Parallel transmission of DS/CDMA signal by orthogonal bases and repeated spreading: the chip-spreading OCDM

We present a new DS/CDMA system, which we call the chip-spreading OCDM system. In the proposed system we convert the chip sequences in each symbol interval into parallel streams and transmit each sequence simultaneously through different orthogonal Walsh basis functions. In the receiver, the received signal is matched to each extended basis-function, the union of the transmitter basis-functions and their delayed replicas, and the chip samples obtained from the matched filter outputs are combined after channel compensation processing. The proposed chip-spreading OCDM system is an embodiment of the concept of potential diversity that combines with the path-diversity of the DS/CDMA system and the frequency-diversity of the OFDM/CDMA system. As a result, the bit error rate of the proposed system is much lower than that of the conventional DS/CDMA system which uses maximal ratio combining. In addition, it can effectively resolve the high peak to average power ratio (PAR) and high sensitivity to frequency offset problems which are critical in multi-carrier systems