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Rachel E Learned, Sanders, A Lockheed Martin Company (U.S.A.)
Andrew C Singer, Sanders, A Lockheed Martin Company (U.S.A.)
A low complexity approach to coding-enhanced multi-user detection is developed to mitigate the problems associated with near-far effect and to permit a more efficient assignment of channel resources relative to current multiple access (MA) communications systems. Through prudent integration of error correction decoding, multi-user and inter-symbol interference equalization and stripping, a low complexity near-far resistant multi-user joint detector/decoder has been developed which exhibits significant performance gains relative to the best known low complexity joint detection/decoding procedures reported in recent literature. Empirical analysis of the coding-enhanced multi-user detector (CMD) for a case of heavy inter-symbol interference and multi-user interference shows a 3 dB improvement over these best known methods.
ic981259.pdf (From Postscript)
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Seong Ill Park, Korea Advanced Institute of Science and Technology (Korea)
Iickho Song, Korea Advanced Institute of Science and Technology (Korea)
Kwang Soon Kim, Korea Advanced Institute of Science and Technology (Korea)
Naoki Suehiro, University of Tsukuba (Japan)
Jooshik Lee, Korea Advanced Institute of Science and Technology (Korea)
In this paper, a new generation and an information construction methods for a modulated orthogonal sequence are suggested: thesequence is generated by only integer sums and modular techniques. The autocorrelation and cross-correlation characteristics of the sequence are investigated via a new procedure. A modified sequence also having the orthogonality and satisfying the mathematical lower bound of the cross-correlation is proposed, and the symbol error probability of the sequence is investigated.
ic981311.pdf (From Postscript) TOP
Yong-Suk Moon, University of Minnesota (U.S.A.)
Mostafa Kaveh, University of Minnesota (U.S.A.)
Laurie B Nelson, University of Minnesota (U.S.A.)
The oblique projection supports the framework to resolve a signal space into desired signal and interference subspaces. This paper presents subspace-based detection methods using the oblique projection for the CDMA channel. For the synchronous case, it is shown that this detector represents the geometrical form of the decorrelating detector, and performs a complete rejection of interfering signals. This paper also suggests the approach of combining the subspace-based detection with the MUSIC algorithm for an asynchronous CDMA channel. It is shown that the BER performance of this detection approach, which depends on the accuracy of the code timing acquisition, is better than that of the blind adaptive demodulation technique.
ic981584.pdf (From Postscript) TOP
Lin Yue, Rice University (U.S.A.)
Don H. Johnson, Rice University (U.S.A.)
Channel characteristics of practical code division multiple access (CDMA) systems are usually unknown and difficult to model accurately. Type-based receivers, without assuming any a priori model, extract signals successfully from background noise. In this paper, we develop type-based receivers that address two major issues in CDMA signal reception: multiple access interference and multipath fading. We first present the type-based receiver with interference suppression capability, assuming the knowledge of the code and timing of the intended user only. We then show that equal-gain combining (EGC) of type-based statistics is the asymptotically optimal technique for diversity empirical detection. Compared with maximal ratio combining of matched filter outputs, the diversity receiver with EGC of type-based statistics assumes less channel knowledge and yields competitive detection performance in Gaussian noise and better performance in Laplacian noise.
ic981260.pdf (From Postscript) TOP
Mohammed H Nafie, University of Minnesota (U.S.A.)
Ahmed H. Tewfik, University of Minnesota (U.S.A.)
We present a progressive refinement approach to M-ary detection problems. The approach leads on average to a logarithmic reduction in the complexity of the detector. It relies on designing binary decision trees that trade complexity with probability of error. We also discuss simplified solutions that can be used in several cases of interest in wireless communications such as CDMA multiuser detection and blind equalization.
ic982364.pdf (From Postscript) TOPAnders Ranheim, Chalmers University of Technology (Sweden)
This paper presents a novel method for jointly estimating the time-delay parameters and detecting the transmitted symbols in a DS-CDMA system. A short training sequeunce is used to get an initial estimate of the time-delay, which is consequently used to detect the symbols. The method then iterates while exploiting signal structure, to improve the performance. Simulation results are presented to compare the algorithm with the decorrelating criterion and the matched-filter receiver in terms of bit-error rate, and with the MUSIC algorithm and the sliding correlator in terms of the variance of the time-delay estimates.
ic981471.pdf (From Postscript) TOP
A. Manikas, Imperial College (U.K.)
S. S. Lim, Imperial College (U.K.)
P. Wilkinson, Imperial College (U.K.)
In this paper a new H-infinity-type delay acquisition/tracking approach is proposed which is based on partitioning of the PN-code matrix of the CDMA users into submatrices which are then used to form a 'state-space' H-infinity-type linear combiner. The proposed novel formulation and approach is robust to modelling errors such as over- and underestimation of the number of signals present and provides a powerful near-far resistant delay-tracking solution in a multiuser DS-CDMA signal environment.
ic985205.pdf (Scanned) TOP
Xiao-feng Wang, University of Victoria (Canada)
Wu-sheng Lu, University of Victoria (Canada)
Andreas Antoniou, University of Victoria (Canada)
A recursive algorithm for updating linear multiuser detectors in code-division multiple-access systems is proposed. Based on this algorithm, a window-based implementation with a signal-based criterion for determining the window length is developed. Performance analysis and numerical experiments are conducted that show the merits of the proposed implementation method.
ic981603.pdf (From Postscript) TOP
Harald Elders-Boll, Aachen University of Technology (Germany)
Hans Dieter Schotten, Aachen University of Technology (Germany)
Axel Busboom, Aachen University of Technology (Germany)
The decorrelating and the linear, minimum mean-squared error (MMSE) detector for asynchronous code-division multiple-access communications ideally are infinite memory-length detectors. Finite memory approximations of these detectors require the inversion of a correlation matrix whose dimension is given by the product of the number of active users and the length of the processing window. With increasing number of active users or increasing length of the processing window, the calculation of the inverse may soon become numerically very expensive. In this paper, we prove that the decorrelating and the linear MMSE detector can both be realized by linear multi-stage interference cancellation algorithms with ideally an infinite number of stages. It will be shown that for serial multi-stage interference cancellation, depending on the signal-to-noise ratio and the number of active users, only a few stages are necessary to obtain the same BER performance as the ideal detectors. Thus, the complexity can be reduced considerably.
ic981249.pdf (From Postscript) TOP
Ramin Baghaie, Helsinki University of Technology (Finland)
Stefan Werner, Helsinki University of Technology (Finland)
Timo I. Laakso, Helsinki University of Technology (Finland)
Pipelined implementation of adaptive Direct-Sequence Code Division Multiple Access (DS-CDMA) receiver is proposed when multiple antennas are utilized for mobile communications. Adaptive multiple-antenna receivers can provide insensitivity to the interfering powers and room for more users or require smaller number of antennas than the matched filter solution. In this paper, a number of approximation techniques are utilized to pipeline the adaptive algorithm used for the proposed multiple-antenna receiver. The resulting pipelined receiver requires minimal hardware increase and achieves a higher throughput or requires lower power as compared to the receiver using the serial algorithm. Simulation results illustrate the signal-to-interference (SIR) versus the relative interfering power for different number of antennas and different levels of pipelining.
ic981660.pdf (From Postscript) TOP