hn Wiley & Sons, Ltd. Making Telecoms Work Table 16.1 Specialist user needs Wide-area coverage Better than cellular particularly in rural areas and/or within buildings in urban environments 'All informed' user capability The ability to hear other users in an 'open' channel 'Instant access' onto available channels Call setup time has to be less than 250 milliseconds Multigroup announcements Wide-area broadcast messages Dynamically changeable priority levels Secure authentication and encryption Voice clarity Includes task optimised noise cancellation, specialist hands-free and whisper phones for covert surveillance Press to talk With option to work full duplex if needed Talk groups Geographical or functional Interworking/interoperability Problematic as we shall see later Storm plans/special event plans Preset response to particular events including disaster recovery contingency planning. Sleeper phones The ability to stun phones remotely and re-enable them as listening or more recently listening and watching and sensing devices. Ruggedised hand sets Waterproof, dustproof, shockproof fireproof and explosionproof handsets Latency has always been important and the benchmark generally has been to deliver onto channel times of less than 250 milliseconds. In terms of radio performance, the most important metric has traditionally been to deliver good rural coverage and good urban inbuilding penetration for two-way voice communication. In Europe this has been achieved by working at VHF or UHF with both the handsets and base stations working at higher powers than cellular radio. The narrow channel spacing used, typically between 6.25 and 25 kHz and the relatively narrow operational bandwidths, typically 5 MHz or less, makes it possible to deliver good receive sensitivity. In the USA there are substantial two-way radio system deployments in the 800-MHz band. In common with European systems these operate at higher power than cellular systems. APCO 25 portables, for example, are allowed to produce 5 watts and the base stations