Two-stage spectrum sensing algorithm for low power signals in cognitive radio

One promising approach to achieve high precision spectrum sensing in a cognitive radio (CR) system is the energy detector based on Wavelet Packet Transform (WPT). However, energy detector spectrum sensing is affected by the Signal to Noise Ratio (SNR). When the SNR is lower than 5 dB, an energy detector may falsely determine some unoccupied sub-channels as occupied [16]. In this paper, a new noise immune algorithm for spectrum sensing is introduced. The technique is suitable for low-power primary user signals such as spread spectrum. The proposed algorithm consists of two detection stages. The first stage depends on energy detection and is used in high SNR cases. The second stage depends on Higher-Order-Statistics (HOS) and is used only if the first stage is failed (at low SNR). This will lead to a reduction in processing time. The use of the proposed technique makes spectrum sensing possible in very low SNR conditions. This allows better utilization of the unoccupied spectrum and high spectrum efficiency usage.