ly as 1981 studies ardised in terms of: were in progress to identify the technical options. Since that time two digital standards have been developed within Europe to the 1. Physical parameters of the radio link e.g. modulation, frame status of interim European Telecommunications Standards by the rate, data rate. European Telecommunications Standards Institute (ETSI), as fol- 2. System and user signalling. lows: 3. Speech transmission. CT2/CAI digital specification 49/5 Base units Line unit coverage zones Cordless handsets = Handset Figure 49.2 Wireless PBX system using antennas 49.3.1 Radio aspects The detail parameters of the radio interface are given in ETSI (1991) but it specifies two level frequency shift keying with Gaus- sian filter shaping and a frequency deviation of 14.4kHz to 25.2kHz With only forty channels available to support the high traffic de- above carrier frequency to represent a binary 1 and equal shifts mands it was clear that the benefit of dynamic channel selection would be needed. Thus both handset and base are required to below the carrier frequency for binary 0. This represents a modula- tion index range of 0.4 to 0.7. As previously noted time division operate on any of the forty channel pairs through selection of the duplex transmission is used with 1ms for each transmit and receive channel with the lowest co-channel and/or adjacent channel inter- ference. This technique is more than adequate to meet the traffic packet. A dead time between transmit and receive bursts has been created to allow transmitters to ramp up and ramp down their power capacity needs of residential and small business operations, but other techniques need to be exercised to raise the effective capacity in a way designed to limit spectral splatter across adjacent channels. This period also permits oscillators to settle between bursts. to meet the requirements of larger business systems. To increase the frequency re-use ability of the system in large buildings cordless business systems will need to use the multi-cell