Comparison of upgrade techniques for mobile communication systems

For current mobile communication systems, two limitations exist which restrict their capacity and range of application. They can be characterised as an equipment limit which is determined by the maximum number of mobile stations that can be supported by a base station with given equipment, and an interference limit, which corresponds to a maximum number of carriers that can be used in a cell if a given signal-to-interference ratio must be guaranteed. Depending on base station (BS) equipment dimensioning and propagation conditions in the cell coverage area, one of the two limits will apply and define a maximum capacity of the base station that cannot be exceeded without modifications of the base station. Several techniques for base station upgrades have been developed which focus on one of the two limits or both. In the paper, traditional techniques such as spectrum upgrade, sectorisation, codec rate reduction and cell splitting are revised and compared to a new technique called A-SDMA (adaptive space division multiple access), which is introduced. Based on the comparison, evolution plans for different areas of application are developed which take these upgrade techniques into account and provide upgrade paths for mobile communication system infrastructures, applicable to current systems such as GSM as well as future systems (UMTS, FPLMTS)