Studying the Effect of Delay Diversity on a DS-CDMA Downlink

Abstract

In this paper, we study the error rate performance of a direct sequence CDMA downlink similar to the CDMA2000 standard. While analytical computation of the error rate is possible in DS-CDMA systems under certain simplifying assumptions, computer simulations are perhaps the only means to quantify the error rate for realistic channel models. Since the delay spread of the multipath channel varies with distance, we investigate the error performance as a function of the distance from the base station. The computer simulations reveal certain interesting results which to our knowledge have not explicitly appeared in open literature.

We compare the RAKE error rate performance under situations of no handoff, soft handoff, independent fading, correlated fading, chip-spaced sampling, sub-chip sampling, and pilot channel cancellation at the mobile receiver. These results indicate that narrow-band DS-CDMA downlink has certain severe shortcomings, and that it may be vital to ensure line of sight propagation for the “near” users, and exploit base-station (macro) diversity for the “far” users (in soft handoff) to ensure adequate error rate performance.

Indexing terms:

• DS-CDMA downlink
• Delay diversity
• Macro-cellular diversity
• Micro-cellular diversity
• Soft handoff

Additional information

Notes on contributors

Sumanth Jagannathan

Sumanth Jagannathan received the BTech degree in electrical engineering from the Indian Institute of Technology (IIT), Madras, in 2003. He is currently working towards the MS degree in electrical engineering at Stanford University, Stanford, CA. He is a member of the Wireless Sensor Networks Lab (WSNL) at Stanford University. His research interests include wireless and digital ommunication systems, multiple antenna systems, wireless ad-hoc and sensor networks, and multi-user formation theory.

K Giridhar

Giridhar received BSc (Applied Sciences) degree from SG College of Technology, Coimbatore, in 1985, and the IE degree in Electrical Communication Engineering from Indian Institute of Science, Bangalore, in 1989, and the PhD degree in Electrical and Computer Engineering from University of California, Santa Barbara, CA, in 1993.

He has also worked for a year each, as a Member of Research Staff at Bharat Electronics, Bangalore, and as a Research Affiliate in Electrical Engineering at Stanford University, California. In 1994, he joined the Indian Institute of Technology, Madras, and currently, is an Associate Professor of Electrical Engineering. His present research interests are in the areas of noncoherent and multiuser detection, space-time processing, adaptive estimation, and various transceiver algorithms for 3G and 4G wireless systems.

He is involved in telecommunication product development activity based on the DECT Wireless in Local Loop system developed by IITM. He has also been a visiting faculty at Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Andhra Pradesh, and at Stanford University, California.