140 Mbit/s co-frequency cross-polarised 16-QAM

The authors present the results of a 16-QAM (quadrature amplitude modulation) cochannel field trial on a 51-km path in the UK using a reference channel, two cofrequency cross-polarized channels together with two adjacent channels 40 MHz apart. The measured transmission quality compares well with the results of the performances prediction model DRUMBEAT, which takes into account fading, interference, and the system signature. An opportunity to study cochannel operation under conditions of severe obstruction occurred in a long-lasting event of unusual subrefraction (k varying down to 0.5). Statistical evaluations of the degrading effects (e.g. cross-polar discrimination) are given. During the six-month measurement period, the results do not indicate any major problems with 16-QAM co-channel operation