## Dealing with interference

#### Because most interference (excluding noise) in communications systems is generated by other items of equipment, it is often possible with good design to minimize the effects of interference. This can be achieved both by judicious selection of modulation and coding format to be the least sensitive to a given type of interference, and also by tackling the causes of the interference. Crosstalk in telephone lines, for example, can be reduced by careful layout of cables, or by replacing cables with optical fibre, which has no external radiation to cause crosstalk. Ghosting caused by multipath can often be cured by using directive antennas to avoid picking up reflections. Some modern cellular base-stations and even some mobile handsets are using adaptive antennas which in real time change the direction of the antenna beam to null out interferers and focus on the wanted signal. #### Co-channel and adjacent channel interference is again controllable by good system planning and good selective filtering within the receiver modem. |

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