avoidance in the white-space world is based on a composite of location awareness and channel scanning to detect the presence or absence of TV channels and beacon detection to detect the presence of wireless microphones. However robust these mechanisms might be, other users of the band, TV broadcasters, wireless microphones and more recently 700-MHz cellular operators at the top of the band and public safety users will need to be convinced that white-space devices do not present a threat either technically or commercially. We return to this topic in Chapter 15. There are also similarities between military radios and specialist mobile radios including radio equipment used by public protection and disaster-relief agencies. This includes a need to ruggedise equipment, make equipment waterproof rather than splashproof, make equipment dustproof and secure. Encryption and access security are covered in Chapter 10 of 3G Handset and Network Design. In the US specialist mobile radio user equipment and network equipment is standardised by the Association of Public Communication Officers. Analogue radios were specified as APCO 16 and digital radios are specified as APCO 25. In the UK and parts of Asia these radios comply with the TETRA radio standard though a standard called TETRAPOL with narrower channel spacing is used in some countries including France. The physical layer implementation of these radios is covered in the wireless radio access network hardware of Chapter 12. Making Telecoms Work Figure 5.2 Inmarsat IsatPhone Pro hand-held terminal. Reproduced with permission of Inmarsat Global Limited. APCO-compliant user devices have 3-watt power amplifiers to deliver deep rural coverage and are relatively narrowband with narrow channel spacing in order to realise good sensitivity on the receive path. Other specialist low-volume but high-value markets include satellite phones. Inmarsat, for example, have a new portable handset³ designed by EMS Satcom (hardware) and Sasken (the protocol stack). This is illustrated in Figure