The functionality of the set-top box requires the set-top box to be a very general name. The functions and structures of various set-top boxes vary widely. Early and widely used set-top boxes may have to count WebTV. The original purpose of WebTV was to use a TV to access Internet sites. A typical WebTV contains a 33.6K or 56K bps Modem that is connected to the Internet via a telephone line and used as a display device. This type of WebTV is equipped with a browser software similar to that on a PC. Users can manipulate the remote mouse, infrared keyboard and other devices to browse the web, or send and receive e-mail. Although such WebTV can also watch the video content on the Web, the TV and Internet channels are separate. This type of WebTV is digital in accessing the Internet, but the data transmission rate is low, while on the TV side, it is still analog, one-way (broadcast mode). With the development of broadband networks, multimedia technologies and digital television, television and computers have found a combination of digital and network concepts. Digital TV and interactive TV have become the trend of TV development. Interactive TV has become an important part of broadband network or information highway. A new generation of set-top boxes is one of the key devices for digital interactive TV. Has become a hot spot of research. The functions of the new generation of set-top boxes should include: 1 receiving analog TV and digital TV programs in broadcast mode, 2 high-speed access to the Internet, sending and receiving e-mail, 3 video on demand (VOD) and music on demand functions, 4 telephones, video telephony, conference television 5, connect VCR, VCD and other consumer electronics products, 6 e-shopping, 7 video games. The technical requirements for digital set-top boxes are: 1 broadband access for high-speed two-way communication networks, efficient use of frequency band resources, 2 digital TV programs and multimedia video in decoding, video and audio processing, and D/A conversion, TV coding, display, etc. Uniform considerations, 3 pairs of canal disturbances, encryption, billing, etc., 4 friendly user interface, the highest possible price/performance ratio, 5 scalability in terms of functionality and performance.
Hardware and Software Structure 1. The hardware structure of the hardware set-top box is very different depending on the function and working mode. But its basic components are generally high-performance processor cores, memory, communication interfaces, data ***, video and audio graphics processors, TV encoding and interfaces, peripheral I / O interfaces. Figure 1 is a block diagram of the composition of a set-top box. The entire hardware system is divided into several subsystems: Network Communication Interface Subsystem This section can have one or more interfaces (front end) for broadband access. Because various transmission media use different modulation methods, different front ends have their own tuner, demodulation code, channel ***, converter, reverse channel transmitter and so on. The front end that can be used includes a cable front end, a satellite front end, a ground microwave front end, and an ADSL front end. A variety of front-ends can be combined with the appropriate device combinations, as well as fully functional modules. Processing and Control Subsystem This is the heart of the set-top box. It consists of a processor, memory, etc., providing signal access and control processing functions, and provides a programmable platform. It implements control of the entire system and specifically performs signal descrambling, demultiplexing, and acquiring MPEG-2 data streams and other packaged data. Audio/video/graphic processing subsystem. The audio/video/graphic data is decoded and processed here, and encoded into SVB, S-Video, and RGB signal outputs. It is mainly composed of MPEG-2 and AC3. , D/A converters for video and audio signals, video signal encoders, etc. · Peripheral interface system This part includes serial and parallel I / O interface, smart card interface, infrared interface, IEEE1394 interface, etc., used to connect wireless keyboard, mouse, and VCR, VCD, digital camera and other equipment. 2. The software system of the software set-top box also has a big difference with the function and structure. Due to the complex functions and high performance requirements, high-end digital set-top boxes are generally based on a real-time operating system and are expanded according to hardware and system functions. Suitable for this application, there are general-purpose operating systems, such as Windows CE, OS-9, pSOS, etc., there are also operating systems developed for set-top boxes, such as Power-TV. The whole software can be generally divided into several levels as shown in Figure 2. The lowest layer is the driver for various hardware components, including MPEG system and processing components, audio and video graphics processing components, and FLASH Memory. ), serial port, parallel port, smart card interface, network communication components, etc. These components are usually dedicated chips and their drivers are directly hardware dependent. In order to facilitate the use of the device by the upper layer software, there is a driver management layer above the driver layer, which manages the underlying physical drive interface from the peripheral interface, MPEG system processing, audio/video/image, communication, etc., thereby facilitating high-level The realization of the function also reduces the burden on the CPU. The next layer is the real-time operating system kernel. This is the core of the entire software system, it is responsible for task scheduling, real-time monitoring, resource allocation. Above the real-time operating system layer is the system control layer and library program. The system control layer provides advanced functions such as video and audio data control, user access interface, communication, channel selection, etc. It also supports the sharing and reuse of these functions by multiple applications. . The interactivity of the system is also controlled and implemented here. Library programs provide functions and programs for system video, audio graphics processing, and more. The highest layer is the application layer, where the functions of various applications are handled, and the necessary functional modules are selected from the system control layer. Generally, each application module is acquired, processed, and displayed under the control of the user. Typical applications include TV channel browsing options, pay TV control, e-mail, Internet browsing, and software downloads. Advanced applications include video on demand, music on demand, telephony, video telephony, conference television, and more. Because multimedia applications, including technology and processing methods, are very different, and are constantly evolving. So the concept of object-oriented and virtual machines is very attractive. Therefore, Java has been widely used in advanced set-top boxes. In order to support Java, the Java engine needs to be included in the download application module of the application layer. Of course, there are also high requirements for the performance of the CPU and system. Due to the requirement of operating system platform, Java execution, real-time processing of video and audio signals, interactive services, set-top boxes require the processing power and memory address space of advanced 32-bit single-chip processors.
CPU selection of the set-top box can be based on PC or embedded PC-based architecture, but also based on high-performance microcontroller architecture. The advantage of using a single chip microcomputer is that the chip has high integration degree, small volume, low power consumption and low price. Since the set-top box is a consumer electronics product, the price is an important factor. In addition, low power consumption means saving monthly electricity bills. Moreover, low power consumption also avoids excessive temperature rise, which improves the reliability and life of the device. At present, high-end single-chip microcomputers are 32-bit or 64-bit RISC structures with speeds of tens or even two or three hundred MIPS, and have powerful peripheral modules, which are very suitable for developing set-top boxes. In order to improve real-time processing capabilities, peripheral functions should also be implemented using dedicated chips. Currently, companies such as Philips, SONY, ST Microelectronics, GI, LSI Logic have dedicated MPEG-2 decoding, video/audio/graphics processing, TV encoding, and cable. A dedicated chip for satellites and other aspects. If the cable front end is used, other special Cable Modem chips can also be used. When selecting these special chips, in addition to factors such as performance, price, interface, etc., it is also necessary to consider whether the standards are met. At present, interactive TV and set-top box are still in the research and development stage. The function and structure of the set-top box still need to be adjusted and modified. It is developed based on high-performance single-chip microcomputer, which can shorten the development cycle and meet the requirements of productization. After the mature design is completed, ROM and ASIC should be customized for the set-top box to simplify the line and reduce costs. If necessary, you can even purchase the patent of the MCU and integrate the MCU core into the chip designed by yourself.
The development trend of digital set-top boxes With the improvement of digital set-top box performance and price reduction, the construction of broadband networks, and the development of network multimedia applications, set-top boxes are gradually entering the practical stage. Due to the participation of many large-scale electronics, computers, communications, and home appliance companies, the development of set-top boxes is not only manifested in the use of higher-performance CPUs and higher-integration, more complete and dedicated VLSI modules, but also in the extension of its functions. Set-top box broadband communication, video and audio processing, Internet access and other capabilities can be shared for a variety of applications. Therefore, the set-top box can be used not only for video on demand, general online browsing, but also for various applications such as telephone/videophone, distance education, entertainment, and e-commerce. This has led to a corresponding change in the design of the set-top box. First of all, many interfaces such as set-top boxes are convenient for accessing cameras, digital cameras, video cameras, game consoles, and printers, disk drives, and PCs. Some set-top boxes have integrated DVD control and driver circuits. Secondly, since the set-top box will be suitable for a variety of purposes, the requirements for implementing more than one application at the same time are also proposed, such as requiring an IP phone while performing VOD (Video On Demand). Therefore, some set-top boxes consider the multi-channel and multi-way service units at the set-top box level. For example, GI's DCT5000+ has three heavy channel structures. Another factor affecting set-top boxes is the intelligence of the home. The set-top box's communication, processing, and expandable storage capabilities can be used for residential security, home appliance control, and more. With the help of set-top boxes, remote residential monitoring and device control over the Internet will also be high performance and low cost. So today's set-top boxes may become a communication, processing, and storage center in the home that connects TVs, audio equipment, telephones, video recording equipment, other household appliances, and security equipment to the outside information highway in the near future. At that time, the set-top box may have to go down the top of the TV set, and people have to give the set-top box a more appropriate name.
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