This paper overviews our highly accurate location service (LCS) system for the Personal Handy Phone System (PHS) infrastructure. It is an enhanced version of the PHS location service that commenced service in May 1998. The system concept, system configuration, and position estimation algorithm are described. Field test results are also presented. We show that the proposed position estimation algorithm reduces the position estimation error by about 50% compared to the conventional cell-ID-based algorithm. NTT DoCoMo Inc. started the enhanced PHS LCS in February 2001.

This paper describes the construction and performance evaluation of a mobile video communication system composed of an H.263 video encoder, decoder, and RF transceiver equipment. It can establish a video connection using a 32 kbits/s wireless channel because it uses automatic repeat request (ARQ) as the error control scheme. Retransmission control can produce excessive transmission delay, but the improved ARQ protocol and coding-rate control scheme adopted by this system minimizes the delay. This ARQ protocol uses short ARQ frame length and an acknowledgement/negative acknowledgement (ACK/NAK) indicator. The coding-rate control scheme uses backward NAK signals to reduce the coding rate of the video encoder as necessary. We measure the transmission delay characteristics of this video system and confirm that the proposed scheme can reduce the delay over a noisy channel. Subjective assessment tests involving videophone usage are also conducted. Test results show that in a noisy channel (BER=3/spl times/10/sup -3/), this system can achieve the same mean opinion store as in a noiseless channel.

This paper presents several interesting technologies that will support the next-generation of mobile wireless communications. First, a higher data transmission system based on the Personal Handy-Phone System (PHS) is introduced which provides 64 and 128 kb/s data services. Multi-slot channel assignment, which decreases blocking probability, is also presented. New wireless access, called PHS-ODS, is proposed. This can adaptively determine whether a received signal is voice or data, and forward the signal to the user's voice or data terminal as appropriate. A wireless agent that combines the conventional mobile agent with information specific to the mobile terminal environment is discussed. Furthermore, the application of AO/DI (always on dynamic ISDN) to wireless system is discussed; its concept and simulated effective data transmission speed are described.

This paper presents the design and performance of a trial fiber-oriented wireless access system with a small packaged optical interface. Signal extraction and frequency arrangement (SEFA) technology is proposed in the trial system to improve the input dynamic range. The designed 40-cc optical interface performance is discussed with respect to an optical loss of 5 and 15 dB. The overall performance of the system, to which the designed optical interface and SEFA technology are implemented, is presented using an /spl pi//4-QPSK signal with a transmission rate of 384 kb/s. It is shown that the receiver sensitivity reaches 8 dB/spl mu/V even if the optical loss is 15 dB.

The authors examine microcell radio systems that use subcarrier transmission and spectrum delivery switch (SDS) techniques to meet traffic demands for a large number of portable phones. Radio signals are transmitted over fibre between base stations (BS) and a central station (CS). Relationships between blocking probability and offered traffic are described as a parameter of SDS ports. Optical link performances, such as link gain and carrier-to-noise ratio (CNR), are presented. Moreover, it is found that using FM techniques can improve the dynamic range by 20 dB compared to conventional methods for the uplink from BS to CS. The proposed technique can also increase the number of transmittable carriers compared to conventional methods for the downlink from CS to BS. This network strategy results in more flexible transmission.>

This paper proposes a newly developed, highly precise cross-polarization interference canceller (XPIC), utilizing digitalized transversal filters. Performance of the digitalized XPIC is solely determined by quantization and tap numbers and is not affected by any circuit imperfection. Moreover, it can be universally applied to different bit rates and various modulation schemes. Performance of the XPIC is analytically estimated for various modulation schemes and various interference conditions. Then, the digitalized XPIC is realized and applied to a 12.5 MB 256 QAM digital radio system. Experimental results have closely conformed with theoretical estimations and it is confirmed that the XPIC is a powerful countermeasure against multipath fading for a future digital radio.