Analog and Digital Video/Audio Fiber Optic Transport Systems

16 January, 2014 (09:26) | Fiber Optic Extenders | By: fiberopticis

Multi-format Analog and Digital Video/Audio Broadcast Fiber Optic Transport Systems described the system requirements of a multi-format analog and digital broadcast over fiber transport platform. In fact, many such transport platforms exist, though the types of video signals, the number of audio channels, and the ability to hot swap modules may vary from solution to solution. A state-of-the-art transport platform would allow for a number of video types and enough audio channels to support secondary audio programming (SAP) and surround sound in addition to standard television signals. This article discusses the various networks that can be configured in a multi-format analog and digital video/audio network. The elements of this transport platform include the following mix-and-match components:

* RS-250C video module with six audio inputs/outputs SDI (SMPTE 259M) video module that transports 16 embedded digital audio channels
* DVB-ASI/SMPTE 310M video module with pre-embedded audio
* Hot-swappable power supply module (universal 85-264 Volts AC)
* 1RU chassis with optics (1310 nm or 1550 nm, depending on system requirements)
* Optional CWDM, DWDM, and EDFA configurations
* Optional optical path redundancy via optical A/B switches

Using these basic components, broadcasters and cable providers can mix-and-match digitized analog video/audio with pure digital video and embedded audio, creating a uniquely flexible system.

Digitized Analog Transmission with Six Audio Inputs/Outputs
Most products on the market today that transport both analog and digital video utilize high-resolution uncompressed 12-bit A/D (analog-to-digital) conversion to transport broadcast quality signals. Employing a high signal-to-noise ratio (SNR) provides excellent broadcast quality video that surpasses the RS-250C short-haul video standard. Six channels of digitized audio, with 24-bit resolution, offers CD-quality sound allowing the end user to meet the FCC’s SAP requirements and additional audio channels required for surround sound programming. Figure 1 illustrates a point-to-point network that uses two digitized video/audio modules, each offering one video and six audio channels, for a total of two digitized analog video channels and 12 CD-quality audio channels on a single fiber.

Figure 1 – Transport of Two Digitized Analog Video and 12 CD Quality Audio Channels.

SDI (SMPTE 259M) and DVB-ASI/SMPTE 310M Transmission with Pre-embedded Audio Signals
In general, most analog/digital transport platforms can carry SDI and DVB-ASI video at the same time. The products can transport SMPTE 259M compliant video at a data rate of 270 Mb/s. Using multiple interfaces, products can typically transport two SDI video streams on one fiber. Analog and digital transport platforms can also transmit either 19.4 to 40 Mb/s DVB-ASI or SMPTE 310M compliant digital signals. Figure 2 illustrates digital transmission of SDI and DVB-ASI/ SMPTE 310M. The units also support the transmission of pre-embedded digital audio channels.

Digitized Analog and DVB-ASI
Figure 3 illustrates a network with the ability to simultaneously transport a combination of analog and digital signals. For example, a studio may need to transport both a broadcast quality analog video and a SMPTE 259M SDI video to a remote location, such as an editing house or a duplication facility.

Figure 3 – Simultaneous Transport of Analog and Digital Signals


Bidirectional Analog and Digital fiber optic Transport

Increase Fiber Capacity with CWDM Technology
CWDM products are passive, bidirectional devices which allow individual wavelengths to be combined for transport over on single-mode optical fiber and separate into individual optical outputs at the receive end, increasing the fiber capacity. Configurations range from simple point-to-point and point-to-multipoint, to large scale video networks over numerous add/drop sites. Figure 4 illustrates the point-to-point configuration for four, eight, and 16 channel systems, ideal for applications such as studio-to-studio, studio-to-transmitter, studio-to-headend, and distance learning.

Figure 4 – Four, Eight, and 16 Channel Point-to-Point Configurations

By incorporating CWDM technology, bidirectional applications for transporting both analog and digital video and associated audio may be configured with ease. Figure 5 shows a bidirectional system that will transmit up to eight optical channels over a single fiber. Each transmission site contains both transmitters and receivers, ideal for headend-to-headend, interactive distance learning, return feeds, and studio-to-studio transmitter links.

Figure 5 – Bidirectional Transmission of Eight Optical Channels

Optical Redundancy Increases System Reliability
Using an optical A/B switch, the analog and digital transport solutions can be configured for fail-safe redundant signal operation. The A/B switch monitors the optical level on the primary fiber. Should the optical level fall below the optical trip threshold, the switch automatically switches to the secondary fiber path without the intervention of the system operator. The unit returns to the primary path when the correct optical power is detected. This configuration allows the user assurance that this useful analog and digital transport technology will not fail. Figure 6 shows unidirectional transmission with optical path redundancy.

Figure 6 – Unidirectional Transmission with Optical Path Redundancy

Analog and Digital Transport Applications

Broadcasters are concerned with retaining the highest quality video and audio throughout the content creation and dissemination process. Fiber optic cable’s inherent EMI and RFI immunity ensures the broadcaster that the signal quality will suffer no degradation as a result of these effects. Fiber’s increased bandwidth increases transmission distance as well.

Figure 7 – Studio-to-Studio Transport

Many broadcasters are making the transition from analog to digital transmission from their towers. Utilizing analog video and DVB-ASI/SMPTE 310M modules, the broadcasters can send content from their broadcast studio directly to the transmission tower over fiber optic cable. At the tower site, and ATSC encoder compresses the signal before transmitting over the air.

Figure 8 – Studio-to-Tower Transport

Studio-to-Headend over fiber
Cable providers offer several level or “tiers” of service to their customers, ranging from local and public access television stations at the low tier, up to digital cable and VOD (Video on Demand) at the high tier. Much of this programming arrives at the cable providers CATV headend in DVB-ASI or analog formats. The digital and analog transport products transmit either analog or DVB-ASI, or both at the same time.

Figure 9 – Studio-to-Headend Transport

Distance Learning
Analog and digital transport can be used to create a large scale video/audio distance learning transport networks capable of supporting an area of many kilometers from headend routing systems to multiple remote school/classroom sites. Using CWDM technology, each remote site can operate on a single wavelength, allowing up to eight sites to be networked. Multiplexed signals from the headend get added or dropped via a CWDM, allowing full two-way interactive video/stereo audio transmission of high quality digital signals. Each remote classroom contains a television and a microphone and camera for receiving and transmitting distance learning programming. This will allow school systems to broadcast lessons from one classroom to many other classrooms while still providing feedback and interaction between the teacher and the students. Figure 10 illustrates a four-channel distance learning/videoconferencing network.

Figure 10 – Four-channel Distance Learning/Video conferencing Network

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