New family of constant-envelope root-of-unity filtered complex spreading sequences with zero cross-correlation properties

Abstract

A novel family of root-of-unity filtered complex spreading sequences is introduced. The new sequences, called constant-envelope root-of-unity filtered zero-cross-correlation (CE-RU-ZCC) sequences, are a nonlinear derivative of a family of polyphase sequences originally proposed by Suehiro et al. (1994). CE-RU-ZCC sequences can be shown to exhibit superior properties compared to the former, with little correspondence with the original Suehiro source sequences, apart from their desirable autocorrelation properties, which are perfectly retained despite the RU-filtering employed. The sequences are shown to be unique in several ways. Firstly, the unique filtering method results in sequences with perfectly constant envelope when modulated onto quadrature carriers, resulting in superior power efficiency compared to Nyquist-filtered sequences. The sequences secondly exhibit zero cross-correlation amongst the members of a family, and are therefore of particular interest in multi-user cellular environments, such as wireless CDMA, where, thirdly, their use results in a significant reduction in multi-user interference (MUI). The new sequences finally have excellent spectral efficiency, their power spectral distributions (densities) being practically equivalent to Nyquist-filtered sequences with sharp spectral roll-off. The paper includes results to verify the various claims made, and compares the CE-RU-ZCC sequences to several of the more commonly known spreading sequence families, such as the binary Gold (1967) family and the family of so-called generalised chirp-like (GCL) sequences originally proposed by Popovic (1992).