Wireless Ad Hoc and Sensor Networks

Background on Networking 171.3.1.2 Cellular Network DesignThe process of frequency allocation to the base stations to decrease theinterference between the neighboring base stations is called frequencyreuse, and is explained in detail in the following section. Frequency reuseconcept is explained by considering the cell shape to be hexagonal. Thehexagonal cell is conceptual and is a simplistic model of the radio coveragefor the base station. This shape, which has been universally adopted,permits easy and manageable analysis of a cellular system. The actualradio coverage of a cell, known as the footprint, differs from the assumedhexagonal structure and can actually be determined from field measurementsand propagation prediction models. The concept of frequency reuseis explained in the next paragraph.Frequency ReuseIntelligent allocation and reuse of channels throughout a coverage regionis important for a cellular radio system. The design process of selectingand allocating channel groups for all of the cellular base stations withina system is called frequency reuse. The concept of cellular frequency reuseis clearly illustrated in Figure 1.2. In the figure, the seven shaded cellsnamed A to G form a cell cluster. This cell cluster is repeated over theentire coverage area. Total available channels are equally distributedamong the cells in a cell cluster. The cells with same name signify thatthey use the same set of channels.The total number of cells in a cluster defined as cluster size is equal to7 for the scenario shown in Figure 1.2. Because each cell contains oneseventhof the total number of available channels, the frequency reusefactor is 1/7. The figure clearly shows the frequency reuse plan overlaidBIndicates ClusterGFBAEGFCDAEGFCDBAECDFIGURE 1.2Illustration of cellular frequency reuse. (From Rappaport, T.S., Wireless Communications:Principles and Practice, Prentice Hall, Upper Saddle River, NJ, 1999. With permission.)