OCDD/CDMA: A new DS/CDMA with orthonormal code diversity detection

The paper presents a new spread spectrum communication system called orthon ormal code diversity detection (OCDD)/CDMA system based on the novel concep t of orthonormal-basis diversity which is a generalization of the existing spread spectrum diversity concepts such as path diversity and frequency div ersity. The OCDD/CDMA system is similar to the conventional DS/CDMA system in the transmitter structure, but is different in the receiver structure as it employs the extended orthonormal basis-function set which is the union of the Walsh basis-functions multiplied by the PN sequences and, optionally , their delayed replicas. The received signal is matched to the extended ba sis functions, and the matched signal components are combined together afte r individual channel compensation. The proposed OCDD/CDMA system exhibits t he bit error performance which is much improved over the conventional DS/CD MA system using the maximal ratio combing. In addition, it is robust to the chip timing error, which becomes more crucial in the future DS/CDMA system s having a higher data rate and smaller chip interval. From the simulation results, we confirm that the OCDD/CDMA system is a unique spread spectrum c ommunication technique that can effectively increase the diversity utilizat ion in the slowly fading channel, overcoming the inherent problems in the D S/CDMA and OFDM/CDMA systems.