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CATS(tm):
High-performance Audio/Video distribution utilizing twisted-pair wires Some readers may be familiar with older, low-performance techniques for sending video over twisted-pair cables. While these techniques may be acceptable for a low-resolution security camera, they simply do not have the performance to handle the high resolution needed for DVD-quality video reproduction. In addition, most of these older techniques need to be "tweaked" for the length of the cable, and even that will not compensate for all of the artifacts and limitations. The BDSP(tm) technology uses an encoding scheme to completely eliminate these problems and instead provide for superb video reproduction unmatched by older technology, with no adjustments needed to compensate for cable length. |
ROBERT TABER is the principal software engineer at Pragmatic Communications Systems. He holds a B.S. degree in Computer Science from Cal Poly, San Luis Obispo. He has more than 22 years experience working in the communications and semiconductor test equipment industries. |
Abstract
This article describes a high-performance system for the distribution and switching of high-quality audio, video, and data signals which are carried over inexpensive twisted-pair wires. The system includes an A/V transmitter unit, an A/V receiver unit, and a crosspoint matrix switching system which allows any of its outputs to be connected to any input, regardless of how the other outputs are connected, for complete multi-source, multi-zone distribution. The distribution system includes an advanced encoding and decoding mechanism which allows for the audio/video signals to be transmitted over a substantial distance without any appreciable degradation in the signal quality, a control system which allows for the switching system to be easily controlled from multiple remote locations, and a bi-directional data communications system which allows for the control signals to be sent along the twisted-pair wires from multiple remote locations. Advantages and applications of this approach are discussed.
Introduction
Pragmatic Communications Systems has invented an entirely new method for the distribution and delivery of high-quality Audio/Video signals over twisted-pair cables. This article describes the features, advantages, and applications of this system, and how it can be used to overcome the problems inherent in traditional approaches, and instead provide a superior level of quality in audio/video distribution.
Background
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There has been a vast improvement in the quality of A/V source equipment available to the consumer as the technology has improved over the years. In the same way that Compact Disk technology has improved the fidelity and clarity of audio material over older tape and vinyl LPs, the recent introduction of DVD players and Digital Satellite receivers has greatly improved the resolution and clarity of video material as well. Therefore, new technology is needed for the distribution of these high fidelity, high resolution A/V sources, so that the quality of the sources is maintained throughout the distribution process. First, let's take a look at some of the limitations and drawbacks with traditional installations.
There are numerous problems that typically occur with traditional installations. The first problem is that most television sets have a limited number of auxiliary audio/video inputs available. If the entertainment system is comprised of more audio/video sources than the television can accept, then some sort of external switching equipment must be provided to gain access to the additional sources. Although there are many different types of simple external switching equipment commercially available, these are not integrated into a high-performance A/V distribution system, nor do they provide any method to alleviate the signal degradation problem discussed next.
The second problem occurs when a television set is located in a different room than the main home entertainment system. Some signals, such as a radio-frequency cable television signal, are easily routed or extended from one room to another by means of a coaxial cable to carry the signal. Other signals, such as the high quality baseband audio and video outputs of a Digital Satellite Receiver system are not easily routed or extended from one room to another, because the baseband signals degrade after a very short distance. All presently employed methods, such as baseband signals over coaxial cables or channel modulators to send radio-frequency signals over coaxial cables, suffer from signal degradation and loss of audio and video quality.
For example, a standard broadcast video signal is limited to a bandwidth of 4.5 megahertz, but the video output signal from a Digital Video Disk player or a Digital Satellite Receiver may have a bandwidth of 6 megahertz or more. When one attempts to send a high bandwidth video signal in baseband form down a coaxial cable, significant frequency attenuation and loss occurs after only a short distance, typically less than fifty feet. This results in an unacceptable picture quality after only a relatively short cable run. In contrast, the CATS(tm) audio/video signal distribution system maintains the full 6 megahertz video bandwidth over a distance up to 1000 feet.
A common technique for video distribution today employs a channel modulator. A channel modulator is a device which modulates the baseband video signal onto a radio-frequency carrier compatible with the tuner of a television set, typically a UHF channel, and sends the signal down a coaxial cable. Conventional radio- frequency channel modulators are limited to a video bandwidth of 4.5 megahertz, which is far below the 6 megahertz bandwidth of a high-resolution video source. Thus, although a channel modulator is capable of sending a video signal over a longer distance than sending baseband video over a coaxial cable, there will still be an inherent attenuation and loss of video bandwidth with a channel modulator, which results in a lower picture quality. In a like manner, a channel modulator also has severe limitations in the bandwidth and quality of any audio signals which are sent in conjunction with the video signal. For example, a channel modulator will limit the bandwidth of the audio signal to less than 15 kilohertz, and it will not be capable of retaining the stereo separation, signal-to-noise ratio, nor other audio qualities present in the high-quality audio output from a compact disk player or a digital video disk player. In summary, a conventional radio-frequency channel modulator is not capable of sending a full 6 megahertz bandwidth video signal, is not capable of sending a full 20 kilohertz stereo audio signal, nor is it capable of utilizing a low-cost transmission medium such as a twisted-pair cable.
Another problem with channel modulators is that they use Amplitude Modulation for the video signal, which is susceptible to RF noise, hum, and other interference on the video signal. Again, this results in a poor picture quality compared to the source material, and inferior video reproduction at the destination location.
A third problem also occurs when a television set is located in a different room than the main home entertainment system, and that is allowing for all of the different audio and video sources to be fully accessible in the remote location. For example, a common situation is that the remote television set will only have access to the cable television signals, and will not have access to the Digital Satellite Receiver, Video Laser Disk Player, or any other equipment located with the main home entertainment system.
It may seem that one possible solution to this problem would be to install individual cables for each piece of equipment, and extend each one of the signals to the remote room. This solution is usually impractical to consider due to the following problems:
- It is usually not practical or not desirable to install such a large number of cables within the wall.
- Many signals cannot be extended in such a manner due to the signal degradation problems discussed above.
- The remote television set would need an external switching system to select among the large number of audio/video sources.
- And also, it is difficult to add equipment to such a system due to the difficulty of running additional cabling through the walls to accommodate the additional signals.
The fourth problem occurs when the user is in a listening or viewing area which is located remotely from the source equipment. Because most Audio/Video source equipment in use are controlled by infra-red remotes, and infra-red signals do not penetrate walls, this poses a problem when a user is in another room or some other location beyond the range of an infra-red remote, since the user would not be able to control the source equipment from the remote location. Some commercially available equipment, commonly known as "IR Extenders," use radio-frequency signals to send the IR commands from one room to another. These units have several drawbacks including unreliable operation and difficulty in operating with a multiplicity of transmitters and receivers. Other types of systems send commands over cables to control the source equipment, but these control systems are not part of a complete system for distribution and switching of high-quality Audio/Video signals.
Figure 1 illustrates a typical installation using previous- generation methods, with a main home entertainment system in one room, and a second television and/or stereo system in another room. There are multiple sets of cables needed to distribute the various audio, video, and control signals. The remote television set will only have access to lower quality audio and video signals, rather than the higher quality audio and video signals available to the main home entertainment system. In addition, the remote television set is likely to be unable to receive signals from certain audio/video source equipment, such as a Digital Satellite Receiver or a Digital Video Disk player, as shown. The primary objective of the Pragmatic approach is to avoid these problems encountered with previous-generation methods, and provide a superior system to switch and distribute high-quality audio/video signals over an inexpensive twisted- pair cable, and thereby provide full access to all types of audio/video source equipment from the remote location, while maintaining the signal quality available from modern A/V equipment.
The "structured wiring" approach being promoted today does nothing to address the problems noted above. Actually, what the "structured wiring" approach does is to perpetuate the problems described above, rather than provide any means to solve these problems.
CATS(tm) System Description
Pragmatic Communications Systems, Inc., proudly announces a new standard for high-performance audio/video distribution. The CATS(tm) (Complete Audio/video Transmission System) essentially consists of an A/V transmitter unit (one for each source), a switcher/router for complete multi-source, multi-zone distribution, and an A/V receiver unit (one at each destination.) An example configuration is shown in Figure 2, with multiple A/V sources being distributed to multiple zones.
Everything starts with a set of A/V source equipment. Each A/V source may consist of a Video Cassette Recorder, Cable tuner, AM/FM tuner, Compact Disk player, Video Laser Disk player, Digital Video Disk player, Digital Satellite Receiver, Camcorder, Security camera, or any other source of Audio and/or Video signals. These audio/video signals are provided to a CATS(tm) transmitter unit. Additional A/V sources may be provided, as shown. The types of these A/V sources may be the same as, or different from, the type of source provided by the first A/V source. For example, the first A/V source may be a Video Cassette Recorder, the second A/V source may be a Digital Satellite Receiver, and the third A/V source may be a Digital Video Disk player. It does not matter what type each individual A/V source may be.
Each CATS(tm) transmitter accepts a set of audio and/or video signals from its associated Audio/Video source. At this point, these audio/video signals accepted by the transmitter unit are in a baseband state. For example, the audio portion will typically be from a "line-level" output of the A/V source, which is the same as baseband audio. Likewise, the video portion will typically be from a "video output" of the A/V source, which is the same as baseband video. The transmitter unit applies an encoding mechanism to the audio and video signals. The encoded signal is then placed on the twisted-pair cable for transmission.
The encoding mechanism used by the CATS(tm) system is known as Bandwidth Domain Signal Processing, or BDSP(tm), an advanced and proprietary (patents pending) signal encoding technology which achieves the high performance, high bandwidth, and high quality of the CATS(tm) system. The BDSP(tm) technology does not use "compression," or other techniques which would lose picture detail or introduce picture artifacts. Instead, the BDSP(tm) technology is specifically designed to preserve the picture detail, and transmit a high bandwidth, high resolution signal, even over a low-cost cable such as unshielded twisted-pair cable.
Some readers may be familiar with older, low-performance techniques for sending video over twisted-pair cables. While these techniques may be acceptable for a low-resolution security camera, they simply do not have the performance to handle the high resolution needed for DVD-quality video reproduction. In addition, most of these older techniques need to be "tweaked" for the length of the cable, and even that will not compensate for all of the artifacts and limitations. The BDSP(tm) technology uses an encoding scheme to completely eliminate these problems with older technology, and instead provide for superb video reproduction unmatched by older technology, with no adjustments needed to compensate for cable length.
Although the primary purpose of the encoder is to meet the objective of transmission and recovery of the audio/video signals over a significant distance and without any appreciable signal degradation, an additional benefit is that it allows for any or all of the encoders to be located a significant distance away from the Crosspoint Switching Matrix. This means that each of the Audio/Video Sources are not required to be located in close proximity to each other, yet the signals from the distant sources are delivered to the switching system with the same quality as the nearby sources.
The heart of the system is the CATS(tm) 8-by-8 switcher/router. The router has a set of inputs, a set of outputs, and a full crosspoint matrix switching system which allows for each one of the inputs to be independently connected to any or all of the outputs. Each input is configured to accept an encoded electronic signal from one of the CATS(tm) transmitter units. Each input and output connection uses a standard RJ-45 connector for ease of connection to the CAT-5 cables.
The router has two ways that it can be controlled. The first way is by an IR remote. The IR signals are picked up by the receiver in the remote location, and sent to the router over the twisted- pair cable, then the router interprets the IR commands to make the desired selection. This allows the router to be easily controlled from any of the remote locations using the built-in control system, without using any additional control system, and this allows for the user to easily select any of the inputs to the router at any time, thus providing full access to all of the A/V sources from the remote location.
The second way to control the router is through an RS-232 port. Commands may be sent to the router from any standard control system, such as AMX, Crestron, Niles, Xantech, or any other control system capable of issuing RS-232 commands. This feature allows the CATS(tm) system to be easily integrated with other control systems, in order to be flexible so that the user can use whatever type of control system is desired.
Each output from the router travels over the CAT-5 cable, up to 1000 feet distance, to a CATS(tm) receiver unit in the destination location. The function of each receiver unit is to accept an encoded signal from the CATS(tm) router, decode the signal back into baseband format, and provide a set of audio/video outputs corresponding to the decoded signals. These A/V outputs may then be connected to the television set and/or stereo system in the destination location.
For example, suppose that one of the A/V source equipment is a Digital Video Disk Player, and that the CATS(tm) transmitter unit accepts the A/V signals from the DVD player, encodes them in a suitable format, provides the encoded signals to input #1 of the CATS(tm) router, and the router has been commanded to connect input #1 to output #3 corresponding to the receiver in that zone, and the receiver accepts the encoded signals sent over the CAT-5 cable, and provides a set of A/V outputs for the decoded, or baseband, signals. The result of this operation is that the receiver in the remote zone provides a set of A/V outputs which are the same as the A/V signals from the DVD Player. Therefore, each of the receivers has access to any of the A/V sources at any time as selected and routed through the CATS(tm) router, and each receiver is thus able to reproduce any one of the signals from the selected A/V source.
The receiver also accepts IR commands for volume control. These include volume up, volume down, and mute. This allows the system to be used with "mono-block" power amplifiers, or other amplifiers which do not have their own volume control.
The receiver has two options for its audio outputs. The first option provides normal line-level stereo audio outputs, which may then be connected to a power amplifier, stereo system, or other method to drive the speakers. In the second option, the receiver is also available with a built-in power amplifier.
Most Audio/Video sources in use are controlled by infra-red remotes. This poses a problem when a user is in another room or some other location beyond the range of an infra-red remote. There needs to be a mechanism for the user to control an A/V source from the remote location where the listening and viewing area is. It was previously explained how IR control signals originating at a remote location are conveyed back to the router, so that the router may be controlled by an IR remote. The router decodes the commands that are destined for it, for the selection of the switching matrix. All other commands are passed on by the router to the destination device, one of the A/V sources, through an IR Emitter from the transmitter. The router contains a suitable routing mechanism which is able to convey the control signals to only the particular A/V source which has been selected by the router.
For example, suppose that the selected A/V source is a Digital Video Disk player, and a user in a remote viewing area desires to issue commands such as "Pause," "Play," and "Stop" to the Digital Video Disk player. These commands are conveyed from the CATS(tm) receiver in the remote location, through the CAT-5 cable to the CATS(tm) 8-by-8 switcher/router, and from there on to the CATS(tm) transmitter. The CATS(tm) transmitter unit passes on these commands to an IR Emitter, which then issues the commands to the Digital Video Disk player to effect the desired operation. This results in an easy to use method for the user in a remote location to be able to control the A/V source equipment, even though the source equipment is located beyond the range of an infra-red remote control unit.
This method of routing the control signals and commands back to the individual audio/video source equipment with an individual IR emitter has a particular advantage for this situation. Suppose that a user has two Digital Satellite Receivers located in close proximity to each other. In a traditional arrangement, the two Digital Satellite Receivers are required to be located in separate locations, so that they can be individually controlled by hand-held infra-red remote control units. Otherwise, both units will respond to the commands that are issued, and it is difficult to control each one individually. In the present example, since each A/V source is coupled to an individual IR emitter, and since the CATS(tm) 8-by-8 switcher/router contains a command routing algorithm, each command is routed and directed from the remote location to the particular A/V source that has been selected, and the command is inhibited from affecting any other A/V source. This allows for two like equipment, such as two Digital Satellite Receivers, to be closely located, yet each source only receives the commands that are destined for it, and the other sources are not adversely affected by commands which are not intended for them.
Advantages
There are numerous advantages to the CATS(tm) system:
(a) Superior audio and video quality. The primary objective and advantage of the CATS(tm) system is to provide a superior level of quality over all other types of systems used today. This is achieved through the use of advanced encoding and signal processing techniques, which results in a high-performance system with capabilities unmatched by traditional approaches.
(b) Uses low-cost twisted-pair cables. Why use twisted-pair?
- It is much lower in cost that the expensive coax typically used today.
- It is much easier to install. This lowers the installation time, lowers the installation costs, and thus allows the installer to complete more jobs in the same amount of time.
- Many homes are pre-wired with CAT-5 already. The ability to use existing wiring when available is a big plus, and is a feature not available to other types of systems.
- There are certain situations where it is not possible or impractical to install coax cable, but CAT-5 is available. In these cases, the CATS(tm) system is clearly the best choice for video delivery over CAT-5 cables.
It should be noted that using coax cable instead of twisted-pair cable will not improve the quality of the video signal provided by the CATS(tm) system. The nature of the encoding mechanism is such that it is completely unaffected by the type of connecting cables used. There is no loss in signal quality from using low- cost twisted-pair cables. Therefore, it only makes sense that the lowest-cost cables should be used, since there is no loss in performance by doing so.
(c) Complete system: distribution, switching, and control. Unlike other systems which provide for only distribution, or only switching, or only control, the CATS(tm) system provides for all of these functions integrated together. Yet, the CATS(tm) system remains versatile enough that it can be combined with other systems, such as a keypad-based control system, so that it can be effectively and efficiently used in conjunction with these other systems, depending on the application and the set of features desired by the user.
(d) Eliminates common problems. The encoding mechanism used by the CATS(tm) system has been specifically chosen so as to avoid the problems of noise, hum, ground loops, and frequency attenuation which plague traditional systems, and instead provide a method for A/V signal distribution which is substantially improved over traditional systems. This not only benefits the user, but it offers a major advantage to the installer because of the increased consistency and quality of the system.
(e) Full access: The combination of the switching and distribution system means that all of the remote zones have full access to all of the source equipment connected to the system. No more "single-point" outputs, such as a DSS receiver connected to only a single TV set. Now all rooms can have complete selection from all of the sources, including high-quality sources such as DVD players and DSS receivers.
(f) The integrated IR control system allows for all aspects of the system to be controlled: the receiver (for volume up, down, and mute,) the router (for source selection,) and the source equipment.
(g) Expandability: The system allows for additional source equipment to be easily added to an existing entertainment system, and the additional A/V signals are made available to all remote locations without adding any additional cables, since the switching and distribution system allows for each of the available A/V signals to be selected and routed to the remote location using the twisted-pair cable.
Other Applications
This article has focused on how this system could be used as part of a home entertainment system. However, the applications of this system are much broader, and includes many other applications needing the electronic switching and distribution of audio, video, and data signals besides home entertainment systems. Examples of some of these other applications may include video distribution for security systems, audio/video distribution for schools, hotels, or conference rooms, video monitors for airports, or other audio/video distribution applications.
For example, the CATS(tm) system has been successfully applied to the A/V distribution from a centralized "Media Center" in a school, which allows for any classroom to select and view any of the available A/V sources. A particular advantage of the CATS(tm) system in this application was the inclusion of the IR control system, so that the source equipment could be easily controlled from each of the classrooms. Contact us or visit our website for more information about this type of application.
Conclusion
The CATS(tm) system represents a quantum leap over traditional approaches to Home Theater or whole-house Audio/Video distribution. The superior signal quality level, the versatility of the system, the fully integrated IR control system, and the complete avoidance of the problems which plague traditional systems, clearly make the CATS(tm) system the best overall approach to audio/video distribution.
The CATS(tm) system has been successfully installed in a variety of applications, including Home Theater applications, schools, video conferencing, security, and individual applications. These installations have all benefited from the superior performance, ease of installation, and the unique advantages of the CATS(tm) system.
About the company
Pragmatic Communications Systems, Inc., was established in 1994 to design, develop, and produce a variety of innovative products for wireless voice, video, and data communications. The majority of our products in the past were primarily designed for industrial and commercial applications. The success of these projects has led to a strong and dynamic technology base, which has been applied to a new generation of products such as the CATS(tm) system described in this article.
For more information:
Pragmatic Communications Systems, Inc.
544 E. Weddell Drive, Unit 8 Sunnyvale, CA 94089
Ph. 408-542-0330 FAX 408-542-0339
email: sales@wireless-experts.com
web: www.wireless-experts.com
