Digital set-top box technology and interactive applications

1 Introduction to the digitization, network, and information as a fundamental characteristic of the 21st century telecom network, computer, network and cable television networks integration process will accelerate the integration of it is interactive television (ITV, Interactive Television). Interactive television is a user-controlled video distribution service, in the programme and the programmes to make a choice in the audience. It uses an asymmetric bidirectional transmission network, the user information through the narrow band of uplink channel to information center, and the information to the user's downlink is a video transmission capability of broadband channel. It is a non-symmetric duplex forms of new TV broadcasting technology. It is modern communication technology and multimedia technology and data compression technology for traditional analog, one-way cable TV, digital, interactive development has laid a solid foundation. Digital set-top box (STB, Set-Top-Box) is an interactive television system is an indispensable part, it is a normal TV and broadband transmission between bridges, through which the user can be viewed in normal TV and high definition images for video on demand (VOD, Video On Demand), home shopping and other services. Therefore, the design of high performance, full-featured digital set-top boxes on the development of interactive television is of great significance. 2 digital set-top box structure, composition and realization of functional analogue television to digital television conversion process continues to accelerate, it's not just about video transmission and display of a field changes, the more important is the use of advanced digital compression technology, multimedia and broadband network technologies, so that the TV broadcast is no longer limited to one-way send audio and video signals, but requires service providers to the user's choice to provide the appropriate service. Analog set-top box only has a TV tuner and decoder function can not meet the requirements, new digital set-top boxes thus came into being. Digital set-top box is a digital television signal into analog conversion equipment, through the digital compression of the image is decoded to restore sound signals to produce analog video and sound signals to deliver to the audience of high-quality television programmes. Digital, interactive, multimedia, multi-function digital set-top box's basic features, including interactive is a digital set-top box's vitality. Because only interaction to make the user's requirements, and in the future, cable television and multimedia broadband network in the most promising is the interactive TV. 2.1 digital set-top-box structure formed by digital set-top box, that is, the four major subsystems control subsystem, signal processing subsystem and the network interface subsystem, user extensions · interface subsystem. Control subsystem: microprocessor control system or the system is the core of digital set-top box, it consists of a CPU, ROM, RAM. Microprocessor by bus to sections harmoniously together, except for the subsystem initialization, you must control the coordination of the various parts together to achieve the overall digital STB. · Signal processing subsystem: from single or multiple pieces of chip components. Where digital tuner to receive from the antenna, ground or cable TV network to the digital signal, and receive instructions from the control system, the notification for the transport layer type, bandwidth, demodulation and decoding information. And then make the channel demodulator, demodulation of video streaming and audio data stream sent to the MPEG-2 decoders and · MPEG-4 decoder. Network interface subsystem: used to implement and video server full duplex communication, targeting different access network, using the appropriate interface. · User interface and extended interface subsystem: and infrared remote control, Panel, game controllers, and other peripherals to communicate, in addition, with the gradual introduction of pay-TV, decryption card and smart card will become indispensable in the digital set-top box. In fact, an integrated digital set-top box from hardware platforms and software systems. The underlying software provides the operating system kernel and various hardware drivers; middleware application software and is dependent on the hardware platform of the underlying software, so that the application does not depend on the specific hardware platform, application software including native storage of application and downloadable applications, through the application to implement various features of the STB. 2.2 digital set-top-box implementation capabilities of digital set-top-box of basic functionality is receiving and decoding of digital TV broadcasting. In addition, the digital set-top box for digital video, digital information and interactive application three core capabilities developed various value-added services, including: · Electronic programme guide EPG (Electronic Program Guide): it provides users with an easy to use, user-friendly, fast access to the necessary programs method, the user can use EPG see one or more channels or even in the near future, all channels on the TV show. · High speed data broadcasting: it is able to provide the user with the stock market, ticket information, electronic newspapers, top sites, and other information. · Online software upgrade: is one of the application of data broadcasting, data broadcasting servers DVB (Digital Video Broadcasting) data broadcast standard will upgrade software broadcasting, digital set-top box to identify the software version number, the version is not at the same time receive the software in order to save on storage of the software to be updated. · Internet access and e-mail: digital set-top boxes are available through the built-in cable modem easily achieve Internet access function, and set-top box built-in browser to surf the Internet, send e-mail, you can provide a variety of interfaces and PC connected. · Conditional access: at its core, scrambling and encryption. Digital set-top box should have the descramble decrypt function, this is an interactive television fees and operating mechanism, through the establishment of a paid service systems, the interactive television industry development in a virtuous cycle of economic base. 3 key technology for digital set-top boxes, digital set-top box set reflects the multimedia, computer, data compression, descrambling algorithm, encryption algorithm, communication technology and network technology development levels, the technical content is very high, its key technologies include: · Reuse and decompression technology: analog signal digitalization, the sharp rise in data volume will be compressedSmall. MPEG-2 (ISO/IEC 13818) video compression standard in interactive television widely adopted, applied to various high definition image quality; MPEG-4 (ISO/IEC 14496) is using object-based coding, it put the images and video split into different objects separately, not only improves data compression ratio, but also can achieve many interactive features based on content, multimedia data compression coding provides a broader platform. With LSI technology and embedded systems technology is widely used, digital set-top-box hardware implementation uses a dedicated chip or digital signal processing (DSP, Digital Signal Processing) chips, CPU core and MPEG-2, MPEG-4 Transport Stream Demultiplexer, DVB common Descrambler, MPEG audio and video codec, and NTSC/PAL encoder integrated to form the core of the STB chip to achieve real-time demultiplexing and real-time data · information processing. Downlink data demodulation and channel decoding technology: compressed data cannot be directly transmitted on the channel, you need to make channel coding and modulation. International and domestic standards are provided on cable network transmission of digital TV and value-added business uses QAM (Quadrature Amplitude Modulation) modulation and RS (Reed Solomon) · error-correcting codes. Uplink data modulation coding: interactive application, you need to consider the uplink data modulation and coding issues commonly adopted 3 way, i.e. using a telephone line transmission uplink data transmission with Ethernet uplink data transmitted through the cable network and uplink data. Since uplink data relative to the downlink data a much smaller, so more use QPSK (Quadrature Phase Shift Keying) or 16QAM modulation · way. Network browsing technology: to achieve the true meaning of the CNN network browsing, and Internet connections in addition to considering the uplink and downlink data, you must also consider running on IP (Internet Protocol). · Real-time operating systems: digital set-top-box operating systems using a real-time operating system (RTOS, Real-Time Operating Sys-tem), as in the current epidemic of VxWorks, Windows CE, etc. RTOS in real-time environments, and consume less memory space, it is responsible for managing local resources and network resources, the provision of basic operation and equipment · access control. Middleware: Middleware (Middleware) technology, that is, open service platform, has become the core of interactive television technology. Middleware is typically used by Java virtual machines, networks, browsers, image and multimedia modules, etc, by defining a complete set of standard application program interface that allows applications independent of the operating system and hardware platform, enables application development becomes more simplified, product openness and more portable, to ensure that set-top box scalability and investment and the effective recovery. 4 MPEG-4 in digital set-top-box interactive application 4.1 MPEG-4 in interactive application advantages as a new standard for video compression, MPEG-4 are beginning to use in multimedia access and interactive television technology, it by defining a format, a framework, rather than a specific algorithm to achieve a more freedom of communication and development environment. MPEG-4 has the following important characteristics, is ideal for interactive multimedia applications. · MPEG-4 supports different kinds of objects and different sources of material for different applications, taking into account the differences between various types of Web performance, and allow multimedia information to common forms of access, was the first to give the user visual style from passive to active, dynamic image standards; · MPEG-4 at a relatively low data rate, still has a very high quality of the video image, it provides more than MPEG-2 MPEG-1 and strong coding algorithms that achieve very low bit rate of multimedia interactive applications in audio and video data. 4.2 MPEG-4 in digital STB in the interactive application in interactive TV applications, digital data can be associated with digital audio and video signals simultaneously transmitted to the user, in order to be able to enjoy the interactive environment. Therefore the development of digital set-top boxes, in addition to the MPEG-2 audio and video capabilities, but also has the following features: · Multimedia stream control; · Output control; · User interface controls; · Synthesis and control drawing; · Restrict access to management; · Electronic program guide to display and control; · Quality management; · Resource management. These features suited to achieving MPEG-4, which is considered MPEG-4 can guarantee system-specific quality of the audio and video data for maximum compression, so that the most efficient use of bandwidth, and supports multimedia interactive Web applications, it can be used to develop this MPEG-4 new digital set-top box. 5 the future of interactive television is the closing of a cable television, in multimedia broadband network construction and the national information infrastructure in occupies a pivotal position. Our country is in digital television and high definition TV is a crucial period of development, interactive television industry booming, thus developing the digital set-top box is particularly important. Digital set-top box is not only important broadband information network, comprising one of the more important and relevant multimedia technology, data compression technology, broadband network technologies will be the future building information freeways of key technologies. Interactive TV is based on the technology, and complement each other, to apply the above technique provides an opportunity to develop new products, this is bound to promote the rapid development of information industry, accelerate the digitization, network, and information of particular importance.