high >>>>> low) Figure 45.8 ERMES protocol timing messages only on channels broadcasting FSI values of 12, 22, 27, no more than 50ms differential delay is measured at the receiver. 29, or 30. The FSNs do not correspond to frequency channel Zoning is employed and the 12 seconds, 16 batch sub-sequences numbers. (Figure 45.9) are allocated to a zone. 45.10.2.3 Transmission 45.11 Indirect satellite paging Several hundred 100/250W transmitter base stations per country The SkyTel service in the US uses a geostationary satellite, West will initially be employed in quasi-synchronous operation. The Star IV, to communicate with a satellite up-link station operating in modulation of adjacent base stations must be synchronised such that C-band using spread spectrum modulation in California, and satel- Figure 45.9 ERMES frequency subset indicators 45/18 Radio paging lite down-link stations across the US. The caller uses the PSTN to BT (1986) The book of the CCIR Radio Paging Code No. 1, make a toll free call from anywhere in the US to the central paging Radiopaging Code Standards Group. computer in Washington D.C. which then passes its calls to the French, R.C. (1984) A high technology v.h.f. radio paging receiver, up-link station in California. Selected paging calls are then trans- IEE 1984 Conference on Mobile Radio Systems, September. mitted via the normal local zone transmitters. The total transmission IEC (1987) No. 489, Part 6, 2nd Ed. time is approximately 20 seconds and it is claimed to have 85% Komura, M. et. al. (1977) New radio paging systems, Japan Tele- coverage of the US population. Redundancy is built into the system com Review, 19, July. by having a second satellite which operates in the Ku-band. The bit Makitalo, O. and Fremin, G. (1970) New system for radio paging error rate of the system is approximately one error in ten million bits over the FM broadcasting network, TELE (English Ed.) XXII, sent. The system can be accessed from the UK by telephoning the Washington number and the u.h.f. pager can be hired i