Cellular wireless networks
Wireless communication tutorial
Wireless cellular networks
The cellular network is an underlying technology for mobile phones, personal communication systems and wireless networks etc. The technology is being developed for the mobile radiotelephone to replace high power transmitter / receiver systems. Cellular networks use lower power, shorter range, and more transmitters for data transmission.
Characteristics of cellular systems
Wireless cellular systems solves the problem of spectral congestion and increases the capacity of the users. The characteristics of cellular systems are as follows -
Offers very high capacity in a limited spectrum.
Reuse of the radio channel in different cells.
Activate a fixed number of channels to serve an arbitrarily large number of users.ateurs by reusing the channel throughout the coverage area.
Communication always takes place between the mobile and the base station (not directly between the mobiles).
Each cellular base station is assigned a group of radio channels in a small geographic area called a cell.
Neighboring cells are assigned different groups of channels.
By limiting coverage within cell boundaries, channel groups can be reused to cover different cells.
Keep interference levels within tolerable limits.
Reuse or frequency planning.
Organization of the wireless cellular network.
The cellular network is organized into several low power transmitters of 100 W or less.
Shape of cells
The coverage area of cellular networks is cells , each cell having its own antenna to transmit the signals. Each cell has its own frequencies. Data communication in cellular networks is served by its base station transmitter, receiver and control unit.
The shape of the cells can be square or hexagonal -
A square cell h as four distant neighbors d and four remote Root 2 d
- Better if all adjacent antennas are equidistant
- Simplifies the choice and switch to a new antenna
A hexagonal cell shape is highly recommended for its coverage and easy calculations. It offers the following advantages -
- Provides equidistant antennas
- The distance from the center to the top is equal to the length of the side
The re-usefrequency usage is the concept of using the same radio frequencies in a given area, which are separated by a considerable distance, with minimal interference, to establish communication.
Frequency reuse offers the following advantages -
- Allows in-cell communications on a given frequency
- Limits exhaust power to adjacent cells
- Allows frequency reuse in neighboring cells
- Use same frequency for multiple conversations
- 10 to 50 frequencies per cell
For example, when N the cells use the same number of frequencies and K is the total number of frequencies used in systems. Then each cell frequency is calculated using the formulas K/N.
In Advanced Mobile Phone Services (AMPS) when K = 395 and N = 7, then the frequences per cell on average will be 395/7 = 56. Here the cell frequency is 56.