In direct-sequence code division multiple access (DS/CDMA) multiuser communication systems with multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) must be considered. The multipath effect usually changes the characteristics of the spreading codes. Modification of the conventional receiver structure is needed to account for the interference of the multipath fading. This paper proposes four adaptive receivers for such multiuser DS/CDMA systems in multipath fading channels. We employ least mean square (LMS) and recursive least squares (RLS) algorithms for both finite impulse response (FIR) and infinite impulse response (IIR) receiver structures. Mean square error (MSE) and convergence analysis are also given in this paper. Simulation results show the performance comparisons of the four proposed receivers.

Smart antennas, with spatial processing, used in code division multiple access (CDMA) multiuser communications can enhance range, reliability and capacity. Moreover, the adaptive beamforming technologies can remove unwanted noise and interference from the received signal. In this paper, we propose four adaptive antenna receiver structures for direct-sequence (DS) CDMA multiuser environment with multipath fading channels. Narrowband and wideband adaptive array receiver structures are considered in this paper. LMS and RLS algorithms are employed in both narrowband and wideband receiver structures to adjust the spreading code coefficients. We call these new schemes as Wiener code filters. The weights of the adaptive beamformer and the spreading code are updated every symbol interval, so the computational complexity is very low. Simulation examples are given to compare the performances of the proposed receiver structures. Analyses are also given for these structures.

A low-voltage and low-power RF mixer for WCDMA applications is presented. The paper presents a novel topology mixer that leads to a better performance in terms of isolation and power consumption for low supply voltage. The measuring results of the proposed mixer achieve: 7 dB power conversion gain, 10.4 dB double side band (DSB) noise figure, -2 dBm input third-order intercept point (IIP3), and the total dc power consumption of this mixer including output buffers is 2.2 mW from a 1 V supply voltage. The current output buffer is about 1.96 mW, the excellent LO-RF, LO-IF and RF-IF isolation achieved up to 49 dB, 39.5 dB and 57.3 dB, respectively.