Set-top box

1. Definition of set-top box
For set-top boxes, there is currently no standard definition. Broadly speaking, any network terminal device connected to a TV can be called a set-top box. From analog channel supplements and analog channel decoders based on cable television networks in the past, to "Villas" Internet set-top boxes that connect telephone lines with TV sets, and integrated receiver decoders (IRDs) for digital satellites (IRD) , Digital terrestrial set-top boxes and cable TV digital set-top boxes can all be called set-top boxes. In a narrow sense, if you only talk about digital devices, set-top boxes can be divided into Internet set-top boxes, digital satellite set-top boxes (DVB-S), digital terrestrial set-top boxes (DVB-T), and cable TV digital set-top boxes (DVB-C) according to their main functions. And the latest IPTV set-top boxes.
Digital TV set-top box is one of the information appliances. It is a consumer electronic product that allows users to watch digital TV programs on existing analog TVs and conduct interactive digital entertainment, education and commercialization activities.

The basic function of a digital set-top box is to receive digital TV broadcasting programs, and it has all broadcasting and interactive multimedia application functions, such as:
(1) Electronic Program Guide (EPG). Provide users with an easy-to-use, friendly interface, and quick access to a way to watch programs that they want to watch. Through this function, users can see the TV programs that will be broadcast on one or more channels or even all channels in the near future;
(2) High-speed data broadcasting. Can provide users with various news such as stock market quotations, ticket information, electronic newspapers, and popular websites;
(3) Online software upgrade. Online software upgrade can be regarded as one of the applications of data broadcasting. The data broadcast server broadcasts the upgraded software according to the DVB data broadcast standard. The set-top box can recognize the version number of the software, receive the software when the versions are different, and update the software stored in the memory;
(4) Internet access and e-mail. The digital set-top box can easily realize the Internet access function through the built-in cable modem. Users can surf the Internet and send emails through the built-in browser of the set-top box. At the same time, the set-top box can also provide various interfaces to connect to the PC, and use the PC to connect to the Internet;
(5) Conditional acceptance. The core of conditional reception is scrambling and encryption, and the digital set-top box should have descrambling and decryption functions. In short, up to now, a variety of value-added services have been developed around the three core functions of digital set-top boxes: digital video, digital information, and interactive applications.

Different operators and different set-top box manufacturers divide STBs into basic, enhanced, and interactive types according to different application habits. Operators have different classifications of STBs according to their understanding and application level of digital TV. Most operators define the basic type as only supporting video and audio services and receiving EPG information, not supporting data browsing and other applications, and put these applications in the so-called enhanced type; define the STB with two-way functions as an interactive type . In fact, it is difficult to distinguish between the basic type and the interactive type in terms of function. Different business purposes will have different divisions. The so-called basic type and enhanced type often use the same hardware platform, and the difference is only the software. Although some manufacturers claim that their STB is interactive or can develop interactive services, due to network reasons, there is no mature interactive application in China. At present, the so-called interactive applications are basically still local. On the basis of interaction.
Different chips are used to form different hardware platforms, and other equipment and interfaces are also different. This constitutes a variety of STBs. For example, adding a modem or network card to the STB constitutes a set-top box with two-way functions; adding a hard disk constitutes a personal video recorder (PVR: Personal Video Recorder), of course, these require the cooperation of software. Set-top boxes of different applications can also be constituted by resident different software on the same hardware platform, and the diversified STB meets the needs of different levels.

1) The development trend of STB
The huge market space and the output value of tens of billions have attracted many businesses to engage in STB production. It is estimated that more than 300 domestic enterprises are engaged in STB production. As of the end of 2004, the number of wired digital users in the country is about 80. There are about 10,000 households, except for the more than 300,000 previously accumulated, the actual number of new users last year will not exceed 500,000. The cruelty of market competition puts the entire industry in a state of loss.
Although operators are currently promoting digital TV on a large scale, moving the entire network as a whole, and distributing STBs to users for free. For this reason, they have also created the Qingdao model, the Foshan experience, and the Hangzhou model, but all these have not brought the STB industry. Prosperity has not promoted the development of STB technology, but has caused a lot of confusion to the digital TV industry. How to adapt to the development of technology and grasp the direction of technology development may no longer just be a problem that manufacturers need to pay attention to. Perhaps it should attract the attention of industry authorities and operators. All parties need to work together to create a good digital TV as soon as possible. Space for sustainable development.

2) Digital TV all-in-one
At present, most of the set-top boxes used in China belong to the basic category. They can receive digital TV programs and can also provide some applications such as e-government services. With the development of digital TV technology, a new type of TV with digital decoding function has been available, and it is currently in the stage of large-scale testing before it is put into production. This new type of integrated TV, which combines the most basic STB and TV functions, will have a major impact on STB's manufacturing and digital TV operations, facing the huge production capacity and new technology of home appliance giants. Products, most STB manufacturers will face the risk of reshuffling.
For operators, the emergence of all-in-ones has also changed operations. In the past, operators not only had to worry about program transmission, but also devoted a lot of energy to users’ STB, and even carried a heavy burden on their backs. Especially in the process of overall translation, they were burdened with huge debts due to the transmission of STB. All of this may be solved very well because of the appearance of the all-in-one machine. In the next 2 to 3 years, according to the national industry plan, more than 35% of domestically produced TV sets will have STB function, which means that more than 1,500 all-in-one TVs will be put on the market every year, and this number will increase in the future. Will continue to climb.

3) Separation of machine card
Machine card separation and all-in-one machine are almost a natural pair. The large-scale manufacturing of TVs not only improves the reliability of products, but also reduces the cost of production. The basis of large-scale manufacturing is that the products produced are consistent, which is not only reflected in the hardware but also in the software. Due to the differences in software, manufacturers cannot produce set-top boxes on a large scale like televisions. Therefore, to achieve large-scale manufacturing, CA is the first problem to be solved.
The meaning of the machine-card separation technology is to make the digital TV receiving equipment (machine) independent of the CA smart card and its software (card), and the two are connected through an interface product (large card or CAM card), and the TV and STB reserve this Universal interface. Before inserting the CA smart card, the software and hardware of all TVs and STBs are the same, and the smart card must first be inserted into a suitable CAM card before it can be inserted into the TV or set-top box to decode the corresponding program. Although on the surface, the use of CAM cards has increased the user's access cost, but because of the break away from the constraints of CA, operators and manufacturers have brought a reduction in use and manufacturing costs, and ultimately brought user access costs. The reduction. Many advantages have made machine-card separation a trend of industrial development. The United States has adopted machine-card separation as a standard for digital TV sets and has defined a mandatory timetable for this. For a large TV production country like China, separation of machine and card will also become the trend and standard of China's industrial development. As products are put on the market in batches, the popularization of digital TVs will help drive the development of digital TV users.

4) Interactive STB
Although the all-in-one machine may replace the popular STB, in the development of digital TV, due to the continuous expansion of the business, the STB software will also continue to improve, especially in the interactive field. With the improvement and application of middleware, STB has become a The low-cost hardware platform can realize multiple applications by changing different software. For operators, interactive applications have huge commercial benefits and are the most important source of profit in the future, and the use of interactive STB can help achieve this goal. Interactive STB also represents the highest level of technology development in set-top boxes, and has a huge space for development.

5) PVR STB
You can store your favorite programs by adding storage devices to the STB. This kind of STB is PVR. Although PVR STB has not yet formed a certain market in China, the strong growth in sales of several million units abroad each year indicates the huge domestic market in the future, and this demand will increase over time.
Double decoding or multiple decoding STB
For domestic operators, especially in the overall translation process, how to solve the problem of users watching digital TV programs on two or more TV sets is a very headache for developers, although it can be achieved through mandatory administrative actions. One card is used to increase the viewing fee, but users cannot understand this mode of operation, and it also makes the promotion of digital TV face great resistance.
Dual decoding STB uses dual decoding chips in one STB or embeds more than two decoding circuits in one chip, and is equipped with two demodulators, so that one STB can output two different programs, and the cost of STB is only Increased by 30% to 50%. The emergence of this new product is undoubtedly a boon for those users who have more than two TV sets. Of course, it is for those operators who hope that users buy more than two STBs and pay more than two program fees. Not good news.

6) DVB and IP are combined into one
The rapid development of IP technology has brought a huge threat to digital TV, but in the short term due to network costs, the two can only coexist and cannot be replaced. Although there are currently so-called STBs with IP functions in the domestic market, these set-top boxes only integrate network cards or bring backhaul channels. Because they cannot meet services such as streaming media, they are not completely a combination of DVB and IP. STB. With the introduction and improvement of chips with MPEG-II and MPEG-IV dual decoding functions, such STBs have been put on the market abroad, which can adapt to different network environments and have broad development prospects. In addition, the development and integration of this technology may bring some unexpected changes to people. Perhaps in the near future, with the development of network technology, a terminal product integrating DVB and IP will become a part of the family. It is connected to home display devices, computers and even other intelligent devices to meet the needs of home informatization.

1) The hardware structure of the set-top box
From the point of view of the composition of the digital TV set-top box, it mainly includes two parts: hardware and software.
From the structural point of view, the set-top box is generally composed of the main chip, memory, tuner and demodulator, return channel, CA (Conditional Access) interface, external storage controller, and video and audio output.

① Tuner demodulator
The function of the tuner and demodulator is to demodulate and restore the transmitted modulated digital signal into a transmission stream. The difference of the tuner and demodulator constitutes different digital set-top boxes, such as satellite set-top boxes for QPSK demodulation (DVB-S) , Cable digital set-top box (DVB-C) for QAM demodulation and terrestrial digital set-top box (DVB-T) for OFDM demodulation. At present, the most popular tuner and demodulator manufacturers on the market include Thomson, Sharp, etc. Although there are some domestic manufacturers that produce tuner and demodulator, their market share is very small.

② Main chip
With the development of chip technology, more and more manufacturers integrate the functions of set-top boxes into one main chip. For example, most manufacturers now integrate CPU, decoder, demultiplexer, graphics processor, and video and audio. The processor is integrated in the chip, and even some chip manufacturers represented by Philips integrate the tuner and demodulator in the chip to form an integrated chip solution, which effectively reduces the cost of the device and improves the reliability.
In the main chip, the received transport stream is first demultiplexed according to the flag information passed by the transport stream, and then the program stream is descrambled according to the descrambling information passed by the CA smart card, and the descrambled TS stream is sent to The video and audio decoder decodes them separately and restores them to AV signals for output. At the same time, various system data tables multiplexed in the TS stream are separated and sent to the set-top box processor for separate output.
In addition, because the CPU and graphics manager are integrated in the main chip, the set-top box can perform more functions. It can run various software to complete many tasks, such as stock receiving, web browsing, etc., and 2D can also be realized through the graphics manager Even 3D graphics processing provides users with a more beautiful interface and realizes various high-quality applications such as interactive games.
Since the CPU is the core of the main chip, the performance of the CPU usually determines the performance of the main chip. The performance of the CPU is generally determined by the main frequency. The higher the main frequency, the higher the performance of the CPU. At present, the fastest CPU frequency has exceeded 400 MIPS, even the most popular and basic set-top boxes currently on the market have a CPU frequency exceeding 50 MIPS. The CPU speed has an inevitable connection with the business system running on it. If you need to run an HTML browser in an STB, 100 MIPS may be the minimum requirement for the CPU. Of course, this also requires the cooperation of memory.

③ Memory
In some respects, a set-top box has many similarities with a PC, and it can even be said to be a simplified PC. The most similarity between the two is the memory. For set-top boxes, memory is mainly divided into Flash memory and SDRAM memory. Flash is used to store the system software and driver of the set-top box.Mobile software, application programs, and some user information can be retained when the system is powered off. At the same time, Flash can update the software loaded on it online to achieve the purpose of upgrading the set-top box software. SDRAM is mainly used to store application data. Many functions of the set-top box require memory to achieve, such as graphics processing, video and audio decoding and demultiplexing, etc., different application requirements, the size of the memory configuration is also different. Although the configuration of large-capacity Flash and SDRAM can reserve enough memory space for future business systems, memory is not a factor that determines whether the software can run. It needs to work with the CPU. Unrealistic high configuration will only cause Resource waste does not contribute to the improvement of STB performance.

④ External storage device
External storage devices generally refer to external hard disks, and large-capacity hard disks can be used to store program streams to meet the individual needs of users. Whether a hard disk can be externally attached to an STB is generally determined by the main chip. Only when the processing power of the CPU reaches a certain level can it support hard disk read and write, and hard disk read and write also requires more memory space.

⑤ Smart card interface
The data in the CA smart card is read through the card reader for the descrambling of digital TV programs. Especially in the development of pay TV today, this is an indispensable part of most STBs. In addition to standard card readers, in some STBs, CI (Common Interface) is also used to complete the reading of CA smart cards. CI is a standard interface defined by the DVB organization for the set-top box and separate hardware modules. The application of this technology originated from PCMCIA enables mass production of set-top boxes, and also brings changes to set-top boxes, and has a wide range of application prospects.

⑥ Return communication interface
With the expansion of set-top box applications, the user's demand for set-top boxes has not only stayed on simply watching video and audio programs. The demand for interactive has made the set-top boxes embedded with return devices, which can include network adapters, modems, etc. The communication interface is used to satisfy the user to send information back to the front end.

⑦ Other equipment interface
With the development of new technology, the physical interfaces of set-top boxes have also been continuously increased, such as RS232 interface, infrared remote control interface, wireless keyboard interface, Wi-Fi interface, etc., so that STB can be connected with cameras, DVDs, PDAs and many other devices.

2) The software system of the set-top box
As a client system, the set-top box needs to be equipped with different software systems in addition to a good hardware platform to enable it to complete various tasks. The software in the set-top box can be divided into three main layers: the application layer, the intermediate interpretation layer, and the driver layer. Each layer contains many programs or interfaces.
① Drive layer
The driver layer includes the driver program and API interface of the set-top box hardware, which is mainly used to complete the operation of the hardware device.
② Intermediate interpretation layer
The intermediate interpretation layer translates the STB application program instructions into instructions that the CPU can recognize, so as to mobilize the hardware devices to complete the corresponding operations through the driver layer. This layer includes embedded operating system, middleware, CA resident software, etc. Although the use of middleware can bring great benefits to the design and application of STB software, the high cost of use, the increase in hardware requirements and the immaturity of technology make middleware rarely used in China. At present, many software designers use software that directly calls the driver layer to write applications. Although this can meet temporary needs, as application requirements increase, using middleware in STB is a good solution.
③ Application layer
The application layer can be divided into two parts: resident application and downloadable application. Different STB software design concepts make these two parts contain different applications. A reasonable plan for the composition of these two parts will help improve the STB. Reliability and response time. At present, there are few applications in domestic set-top boxes, mainly EPG, data broadcasting, stocks, simple downloading games, etc., and the charm of digital TV does not lie in watching TV, but in this kind of business application based on the digital TV platform. The application will improve some people's daily life customs. With the construction of two-way networks and the popularization of interactive applications, there will be more and more interactive applications, which will also bring unpredictable value-added income to operators. The technical content of the cable TV digital set-top box is very high, which reflects the development level of multimedia, computer, digital compression coding, encryption and descrambling algorithms, encryption and decryption algorithms, communication technology and network technology.
※Add descrambling technology
The scrambling and descrambling technology is used to encrypt and decrypt digital programs. Its basic principle is to use the method of scrambling control word encryption and transmission, and the user terminal uses the IC card to decrypt it. In the MPEG transport stream, there are two data streams related to the transmission of control words: authorization control information (ECMs) and authorization management information (EMMs). The control words encrypted by the service key (SK) are transmitted in ECMs. It also includes program information such as program source, time, content classification, and program price. The service key that encrypts the control word is transmitted in the authorization management, and the service key must be encrypted by the user's personal distribution key (PDK) before transmission. EMMs also include the address and user authorization information, such as the user can see Programs or time periods, viewing fees paid by users, etc. The user's personal distribution key (PDK) is stored in the user's smart card (Smart Card). On the user side, the set-top box obtains the PID values of EMM and ECM according to the CA-descriptor in the PMT and CAT tables, and then filters the ECMs and EMMs from the TS stream, and sends them to the Smart Card through the Smard Card interface. Smart Card first reads the user’s personal distribution key (PDK), uses PDK to decrypt EMM, takes out SK, then uses SK to decrypt ECM, takes out CW, and sends CW to the descrambling engine through the Smart Card interface. Using CW, the scrambled transmission stream can be descrambled. Adding and descrambling technology is divided into simulcrypt and multi-density technology. Simulcrypt technology is the application of two or more conditional access (CA) systems to the same network platform. From the perspective of cable TV stations, it is an environment for technology selection and competition. Multi-density technology requires that the set-top box adopts CI technology, so that the same set-top box can receive encrypted programs of different CA systems. From the perspective of users, they will not be restricted by buying a set-top box that is a CA, and users have the possibility to choose their CA services.

The digital set-top box is not only a user terminal, but also a network terminal. It enables analog TVs to shift from passively receiving analog TVs to interactive digital TVs (such as video-on-demand, etc.), and can access the Internet, allowing users to enjoy the full range of TV, data, and language. Directional information services. At present, some people think that the set-top box is used to make the TV go online, which is a misunderstanding in understanding. In fact, the digital set-top box is a member of the broadband integrated information network before the popularization of digital TV. With the development of digital technology, multimedia technology and network technology, the built-in and overall cost of digital set-top boxes will be reduced, allowing most users to realize multiple services such as entertainment and Internet access on ordinary analog TVs.
In short, set-top boxes, as the iconic products of digital TV, have a broad space for development. With the development of digital TV applications, chip technology and software technology, STB's functions are bound to become more and more powerful, and can provide operators and users with more services to meet the needs of different levels.

How far(long) the transmitter cover?

The transmission range depends on many factors. The true distance is based on the antenna installing height , antenna gain, using environment like building and other obstructions , sensitivity of the receiver, antenna of the receiver . Installing antenna more high and using in the countryside , the distance will much more far.

EXAMPLE 5W FM Transmitter use in the city and hometown:

I have a USA customer use 5W fm transmitter with GP antenna in his hometown ,and he test it with a car, it cover 10km(6.21mile).

I test the 5W fm transmitter with GP antenna in my hometown ,it cover about 2km(1.24mile).

I test the 5W fm transmitter with GP antenna in Guangzhou city ,it cover about only 300meter(984ft).

Below are the approximate range of different power FM Transmitters. ( The range is diameter )

0.1W ~ 5W FM Transmitter ：100M ~1KM

5W ~15W FM Ttransmitter : 1KM ~ 3KM

15W ~ 80W FM Transmitter : 3KM ~10KM

80W ~500W FM Transmitter : 10KM ~30KM

500W ~1000W FM Transmitter : 30KM ~ 50KM

1KW ~ 2KW FM Transmitter : 50KM ~100KM

2KW ~5KW FM Transmitter : 100KM ~150KM

5KW ~10KW FM Transmitter : 150KM ~200KM

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1.How far you want to cover in diameter ?
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