On the design and use of 256QAM radio-relay systems

Radio-relay systems currently provide a significant fraction of the total long-haul capacity in the UK telecommunication network. The need to reduce transmission costs and to use the spectrum more efficiently has led to the adoption of higher level modulation techniques such as 16QAM, 64QAM, 256QAM etc. The systems which employ these higher level modulation techniques are potentially more sensitive to multipath propagation effects, intersystem interference and thermal noise as well as the degradations imposed by practical manufacturing constraints. The paper examines the features and potential problems associated with the use of 256QAM systems in an existing radio network to meet current transmission performance standards