r unique codes to share this frequency band. The common control channels are also spread over the CDMA band by their own spreading codes, which are known by the MSs. When a MS is in the idle mode it uses the code of the FOCC to listen to the network and to be able, for example, to receive a paging message in the case of an incoming call. When a call is connected, a new code is allotted to the user for dedicated speech communication. CDMA is an interesting technology and it provides many other fea- tures that we have not discussed, such as soft handover or handoff. To per- form those tasks, a MS might use more than one BS (operating at the same carrier frequency) at the same time with the different codes. Multiple BSs receive a signal from the MS simultaneously and the MS combines signals received from different BSs. The MS does not need to switch over from one BS to another at a certain time instant as is done with the hard handover in FDMA/TDMA networks. We restrict our discussion about CDMA and other cellular systems to brief introductions of the most important networks. For further information about CDMA, the reader should refer to, for example, [1]. Introduction to Telecommunications Network Engineering 5.4.5.7 Japanese Digital Cellular (JDC) JDC system is also known as personal digital cellular (PDC). It is a separate system from the previous analog one but it utilizes dual-mode terminals that are able to use existing analog systems as well. The network technology is close to that of the European GSM. 5.4.6 Third Generation Cellular Systems The main forces behind development of the third generation systems (3G) have been driven by the second generation systems' low performance data services, incompatible service in different parts of the world, and lack of capacity. In the 1990s, the ITU started a project to develop a future global 3G system, which is known today as International Mobile Communications (IMT)-2000. 5.4.6.1 IMT-2000 The IMT-2000 system was designed to be a global system for third genera- tion m