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Received Jun 18, 2017; Accepted Oct 18, 2017
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1. Introduction
Load balancing is a mechanism whereby overloaded BTSs distribute some of their traffic to less loaded neighbors in order to make the radio resource more efficient [1].
Telecommunication infrastructures originally designed to carry a defined amount of traffic are often congested by an overwhelming request of resources. A naive solution is to expand the infrastructure to match the increasing demand. Due to limitations in available space and shortness of resources, this solution is not possible. The best solution is to carefully tune the parameters of the existing system to accommodate the new traffic demands [2].
There are a number of methods to balance traffic load among BTS [3]. One of the most important methods is based on antenna down tilting [4]. With the down tilt, one directs the antenna radiation further down to the ground. The down tilt is advisable when one wishes to decrease interference and coverage in some specific areas, each BTS to meet only its designed area. When selecting the optimum tilt angle, the goal is to have as high signal strength as possible in the area where the BTS should be serving traffic [4]. Beyond the serving area of the BTS, the signal strength should be as low as possible. A too aggressive down tilting strategy however leads to an overall loss of coverage and creates coverage holes which eventually lead to call drop.
The second method is to adjust the BTS coverage by varying transmitter power. A minimal transmitter power effectively disallows more distant mobiles to access the BTS, thereby decreasing the coverage area and prohibiting distant mobile users to access the BTS [5]. Hence, reducing BTS coverage area runs at the danger of creating coverage holes. Having the coverage holes on the cellular system adversely affect the performance...