Non-contiguous frequency division spread OFDM with polyphase spreading for overlay cognitive radio and dynamic spectrum access networks

In this paper, we propose a novel multi-carrier transmission platform, namely non-contiguous frequency division spread OFDM (NC-FD-SOFDM), for cognitive radio and dynamic spectrum access networks. By combining the benefits of frequency diversity, polyphase spreading code and multiuser- detection (MUD) gain together, this new platform not only offers the capability of operating over multiple noncontiguous frequency bands and making it suitable for overlay cognitive radio systems, it provides excellent BER performance as well. Specifically, by decomposing the available subcarriers in a cognitive radio environment into multiple non-contiguous subsets, the proposed scheme is able to spread data symbols across multiple non-contiguous subcarriers to exploit frequency diversity. Furthermore, due to the fact that the total number of subcarriers within each subset is small, an optimal maximum likelihood MUD receiver can be built at reasonable complexity. Finally, by exploiting polyphase Carrier Interferometry (CI) spreading codes, the number of subcarriers in each subset no longer has limitation. Simulation results over various multi-path fading channels and spectrum availability scenarios confirm the performance gain of the proposed scheme over conventional noncontiguous OFDM and non-contiguous SOFDM systems