The working principle of the network TV set-top box
1. The composition of the network set-top box
The network set-top box consists of high Frequency head, QAM demodulator, TS stream demultiplexer, MPEG-2 decoder, PAUNTSC video encoder, embedded CPU system and peripheral interface, CA module and upstream data modulator. The working principle is shown in the attached picture.
The working process of the network set-top box is roughly as follows: the tuner receives the high-frequency signal from the wired network, completes the channel decoding through the QAM demodulator, and separates the audio, video and other data information from the carrier. Teleportation Gate Shu. A transport stream generally contains multiple audio and video streams and some data information. The demultiplexer is used to distinguish different programs, extract the corresponding audio, video stream and data stream, and send it to the MPEG-2 decoder and corresponding analysis software to complete the restoration of digital information. For pay TV, the conditional access module descrambles the audio and video streams, and uses smart cards with functions to identify users and perform billing to ensure normal viewing by legitimate users. The MPEG-2 decoder completes the decompression of audio and video signals, restores analog audio and video signals through video encoder and audio D/A conversion, displays high-quality images on conventional color TV sets, and provides multi-channel stereo programs .
The network set-top box is the fusion product of computer and TV in terms of function, but the structure is different from the two. From the point of view of signal processing and application operation, the set-top box includes the following layers:
(1) Physical layer and connection layer: including high-frequency tuner, QPSK, QAM, OFDM, VSB demodulation, convolution decoding, de-interleaving, Reed-Solomon decoding, and energy dispersal solution.
(2) Transport layer: including demultiplexing, which divides the transport stream into video, audio and data packets.
(3) Program layer: including MPEG-2 video decoding. MPEG/AC-3 audio decoding.
(4) User layer: including service information, electronic program table, graphical user interface (GUI), browser, remote control, conditional access, and data decoding.
(5) Output interface: including analog video and audio interface, digital video and audio interface, data interface, keyboard, mouse, etc.
2.Key technologies of digital TV set-top boxes
The network set-top boxes reflect multimedia, computer, data compression coding, encryption and descrambling algorithms, encryption and decryption algorithms, Communication technology and network technology development level, so the technical content is very high, and the key technologies involved are:
(1) Multiplexing and decompression technology: After the analog signal is digitized. As the amount of information increases dramatically, data compression is essential. The MPEG-2 video compression standard is widely used in digital television and is suitable for a variety of definition image qualities:
MPEG-4 uses an object-based compression coding method, which divides the image and video into different The separate processing of objects not only improves the data compression ratio, but also realizes many content-based interactive functions, providing a broader platform for multimedia data compression and coding.
With the wide application of large-scale integrated circuit technology and embedded system technology, the hardware implementation of digital set-top box mostly adopts dedicated chips or digital signal processing (DSP, Digital Signal Processing) chips, which integrate the CPU core with MPEG-2, MPEG4 transport stream demultiplexer, DVB universal descrambler, MPEG audio and video decoder and NTSC/PAL encoder are integrated to form the core chip of STB. In order to realize real-time demultiplexing and real-time data information processing. Customer Service QQ:194923708
(2) Downlink data demodulation and channel decoding technology: The compressed data cannot be directly transmitted on the channel, and channel coding and modulation are required. The digital TV and value-added services usually transmitted in the cable television network mostly use QAM (Quadrature Amplitude Modulation) modulation mode and RS (ReeDSolomon) error correction coding.
(3) Modulation and coding of upstream data: In interactive applications, three methods are commonly used, namely, the use of telephone lines to transmit upstream data. Use Ethernet to transmit upstream data and transmit upstream data through wired network. Since the uplink data is much less than the downlink data, OP-SK (QuadraturePhaseShiftKeying) or 160AM mode is mostly used for modulation.
(4) Internet browsing technology: In order to realize the real Internet browsing, in addition to the upstream and downstream data, the connection between the cable TV network and the Internet must also consider running IP (Internet Protocol) on it.
(5) Real-time operating system: The operating system in the digital set-top box adopts a real-time operating system (RTOS.Real-TimeOperatingSvstem). RTOS can work in a real-time environment and occupy a small memory space. It is responsible for Manage local resources and network resources, provide basic operational functions and access control of devices.
(6) Middleware technology: Middleware technology, that is, an open business platform, has become the core technology of interactive TV. Middleware is usually composed of Java virtual machine, web browser, image and multimedia modules, etc. By defining a complete set of standard application program interfaces, the application program is independent of the operating system and hardware platform. The development of the application program becomes simpler, and the openness and portability of the product are stronger, so as to ensure the expansibility of the set-top box and the effective recovery of investment.
Concluding remarks
Interactive TV is the future development direction of cable TV, and it plays an important role in the construction of multimedia broadband network and national information infrastructure. We are currently in a critical period for the development of digital TV and high-definition TV, and the interactive TV industry is booming, so it is very necessary to understand digital TV technology and digital set-top boxes.
