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11
Decision Feedback Multiuser Detection: A Systematic Approach
, 1999
"... A systematic approach to decision feedback multiuser detection is introduced for the joint detection of symbols of K simultaneously transmitting users of a synchronous correlated waveform multipleaccess (CWMA) channel with Gaussian noise. A new performance criterion called symmetric energy is defi ..."
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Cited by 53 (11 self)
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A systematic approach to decision feedback multiuser detection is introduced for the joint detection of symbols of K simultaneously transmitting users of a synchronous correlated waveform multipleaccess (CWMA) channel with Gaussian noise. A new performance criterion called symmetric energy is defined which is a lownoise indicator of the joint error rate that at least one user is detected erroneously. Even the best linear detectors can perform poorly in terms of symmetric energy compared to the maximumlikelihood detector. A general class of decision feedback detectors is defined with O(K) implementational complexity per user. The symmetric energy of arbitrary DFD's and bounds on their asymptotic effective energy (AEE) performance are obtained along with an exact biterror rate and AEE analysis for the decorrelating DFD. The optimum DFD that maximizes symmetric energy is obtained. Each one of the optimum, decorrelating, and conventional DFD's, that correspond to the orders in which the users can be detected, are shown to outperform the linear optimum, decorrelating, and conventional detectors, respectively, in terms of symmetric energy. Moreover, algorithms are obtained for determining the choice of order of detection for the three DFD's which guarantee that they uniformly (userwise) outperform their linear counterparts. In addition to optimality in symmetric energy, it is also shown that under certain conditions, the optimum DFD achieves the AEE performance of the exponentially complex maximumlikelihood detector for all users simultaneously. None of the results of this paper make the perfect feedback assumption. The implications of our work on power control for multiuser detection are also discussed.
Convergence of linear interference cancellation multiuser receivers
 IEEE Trans. Commun
, 2001
"... Abstract—We consider the convergence in norm of several iterative implementations of linear multiuser receivers, under the assumption of long random spreading sequences. We find that asymptotically, linear parallel interference cancellation diverges for systems loads of greater than about 17%. Using ..."
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Cited by 16 (3 self)
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Abstract—We consider the convergence in norm of several iterative implementations of linear multiuser receivers, under the assumption of long random spreading sequences. We find that asymptotically, linear parallel interference cancellation diverges for systems loads of greater than about 17%. Using known results from the theory of iterative solutions for linear systems we derive optimal or near optimal relaxation parameters for parallel (first– and secondorder stationary, Chebyshev) and serial cancellation (successive relaxation) methods. An analytic comparison of the asymptotic convergence factor for the various methods is given. Simulations are used to verify results for finite size systems. Index Terms—CDMA, interference cancellation, iterative methods, multistage receivers, multiuser receivers, random sequences. I.
On the Performance of Linear Parallel Interference Cancellation
, 1999
"... 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 ..."
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Cited by 12 (0 self)
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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 twostage LPIC detector to the original multistage detector proposed by Varanasi and Aazhang for CDMA systems. The general Mstage 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...
On the Dimensional Limitations of Linear Multiuser Detection
 In Proc. 36th Annual Allerton Conference on Communication, Control, and Computing
, 1998
"... Limitations on the interference suppression capabilities of linear multiuser detection due to dimensional constraints are studied in this paper. Generalized linear multiuser detection is defined for CDMA systems with arbitrary modulation and coding schemes and channel characteristics. Conditions are ..."
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Cited by 1 (1 self)
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Limitations on the interference suppression capabilities of linear multiuser detection due to dimensional constraints are studied in this paper. Generalized linear multiuser detection is defined for CDMA systems with arbitrary modulation and coding schemes and channel characteristics. Conditions are derived for the existence of linear decorrelators in this general framework and a solution for the generalized linear decorrelator is presented when it exists. This theory is applied to determine the ecacy of linear multiuser detection in important scenarios that include the presence of user asynchronism, multipath propagation, error control coding and block modulation (such as Mary orthogonal modulation in IS95 uplink). Ways to overcome the dimensional limitations of linear multiuser detection are to use larger symbol constellations that span a smaller number of dimensions, or to employ nonlinear techniques such as nonlinear multistage interference cancellation.
SINR, Power Efficiency, and Theoretical System Capacity of Parallel Interference Cancellation
, 2000
"... In this paper, we analytically derive an exact expression for the SINR of the twostage parallel interference cancellation (PIC) multiuser detector in a synchronous, nonorthogonal, binary, CDMA communication system. In order to obtain an intuitive understanding, we consider an approximation to the S ..."
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Cited by 1 (0 self)
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In this paper, we analytically derive an exact expression for the SINR of the twostage parallel interference cancellation (PIC) multiuser detector in a synchronous, nonorthogonal, binary, CDMA communication system. In order to obtain an intuitive understanding, we consider an approximation to the SINR expression that is well justified in scenarios where the error probability of the matched filter detector is reasonably low. Given a specific SINR requirement for each user in the system, we derive an expression for the minimum transmit power necessary to meet this requirement when the twostage PIC detector is used. We also derive an expression for a measure of the theoretical system capacity of PIC, defined as the maximum number of users possible in a system with finite available transmit power. Analytical results comparing PIC to the successive interference cancellation (SIC) detector and matched filter (MF) detector show that PIC requires less total transmit power and has greater the...
Successive Interference Cancellation Using Constellation Structure
"... Abstract—An approach to successive interference cancellation is presented that exploits the structure of the combined signal constellation in a multiuser system. The asymptotic conditional efficiency of a successive detector is defined, based on the conditional probability of error at high signalto ..."
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Cited by 1 (1 self)
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Abstract—An approach to successive interference cancellation is presented that exploits the structure of the combined signal constellation in a multiuser system. The asymptotic conditional efficiency of a successive detector is defined, based on the conditional probability of error at high signaltonoise ratio (SNR), as a quantitative measure for evaluating detector performance at each stage of successive detection. The joint successive interference canceller (JSIC) that jointly detects consecutive users in an ordered set is proposed as an improvement over the conventional successive interference canceller (SIC). The maximal asymptotic conditional efficiency successive interference canceller (MACESIC) and its JSIC equivalent (MACEJSIC) are also derived as the multiuser detectors that achieve the highest asymptotic conditional multiuser efficiency at each stage of successive detection among all possible SIC and JSIC detectors, respectively, given any particular ordering of user signals. The ordering of users achieving the highest asymptotic conditional efficiency at each stage of successive detection is derived. Performance bounds based on the signal constellation structure are derived to quantify the gain of the MACEJSIC detector compared to the MACESIC detector. Index Terms—Asymptotic efficiency, convex optimization, detection, interference cancellation, multiuser detection. I.
Multistage Detection Using Constellation Structure
"... Abstract — A structural approach to multistage detection is proposed where the joint information between interfering users is utilized to give better soft decisions on the user bits in each stage or iteration. The key idea is to use the structure of the multiuser signal constellation to achieve hi ..."
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Abstract — A structural approach to multistage detection is proposed where the joint information between interfering users is utilized to give better soft decisions on the user bits in each stage or iteration. The key idea is to use the structure of the multiuser signal constellation to achieve higher performance in terms of the biterrorrate, particularly at high SNR, and reduce the possibility of error propagation or limit cycles. A maximal asymptotic efficiency detector is employed as the first stage to generate better initial estimates of the user bits, followed by a local maximum likelihood kernel for subsequent stages. The proposed detector is particularly attractive for heavily correlated or overloaded multiuser systems. The proposed multistage detector also includes the possibility of known memoryless nonlinearity in the system, e.g., the nonlinearity introduced due to saturation by the downlink RF amplifier in satellite communication systems. I.
Interference Suppression for Memoryless Nonlinear Multiuser Systems Using Constellation Structure
"... Abstract—A generalized concept of interference suppression is introduced for multiuser systems with a known memoryless transmit nonlinearity, such as in the downlink amplifier of a satellite communication system. By considering the operation of commonly used multiuser detection techniques from a vi ..."
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Abstract—A generalized concept of interference suppression is introduced for multiuser systems with a known memoryless transmit nonlinearity, such as in the downlink amplifier of a satellite communication system. By considering the operation of commonly used multiuser detection techniques from a viewpoint of constellation structure, we extend these notions to nonlinear multiuser systems. We also analyze the performance of such multiuser detectors in terms of their asymptotic multiuser error exponents, which reduce to the asymptotic multiuser effective energies for the respective detectors in the absence of nonlinearity. The asymptotic conditional error exponent is introduced as a quantitative measure for evaluating nonlinear multiuser detectors based on the conditional probability of error at high signaltonoise ratio (SNR). The optimal affine detector that maximizes the asymptotic error exponent for a given user is derived
1 Successive Interference Cancellation using Constellation Structure
"... An approach to successive interference cancellation is presented that exploits the structure of the combined signal constellation in a multiuser system. The asymptotic conditional efficiency of a successive detector is defined, based on the conditional probability of error at high signaltonoise r ..."
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An approach to successive interference cancellation is presented that exploits the structure of the combined signal constellation in a multiuser system. The asymptotic conditional efficiency of a successive detector is defined, based on the conditional probability of error at high signaltonoise ratio (SNR), as a quantitative measure for evaluating detector performance at each stage of successive detection. The joint successive interference canceller (JSIC) that jointly detects consecutive users in an ordered set is proposed as an improvement over the conventional successive interference canceller (SIC). The maximal asymptotic conditional efficiency successive interference canceller (MACESIC) and its JSIC equivalent (MACEJSIC) are also derived as the multiuser detectors that achieve the highest asymptotic conditional multiuser efficiency at each stage of successive detection among all possible SIC and JSIC detectors, respectively, given any particular ordering of user signals. The ordering of users achieving the highest asymptotic conditional efficiency at each stage of successive detection is derived. Performance bounds based on the signal constellation structure are derived to quantify the gain of the MACEJSIC detector compared to the MACESIC detector. I.
Improved Multistage Parallel Interference Cancellation Using Limit Cycle Mitigation
"... Abstract — This paper describes a new technique for improving the performance of multistage parallel interference cancellation (PIC) multiuser detection. The focus of the paper is on the harddecision multistage PIC detector due to the fact that it possesses two desirable properties: (a) very low co ..."
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Abstract — This paper describes a new technique for improving the performance of multistage parallel interference cancellation (PIC) multiuser detection. The focus of the paper is on the harddecision multistage PIC detector due to the fact that it possesses two desirable properties: (a) very low computational complexity in binary communication systems and (b) the optimum (joint maximum likelihood) bit estimates are a fixed point of the harddecision PIC iteration. Unfortunately, the harddecision PIC iteration is also known to sometimes demonstrate two modes of undesirable convergence behavior: convergence to nonoptimum fixed points and limit cycles. This paper demonstrates that limit cycles tend to occur with much greater probability than convergence to nonoptimum fixed points. To improve the performance of the harddecision multistage PIC detector, we propose a reactive limit cycle mitigation algorithm. The results suggest that significant performance improvements may be possible in some cases with only modest increases in computational complexity. I.