ber of 1.8GHz channels dependent upon the predicted traffic demand of the particular location. The size of the cell depends upon a number Call set up of factors, namely, terrain, traffic density, quality and local clutter. Within the PCN, system cells are expected to vary in size from a few Consider the simplified network in Figure 48.2. 'A' is a customer on decades of metres to several kilometres. Functions within the BTS the PCN who wishes to make a call to 'C', a customer on the PSTN. include radio transceiver, channel coding, radio signalling, fre- 'A' is registered on the PCN. 'A' dials 'C'. The call is passed from quency hopping, paging control, access detection, measurements, the BTS to the MSC via the BSC. The MSC recognises that it is a encryption, radio channels. call destined to the PSTN and selects an outgoing route. The route to the PSTN must include an echo canceller (EC). The PSTN routes 48.4.2 Base station controller (BSC) the call to 'C'. 'C' answers and conversation commences. The echo canceller is required due to the long delay in the radio The BSC provides all the necessary local radio control features, i.e. subsystem, and as the call will be going to a two wire PSTN, intra-BSC handover, power control and channel allocation. The customer echo would be introduced. To PSTN Figure 48.1 Main elements within a PCN network Planning a PCN 48/5 Figure 48.2 Simplified PCN network Now consider the situation where 'A'(customer on PCN) wishes 3. Are there any other limiting factors? to call 'B', also a customer on the PCN. 'A' dials 'B'. The call is passed to the MSC via the BSC. The MSC Given the above, the BSC allows the network operator to optimise recognises that it is a call destined to B. The PCN sends a query to the BSC location in order to reduce local transmission costs. the HLR to find the location of B. The MSC is advised that B is registered on VLR at MSC 2 and is given B's routeing number. MSC 1 routes the call to MSC 2, MSC 2 VLR identifies B as being a 48.6.1.1 BSC support of BTS's particul