Abstract
An asynchronous direct sequence code division multiple access (DS-CDMA) system employing periodic spreading sequences is considered to be operating in a frequency selective channel. The cyclostationary spread signal is received at multiple sensors and/or is sampled multiple times per chip (oversampling), leading to a stationary vector-valued received signal. Hence, such a model represents a very particular multi-input multi-output (MIMO) system with plentiful side information in terms of distinct spreading waveforms for the input signals. Depending upon the finite impulse response (FIR) length of the propagation channel, and the processing gain, the channel of a certain user spans a certain number of symbol periods, thus inducing memory or intersymbol interference (ISI) in the received signal in addition to the multiple-access interference (MAI) contributed by concurrent users. The desired user’s multipath channel estimate is obtained by means of a new blind technique which exploits the spreading sequence of the user and the second-order statistics of the received signal. The blind minimum mean square error-zero forcing (MMSE-ZF) receiver or projection receiver is subsequently obtained. This receiver represents the proper generalization of the anchored MOE receiver [1] to the asynchronous case with delay spread. Classification of linear receivers obtained by various criteria is provided and the MMSE-ZF receiver is shown to be obtainable in a decentralized fashion by proper implementation of the unbiased minimum output energy (MOE) receiver, leading to the minimum variance distortionless response (MVDR) receiver for the signal of the desired user. This MVDR receiver is then adapted blindly by applying Capon’s principle. A channel impulse response is obtained as a by-product. Lower bounds on the receiver filter length are derived, giving a measure of the ISI and MAI tolerable by the receiver and ensuring its identifiability.
Résumé
Cet article traite du problème de l’annulation de brouillage dans un système à accès multiple par répartition en code (AMRC) à séquence directe pour des canaux sélectifs en fréquence et des conditions asynchrones. Le signal étalé cyclostationnaire est reçu par des antennes multiples ou est sur échantillonné par rapport à la période des bribes. Il est donc converti en un signal vectoriel sta-tionnaire. Le sur-échantillonnage ou les antennes multiples donnent naissance à un système à entrées et sorties multiples (MIMO) disposant de nombreuses connaissances a priori relatives à la forme des séquences d’étalement distinctes pour les signaux d’entrée (utilisateurs), En fonction de la longueur de la réponse impulsionnelle finie (RIF) du canal de propagation et du facteur d’étalement, le canal d’un utilisateur déterminé s’étale sur un certain nombre de symboles, engendrant une interférence intersymbole (ISI) qui s’ajoute au brouillage d’accès multiple (MAI) dû aux utilisateurs concurrents. L’estimation du canal de l’utilisateur voulu est obtenue par une nouvelle technique aveugle qui utilise la séquence d’étalement de l’utilisateur et la statistique d’ordre deux du signal reçu. Le récepteur à forçage de zéro minimisant l’erreur quadratique moyenne (MMSE-ZF) s’en déduit. Ce récepteur généralise au cas asynchrone et pour les canaux à trajets multiples le récepteur ancré qui minimise l’énergie à la sortie (MDE) [1]. Différents récepteurs linéaires sont obtenus par critères divers. On montre que le récepteur MMSE-ZF peut être réalisé d’une manière décentralisée en appliquant le critère MOE non biaisé, conduisant au récepteur à réponse sans distorsion et à variance minimale (MVDR) pour le signal de l’utilisateur donné. Le récepteur MVDR est ensuite adapté en aveugle en appliquant le principe de Capon. Cela donne, par ailleurs, l’estimation de la réponse impulsionnelle du canal. En établissant des bornes inférieures sur la longueur du filtre de réception, on obtient une estimation de l’ISI et du MAI tolerable par le récepteur, ainsi que des conditions d’identificabilité de celui-ci.
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References
Honig (M.), Madhow (U.), Verdù (S.). Blind adaptive multi-user detection,IEEE Trans, on Info. Theory,41 pp. 944–960, (July 1995).
Verdu (S.). Multiuser detection. Cambridge University Press. 1998.
Concept Group Alpha-Wideband ds-cdma, European Telecommunications Standards Institue, (December 1997).
Viterbi (A. J.), CDMA Principles of spread spectrum Communications.Reading, Mass.:Addison-Wesley, (1995).
DuelHallen (A.), Holtzman (J.), Zvonar (Z). Multi-user detection for cdma systems, IEEE Personal Communications Magazine, pp 46–58. (April 1995).
Verdù (S.). Minimum probability of error for asynchronous Gaussian multiple access channels,IEEE Transactions on Information Theory,32, pp. 85–96, (Jan. 1986).
Lupas (R), Verdù (S.). Linear multiuser detectors for synchronous code-division multiple access channels.IEEE Transactions on Information Theory,35, pp. 123–136, (Jan. 1989).
Lupas (R), Verdù (S.). Near-far resistance of multiuser detectors in asynchronous channels,IEEE Transactions on Communications,38, pp. 496–508, (April 1990).
Madhow (U.), Honig (M.), mmse interference suppression for direct-sequence spread-spectrum cdma,IEEE Transactions on Communications,42, pp. 3178–3188. (Dec. 1994).
Madhow (U.). Blind adaptive interference suppression for direct-sequence cdma, Proc. of the IEEE, pp. 2049–2069, (October 1998).
Sklar (B.). Rayleigh fading channels in mobile digital communication systems - characterization & mitigation,IEEE Communications Magazine,35, pp. 90–109, (July 1997).
Tsatsanis (M. K.). Inverse filtering criteria for cdma systems,IEEE Transactions on Signal Processing,45, pp. 102–112. (Jan. 1997).
Tsatsanis (M. K.), Xu (Z.). On minimum output energy cdma receivers in the presence of multipath, in Proc. Conf. on Information Sciences and Systems, (Johns Hopkins University, MD), pp. 102–112. (March 1997).
Ghauri (I.), Slock (D. T. M.). Blind optimal mmse receiver for asynchronous CDMA in the presence of multipath, in Proc. 31st Asilomar Conf: on Signals, Systems & Computers, (Pacific Grove, CA),(November 1997).
Gesbert (D.), Sorelius (J), Paulraj (A). Blind multiuser mmse detection of cdma signals, in Proc. ICASSP. (Seattle, WA), (May1998).
Wang (X.), Poor (V). Blind equalization and multiuser detection in dispersive cdma channels,IEEE Transactions on Communications,46, pp. 91–103, (January 1998).
Torlak (M.), Xu (Z.). Blind multiuser channel estimation in asynchronous cdma systems,IEEE Trans. on Communications. 45, pp. 137–147, (January 1997).
Paulraj (A. J.), Papadias (C. B.). Space-time processing for wireless communications. IEEE Signal Processing Magazine, pp. 49–83, (November 1997).
Schlegel (C.), Roy (S.), Alexander (P.), Xiang (Z.). Multiuser projection receivers,IEEE J. on Selected Areas in Communications,14, pp. 1610–1618, (October 1996).
Slock (D. T. M.). Blind joint equalization of multiple synchronous mobile users using oversampling and/or multiple antennas. in Proc. 28th Asilomar Conf on Signals, Systems & Computers, (Pacific Grove, CA), (November 1994).
Johnson (D. H.) Dudgeon (D. E.). Array signal processing -Concepts and techniques, Englewood Cliffs, NJ: Prentice Hall, (1993).
Stoica (P.), Moses (R. L.). Introduction to spectral analysis. Upper Saddle River, NJ: Prentice: Hall, (1997).
Tong (L.), Zhao (Q.). Blind channel estimation by least squares smoothing, in Proc. ICASSP, (Seattle, WA), (May 1998).
Ghauri (I.), Slock (D. T. M.). Blind channel and linear mmse receiver determination in ds-cdma systems, inProc. ICASSP’99,5, (Phoenix, AZ), pp. 2699–2702, (March 1999).
Zhao (Q.), Tong (L.). Semi-blind equalization by least squares smoothing, in Proc. 32nd Asilomar Conf. on Signals, Systems & Computers, (Pacific Grove, CA) (November 1998).
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Eurécom’s research is partially supported by its industrial partners : Ascom, Cegetel, France Telecom, Hitachi Telecom, Hitachi, IBM France, Motorola, Swisscom, Texas Instruments, and Thomson CSF
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Ghauri, I., Dirk, T.M. Blind decentralized projection receiver for asynchronous CDMA in multipath channels. Ann. Télécommun. 54, 379–391 (1999). https://doi.org/10.1007/BF02997760
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DOI: https://doi.org/10.1007/BF02997760
Key words
- Code division multiple access
- Direct sequence spread spectrum
- Multipath propagation
- Signal interference
- Intersymbol interference
- Nonsupervised learning
- Mean square error
- Antenna array
- Optimum receiver
- Signal detection
- Complex signal