Title :
A maximum likelihood approach to blind multiuser interference cancellation
Author :
Bugallo, Mónica F. ; Míguez, Joaquín ; Castedo, Luis
Author_Institution :
Dept. de Electron. e Sistemas, Coruna Univ., Spain
fDate :
6/1/2001 12:00:00 AM
Abstract :
This paper addresses the problem of blind multiple access interference (MAI) and intersymbol interference (ISI) suppression in direct sequence code division multiple access (DS CDMA) systems. A novel approach to obtain the coefficients of a linear receiver using the maximum likelihood (ML) principle is proposed. The method is blind because it only exploits the statistical features of the transmitted symbols and Gaussian noise in the channel. We demonstrate that an adequate linear constraint on these coefficients ensures that the desired user is extracted and the resulting linearly constrained maximum likelihood linear (LCMLL) receiver can be efficiently implemented using the iterative space alternating generalized expectation-maximization (SAGE) algorithm. In order to take advantage of the diversity inherent to multipath channels, we also introduce a blind RAKE multiuser receiver that proceeds in two steps. First, soft estimates of the desired user transmitted symbols are obtained from each propagation path using a bank of appropriate LCMLL receivers. Afterwards, these estimates are adequately combined to enhance the signal-to-interference-and-noise ratio (SINR). Computer simulations show that the proposed blind algorithms for multiuser detection are near-far resistant and attain convergence using small blocks of data, thus outperforming existing linearly constrained minimum variance (LCMV) blind receivers
Keywords :
Gaussian noise; code division multiple access; convergence of numerical methods; dispersive channels; diversity reception; interference suppression; intersymbol interference; iterative methods; land mobile radio; maximum likelihood estimation; multipath channels; multiuser channels; optimisation; radio receivers; signal detection; spread spectrum communication; DS CDMA systems; Gaussian noise; ISI suppression; LCMLL receivers; SINR; blind RAKE multiuser receiver; blind algorithms; blind multiuser interference cancellation; computer simulations; convergence; direct sequence code division multiple access; diversity; intersymbol interference; iterative SAGE algorithm; linear constraint; linear receiver coefficients; linearly constrained maximum likelihood linear receiver; maximum likelihood approach; mobile communication systems; multipath channels; multiuser detection; near-far resistant algorithms; propagation path; signal-to-interference-and-noise ratio; soft estimates; space alternating generalized expectation-maximization; statistical features; time dispersive channels; transmitted symbols; user transmitted symbols; Direct-sequence code-division multiple access; Gaussian noise; Intersymbol interference; Iterative algorithms; Maximum likelihood detection; Maximum likelihood estimation; Multiaccess communication; Multipath channels; Multiple access interference; RAKE receivers;
Journal_Title :
Signal Processing, IEEE Transactions on