rk architecture of the 4G networks is not yet defined, but some industry experts expect the system to be a layered one as shown in Figure 5.1. As seen in the figure, the next generation network is expected to be a combination of existing and advanced technologies with seamless handovers between Advanced Cellular Network Planning and Optimisation Edited by Ajay R Mishra © 2007 John Wiley & Sons, Ltd Fourth Generation Mobile Networks Distribution Layer e.g. DAB/DVB Mobile Layer GSM/ EGPRS/ UMTS Hot Spot Layer e.g. WLAN Personal Network e.g. Bluetooth Fixed Layer e.g. wired telephony Figure 5.1 Layered structure of a next generation network (DAB, digital audio broadcasting; DVB, digital video broadcasting) technologies irrespective of the geographical location, having high data rates, high capacity, high quality of service and low costs. The 4G network hierarchy is expected to consist of four broad levels of networks: the personal networks, the local networks, the cellular networks and the satellite based networks (distribution networks). Above the personal networks are the local networks, which may consist of LANs using wireless LAN technology. These LANs normally have a greater coverage area than personal networks and may be used in hotspots like cafes, hotels and airports. The cellular network level comes next, which will consist of existing 2G and 3G cellular networks, as well as the enhanced cellular networks, and at the highest level will be the satellite based mobile networks, having the largest of the coverage areas of all the network levels. As a result of this multilevel hierarchy, the 4G user devices will be expected to perform vertical handovers as well as horizontal handovers. Horizontal handovers will take place within one network level and may include soft handovers and hard handovers. On the other hand, vertical handovers will be performed between different network levels. Here is an example. User devices, e.g. a laptop that is using WLAN to communicate with servers within office premises, would perf