The performance of preRAKE diversity combining based on QPSK modulation in time-division duplex CDMA mobile communications

This paper analyzes the performance of preRAKE techniques, which is proposed for the time-division duplex (TDD) code-division multiple-access (CDMA) systems, based on quarter phase-shift keying (QPSK) modulation. From the results we find that QPSK has the advantage of stability over BPSK while both of them have the same average bit error rate (BER). This advantage, together with the superiority over the RAKE receiver of moving the circuitry from the mobile unit (MU) to the base station (BS), makes the preRAKE technique useful in TDD systems.