This paper proposes a direct blind equalization algorithm based on the multiple-shift correlation (MSC) property of the received data. Employing adaptive beamforming technique, we develope a partially adaptive channel equalizer (PACE) which allows the number of the adaptive weights to be less than the number of all the channel parameters. The PACE is with fast convergence speed and low implementation complexity. This paper also analyzes the effect of mismatch of channel order estimation due to small head and tail of the channel impulse response. From the analysis, we show the performance degradation is a function of the optimal output signal-to-interference plus noise ratio (SINR), the optimal output power and the control vector. We also propose a simple iterative method to reudce the performance degradation. Analysis of this proposed iterative method is also performed. Some simulation examples are demonstrated to show the effectiveness of the proposed blind channel equalizer and the performance analysis.

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.

In addition to additive thermal noise, a received direct-sequence spread spectrum (DS/SS) signal may suffer from intersymbol interference (ISI) and interference caused by cochannel narrowband users or other narrowband radio frequency interference (RFI). This paper presents a workable solution for removing narrowband interference (NBI) and reducing ISI or inter-chip interference (ICI) when the communication channel can be modeled as an FIR filter and the NBI comes from multiple CW tones, an AR-modeled Gaussian process, or a BPSK signal. Unlike earlier solutions, the proposed scheme is capable of performing the functions of NBI-rejection, ISI/ICI suppression and data detection (code despreading) simultaneously. It is easy to implement and, more importantly, it yields lower bit error rate (BER) and smaller mean squared error (MSE).

Conventional narrowband interference (NBI) rejection algorithms often assumed perfect pseudo-noise (PN) code synchronization. The functions of NBI rejection and code tracking are performed separately and independently by an adaptive filter and a code tracking loop, respectively. This paper presents two new receiver structures for direct sequence spread spectrum (DS/SS) systems, one operates in coherent mode and the other operates in noncoherent mode. Both receivers are designed to suppress NBI and minimize tracking jitter. Numerical results show that the proposed coherent receiver performs as good as the conventional receiver that uses an LMS NBI rejection filter with zero tracking jitter. The noncoherent receiver, when compared with the coherent one, suffers less than 3 dB degradation for bit error probability smaller than 10-3.

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.