Linearly Constrained Minimum Variance Beamforming using Modified Variable Step Size LMS Adaptive Alogirthm

Abstract

A generalized sideiobe-cancelling structure is employed in which a non-adaptive beamformer operates in parallel with an adaptive beamformer. The effects of orthogonal and nonorthogonal complement constraint matrices are analyzed under the application of steering direction constraint. An unconstrained Varaible Step Size LMS (VSS-LMS) power minimization algorithm is employed to adapt the delay line weights. The application of non-orthogonal complement constraint matrix is violation of Frost's procedure, but this enhances interference and sidelobe cancellation action at the cost of high misadjustment in weight adjustment. But misadjustment is reduced using VSS-LMS algorithm, which has been implemented with significant changes, making it to work in Fixed Step Size LMS (FSS-LMS) as well as in VSS-LMS mode.

Simulation results are presented to support the analysis and to compare the performance of modified algorithm with FSS-LMS algorithm. The GSC beamformer shows better performance with non-orthogonal complement constraint matrix and it is easy to implement because of lesser complexity due to modifications in adaptive algorithm.

Indexing terms:

• Adaptive filters and algorithms
• Adaptive antenna array processing
• GSC (Generalized Sidelobe Canceller)
• LCMV (Linearly Constrained Minimum Variance) beamformer

Additional information

Notes on contributors

Amit Kumar Kohli

Amit Kumar Kohli was born in Ludhiana, Panjab, India, on April 28, 1978. He received BTech degree with Honor from Guru Nanak Dev Engineering College, Ludhiana and ME with highest honor from Thapar Institute of Engineering and Technology (deemed university), Patiala, India, in 2000 and 2002 respectively.

He is currently doing PhD in Electronics & Communication Engineering at Indian Institute of Technology, Roorkee. His main interest is mobile radio communications, adaptive signal processing and its applications.

He received Institution Medal and Gold Medal for academic performance in 2001 and 2002 respectively.

Rajiv Saxena

Rajiv Saxena was born in Gwalior, Madhya Pradesh, India, on August 31, 1961. He received the BE (Electronics and Telecommunication Engineering) degree from Jabalpur University in 1982 and ME (Digital Techniques and Data Processing) degree in 1990 from Jiwaji University, Gwalior. He obtained PhD degree in Communication Engineering from University of Roorkee, Roorkee in 1996. Dr Saxena is a Life Fellow of IETE and Life Member of CSI and ISTE. Since 1984 he has been with Madhav Institute of Technology and Science, Gwalior, where he is currently a Professor and Head of Electronics, CSE and IT Department. In June 2000, he joined Thapar Institute of Engineering and Technology, Patiala (on lien with MITS, Gwalior for a period of two years) as Professor in Electronics & Communication engineering, where he also served as Professor and Head, Electronics and Communication Engineering Department. His research interests include Signal Processing and Communication Engineering. He has published research articles in refereed journals and proceedings of conferences of international repute.