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48
Iterative (turbo) soft interference cancellation and decoding for coded CDMA
 IEEE Trans. Commun
, 1999
"... Abstract — The presence of both multipleaccess interference (MAI) and intersymbol interference (ISI) constitutes a major impediment to reliable communications in multipath codedivision multipleaccess (CDMA) channels. In this paper, an iterative receiver structure is proposed for decoding multiuse ..."
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Cited by 393 (19 self)
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Abstract — The presence of both multipleaccess interference (MAI) and intersymbol interference (ISI) constitutes a major impediment to reliable communications in multipath codedivision multipleaccess (CDMA) channels. In this paper, an iterative receiver structure is proposed for decoding multiuser information data in a convolutionally coded asynchronous multipath DSCDMA system. The receiver performs two successive softoutput decisions, achieved by a softinput softoutput (SISO) multiuser detector and a bank of singleuser SISO channel decoders, through an iterative process. At each iteration, extrinsic information is extracted from detection and decoding stages and is then used as a priori information in the next iteration, just as in Turbo decoding. Given the multipath CDMA channel model, a direct implementation of a slidingwindow SISO multiuser detector has a prohibitive computational complexity. A lowcomplexity SISO multiuser detector is developed based on a novel nonlinear interference suppression technique, which makes use of both soft interference cancellation and instantaneous linear minimum meansquare error filtering. The properties of such a nonlinear interference suppressor are examined, and an efficient recursive implementation is derived. Simulation results demonstrate that the proposed lowcomplexity iterative receiver structure for interference suppression and decoding offers significant performance gain over the traditional noniterative receiver structure. Moreover, at high signaltonoise ratio, the detrimental effects of MAI and ISI in the channel can almost be completely overcome by iterative processing, and singleuser performance can be approached. Index Terms — Coded CDMA, instantaneous MMSE filtering, multiuser detection, soft interference cancellation, Turbo processing.
Spectral Efficiency of CDMA with Random Spreading
 IEEE TRANS. INFORM. THEORY
, 1999
"... The CDMA channel with randomly and independently chosen spreading sequences accurately models the situation where pseudonoise sequences span many symbol periods. Furthermore, its analysis provides a comparison baseline for CDMA channels with deterministic signature waveforms spanning one symbol per ..."
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Cited by 270 (22 self)
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The CDMA channel with randomly and independently chosen spreading sequences accurately models the situation where pseudonoise sequences span many symbol periods. Furthermore, its analysis provides a comparison baseline for CDMA channels with deterministic signature waveforms spanning one symbol period. We analyze the spectral efficiency (total capacity per chip) as a function of the number of users, spreading gain, and signaltonoise ratio, and we quantify the loss in efficiency relative to an optimally chosen set of signature sequences and relative to multiaccess with no spreading. White Gaussian background noise and equalpower synchronous users are assumed. The following receivers are analyzed: a) optimal joint processing, b) singleuser matched filtering, c) decorrelation, and d) MMSE linear processing.
Iterative Detection in CodeDivision MultipleAccess with Error Control Coding
, 1998
"... A codedivision multipleaccess system with channel coding may be viewed as a seriallyconcatenated coded system. In this paper we propose a low complexity method for decoding the resulting inner code (due to the spreading sequence), which allows iterative (turbo) decoding of the seriallyconcate ..."
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Cited by 72 (15 self)
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A codedivision multipleaccess system with channel coding may be viewed as a seriallyconcatenated coded system. In this paper we propose a low complexity method for decoding the resulting inner code (due to the spreading sequence), which allows iterative (turbo) decoding of the seriallyconcatenated code pair. The perbit complexity of the proposed decoder increases only linearly with the number of users. Performance within
Iterative Multiuser Detection for CDMA with FEC: NearSingleUser Performance
 IEEE TRANS. COMMUN
, 1998
"... This paper introduces an iterative multiuser receiver for direct sequence codedivision multiple access (DSCDMA) with forward error control (FEC) coding. The receiver is derived from the maximum a posteriori (MAP) criterion for the joint received signal, but uses only singleuser decoders. Iteratio ..."
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Cited by 55 (9 self)
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This paper introduces an iterative multiuser receiver for direct sequence codedivision multiple access (DSCDMA) with forward error control (FEC) coding. The receiver is derived from the maximum a posteriori (MAP) criterion for the joint received signal, but uses only singleuser decoders. Iterations of the system are used to improve performance, with dramatic effects. Singleuser turbo code decoders are utilized as the FEC system and a complexity study is presented. Simulation results show that the performance approaches singleuser performance even for moderate signaltonoise ratios.
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 20 (5 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.
Iterative detectors for trelliscode multipleaccess
 IEEE Transactions on Communications
, 2002
"... Abstract—Trelliscode multipleaccess (TCMA) is a narrowband multipleaccess scheme based on trelliscoded modulation. There is no bandwidth expansion, so users occupy the same bandwidth as one single user. The load of the system, in number of bits per channel use, is therefore much higher than the ..."
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Cited by 12 (1 self)
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Abstract—Trelliscode multipleaccess (TCMA) is a narrowband multipleaccess scheme based on trelliscoded modulation. There is no bandwidth expansion, so users occupy the same bandwidth as one single user. The load of the system, in number of bits per channel use, is therefore much higher than the load in, for example, conventional codedivision multipleaccess systems. Interleavers are introduced as a new feature to separate the users. This implies that the maximumlikelihood sequence detector (MLSD) is now too complex to implement. Iterative detectors are therefore suggested as an alternative to the joint MLSD. The conventional interference cancellation (IC) detector has lower complexity than the MLSD, but its performance is shown to be far from acceptable. Even after a novel improvement of the IC detector, the performance is unsatisfactory. Instead of using IC, another iterative detector is suggested. This detector updates the branch metric for every iteration, and avoids the standard Gaussian approximation. Simulations show that the performance of this detector can be close to singleuser performance, even when the interleaver and the phase offset are the only userspecific features in the TCMA system. Index Terms—Interference cancellation, iterative methods, multipleaccess technique, trelliscode multipleaccess, trelliscoded modulation. I.
Joint Decoding and Channel Estimation for Linear MIMO Channels
, 2000
"... We consider the problem of joint decoding and channel estimation for linear multipleinput multipleoutput channels. We assume that the receiver has no apriori knowledge of the channel parameters. The amount of training data required is reduced by using a decision feedback approach to iteratively imp ..."
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Cited by 9 (0 self)
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We consider the problem of joint decoding and channel estimation for linear multipleinput multipleoutput channels. We assume that the receiver has no apriori knowledge of the channel parameters. The amount of training data required is reduced by using a decision feedback approach to iteratively improve channel estimates. We present experimental results for joint channel estimation and decoding of spacetime channels. I. Introduction Linear multiple input multiple output (MIMO) channels occur frequently in communications systems. Such channels are of interest whenever simultaneously transmitted signals are nonorthogonal, or are distorted by the channel in such a way that they are correlated at the receiver. The di#erent channel inputs may be statistically independent (for example the various users of a multiple access system), or dependent (for example an OFDM system with intercarrier interference or a spatial diversity channel). In either case, the optimal receiver will generally...
Iterative Multiuser Detection Using Antenna Arrays and FEC on Multipath Channels
 IEEE J. Sel. Areas in Comms
, 1999
"... This paper investigates a multipleaccess communication receiver system that receives coded data modulated using either directsequence code division multiple access or narrowband binary phase shift keying, with an antenna array in a multipath propagation environment. We describe an iterative receiv ..."
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Cited by 8 (0 self)
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This paper investigates a multipleaccess communication receiver system that receives coded data modulated using either directsequence code division multiple access or narrowband binary phase shift keying, with an antenna array in a multipath propagation environment. We describe an iterative receiver that improves the initial estimates from the antenna array, and therefore reduces the multiple access interference. Simulation results show that the bit error rate performance approaches that obtained when only one user's signal is incident on the array. This occurs even with a large number of users in comparison to the product of the spreading gain and array size. Index Terms Array signal processing, channel coding, code division multiple access, iterative methods, multiuser channels, turbo codes.
An Iterative Multiuser Detection Receiver for 3GPP with Antenna Arrays: Performance in Terms of BER, Cell Size and Capacity
, 2002
"... This paper discusses the implementation of a very powerful but computationally efficient, iterative multiuser detector, intended for use as the basestation physical layer receiver for Wideband CDMA. This multiuser detector is unique in that it is fully compliant with the release '99 3GPP stand ..."
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Cited by 7 (4 self)
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This paper discusses the implementation of a very powerful but computationally efficient, iterative multiuser detector, intended for use as the basestation physical layer receiver for Wideband CDMA. This multiuser detector is unique in that it is fully compliant with the release '99 3GPP standard, a result that has not been shown before. The transmitter chain is discussed before the channel model used is introduced. The receiver design approach is then discussed. Special consideration is given to show how channel estimation is integrated into the receiver. We show single cell performance results that indicate a capacity increase of approximately three times over the "conventional" receiver implementation is possible (with and without antenna arrays). Results are then shown using a cell dimensioning simulation tool to indicate the overall gain in terms of increase in cell size. Here we can show that a gain of approximately 50% of the cell size is possible with such a multiuser detection approach. The dimensioning tool is also used to show the increase in capacity for a fixed cell size. Here we can show that a gain in the order of 330% is possible, compared to a conventional receiver approach.