Broadcasting data in the FM band by means of adaptive contiguous band insertion and precancelling techniques

Simultaneous broadcasting of digital data and existing analog FM is investigated. A suboptimum method of linearly combining the analog FM signal with a low level multitone signal is proposed and evaluated. The analog FM signal is to be recovered with a standard FM receiver. The digital multitone signal is added symmetrically at the band edges of the 200 kHz FM signal in contiguous bands with variable width. To maximize the data rate, the digital bandwidth is maximized subject to a maximum allowed distortion of the analog FM signal. The impact of the analog FM signal on digital reception is cancelled by means of transmitter precancelling techniques. Conditions for precancelling techniques for multipath channels are formulated. The main advantage of the contiguous band insertion (CBI) method is that the rate of the control channel is considerably lower compared to previous near optimum methods of carrier insertion without significant reduction in data rate. We present a number of numerical results for acoustical signals