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Adaptive multi-stage parallel interference cancellation receiver for multi-rate DS-CDMA system
Abstract
An adaptive multi-stage parallel interference cancellation (PIC)
receiver is considered for a multi-rate DS-CDMA system. In each stage of
the adaptive multi-stage PIC receiver, multiple access interference
(MAI) estimates are obtained using the sub-bit estimates from the
previous stage and the adaptive weights for the sub-bit estimates. The
adaptive weights are obtained by minimizing the mean squared error
between the received signal and its estimate through a least mean square
(LMS) algorithm. It is shown that the adaptive multi-stage PIC receiver
achieves smaller BER than the matched filter receiver, multi-stage PIC
receiver, and multi-stage partial PIC receiver for the multi-rate
DS-CDMA system in a Rayleigh fading channel
... Therefore, an alternative to skip finding the inverse of the cross-correlation matrix by admitting a small degradation in performance, merits special attention. In [9], a multistage PPIC receiver for multirate DS-CDMA system using adaptive partial cancellation factors (PCF) was introduced. The multiuser receiver proposed in [9], has the following drawbacks. ...
... In [9], a multistage PPIC receiver for multirate DS-CDMA system using adaptive partial cancellation factors (PCF) was introduced. The multiuser receiver proposed in [9], has the following drawbacks. First of all, using the adaptive approach adds additional complexity to the scheme. ...
... In this receiver, the period of the highest-rate user is considered as the window of interference cancellation and eventually, after the required number of interference cancellation stages, all subsymbols along the period of each user will be added up in order to estimate the symbol of each user. Our proposed scheme provides the following new features compared to [9]. First of all, the channel has been extended to a frequency-selective fading channel instead of a flat-fading channel. ...
In this paper, we present a new subsymbol-based multistage multiuser receiver using partial parallel interference cancellation (PPIC) scheme for uplink multirate wideband UMTS-CDMA signals over a multipath fading channel. The multiuser detection process will take place during the window of the highest-rate user's symbol period which makes the proposed scheme more feasible to be implementated compared to the recently-proposed methods. Through numerical simulations, it will be shown that a considerable improvement in performance is gained through the stages of interference cancellation.
... Many multiuser Detectors (MUD) algorithms have been proposed in the literature to eliminate the MAI [5]. There are two main varieties of interference cancellation schemes, Serial Interference Cancellation (SIC) and Parallel Interference Cancellation (PIC) [6]. PIC can be classified into two categories, linear PIC (LPIC), and non Linear PIC. ...
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.
... In [9] Rennuci found an analytical solution to optimizing the partial cancellation factor. In [10, 11] the decision threshold for partial cancellation is adjusted according to statistic of its matched filter (MF) outputs. This partial cancellation factor requires K-Implementation. ...
... In [9] Rennuci found an analytical solution to optimizing the partial cancellation factor. In [10, 11] the decision threshold for partial cancellation is adjusted according to statistic of its matched filter (MF) outputs. This partial cancellation factor requires K-Implementation. ...
In this paper, a technique for improving parallel interference cancellation (PIC) receivers with linear estimators is studied
in a CDMA system under power control and near-far case. By multiplying the received signal for each user in early stages by
a factor superior than unity, the proposed technique significantly reduces the harmful impact of the bias upon BER performance
and requires only vector implementation under power control. In order to make the analysis more tractable, the proposed bias
mitigation technique is described for a synchronous multi-user communication scenario with binary signalling, non-orthogonal
multiple access interference in an additive white Gaussian noise channel.
We provide a rigorous mathematical analysis of two communication
strategies: soft decode-and-forward (soft-DF) for relay channels, and
soft partial interference-cancelation (soft-IC) for interference
channels. Both strategies involve soft estimation, which assists the
decoding process. We consider LDPC codes, not because of their practical
benefits, but because of their analytic tractability, which enables an
asymptotic analysis similar to random coding methods of information
theory. Unlike some works on the closely-related demodulate-and-forward,
we assume non-memoryless, code-structure-aware estimation. With soft-DF,
we develop {\it simultaneous density evolution} to bound the decoding
error probability at the destination. This result applies to erasure
relay channels. In one variant of soft-DF, the relay applies Wyner-Ziv
coding to enhance its communication with the destination, borrowing from
compress-and-forward. To analyze soft-IC, we adapt existing techniques
for iterative multiuser detection, and focus on binary-input additive
white Gaussian noise (BIAWGN) interference channels. We prove that
optimal point-to-point codes are unsuitable for soft-IC, as well as for
all strategies that apply partial decoding to improve upon single-user
detection (SUD) and multiuser detection (MUD), including Han-Kobayashi
(HK).
Parallel interference cancellation (PIC) is a family of low complexity multi-user detection methods for DS/CDMA systems. The performance of the multistage PIC depends on the decision function used in the interference cancellation. In this paper, we propose to provide the performance of PIC receiver using Xha function `clipping' with respect to decision threshold value. The decision threshold determines how much MAI is to be cancelled with hard decision and high probability. Otherwise, we used a soft bit decision to cancel only the interference of unreliable users form the received signal. This approach is original compared to PIC receiver with decision thresholds using null zone hard decision. It is shown that the proposed detector performs well under realistic conditions, particularly in the case of error optimisation of decision threshold value.
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.
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.
This paper deals with multi-user detection techniques in asynchronous
multibeam satellite communications. The proposed solutions are based on
successive interference cancellation architecture (SIC) and channel decoding
algorithms. The aim of these detection methods is to reduce the effect of
cochannel interference due to co-frequency access, and consequently, improves
the capacity of the mulitbeam communications systems, by improving frequency
reuse. Channel estimation allows the determination of interference
coefficients, which helps their effects compensation. The developed multiuser
detections techniques are iterative. Therefore, detection quality is improved
from a stage to another. Moreover, a signals combining method, which is
integrated into these detection solutions, enhances their capability. The
proposed solutions are evaluated through computer simulations, where an
asynchronous multibeam satellite link is considered over an AWGN channel. The
obtained simulation results showed the robustness of these multi-user detection
techniques.
In this paper, iterative multi-user detection techniques for multi-beam
communications are presented. The solutions are based on a successive
interference cancellation architecture and a channel decoding to treat the
co-channel interference. Beams forming and channels coefficients are estimated
and updated iteratively. A developed technique of signals combining allows
power improvement of the useful received signal; and then reduction of the bit
error rates with low signal to noise ratios. The approach is applied to a
synchronous multi-beam satellite link under an additive white Gaussian channel.
Evaluation of the techniques is done with computer simulations, where a noised
and multi-access environment is considered. The simulations results show the
good performance of the proposed solutions.
We formulated a Bayes optimum watermarking decoder and derived sub-optimum decoding algorithms for spread spectrum digital
image watermarking. The optimum decoder can be obtained by considering the posterior probability under the Gaussian assumption
for noise and attacks. The amount of calculation for the decoder is NP-hard. We, therefore, need to derive sub-optimum decoding
algorithms in order to decode the watermarks. The proposed decoders are multiple watermark decoders that estimate multiple
watermarks at the same time. These methods are based on the multi-stage demodulation method and the partial interference cancellation
method, which are two CDMA multiuser demodulation methods. We applied them to the digital watermarking scheme. When the original
image is blind, the image itself is regarded as noise. We, therefore, evaluated bit error rates both for cases when the original
image is informed and blind. As a result, we found both the multi-stage watermark decoder and the partial interference cancellation
decoder were effective for watermarking. The latter performed better than the former.
In this paper, we propose a new method of channel estimation for asynchronous additive white Gaussian noise channels in satellite communications. This method is based on signals correlation and multiuser interference cancellation which adopts a successive structure. Propagation delays and signals amplitudes are jointly estimated in order to be used for data detection at the receiver. As, a multiuser detector, a single stage successive interference cancellation (SIC) architecture is analyzed and integrated to the channel estimation technique and the whole system is evaluated. The satellite access method adopted is the direct sequence code division multiple access (DS CDMA) one. To evaluate the channel estimation and the detection technique, we have simulated a satellite uplink with an asynchronous multiuser access. Comment: 14 pages, 9 figures
We provide a rigorous mathematical analysis of two communication strategies:
soft decode-and-forward (soft-DF) for relay channels, and soft partial
interference-cancelation (soft-IC) for interference channels. Both strategies
involve soft estimation which assists the decoding process. We consider LDPC
codes, not because of their practical benefits, but because of their analytic
tractability, which enables an asymptotic analysis similar to random coding
methods of information theory. Unlike some works on the closely-related
demodulate-and-forward, we assume non-memoryless, code-structure-aware
estimation. With soft-DF, we develop {\it simultaneous density-evolution} to
bound the decoding error probability at the destination. This result applies to
erasure relay channels. In one variant of soft-DF, the relay applies Wyner-Ziv
coding to enhance its communication with the destination, borrowing from
compress-and-forward. To analyze soft-IC, we adapt existing techniques for
iterative multiuser detection, and focus on binary-input additive white
Gaussian noise (BIAWGN) interference channels. We prove that optimal
point-to-point codes are unsuitable for soft-IC, as well as for all strategies
that apply partial decoding to improve upon single-user detection (SUD) and
multiuser detection (MUD), including Han-Kobayashi (HK).
Different modulation schemes supporting multiple data rates in a Direct Sequence Code Division Multiple Access (DS-CDMA) system are studied. Both AWGN and multipath Rayleigh fading channels are considered. It is shown that the multi processing-gain scheme and the multi-channel scheme have almost the same performance. However, the multi-channel scheme may have some advantages due to easier code design and multiuser receiver construction. The drawback though, is the need for linear amplifiers also in mobile terminals. A multi-modulation scheme is also possible, but the performance for the users with the high data rates are significantly worse than for the other schemes. Furthermore multi chip-rate, parallel combinatory spread spectrum (PC/SS), pulse position modulation (PPM) and variable duty cycle schemes are discussed briefly.
An adaptive multistage parallel interference cancellation technique based on the partial interference cancellation (IC) approach of Divsalar and Simon (see Tech. Rep. 95-21, JPL Publication, 1995) was proposed by Xue, Weng, Le-Ngoc and Tahar (see Proc. of VTC'SS, Vancouver, Canada, 1999) for multipath fading channels. In this paper, the proposed technique is applied to develop a receiver structure in an AWGN environment. Unlike the scheme of Divsalar et al., the weighting factors in this proposed scheme are derived by minimizing the mean-square error between the received signal and its estimate through an LMS algorithm. Neither training sequence nor pilot signal is needed. The complexity of the proposed adaptive multistage PIC structure is much lower than that of linear multiuser detectors. Simulation results show the superior performance of the proposed receiver structure over an AWGN channel and in various conditions
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
A multiuser detection strategy for coherent demodulation in an
asynchronous code-division multiple-access system is proposed and
analyzed. The resulting detectors process the sufficient statistics by
means of a multistage algorithm based on a scheme for annihilating
successive multiple-access interference. An efficient real-time
implementation of the multistage algorithm with a fixed decoding delay
is obtained and shown to require a computational complexity per symbol
which is linear in the number of users K . Hence, the multistage
detector contrasts with the optimum demodulator, which is based on a
dynamic programming algorithm, has a variable decoding delay, and has a
software complexity per symbol that is exponential in K . An
exact expression is obtained and used to compute the probability of
error is obtained for the two-stage detector, showing that the two-stage
receiver is particularly well suited for near-far situations,
approaching performance of single-user communications as the interfering
signals become stronger. The near-far problem is therefore alleviated.
Significant performance gains over the conventional receiver are
obtained even for relatively high-bandwidth-efficiency situations
This paper presents the performance of groupwise successive
interference cancellation (GSIC) in a DS-CDMA system with multiple data
rates (multirate). The performance is evaluated both in AWGN and
Rayleigh fading channels. In the GSIC scheme users with the same data
rate are grouped and detected, using either a matched filter or a
parallel interference cancellation (PIC) receiver, interference between
the groups is cancelled in a successive order. The results show that in
a multirate system the GSIC yields a better performance than the PIC
receiver. Further a delay error of 0.1 Tc is found to be
tolerable
This report considers a general parallel interference cancellation scheme that significantly reduces the degradation effect of user interference but with a lesser implementation complexity than the maximum-likelihood technique. The scheme operates on the fact that parallel processing simultaneously removes from each user the interference produced by the remaining users accessing the channel in an amount proportional to their reliability. The parallel processing can be done in multiple stages. The proposed scheme uses tentative decision devices with different optimum thresholds at the multiple stages to produce the most reliably received data for generation and cancellation of user interference. The 1-stage interference cancellation is analyzed for three types of tentative decision devices, namely, hard, null zone, and soft decision, and two types of user power distribution, namely, equal and unequal powers. Simulation results are given for a multitude of different situations, in particular, those cases for which the analysis is too complex.
A multi-stage partial parallel interference cancellation receiver
is proposed for the multi-rate DS-CDMA system which adopts the multiple
processing gain scheme. In each stage of the proposed receiver, partial
cancellation is performed with an adaptive decision threshold which is
computed from the matched filter outputs of the previous stage. The BER
performance of the proposed receiver is obtained by simulation in a
Rayleigh fading channel. It is shown that the proposed receiver achieves
smaller BER than the multi-stage parallel interference cancellation
receiver and extended group-wise successive interference cancellation
receiver in the multi-rate DS-CDMA system
This work is an extension of the multi-rate LMMSE detectors (Ge
1997) for asynchronous multi-rate CDMA systems. The proposed LMMSE
detectors can work on dual-rate mode according to different
quality-of-service (QoS) requirements and computational constraints. In
using the proposed multirate LMMSE detectors, only the signature and
timing information of the desired user are required. The proposed
detectors can achieve better detection performance with less computation
than the dual-rate decorrelating detectors. Adaptive schemes of
implementing the proposed detectors can handle both synchronous and
asynchronous channels as long as the signature and timing information on
the desired user is available
This paper addresses the use of decorrelating detectors for a dual rate DS/CDMA system that serves both low bit rate and high bit rate users. We assume that in an interval of duration T
0, a low rate user transmits one bit while a high rate user transmits M bits. Applying a standard decorrelator to the interval of duration T
0 yields an M bit processing delay for high rate users and a computational complexity that grows with M. In this paper, we propose a decorrelator that generates bit decisions for each high rate user in every subinterval of duration T0/M. To decode a low rate user, a soft decoding rule applies maximal ratio combining on M separate decorrelated outputs of each low rate user. The soft decoding dual rate decorrelator eliminates the bit processing delay for high rate users and also reduces the computational complexity of a standard decorrelator. Further, it is shown that the asymptotic efficiency of the standard decorrelator is greater than or equal to the proposed decorrelator. By evaluation, it is observed that when the signature sequences have good correlation properties, the proposed soft decoding decorrelator is found to perform nearly as well as the standard decorrelator. However, when the signature sequences have high cross-correlation, then the proposed decorrelator suffers in terms of bit error rate while retaining the near-far resistance property.
The basis for any air interface design is how the common
transmission medium is shared between users (i.e., multiple access
scheme). The underlying multiple access method for all mobile radio
systems is FDMA. The performance of TDMA and CDMA has been subject to
vigorous debate, without any definitive conclusions. This article gives
an overview of worldwide research and standardization activities related
to the multiple access schemes for third-generation mobile
communications systems IMT-2000 and UMTS