Recently, decorrelator-based receivers have been investigated for demodulat
ing data in a dual-rate synchronous direct-sequence code division multiple-
access (DS/CDMA) system. The proposed receivers were a high-rate decorrelat
or (HRD) matched to the data rate of the high-rate users and a low-rate dec
orrelator (LRD) matched to the data rate of the low-rate users. In this pap
er, the probabilities of error attainable for high-rate and low-rate users
with the use of the HRD and the LRD are analyzed. It is proven that the LRD
offers superior performance to that of the HRD for all users. Asymptotic a
nalysis provides bounds for the performance difference for high-rate users.
The results are generalized to multirate systems. To increase fidelity, a
sliding-window decorrelator (SWD) is proposed which demodulates a high-rate
user's data by a soft-decoding rule from the outputs of several decorrelat
ors sliding along the received signal sequence. The results show that it pe
rforms better than the HRD while maintaining smaller demodulation delay and
computational complexity than the LRD. To further exploit the characterist
ics of multirate systems, a decorrelating decision-feedback detector is pro
posed and its asymptotic multiuser efficiency is analyzed. It is shown that
this detector incurs little demodulation delay for high-rate users and pro
vides better performance for low-rate users than that of the LRD when the e
nergies of the interfering users are comparable to that of the desired user
.