Hitoshi Takanashi

Dynamic base station selection for personal communication systems with distributed control schemes

Distributed control schemes allow base stations in personal communication systems to be placed at locations corresponding to high expected traffic. This flexible base station placement creates significant overlapping coverage areas that can be utilized to improve system performance [1]. A new technique for dynamic base station selection in systems with overlapping cells is considered and its effect on traffic performance is characterized. The technique realizes robust performance for personal communication systems in fluctuating and heavily tapered traffic. A mathematical analysis based on a state transition model is used to evaluate performance of a system that employs the proposed technique. The results indicate that improved blocking probability and carried traffic performance are obtainable. Computer simulations were undertaken confirm the analytical results.

Frequency-segregated dynamic channel allocation for asynchronized TDMA/TDD frame among base stations

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.

High-Quality and High-Speed Wireless Multimedia Transmission Technologyfor Personal Handy Phone System

The Personal Handy-phone System (PHS), developed as a PCS, has been very widely accepted. This system offers many benefits as the infrastructure of the mobile data communication services that are expected to be available soon with the popularity of nomadic computing. Data communication systems based on PHS and some applications are proposed in this paper. One of the key technologies, an error control scheme, is also introduced. Three kinds of possible system configurations are discussed as a data communication platform for PHS. One of them has an ARQ function which corrects all errors that occur in the propagation path. Conventional application software on nomadic computers can be used in the mobile environment because this ARQ function is installed as a lower layer protocol. The introduced system connects all mobile computers to all servers that are on the networks which include ISDN, the conventional analog PSTN, cellular networks and PHS networks.

SIR Weighting Combining Diversity Using Matched Filter for Personal Communication Systems

We propose a novel SIR weighting postdetection combining diversity scheme with a new accurate SIR estimation method. The SIR is estimated and used as the weighting factor to compensate severe cochannel interference, one of the most important issues for PCS in terms of frequency utilization. Theimprovement offered by the proposal depends on SIR estimation accuracy.The SIR is, in this paper, estimated by a matched filter where theauto-correlation between received signal and unique word is calculated. Computer simulationsconfirm that the SIR of each diversity branch can be estimated easily andaccuratelyby the proposed SIR estimation method. The proposed diversity scheme achievesaperformance very close to that of ideal SINR weighting diversity underRayleighfading with severe cochannel interference. When average SIR = 10 dB and thenumber of branches(L)=4, the proposed diversity scheme lowers the requiredEb/N0 by 5 dB at BER = 1×10-3compared to conventional maximal ratio combining diversity. This paper alsopresentsthe unique word length required to realize adequate performance, i.e.,robustnessagainst high-pitch Rayleigh fading.

Pre-repeat go-back-n ARQ with error prediction in fading channel

A novel go-back-n (GBN) ARQ scheme using the pre-repeat (PR) technique is proposed and its efficiency is investigated by computer simulations. It is efficient in digital cordless-phone systems using TDMA-TDD under slow fading environments. In those systems, transmission errors are mainly caused by Rayleigh fading. Since the fading changes the signal level very slowly compared to the TDMA-TDD frame period, transmission errors in the up-link channel match those in the down-link channel. In the proposed technique, this correlation is utilized to predict errors occurring in the transmitted slots. Using the predicted error, retransmission is made before the request from the receiver is received. By using the PR-GBN scheme only at the transmitter, the data throughput is improved over conventional GBN. In this paper, the throughput efficiency of PR-GBN and conventional GBN are calculated and compared under PHS (Personal Handy-phone System) conditions. As a result, the proposed scheme is shown to improve the throughput efficiency; the gain in Eb/No is 4.2 dB at the throughput of 0.9.