08-11-2012, 05:52 PM
Cellular Concepts
Cellular.pptx (Size: 141.01 KB / Downloads: 30)
Introduction
Early days a mobile phone had to stay within the coverage area.
So engineers proposed hexagonal cells for mobile phones.
The centers cell have directional antennas that would transmit/receive.
The technology to implement these ideas did not exist because of frequency allocation.
So they go for the concepts of frequency reuse and handoff, as well as a number of other concepts.
Directional antennas
2-way-radio cell towers were at the centers of the cells.
Each tower has three sets of directional antennas aimed in three different directions with 120 degrees for each cell.
This provides a minimum of three channels for each cell.
Movement from cell to cell and handover
The signal is manually switched from one frequency to another as needed.
Switching from one cell frequency to a different cell frequency is done electronically. This is called the handover or handoff.
The mobile unit then automatically switches from the current channel to the new channel and communication continues.
Conclusion
Advantages
Increased capacity
Reduced power use
Larger coverage area
Reduced interference from other signals
Disadvantages
Higher frequency is the only one disadvantage when comes into coverage.