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14
Noncoherent Multiuser Detection for CDMA Systems with Nonlinear Modulation: A NonBayesian Approach
 in Proc. IEEE Int. Symp. Information Theory
, 2001
"... This paper considers the problem of multiuser detection for a system in which each user employs nonlinear modulation, with an emphasis on noncoherent detection techniques which do not require knowledge of the users' channel parameters at the receiver. Our goals are to gain fundamental insight into t ..."
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Cited by 18 (6 self)
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This paper considers the problem of multiuser detection for a system in which each user employs nonlinear modulation, with an emphasis on noncoherent detection techniques which do not require knowledge of the users' channel parameters at the receiver. Our goals are to gain fundamental insight into the capabilities of multiuser detection in such a setting, and to provide practical algorithms that perform better than conventional matched filter reception. We begin by providing fundamental performance benchmarks by considering coherent maximum likelihood (ML) detection, which requires knowledge of the users' channel parameters, as well as noncoherent detection, formulated in a nonBayesian generalized likelihood ratio test (GLRT) framework. The asymptotic performance of each detector, as the noise level vanishes, is characterized, yielding simple geometric criteria for nearfar resistance. In general, both the ML and GLRT detectors have complexity which is exponential in the number of users. We therefore propose the more practical sequential decision projection (SDP) detector, which has complexity which is quadratic in the number of users. It is shown that the SDP detector has nonzero asymptotic efficiency if the users' powers are suitably disparate.
A framework for spectrally efficient noncoherent communication
, 2000
"... Abstract—This paper considers noncoherent communication over a frequencynonselective channel in which the timevarying channel gain is unknown a priori, but is approximately constant over a coherence interval. Unless the coherence interval is large, coherent communication, which requires explicit c ..."
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Cited by 17 (4 self)
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Abstract—This paper considers noncoherent communication over a frequencynonselective channel in which the timevarying channel gain is unknown a priori, but is approximately constant over a coherence interval. Unless the coherence interval is large, coherent communication, which requires explicit channel estimation and tracking prior to detection, incurs training overhead which may be excessive, especially for multipleantenna communication. In contrast, noncoherent detection may be viewed as a generalized likelihood ratio test (GLRT) which jointly estimates the channel and the data, and hence does not require separate training. The main results in this paper are as follows 1) We develop a “signal space ” criterion for signal and code design for noncoherent communication, in terms of the distances of signal points from the decision boundaries. 2) The noncoherent metric thus obtained is used to guide the design of signals for noncoherent communication that are based on amplitude/phase constellations. These are significantly more efficient than conventional differential phaseshift keying (PSK), especially at high signaltonoise ratio (SNR). Also, known results on the highSNR performance of multiplesymbol demodulation of differential PSK are easily inferred from the noncoherent metric. 3) The GLRT interpretation is used to obtain nearoptimal lowcomplexity implementations of noncoherent block demodulation. In particular, this gives an implementation of multiple symbol demodulation of differential PSK, which is of linear complexity (in the block length) and whose degradation from the exact, exponential complexity, implementation can be made as small as desired. Index Terms—Differential phaseshift keying (PSK), differential quadrature amplitude modulation (QAM), generalized likelihood ratio test (GLRT), noncoherent communication, noncoherent distance. I.
Noncoherent Multiuser Detection for Nonlinear Modulation over the RayleighFading Channel
, 2001
"... The jointly optimum noncoherent multiuser detector is obtained for nonlinear nonorthogonal modulation over the frequency nonselective Rayleighfading multipleaccess channel. Upper and lower bounds on average biterror probability are derived. While these bounds are numerically computable, they are ..."
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Cited by 9 (7 self)
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The jointly optimum noncoherent multiuser detector is obtained for nonlinear nonorthogonal modulation over the frequency nonselective Rayleighfading multipleaccess channel. Upper and lower bounds on average biterror probability are derived. While these bounds are numerically computable, they are too complicated to give insight into the relative influence of system parameters on the essential behavior of the biterror rate. Hence this paper develops an asymptotic analysis of the average biterror probability. In particular, it is shown that the upper and lower bounds are asymptotically convergent. An exact formula for the asymptotic efficiency of the optimum noncoherent detector is derived. Interestingly, the asymptotic efficiency is found to be positive and independent of the signal strengths of the interfering users. In contrast, the noncoherent detector which would be optimal in a singleuser channel (the "conventional detector"), when used over the multiuser channel, has an asymptotic efficiency that is identically equal to zero no matter what the powers of the interferers may be. While the performance analysis of the optimum detector provides the fundamental limit on achievable error rate, the implementational complexity of the optimum detector is exponential in the number of users. As a lowcomplexity alternative, a decorrelative energy detector is also proposed and analyzed in terms of error probability and asymptotic efficiency.
Noncoherent MMSE Multiuser Receivers and Their Blind Adaptive Implementations
 IEEE Trans. Commun
, 2002
"... Three noncoherent minimum meansquared error (MMSE)based multiuser receivers are proposed for multipulse modulation. These receivers have a common MMSE prefilter and are followed by one of three phaseindependent decision rules. The simplest decision rule selects the maximum magnitude of the MMSE f ..."
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Cited by 5 (2 self)
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Three noncoherent minimum meansquared error (MMSE)based multiuser receivers are proposed for multipulse modulation. These receivers have a common MMSE prefilter and are followed by one of three phaseindependent decision rules. The simplest decision rule selects the maximum magnitude of the MMSE filter outputs, and the other two account for the secondorder statistics of the residual multipleaccess interference that remains after MMSE filtering. Blind adaptive algorithms are then proposed for the three noncoherent MMSE receivers. The common adaptive algorithm for the MMSE prefilter, which is based on the stochastic approximation method, is shown to converge in the meansquared error sense to the nonblind MMSE prefilter. Our convergence analysis yields new insight into the tradeoff between the rate of convergence and the residual meansquared error. The noncoherent blind receivers obtained here do not require the knowledge of the received signals of any of the interfering users, and are hence wellsuited for distributed implementation in cellular wireless networks or in communication systems that must operate in noncooperative environments.
Modulation and Coding for Noncoherent Communications
, 2002
"... Until recently, the theory of noncoherent communications was premised on the use of orthogonal multipulse modulation such as frequency shift keying. The main drawback of this modulation scheme has been its poor spectral efficiency (rate/bandwidth). This paper considers instead the more general non ..."
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Cited by 4 (3 self)
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Until recently, the theory of noncoherent communications was premised on the use of orthogonal multipulse modulation such as frequency shift keying. The main drawback of this modulation scheme has been its poor spectral efficiency (rate/bandwidth). This paper considers instead the more general nonorthogonal multipulse modulation (NMM) technique. Optimal and suboptimal noncoherent detection strategies for NMM are reviewed and their asymptotic (high SNR) performances are characterized for the additive Gaussian as well as the Rayleigh fading channels. The resulting nonEuclidean distance measures are then used to design NMM signal sets that yield significantly higher bandwidth efficiencies than their orthogonal counterparts. NMM in conjunction with convolutional coding is also studied as a way to improve energy efficiency. Several optimal convolutional codes are examined together with our signal designs. An introduction to equalization on the noncoherent channel is also presented and illustrated by example. This paper thus contains several new results and attempts at the same time to give a tutorial exposition of the subject of noncoherent communications.
Noncoherent MMSE Interference Suppression for DSCDMA
 in Proc. IEEE Int. Conf. Commun. (ICC
, 2001
"... Abstract — In this paper, a novel robust noncoherent receiver for MMSE interference suppression for DS–CDMA is proposed. The receiver consists of an MMSE filter and a decision–feedback differential detector (DF–DD). The performance of the proposed scheme is investigated analytically and by computer ..."
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Cited by 4 (1 self)
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Abstract — In this paper, a novel robust noncoherent receiver for MMSE interference suppression for DS–CDMA is proposed. The receiver consists of an MMSE filter and a decision–feedback differential detector (DF–DD). The performance of the proposed scheme is investigated analytically and by computer simulations. It is shown that the loss compared to coherent MMSE interference suppression is limited and can be made arbitrarily small by increasing the observation window used for calculation of the reference symbol of the DF–DD. For adjustment of the MMSE filter coefficients a noncoherent normalized least– mean–square (NC–NLMS) algorithm is proposed which is roboust against channel phase variations. 1.
Noncoherent DecisionFeedback Multiuser Detection
, 2000
"... The problem of noncoherent multiuser detection for multipulse modulation over the Gaussian multiuser channel is studied. It is assumed that neither the energies nor the carrier phases of the signals of any of the users are available at the receiver. Recently, a postdecorrelative generalized likelih ..."
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Cited by 3 (0 self)
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The problem of noncoherent multiuser detection for multipulse modulation over the Gaussian multiuser channel is studied. It is assumed that neither the energies nor the carrier phases of the signals of any of the users are available at the receiver. Recently, a postdecorrelative generalized likelihood ratio test (GLRT) based detector was proposed as a solution to this problem. In this paper, we introduce the concept of noncoherent decision feedback (DF) that forms the basis for an improved solution to the same problem. The users are detected sequentially in some fixed order, and the decision for a particular user takes advantage of the reduction of uncertainty associated with the signal space resulting from decisions already made for previous users. In contrast to coherent DF, therefore, the feedforward and feedback transformations in the noncoherent case are themselves functions of the matched filter outputs. An efficient implementation of the noncoherent DF detector for Mary modulation and aedimen sional signal space requires O(Mae) computational complexity per user. Upper and lower bounds on its symbol error probability are obtained. It is shown that significant improvements over the postdecorrelative GLRTbased detector are often possible. Sufficient conditions are obtained which guarantee, without ignoring errorpropagation effects, that the high signaltonoise performance of the DF strategy can be as good as its genieaided version in which perfect past users' decisions are used.
Constrained detection for noncoherent nonlinear multiuser communications
 In Proceedings of 34th Asilomar Conference on Signals, Systems and Computers
, 2000
"... sinhar @ winlab.rutgers.edu yener @ eecs.lehigh.edu ryates @ winlab.rutgers.edu We consider noncoherent multiuser detection techniques for a system with users employing nonlinear modulation using nonorthogonal signals. Our aim is to investigate nearoptimum noncoherent multiuser detection techniques ..."
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Cited by 3 (3 self)
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sinhar @ winlab.rutgers.edu yener @ eecs.lehigh.edu ryates @ winlab.rutgers.edu We consider noncoherent multiuser detection techniques for a system with users employing nonlinear modulation using nonorthogonal signals. Our aim is to investigate nearoptimum noncoherent multiuser detection techniques that utilize the structure of the received signuls while retaining reasonable complexity. We explore detectors that are derived using nonlinear programming approximations of the maximum likelihood multiuser detector as well as soft interference cancellers. We also propose a class of detectors called the partial detectors which improve the perfomnce of the decorrelator and MMSE type detectors. We evaluate the proposed detectors ’ performunce to provide numerical comparisons. I.
Beamforming, diversity, and interference rejection for multiuser communication over fading channels with a receive antenna array
 IEEE Trans
"... Abstract—We considerary communication with users over a space diversity channel, consisting of a single transmit antenna for each user and multiple receive antennas. We examine two different flat fading models, namely, phase coherent wavefront fading and noncoherent elementtoelement fading. In th ..."
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Cited by 1 (0 self)
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Abstract—We considerary communication with users over a space diversity channel, consisting of a single transmit antenna for each user and multiple receive antennas. We examine two different flat fading models, namely, phase coherent wavefront fading and noncoherent elementtoelement fading. In the case of wavefront fading, the fade is constant across the face of the receive antenna and we can associate an angle of arrival to the signal. We present a variation of the MUSIC algorithm for estimating this parameter and use it to form a spatial beam. In the case of noncoherent elementtoelement fading, the fading path to each sensor is different (although possibly correlated) and no angle of arrival can be exploited for conventional beamforming. For each channel model, we develop several detection strategies which assume various amounts of prior information about the fading. We then consider blind extensions of these detectors based on subspace tracking, which do not require a prior model for the interfering users ’ signals. Index Terms—Antenna arrays, blind detection, direction of arrival (DOA) estimation, diversity reception, fading channels, interference rejection, multiuser detection, space–time processing. I.
Softdecision metrics for coded orthogonal signaling in symmetric alphastable noise,” ICASSP 2005
"... This paper derives new soft decision metrics for coded orthogonal signaling in symmetric αstable noise, which has been used to model impulsive noise. In addition to the optimum metrics for Gaussian (α =2) noise and Cauchy (α =1) noise, a class of generalized likelihood ratio (GLR) metrics with lowe ..."
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Cited by 1 (1 self)
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This paper derives new soft decision metrics for coded orthogonal signaling in symmetric αstable noise, which has been used to model impulsive noise. In addition to the optimum metrics for Gaussian (α =2) noise and Cauchy (α =1) noise, a class of generalized likelihood ratio (GLR) metrics with lower side information requirements is derived. Through numerical results for a turbo code example, the Cauchy decoder is found to be robust for a wide range of α, and GLR metrics are found which provide performance gains relative to the Gaussian metric, but with lower complexity and less a priori information. 1.