e regarded as a hybrid it saw commercial service before it, opening in late 1981. technology system, and several of its characteristics such as time NMT450 uses a channel spacing of 25kHz, speech modulation slotted signalling channels and continuous signalling during call being analogue FM with a peak frequency deviation of 5kHz, the have been carried through into the GSM system design. same as standard PMR practice. NMT900 also uses a frequency Coming later to the European scene, C450 has chiefly only served deviation of 5kHz, but with a 12.5kHz channel spacing to double the German market, although systems are also operating in Portugal the number of available channels, albeit with a degraded adjacent and South Africa. channel rejection performance which must be taken into account during frequency planning. Signalling is at 1200 bit/s using audio 47.4.5 fast frequency shift keying (FFSK). Error protection of the signall- ing information is by means of a Hagelbarger convolutional forward The GSM standard was developed as a joint initiative by the mem- error correcting code. bers of the Conference of European Posts and Telecommunications NMT was designed from the outset to support international roam- administrations (CEPT) with the eventual aim of building a unified ing and was first implemented with full four nation roaming in the pan-European network, giving the user a near uniform service four participating countries (Norway, Sweden, Finland and Den- throughout all European countries. An added bonus of a common mark). Since then NMT450 has been deployed in many other standard should be lower terminal equipment prices through econ- European countries (Austria, Spain, Netherlands, Belgium, Luxem- omies of scale. bourg, France, Iceland, Faroe Is., Turkey and Hungary) but due to Work on the standard started in 1982, and by 1987 all the basic differences in the frequency allocations in the 450MHz band be- architectural features were decided. The full Phase 1 specification tween countries, not all networks are fully 