Transmit diversity offers an advantage in the forward link of the cdma2000 system by balancing the spectrum efficiency in the uplink and downlink. Three schemes for performing transmit diversity are examined in this paper-orthogonal transmit diversity, time switched transmit diversity, and selection transmit diversity for vehicular, indoor-outdoor pedestrian and indoor office environments. Also considered are some issues related to implementation complexity in the mobile handset. Under certain channel conditions, we show that low rate feedback of antenna selection and no forward link power control offers performance advantages over transmit diversity schemes with forward link power control and no antenna selection.

When IS-95 CDMA mobiles are close to an AMPS base station, the radio frequency portion of the mobile often produces product signals in the baseband CDMA signal. In some cases, AMPS products will decrease the demodulation performance causing the IS-95 CDMA mobile to drop a call. To minimize the impact to existing mobile receiver designs, a technique is described for reducing intermodulation products by first detecting when the products are significant and then switching the low noise amplifier in the IS-95 CDMA mobile between a high and low gain state. This paper presents a detector for AMPS intermodulation products and the performance of this detector using data collected in CDMA networks in Los Angeles.

We consider an additive white Gaussian noise multiple-access channel and investigate the performance degradation of several multiuser detectors due to imperfect knowledge of the channel parameters, induced by either estimation errors or sampling/quantization of the receiver's sufficient statistics. The symbol error rates and the asymptotic multiuser efficiencies (AMEs) of these detectors are examined as functions of both true and approximated channel parameters for 2 asynchronous users. The results quantify the loss of near-far resistance due to parameter estimation errors and demonstrate that detectors which are optimal for ideal conditions are often more sensitive to parameter mismatch. Examples are given which illustrate a reverse ordering of the symbol error rates for these detectors in the high signal-to-noise regime, and also illustrate cases when the conventional matched filter detector exhibits superior performance over multiuser detectors.

A conjugate-gradient (CG) constant-modulus adaptive processor is proposed. For the generalized sidelobe canceler (GSC) signal processing configuration, this algorithm, CG-GSC, exhibits improved convergence over previous methods. Theoretical expressions are presented for convergence and weight update of a linearly constrained constant modulus generalized sidelobe canceler. Theoretical expressions are then derived for the conjugate direction vectors. These vectors are used to update the filter weights for a conjugate gradient adaptation rule. A simulation study of the conjugate adaptation rule reveals the increase in convergence rate for the generalized sidelobe canceler. Performance comparisons of the CG-GSC and a first-order gradient GSC for a BPSK signal with multipath and white noise interference indicate that the CG-GSC adaptation rule not only increases convergence by a factor of five compared to the first-order gradient GSC, but in some instances improves the bit error rate of the demodulated BPSK signal.>

A report is presented on experiments using a colored-noise assumption Kalman filter to enhance speech additively contaminated by colored noise, such as helicopter noise and jeep noise, with a particular application to linear predictive coding (LPC) of noisy speech. The results indicate that the colored-noise Kalman filter provides a significant gain in SNR, a clear improvement in the sound spectrogram, and an audible improvement in output speech quality. The authors demonstrate that such gains are unavailable with white noise assumption Kalman and Wiener filters. The colored-noise prefilter greatly enhances the quality and intelligibility of LPC output speech for noisy inputs.>