Mutsumu Serizawa

Location registration and paging for in-building personal multi-media communication systems

This paper describes a novel mobility management scheme which is efficient for multi-media in-building mobile communication systems. Most in-building mobile communication systems will be realized in a pico-cellular structure. An in-building user mobility model to be used for designing a pico-cellular systems mobility management scheme is first established. Then proposed is a novel location registration and paging scheme which can simultaneously cope with the bursty location registration traffic and the increased paging traffic. In addition, this scheme can cope with the call set up delay requirements in multi-media communication. The performance of the proposed scheme has been evaluated by computer simulation in which the user mobility model at lunch time in an office building is used.

SDL-Net: a wireless access link to broadband multimedia networks

SDL-Net (Super high speed DownLink Network) is proposed as a wireless access link to a broadband multimedia network, and its basic features are described. In the SDL-Net, the transmission data rate in downlink is 30 to 300 times faster than the transmission data rate in uplink. With this asymmetric architecture, most of multimedia personal communication services are realized through hand-held portable multimedia terminals. The SDL-Net is economically constructed by additionally installing high speed downlink transmitters in existing narrowband personal communication networks. By combining high speed downlink with narrowband links, both seamless CBR services such as voice communication and spot beam VBR services such as electronic publishing are realized.

A radio access scheme for CSMA/CD LAN

The utilization of a carrier-sense multiple access with collision detection (CSMA/CD) local area network (LAN) as an inter-radio-port transmission medium and an autonomous macroscopic diversity, based on bus contention selective control is proposed for a local area radio network. In this scheme, a radio packet transmitted by a mobile terminal can be captured by several radio ports that are connected to CSMA/CD LAN. The radio port that has captured the packet most reliably transmits the packet into the LAN. The performance of the autonomous diversity port selection is analyzed, and it is shown that satisfactory performance is obtained with the proposed scheme.<<ETX>>

The effective interleaving scheme against the shadowing in S-band digital mobile satellite broadcasting system

We propose an improved interleaver that has a better performance against the shadowing which is peculiar to the S-band digital mobile satellite broadcasting system. The scheme of interleaver proposed here is the modified convolutional interleaver that offers much robustness compared to the conventional periodic one. Our result shows that the performance of the proposed scheme is superior to that of the conventional periodic interleaver when the shadowing extends within one third of the total interleaving delay.

S-band digital mobile satellite broadcasting system

The digital satellite mobile broadcasting system is one of the most attractive candidates of the next-generation vehicular information systems. However, we have a number of problems to overcome in order to realize such a system technologically and commercially. One of the most serious problems is the service deterioration caused by shadowing. A possible answer to the shadowing problems is the installation of the gap filler and transmission techniques adequate to the utilization of the gap filler. Since each multipath can be demodulated separately and then combined with each other utilizing the RAKE receiver, code division multiplexing (CDM) can provide good transmission quality. In this work we have adopted a combination of the satellite and the gap filler, using CDM with pilot signals as the means of transmission. The system architecture and parameters of this system are described in detail. Moreover, an experimental system was constructed and field experiments were carried out. We conclude that the proposed system can provide high-performance multimedia services.

Broadband multi-media communication system with asymmetric wireless access link, SDL-Net

SDL-Net (super high speed downlink network) is proposed as a wireless access link to a broadband multi-media network, and its physical-layer and datalink-layer protocols are described. In SDI-Net, the transmission data rate in the downlink is 100 to 1000 times faster than the transmission data rate in the uplink. Since the backward channel is much narrower than the forward channel, a sophisticated ARQ technique is indispensable for errorless data transmission through such an asymmetric air interface. Considering the ARQ scheme and the transmission quality in the downlink, the downlink throughput and the uplink traffic are investigated for large file transfer services such as an electronic publishing. The round trip delay which is one of the important performance measures, is analyzed. The backbone networks for the SDL-Net are also discussed.

Network and protocol architectures of hybrid multimedia mobile access communication system

We present a network architecture of the hybrid multimedia mobile access communication (MMAC) system through which a number of broadband multimedia mobile communication services are provided for hand-held, small radio terminals. In the hybrid MMAC system, the conventional personal communication system (PCS) link is used for uplinks while the broadband radio link under development in the MMAC Promotion Council is utilized for downlinks. The hybrid MMAC system has a lot of advantages such as the small terminal size, the low terminal cost and the smooth introduction of the full standard MMAC system, which is a bi-directional broadband system. In this paper, the concept and the network architecture of the hybrid MMAC system are presented. The protocol stacks and the operation sequences of this system are also described.

DS-SS code acquisition in a rapid fading environment

In CDMA mobile communication systems, a frequency-spread pilot signal often plays an important role, e.g., for synchronization and for channel impulse response measurement; therefore it usually is given a quite large process gain. However, in a fast fading environment, the received pilot signal level may decrease making synchronization performance deteriorate substantially. In the analysis, modeling the temporal fading function as a lowpass-filtered complex Gaussian process, it is shown that the probability density function (pdf) of the despread signal level follows a Rayleigh distribution whose variance is given by a summation of the discrete-time sampled values of the impulse response of the lowpass filter. The pdf then is used to obtain the mean acquisition time. It is shown that there is no advantage in using a long code when the Doppler frequency is high. The optimum code length is determined as a function of the maximum Doppler frequency. Furthermore, a rapid PN code acquisition scheme expected to be robust under fast fading conditions is proposed. The scheme is based on partial code correlation and a majority decision rule. Partial code correlation is less influenced than full code correlation by a rapid fading and the majority decision rule reduces the misdetection and false alarm probabilities. The optimum parameter values for the proposed scheme are also determined. For a large process gain signal, the partial code length should be optimized for the maximum Doppler frequency.

Feedback parallel interference cancellation system using turbo code

In this paper, a parallel interference cancellation system using turbo codes is proposed. In general, canceller systems suffer from errors in the initial decision and those errors cause performance degradation. We use turbo decoding in the initial decision in order to remove the errors. Moreover, we aim to improve the performance by feedback of the signal after cancellation. The proposed system has two types of feedback: iteration of the turbo decoder and feedback after cancellation. We evaluate the BER performance of the proposed system and the optimal number of both iterations and feedback. As a result of the computer simulation, the BER performance of the proposed system greatly improved and was superior to the conventional cancellation system.

A novel carrier frequency offset estimation scheme for OFDM systems utilizing correlation with a pilot symbol without null sub-carrier

The orthogonal frequency division multiplexing (OFDM) carrier frequency offset estimation scheme is investigated. The carrier frequency offset is detected by monitoring a certain pattern of the frequency domain power differences along the sub-carriers of the pilot symbol. The power differences are raised by inter sub-carrier interference (ICI). In order to estimate the carrier frequency offset effectively, the time domain filtering (windowing) is carried out. The carrier frequency offset estimation performances corresponding to the pre-determined sequences which are transmitted as a pilot symbol are evaluated by computer simulations. Peak-to-average power ratio characteristics are also investigated. The results show that the proposed scheme is effective even for the frequency selective fading channel.