r Each dedicated channel has its own control channel for performance monitoring and control. Figure 5.3 The main types of radio channels. Introduction to Telecommunications Network Engineering of the common control channel the MSs send, for example, call-request mes- sages in the case of outgoing calls and location update messages when they notice that they have arrived in a new location area. One dedicated user channel or a traffic channel is allocated for each call. During an call, a MS is said to be in dedicated mode. Each dedicated channel requires the transmission of control information in addition to speech transmission. This is needed for transmission power control of mobile stations and for transmission of performance monitoring information from MSs to the network. When the call is cleared the dedicated channel is released and available for other users. In Figure 5.3 we see that BSs are connected to the mobile switching center by a radio relay system or by a cable line (optical or copper cable). Especially in rural areas microwave links are attractive because cables are usu- ally not available for BSs and they are very expensive to install. Microwave radio requires and antenna but this is not a problem-an antenna tower is always available because it is needed for the BS antennas. Operating Principle of a Cellular Network In the fixed telephone network each subscriber is identified by the number of a certain subscriber loop that is connected to a certain telephone socket. In the case of a cellular telephone the identification is in the telephone set (MS) itself. The cell structure of the network and the mobility of the user require the cellular network to keep track of the location of each MS in order to be able to route a call to the destination. We now review the principles of how the cellular network manages the mobility of users and how calls are initiated and received. We introduce the operation of a cellular network in general; therefore, the terms and operation presented may not be consistent with t