Conditional Access System's Research And Realization

Conditional Access System (CAS) has run well for more than 20 years on international. Moreover these system functions are quite formidable, and the costs are also quite high correspondingly. But the TV progarmes which need paying just start in our country. In the past, the main income of the television program operators was depended on the advertisments.With development of the cable TV and satellite TV, revenue which only depends on the advertisments can't support the construction and operation expense of the rapid growing network. At present, some administrative divisions have started the management systems which have implemented the separation of network from cable broadcasting station ,and some industrial cable broadcasting stations also have begin to attempt comprehensive transition from the welfare systems to the compensated service systems.This article develops one kind of simple digital television (DTV) CAS under the user needs. The cost of front end and terminal end for this system is lower a lot correspondingly than others. And this system satisfies the requirements of the user of many small counties, small cities, the large-scale institutions, the guesthouse innes of China and so on. The requirements are that the users want to watch DTV and the broadcast television stations want to charge and control the user.The paper elaborating the digital television (DTV) development situation and its the merit, introduces the present CAS related standard MPEG-2, DVB (Digital Video Broadcasting),and introduces the DVB CAS related technology of entitling and managing technology of scrambler/descrambler, encryption/di-encryption and so on;Emphatically I has studied system principle, the plan of the simple CAS and the technology of realizing scrambling and descrambling with FPGA/CPLD which I participated in personally.This sysytem hasconfirmed the system function specifically in practice, and achieved the anticipated goal: This case achieves the target of charging and controling to the users with low cost. Finally it carries on the forecast to the developmental prospects of DTV CAS.