Method and system for broadcasting a digital data signal within an analog TV signal using Orthogonal Frequency Division Multiplexing

摘要

The present invention relates to a method and system for transmitting digital data within an analog TV signal. Digital data are received from a data source. The digital data are then multilevel encoded and a plurality of data symbols in dependence thereupon is provided. Each of the plurality of data symbols is modulated in frequency domain onto a carrier of a plurality of carriers such that each carrier carries a different data symbol. The modulation step is based on an OFDM method and is performed using a serial to parallel converter. After modulation a digital data signal is provided. Some carriers of the plurality of carriers are turned off in the modulation process in order to shape the spectrum of the digital data signal such that the spectrum of the digital data signal comprises notches at locations coinciding with locations of spectral components in the vestigial sideband of the video carrier of the analog TV signal. The width of the notches is determined such that degradation of the analog TV signal due to the transmission of the digital data within the analog TV signal is substantially reduced. After IFFT transformation into time domain and D/A conversion the digital data signal is combined with the analog TV signal by inserting the digital data signal in the vestigial sideband of the video carrier. The digital data broadcasting technique according to the invention is capable of transmitting digital data within an analog TV signal at a substantial higher data transmission rate than prior art systems without causing any degradation to the picture quality noticeable to non-expert viewers.