| 摘要 |
<p>A method and system for scrambled transmission of an information signal having a regular, repeating information rate from which a receiver (32) of the information signal derives synchronizing information as in a television video signal. The information signal (VID) from a source (12) is summed (24) with a scrambling signal (26) having a frequency (Fj) which is a function of the information rate (Fh) plus an error quantity (B) within a predetermined bandwidth, namely that of the synchronizing circuitry in the normal information receiver (32). The sum of the information signal (VID) and the scrambling signal is transmitted (20) as the scrambled information signal (SVID). In a television scrambling system (10), the information signal (VID) is a television video signal (12) and the information rate (Fh) is a video synchronizing rate, preferably the horizontal line rate (FH). The television information signal also includes an audio signal (AUD) from an audio source (14) which is scrambled by mixing (28) the audio signal (AUD) with a carrier signal (Fj/D) related to the video synchronizing rate, to produce a lower sideband (SAUD) which is transmitted as the television audio signal. The frequency of the scrambling signal Fj is defined by th equation Fj = A.Fh + B, where A is an integer, B is the value error quantity, and Fh is the information rate. To increase scrambling security, the frequency of the scrambling signal may be modified periodically (50). Also disclosed is a method and system for decoding or unscrambling (34, 36, 38, 40) the scrambled information signal (SVID).</p> |
