Adaptive Parallel Interference Cancellation Research Articles

Performance Comparison of Adaptive filtering Algorithms for Parallel Interference Cancellation in Asynchronous MC DS-CDMA Systems

The Bit Error Rate (BER) comparison of Adaptive Parallel Interference Cancellation (APIC) algorithms in asynchronous Multicarrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA) system is introduced. The APIC is used to eliminate the Multiple Access Interference (MAI) in MC-DS-CDMA system. The Adaptive filtering algorithms considered are, Normalized Least Mean Squares (NLMS), Variable Step Size Normalized Least Mean Squares (VSS-NLMS), and Generalized Normalized Gradient Descent (GNGD) algorithms. These algorithms are used in coincidence with APIC system for updating cancellation weights. The performance comparison between these algorithms is performed via extensive computer simulations. Simulation results demonstrate that the VSSNLMS algorithm outperforms all other algorithms, the NLMS is modular, while the worst performance is obtained by GNGD.

Performance of NLMS-based Parallel Interference Cancellation (PIC) For Up-Link CDMA Systems

Parallel interference cancellation (PIC) is a promising detection technique to suppress multiple access interference (MAI) for up-link direct-sequence CDMA (DS-CDMA) systems. Adaptive PICs are attractive due to its low implementation complexities and good performance. In this paper, we propose a general framework for analyzing the bit error rate (BER) and convergence performance of the normalized LMS (NLMS) based PIC. To further improve the convergence speed of the PIC system, a novel switch-mode noise-constrained NLMS (SNC-NLMS) algorithm for the adaptive multistage PIC (AMPIC) is also proposed. Simulation results show that the analytical results are reasonably accurate and the SNC-NLMS AMPIC outperforms the NLMS-based one, if the algorithm parameters are properly chosen.

Low Complexity Selective Adaptive Multicarrier DS-CDMA Receiver

In this paper, selective adaptive (SA) receiver for Multicarrier Direct Sequence Code Division Multiple Access (MC DS-CDMA) system is presented. This receiver has high performance and at the same time reduces the multiple access interference (MAI) of the MC DS-CDMA) system with low computational complexity. The performance of SA receiver is measured in terms of the bit error rate (BER). An upper bound expression of the BER for the SA receiver under Rayleigh fading channel condition is derived and validated by computer simulations. Moreover, the implementation complexities of the SA receiver is compared with the Adaptive Parallel Interference Cancellation (APIC) receiver.

Adaptive parallel interference cancellation for CDMA systems—A weight selection and filtering scheme

Parallel interference cancellation (PIC) is a well-known multiuser detection algorithm in direct-sequence code-division multiple-access (DS-CDMA) systems. It is typically implemented with a multi-stage architecture. One problem associated with the PIC is that unreliable interference cancellation may occur in the early stages and the system performance may be degraded. Thus, the partial PIC detector was developed to control the cancellation level by use of interference cancellation factors. Partial PIC can be implemented with an adaptive form, in which optimal weights are derived using the least mean square (LMS) algorithm. In this paper, we propose an algorithm improving the conventional adaptive partial PIC. The main idea is to reduce the number of active weights in the LMS algorithm, and to perform weight post-filtering such that the resultant excess mean square error can be reduced. We also analyze the performance of the proposed algorithm and derive the bit error rate of the second stage output. Simulation results verify that the proposed algorithm outperforms the conventional partial PIC, and derived analytical results are accurate.

Adaptive Two-Stage GSC-Based PIC Detection for Time-Varying MIMO Channels

Adaptive parallel interference cancellation (PIC) has been recently proposed for the signal detection in multiple- input multiple-output (MIMO) systems. However, it suffers from error propagation when operated in time-varying channels. In this letter, an adaptive two-stage PIC with the minimum variance (MV) criterion is proposed to solve the problem. Adaptation with the MV criterion is realized with a decision feedback generalized sidelobe canceller (DFGSC). In the first-stage cancellation, a special structure involving dual DFGSCs is developed. All adaptation operations are implemented with the least-mean-square (LMS) algorithm. Simulations show that the proposed adaptive PIC detection can significantly outperform the conventional adaptive PIC detection in time-varying MIMO channel environments.

Performance analysis of an adaptive two-stage PIC CDMA receiver in AWGN channels

Parallel interference cancellation (PIC) is considered a simple yet effective multiuser detector for direct-sequence code-division multiple-access (DS-CDMA) systems. However, its performance may deteriorate due to unreliable interference cancellation in the early stages. Thus, a partial PIC detector, in which partial cancellation factors (PCFs) are introduced to control the interference cancellation level, has been developed as a remedy. Recently, an interesting adaptive multistage PIC algorithm was proposed. In this scheme, coefficients combining the channel responses and optimal PCFs are blindly trained with the least mean square (LMS) algorithm. The algorithm is simple to implement, inherently applicable to time-varying environments, and superior to the non-adaptive type of partial PICs. Despite its various advantages, its performance has not been theoretically analyzed yet. The contribution of this paper is to fill the gap by analyzing an adaptive two-stage PIC in AWGN channels. We explicitly derive the analytical results for optimal weights, weight-error means, and weight-error variances. Based on these results, we finally derive the output bit error rate (BER) for each user. Simulation results indicate that our analytical results highly agree with empirical ones.

A Novel Adaptive Detection Scheme based on Parallel Interference Cancellation for V-BLAST System

In this paper, in order to reduce the computational complexity of the detector of vertical Bell Laboratories layered space-time (V-BLAST) system over time-varying channels, an adaptive detection scheme is proposed based on parallel interference cancellation (PIC). The presented scheme has three units, which are primary adaptive detector, detection ordering determiner, and adaptive PIC detector. The proposed scheme can employ many of known adaptive algorithms for detection of V-BLAST system. In this paper, we present computational complexity of the proposed scheme using LMS, RLS, APA and AMSER adaptive algorithms and evaluate its performance with numerical simulations.

A Multiuser Detection Receiver Using Blind Antenna Array and Adaptive Parallel Interference Cancellation

In this paper, the problem of multiuser detection for synchronous code division multiple access systems in both additive white Gaussian noise and multipath channels is addressed. A new multiuser detection receiver that uses an adaptive blind array along with an adaptive parallel interference canceler is proposed. The replacement of a conventional antenna array with a two-dimensional RAKE receiver is also considered for frequency selective Rayleigh fading channels. By using a constrained optimization criterion along with the gradient-projection algorithm, a blind algorithm for the adaptation of the array response vector is proposed. The new algorithm is superior to a few typical blind algorithms in the literature in terms of both performance and computational complexity. The proposed receiver has the ability to cancel very strong multiple access interference coming from the same direction as the desired signal. Simulation results are presented to show the excellent performance of the proposed combination scheme in comparison to that of using either a multiuser detection or adaptive antenna arrays in a severe near-far situation.

Adaptive parallel interference cancellation receiver in CDMA satellite system

AbstractFuture satellite communication systems will be characterized by broadband, multimedia services, and large capacity of mobile terminals. Low Earth Orbit (LEO) system with multiple spot‐beams per satellite using Code Division Multiple Access (CDMA) is a good choice. In this paper, an adaptive parallel interference cancellation detector is proposed for reverse link with both intra‐beam and inter‐beam multiple access interference (MAI). The proposed linear adaptive receiver achieves essential advantages with respect to MAI with a little more complex than the conventional matched‐filter receiver. The receiver structure is all feed‐forward and more stable than many other multiuser detectors. We then study several adaptive algorithms with the aid of training sequence, and compare them with blind algorithm in order to find the good tradeoff among the performance, complexity and bandwidth‐extension. With only small modification, the receiver can work well in multirate cases which are usually hopeful in multimedia services. With the test of simulations under AWGN and time‐varying Rician channels, the proposed receiver can reach good performance with considerable increasing user capacity. Copyright © 2003 John Wiley & Sons, Ltd.

A selective and adaptive interference cancellation scheme for code division multiple access systems

In this paper, a new selective and adaptive parallel interference cancellation technique is presented for code division multiple access systems. The proposed technique performs a parallel interference cancellation in multistage, and the computational complexity is reduced by applying the cancellation to unreliable signals only. The performance of the proposed scheme is investigated through computer simulations. When the power control is perfect, the proposed scheme has similar or slightly better performance compared to the conventional (adaptive) parallel interference cancellation schemes. When the power control is imperfect and when there exists multipath fading, the proposed scheme performs better than the other schemes.

Adaptive multistage parallel interference cancellation for CDMA

Although the multistage interference cancellation detector is simple in structure, its performance degrades when the number of active users becomes large. In some cases, the performance is even worse than that without cancellation, due to the lack of the exact knowledge of the interfering signal in cancellation. Partial interference cancellation suggested by Divsalar and Simon (see IEEE Trans. Commun., vol.46, p.258-68, 1998) tries to remedy this weakness by reducing the cost of a wrong interference estimation through a weight in each stage. This paper presents an adaptive multistage structure based on the partial interference cancellation approach. In this structure, the weights are obtained by minimizing the mean-square error between the received signal and its estimate through a least mean square (LMS) algorithm. The resulting weights contain reliability information for the hard decisions made in the previous stage. Neither a training sequence nor a pilot signal is needed in the proposed scheme, and its complexity is much lower than that of linear multiuser detectors. Simulation results show that the proposed scheme can outperform some of the existing interference cancellation methods in both the additive white Gaussian noise (AWGN) and the multipath fading channels.