Digital TV set-top box

Digital TV set-top box

1. What is a digital TV set-top box? The full name of the set-top box is "digital TV set-top box ). It is a conversion device that converts digital TV signals into analog signals. It decodes and restores digital compressed images and sound signals into analog signals and sends them to common TVs.
A digital TV set-top box is a device that converts digital TV signals into analog signals. It decodes and restores digital compressed images and sound signals to generate analog video and sound signals, high-quality TV programs are provided to the audience through TV monitors and audio devices. The current digital TV set-top box has become an embedded computing device with a complete real-time operating system that provides powerful CPU computing capabilities to coordinate and control various hardware facilities of the set-top box, it also provides easy-to-operate graphical user interfaces, such as electronic program guides for enhanced TVs, and graphic program introductions and background materials. At the same time, the set-top box has the "Dummies" capability, so that through the internal software functions and a slight two-way transformation of the network, it is easy to implement various services, such as Internet browsing, on-demand video streaming, home e-commerce, and telephone communication.
TV from black and white TV to the color of the transition, the use of a compatible approach, PAL-D in China has continued until now.
The transition from analog TV to high-definition digital TV is a leap transition. It can be said that it cannot be directly compatible. That is to say, all the current analog TV cannot be used, so it is unrealistic to put it in place in one step, at present, countries have adopted a transitional approach-both digital set-top boxes. After using digital set-top boxes, digital signals are converted into analog signals and input to the current analog TV display information, in this way, the interference and loss caused by the transmission of TV signals are effectively avoided, and the signal quality of TV reception is greatly improved. This is just a kind of transition. Because the scanning line of the analog TV has been fixed, it is quite far from the high-definition digital TV.
High Definition Digital TV (HDTV) is the future development direction. By now, all analog TVs have been eliminated, and TV Station shooting, recording, and editing devices have also been replaced, what people will see on TV screens will be high-definition TV pictures and more functions. HDTV will bring TV into a new era.
Someone asked if the current digital set-top box receives a high-definition digital TV signal? No. After a digital set-top box is used, the digital signal is converted into a analog signal and input to the current analog TV to display information. In this way, although the signal quality of the TV reception has been greatly improved, the scanning line of the analog TV has been fixed, so it is still quite far from the high-definition digital TV. This is just a kind of transition.
　

Ii. Main technologies of digital TV set-top boxes
Channel Decoding, source decoding, upstream data modulation coding, embedded CPU, MPEG-2 decompression, set-top box software, display control and disturbing technology is the main technology of digital TV set-top box.
(1) Channel Decoding
The Channel Decoding Circuit in the digital TV set-top box is equivalent to simulating the high frequency head and Intermediate Frequency Amplifier in the TV. In a digital TV set-top box, high-frequency headers are required, but the tuning range includes satellite channels, terrestrial television receiving channels, and cable television supplementary channels. According to the existing DTV modulation methods, Channel Decoding should include the following functions.
(2) source decoding
After the analog signal is digitalized, the amount of information is surging and corresponding data compression standards must be adopted. Digital television broadcasting adopts MPEG-2 video compression standard and applies to multiple Quality definitions. Audio currently has two standards: AC-3 and MPEG-2. The source decoder must adapt to different encoding policies to correctly Restore original audio and video data.
(3) modulation and coding of Upstream data
For interactive applications, modulation and coding of Upstream data must be considered. Currently, three methods are widely used, which use telephone lines to transmit upstream data, Ethernet cards to transmit upstream data, and wired networks to transmit upstream data.
(4) embedded CPU
The embedded CPU is the heart of a digital TV set-top box. After the data is decoded through the channel, it must be deduplicated first, and the transmission stream is divided into video and audio to split the video, audio, and data, more than 32 programmable PID filters are integrated into the CPU dedicated to the digital TV set-top box, two of which are used for video and audio filtering, and the other are used for PSI, Si, and private data filtering. The CPU is the operating platform of an embedded operating system. It must be integrated with the operating system for network management, display management, and conditional receipt Management (IC card and smart card) video and text decoding, data decoding, OSD, up/down Conversion of video signals, and other functions. To achieve these functions ~ The 64-bit CPU expands many new features and continuously increases the speed to meet the needs of high-speed networks and 3D games.
(5) decoding MPEG-2
MPEG-2 is one of the key technologies in digital TV, the current practical video digital processing technology is basically built on the basis of MPEG-2 technology, MPEG-2 is included from network transmission to High Definition TV all norms. MP @ ll is used for VCD. H.263 and H.261 for videophone meetings and videophone are their subsets. MP @ ML is used for DVD, sdtv, and MP @ MH for HDTV.
The MPEG-2 image signal processing method is completed in four steps: Motion Prediction, DCT, quantization, and variable length coding.
The MPEG-2 decompression circuit Contains video, audio decompression, and other features. To complete the decoding of the main screen and sub-screen in video processing, it is best to have a hierarchical decoding function. The image and text TV can be added to the main screen with the apha overlay function. This requires that the decoder be able to describe the image of the main screen and the image and text TV data at the same time, with high speed and processing capabilities. OSD is a single-color or pseudo-color subtitle. It is mainly used for user operation prompts.
In terms of audio, due to the European DVB using MPEG-2 sound, the United States ATSC using Dolby AC-3, So audio decoding has the above two functions.
(6) digital TV set-top box Software
After TV digitalization, software technology plays a more important role in digital TV technology. In addition to audio/video decoding, audio/video decoding is implemented by hardware, including TV content reproduction, operation interface implementation, and data broadcast business implementation, software is required to interconnect the set-top box with the PC and the Internet, as follows:
1 hardware driver layer software: driver Driver hardware functions, such as RF modem, transmission demultiplexing, A/V decoder, OSD, video encoder, etc.
2. embedded real-time multi-task operating system: Compared with the desktop computer operating system, the embedded real-time operating system is not installed on hard disks. The system structure is compact, features are relatively simple, and resources are less expensive, it is easy to solidify in memory. The function of the embedded operating system is similar to that of DOS on a PC and that of windows. You can use the embedded operating system to perform man-machine interaction and specify the user. You can specify multiple receiving methods, such as keyboard, mouse, voice, touch screen, and infrared remote control.
3 middleware: the open business platform features product development and production based on a business platform. The open business platform provides an independent operation mode for each link, each link has its own profit and can generate multiple suppliers. Only the open business platform can ensure the scalability of the set-top box and ensure the effective recovery of investment.
4. Upper-layer application software: implements various service functions provided by service providers, such as electronic program guides, quasi-Video-on-Demand videos, on-demand videos, data broadcast, IP phones, and visual phones. The upper-layer application software is independent of the STB hardware. It can be used on various STB hardware platforms to eliminate the hardware dependency of the application software.
(7) Display Technology
As far as television and computer monitors are concerned, CRT display is a mature technology. However, the problem becomes complicated when low-resolution TV sets display text, especially smaller than 24x24 characters. The TV's picture tube is a high-pitch low-resolution tube that is only suitable for displaying images of 720x576 or 640x480. Its deflection system is fixed and unchanged, it is designed for 525 rows of 60Hz or 625 rows of 50Hz, and there are 18 or more digital TV display formats. Internet access must comply with the VESA format. Obviously, the TV display system cannot adapt to so many formats. In addition, the TV uses a low frame rate line-by-line scanning method. When the image and text are displayed, the Brightness Signal flashes background and the horizontal line flashes between lines. If you convert a line-by-line scanned computer image to a TV, the horizontal edge will only appear in the odd or even field, and the screen display time is close to the human eye for the moment, the edge will flash badly. Therefore, if you want to use a TV to access the Internet, you must remedy the defects displayed on the TV.
Based on the technical difficulty and cost, two methods are used to improve the performance. One is the anti-Flicker filter, which adds one row of adjacent three rows of images proportionally, this method is called the three-row filtering method to reproduce images that only appear in a single field in each game. The three-row filtering method is easy to implement. However, this reduces the definition of the image and is suitable for television sets that use interlace scanning. Another method is to convert the line-by-line scan into a row-by-line scan, and increase the frame rate appropriately. In this way, the number of scanned rows and the number of fields must be multiplied. In order to make the number of images increase, to ensure the continuity of the motion picture, it is necessary to perform operations, on-site insertion operations and motion compensation. Dedicated chips and complex technologies must be used to achieve the operation, in this way, the quality of computer graphics displayed on the TV is very good, but it must be achieved on a TV with a row-by-row and double scan function. In addition, when the resolution is higher than the HDTV and VESA signals of the analog TV are played on the TV, only part of the screen can be displayed, which must be reduced. This is like PIP, which requires loss of lines and fields. To ensure image continuity, interpolation is also required.
(8) disturbing Technology
The disturbing technology is used to encrypt and decrypt digital programs. The basic principle is to use the Scrambling Method to Control encrypted transmission of words, and the client uses the IC card for decryption. In the mpeg transmission stream, there are two data streams related to the control word transmission: Authorization Control Information (ecms) and authorization management information (EMMS ). The control words encrypted by the Business key (SK) are transmitted in ecms, including program source, time, content classification, program price, and other program information. The business key encrypted by the control word is transmitted in the authorization management information, and the Business key must be encrypted by the user's personal distribution key (PDE) before transmission. Emms also includes addresses and user authorization information, such as the programs or time periods that users can watch and the video fees paid by users.
The user's personal distribution key (PDK) is stored in the user's smart card. on the user's client, the set-top box obtains the PID values of EMM and ECM Based on the ca-descriptor in the PMT and CAT tables, then, the ecms and Emms are filtered out from the TS stream and sent to the smart card through the smart card interface. Smart card first reads the user's personal distribution key (PDK), decrypts EMM with PDK, retrieves SK, decrypts ECM with SK, and retrieves CW, and send the CW to the disturbing engine through the smart card interface. The disturbing engine can use CW to undisturb the disturbed transmission stream.
5 development status of digital TV set-top box in China
The digital TV set-top box will change our existing TV concept and provide a brand new consumer terminal for the Internet, in addition, this consumption terminal will be more popular, convenient, and attractive than any other terminal such as PC, mobile phone, and PDA. With the trial broadcast of Cable Digital TVs in various regions, the promotion of digital TV set-top boxes has made great strides compared with those of a few years ago. However, digital set-top boxes have not been widely used in China, for several reasons:
(1) the technology of digital set-top boxes is high, and there are not many real products. In fact, most of the VOD products of many manufacturers are in the concept stage.
(2) bidirectional network transformation and quality problems. As the number of TV set-top boxes is greatly restricted by network bandwidth, especially the current weak network development base in China, and various network resources are regarded as their respective arrays, it is still time to popularize them in a wide range.
(3) poor services and a lack of professional ICP, that is, poor information and program resources. For example, one of the major difficulties in the promotion and application of VOD businesses is the opening of the program source, the film source, and copyright. The establishment of the National Cable TV backbone network and the emergence of professional service providers can alleviate this problem to some extent. Many manufacturers have developed VoD Systems Based on hotels, hotels, and residential areas to avoid this problem.
(4) The cost is high, which is not small for most users. The consumer psychology of Chinese people is able to afford a large one-time purchase cost, but is not willing to accept the long-term continuous, no obvious return for the consumption payment.
Although the promotion of the current digital set-top box has been greatly restricted, the digital TV set-top box is not only a user terminal, but also a network terminal, it enables analog TVs to switch from passive analog TVs to interactive digital TVs (such as on-demand videos) and access the Internet, allowing users to enjoy all-round information services such as TV, data, and language. With the development of digital technology, multimedia technology and network technology, the functions of digital TV set-top boxes will be gradually improved, especially the development of single-chip PC technology, which will lead to the decrease of built-in and overall costs of digital TV set-top boxes, this allows most users to provide entertainment, Internet access, and other services on a common analog TV.

Iii. New Trends in digital TV set-top boxes

Digital TV set-top box faces elimination new standards next year listing

It is reported that federal regulation managers have adopted new equipment standards in eastern United States to speed up the transformation to digital TVs with higher audio and video quality.

The Federal Communications Commission (FCC) passed the device standards that allow digital TV signals to be directly connected to television sets without the need for set-top boxes and additional cables in a 5-to-0 vote. To watch a pay-as-you-go TV, users need to insert a security card provided by their cable TV service provider into the TV.

Manufacturers hope to sell high-definition TVs with this plug-and-play technology by the end of tomorrow. They said the decision by the Federal Communications Commission would increase consumer demand and stimulate companies to increase production, further popularizing the new TV set.

Unlike traditional analog TVs, digital TV signals use computer languages, which provide clearer images and other potential performances, such as Internet access, video games, and multiple programs on the same channel. Digital signals can be transmitted via satellite, wired, or wireless broadcast.

Digital TV set-top box

1. What is a digital TV set-top box? The full name of the set-top box is "digital TV set-top box ). It is a conversion device that converts digital TV signals into analog signals. It decodes and restores digital compressed images and sound signals into analog signals and sends them to common TVs.
A digital TV set-top box is a device that converts digital TV signals into analog signals. It decodes and restores digital compressed images and sound signals to generate analog video and sound signals, high-quality TV programs are provided to the audience through TV monitors and audio devices. The current digital TV set-top box has become an embedded computing device with a complete real-time operating system that provides powerful CPU computing capabilities to coordinate and control various hardware facilities of the set-top box, it also provides easy-to-operate graphical user interfaces, such as electronic program guides for enhanced TVs, and graphic program introductions and background materials. At the same time, the set-top box has the "Dummies" capability, so that through the internal software functions and a slight two-way transformation of the network, it is easy to implement various services, such as Internet browsing, on-demand video streaming, home e-commerce, and telephone communication.
TV from black and white TV to the color of the transition, the use of a compatible approach, PAL-D in China has continued until now.
The transition from analog TV to high-definition digital TV is a leap transition. It can be said that it cannot be directly compatible. That is to say, all the current analog TV cannot be used, so it is unrealistic to put it in place in one step, at present, countries have adopted a transitional approach-both digital set-top boxes. After using digital set-top boxes, digital signals are converted into analog signals and input to the current analog TV display information, in this way, the interference and loss caused by the transmission of TV signals are effectively avoided, and the signal quality of TV reception is greatly improved. This is just a kind of transition. Because the scanning line of the analog TV has been fixed, it is quite far from the high-definition digital TV.
High Definition Digital TV (HDTV) is the future development direction. By now, all analog TVs have been eliminated, and TV Station shooting, recording, and editing devices have also been replaced, what people will see on TV screens will be high-definition TV pictures and more functions. HDTV will bring TV into a new era.
Someone asked if the current digital set-top box receives a high-definition digital TV signal? No. After a digital set-top box is used, the digital signal is converted into a analog signal and input to the current analog TV to display information. In this way, although the signal quality of the TV reception has been greatly improved, the scanning line of the analog TV has been fixed, so it is still quite far from the high-definition digital TV. This is just a kind of transition.
　

Ii. Main technologies of digital TV set-top boxes
Channel Decoding, source decoding, upstream data modulation coding, embedded CPU, MPEG-2 decompression, set-top box software, display control and disturbing technology is the main technology of digital TV set-top box.
(1) Channel Decoding
The Channel Decoding Circuit in the digital TV set-top box is equivalent to simulating the high frequency head and Intermediate Frequency Amplifier in the TV. In a digital TV set-top box, high-frequency headers are required, but the tuning range includes satellite channels, terrestrial television receiving channels, and cable television supplementary channels. According to the existing DTV modulation methods, Channel Decoding should include the following functions.
(2) source decoding
After the analog signal is digitalized, the amount of information is surging and corresponding data compression standards must be adopted. Digital television broadcasting adopts MPEG-2 video compression standard and applies to multiple Quality definitions. Audio currently has two standards: AC-3 and MPEG-2. The source decoder must adapt to different encoding policies to correctly Restore original audio and video data.
(3) modulation and coding of Upstream data
For interactive applications, modulation and coding of Upstream data must be considered. Currently, three methods are widely used, which use telephone lines to transmit upstream data, Ethernet cards to transmit upstream data, and wired networks to transmit upstream data.
(4) embedded CPU
The embedded CPU is the heart of a digital TV set-top box. After the data is decoded through the channel, it must be deduplicated first, and the transmission stream is divided into video and audio to split the video, audio, and data, more than 32 programmable PID filters are integrated into the CPU dedicated to the digital TV set-top box, two of which are used for video and audio filtering, and the other are used for PSI, Si, and private data filtering. The CPU is the operating platform of an embedded operating system. It must be integrated with the operating system for network management, display management, and conditional receipt Management (IC card and smart card) video and text decoding, data decoding, OSD, up/down Conversion of video signals, and other functions. To achieve these functions ~ The 64-bit CPU expands many new features and continuously increases the speed to meet the needs of high-speed networks and 3D games.
(5) decoding MPEG-2
MPEG-2 is one of the key technologies in digital TV, the current practical video digital processing technology is basically built on the basis of MPEG-2 technology, MPEG-2 is included from network transmission to High Definition TV all norms. MP @ ll is used for VCD. H.263 and H.261 for videophone meetings and videophone are their subsets. MP @ ML is used for DVD, sdtv, and MP @ MH for HDTV.
The MPEG-2 image signal processing method is completed in four steps: Motion Prediction, DCT, quantization, and variable length coding.
The MPEG-2 decompression circuit Contains video, audio decompression, and other features. To complete the decoding of the main screen and sub-screen in video processing, it is best to have a hierarchical decoding function. The image and text TV can be added to the main screen with the apha overlay function. This requires that the decoder be able to describe the image of the main screen and the image and text TV data at the same time, with high speed and processing capabilities. OSD is a single-color or pseudo-color subtitle. It is mainly used for user operation prompts.
In terms of audio, due to the European DVB using MPEG-2 sound, the United States ATSC using Dolby AC-3, So audio decoding has the above two functions.
(6) digital TV set-top box Software
After TV digitalization, software technology plays a more important role in digital TV technology. In addition to audio/video decoding, audio/video decoding is implemented by hardware, including TV content reproduction, operation interface implementation, and data broadcast business implementation, software is required to interconnect the set-top box with the PC and the Internet, as follows:
1 hardware driver layer software: driver Driver hardware functions, such as RF modem, transmission demultiplexing, A/V decoder, OSD, video encoder, etc.
2. embedded real-time multi-task operating system: Compared with the desktop computer operating system, the embedded real-time operating system is not installed on hard disks. The system structure is compact, features are relatively simple, and resources are less expensive, it is easy to solidify in memory. The function of the embedded operating system is similar to that of DOS on a PC and that of windows. You can use the embedded operating system to perform man-machine interaction and specify the user. You can specify multiple receiving methods, such as keyboard, mouse, voice, touch screen, and infrared remote control.
3 middleware: the open business platform features product development and production based on a business platform. The open business platform provides an independent operation mode for each link, each link has its own profit and can generate multiple suppliers. Only the open business platform can ensure the scalability of the set-top box and ensure the effective recovery of investment.
4. Upper-layer application software: implements various service functions provided by service providers, such as electronic program guides, quasi-Video-on-Demand videos, on-demand videos, data broadcast, IP phones, and visual phones. The upper-layer application software is independent of the STB hardware. It can be used on various STB hardware platforms to eliminate the hardware dependency of the application software.
(7) Display Technology
As far as television and computer monitors are concerned, CRT display is a mature technology. However, the problem becomes complicated when low-resolution TV sets display text, especially smaller than 24x24 characters. The TV's picture tube is a high-pitch low-resolution tube that is only suitable for displaying images of 720x576 or 640x480. Its deflection system is fixed and unchanged, it is designed for 525 rows of 60Hz or 625 rows of 50Hz, and there are 18 or more digital TV display formats. Internet access must comply with the VESA format. Obviously, the TV display system cannot adapt to so many formats. In addition, the TV uses a low frame rate line-by-line scanning method. When the image and text are displayed, the Brightness Signal flashes background and the horizontal line flashes between lines. If you convert a line-by-line scanned computer image to a TV, the horizontal edge will only appear in the odd or even field, and the screen display time is close to the human eye for the moment, the edge will flash badly. Therefore, if you want to use a TV to access the Internet, you must remedy the defects displayed on the TV.
Based on the technical difficulty and cost, two methods are used to improve the performance. One is the anti-Flicker filter, which adds one row of adjacent three rows of images proportionally, this method is called the three-row filtering method to reproduce images that only appear in a single field in each game. The three-row filtering method is easy to implement. However, this reduces the definition of the image and is suitable for television sets that use interlace scanning. Another method is to convert the line-by-line scan into a row-by-line scan, and increase the frame rate appropriately. In this way, the number of scanned rows and the number of fields must be multiplied. In order to make the number of images increase, to ensure the continuity of the motion picture, it is necessary to perform operations, on-site insertion operations and motion compensation. Dedicated chips and complex technologies must be used to achieve the operation, in this way, the quality of computer graphics displayed on the TV is very good, but it must be achieved on a TV with a row-by-row and double scan function. In addition, when the resolution is higher than the HDTV and VESA signals of the analog TV are played on the TV, only part of the screen can be displayed, which must be reduced. This is like PIP, which requires loss of lines and fields. To ensure image continuity, interpolation is also required.
(8) disturbing Technology
The disturbing technology is used to encrypt and decrypt digital programs. The basic principle is to use the Scrambling Method to Control encrypted transmission of words, and the client uses the IC card for decryption. In the mpeg transmission stream, there are two data streams related to the control word transmission: Authorization Control Information (ecms) and authorization management information (EMMS ). The control words encrypted by the Business key (SK) are transmitted in ecms, including program source, time, content classification, program price, and other program information. The business key encrypted by the control word is transmitted in the authorization management information, and the Business key must be encrypted by the user's personal distribution key (PDE) before transmission. Emms also includes addresses and user authorization information, such as the programs or time periods that users can watch and the video fees paid by users.
The user's personal distribution key (PDK) is stored in the user's smart card. on the user's client, the set-top box obtains the PID values of EMM and ECM Based on the ca-descriptor in the PMT and CAT tables, then, the ecms and Emms are filtered out from the TS stream and sent to the smart card through the smart card interface. Smart card first reads the user's personal distribution key (PDK), decrypts EMM with PDK, retrieves SK, decrypts ECM with SK, and retrieves CW, and send the CW to the disturbing engine through the smart card interface. The disturbing engine can use CW to undisturb the disturbed transmission stream.
5 development status of digital TV set-top box in China
The digital TV set-top box will change our existing TV concept and provide a brand new consumer terminal for the Internet, in addition, this consumption terminal will be more popular, convenient, and attractive than any other terminal such as PC, mobile phone, and PDA. With the trial broadcast of Cable Digital TVs in various regions, the promotion of digital TV set-top boxes has made great strides compared with those of a few years ago. However, digital set-top boxes have not been widely used in China, for several reasons:
(1) the technology of digital set-top boxes is high, and there are not many real products. In fact, most of the VOD products of many manufacturers are in the concept stage.
(2) bidirectional network transformation and quality problems. As the number of TV set-top boxes is greatly restricted by network bandwidth, especially the current weak network development base in China, and various network resources are regarded as their respective arrays, it is still time to popularize them in a wide range.
(3) poor services and a lack of professional ICP, that is, poor information and program resources. For example, one of the major difficulties in the promotion and application of VOD businesses is the opening of the program source, the film source, and copyright. The establishment of the National Cable TV backbone network and the emergence of professional service providers can alleviate this problem to some extent. Many manufacturers have developed VoD Systems Based on hotels, hotels, and residential areas to avoid this problem.
(4) The cost is high, which is not small for most users. The consumer psychology of Chinese people is able to afford a large one-time purchase cost, but is not willing to accept the long-term continuous, no obvious return for the consumption payment.
Although the promotion of the current digital set-top box has been greatly restricted, the digital TV set-top box is not only a user terminal, but also a network terminal, it enables analog TVs to switch from passive analog TVs to interactive digital TVs (such as on-demand videos) and access the Internet, allowing users to enjoy all-round information services such as TV, data, and language. With the development of digital technology, multimedia technology and network technology, the functions of digital TV set-top boxes will be gradually improved, especially the development of single-chip PC technology, which will lead to the decrease of built-in and overall costs of digital TV set-top boxes, this allows most users to provide entertainment, Internet access, and other services on a common analog TV.

Iii. New Trends in digital TV set-top boxes

Digital TV set-top box faces elimination new standards next year listing

It is reported that federal regulation managers have adopted new equipment standards in eastern United States to speed up the transformation to digital TVs with higher audio and video quality.

The Federal Communications Commission (FCC) passed the device standards that allow digital TV signals to be directly connected to television sets without the need for set-top boxes and additional cables in a 5-to-0 vote. To watch a pay-as-you-go TV, users need to insert a security card provided by their cable TV service provider into the TV.

Manufacturers hope to sell high-definition TVs with this plug-and-play technology by the end of tomorrow. They said the decision by the Federal Communications Commission would increase consumer demand and stimulate companies to increase production, further popularizing the new TV set.

Unlike traditional analog TVs, digital TV signals use computer languages, which provide clearer images and other potential performances, such as Internet access, video games, and multiple programs on the same channel. Digital signals can be transmitted via satellite, wired, or wireless broadcast.