co-channel interference

Co-channel interference or CCI is crosstalk from two different radio transmitters using the same channel. Co-channel interference can be caused by many factors from weather conditions to administrative and design issues. Co-channel interference may be controlled by various radio resource management schemes. Cellular mobile networks In cellular mobile communication (GSM & LTE Systems, for instance), frequency spectrum is a precious resource which is divided into non-overlapping spectrum bands which are assigned to different cells (In cellular communications, a cell refers to the hexagonal/circular area around the base station antenna). However, after certain geographical distance, these frequency bands are re-used, i.e. the same spectrum bands are reassigned to other distant cells. The co-channel interference arises in the cellular mobile networks owing to this phenomenon of frequency reuse. Thus, besides the intended signal from within the cell, signals at the same frequencies (co-channel signals) arrive at the receiver from the undesired transmitters located (far away) in some other cells and lead to deterioration in receiver performance. Adverse weather conditions For FM, vertical layering of moisture content and temperature in the atmosphere (inversion layers) can occasionally cause signals to travel hundreds or thousands of kilometres further than usual. An inversion layer (or duct) is most commonly observed over high pressure regions and may affect radio signals for several hours to several days. The phenomenon is commonly referred to as anomalous propagation and is more likely in hot, dry weather in late summer. Poor frequency planning Poor planning of frequencies by broadcasters can cause CCI, although this is rare. A very localised example is Listowel in the south-west of Ireland. The 2RN UHF television transmitter systems in Listowel and Knockmoyle (near Tralee) are on the same frequencies but with opposite polarisation. However, in some outskirts of Listowel town, both transmitters can be picked up causing heavy CCI. This problem forces residents in these areas to use alternative transmitters to receive RTÉ programming.