l pattern or other choices. The typical clusters contain 4, 7, 12, or 21 cells. In order to work properly, a cellular system must verify the following two main conditions: The power level of a transmitter within a single cell must be limited in order to reduce the interference with the transmitters of neighboring Figure 1-2 The older way of handling mobile communications. Up to 20-25 miles Overlap System Areas 200 Watt Output Up to 75 miles Could get service from either transmitter, causing interference. Up to 20-25 miles System Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to GSM Introduction to GSM cells. The interference will not produce any damage to the system if a distance of about 2.5 to 3 times the diameter of a cell is reserved between transmitters. The receiver filters must also conform. Neighboring cells cannot share the same channels. In order to reduce the interference, the frequencies must be reused only within a certain pattern. The pattern may also be a seven-cell pattern, which is shown in Figure 1-3. In order to exchange the information needed to maintain the communi- cation links within the cellular network, several radio channels are reserved for the signaling information. Sometimes we use a 12-cell pattern with a repeating sequence. The 12-cell pattern is really a grouping of three four-cell clusters, as shown in Figure 1-4. The larger the cell pattern, the more the coverage areas tend to work. In general, the larger cell patterns Figure 1-3 The seven-cell pattern. (Source: ETSI) Figure 1-4 The 12-cell pattern. (Source: ETSI) Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to GSM Chapter 1 are used in various reuse patter