Cellular Concept PDF

Chapter 3 Cellular Concept 1 WireLess networking 12/13/2024 5:01 PM  Sections 3.1. Introduction 3.2. Frequency Reuse 3.3. Channel Assignment Strategies 3.4. Handoff Strategies 3.5. Interference and System Capacity 3.6. Trunking and Grade of Serv...

Chapter 3 Cellular Concept 1 WireLess networking 12/13/2024 5:01 PM  Sections 3.1. Introduction 3.2. Frequency Reuse 3.3. Channel Assignment Strategies 3.4. Handoff Strategies 3.5. Interference and System Capacity 3.6. Trunking and Grade of Service 3.7. Improving Capacity in Cellular Systems 2 WireLess networking 12/13/2024 5:01 PM  3.1. Introduction  The design objective of early mobile systems was to achieve a large coverage area by using a single, high powered transmitter with an antenna mounted on a tall tower.  The approach achieved very good coverage.  The disadvantage is the impossibility of frequency reuse.  Any attempts to achieve frequency reuse would result in interference.  The bell mobile system in New York city in 1970s only support a maximum of 12 3 simultaneous WireLess networking calls over a 1000 square miles. 12/13/2024 5:01 PM Cont…  The figure below shows cellular Concept 4 WireLess networking 12/13/2024 5:01 PM  Cont…  Increased demand for mobile services became imperative to restructure the radio telephone system to achieve high capacity with limited radio spectrum while at the same time covering very large areas.  The cellular concept was a major breakthrough in solving the problem of spectral congestion and user capacity.  The concept is replacing a single high power transmitter (large cell) with many low power transmitters (small cells).  Each base station is allocated a portion of the total 5 number of channel available to the entire WireLess networking system. 12/13/2024 5:01 PM  Cont…  Nearby base stations are assigned different groups of channels.  This fundamental principle is the foundation for all modern wireless communication systems.  The concept allows mobile within a country or continent to be manufactured with the same set of channels.  Any type of mobile can be used anywhere within the region. 6 WireLess networking 12/13/2024 5:01 PM  3.2. Frequency Reuse  Cellular radio systems rely on an intelligent allocation and reuse of channels throughout a coverage region.  Each cellular base station is allocated a group of radio channels to be used within a small geographic area called a cell.  Base stations in adjacent cells are assigned channel groups which contain completely different channels than neighboring cells.  The base station antennas are designed to achieve the desired coverage within the WireLess networking 12/13/2024 5:01 PM 7 particular cell.  Cont…  The group of channels used to cover different cells that are separated from one another by distances large enough to keep interference levels within tolerable limits.  The design process of selecting and allocating channel groups for all of the cellular base stations within a system is called frequency reuse or frequency planning.  The figure below shows the concept of 8 cellular frequency reuse. WireLess networking 12/13/2024 5:01 PM 9 WireLess networking 12/13/2024 5:01 PM  Cont…  The hexagonal cell shape is conceptual and a simplistic model of the radio coverage.  It has been universally adopted since the hexagon permits easy and manageable analysis of a cellular system.  The actual radio coverage of a cell is known as the footprint and is determined from field measurements or propagation prediction models.  The real footprint is amorphous in nature.  A regular cell shape is needed for systematic system design and adaptation for future growth. 10 WireLess networking 12/13/2024 5:01 PM  Cont…  Hexagon closely approximates a circular radiation pattern.  Choosing a circle to represent the coverage area might seem natural.  Adjacent cells cannot be overlaid upon a map without leaving gaps or creating overlapping regions.  Omnidirectional antennas are used in center-excited cells.  Sectored directional antennas are used in corner-excited cells. 11 WireLess networking 12/13/2024 5:01 PM  Cont…  Consider a cellular system which has a total of S duplex channels.  Each cell is allocated a group of k channels (k