Equalisers for GSM

Discusses the suitability of different types of equaliser for use in terminal equipment for pan European digital cellular radio. The latter is a new radio standard for mobile telecommunications which applies across most of Western Europe and is due to become operational from June 1991. The telephone system is also referred to as the GSM system after Groupe Speciale Mobile-the committee set up by CEPT to define the new radio standard. Service is provided by high capacity radio links from base stations to three types of telephone: vehicle mounted, transportable and handportable. A critical part of the GSM system is maintaining the integrity of the radio link in the presence of noise, interference and fading multipath. There are three key elements in the receiver structure: RF/IF signal processing, the equaliser and the channel decoder. Only the equaliser overcomes multipath, and the structure of this element is discussed in this paper. GSM have specified that delays, due to multipath propagation spanning 16 μs must be equalised. Two approaches to achieving this are considered; an equaliser based on the Viterbi algorithm (VA) and a decision feedback equaliser (DFE)