Understanding directional load balancing using per call measurement data

Several load balancing techniques have been proposed and studied for CDMA systems using a variety of simulation-based data-sets. In this study, we present actual call data captured at Wellington, New Zealand, from their leading telephone services provider, in order to understand how calls in the active-set are shared amongst cell-sites. Two groups of cell-sites are analysed to understand this phenomenon including (a) the busiest cell-sites, which experience the highest call volume and (b) the cell-sites with the poorest coverage or reference pilot signal strength. We obtain a day long trace on the date of an All Blacks Rugby game in Wellington, New Zealand and further delineate the rush-hour data on this day. Rush hour is defined as the hour at which the most calls are placed during the day, which co-incided with the time at which the Rugby game started. We observe that the busiest sites are located in downtown Wellington and calls in the active set migrate in the direction of caller traffic, which was moving towards the Westpac stadium, where the Rugby game was held. Calls are not picked up by the nearest neighbors (to the busiest sites) and are absorbed by the neighbors that are proximal to the stadium, suggesting directional load balancing. In the case of cell-sites with poor coverage, the load is distributed amongst the nearest neighbors, when the coverage of a particular cell-site reduces, over time.