MC - CDMA with Quadrature Spreading for WirelessCommunication

Multi-Carrier CDMA (MC-CDMA) systems using the Orthogonal Frequency Division Division Multiple Access (OFDM) technique resolve the frequency se-lectivity in multipath fading channels and have good spectral properties. The addition of a spread spectrum component to the OFDM introduces a frequency diversity gain that can combat deep multipath fading situations. In this paper a MC-CDMA system operating over frequency selective, slowly fading channels is considered and its performance is studied analytically and by computer simulations. We consider the downlink of a cellular radio system where for each user a BPSK modulation and a quadrature (complex) spreading code is used. The spreading codes are arranged in a way that reduces the eeect of the multipath fading channel and restores some of the orthogonality losses between users. The obtained results show considerable performance improvement compared to conventional OFDM and to MC-CDMA that uses single spreading codes. The eeect of frequency oosets on the system performance is also addressed in this paper. Its superior performance and low complexity receiver make MC-CDMA with quadrature spreading codes suitable for future wireless communication systems to achieve the requirements of high quality services, high speed, and low cost-receiver.