| Abstract: | Chaotic sequence has been applied in Cognitive Radio(CR) to exert the enormous potential spectral utilization and enhance the transmission security. However, since there is not strict orthogonality between chaotic signals, intra-signal interference(ISI) will be introduced into the demodulation. Here, an anti-interference orthogonal-frequency-division-multiplexing(OFDM) chaotic modulation named Walsh-sequence chaotic CR(WS-CCR) is proposed for cognitive radio. By constructing the strictly orthogonal chaotic signal based on Walsh sequence, the ISI component, which is produced by frequency offset in previous CR, can be eliminated during the demodulation. Moreover, the chaotic sequence can also be applied to scramble subcarriers to relieve the interference caused by malicious attacks. Gaussian approximation method is adopted to obtain the exact performance analysis of WS-CCR over Additive White Gaussian Noise(AWGN) channel and Rayleigh multipath fading channel. Results show that, with subcarriers scrambling by chaotic sequence, anti-interference performance and transmitting security can be signi?cantly improved in WS-CCR. Importantly, due to the absence of ISI component, the bit-error ratio(BER) performance of WS-CCR is better than that of the previous CR system. |
