Adaptive countermeasures for high capacity digital radio-relay systems

Reviews the techniques which either enable more efficient use of spectrum or improve overall transmission performance. These techniques include adaptive channel equalisation, antenna diversity, both of which can minimise distortion caused by multipath fading, and cross-polar interference cancellation to allow frequency reuse on the same hop. The effectiveness of these techniques can be gauged by the performance improvement `factor´ which is defined as the ratio of the outage of a system operating without a countermeasure to that of a system using the countermeasure. Where possible, the results given are derived from trial radio systems both in the laboratory at BTRL and on a 51 km test link in the field. This link was deliberately chosen for its susceptibility to a high incidence of multipath fading caused by its proximity to the North Sea, and the land mass of Western Europe. The current (December 1988) configuration of this link, with RBQPSK and 16QAM equipment, and a Microwave Link Analyser (MLA) experiment is shown