A synchronous Q2PSK DS-CDMA system: system conceptualisation, implementation and performance analysis

This paper describes the implementation of a spectrally efficient 4-dimensional Q²PSK (quadrature-quadrature phase shift keying) DSSS modulation strategy. By using Q²PSK, combinations of four, two or one data streams can be modulated in parallel in the same bandwidth as normally occupied by a QPSK system. This allows for even greater flexibility in terms of data throughput rate and reliability in accordance with the prevailing channel conditions. The disadvantages of the Q²PSK modulation strategy, such as its inherent sensitivity to phase distortion, can be effectively mitigated by employing the multidimensional spreading technique proposed in this paper. Finally, the efficiency of the proposed Q²PSK DS-SSMA system is assessed and demonstrated in a multi-user interference (MUI) environment by means of computer simulation. Very promising results is demonstrated with relatively short sequences used in the simulation studies