Techniques to increase cell capacity | frequency reuse,spatial isolation

This page mentions frequency reuse and spatial isolation techniques to increase cell capacity. It compares benefits and drawbacks of frequency reuse and spatial isolation.

There are two main ways to increase the cell capacity.
•  frequency reuse and •  spatial isolation

frequency reuse

frequency reuse

The figure-1 depicts the frequency reuse concept in gsm radio frequency planning. As shown frequency in one cell can be reused in another cell. This concept results into intercell interference when power of the transmitted signal is large enough. Refer GSM RF Planning which mentions frequency reuse patterns used in GSM network deployment.

In satellite systems, frequency reuse effectively doubles satellite bandwidth and capacity of satellite. Typically satellite bandwidth composed by pair of 12 transponders. There will same frequency channel in one transponder and the other satellite transpoder. Using this method, two transponders transmit on the same frequency. This results into intra cell interference and inter cell interference. As a result spatial isolation has been empoyed.

spatial isolation

spatial isolation

This technique employs use of narrow beamwidth antennas. Each of these antennas focuses on narrow region of the earth and hence will results into increase in capacity of the cell. This is because different earth stations can use the same frequencies. There will not be any interference as these will be highly directional type of antennas. These antennas are known as spot beam antennas or smart antennas. Figure-2 depicts that same antenna is used to provide cellular service at same frequency to the different mobile users or subscribers using narrow focused beams. Refer beamforming smart antenna design.

In satellite systems, extra sets of satellite transponders are employed. Moreover special antenna techniques are employed to segregate the inputs as well as outputs. For example, usually satellite can use max. up to 4 sets of 12 transponders each, all using the same RF frequencies. With frequency reuse techniques and using spot beam antennas, a total of 48 satellite transponders can be used.

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