PRE-INTERFERENCE CANCELER FOR DIGITAL MICROWAVE RADIO SYSTEMS

As radio communication has progressed, reduction of intersystem interf erence has become a problem. In a conventional interference canceller, the interference signal as a source of cancellation is obtained at th e receiving station and the interference component in the desired sign al is canceled based on this interference signal. However, the interfe rence signal for cancellation may not be obtained at the receiving sta tion. As a remedy, an extraction and reinjection-type interference can celler has already been proposed. In this paper, a pre-interference ca nceller is proposed in which, if the transmitting station of the desir ed signal and that of the interference signal are identical, the inter ference signal is mixed with the desired signal from the transmitting station beforehand and the interference signal leaking into the desire d signal is cancelled at the receiving station. First, the applicable range and the fundamental configuration of the present canceller are p resented. Subsequently, the method for determining the amplitude and p hase of the interference signal injected into the desired signal of th e transmitting station and the method for evaluation of the cancellati on effect are presented theoretically. Next, an experiment is carried out with the desired signal of 16 QAM or 256 QAM and the interference signal of 256 QAM. Interference improvement by about 20 dB is obtained for both the 16 and 256 QAM signals. Also, the response speed of cont rol for the fading is 60 ms. In addition to the validity of the theore tical results, effectiveness of the proposed canceller is shown.