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64
Iterative multiuser joint decoding: unified framework and asymptotic analysis
- IEEE TRANS. INFORM. THEORY
, 2002
"... We present a framework for iterative multiuser joint decoding of code-division multiple-access (CDMA) signals, based on the factor-graph representation and on the sum-product algorithm. In this framework, known parallel and serial, hard and soft interference cancellation algorithms are derived in a ..."
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Cited by 116 (3 self)
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We present a framework for iterative multiuser joint decoding of code-division multiple-access (CDMA) signals, based on the factor-graph representation and on the sum-product algorithm. In this framework, known parallel and serial, hard and soft interference cancellation algorithms are derived in a unified way. The asymptotic performance of these algorithms in the limit of large code block length can be rigorously analyzed by using density evolution. We show that, for random spreading in the large-system limit, density evolution is considerably simplified. Moreover, by making a Gaussian approximation of the decoder soft output, we show that the behavior of iterative multiuser joint decoding is approximately characterized by the stable fixed points of a simple one-dimensional nonlinear dynamical system.
Minimum mean-squared error iterative successive parallel arbitrated decision feedback detectors for DS-CDMA systems
- in Proc. IEEE Int. Conf. Acoust., Speech, Signal Process
, 2008
"... Abstract—In this paper we propose minimum mean squared error (MMSE) iterative successive parallel arbitrated decision feedback (DF) receivers for direct sequence code division multiple access (DS-CDMA) systems. We describe the MMSE design criterion for DF multiuser detectors along with successive, p ..."
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Cited by 62 (51 self)
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Abstract—In this paper we propose minimum mean squared error (MMSE) iterative successive parallel arbitrated decision feedback (DF) receivers for direct sequence code division multiple access (DS-CDMA) systems. We describe the MMSE design criterion for DF multiuser detectors along with successive, parallel and iterative interference cancellation structures. A novel efficient DF structure that employs successive cancellation with parallel arbitrated branches and a near-optimal low complexity user ordering algorithm are presented. The proposed DF receiver structure and the ordering algorithm are then combined with iterative cascaded DF stages for mitigating the deleterious effects of error propagation for convolutionally encoded systems with both Viterbi and turbo decoding as well as for uncoded schemes. We mathematically study the relations between the MMSE achieved by the analyzed DF structures, including the novel scheme, with imperfect and perfect feedback. Simulation results for an uplink scenario assess the new iterative DF detectors against linear receivers and evaluate the effects of error propagation of the new cancellation methods against existing ones. Index Terms—DS-CDMA systems, multiuser detection, decision feedback structures, iterative detection, iterative decoding. I.
Evolution Analysis of Low-Cost Iterative Equalization in Coded Linear Systems with Cyclic Prefixes
- IEEE J. Sel. Areas Commun
, 2008
"... Abstract—This paper is concerned with the low-cost iterative equalization/detection principles for coded linear systems with cyclic prefixes. Turbo frequency-domain-equalization (FDE) is applied to systems that may contain the joint effect of multiple-access interference (MAI), cross-antenna interfe ..."
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Cited by 36 (18 self)
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Abstract—This paper is concerned with the low-cost iterative equalization/detection principles for coded linear systems with cyclic prefixes. Turbo frequency-domain-equalization (FDE) is applied to systems that may contain the joint effect of multiple-access interference (MAI), cross-antenna interference (CAI) and inter-symbol interference (ISI). We develop an SNR-variance evo-lution technique for the performance evaluation of the proposed systems. Numerical results in various channel environments demonstrate excellent agreement between the predicted and simulated system performance. Index Terms—cyclic prefix, multiuser MIMO ISI channel, Turbo FDE, SNR-variance evolution. I.
Analysis and optimization of CDMA systems with chip-level interleavers
- IEEE Journal on Selected Areas in Communications
"... Abstract—In this paper, we present an unequal power allo-cation technique to increase the throughput of code-division multiple-access (CDMA) systems with chip-level interleavers. Performance is optimized, respectively, based on received and transmitted power allocation. Linear programming and power ..."
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Cited by 32 (14 self)
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Abstract—In this paper, we present an unequal power allo-cation technique to increase the throughput of code-division multiple-access (CDMA) systems with chip-level interleavers. Performance is optimized, respectively, based on received and transmitted power allocation. Linear programming and power matching techniques are developed to provide solutions to systems with a very large number of users. Various numerical results are provided to demonstrate the efficiency of the proposed techniques and to examine the impact of system parameters, such as iteration number and interleaver length. We also show that with some very simple forward error correction codes, such as repetition codes or convolutional codes, the proposed scheme can achieve throughput reasonably close to that predicted by theoretical limit in multiple access channels. Index Terms—Code-division multiple-access (CDMA) , iterative detection, linear programming, multiuser detection, power alloca-tion. I.
Layered Space-Time Codes for Wireless Communications using Multiple Transmit Antennas
- In IEEE Proceedings ofInternational Conference on Communications (ICC’99
"... Abstract − Multiple-antenna systems provide very high capacity compared to single antenna systems in a Rayleigh fading environment. Space-time codes are channel codes designed to exploit this high capacity for multiple-antenna systems without requiring instantaneous channel knowledge at the transmit ..."
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Cited by 28 (1 self)
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Abstract − Multiple-antenna systems provide very high capacity compared to single antenna systems in a Rayleigh fading environment. Space-time codes are channel codes designed to exploit this high capacity for multiple-antenna systems without requiring instantaneous channel knowledge at the transmitter. A practical concern for high data rate space-time codes is their decoding complexity. The decoding complexity with ML criterion can be prohibitively large. In this paper, we focus on layered space-time (LST) codes. Two types of LST codes, the horizontally-layered space-time (HLST) codes and the diagonally-layered space-time (DLST) codes, are presented. We analyze the performance of both types of LST codes under slow and fast fading conditions. We conclude that, in a slow fading environment, DLST codes have superior performance over HLST codes. The design criteria for DLST codes are proposed. I.
Joint Iterative Decoding of Serially Concatenated Error Control Coded CDMA
- IEEE Journal on Selected Areas in Communications
, 2001
"... Joint iterative decoding of multiple forward error control (FEC) encoded data streams is studied for linear multiple access channels, such as code-division multiple access (CDMA). It is shown that such systems can be viewed as serially concatenated coding systems, and that iterative soft-decision de ..."
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Cited by 28 (6 self)
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Joint iterative decoding of multiple forward error control (FEC) encoded data streams is studied for linear multiple access channels, such as code-division multiple access (CDMA). It is shown that such systems can be viewed as serially concatenated coding systems, and that iterative soft-decision decoding can be performed successfully. To improve power efficiency, powerful FEC codes are used. These FEC codes are themselves serially concatenated. The overall transmission system can be viewed as the concatenation of two error control codes with the linear multiple access channel, and soft-decision decoders are used at each stage.
Minimum mean-squared error multiuser decision-feedback detectors for DSCDMA
- IEEE Trans. Commun
, 2002
"... for direct-sequence code-division multiple access, based on the minimum mean-squared error (MMSE) performance criterion, are described. Both successive and parallel feedback (interference cancellation) with hard decisions are considered. An iterative DFD is presented, which consists of cascaded DFDs ..."
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Cited by 23 (4 self)
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for direct-sequence code-division multiple access, based on the minimum mean-squared error (MMSE) performance criterion, are described. Both successive and parallel feedback (interference cancellation) with hard decisions are considered. An iterative DFD is presented, which consists of cascaded DFDs, each performing successive cancellation. The two-stage DFD achieves the single-user bound in the absence of error propagation, and performs significantly better than an MMSE DFD with parallel feedback. The filter structures are generalized to include finite impulse response feedforward and feedback matrix filters, which account for asynchronous users and intersymbol interference. The effect of error propagation is illustrated through simulation. Both uncoded and coded performance results are presented. Although error propagation can significantly degrade performance, the DFDs still offer a significant performance gain relative to linear MMSE detection. Index Terms—Code-division multiple access (CDMA), decision feedback, interference cancellation, interference suppression, multiuser detection. I.
Multiple access demodulation in the lifted signal graph with spatial coupling
- IEEE Transactions on Information Theory
, 2013
"... Abstract—Demodulation in a random multiple access channel is considered where the signals are chosen uniformly randomly with unit energy, a model applicable to several modern trans-mission systems. It is shown that by lifting (replicating) the graph of this system and randomizing the graph connectio ..."
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Cited by 22 (8 self)
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Abstract—Demodulation in a random multiple access channel is considered where the signals are chosen uniformly randomly with unit energy, a model applicable to several modern trans-mission systems. It is shown that by lifting (replicating) the graph of this system and randomizing the graph connections, a simple iterative cancellation demodulator can be constructed which achieves the same performance as an optimal symbol-by-symbol detector of the original system. The iterative detector has a complexity that is linear in the number of users, while the direct optimal approach is known to be NP-hard. However, the maximal system load of this lifted graph is limited to α < 2.07, even for signal-to-noise ratios going to infinity – the system is interference limited. We then show that by introducing spatial coupling between subsequent lifted graphs, and anchoring the initial graphs, this limitation can be avoided and arbitrary system loads are achievable. Our results apply to several well-documented system proposals, such as IDMA, partitioned spreading, and certain forms of MIMO communications. Index Terms—random signaling, iterative decoding, optimal joint detection I.
A unified approach to multiuser detection and space-time coding with low complexity and nearly optimal performance
- in Proc. 40th Allerton Conf., 2002
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