Wireless communications are expected to be the dominant mode of access technology in the next century. Besides voice, a new range of services such as multimedia, high-speed data, etc. are being offered for delivery over wireless networks. Mobility will be seamless, realizing the concept of persons being in contact anywhere, at any time. Two developments are likely to have a substantial impact on the mobile communications systems deployed in the twenty-first century: the adoption of International Mobile Telecommunications-2000 and wireless asynchronous transfer mode (ATM). They are two different but cooperative approaches to providing high-speed wireless access. The limitations of the radio-frequency spectrum and radio channel propagation impose special constraints on the technologies of systems to be deployed. To make future mobile systems globally acceptable, standardization efforts are underway in the International Telecommunications Union and the ATM Forum. This paper reviews the international standardization efforts, the challenges to the technologies imposed by the radio spectrum limitations, radio channel propagation-induced distortions, and possible solutions. Evolution, migration, and architecture issues also are discussed.

Recent progress in communications technology is about to bring on dramatic changes in business and home life. NTT laboratories began personal multimedia communications (PMC) services experiments to achieve personalized multimedia communications services. In 1990, NTT announced the visual intelligent and personalized (VI&P) communications services plan as its service vision for the beginning of the 21st century. NTT's phase 1 experiments based on this VI&P plan focused on N-ISDN services. The phase 2 experiments focused on creating new applications based on optical communications and ATM technology. The sudden increase in the number of cellular phones, reflects the rising demand for person-to-person communication, even for private use. The P in VI&P symbolizes this latest trend. Taking this into consideration, the phase 3 experiments concentrate on personal-use multimedia service based on wireless access by means of the personal handy phone system (PHS) and satellites. This paper describes the phase 3 experiments and the technology involved. Subjects discussed in some detail are high-speed digital data communication services using PHS terminals, personal mobility using premises intelligent network, and the nomad office using communication satellite. Possible future personal communication services are also proposed.

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.

A novel long haul 5 GHz 16 QAM digital radio system, which has 200 Mbit/s transmission capacity within the 40 MHz interleaved channel allocation, is proposed and described. It is designed to be overbuilt on existing FDM-FM routes with an approximately 50 km repeater spacing. To achieve the 5 bit/s/Hz RF spectral efficiency, the 16 QAM modulation and Nyquist cosine roll-off spectral shaping techniques (\alpha = 0.5) are investigated. Then a new signal shaping filter, differential encoding and carrier recovery techniques are presented. Finally, the effects of TWT amplifier nonlinearity on a 16 QAM signal are experimentally investigated.