What is the working principle of digital TV set top box?
In fact, the digital set top box is a transform device that converts digital signals into analog signals.Most of the time we have this kind of doubt. Since the analog signals from TV stations are received, the TV receiver must also be analog signals, so why use digital set-top boxes? Now life, we always hope that their TV can broadcast high-definition TV, from analog TV to high definition digital TV transition, is a leap of transition, can be said that can not be directly compatible, that is to say at present all of the analog TV is not used, so in one step is not realistic. Usually it is: the TV station will first analog signals into digital signals, digital set-top box transfer home after the digital signal into analog signal input to the analog TV now display information, which can effectively avoid interference and lead to loss of TV signal in the transmission process, the TV signal quality has been greatly improved.
(8) scrambling technique: scrambling technique is used to encrypt and decrypt digital programs. The basic principle is to use the scrambling control word to encrypt the transmission method, and the user uses the IC card to decrypt. In the MPEG transport stream, there are 2 data streams associated with the control word transmission: the authorization control information (ECMs) and the authorization management information (EMMs). The control word after encryption by the business key (SK) is transmitted in ECMs, including program source, time, content classification and program price. The business key encrypted with the control word is transmitted in the authorization management information, and the business key is encrypted by the user's personal distribution key (PDE) before being transmitted. EMMs also includes addresses, user authorization information, such as programs or time periods that users can watch, user ratings, etc..The user's personal key distribution (PDK) stored in the user's smart card (Smart Card), at the user end, the set-top box based on PMT and CAT in CA - descriptor, EMM and ECM PID, and then filter out the ECMs and EMMs from the TS stream, and through the Smart Card interface to Smart Card. Smart Card first read the user's personal key distribution (PDK), remove the SK of EMM decryption, with PDK, and then use SK to remove the CW decryption, ECM, and CW through the Smart Card interface to descramble engine, transmission and descrambling engine using CW can be scrambled stream descrambling.
