Multi-carrier DS-CDMA using frequency spread coding

In this paper, a type of multi-carrier direct sequence code division multiple access (MC-DS-CDMA) system which uses frequency spread coding is proposed and investigated for the down-link. An MC-DS-CDMA system is a combined system of CDMA and multi-carrier modulation. This system is often categorized as a "serial to parallel (S/P) type" system because serial to parallel converted data symbols are transmitted. They use different sub-carriers which are narrow-band DS waveforms. In this system, benefits of path or frequency diversity can not be obtained because of the narrow-band transmission of each data symbol. In order to benefit from the diversity, we propose to adopt frequency spread coding in an MC-DS-CDMA system. The proposed system exploits frequency diversity without additional redundancy, i.e., no frequency or time redundancy is required to improve the performance. Computer simulation is carried out in a frequency selective fading channel and the results show its effectiveness in terms of average bit error rate (BER). Furthermore, the proposed system is compared with a multi-carrier (MC-) CDMA system which is often categorized as a "copy type" system and a single-carrier (SC-) DS-CDMA system using a RAKE receiver.