TP A-LAW PCM A-LAW PCM CCITT G.711 CCITT G.711 Figure 48.8 BSS interfaces 1. Base Transceiver Station functions: interface to Mobile Sta- The channel spacing is 200kHz, and the transmitted signals are tions at 1800MHz; encryption; channel coding and interleav- approximately 120kHz wide. The modulation method is GMSK ing; frequency hopping execution; random access detection; with a BT product of 0.3 (i.e. the baseband data is filtered in a provision of control channels; transcoding/rate adaptation; up- Gaussian filter with a bandwidth of 0.3 times the bit rate). This link measurements, including timing advance; observation and allows baseband data to be transmitted at 270.833kbit/s using only reporting of idle channels. 120kHz of spectrum. The specifications for receiver dynamic range, 2. Base Station Controller functions: channel allocation; radio transmitter spurious emissions and intermodulation products are channel management; frequency hopping management; access particularly stringent to ensure satisfactory operation in a dense grant; processing of measurements; power control; handover; traffic environment. paging. The highest power class for PCN Base Stations is 20W, measured at the output of the transmitter. However, before this 20W reaches Traffic channels are set up between the Mobile Station and the the antenna, it must pass through a power combining network which MSC. Speech from the handset is encoded digitally using an effi- couples all the transceivers in the BTS to the same antenna connec- cient algorithm ('RPE-LTP') which reduces the analogue speech to tor. The choice of the correct combining method is crucial to avoid 16kbit/s datastream. This 16kbit/s undergoes coding to improve the unnecessary losses. error protection, and is carried through the network as follows: Two methods exist: hybrid combining, and tuned cavity combin- ing. Hybrids have the advantage of small size, low cost, and broad- 1. MS to BTS (the Um interface). Each voice channel from a band operation, but the losses incurred becom