Masanori Taketsugu

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>>

A new highly efficient multicast protocol on ad hoc network under slow fading environments

This paper proposes a new data link layer protocol for multicast communications on ad hoc TDMA mobile networks, which accomplishes highly efficient transmission throughput in slow fading environments. The ad hoc network structure assumed in this paper is a network with a proxy access point which relays broadcasting messages among the terminals. The proposed multicast data link protocol integrates a retransmission control function with a flow control function by a collision based procedure. This collision based procedure using a negative acknowledgement (NAK) message can improve throughput owing to the effective retransmission achieved by the NAK message. Moreover, the proposed protocol achieves the flow control function by introducing the collision procedure of the NAK message with a sending message from a sender in order to facilitate a complete transmission guarantee in the upper layer. Its throughput performance is evaluated by computer simulations in applying this protocol to the Japanese Personal Handyphone System (PHS). It is shown that, under the conditions of 1% frame error rate (which can be considered as the mobile groupware condition) the realizable effective transmission rate is about 28 kbps with a physical layer transmission rate of 32 kbps, and it suffers from no degradation regardless of the network layer packet length or the number of the group members.