rial and error methods that may be valid for some parts of the network and invalid for other parts. Then, during network deployment, some more measurements are made and the parameters are fine-tuned again. Once the network goes 'live', the drive test and NMS statistics help in further fine-tuning of the parameters, and it is at this point that a set of default parameters is created for the whole network. However, as the network is inhomogeneous, these default parameters may not be sufficiently accurate in all regions, thereby bringing down the overall network quality - and leading to a reduction in revenue for the network operator. Radio network optimization must be a continuous process that begins during the pre- launch phase and continues throughout the existence of the network. Transmission Network Planning and Optimisation 3.1 BASICS OF TRANSMISSION NETWORK PLANNING 3.1.1 The Scope of Transmission Network Planning In the GSM system, the transmission network is generally considered to be the network between the base stations and the transcoder sub-multiplexers (TSCM). The transmission network connects the radio network to the mobile switching centre (MSC), and hence, by virtue of its position and functionality, it acquires an important position in the mobile network infrastructure (see Figure 3.1). Ater' O&M Interface Figure 3.1 Scope of transmission network planning Fundamentals of Cellular Network Planning & Optimisation A.R. Mishra. C 2004 John Wiley & Sons, Ltd. ISBN: 0-470-86267-X TRANSMISSION NETWORK PLANNING AND OPTIMISATION Base Transceiver Station Filter Transmission Output/ System interface Input Transmission 2 MCC (TRU) 8 KCC TRX 1 A-bis Transmission TRX 2 TRX 3 Figure 3.2 Transmission system in BTS 3.1.2 Elements in a Transmission Network Base Station Transceiver (BTS) An overview of the BTS is provided in Chapter 2. Here we look at the BTS from the transmission planning perspective (i.e. the transmission system within a base station) as shown in Figure 3.2. The base station consists of a transmiss