5. Cellular networks
In today’s context, cellular networks play an important role in concern of telecommunication. Most of the today’s networks are mobile networks and other types of networks are getting less popular with the efficiency and easiness of mobile networks.
Personal requirements are usually fulfilled using cellular networks. Cellular networks are built with major principles which allow the subscribers to travel with in a large area without losing the connection with the server.
Major dissimilarities in between a cellular network and other fixed networks are listed below.
Some of the key principles used in cellular networks are;
• Frequency reuse
Thus, the principle of cellular systems is to divide a large geographic service area into cells with diameters from about 2 to 50 km, each of which is allocated a number of RF channels.
Transmitters in adjacent cells operate on different frequencies to avoid interference. Since, however, the transmit power and antenna height in each cell are relatively low, cells that are sufficiently far apart can reuse the same set of frequencies without causing co-channel interference. Figure 7.4.14 shows typical frequency reuse patterns in cellular systems.
The power of the cellular concept is that interference is not related to the absolute distance between cells, but to the ratio of the distance between co-channel cells to the cell radius.
Therefore, it is the system engineer’s responsibility to decide how many radio channels or “circuits” would be created through reuse. The amount of co-channel interference in the 4-cell reuse pattern shown in Figure 7.4.14 would be more than in the 7-cell reuse pattern.
However, using a 4-cell reuse pattern would create a larger number of channels than a 7-cell pattern in the same geographical area. The cellular system planner has to balance the number of channels (which would lead to the capacity of the system) with the amount of co-channel interference that is tolerable.
• Cell splitting
Another attractive feature of the cellular concept is cell splitting. Larger cells can be easily reduced into smaller-radius cells over a period of time through cell splitting as shown in Figure 7.4.15.
When traffic reaches the point in a particular cell such that the existing allocation of channels in that cell could no longer support a good grade of service, that cell would be subdivided into a number of smaller cells – with even lower transmitter power – fitting within the area of the former cell. The reuse pattern of channels could then be repeated on a new, smaller scale.
The theoretical coverage range and capacity of a cellular system are therefore unlimited. As the demand for cellular mobile service grows, additional cells can be added, and as traffic demand grows in a given area, cells can be split to accommodate the additional traffic.
Read more
Follow Us