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ON THE CORRELATION OF SPREADING SEQUENCES COMBINED WITH NONLINEAR OQPSK SIGNALS

Cercas, F. ; Rodrigues, R.Rodrigues ; Dinis, R.

ON THE CORRELATION OF SPREADING SEQUENCES COMBINED WITH NONLINEAR OQPSK SIGNALS, Proc IASTED International Conf. on Signal Processing, Pattern Recognition and Applications - SPPRA, Innsbruck, Austria, Vol. *, pp. * - *, February, 2011.

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Abstract
This paper investigates the main correlation properties of some spreading sequences when applied to a system using nonlinear OQPSK-type modulations, since this is an important topic for present and future wireless communications. These signals, that include as special cases CPM schemes (Continuous-Phase Modulation), can be designed to have very low envelope fluctuations or even a constant envelope, making them compatible with a very low cost and power efficient grossly nonlinear amplification. We use an analytical method to derive both the autocorrelation and the cross-correlation of those signals. The resulting expressions are then applied to Maximum-Length (ML) sequences, Gold Codes and TCH (Tomlinson, Cercas, Hughes) sequences. It is shown that TCH sequences have better autocorrelation and cross-correlation properties when submitted to a nonlinear system. These results can be applied in multi-user detection, spreading, synchronization, channel estimation and many other relevant issues for the radio interface of any communication system.