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Interference Cancellation

21 Hydref 2005

Interference Cancellation techniques are any technique or combination of techniques that allow an existing receiver to operate with higher levels of co-channel interference. The motivation of improving a receiver’s performance in co-channel interference is to increase the spectrum efficiency of a system usually by allowing a greater geographical re-use of frequencies (although in the case of CDMA systems improved spectrum efficiency usually comes by allowing greater use of the orthogonal code space). It is a general principle that a communication system should be designed to avoid interference in the first place, either through network planning or with effective radio resource management and medium access control. However, increasing use of license exempt spectrum means that interference is unavoidable and so the radio system must not only avoid interference but also mitigate against its presence.

A key point is that the strategies employed to mitigate interference are very dependent on the source of the interference and its relationship to the wanted signal. The use of interference cancellation techniques can also make systems more reliable, either by design or by incorporating additional signal processing into existing systems, where a retro fitment is practical. Interference cancellation techniques have long been applied to radio systems in conjunction with adaptive arrays, primarily in military applications, but also in some civil applications. Adaptive arrays exploit the spatial separation of the wanted and interfering signals to spatially filter or cancel the interfering signals. In some applications the use of an antenna array is prohibitive, for example in a mobile radio handset, and modifications to detection techniques have been devised that permit interference cancellation using a single antenna.

Recently so called Single Antenna Interference Cancellation (SAIC) techniques have been introduced into the GSM standard where modified handsets can operate at lower signal to interference ratios than unmodified handsets, permitting greater frequency re-use and hence greater capacity for a fixed amount of spectrum.

Project status

Alongside completion of the simulation work, the costs associated with implementing interference cancellation will be studied. Finally, the regulatory issues associated with the implementation of the interference cancellation technique will be assessed and methods for promoting the adoption of interference cancellation techniques will be identified. The project is now complete and you can download the final report below.