A CDMA System Based upon Spectrally Overlapping Low Rate Convolutionally Coded Signals |
The authors propose a new CDMA system based upon frequency staggered, convolutionally encoded QPSK signals and a new type of decoder. In this system co-channel interference is emanating from two or three users and the spreading bandwidth is restricted to two, three or four times the data bit rate. The new CDMA system, designed for mobile satellite communications, is capable of operation in an interference environment and it makes use of 1/2 rate convolutionally encoded data modulating QPSK carriers. Since the decoder is based upon cross-correlation, the cross-correlation between two encoded QPSK signals is analysed. The results of this analysis present the variation of standard deviation of the magnitude of the cross-correlation, when the carrier frequency offset is varied. A new detector, the cross-correlation convolutional (XC) decoder, which makes up part of this system is described. The error rates which are produced using the XC-decoder and the Viterbi decoder are evaluated and compared against Gaussian noise and the co-channel interference. These results are being dealt with, and the system capacity is compared with the capacity of be FDMA currently in use in satellite communication
Abu-Rgheff MA, Tomlinson M