1 Levenberg-Marquardt Computation of the Block Factor Model for Blind Multi-User Access in Wireless Communications by Dimitri NION and Lieven DE LATHAUWER Laboratoire ETIS, CNRS UMR 8051 6 avenue du Ponceau, 95014 CERGY FRANCE 14 th European Signal Processing Conference EUSIPCO 2006 September 4-8, Florence, ITALY
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Levenberg-Marquardt Computation of the Block Factor Model for Blind Multi-User
Access in Wireless Communications
by Dimitri NION and Lieven DE LATHAUWER
Laboratoire ETIS, CNRS UMR 80516 avenue du Ponceau, 95014 CERGY
FRANCE
14 th European Signal Processing Conference
EUSIPCO 2006
September 4-8, Florence, ITALY
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Keywords
� Research Area: Blind Source Separation (BSS)
� Application: Wireless Communications (DS-CDMA system here)
� Assumptions: No knowledge of the channel, neither of CDMA codes, noise level and antenna array response (BLIND approach)
� Objective: Separate each user’s contribution and estimateinformation symbols
� Method: - Deterministic: relies on multilinear algebra
- How? store observations in a third order tensor anddecompose it in a sum of users’ contributions
� Power: - No orthogonality constraints between factors
- Tensor Model « richer » than matrix model
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Introduction
1. PARAFAC Decomposition1.1 Concept1.2 Uniqueness of the decomposition1.3 Application: direct path propagation1.4 Algorithm: Standard ALS
2. Block Factor Model (BFM) Decomposition2.1 Problem: multipath propagation with ISI2.2 Received Signals: Analytic and algebraic forms2.2 Uniqueness of the Decomposition2.4 Algorithms: ALS vs. Levenberg-Marquardt
3. Simulation Results
Conclusion
Plan
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Overview of a wireless communication system
Introduction
� The R users transmit at the same time within the same bandwidthtowards the antenna array.
� We want to estimate their signals without knowledge of the learning seq. (i.e. BLIND estimation)
Antenna array
(K antennas)
user1 Base Station
userR
= learning sequence
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Blind Signal Separation: Why?Introduction
Several motivations among others:
� Elimination or reduction of the learning frames: more than40 % of the transmission rate devoted to training in UMTS
� Training not efficient in case of severe multipath fading or fast time varying channels