Performance Evaluation of Adaptive Non-contiguous MC-CDMA and Non-contiguous CI/MC-CDMA for Dynamic Spectrum Access

In this paper, we present a quantitative performance evaluation of non-contiguous multi-carrier code vision multiple access (NC-MC-CDMA) for cognitive radio in a dynamic spectrum access (DSA) network. In a DSA network, multi-carrier based cognitive radio transceivers need to deactivate some of its subcarriers to avoid interference to primary users. However, by deactivating subcarriers, orthogonality among different spreading codes are lost, leading to poor BER performance. The performance of the NC-MC-CDMA can be improved by adaptive spreading code adjustment to compensate for the loss of orthogonality. However, since Hadamard-Walsh codes only exist for certain code length, loss of orthogonality can only be minimized instead of eliminated for many cases. On the other hand, orthogonal Carrier Interferometry codes exist for code length of any integer. Hence, by applying non-contiguous CI/MC-CDMA into DSA, the loss of orthogonality among spreading codes caused by deactivating subcarriers can be eliminated. As a direct result, adaptive NC-CI/MC-CDMA significantly outperforms adaptive NC-MC-CDMA using Hadamard-Walsh codes.