Digital set-top box

Product introduction

The user connects the cable feeder to the digital set-top box, and then uses the AV cable to connect to the TV's AV input terminal, and then uses the digital set-top box remote control to perform channels and programs Choice.

Digital TV is broadcast in the TV's AV program. When watching, the TV program is converted to the channel that usually plays DVDs or videos. All digital TV programs are in the AV channel. When selecting, you need to use the set-top box remote control According to the menu operation, the operation process is similar to that of playing DVD. If you do not watch digital TV programs, press the AV switch button on the TV remote control to return to the original program.

Working principle

The various modules of the set-top box work together in the high-speed Internet access. The user first requests a URL by sending a command. In a transaction process using the PPP point-to-point protocol, the command finally reaches the modem shared rack of the Internet service provider. Then through the dynamic allocation method, the user obtains the IP address used in this transaction and sends the request to the Internet. When the content of the Internet is found, it is then sent to the Internet Service Provider (ISP), and then the ISP router is responsible for sending it to the cable TV network, and finally back to the user's set-top box. In the cable TV set-top box, the information content is intercepted. The set-top box completes the task of a gateway between the TV and the cable network. Its task is to manage IP communication traffic, with the ability to control users' access to the network. Once the IP packet reaches the set-top box, it separates the video signal from the packet, decodes the data in it, and then sends it to the browser for preparation Display on the TV.

Because Cable Modem requires users to configure a computer to access the Internet, which affects the expansion of the user layer, and the use of a set-top box does not require a computer, a TV is sufficient, so the market prospect of the set-top box may be promising. Information users are transitioning from businesses to homes, network bandwidth is transitioning from narrowband to broadband, user access devices are transitioning from PCs to TVs with set-top boxes (STBs), the user interface is transitioning from Windows to TV remote key interfaces, and information content is transitioning from serving enterprises The transition to serving the people's lives is the general direction of the development of network services, and the set-top box (STB) is obviously a stage in this general direction.

Product features

Digital TV set-top boxes can receive MPEG-2 digital TV transport streams and various data information, through demodulation, demultiplexing, decoding, and video and audio encoding, Watch digital TV programs and various data information on a color TV. The basic function of a digital TV set-top box is to receive digital TV broadcast programs, and it has all the functions of broadcasting and interactive multimedia applications, including:

(1) Electronic program guide: It provides users with an easy-to-use interface Very friendly, you can quickly access the way you want to watch the program, and users can see the TV programs that will be played on each channel through this function.

(2) Support interactive applications such as quasi-video-on-demand, video-on-demand, interactive games, etc.

(3) High-speed data broadcasting: It can provide users with various information such as stock market quotations, ticket information, electronic newspapers, and popular networks.

(4) Internet access and e-mail: The digital TV set-top box can realize the Internet access function through the built-in cable modem. Users can surf the Internet through the built-in browser of the set-top box, send e-mails, or provide various interfaces to connect to the PC, and use the PC to access the Internet.

(5) Online software upgrade: It can be regarded as one of the applications of data broadcasting. The data broadcast server transmits the upgraded software to the set-top box, and the set-top box can identify the version number of the software, receive the software when the versions are different, and update the software stored in the memory.

(6) Conditional reception: The core of conditional reception is scrambling and encryption, and the digital TV set-top box should have descrambling and decryption functions.

With the development of digital TV and network technology, the functions of digital TV set-top boxes will be more perfect, especially the development of single-chip PC technology, which will promote digital TV set-top boxes to highly integrate various parts of the hardware in the physical structure , To form the STB core chip, thereby reducing the volume, reducing costs, and improving performance. The external interface will be more abundant. It can be connected to the digital camera through the USB interface, and the hard disk can be connected to the IDE interface to realize program storage. Interactive set-top boxes will become the mainstream of digital TV set-top boxes. Users can not only watch digital TV on analog color TVs, but also realize entertainment and Internet access.

Hardware composition

Important modules

(1) Network interface module (NIM): The network interface module completes the channel demodulation and channel decoding functions, and the The transport stream (TS) of audio and other data information.

(2) Source data transport stream demultiplexer: The transport stream generally contains multiple audio and video streams and some data information. The transport stream demultiplexer is used to distinguish different programs and extract the corresponding The audio and video streams and data streams are sent to the video and audio decoder and corresponding analysis software.

(3) Conditional access module: For pay TV, the conditional access module also descrambles the audio and video streams, and uses smart cards with user identification and memory functions to ensure normal viewing by legitimate users.

(4) Video and audio decoder and post-processing: MPEG-2 decoder completes the decompression of audio and video signals, and restores analog audio and video signals through video encoder and audio D/A conversion. Display high-quality images on analog TV sets and provide multi-channel stereo programs.

(5) Embedded CPU and memory module and interface circuit: Embedded CPU is the heart of the digital TV set-top box. It and memory module are used to store and run the software system and control each hardware module. The interface circuit provides a wealth of external interfaces, including universal serial interface USB, Ethernet interface and RS232, analog and digital video and audio interfaces, data interfaces, etc.

Modulation and demodulation module

The digital set-top box works in the state of the cable TV network, and the cable TV network adopts analog transmission, so the digital signal must be modulated and demodulated before it can be transmitted in the analog channel The modem is a key component of the system. It is technically similar to the principle of a telephone modem, but uses a higher modulation method. The downlink mostly uses 64QAM or 256QAM. In DVB-C (Digital Video Broadcast by Cable) and DAVIC, 64QAM is used. As a standard modulation method, take Motorola's MC92305QAM demodulation chip as an example. The digital signal rate using 64QAM modulation on the 7M analog bandwidth can reach 42Mbit/S. There are two methods for uplink, one is to use the telephone line as the uplink channel , The other is to use the uplink channel of the two-way HFC network, and when the HFC network is used, QPSK is used as the modulation scheme. The QAM or QPSK modulator modulates the MPEG format data stream in a standard PAL channel, and sends it together with other video modulation signals.

Codec module

Because of the use of analog channels, in order to ensure the reliability of data transmission and low error rate, forward error correction coding is essential. DVB uses Reed Solomon Encoding, RS code is a kind of multi-system BCH code with strong error correction ability.

MPEG II decoding module

The core of the digital set-top box is digital video technology. The MPEGII decoding module can be called a core module other than the CPU. MPEG II digital transmission adopts interleaving coding. First, the code stream needs to be de-interleaved, the video, audio, and data code streams are separated, and the video code is decoded. After the above steps, the MPEGII code stream becomes video (CCIR656 format) and audio digital signals. The MPEG multiplexer combines each program stream and data stream together, and sends the MPEG2 data format with 188 bytes as a frame to the radio frequency modulator and provides an electronic program guide (EPG).

Digital video encoder and audio DAC

The "peripherals" of digital set-top boxes are TV sets and sound systems. Digital audio and video signals must be converted into analog audio and video signals. Take the company’s MC44724 as an example. MC44724 can convert ITU601, 656 standard 4:2:2 parallel video data into PAL or NTSC format video, S-Video, Y/Cb/Cr or R/G/B, extended VBI( Vertical Blanking Interval) information input port is used to display graphic information. Audio DAC is very common and will not be introduced here. Modern audio systems support Dolby Pro Logic and Lucasfilm Home THX home theater systems. Digital audio signal processing chips need to be used to process digital audio signals before audio DAC. There are two ways to process digital audio signals with dedicated processing chips and digital signal processing chips DSP. .

Graphics control module

and video graphics mixer digital set-top boxes on the other hand need to provide computer-like complex graphics or even three-dimensional graphics, the system needs to have powerful two-dimensional and three-dimensional graphics acceleration Chip, and it is necessary to mix and superimpose the graphics and video signals for display. This kind of function is similar to the existing subtitle machine.

Media Access Control Module MAC

The digital set-top box can be regarded as a Cable Modem in network communication. The IP router receives the on-demand signal from the client through the PSTN (Public Telephone Network) and Transfer to Internet server/router. Mainly referring to the DAVIC and IEEE 802.14 standards, IEEE802.14 advocates the use of ATM and defines the ATM layer on the 802.14 MAC access layer. DAVIC also defines the Ethernet and ATM standards.

Rewritable DVD

Existing digital set-top boxes work completely in a network environment, and can only use smart cards to store information such as personal account numbers, decoding numbers, etc., without local big data Storage function, all information needs to be obtained from the Internet, regardless of network conditions or in the future, media such as CD-ROM is still a major method of large-capacity information transmission. The disadvantage of CD-ROM is that the information cannot be updated. The use of rewritable DVD can not only use the huge information on the disc, but also update the data through the Internet to keep the data on the DVD disc up-to-date. DVD should become an important spare module for digital set-top boxes.

Add descrambling module and copyright protection module

In cable TV operations, pay TV is a major business, and digital set-top boxes must have the function of adding and descrambling TV signals. Due to the use of digital signals, descrambling is easier and more dense than analog signals. DVB has related definitions for the descrambling function. On the other hand, the use of digital signals increases the difficulty of copyright protection, and the Macrovision generator is used for Protection of moving images.

Machine chipset

The machine chip of the network TV set-top box is a STMicroelectronics core. According to the market research organization IMS forecast, by 2015, the DOCSIS 3.0 client device The volume will reach 49 million. This kind of circulation shows that the trend of network TV set-top boxes is considerable. STMicroelectronics (ST) has launched a cable modem system single chip that complies with the latest DOCSIS 3.0 standard. It can integrate 16 downlink channels and 4 uplink channels into one channel respectively, so that the uplink and downlink data transmission speed can reach 108Mbps and 800Mbps respectively. The data rate of this product is significantly faster than the modems sold on the market, allowing multiple users to experience high-quality full-HD multimedia and interactive network services through the same home network at the same time. ST's cable modem research and development experience is the guarantee of high data rates.

STMicroelectronics' DOCSIS 3.0 cable modem technology uses an ARM Cortex-A9 dual-core processor for applications such as routers, switches, phones, security and media servers. Because it can support multimedia functions and encryption algorithms for pay TV and network media services, the new products will be used by STMicroelectronics as the core of various application ICs, including cable set-top boxes, media gateways with/without video output, and cables Modem.

Laurent Remont, vice president of STMicroelectronics' Digital Fusion Business Group and general manager of unified platform products, said: "The functions and performance standards of DOCSIS 3.0 enable cable TV operators to provide innovative services and improve service quality in the future. . Our DOCSIS 3.0 modem technology is superior to similar technologies on the market, and will assist customers in developing advanced products, providing high-quality content and new services, such as home automation, home security and remote health monitoring."

< p>Data Over Cable Service Interface Specifications (DOCSIS) is one of the main cable modem standards adopted by global cable TV service providers and related equipment suppliers. DOCSIS technology includes the EuroDOCSIS standard used throughout Europe, allowing cable operators to provide video, voice, and data three-network convergence services.

The latest DOCSIS 3.0 standard supports Internet TV protocols, allowing cable operators to provide video-on-demand and video streaming, and supports next-generation Internet protocols to provide the public with better service content .

Moreover, DOCSIS 3.0 also introduces channel integration technology into cable modems. This flexible technology enables equipment to achieve high performance above 100Mbps. DOCSIS 3.0 is a key technology to provide interactive multimedia services and high-speed Internet experience for multiple users at the same time.

Software system

In the set-top box, the software system is an important part. The work of the main controller is completed by the execution of the software.

The basic software structure of the set-top box. The operating system generally uses a real-time operating system. In this operating system, the main tasks such as process scheduling, interrupt management, memory allocation, inter-process communication, exception handling, and clock extraction are completed. The hardware driver part provides drivers for peripheral hardware devices, including I2C bus, asynchronous serial communication port, parallel communication port, non-volatile memory, keyboard, remote control, tuner, channel decoding module, etc. The graphic interface is mainly used to complete the graphic display function, so as to provide users with a friendly graphic user interface. Audio decoding and video decoding drivers are used to control the work of audio decoding and video decoding hardware. The demultiplexing and data table extraction module mainly controls the code stream demultiplexing and data table extraction operations. The application programming interface maps all hardware-related low-level functions to a unified interface, and provides some common processing functions that have nothing to do with hardware, such as network protocol, graphic format analysis, business information data table analysis, etc. The conditional access driver is used to complete the work and software interface of conditional access processing. The application programming interface provides a common programming interface for the application, shielding the application from the hardware, making the application independent of the hardware. In this way, it is easy to realize the portability of the application.

Middleware

Middleware is the software platform of the digital TV receiving system, which provides the operating environment and software interface for digital TV applications. As an independent software layer in the digital set-top box, middleware separates the application software from the underlying hardware and operating system, defines a unified interface for the operating system and the driver, and defines a unified interface for the application program. Broadcast and television services and value-added services also provide a unified interface. Middleware defines a set of relatively complete and standard application program interfaces, making application programs independent of operating systems and hardware platforms, thereby making application development easier and making products more open and portable. It usually consists of a Java virtual machine, a web browser, image and multimedia modules, etc. The middleware separates the application software from the hardware-dependent driver layer software, so that the application software does not depend on the specific hardware platform.

SI/EPG

Service information (SI) includes: program service group association table (BAT), program service description table (SDT), program segment information table (EIT), operation State table (RST), time and date table (TDT), time offset table (TOT), etc. Through these data tables, the set-top box can provide users with information such as the content description of the program, the type of the program, the playing time of the program, and the rating of the program. The set-top box extracts these data tables in the demultiplexing process, analyzes and processes them, and then provides them to the user through the user interface to form an electronic program guide (EPG). The user browses the information, makes a selection, and tells the set-top box to extract the corresponding program stream or data stream according to the user's selection through input devices such as remote control, keyboard or keys.

Program search

In the analog TV system, the search of TV channels only needs to be carried out one by one according to frequency. In the digital TV system, there is no longer a one-to-one correspondence between channels and program services, and the parameters of the channel transmission system can also be configured in multiple ways. Therefore, the search of program services by the set-top box should be designed corresponding to the front-end broadcasting system. Generally, the operator designates a fixed channel as a channel for publishing channel configuration information. The channel parameters are pre-built in the set-top box.

Overprinting subtitles

Because the digital TV system itself has multi-service functions, overprinting display is also the basic function of the set-top box, so the function of overprinting subtitles can be better realized in the digital TV set-top box. Overprint subtitles can be turned on and off according to the user's choice.

Because the software in the set-top box is very complicated, some errors are inevitable. In addition, as the business continues to change, the functions of the software also need to be continuously improved. Therefore, software updates have become an important requirement. The implementation methods of software update include online broadcast download update and stand-alone local update. The stand-alone local update is achieved by programming the program into the FLASH memory through the dedicated data port on the set-top box, or by replacing the program RON. The online broadcast download update is to insert the updated software into the code stream through a specific protocol at the front end of the system and send it to the set-top box.

China's development

China's set-top boxes are developing rapidly. Digital set-top boxes are also called TV boxes and other abbreviations. At present, digital set-top boxes can be divided into three categories, one is digital set-top boxes that focus on shopping, the other is digital set-top boxes that target young people, and the other is only designed for parents. Digital set-top box orange bean box. Due to a series of changes in resource supply or product demand in the set-top box industry, this industry is gradually shifting from other countries or regions to production and manufacturing in China. China has become the world's largest set-top box manufacturing center. In 2007, the Chinese set-top box market was dominated by wired set-top boxes. The set-top box market has shipped more than 65 million units, an increase of 41.3% compared to 2006. The domestic shipment of set-top boxes exceeded 30 million units, an increase of 49.32% compared to 2006. The domestic market’s set-top box shipments exceeded foreign markets for the first time; the number of cable set-top boxes in the market exceeded 25 million at the end of 2007, an increase from 2006 Nearly 60%. In 2008, China's digital TV entered a period of vigorous development. In addition to cable digital TV still showing a strong growth momentum, terrestrial digital TV also has a breakthrough development with the opportunity of the 2008 Olympic Games. In 2008, despite the impact of objective factors such as snow disasters, earthquakes, and the global financial crisis, China's set-top box market was still in a business cycle.