency-hopping communication over multiple frequency bands. The detection performance of the Fast Fourier Transform (FFT) Average Ratio (FAR) algorithm is obtained in closed-form, for a given FFT size and number of PUs. The effective throughput of the Secondary Users (SU) is formulated as an optimization problem with a constraint on the maximum allowable interference on the primary network. Given the hopping period of the PUs, the sensing duration that maximizes the SU throughput is derived. The results are validated using Monte Carlo simulations. Further, an implementation of the FAR algorithm on the Lyrtech (now, Nutaq) small form factor software defined radio development platform is presented, and the performance recorded through the hardware is observed to corroborate well with that obtained through simulations, allowing for implementation losses.
5 Figures and Tables
Fig. 1. Typical frequency-band occupancies in a multiple FH-PU network.
Fig. 3. Optimal throughput for N = 64, Nh = 1024. For the simulation result, the optimal throughput was obtained by sweeping a range of M and threshold, and choosing the pair that offered the best throughput.
Fig. 4. Comparison of FAR with the conventional ED , with and without noise variance uncertainty. Here, N = 64, M = 128, L = 3, and the detectors are designed with a target false alarm probability of 0.01.
Fig. 5. Comparison of ROCs from simulations and experiments, at different M and SNRs. The implementation loss is about 1 dB.
Fig. 6. Optimum CR throughput Vs. Ns, comparing the hardware implementation with simulated curves.
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