A new selective-repeat (SR) ARQ scheme using the pre-repeat (PR) technique is proposed. The proposed scheme is efficient in digital cordless-phone systems employing TDMA-TDD under slow fading environments. Because fading affects both up-link channel and down-link channel simultaneously, the occurrence of error in the up-link channel is closely correlated with that in the down-link channel. This characteristic can be applied to predict errors in transmitted data by observing received signal. In this paper, throughput efficiency of the proposed scheme is investigated by computer simulation, and is compared with conventional SR-ARQ. It indicates that the proposed scheme is advantageous to transmission with a long round-trip delay.

We propose a novel wireless multimedia communication system. It provides a new data communication service by integrating packet-switched and circuit-switched channels. Future wireless multimedia systems must treat data communication calls efficiently to achieve high radio resource utilization. In the proposed system, a data communication user first establishes a packet-switched link to a remote server which is connected to a LAN, or an ISP (Internet Service Provider). Once a packet-switched link is established, the user is always offered real-time e-mail service or push services from the Internet over the packet-switched channel. When there is more information to be transferred than can be handled by the packet-switched channel, a circuit-switched link is established that replaces the packet-switched link to realize high speed data transmission. This replacement is performed automatically. Once the data transfer is completed, the circuit-switched link falls back to the packet-switched link. Thus, radio resource utilization is increased because the circuit-switched link is established only when really needed. This paper describes the proposed system concept, system configuration and system capacity as estimated by computer simulations. The results show that the proposed system improves system capacity by about 7% compared to conventional systems. Moreover, the blocking probability of data communication calls can be strongly reduced compared to conventional systems.

This article proposes an effective error control scheme, MODS-ARQ, for PHS data communications. This scheme is based on SR-ARQ, which was modified to increase the maximum transmission speed. The throughput efficiencies achieved using the MODS-ARQ protocol were estimated by computer simulations and laboratory tests. MODS-ARQ achieves a maximum transmission speed of 29.2 kbit/s and more than 20 kbit/s under poor transmission conditions. The proposed MODS-ARQ is a very effective and simple error control technique for use in designing a mobile data communications infrastructure based on PHS.

We propose a novel dynamic slot allocation (DSA) algorithm with a distributed control scheme for mobile multi-media TDMA systems. In TDMA systems, it is possible to raise the data transmission rate by allocating multi-slots to data communication calls. For example, the data transmission speed with 2 slots assigned is double that with 1 slot. The proposed DSA scheme makes it possible for mobile multi-media TDMA systems to achieve high spectrum utilization. The proposed algorithm decreases the number of slots assigned to data calls under high traffic loads and increases it under low traffic loads. The main feature of the proposed scheme is that the number of slots assigned to data calls changes dynamically according to interference levels. The proposed DSA algorithm is evaluated by computer simulations. The results show that the proposed DSA algorithm improves the blocking probability characteristics by about 30% compared to fixed slot allocation (FSA). Moreover, it realizes higher average transmission throughput performance under low traffic; the proposed DSA method decreases the forced termination rate by 2/3 compared to the FSA method

We propose a novel dynamic channel allocation (DCA) algorithm with a distributed control scheme for mobile radio systems in which the TDMA/TDD frames of inter-base station links are not synchronized. TDMA/TDD is one of the best radio access technologies for mobile radio systems such as PHS and DECT because the same frequency is used by the forward and reverse links and many hardware parts can be commonly used in the transmitter and the receiver. A distributed control scheme significantly facilitates dynamic channel allocation, however, it makes it difficult to synchronize TDMA frames among the base stations. This asynchronization degrades the frequency utilization because one slot may interfere with two slots of a near-by base station. Furthermore, the EIRP difference between the forward and reverse links of TDMA/TDD severely degrades the frequency utilization factor if the TDMA frame phase is not synchronized. This paper proposes a frequency-segregated dynamic channel allocation scheme that makes it possible to use some of the inactive forward link channel resources for asynchronized TDMA/TDD. Those resources cannot be utilized because of excessive interference that cannot be avoided by a conventional DCA algorithm. The proposed DCA algorithm is evaluated by computer simulations. The results indicate that the proposed DCA algorithm improves blocking probability characteristics by 10-20%. This algorithm compensates the defects of TDMA/TDD due to the asynchronized frame and unbalanced EIRP