is installed in a localized area to meet some specific requirements. Cell breathing One problem encountered with CDMA systems is known as cell breathing. When traffic in a cell increases, SO does the interference level and as a result the power levels of the mobiles must increase. Particularly towards the edge of a cell where higher power levels are required anyway, a point is reached where the mobile cannot increase its power level any more and reception is lost. It can be seen that there will be areas where there is no coverage if traffic is high. To prevent this problem, careful network planning is required to ensure it can cope with the peak levels of traffic that will be encountered. 280 Newnes Guide to Radio and Communications Technology TD-SCDMA Time Division Synchronous CDMA is a third generation cellular telecommunications system that has been developed in China. It uses unpaired channels, i.e. send and receive are on the same frequency and accordingly uses time division duplex to enable data to be sent in both directions. In order to enable the transmit-receive changeovers to occur at the same time SO that interference between cells is reduced, all the cells are synchronized. Also the signals within the different base stations and mobiles are synchronized to ensure complete orthogonality of the spreading codes SO that the different CDMA signals being transmitted at the same time can be effectively decoded with the minimum of interference between them. A further feature of the system that may be implemented in years to come is that smart antennas can be used. These will detect the approximate location of the mobile user and beam the signal in that direction. In this way power can be delivered only where it is needed and interference is reduced. The system provides a variety of different data rates for different types of service. Voice data is at a rate of 8 kbps, while fax is transmitted at 9.6 kbps. For data applications a variety of data rates up to 2.048 Mbps can be used. The basic system comprises th