Explain different methods to reduce the co-channel interference

8. Explain different methods to reduce the co-channel interference.

The different methods used to reduce co-channel interference are broadly classified into three.

They are

1. By providing large separation among the two co-channel cells.

2. By reducing the antenna heights at the base station.

3. By the usage of directional antennas at the base station.

The first two techniques ne not employed because they have disadvantageous effects i.e., method 1 is responsible for reducing the system efficiency for increase in number for frequency range channels. While method 2 is responsible for reducing the reception level at the mobile unit. The method 3 is most commonly used because, along with reducing co-channel interference, it also increases the channel capacity (during heavy traffic).

There are different techniques to generate directional antennas

1. Tilting the antenna and creating a notch along the unwanted space.

2. Using umbrella patterns.

3. Using parasitic elements.

1. Tilting the Antenna: The tilting of an antenna in a desired manner produces an energy pattern with a notch in the desired direction. Hence, ibis notch prevents the co-channel interference problem. The tilting of the antenna is done in two ways.

(1) Electrically

(ii) Mechanically

In the electronic down tilting, the phases between the elements of a co-linear array antenna are varied. In the mechanical down tilting the physical rotation of antenna is occurred.

2. Umbrella Pattern: The umbrella pattern is obtained with the help of a staggered discone antenna. The umbrella pattern reduces the long distance co-channel interference problems, particularly cross talk. Even though, the umbrella pattern is not used for a directional antenna pattern, it can be used for an omnidirectional antenna pattern. In hilly areas, where the height of antenna cannot be increased to cover weak signal spots, results in co-channel interference. In this case also we can use umbrella pattern. The umbrella pattern allows us to increase the antenna height but, we can still decrease cochannel interference.

3. Parasitic Elements: The use of parasitic elements provides the desired pattern and hence we can avoid the cochannel interference. This antenna combination has a parasitic antenna and a driving antenna, the driving antenna is the source of current flowing in the parasitic antenna. The different combinations of their arrangements produce different patterns as described below.

When the lengths of the elements are identical and closely spaced the current flowing through the parasitic clement is strong. This creates equal level of patterns.

When the length of parasite is more than drive antenna, the parasite act as reflector and the pattern in the reflected direction is more.

When the length of parasite is less than drive antenna, the parasite acts as a director and the pattern is more inclined in the forward direction. These three patterns are illustrated in figure (a) figure (b) and figure (c) respectively.