to- multipoint radio applications, Br Telecom Technol J., 2, (2), In future systems, three issues are likely to be important: cost, pp. 19-24. spectrum efficiency and delay associated with multipoint systems. Bannister, G. and Capewell, C. (1988) The Australian digital radio The use of higher level modulation schemes (e.g. 16 QAM) would concentrator system DRCS IEE International Conference on lead to an increase in spectral efficiency and potential reduction in Rural Telecommunications, London, U.K., Conference Publica- delay. However, counter measure techniques now commonly used tion No.286, pp. 56-62. on trunk radio systems would then need to be carefully adapted to Battistig, G. et. al. (1985) A simple point-to-multipoint subscriber increase the system range and reduce costs. radio system in the 1.5GHz band, IEEE International Con- TDM/TDMA techniques are also being employed in fibre systems ference on Communications, ICC'85, Chicago, U.S.A., pp. 23.3. for application in the local loop (Oakley, 1988; Hoppitt, 1989). In Battistig, G. Marczy, A. and Rona, P. (1986) IER, a subscriber radio such systems, the use of passive splitters ensures that no electronics system in the 1.5GHz band, Proceedings of the Eighth Collo- is used between the exchange and the subscribers' premises. There quium on Microwave Communications, Budapest, Hungary, pp. are advantages in making the TDM/TDMAsub-system for provid- 19-20. ing telephony over passive optical networks (TPON) such that they Beaupre, D.M. (1983) Five years of TDMA subscriber radio IEEE can be readily employed for radio use. This provides additional International Conference on Communications, ICC'83, Boston, flexibility in employing the most appropriate medium (radio or U.S.A. pp. 375-379. fibre) in different circumstances whilst using common Beaupre, D.M. Le-Ngoc, T. and Zavitz, H.J. (1984) A new point-to- TDM/TDMA sub-systems and network interfaces. multipoint microwave radio system, 6th International Sympo- References 52/13 sium on Subscriber Loops and Services, ISS