DocumentCode :
1213754
Title :
Broadband beamforming for joint interference cancellation and turbo equalization
Author :
Koca, Mutlu ; Levy, Bernard C.
Author_Institution :
Dept. of Electr. & Electron. Eng., Bogazici Univ., Istanbul, Turkey
Volume :
4
Issue :
5
fYear :
2005
Firstpage :
2244
Lastpage :
2255
Abstract :
This paper considers the turbo equalization of trellis-coded modulated (TCM) broadband wireless signals that are affected by both intersymbol interference (ISI) due to multipath propagation and cochannel interference (CCI) due to the presence of adjacent users. Long channel dispersion causing both impediments to be severe makes the direct application of trellis-based turbo equalizers impossible, particularly for high-order signal modulations. For this reason, we present two computationally feasible space-time turbo receiver architectures employing linear antenna arrays and broadband beamformers. The first receiver uses a beamformer for joint rejection of interfering signals and shortening of the channel corresponding to the desired signal so that a scalar trellis-based turbo equalizer can be applied to its output. At each beamformer branch, the composite effect of the CCI and the white channel noise is viewed as colored noise. Because trellis search algorithms are limited to cases where the observation noise is white, this imposes quadratic noise whitening constraints on the beamformer design that is solved by a Lagrangian relaxation approach. The second receiver architecture removes the dependence on trellis search techniques for equalization by implementing the turbo equalizer directly with a soft-information-aided broadband beamformer at its front end and a soft-input soft-output (SISO) decoder at its back end. We outline the design considerations associated with each receiver and present bit error rate (BER) simulations for the turbo equalization of 8-phase-shift keying (PSK) TCM signals.
Keywords :
AWGN channels; broadband antennas; channel coding; cochannel interference; dispersive channels; equalisers; error statistics; interference suppression; intersymbol interference; linear antenna arrays; multipath channels; radio receivers; space-time codes; trellis coded modulation; turbo codes; wireless channels; BER; Lagrangian relaxation approach; bit error rate; broadband beamforming; broadband wireless signal; channel dispersion; channel shortening; cochannel interference; colored noise; interference cancellation; interference rejection; intersymbol interference; linear antenna array; multipath propagation; phase shift keying; quadratic noise; soft information; soft-input soft-output decoder; space-time turbo receiver architecture; trellis search technique; trellis-coded modulation; turbo equalization; white channel noise; Array signal processing; Bit error rate; Broadband antennas; Colored noise; Equalizers; Interference cancellation; Intersymbol interference; Linear antenna arrays; Radiofrequency interference; White noise; Broadband beamforming; channel shortening; interference rejection; noise whitening; soft-output decoding; turbo equalization;
fLanguage :
English
Journal_Title :
Wireless Communications, IEEE Transactions on
Publisher :
ieee
ISSN :
1536-1276
Type :
jour
DOI :
10.1109/TWC.2005.853815
Filename :
1532210
Link To Document :
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