Frequency selective fade effects and bandwidth considerations in COST 235

Working Group 1 in the COST 235 Project study frequency selective effects and their impact on digital radio links. For fixed communication links the trend for many years has been of increasing the capacity without necessarily a larger bandwidth, e.g., 155 Mbit/s or 622 Mbit/s links in the synchronous digital hierarchy (SDH) network. This lead to complex techniques that are more sensitive to distortion caused by propagation as well as other sources. The techniques used to achieve a greater transmission capacity are higher levels of modulation by combining more bits into a single symbol and by use of dual polarisation. The multipath mitigation techniques cover various diversity reception schemes, transmit power control, channel equalisers, and error correction coding. A deeper understanding of multipath propagation mechanisms is needed both for the development of the various prediction techniques as well as the development of equipment. The Working Group has compiled a database for testing purposes of existing and new prediction methods. It has been of particular importance to include measurements of performance, e.g. bit error rates (BER), as part of the data to be able to give recommendations regarding the merits of various prediction methods.