n users are actually sending or receiving data. Rather than dedicating a radio channel to one mobile user for a fixed period of time, the available radio resources can be concurrently shared by several users. This efficient use of the scarce radio resources means that a larger number of GPRS users can share the same bandwidth and be served from a single cell. The actual number of users supported depends on the application being used and how much data each user has to send or receive. Because the spectrum efficiency is improved in GPRS, it is not as necessary to build idle capacity that is only used during peak transmit hours. GPRS therefore lets the operator maxi- mize system usage and efficiency in a dynamic and flexible way. In fact, all eight time slots of a TDMA frame can be made available to each user. However, as the number of simultaneous users increases, colli- sions will occur between the randomly arriving data packets. This will cause queuing delays on the downlink. Therefore, the effective throughput perceived by each user decreases, but more gracefully. The idea of concate- nation or aggregation of the time slots to be available to one user makes this far more palatable for the end user to understand how he or she can bundle services together and run the data faster. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hil Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. GPRS Introduction Chapter 2 Cells and Routing Areas The geographic coverage area of a GPRS network is divided into smaller areas known as cells and routing areas, as shown in Figure 2-14. A cell is the area that is served by a set of radio base stations. When a GPRS mobile station wants to send data or prepare to receive data, it searches for the strongest radio signal that it can find. Once the mobile scans for the strongest signal and locates the strongest base station, it then notifies the network of the cell it is re