Analytical computation of the correlation of spreading sequences for nonlinear OQPSK-type modulations

Abstract

In this paper we study the behavior and correlation properties of some spreading sequences when applied to a system using nonlinear offset quadrature phase-shift keying-type modulations. These signals, which include as special cases continuous-phase modulation schemes, 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 the correlation of those signals. The resulting expressions are then applied to maximum-length sequences, Kasami, and Tomlinson, Cercas, Hughes sequences. It is shown that Tomlinson, Cercas, Hughes sequences have better correlation properties than other spreading sequences.