Sub-Nyquist Cyclostationary Detection for Cognitive Radio

TL;DR

This paper introduces a sub-Nyquist cyclostationary detection method for cognitive radio that efficiently recovers the cyclic spectrum from fewer samples, outperforming energy detection especially at low SNRs.

Contribution

It proposes a structured compressed sensing algorithm for cyclic spectrum recovery from sub-Nyquist samples and derives bounds on the sampling rate needed for perfect reconstruction.

Findings

Cyclic spectrum can be recovered at 4/5 of Nyquist rate without sparsity.

Sparse signals allow recovery at 8/5 of Landau rate.

Cyclostationary detection outperforms energy detection at low SNRs in sub-Nyquist regime.

Abstract

Cognitive Radio requires efficient and reliable spectrum sensing of wideband signals. In order to cope with the sampling rate bottleneck, new sampling methods have been proposed that sample below the Nyquist rate. However, such techniques decrease the signal to noise ratio (SNR), deteriorating the performance of subsequent energy detection. Cyclostationary detection, which exploits the periodic property of communication signal statistics, absent in stationary noise, is a natural candidate for this setting. In this work, we consider cyclic spectrum recovery from sub-Nyquist samples, in order to achieve both efficiency and robustness to noise. To that end, we propose a structured compressed sensing algorithm, that extends orthogonal matching pursuit to account for the structure imposed by cyclostationarity. Next, we derive a lower bound on the sampling rate required for perfect cyclic spectrum recovery in the presence of stationary noise and show that it can be reconstructed from samples obtained below Nyquist, without any sparsity constraints on the signal. In particular, in non sparse settings, the cyclic spectrum can be recovered at $4/5$ of the Nyquist rate. If the signal of interest is sparse, then the sampling rate may be further reduced to $8/5$ of the Landau rate. Once the cyclic spectrum is recovered, we estimate the number of transmissions that compose the input signal, along with their carrier frequencies and bandwidths. Simulations show that cyclostationary detection outperforms energy detection in low SNRs in the sub-Nyquist regime. This was already known in the Nyquist regime, but is even more pronounced at sub-Nyquist sampling rates.