This paper analyzes the performance of the linear parallel interference cancellation (LPIC) multiuser detector in a synchronous multiuser communication scenario with binary signaling, nonorthogonal multiple access interference, and an additive white Gaussian noise channel. The LPIC detector has been considered in the literature lately due to its low computational complexity, potential for good performance under certain operating conditions, and close connections to the decorrelating detector. In this paper, we compare the performance of the two-stage LPIC detector to the original multistage detector proposed by Varanasi and Aazhang for CDMA systems. The general M-stage LPIC detector is compared to the conventional matched filter detector to describe operating conditions where the matched filter detector outperforms the LPIC detector in terms of error probability at any stage M. Analytical results are presented that show that the LPIC detector may exhibit divergent error probability perf...

In this paper, a novel multiuser detector for direct sequence code-division multiple-access (DS-CDMA) is proposed. The receiver performs iterated soft decision interference cancellation (ISDIC) based on multiuser interference suppression filters designed for minimization of the mean-squared error. Assuming a complex modulation format, we show that the multiuser interference becomes rotationally variant in course of the iterations. Regarding this rotational variance in the design of the multiuser interference suppression filter, the presented iterative multiuser detector achieves significant performance gains compared to conventional ISDIC employing a standard MMSE filter which is optimum only for rotationally invariant multiuser interference.

Successive interference cancellation, in conjunction with very low rate convolutional codes, has been shown to approach the Shannon capacity of a Gaussian channel [1]. This approach to CDMA is very well suited to asynchronous (uplink) wireless channels. However, accurate phase and amplitude estimation is required for effective operation. In this paper, we develop a power control algorithm specifically designed to relax the requirements on estimation accuracy. Using this power control algorithm in conjunction with superorthogonal codes and successive interference cancellation, it is shown that even with average estimation error up to 30%, the capacity over an IS-95 CDMA system can be increased by an order of magnitude. I.

Successive interference cancellation (SIC) is a family of low complexity multiuser detection methods for DS/CDMA systems. The performance of the multistage SIC depends on the decision function used in the interference cancellation iterations, whether hard decision, soft decision or linear decision. Due to error propagation, multistage SIC with hard data bit decisions may perform more poorly than multistage SIC with linear or soft decision functions. We propose and analyze a family of generalized unit-clipper bit decision functions that better combine linear and hard decisions. Performance within 0.4 dB of the single-user bound can be obtained. We then robustify the above soft-decision SIC to time delay errors as large as half a PN chip.

Abstract—Least mean square-partial parallel interference cancelation (LMS-PPIC) is a partial interference cancelation using adaptive multistage structure in which the normalized least mean square (NLMS) adaptive algorithm is engaged to obtain the cancelation weights. The performance of the NLMS algorithm is mostly dependent to its step-size. A fixed and non-optimized step-size causes the propagation of error from one stage to the next one. When all user channels are balanced, the unit magnitude is the principal property of the cancelation weight elements. Based on this fact and using a set of NLMS algorithms with different step-sizes, the parallel LMS-PPIC (PLMS-PPIC) method is proposed. In each iteration of the algorithm, the parameter estimate of the NLMS algorithm is chosen to match the elements ’ magnitudes of the cancelation weight estimate with unity. Simulation results are given to compare the performance of our method with the LMS-PPIC algorithm in three cases: balanced channel, unbalanced channel and time varying channel. I.

In this paper, we propose a reduced complexity and power efficient System-on-Chip (SoC) architecture for adaptive interference suppression in CDMA systems. The adaptive Parallel-Residue-Compensation architecture leads to significant performance gain over the conventional interference cancellation algorithms. The multi-code commonality is explored to avoid the direct Interference Cancellation (IC), which reduces the IC complexity from O(K 2 N) to O(KN). The physical meaning of the complete versus weighted IC is applied to clip the weights above a certain threshold so as to reduce the VLSI circuit activity rate. Novel scalable SoC architectures based on simple combinational logic are proposed to eliminate dedicated multipliers with at least 10 × saving in hardware resource. A Catapult C High Level Synthesis methodology is apply to explore the VLSI design space extensively and achieve at least 4 × speedup. Multi-stage Convergence-Masking-Vector combined with clock gating is proposed to reduce the VLSI dynamic power consumption by up to 90%.

In this paper, we investigate the performance of adaptive interference cancellation receivers for the wideband code division multiple access (WCDMA) uplink physical data channel. For the WCDMA uplink waveform, we derive a blind adaptive receiver (BAR) based on the constant modulus algorithm (CMA), and an multistage adaptive parallel interference cancellation (APIC) receiver. In order to improve the performance of the APIC receiver, we propose a hybrid APIC (H-APIC) receiver structure which uses the CMA based BAR as the first stage of the APIC. We evaluate and compare the performance of the above receivers in a nearfar scenario and show that the proposed H-APIC receiver performs better than the APIC receiver. I.

newselecTCx and adaptive parallelinterferenc cterferenc tecerfer is presented for crf division multiple aclti systems. The proposed tecosedf performs a parallelinterferenc cterferenc in multistage, and thecfxxxVVfRTME cV6fcVVf isreduc6 by applying thecfM-CxCfRT6 to unreliable signals only. Theperformanc of the proposedscpos is investigated throughcoughfM simulations. When the powercwerfq isperfecq the proposedscpos has similar or slightly betterperformanc crforma to thecfMC[-EfRq- (adaptive) parallelinterferenc cterferenc scterfe When the power cowerf is imperfec and when there exists multipath fading, the proposedscpos performs better than the otherscerfxE ? 2002 Elsevier Scvier B.V. All rights reserved.

Robust blind PIC with adaptive despreader and improved

Abstract—We address the problem of joint beamforming and multipath channel parameters estimation in Wideband Code Division Multiple Access (WCDMA) communication systems that employ Multiple-Access Interference (MAI) suppression techniques in the uplink (from mobile to base station). Most of the existing schemes rely on time multiplex a training sequence with the user data. In WCDMA, the channel parameters can also be estimated from a code multiplexed common pilot channel (CPICH) that could be corrupted by strong interference resulting in a bad estimate. In this paper, we present new methods to combine interference suppression together with channel estimation when using multiple receiving antennas by using adaptive signal processing techniques. Computer simulation is used to compare between the proposed methods and the existing conventional estimation techniques. Keywords—Adaptive arrays, channel estimation, interference cancellation, wideband code division multiple access (WCDMA). D I.