Abstract: The present invention is directed to the implementation of a reliable data communications system using the horizontal scan lines of video signals, and is particularly concerned with the minimization of problems which are caused as a result of false acquisition of horizontal scan lines and missed or dropped lines. In accordance with the present invention, a two-tier approach to receiving data transmitted via television signals is used. The two-tier approach includes a search mode and a lock mode. The present system operates on the principle that if a horizontal scan line (or lines) has been perfectly identified to contain data for successive fields of a video signal, then this scan line (or lines) can be presumed to be a valid data bearing scan line (or lines) in fields of the video signal yet to be received. The lock mode is then utilized to favor the retrieval of what would otherwise be missed or dropped horizontal scan lines were the system operating in the more restrictive search mode.

Abstract: An encoding technique for data that enables the data to be reliably transmitted via television signals, even when impulse noise may be present, uses a two-fold approach for forward error correction. As a first step, the data is assembled into blocks of suitable length and each block is encoded with an error correcting code to enable individual bit errors to be identified and corrected at the receiving end. In addition, the blocks of data are interleaved over several different lines of information. Each line of information is transmitted during the vertical blanking interval in a respective field of a video signal. At the receiving end, the individual lines of data are reassembled into the blocks of information. If impulse noise or other disruptions cause one of the lines to be lost, the result at the receiving end would only be the loss of one bit of data in each block. The error correcting code with which each block is encoded enables this individual bit error to be identified and corrected.