Introduction
Digital Satellite TV has developed rapidly in recent years, the use of geostationary satellites to digital encoding of television signal transmission to the client as a form of radio and television. There are two main ways. One is the digital TV signal transmission to the cable end, and then converted to analog by a cable television station sent to the user's home. This form has been popular in the world for many years. Another way is to transmit digital TV signals directly to the user's home that is: Direct to Home (DTH) mode. U.S. Direct TV is the first application of this technology

Satellite TV Preview
Satellite television operating companies. Compared with the first approach, DTH satellite emission power mode, the antenna can be smaller, the average family can use. At the same time, can provide user authentication and encryption management to digital television, pay per view television (PPV), high-definition television and other types of advanced television services, without the middle part of restrictions. In addition, methods can also carry out a number of DTH television services other than digital information services, such as the INTERNET high speed downloads, interactive television.
DTH in the international arena there are two standards, the European standard DVB-S and U.S. standards DigiCipher. But increasingly in the global DVB standard widely used in the emerging U.S. DTH company Dish Network also uses the DVB standard.
Composition
A typical DTH system consists of six parts:
1) front-end system (Headend)
Front-end system consists of video and audio compression encoders, multiplexers and other components. The main task is to front-end system for digital television signal encoding, the use of statistical multiplexing technology, in a limited frequency band satellite transponders to transmit more programs. DTH by MPEG-2 standard for video and audio signal compression, using dynamic statistical multiplexing technology, can upload a 27MHz transponder vote Chi? 0 sets of TV shows.
2) transmission and uplink system (Uplink)
Transmission and uplink systems, including front-to-uplink station communications equipment and uplink equipment. Transmission main IF transmission and digital baseband transmission two.

Receiver (1
3) Satellite (Satellite)
DTH systems use high-power direct broadcast satellite or communications satellite. Due to technical and cost reasons, some DTH system uses high-power communications satellite, the United States and Canada adopt a more appropriate DTH company dedicated high-power direct broadcast satellite (DBS).
4) User Management System (SMS)
DTH user management system is the heart of the system, mainly the following functions: Xiaobian recommend
A. Registration and management of user information.
B. purchasing and packaging programs.
C. Development of program standards and user billing charges.
D. Market forecasts and marketing.
User management system mainly consists of user information and program information database management system and to answer user questions and provide a variety of customer service Call Center form.
5) The conditional access system (CA)
Conditional access system has two main functions:
A. The program data encryption.
B. of the program and authorize users.
DTH on the current international system of conditional access systems used are: U.S. NDS, Israel, Irdeto, France Via Access, Switzerland, Nagra Vision, etc.
U.S. companies and the use of Direct TV Direct TV Star Choice Canadian technology companies using NDS conditional access system; U.S. Dish Network (Echostar) and the use of Echostar's technology companies in Canada to use Bell ExpressVu is the Nagra Vission conditional access system.
6) users receiving system (IRD)
DTH users receiving system consists of a small satellite dish antenna (Dish) and integrated receiver decoder (IRD) and smart card (Smart Card) form.
IRD is responsible for four main functions:
A. decoded program data stream, and output to a TV.
B. The use of smart card key (dreambox 500) to decrypt.
C. receive and process a variety of user commands.
D. Download and run the variety of applications.
DTH system, the IRD is not a simple hardware device, it also includes a large number of operating systems and application software. IRD is currently more successful operating system is Open TV. U.S. Dish Network has begun to gradually upgrade the user's IRD to Open TV system.

D. Market forecasts and marketing.
User management system mainly consists of user information and program information database management system and to answer user questions and provide a variety of customer service Call Center form.
5) The conditional access system (CA)

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