Toshihito Kanai

Autonomous reuse partitioning in cellular systems

A simple, decentralized procedure for adaptive channel allocation, autonomous reuse partitioning (ARP), is proposed. Radio channels are viewed in the same order at any base station, and the first channel that satisfies a carrier-to-interference ratio (CIR) threshold is allocated. ARP easily achieves reuse partitioning, in which channels higher in the order are reused at shorter distance by mobile stations from which stronger signal levels are received. An efficient frequency reuse pattern helps ARP to improve traffic handling capacity while avoiding interference. Performance was evaluated by means of computer simulation in which a system accommodating portable units with 70 channels is assumed. Compared with random channel allocation, ARP doubles traffic handling capacity and decreases the probability of interference by 1/4. Actual transmitter power control is shown to improve capacity by 9%. ARP improves traffic handling capacity at the cost of CIR margin in each channel. This can create problems for mobile stations, such as car-mounted units, which suffer rapid fluctuation in signal levels.<<ETX>>

A handoff control process for microcellular systems

A handoff control process, which can handle frequent cell-boundary crossings by mobile radio users in microcellular systems, is presented. Handoff determination criteria are investigated under microcellular propagation models. As a result, it is shown that relative field strength measurement should be applied because of its almost twice higher spectrum efficiency than that of relative distance measurement. In application, measurement frequency greatly increases due to not only cell size reduction but also microcellular propagation characteristics. In order to solve this problem, a mobile-station-originated handoff process is proposed. This process becomes feasible in a TDMA (time-division multiple-access) system because mobile stations can be easily equipped with a measurement function.<<ETX>>

Experimental digital cellular system for microcellular handoff

An experimental digital cellular system composed of a private branch exchange (PBX)-based MSC (mobile switching center), three base stations, two mobile stations, and a radio channel simulator, is developed. The system uses a mobile originated handoff process; i.e. a mobile station requests a handoff to the MSC based on signal strength from surrounding base stations. All control channels are multiplexed on the same carrier so that mobile stations can monitor signal strength quickly. Experimental results show that a handoff decision can be made within a second, even under slow fading (such as walking speed), which agrees with the theoretical calculation very well. It is shown that the whole handoff procedure works reliably under a typical microcell propagation condition.<<ETX>>