Space Division Multiple Access Considerations in CDMA Cellular Systems

Pieter van ROOYEN  Michiel P. LOTTER  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E81-A   No.11   pp.2251-2260
Publication Date: 1998/11/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: INVITED PAPER (Special Section on Spread Spectrum Techniques and Applications)
space division multiple access (SDMA),  CDMA,  non-uniform subscriber distribution,  antenna arrays,  

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Space Division Multiple Access (SDMA) will form an important part of the new Wideband Code Division Multiple Access (WCDMA) standard that will realize the Universal Mobile Telephone System (UMTS). This paper addresses a few issues of importance when SDMA techniques are used in a cellular CDMA system. Firstly, a brief overview of SDMA techniques are presented followed by a theoretical analysis of a SDMA/CDMA system. The analysis is focused on a single cell, multipath Rayleigh fading scenario with imperfect power control. As system performance measure Bit Error Rate (BER) is used to investigate the influence of user location, number of antennas and power control error. An important parameter in a SDMA system is the antenna array element spacing. In our analysis a Uniform Linear Array (ULA) is considered and a measure is defined to determine the optimal antenna element spacing in a CDMA cellular environment. Normally the mobile users in a cell are assumed to be uniformly distributed in cellular performance calculations. To reflect a more realistic situation, we propose a novel probability density function for the non-uniform distribution of the mobile users in the cell. It is shown that multipath and imperfect power control, even with antenna arrays, reduces the system performance substantially.