NDLI: Iterative CDMA Multiuser Receiver With Soft Decision-Directed Channel Estimation

Content Provider	IEEE Xplore Digital Library
Author	Wehinger, J. Mecklenbrauker, C.F.
Copyright Year	1991
Abstract	We develop an iterative code-division multiple-access (CDMA) receiver for multipath block-fading channels in the uplink. The mean-square error (MSE) of the channel estimates is reduced iteratively by using soft data estimates as additional pilots. The multiuser detector performs parallel interference cancellation (PIC) with subsequent linear filtering. We consider a single-user matched filter (SUMF) and develop a low-complexity linear minimum MSE (LMMSE) filter for intersymbol interference (ISI) channels that allows for 33% more users than the SUMF. We investigate two choices of training sequences for initial channel estimation. The first is a random pilot symbol sequence modulated by a short spreading sequence (RAND), and the second is a perfect root of unity sequence (PRUS) used as long sounding chip sequence. We observe that the RAND scheme approaches the single-user bound up to 2 dB and in case of PRUS up to 1 dB at a target bit error rate (BER) of 10^-3. Further, several channel estimators are developed that use various combinations of soft decision symbols and statistical a priori knowledge about the channel. These are the approximated least-squares (ALS), approximated linear MMSE (ALMMSE), and linear MMSE (LMMSE) estimators. The iterative estimators show an improvement of 2.5 and 5 dB with PRUS and RAND pilots, respectively, over estimators that do not exploit soft feedback symbols at a BER of 10 ^-3. The ALS is sacrificing less than 0.6 dB to obtain a BER of 10^-3 in a system at load 1.5 when compared with the ALMMSE and LMMSE schemes. The load is understood as the ratio of the number of users to the spreading factor. This paper shows that significant improvements in system capacity can be achieved in multipath scenarios with low-complexity choices of multiuser detectors and channel estimators
Sponsorship	IEEE Signal Processing Society
Starting Page	3922
Ending Page	3934
Page Count	13
File Size	606162
File Format	PDF
ISSN	1053587X
Volume Number	54
Issue Number	10
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2006-10-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Multiaccess communication Channel estimation Bit error rate Detectors Matched filters Intersymbol interference Interference cancellation Maximum likelihood detection Nonlinear filters Linear approximation training sequences Code-division multiple access (CDMA) iterative channel estimation iterative receiver linear multiuser detection overloaded system parallel interference cancellation perfect root of unity sequences random spreading
Content Type	Text
Resource Type	Article
Subject	Signal Processing Electrical and Electronic Engineering

Sl.	Authority	Responsibilities	Communication Details
1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
5	Website/Portal (Helpdesk)	Queries regarding NDLI and its services	support@ndl.gov.in
6	Contents and Copyright Issues	Queries related to content curation and copyright issues	content@ndl.gov.in
7	National Digital Library of India Club (NDLI Club)	Queries related to NDLI Club formation, support, user awareness program, seminar/symposium, collaboration, social media, promotion, and outreach	clubsupport@ndl.gov.in
8	Digital Preservation Centre (DPC)	Assistance with digitizing and archiving copyright-free printed books	dpc@ndl.gov.in
9	IDR Setup or Support	Queries related to establishment and support of Institutional Digital Repository (IDR) and IDR workshops	idr@ndl.gov.in

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