Power balancing and hot spot cell traffic relief in a CDMA cellular system

Pao Yue-kong Library Electronic Theses Database

Power balancing and hot spot cell traffic relief in a CDMA cellular system


Author: Lai, Yiu-man
Title: Power balancing and hot spot cell traffic relief in a CDMA cellular system
Degree: M.Sc.
Year: 1996
Subject: Code division multiple access
Cell interaction
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: iii, 117, [6], 42 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1230685
URI: http://theses.lib.polyu.edu.hk/handle/200/3502
Abstract: Spread-spectrum multiple-access systems usually require some form of power control when the terminals are mobile, in order to prevent signals from nearby units from swamping out more distant signals. Power control is even more essential when the system is a cellular one, due to the interference from cell to cell. In the project, we investigate power control system that permits the signal-to-interference ratio ( SIR ) of every signal to be equalized within each cell and, optionally, from cell to cell throughout the system, for both upstream (mobile to base station) and downstream (base station to mobile) signals. The method is analyzed mathematically and results of a computer simulation are presented. Downstream power control eliminates the so-called 'corner effect', and upstream power control eliminates the so-called 'near-far effect'. We conclude that power control within cell is essential for the efficient operation of the system, and is mathematically easy to accomplish. By comparison, cell-to-cell power balancing has a more marginal effect on the system efficiency and is more difficult to perform in uniform distribution. An improvement of 3 users in upstream and 4 users in downstream ( per cell ) greater than that of power control within cell are achieved by using cell-to-cell balancing for uniform distribution. Another issue is that in reality, during the operation of a cellular system , unexpected growth traffic may develop in a particular cell and create local traffic congestion. Mobiles reassignment to other stations of light traffic may be a viable solution to alleviate congestion. Sophisticated handoff and call admission control algorithm should be planned to handle hot spot in the system. The feasibility and algorithm of using cell-to-cell power balancing technique to tackle the above scenario is studied. The hot spot traffic of a particular base station is simulated and reassignment of those affected mobile users to the nearby base stations performed. Rebalancing of SIR value for the system is studied in order to find out the service quality of whole system. We conclude that although cell-to-cell power balancing has marginal effect in improving the system capacity under normal situation ( uniform distribution and non-hot spot traffic). However, by performing mobile reassignment combining with cell-to-cell power balancing, the system wide SIR improves significantly in hot spot scenario. An improvement of nearly 3.2 dB in SIR is achieved. The hot spot cell of traffic 3.25 times larger than nominal load (or 4.33 times larger than nearby cells ) is affordable in the system.

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