12.5 kHz channels using GMSK. Tetrapol delivers very good range when used for voice services but is bandwidth limited for multimedia. WiDEN WiDEN is an evolved version of iDEN, the Integrated Digital Enhanced Network standard developed by Motorola in the early 1990s. The frame/slot structure is either 3 slot or 6 slot similar to cellular US TDMA. When combined with 64-level QAM modulation this can deliver per user data rates in the order of 100 kbit/s, but no WiDEN products are presently available. 16.8 APCO 25 APCO25/Project 25 handsets have 12.5-kHz or 6.25-kHz channel spacing and a one- or two- slot air interface using QPSK. The handsets have good range performance but are bandwidth limited for multimedia. Manufacturers include Motorola, Tait, Maxon and Bosch. As can be seen, none of the available two-way radio technologies summarised in Table 16.2 are ideal for multimedia. The standards that are capable of supporting the higher data rates needed do not yet have products available. Table 16.2 Comparison of present two-way radio technologies Digital PMR (DMR 446 ETSI) TETRA TEDS TETRAPOL WiDEN APCO25 6.25 kHz or 12.5 kHz TETRA is a 4 slot Originally WiDEN an evolved 12.5 kHz one channels or 12.5 kHz 25 kHz channel developed by version of iDEN or two with two time slots, 2 spaced physical MATRA now which time slot level or 4-level FSK, layer, TETRA EADS, a traditionally uses channels or supports peer-to-peer TEDS is an narrowband a 25-kHz channel 6.25 kHz in unlicensed evolved version 12.5 kHz air with 3 or 6 time channels, spectrum or through a with channel interface slots very similar repeater or trunked spacing scaleable using GSMK. to TDMA cellular modula- system, typically uses up to 150 kHz and Very good for where a 30-kHz tion, 9.6 very low bit rate 2 modulation long-range channel is divided K/bit/s kbit/s codecs and options up to voice, into 3 or 6 time data rate power output limited 64-level QAM bandwidth slots, potentially to 500 milliwatts yielding potential limited for 100 kbits/s data gross data rat