ased on a low fixed monthly fee and the fee based on the amount of transmitted and received data. This is makes GPRS superior to earlier circuit-switched alternatives, such as HSCSD. 5.8 Problems and Review Questions Problem 5.1 What are the main advantages of cellular systems compared with the old gen- eration radio telephone systems that did not utilize a cellular network structure? Introduction to Telecommunications Network Engineering Problem 5.2 An analog radio telephone network has a frequency band of 100 (bidirec- tional) FDMA channels. The network covers a 50 X 50-km urban area. Give the maximum number of simultaneous calls in the network if (a) only one base station is in use; (b) the network is upgraded to a cellular network with a cell size of 10 X 10 km and the frequency reuse ratio is 1:9 (each channel is used again in every ninth cell); (c) cell size is reduced to 1 X 1 km; and (d) cell size is reduced further to 0.35 X 0.35 km (that is, equal to the minimum size of cells in early GSM). For simplicity, assume here that the cells are rec- tangular and all channels are used as traffic channels. [Hint: Divide all chan- nels of the network between a cell cluster (group) of nine cells. Then repeat this cluster to cover the geographical area of the network.] Problem 5.3 What are the two main types of channels used in each cell of a cellular mobile system? Problem 5.4 What is handover? Explain the handover principle, that is, how it is carried out in a cellular network. Problem 5.5 How does the cellular network route an incoming call to a subscriber located anywhere in the network or even in a different country? What are the roles of the HLR and VLR in the routing of an incoming call? Problem 5.6 Explain the main phases that occur in the radio interface of a cell when an outgoing call is requested. Explain also what happens when an MS in a cellu- lar network receives an incoming call. Problem 5.7 Explain the applications of cordless telephones. How do cordless systems basically differ from cellular systems