To realize S-band mobile satellite communications and broadcasting systems, the onboard mission system and equipment were designed for the Japanese Engineering Test Satellite VIII. The system performs voice communications using handheld terminals, high-speed data communications, and multimedia broadcasting through a geostationary satellite. To enhance system efficiency and flexibility, the onboard mission system features phased-array-fed reflector antennas with large antenna diameter and baseband switching through onboard processors. Configurations and performance of the subsystems and key onboard equipment, large deployable reflectors, feed arrays, beam forming networks and onboard processors, are presented. The S-band mobile systems and onboard equipment will be verified through in-orbit experiments scheduled for 2002.

The dynamic channel assignment (DCA) strategy proposed here uses information on the mobile station speed and direction of motion to reduce the number of forced call terminations and channel changes in micro cellular systems. This SMD (speed and moving direction) strategy is compared with the main DCA strategies by simulating a one-dimensional service area covering a road on which there are high-speed mobile stations (HSMSs) and low-speed mobile stations (LSMSs).The simulation results show that the SMD strategy has the best performance in terms of forced call termination and channel change. The performance difference between the SMD strategy and the other DCA strategies increases as cell size decreases and as HSMS speed increases. While the SMD strategy does not yield the best total call blocking rate, its total carried load is the best when cells are small and HSMS speed is high. Also, the SMD performance improves when the HSMS offered load is small and the LSMS offered load is large. Although the SMD strategy requires information on the speed and direction of each mobile station and it increases call blockings somewhat, it reduces the number of forced call terminations and channel changes considerably, which is important in micro cellular systems.

This paper proposes Channel Reservation for Ahead Cells (CRAC)" scheme for street micro-cellular systems. The scheme enables mobiles to reserve the same channel over several cells at once. This paper analyzes both CRAC and FCA (Fixed Channel Assignment) in a ring-shaped service area where high speed mobiles and low speed mobiles move. In the analysis, the priority control which prioritizes hand-off calls and reservation calls over new calls over new calls is also taken into account. Obtained results include the blocking rate, the forced call termination rate, the average number of channel changings and the system utilization. From numerical results, CRAC is found to perform better than FCA with regard to the average number of channel changings and the forced call termination rate.

In estimating the performances of Distributed control Dynamic Channel Assignment (DDCA) strategies in sector cell layout systems, we find that sector cell layout systems with DDCA achieved a large system capacity. Moreover, we also indicate the problem, which is the increase of occurrences of cochannel interference, raised by using DDCA in sector cell layout systems. The new channel assignment algorithm, which is called Channel Searching on Direction of Sector (CSDS), is proposed to cope with the problem. CSDS assigns nominal channels to each sector according to their direction so that the same frequency channel tends to be used in sectors having the same direction. We show, by simulations, that CSDS is an adequate algorithm for sector cell layout systems because it significantly improves performance on co-channel interference while only slightly decreasing system capacity.