An improved widely linear receiver for cyclostationary CDMA systems with OQPSK modulation

An improved widely linear (WL) receiver is proposed for direct-sequence code-division multiple-access (DS-CDMA) systems that employ aperiodic spreading sequences with offset quadrature phase shift keying (OQPSK) modulation. The modulation scheme generates improper complex multiple-access interference (MAI) and necessitates the use of WL receivers. Focus is on bandlimited pulse shapes and inherent cyclostationarity (CS) of the uncoded received signal. The enhanced WL receiver replaces the conventional chip-matched filter (CMF) with new filters that exploit the CS of the received signal through frequency-shifting. The proposed WL receiver is shown to outperform the classical strictly linear (SL) receiver when the interfering users are high-powered, which may exist to support high data rate services. Numerical results are presented to demonstrate the performance gain of the WL receiver over the SL receiver in output signal-to-noise ratio (SNR).