Wednesday, January 26, 2011
【 Weak current College 】 digital set-top box for the schema and design of key 】
Digital TV is a cell phone from another killer application, to the living room as core, constantly integrating family other audio-visual and information equipment, the formation of multiple applications of the home network; plus, digital TV and mobile phone to the integration of development, mobile TV (Mobile TV) is already in full swing in promoting around the world. When the TV broadcast system and network, even when combined with mobile cellular systems, including video, voice and data services are natural convergence trends to diversity, which is a separate form complex than in the past, many applications, and digital machine box (Set-top-box) is located in the heart of this schema, the challenges faced by the design really heavy. According to the TV show the send pipeline, digital set-top boxes can be divided into digital terrestrial set-top box (Terrestrial), digital satellite (Satellite), set-top box and digital cable set-top box (Cable), as well as through Internet (xDSL, Cable Modem, fiber) IP set-top box, etc. Overall, digital set-top box technology spindle orientation support HDTV (High Definition TV) and interactive (Interactive) development, but there are still different market areas and application of bias. In order to achieve product differentiation, joined hard drive digital video recorder (DVR) and the integration of home networking features home network gateway (Residential Gateway, RG), is also important for digital set-top box design direction.
System architecture of a digital set-top box is made of soft and hardware, hardware can be divided into the main unit to receive broadcast signals and convert them to digital transmission streaming front-end (front-end, FE) chip, i.e. tuners (tuner) and regulation/modem (modulator/demodulator); back-end chip including TV decoder/encoder (NTSC/PAL decoder/encoder), Transport, MPEG-2 MPEG-2
Or HL decoder, microprocessors, graphics, audio processor, audio DAC, video DAC; and DRAM/SDRAM, Flash memory, power supplies, components, and other standard discrete components. More advanced product will integrate security chip, modems (modem) or home networking chips, and a video of the hard drive (HDD). (Figure 1) to support DVR function in set-top box decoder chip block diagram.
Figure 1 have DVR function block diagram of a set-top box decoder (for example by STx5100)
More powerful and diverse capabilities and greater integration of the digital set top box in the hardware section. In feature, TV decoder stress can do dual-DVR dual-TV and, in addition to being able to decode and display digital and analog TV broadcast signals both, also can decode two synchronization standard analytic power video, then send to multiple different TV playback or recording to hard disk. There are also so-called PAP (high resolution dual screen) and PIP (composite video) feature to the same screen displays two different high resolution television screen, you can individually arranged side by side or up and down. In integrated, in order to maintain the design flexibility, usually in the system of the front-end and back-end chips is the separation of configuration, but also will both consolidate into a single package, and thus to a large number of production applications offer better cost-effectiveness. The chip itself is facing in the direction of SoC, especially in core decoder chip, the chip will be advanced 90nm process, such as in a chip to integrate various functions, including high-performance CPU, video decoding circuit and various peripheral devices, please refer to (Figure 2).
Figure 2 set-top box chip iDTV processor hardware architecture diagram (for example the STD2000)
In the software section, including the operating system and real-time operating system (RTOS), offers interactive features such as intermediaries of MHP software (Middleware) and application program interfaces (APIs) and electronic listings (EPG), application software or conditional-access (Conditional Access, CA) security feature. Interface you need to support the security module (POD module), common interface (CI), smart cards (smart card/reader), high speed interface (USB, IEEE 1394, and serial ATA), etc. CA, CI, POD and other technical difficulty, is also in the selection of equipment, video processing chip solutions, still need further consolidation and development topics.
Key: video conversion processing
Video conversion processing is undoubtedly the main STB, encoding/codec (CODEC) as if the STB's heart. The current television broadcasting industry is still in the compresses for basic video MPEG-2 specifications, but actively steering MPEG-4, H.264/AVC (i.e. MPEG-4 Part 10) and next-generation codec VC-1, etc. Introduction of new specifications for operators who have many benefits, the most obvious example is that they can pass limited bandwidth transfer more programme channels, or to provide high definition TV.
To MPEG-2 and h.264 to compare, in transport HDTV content, the former need 20Mbps bandwidth, which simply 8Mbps bandwidth can provide the same quality, both poor 2.5 to 3 times. In addition to bandwidth considerations, the adoption of a new video compression specification also brings other advantages, for example in a program recording PVR/DVR function in set-top box, the greater the compression rate means that can store more capacity; in addition, the new specification also provides object-oriented interactive features, as well as intra-split screens, and other value-added features.
Currently on the market were not clear to a specific generation specification gets close, in the transitional period, set-top box only supports many kinds of specifications. MPEG-4 Although the advent of longer, many manufacturers strongly supported, but it's inherently exist some difficult to overcome the bottleneck, let it develop over the remarkable difficult.
MPEG-4 biggest problem is that specifications are too complex, and the video is just one of the defined MPEG-4 (lS014496-2 MPEG-4 Part 2). This complex of produces parts compatibility posed problems: some content is not clear enough, or not enough open; some do a compromise deal, but cause interoperability problems. For example, since MPEG-4 allows customised output specifications, thus causing the coexistence of various specifications, such as a well-known Divx format and Microsoft's wmv specifications, but too many specifications also lets service providers popularity. Another reason that criticized, it is to get the MPEG-4 commercial take provable Kuang, waste, and to afford the high cost of use.
In comparison, although H.264 is also a complex standard, but it is only for video do develop, also has access to MPEG/lS0 and ITU two major international standards organizations, and it is currently able to provide the best video compression efficiency specifications, or royalties, since 2003 the introduction of the standard, i.e. on HDTV, HD-DVD, cell phones and video streaming, and other businesses produce great attraction. Not only that, when the H.264 in formulating and taking into account the existing systems of MPEG-2 interoperability issues, therefore, in today's infrastructure could be in H.264 embedded MPEG-2 transport stream (TS) sent. The application of H.264 and sampling rate please refer to the (table 1).
However, the effectiveness in improving compression, encoding H.264 also greatly increased computational complexity and therefore need to consume more computing resources. In this case, set-top box must be in a more efficient processors, or to exclusive CODEC accelerator hardware to complete the task. In addition, high-quality, low-complexity algorithm for h.264 codec is also a great help to ST, has made a motion estimation and rate control algorithm, as well as for H.264 decoding of error detection and hide algorithms, allowing a decoder to bear and hides data packet loss, packet in the wireless network to achieve the best performance of IP networks. Video transcoding (Transcoding)
As digital home network core position in set-top boxes, in addition to television programmes broadcast, video conversion is also a family as a DVD, PMP, digital cameras, and other various devices of interconnection centres. In order to make video content between devices for playback and access, set-top box also has a video transcoding capabilities, also is to adjust bit bit rate to meet special channel rate or storing format; or to change the resolution, such as high definition (HD) video streaming to standard resolution (SD) TV or mobile terminal in CIF SD video, and so on.
Figure 3 DBS MPEG-2 go H.264 encoding conversion technology
ST's advanced systems technology (AST) Group developed dynamic bit streaming programming (Dynamic Bitstream Shaper, DBS) technology, take the optimization algorithms for supporting MPEG-2 and H.264 bitrate, between xunkuang rate, xunkuang size changes with the coding standard. Its development is aimed at reducing video transcoding architecture complexity, operation consumes energy, memory requirements, as well as operation latency, so that the video content does not need to go through another encoding (re-encoding) which can get the same or better quality.
Key: digital content management technology
Enter the era of digital content, it is difficult to copy pirated, it also became a television service providers towards digital TV, or IPTV is one of the most concerned about, is responsible for receiving conversion digital content of set-top box, it will be assigned with the task of the copyright control. Current digital TV content management technology practice, with the conditions of access (CA) and digital rights management (DRM) is considered a basic protection mechanisms, emerging standards in more attention is secure video processor Union (Secure Video Processor Alliance, SVPA) standard launched by the SVP. The following will be discussed separately: conditional access (CA), CA is a system service provider operating digital TV business a key mechanism that provides for the broadcast networks "addressing management" (Addressability), its focus is the television channel and user permissions. User needs through proprietary set-top box or smart card to obtain authorization to untie the scrambling code (Scrambling). In addition to scramble, the CA will also receive control user management information, including user name, address, card number, billing, and so on, and with a back-end customer management and billing system to provide more personalised value-added services.
Since the CA must deal with complex problems such as calculus descrambling, was more difficult to set-top box manufacturers across the threshold, but also to master this technology company of the great advantages. Past CA often and specific system design of the company's proprietary set-top box tied together user once to swap system, along with STB. This is in addition to causing system company and user problems, but also make set-top boxes for low limits SBAS, related organizations, or Government policy is committed to promoting CA from set-top-box independent out of isolation and card.
With DVB, system originally only CA do common scrambling (DVB Common Scrambling), operation (Operation) and management (Management) is open to system design can be developed. Currently DVB for Central Office and the client makes synchronous encryption respectively (Simulcrypt) and multiple decryption (Multicrypt) programmes to resolve problems on the Exchange operations. In addition, the United States, Europe and Asia, many countries have machine card separation dependingFor the television industry's established policy. At present the CAM (CA module) independent design approach there are three types, namely-PCMCIA, USB, or smart card, PCMCIA is among the mainstream market, including the United States and Europe POD standard DVB-C standards are fundamental to its PCMCIA physical interface. DRM CA addressing function could do on channel and user rating control, but for individual programmes content protection and licensing is not caught, in this case, there is a need to further adopt DRM mechanism to provide content management. The two are mutually reinforcing, CA is the system operators of program management and trading tools, and DRM is the content publisher's self-protection mechanism.
DRM is license management (License Management) strategy, which is composed of digital content publishers on the original file is encrypted (128 bit or 156 bit symmetric algorithm), and add the header to join author, version number, release dates, and other copyright information. When users want to through the network or obtain directly from the CD, the system automatically checks have no corresponding license (LICENSE), authentication methods including insert IC card, IKEY (a USB authentication tokens), or through network authentication server to authenticate the account number and password.
The establishment of the entire DRM architecture is divided into three layers: user interface, application software, DRM users authentication subsystem, as well as the most basic encryption engine. Which user authentication subsystem is the key to IPTV business implementation, there are many authentication systems, two more typical IPTV DRM system using Kerberos and PKI authentication mechanism.
In addition, DRM specifications, the specifications on the market today is divided, the most attention is Windows Media DRM and Open Mobile Alliance's OMA DRM 1.0/2.0 specifications, including UT-DRM, NDS, SecureMe dia, WideVine, BesDRM specifications. In order to allow users to watch video content from different sources, today's STB had to try to support the DRM specifications on the market.
Figure 4 different DRM interoperability problems of specification
DRM-protected content conception is good, but instead of creating market specifications development site, please refer to (Figure 4). In order to make various DRM specification to interoperability, including HP, Philips Electronics, ST, Samsung Electronics, Sony Corporation and twentieth century Fox Film Corporation, 40 companies have formed a coalition of Coral, which is dedicated to providing WEB-based and home networking device security transfer content interoperability. At present, the Organization has published a new interoperability layer that can support multiple DRM schemes, please refer to the schema (Figure 5), however, Microsoft and Apple specifications of the two companies is still the exception.
Figure 5 Coral Union to DRM interoperability layer node down
SVP standard mainly by the SVP Alliance promotion, has access to over 20 major media and technology manufacturers support, ST is the standard launched one of the members. SVP Alliance's main job is in digital home networks, and digital TV, set-top box, DVR, portable media players and other consumer electronic applications to promote their SVP content protection technology.
SVP with CA and DRM mechanisms, complementary to digital content to provide better protection and management. By SVP technology, media companies are free to set its DRM specification to the content of its work, and come from a CA system of rules to the SVP format, then through support SVP featured personal video recorder, DVD recorder or PMP and other device decryption revert to the original content is presented to the audience.
Basically, SVP technology is a hardware-based security solution that provides encryption, transmit and receive content and how to use your content through secure channels. Its hardware core just less than 20 million gate gate, and running a security software stack. This is a low-cost, appropriate for the future application of the solution and, therefore, ST's digital video processor and decoder has general support SVP standards.
In response to market changes, digital set-top boxes must be able to provide the convenience of product development and upgrade flexibility, this includes the device development level and end users use the dimension. The development dimension, the key components of the manufacturers will provide the perfect design reference platform, allowing equipment manufacturers to speed up development time, and can have both on the basis of the design flexibility to add new features to launch differentiated or upgrade products. In the Terminal part of the set-top box is also required to have a software upgrade, which is simply passed to the remote network to download updates, you can upgrade their software or firmware.
As digital set-top box is a collection of various functions of the Hub, coupled with the market technology, standards and application needs change very quickly, in order to meet the needs of all parties and long service life of the universal set-top box, is not easy. In addition to the above video conversion processing and content management of key design, digital satellite, terrestrial and cable television service, the signal return path's interactive is the overall system of important bottleneck; part of the IPTV, although interactive is good at, but how do you ensure that the streaming video quality of service (QoS), and can provide HDTV service, is also a very big challenge. Of course, there are additional challenges and opportunities before us, such as digital TV and cable/mobile phone integration, etc., we continue to invest observation.