e excessive when mobile consists of a TDMA timeslot with a gross bit rate of more than 4 transmitters are to be combined. Tuned cavity filters 22.8kbit/s. On each RF carrier at the BTS, 8 TDMA timeslots have the advantage of low loss, regardless of the number of trans- are available. mitters to be combined, but they are large, expensive, and require 2. BTS to BSC (the A-bis interface). Each voice channel consists some method of remote retuning. Generally, hybrids will tend to of a 16kbit/s data stream. Typically, this will be carried on a dominate because PCN networks will probably have no more than 2Mbit/s datalink, with four 16kbit/s voice circuits being multi- 4 transceivers at the majority of sites, and the slightly higher losses plexed onto each 64kbit/s slot. will be offset by the fact that retuning is not necessary. 3. BSC to MSC (the 'A' interface). Each voice channel will have been 'transcoded' from 16kbit/s to 64kbit/s A-Law PCM for connection to the MSC and onwards to the network. This transcoding will normally take place at the MSC end of the 48.9.3.1 Diversity BSC to MSC link. PCN base stations typically offer receiver space diversity. The 48.9.3 Radio frequency characteristics of PCN method of combining is different from vendor to vendor, but will at least require separate receivers and two separate receive antennas. The gain on the uplink is typically 4dB or SO. There is no downlink The PCN BTS transmits and receives in the 1800MHz band. In the gain. UK the following frequency allocations have been licensed: 1. Sub Band A. Ch 563 to 636. BTS Receive 1720.4MHz to 1735.0MHz. BTS Transmit 1815.4MHz to 1830.0MHz. 48.9.3.2 Frequency hopping 2. Sub Band B. Ch 671 to 744. BTS Receive 1742.0MHz to 1756.6MHz. BTS Transmit 1837.0MHz to 1851.6MHz. Frequency hopping can be implemented on PCN base stations. On 3. Sub Band C. Ch 811 to 884. BTS Receive 1770.0MHz to each successive frame, the MS and BTS can change frequency 1784.6MHz. BTS Transmit 1865.0MHz to 1879.6MHz. giving a maximum of 216 hops per second. T