Visibility State Model for Base Station Cooperation in Cellular Mobile Systems

Base Station (BS) Cooperation technology is expected for the future radio access technology in cellular architecture to improve user throughput at cell edge regions. The effectiveness of the technology highly depends on the radio transmission quality from the BSs in cooperation. The visibility state between a BS and a mobile station (MS) dominates the radio transmission quality at higher frequency bands expected for next generation cellular systems such as IMT-Advanced. In order to evaluate the performance of the BS cooperation technology, this paper establishes a visibility state model between BSs and an MS in typical urban areas with high-rise buildings. The visibility state is simulated using three- dimensional building maps of several areas in Tokyo metropolitan regions. This paper first analyzes the changes in the visibility state between BSs and the MS to establish the visibility state transition model in terms of the number of visible BSs from the MS. The visible state hold distance, which is the metrics of the dynamics in the visibility state transition, is then evaluated. From the results of these analyses, the paper clarifies that the visibility state holding distance could approximately be expressed as an exponential function of the visibility probability between a BS and an MS.