Space-Time Adaptive MMSE Multiuser Receiver Structures for Wideband CDMA Systems

Abstract

In this paper we propose computationally efficient space-time multiuser adaptive minimum mean square error (MMSE) receivers using affine projection adaptive (APA) filtering algorithm for asynchronous wideband code division multiple access systems (W-CDMA) in multipath channels. It is found that APA algorithm outperforms normalized least mean square (NLMS) algorithm in convergence characteristics with significant reduction in computational complexity as compared to recursive least square (RLS) algorithm. Three adaptive multiuser receiver architectures are considered, all employ chip-matched filter (CMF) at their front end. In the first two architectures perfect estimation of time delay of individual user is assumed and one CMF is employed per user. The difference between two architectures is that, in the first the samples collected from CMFs are cross-coupled and in the second architecture samples collected for individual users are not combined. In the third architecture, there is no need to estimate the time delay, but fractional sampling is used. It is shown that first architecture outperforms the other two architectures by virtue of its diversity advantage. It is also shown that by exploiting the spatial diversity (using multiple antennas at the receiver) significant improvement can be achieved in the output signal-to-interference-and-noise ratio (SINR).

Indexing terms:

• CDMA systems
• Multiple access interference
• Multiuser detection
• Multipath fading
• Diversity

Additional information

Notes on contributors

Aditya Trivedi

Aditya Trivedi is working as Reader in the Department of Electronics and Computer Science and Engineering with the Madhav Institute of Technology and Science, Gwalior, India. He received his bachelor degree (Electronics) from the same institute in 1987. He did his M Tech (Communication Systems) from IIT Kanpur in 1997. He obtained his doctorate from IIT Roorkee in 2004 in the area of wireless communication engineering. His teaching and research interest include Digital communication, CDMA systems, Signal processing, and Networking. He has published 10 papers in various national and international conferences.

D K Mehra

D K Mehra was born in Amritsar, India, on May 25, 1946. He received the BE and ME degree in electrical communication engineering from the Indian Institute of Science, Bangalore, India in 1968 and 1970, respectively, and the PhD degree from the Indian Institute of Technology, Kanpur, India in 1978.

In 1975, he joined the Electronics and Computer Engineering Department of Indian Institute of Technology Roorkee (Previously University of Roorkee), India, where he became a Professor in 1987. His main teaching and research interests are in the area of adaptive signal processing techniques and their applications for interference suppression in CDMA systems and digital communication over fading dispersive channels.