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1. The Development History of Set-top Boxes
Set top box (STB) originated in the early 1990s as a descrambling device designed by cable television stations in Europe and America to solve the problem of cable television viewing fees. The use of set-top boxes as auxiliary equipment for digital television (DTV) began in the late 1990s when European and American countries tried to broadcast digital television and high-definition digital television (HDTV). Its main function is to enable users to watch digital TV programs and high-definition digital TV programs on existing analog televisions, providing digital/analog signal conversion function. This type of set-top box is commonly referred to as a digital TV set-top box. The digital TV set-top box has network environment characteristics and conditional access function. The so-called network environment characteristics refer to the different set-top boxes used in different television broadcasting networks. According to the ETSI definition, there are three types of digital television transmission systems: digital television set-top box DVB-C for receiving cable television, digital television set-top box DVB-S for receiving digital satellite television, and digital television set-top box DVB-T for receiving terrestrial broadcasting television.
In recent years, with the development of broadband networks, internet applications have become increasingly widespread, and people have sprouted the idea of using the internet to watch TV. Especially with the booming development of IPTV, the terminal market has become active, and telecommunications equipment manufacturers have invested in the research and development and production of set-top boxes. Original digital TV set-top box manufacturers are also testing bidirectional IP set-top boxes. The set-top box has evolved from a single dedicated set-top box for descrambling or digital to analog conversion to an IPTV set-top box that supports multiple access methods and IPs, has multiple encoding and decoding capabilities, and graphical browser functions. It can support business functions such as video on demand, time-shifted television, network browsing, information services, remote education and healthcare, interactive games, and more, including digital television. In the future, IPTV set-top boxes will be widely used as a home digital platform in the expanding field of interactive multimedia digital content services.
2. Technical requirements for IPTV set-top boxes
IPTV business is a brand new business model that brings consumers a network enjoyment that integrates information, entertainment, learning, and shopping. Personal computers, set-top boxes, televisions, or 3G mobile phones can all serve as terminals for IPTV services. From the perspective of suitability for the consumption habits and comfort of a large number of users, set-top boxes and televisions should be the mainstream terminals of IPTV in the future. When it comes to the technical requirements for IPTV set-top boxes, we mainly consider two aspects: the first is the need to achieve business, and the second is the need for user experience.
IPTV can provide services such as live television, video on demand, time shifted television, visual services, information services, online browsing, interactive games, and future expandable services. The main business characteristics of IPTV are reflected in the form of interactive multimedia retrieval and playback. Interaction requires the network to have bidirectional capabilities, and retrieval requires bidirectional information exchange. Broadcasting control also requires interaction; Play requires sufficient access bandwidth and Media Transfer Protocol; Multimedia requires audio and video encoding and decoding capabilities. Therefore, in order to achieve IPTV business applications, IPTV set-top boxes are required to have basic business functions such as supporting the reception of online live TV programs, video on demand, and time shifted on-demand. At the same time, they should also have expanded functions such as internet browsing and information services, electronic program guides (EPGs) and program retrieval, as well as interactive games and software online upgrades. As an IPTV business terminal, set-top box devices should have an open system architecture to adapt to the constantly upgrading and expanding business needs; Fully considering network environment and protocol factors, it is required to have at least two types of uplink network interfaces and support multiple access authentication protocols and IPs; Requirements include audio and video media encoding and decoding functions, as well as business application and management functions. In short, from a business perspective, IPTV set-top boxes need to have open business capabilities to meet the constantly evolving business needs.
From the perspective of user experience needs, the change brought by IPTV business is to transfer the study experience of traditional internet PC terminals watching streaming videos to the living room, change the forward leaning posture to the backward leaning posture, and change the keyboard operation to remote control operation. These changes require that the design of IPTV set-top boxes should fully consider the vast user base accustomed to operating televisions, and strive to maintain the characteristics of simple operation, moderate cost-effectiveness, and durability. According to different consumer needs of users. The set-top box should be designed in different levels of high, medium, and low to meet various levels of consumer groups.
In the design process of IPTV set-top boxes, a series of key technologies are needed to meet the above requirements, including audio and video encoding and decoding technology, graphics and image display technology, media streaming/control technology (protocol), middleware technology, embedded systems, and various interface technologies.
3. Technical solutions for IPTV set-top boxes
Early set-top boxes could only provide video services, and the technical focus was mainly on the video part. The ultimate goal of IPTV business is to achieve the integration of video, voice, and data, and provide three network integration services through IPTV set-top boxes. It is precisely because IPTV set-top boxes can serve as a link to simultaneously provide video, voice, and data fusion services, combined with broadband access and wireless networks, that a truly networked home environment can be created.
The application process of IPTV set-top boxes generally involves connecting business content to the set-top box through a broadband network, and using the set-top box remote control or keyboard to request video content from the broadband network. The broadband network transmits the required video signal to the user end, which is decoded by the set-top box and output on the TV. Implement video on demand or web browsing, etc.
At present, there are roughly three levels of set-top box products that can support IPTV business, namely basic, enhanced, and super strong. The so-called basic type refers to the set-top box that can support IPTV basic services, provide electronic program listings, achieve the playback of network TV programs, and can perform basic playback control. The enhanced set-top box not only has basic functions, but also provides functions such as internet browsing, visual business, text information, and simple games. The ultra strong high-end set-top box is equivalent to a home digital entertainment center, which can not only provide basic and expanded IPTV services, but also achieve high value-added functions such as video interactive games and personal video storage.
3.1 Hardware structure of IPTV set-top box
Set top box equipment is composed of hardware and software. Different levels of set-top boxes use different system platforms and software architecture, so their functions are different. There are basically three types of platforms in terms of hardware structure, namely dedicated chip architecture, multimedia digital signal processor (DSP) architecture, and X86 architecture based platforms. Most software structures adopt hierarchical and modular structures, as well as middleware structures.
The hardware structure of a set-top box consists of a core control unit, media processing unit, and various interfaces, as shown in Figure 1. The core control unit generally uses embedded system processor chips and can run real-time operating systems. The media processing unit generally selects ASIC dedicated decoding chips or digital signal processors based on the cost of the set-top box, and there are also software decoding implementations. The IPTV set-top box interface is much richer than other TV set-top boxes, and the network side interface can be configured as a high-speed Ethernet interface, ADSL interface, wireless LAN interface, or even EPON or cable interface according to different network access methods. The basic configuration of the media playback interface includes composite audio and video terminals and S terminals, while higher configurations can include YpbPr, YCbCr, and digital audio output interfaces. Control interface refers to the interface for users to operate and control set-top boxes, typically using infrared remote controls, as well as infrared remote keyboards or WiFi technology. In addition to the necessary interfaces for the basic business applications mentioned above, other extension interfaces such as USB interface, serial interface, Z interface, smart card interface, etc. can be configured according to business needs.
From Figure 1, it can be seen that the core components of an IPTV set-top box are the CPU and codec. The strength of set-top box functionality is directly related to the selection of core devices of different grades. The currently visible set-top box products are mainly based on the following three structures:
Figure 1 Hardware structure of IPTV set-top box
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(1) Architecture based on dedicated chips (SOC+ASIC)
In addition to the processor, the special video image processing chip also integrates some intelligent modules, such as audio and video input and output, and some also integrate image compression and hardware acceleration modules. Essentially, both dedicated video compression chips and general-purpose video processing chips belong to SOC (system on chip), with the difference being that the former comes with fixed compression modules, fixed processing methods, and fixed microcode, while the latter requires product developers to develop video compression algorithm programs.
The traditional set-top box based on ASIC/SOC structure, due to its full hardware chip implementation scheme, makes it difficult for operators to achieve effective software upgrades, and its network adaptability also has significant issues. However, due to the low cost of set-top boxes based on this structure, in the initial stage of IPTV business, business operators generally provide users with free set-top boxes. Using a dedicated chip structure of set-top boxes can ensure basic business while saving operating expenses, undoubtedly playing a good role in business promotion.
(2) Architecture Based on Multimedia Digital Signal Processor
IPTV set-top box based on multimedia processor technology uses high-performance digital signal processor and embedded system on a chip as the hardware platform. DSP is mainly used for video and audio decoding processing, and embedded real-time operation system on a chip is used to control and process data from various interfaces and operation requirements. Adopting a multimedia digital processor architecture can easily achieve MPEG-2/4 video and audio processing, H.264 video processing, and also support other encoding and decoding standards for IPTV. The primary indicator for evaluating IPTV set-top boxes is their ability to support media formats. Because there is currently no unified standard for the media format used for IPTV services, and various operators are also in the testing and selection stage, set-top boxes based on multimedia digital signal processor architecture can flexibly write different encodings or directly make dual decoding forms.
Embedded systems are the product of the combination of computer, communication, semiconductor, microelectronics, voice/image/data transmission and processing technologies with specific application objects. Generally speaking, embedded systems are composed of four parts: embedded chips, embedded software, embedded operating systems, and embedded system development tools. Embedded chips include embedded microprocessors, embedded microcontrollers, embedded digital signal processors, and embedded systems on chip. With the rapid development of RISC (Reduced Instruction Set Computer) technology and microelectronics technology, the functions of embedded chips are becoming stronger and the volume is becoming smaller.
An embedded real-time operating system is different from a desktop computer operating system in that it is not installed on a hard drive, but is fixed in memory. Embedded operating systems have a compact structure, relatively simple functions, and low resource overhead. Currently, there are mainly three types: Windows CE, Linux, and VxWork, with the first two being more widely used. Windows CE is mainly used on high-end set-top boxes, bringing convenience to the networking of devices such as set-top boxes and PCs. But the cost is not cheap. For mid range set-top box products, choosing the Linux operating system is more reasonable. According to a report released by market research firm Strategy Analytics. In the global set-top box market, the Linux operating platform has become the main choice for IPTV set-top boxes. Because the Linux platform not only supports many advanced features, such as video recording and IP transmission, but also is very economical and does not require license fees.
(3) X86 based architecture
Compared to embedded systems based on RISC architecture CPU, embedded systems based on X86 architecture CPU have the following advantages: firstly, it can encode and decode files in different formats, such as MPEG-2, MPEG-4, WMA, etc., allowing multimedia audio and video devices based on this embedded platform to handle various video sources. Secondly, the Windows CE operating system has a complete set of integrated multimedia functions and extremely rich application programs, which shortens the development cycle of IPTV set-top boxes and is suitable for developing advanced IPTV set-top boxes. The inherent desktop compatibility of this operating system allows set-top box developers to easily expand the functionality of IP set-top boxes using a large number of applications prepared for Windows XP.
The set-top box based on X86 architecture, due to its embedded Windows CE real-time operating system, has a relatively complete set of application software, low maintenance costs, and can be easily shared with PC resources. Due to the high development cost of this set-top box product, although it is powerful and comparable to PC, it can only face high-end consumer groups, at least initially it will not be very attractive to ordinary consumers.
3.2 Software structure of IPTV set-top box
As a client product, IPTV set-top boxes not only have a good hardware platform, but also require the cooperation of software systems to achieve IPTV business functions. The software of set-top boxes mostly adopts a hierarchical structure, which is generally divided into three layers: application layer, intermediate interpretation layer, and resource layer. Each layer includes many programs and programming interfaces, as shown in Figure 2.
Figure 2 Software structure of IPTV set-top box
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Figure 2 divides the three layer structure of set-top box software, where the resource layer software includes real-time operating systems and drivers for set-top box hardware, mainly used to complete operations on hardware devices. The main function of the explanation layer is to translate set-top box applications into instructions that the CPU can recognize, and to mobilize hardware devices to complete corresponding operations. The application layer can be divided into built-in applications and download applications to realize business applications such as TV play, video on demand, EPG, DRM (digital rights management management), game download, etc.
Different set-top box manufacturers have different design concepts for IPTV set-top box software. In the design of implementing IPTV services, software is developed based on business processes defined between business platforms and set-top boxes, as well as utilizing common service software or middleware located between underlying system resources and business applications. However, the overall trend is still to adopt a method of isolating business application software from underlying hardware and operating system software, and using middleware is a good choice. Middleware separates the applications in the set-top box from the underlying system components, making the development of applications independent of the hardware platform. It can provide a series of application programming interfaces (APIs) with open standards, suitable for different operating systems and hardware environments. The use of middleware technology can reduce the difficulty of application development and improve research and development efficiency.
4. The standardization process and future development direction of IPTV set-top boxes
IPTV, as an emerging broadband network service, is increasingly receiving widespread attention in the industry. Especially for products like set-top boxes that resemble home digital platforms, they are increasingly sought after by telecommunications equipment manufacturers, television equipment manufacturers, as well as computer and home appliance product manufacturers. Due to differences in industry understanding of IPTV business and product design concepts, IPTV set-top boxes