METHOD AND APPARATUS FOR PROTECTING DIGITAL TERRESTRIAL TELEVISION BROADCASTS DISTRIBUTED BY SATELLITE LINK

摘要

The invention is a method for coding/decoding MPEG transport flows, and an apparatus for carrying out said coding and decoding, with a view to protecting transmissions whose broadcast cannot be controlled, for example satellite transmissions. The method encodes the payload of the transport flow packets without modifying the header or adaptation field. This enables a modulator or remultiplexer to modify the program clock reference (PCR) which is contained in the adaptation field of the transport flow packet. The codes used in the encoding will depend on the program identifier (PID) of the packet and the instantaneous state of the transport flow (extracted from the dates and hours chart, or any other dynamic source), which enables complete diversity in packet coding. The implementation of the coder-decoder of transport packets takes place on a micro-programmed processor, specific hardware or logic programmable device (FPGA). Such a device is capable of extracting the transport packet, deciding the encryption, calculating the packet coding code and applying the encryption to the payload, while complying with the packet transmission rate. Said device can be integrated in a DVB (CI) common interface module which can be connected to any receiver/decoder compatible with CL. In this scenario and to enable the standard receivers compatible with CI modules to tune and select a service, the transport flow packets which include services information tables, (such as the program association table, the network information table and those that are filled in) would not be encrypted. Given that it is the CI module (not the receiver) which performs the decoding, the encoding algorithm can be customised depending on the application. The invention offers a method and an apparatus which distribute terrestrial digital television broadcasts by using satellite links, while complying with content broadcast restrictions defined by the intellectual property rights (IPRs) of said restrictions. Satellite distribution is very economic in comparison with distribution by terrestrial segments. However, the satellite cover zone cannot be controlled and usually extends over an area which exceeds the target zone, which could infringe the above-mentioned intellectual property rights. The method presented herein enables use of an encoded satellite transmission in order to prevent non-authorised access to the contents, without adding additional traffic, which is especially appropriate if the content is to be redistributed on single-frequency terrestrial networks. In addition, it does not impose any restriction in conditional access systems used during the original transmission and can be implemented at the receiver end by using common interface modules connected to satellite receivers. This makes it possible to reuse satellite receivers which may already be deployed.