Development history
Set top box (STB) originated in the early 1990s. At that time, it was mainly a solution designed by European and American cable TV stations to solve the problem of cable TV viewing fees. Harassing equipment. The set-top box as a digital television (DTV) auxiliary equipment started from the trial broadcast of digital television and high-definition digital television (HDTV) in European and American countries in the late 1990s. Its main function is to enable users to watch digital TV programs and high-definition digital TV programs with original analog TV sets, that is, to provide digital/analog signal conversion functions. This type of set-top box is usually called a digital TV set-top box. Digital TV set-top boxes have network environment characteristics and conditional access functions. The so-called network environment characteristics refer to the different set-top boxes used in different TV broadcasting networks. According to the three digital TV transmission standards defined by ETSI, there are: digital TV set-top box DVB-C for receiving cable TV, digital satellite TV receiving There are three types of TV set-top boxes DVB-S and digital TV set-top boxes DVB-T for receiving terrestrial broadcast TV.
In recent years, with the development of broadband networks, the Internet has become more and more widely used, and people have germinated the idea of using the Internet to watch TV. In particular, the vigorous development of IPTV has spurred the activity of the terminal market. Telecommunication equipment manufacturers have invested in the R&D and production of set-top boxes. The original digital TV set-top box manufacturers are also experimenting with two-way IP set-top boxes. The set-top box has evolved from a single dedicated set-top box for descrambling or digital/analog conversion to support multiple access methods and IP, with multiple encoding and decoding capabilities and graphic browser functions, and can support video-on-demand, time-to-time services including digital TV. An IPTV set-top box with business functions such as mobile TV, web browsing, information services, distance learning, medical treatment, and interactive games. In the future, IPTV set-top boxes will be widely used in the expanding field of interactive multimedia digital content services as a home digital platform.
Classification
Digital satellite set-top box
This type of set-top box is also called integrated service receiver (LIM), which is used to receive digital satellite broadcast programs. This type of set-top box has been commercialized a few years ago, and there are professional LIMs as well as personal LIMs. Many of the TV programs I have seen are received by cable TV stations from satellites through professional LIM, and then sent to users' homes through cable TV. Personal LIM is not popular in my country, but it has a better market abroad. The main function of this type of set-top box is to receive digital TV broadcasts, and it also supports applications such as data broadcasts and teletext. But because its transmission platform is a satellite channel, it is difficult to support interactive applications. Digital satellite set-top boxes basically adopt the DVB-S (Digital Video Broadcast Satellite) standard, and there are commercial products at home and abroad.
Digital terrestrial set-top box
The function of the digital terrestrial set-top box is similar to that of the digital satellite set-top box, except that the transmission medium is changed from a satellite channel to a terrestrial broadcast channel. The frequency used by this type of set-top box is the same as that of the cable TV. However, because the wireless channel is much more complicated than that of the cable TV network, its signal transmission technology is also quite different from that of the digital cable TV set-top box.
There are three main digital terrestrial broadcasting standards in the world: DVB in Europe, ATSC in the United States and DTTB (Digital Terrestrial Television Broadcasting) scheme of ISDB-T (Integrated Services Digital Broadcasting) system in Japan. DTTB is actually a variant of DVB-T, ATSC receiving equipment is called DTV, and DVB receiving equipment is called standard digital TV. However, in a relatively short period of time, DTV and standard digital TV cannot be reduced to the price of analog TV, and digital terrestrial broadcast programs must be displayed on the analog TV through a digital terrestrial set-top box.
The key technology of digital terrestrial set-top boxes is coded orthogonal frequency division multiplexing (CODFM), which can effectively solve the problems of multipath reception and adjacent channel interference in digital terrestrial broadcasting. In an analog TV broadcasting system, multipath reception can cause image ghosting. In a digital TV broadcasting system, certain phases of multipath signals may be superimposed between the signals, resulting in reception failure. In addition, there will be adjacent channel interference between digital broadcast signals and analog broadcast signals and between digital broadcast signals. If digital broadcasts want to use adjacent channel technology to improve bandwidth utilization, the effective radiation power in the channel must be lower than that of analog TV broadcasts. Effective radiated power, and the spectral power density should be kept constant. Orthogonal frequency division multiplexing CODFM overcomes the above problems. It divides the serial data stream into multiple bit symbols, each of which can have thousands of bits, and then uses these bits to modulate and place them in a frequency band. A small number of thousands of mutually orthogonal carriers. By setting the guard interval of these carriers and the position of the sideband energy, the energy of a specific carrier on the adjacent channel is zero, thereby providing better adjacent channel suppression capability.
Digital cable TV set-top box
The basic principle of digital cable TV set-top box is the same as digital satellite set-top box and digital terrestrial set-top box, except that the signal transmission medium is the all-cable network or Hybrid fiber/coaxial network. However, due to the better transmission quality of the cable TV network and the maturity of cable modem technology, this type of set-top box can realize various interactive applications, and is widely favored by the industry. Digital cable TV set-top boxes basically adopt the DVB-C (Digital Video Broadcast) standard.
In fact, this type of set-top box can support almost all broadcast and interactive multimedia applications, such as digital TV broadcast reception, electronic program guide EPG, quasi video on demand (NVOD), pay-per-view (PPV) , Software online upgrade, data broadcasting, Internet access, e-mail, IP phone and video on demand, etc.
Function requirements
Media processing function requirements
The media processing functions required by basic services and extended services shall be supported. For basic services, one or more of AVS video, MPEG-2, MPEG-4, MPEG-4Part10/H.264, SMPTEVC-1 can be selected as the video decoding standard; audio decoding can use MPEG-2/4AAC, MPEG-2 audio, Dolby AC3/5.1, MPEG-1Layer2 and MP3, etc. When the technology and business are more mature, one or two will be determined as the audio and video codec standards for IPTV. For extended services, image display formats such as CIF or QCIF and H.261 or H.263 video codec standards must be supported, and G.711 audio codec standards must be supported. G.723, G.728, G.729 can also be used. Audio codec standards. The reason for adopting the multi-option method is mainly to consider the patent fees of various audio and video codec standards, etc. There is no definite standard.
In addition, the set-top box needs to support graphics display with resolutions of 640×480, 720×576, 352×288, and each pixel supports at least 16-bit color; it supports simultaneous display of multiple planes, which can be used Tile or superimpose images; support the ability to display characters and Chinese characters, and the encoding of Chinese characters should meet the requirements of GB18030.
Interactive function requirements
The set-top box needs to provide interactive content selection and content interactive control two types of interactive functions. The interactive content selection function supports interactive processes such as using the portal navigation menu to select content, perform program search, and exchange authentication information with the authentication system of the service platform. The content control function is mainly aimed at the function of interactive control commands between the set-top box and the IPTV service platform to control content information when implementing on-demand services.
Management function requirements
Software upgrade function. The set-top box can provide application software interfaces, and obtain the ability to support new services through online or local software upgrades. It must be able to obtain the latest software version number through the network or peripheral storage devices and determine whether it needs to be upgraded, or obtain the latest through HTTP(S) or FTP Version file. If the upgrade fails, the set-top box must still be able to work normally, and the software version must be checked when it is turned on.
Log function. The set-top box must realize the management of the local version information and system information and the diagnosis of error information, and form a double backup log file. Fill in the log when the status changes; upload the log file when the set-top box is turned on, and upload the log file every 24h.
Remote configuration function. The set-top box must be able to perform functions such as restarting, downloading, setting parameter values, restoring factory settings, setting parameter attributes, deleting device registration, and restoring the minimum kernel.
Local configuration function. Including the configuration of the set-top box information through the local area network (the set-top box provides a web configuration interface) and the user configures the set-top box through the remote control. The configuration information includes the IPTV service management system domain name, network access method, network access account/password, static IP, Gateway, DNS server, DHCP and user service number/password, etc.
Hardware interface requirements
The basic hardware configuration of the set-top box should have three types of physical interfaces, namely, the uplink network interface, the downlink audio and video interface and the infrared remote control interface. A variety of auxiliary interfaces can be configured as required. Interface.
Network-side interface: one or more interfaces can be configured as required. Interface types include high-speed Ethernet interface 10/100Base-T, ADSL interface (optional for devices with built-in xDSLModem), wireless LAN interface (any of the following wireless LAN access standard interfaces can be provided according to access conditions. In 2.4 In the GHz band, the transmission rate is 11Mbit/s, which should comply with the IEEE802.11b standard; in the 5.8GHz band, the transmission rate is 54Mbit/s, which should comply with the IEEE802.11a standard; in the 2.4GHz band, the transmission rate is 54Mbit/s , Should comply with the IEEE802.11g standard).
Audio and video interface: video output interface has composite video output terminal and S-Video video output terminal; audio output interface has analog audio output interface and digital audio output interface.
Infrared interface: It specifies the transmission distance, infrared emission angle and the minimum angle of infrared signal received by the set-top box to control the set-top box by the infrared remote control. The specific performance requirements should meet IrDA1.1 Basic requirements of the protocol (fast infrared protocol).
Auxiliary interface: optional, including USB interface, downstream Ethernet interface, Z interface, serial interface, etc.
Communication protocol requirements
As a terminal device for IP network access, IPTV set-top boxes must support a series of business-related IPs. The IP involved in the set-top box can be summarized as: related protocols involved in the access process, including PPPoE, DHCP, IEEE802.1x; file/text transfer protocols, including TFTP, FTP, HTTP; media transfer protocols, including real-time transfer protocols ( RTP) and a transmission protocol that complies with ISO/IEC13818-12000; Internet group management protocols, including IGMP supporting multicast (should comply with RFC2236); media playback control protocols, including real-time streaming RTSP (should comply with RFC2326); Management protocols, including user terminal wide area network management protocol TR069 and Simple Network Management Protocol SNMPv2 defined by the DSL Forum; network time synchronization protocol, you can choose Network Time Protocol (NTP) or Simple Network Time Protocol (SNTP).
Security requirements
The set-top box should support AAA authentication, and the necessary information should be provided when accessing the IP network, including the user identification code or user name and password. It can be used only after authentication and authorization Various services provided by the IPTV service platform; at the same time, it supports machine-card separation, and uses smart card technology to store user information in hardware encryption. Digital rights management security requirements: The digital rights protection of the network is implemented by the content provider or service provider, and the information transmitted to the user terminal should be information with DRM. The STB needs to have the corresponding version for the service platform DRM to provide content copyright protection.
Structure
Hardware Structure
The digital cable TV set-top box is composed of four subsystems.
Control subsystem: This is the heart of the set-top box, which is composed of CPU, ROM and RAM, provides signal access and control processing functions, and provides a programmable platform. In addition to being responsible for the initialization of each subsystem, it must also control the coordination of various parts and specifically complete the decryption and descrambling of the signal, demultiplex, and obtain MPEG-2 data streams and other packaged data.
Digital processing subsystem: The compressed and encoded sound data is decoded by the audio decompressor and output to the D/A converter to obtain the audio signal of the TV. The compressed and encoded video data is decoded by the video decompressor, and its output is mixed with the graphics generated by the OSD system, and then supplied to the TV through the NTSC/PAL/SECAM encoder. This part generally uses dedicated chips.
Network interface subsystem: realize duplex communication with video server. According to the difference of the access network, the corresponding interface is adopted.
User/public interface and extended interface subsystem: communicate with peripherals such as infrared remote control, game controller, smart card, decryption card, etc.
Software structure
The software structure of the set-top box has 4 layers.
Hardware driver layer: Located at the bottom of the software structure, it controls the initialization and work of each module.
Kernel layer: Generally, it is a small operating system, which completes the creation of processes and the communication between execution processes, as well as the allocation and management of resources.
Command parsing layer: shield the following layers from the application layer to analyze commands issued by applications and users.
Application layer: Located at the top layer of the software structure. Possible applications include electronic program browsing, video players, etc.