Cognitive-engined spectrum-fragmented synchronous MC-CDMA based on generalized hadamard codes

In Cognitive Radio (CR), in order to avoid interference in the Primary Users (PU), some subcarriers need to be deactivated. In systems based on Multicarrier Code Division Multiple Access (MC-CDMA), this causes losing orthogonality among different spreading codes, leading to poor Bit Error Rate (BER) performance. The performance of such system can be improved by using Generalized Hadamard Codes (GHC) instead of conventional Hadamard codes which avoids the loss of orthogonality. This is due to the fact that unlike conventional Hadamard codes, GHC are conjectured to exist for any arbitrary length. In this paper, we propose using a novel spreading code, namely, GHC for synchronous MC-CDMA in CR networks. The new spreading codes help the CR systems maintaining the data rate while improving the performance by eliminating the orthogonality loss. Finally, the performance of the MCCDMA system using GHC is evaluated and it is shown that the proposed system outperform the system with conventional Hadamard codes.