Adaptive PN code acquisition using automatic censoring for DS-CDMA communication.

This paper compares parallel acquisition with hybrid acquisition in terms of mean acquisition time in code acquisition system of forward link and reverse link of direct sequence code division multiple access (DS-CDMA) system. The mean acquisition time of the hybrid and parallel acquisitions is derived from the distribution of the multiple correct code-phase offsets. Especially, the mean acquisition time of the hybrid acquisition scheme is derived by considering both case 1 (the correct code-phase offsets are included in one subset) and case 2 (the correct code-phase offsets exist at the boundary of two subsets), which are caused by the distribution of the correct code-phase offsets in the subset. Results are provided for the performance comparison between hybrid acquisition and parallel acquisition under the same hardware complexity in the forward and reverse links. In our performance evaluation of code acquisition in DS-CDMA system, the hybrid acquisition shows a better performance than the parallel acquisition in terms of mean acquisition time of the both links in the frequency-selective Rayleigh fading channel.

In this paper a variable step-size algorithm for adaptive decision feedback equalizer (DFE) for turbo coded direct-sequence code division multiple access (DS/CDMA) communication systems is presented. The proposed adaptive equalizer is using a performance of the system or bit error rate to control the adaptation process of the DFE. By this technique, the performances of the proposed adaptive equalizer cooperate with the attractive soft output Viterbi algorithm (SOVA) of turbo decoder for the DS/CDMA system provides a good statistical in non-stationary channel condition scenario. The simulation results confirm that the performance of the proposed system in terms of bit error rate has been improved over the finite impulse response (FIR) equalizer.

A method is developed for resolving channel multipath components in direct-sequence code division multiple access (DS-CDMA) communications. Components spaced closer than a chip interval of a sequence are separable by the technique. The method is based on the constrained iterative deconvolution using the method of projection onto convex sets (POCS). A new POCS constraint is derived which utilizes the noise covariance modified by a matched filter. Simulation results for m-sequences and binary phase shift keying (BPSK) modulation are presented.

In this paper adaptive algorithms that may be used for spatial filtering or spatio-temporal filtering in a direct sequence code division multiple access (DS-CDMA) communication system are compared on the basis of signal-io-interference-and-noise-raiio (SINE,) improvements, algorithm convergence rates, capacity enhancement, and computational complexity. Algorithms that have already been proposed as well as some new algorithms are presented for this application. These algorithms fall into two categories: (1) conventional algorithms and (2) channel estimation algorithms. The conventional algorithms use knowledge of a desired reference signal and measurements of the received signal to adapt the antenna weights. In contrast, the channel estimation algorithms use properties of the underlying code structure of DS-CDMA systems to estimate the array response vectors. The estimated array response vectors are then used to determine appropriate antenna weights, either directly or via Capon beamforming.

A new RLS adaptive algorithm with variable forgetting factor for direct sequence code division multiple access (DS-CDMA) communication system is presented. Intersymbol interference (ISI) arises due to multipath propagation, which destroys the code orthogonality, gives rise to multiple access interference(MAI). Therefore, the objective of this paper is to minimize the effect of ISI with a long impulse response environment based on the proposed receiver. We consider an adaptive Laguerre lattice equalizer which applies an optimal method based on the variable step-size least mean square (VSLMS) algorithm for adaptable forgetting factor RLS algorithm to improve bit error rate (BER) performance of the receiver.

The performance of a multi-user chaos-based direct sequence code division multiple access (DS-CDMA) communication system with a sequence synchronisation unit incorporated is examined. Synchronisation is achieved through code acquisition and maintained through the code tracking phase. The performance of the proposed system is evaluated in a Rayleigh fading channel with additive white Gaussian noise and interuser interference. Results are compared to a fade-free channel. It is shown that, although the system is robust to the influence of noise and interuser interferences, it fails to satisfy the maximum allowable bit error rate limit of 10−3 in the Rayleigh fading channel.

In this paper, we consider direct sequence code division multiple access (DS-CDMA) communications, (wireless LAN in the ISM band), where the undesired DS-CDMA signals have different PN sequence lengths compared with the desired DS-CDMA signal. In this situation the conventional orthogonal matched filter (OMF) receiver's performance is poor, and so we propose a new OMF receiver to take into account these undesired signals. We show, through computer simulations, that our proposed OMF receiver will outperform the conventional OMF receiver.

Direct sequence code division multiple access (DS-CDMA) communications is a promising approach to cellular mobile communication, which operates in an environment characterised by multipath fading. Assuming perfect power control, the problem of adjacent cell interference is considered

A generalized code acquisition scheme for direct-sequence code-division multiple-access systems with multiple antennas is proposed over frequency-selective fading channels. The proposed scheme is developed on the framework of a generalized configuration of multiple antennas and correlators. The nonconsecutive search method is generalized and extended to multiple antenna systems to exploit multipath signals in improving acquisition performance over frequency-selective fading channels. The proposed scheme also adopts a hybrid decision strategy to make effective decisions on acquisition. The mean acquisition time performance of the proposed acquisition scheme is analyzed and evaluated in frequency-selective Rayleigh-fading channels with general multipath delay profiles and spatial-fading correlations. The effects of nonconsecutive search on mean acquisition time are investigated for various channel environments, and the optimal choice of decision strategy is discussed. Furthermore, effects of various configurations of multiple antennas and correlators, decision thresholds, and correlation interval on the performance are also investigated.

The convolutionally coded multi-antenna transmission technique proposed in Ban et al., (1997), for direct sequence code division multiple access (DS-CDMA) systems is studied in a wideband CDMA (WCDMA) system. The performance of the considered scheme operating over frequency-selective Rayleigh fading channels is evaluated by analysis and computer simulations. The multi-antenna transmission scheme is shown to provide performance improvement over single-antenna transmission when the fading is slow and the number of users is low. However, at high system loads the performance is pronouncedly limited due to additional interference between the antennas.

We propose to use power pins to carry data signals while simultaneously delivering power. A direct superposition of a data signal on a power pin would fail due to the inherent high noise level on power lines and this precludes the possibility for multiple data channels. To address the problem, we suggest adoption of the UWB (ultra wideband) and direct sequence-code division multiple access (DS-CDMA) communication technologies. Because of the wide bandwidth, a UWB signal can reduce its average power level practically to the noise level. DS-CDMA further mitigates the noise and allows multiple data channels to share interconnected power lines. We studied the feasibility of the proposed scheme through SPICE simulations and present the simulation results.

The evaluation of a hybrid acquisition performance has been considered for the pilot signal in the direct sequence code division multiple access (DS/CDMA) forward link. The hybrid acquisition is introduced by the combination of two schemes, parallel and serial acquisitions. The mean acquisition time of the proposed scheme is derived by considering both case 1 (the correct code-phase offsets are included in one subset) and case 2 (the correct code-phase offsets exist at the boundary of two subsets), which are caused by the distribution of correct code-phase offsets in the subset. Detection, false alarm, and miss probabilities are derived for the cases of multiple correct code-phase offsets and multipath Rayleigh fading channel. Results are provided for the acquisition performance with respect to design parameters such as postdetection integration length in search and verification modes, subset size, and number of I/Q noncoherent correlators. Also, comparison between the hybrid acquisition and the fully parallel acquisition is provided in terms of the minimum mean acquisition time.

Oblique projectors can be useful for interference suppression in direct-sequence code-division multiple-access (DS/CDMA) communication systems. In this paper, we propose a recursive oblique projector that exploits the Gram-Schmidt process. When increasing or decreasing the number of accessed users in the system, the oblique projector can be updated recursively by using the proposed method. Simulation results demonstrate that the proposed method is more computationally efficient than the conventional construction process of oblique projectors without the degradation of bit-error-rate (BER) performance in the DS/CDMA system.

This paper considers the application of I-Q trellis coded modulation (TCM) techniques to synchronous direct sequence code division multiple access (S-DS/CDMA) communication over frequency-selective fading mobile radio channels. The effect of the optimum adaptive coherent RAKE receiver structure with selection of the largest outputs is studied and an exact analytical expression for the pairwise error probability is obtained. This expression is used to evaluate the average BER upper bound through the transfer function bounding technique. The influence over the average BER of various system parameters like the number of active users, the number of selected outputs or sequence length are considered.

A simple direct sequence-code division multiple access receiver that combines adaptive beamforming with parallel interference cancellation in a multipath fading channel is proposed and analyzed. A fast adaptation, conjugate gradient algorithm is used to find the optimum beamformer weights. By beamforming, the desired user's signal is enhanced and the cochannel interference from other directions is reduced. For in-beam multiple access interference reduction, a parallel interference canceller is used in each RAKE finger. In the demodulation process, we propose a new demodulation method in which the incoming signal is correlated with the effecting spreading code rather than the physical spreading code called the effective matched filter. A new combining method called equivalent maximal ratio combining is also proposed and analyzed. The average uncoded bit error rate as a function of the average antenna signal-to-noise ratio and the number of receiving antennas is examined in a frequency selective Rayleigh fading channel for all proposed receiver structures. Both simulation and analysis show an increase in system capacity as a function of the number of antennas and the number of interferers canceled per finger.