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Multi-format Analog and Digital Video/Audio Broadcast Transport Systems


Broadcasters and cable providers, faced with the impending FCC mandated deadline to digitize all over-the-air transmission, need a multi-format analog and digital transmission solution. As the term implies, these multi-format systems allow the broadcast and cable industries to either transmit digitized analog video/audio channels, purely digital video/audio channels, or both formats at the same time, allowing them to maintain their current quality of service (QoS) while they make the transition to the all-digital broadcast requirements outlined in the Telecommunications Act of 1996. In addition to meeting HDTV transmission capabilities, the systems usually satisfy the requirements of additional audio SAP (Secondary Audio Programming) channels, also mandated by the FCC in accordance with the Americans with Disabilities Act of 1990. The flexibility of these systems allows broadcasters and cable service providers the convenience of a smooth transition from an all-analog transmission scheme to all-digital. Figure 1 illustrates a system that can transport analog and digital video signals simultaneously.

Figure 1 — Simultaneous transmission of Digital and Analog Video Signals

Simultaneous transmission of Digital and Analog Video Signals

System Requirements

A transitional transport platform should offer a variety of features to accommodate today's digitized analog transmission as well as tomorrow's digital transmission. First, the system should offer broadcast-quality RS-250C short-haul transmission that includes enough audio channels to meet stereo audio as well as SAP and surround sound transmission. Second, the system should offer broadcast-quality, all-digital transmission that complies with the SMPTE 259M DTV television transmission standard. This standard defines the transmission equipment required to transmit digital video signals. Third, the system should comply with other standards, such as " title="smpte_310m">SMPTE 310M and DVB-ASI, to provide maximum system flexibility. Ideally, these transport options should be interchangeable within the system, allowing broadcasters and cable providers to upgrade their transmission system without replacing 100% of their currently installed hardware. Table 1 outlines a few basic performance parameters of these various signals.

Table 1 - Elements of an Analog and Digital Transport System
Parameter Digitized RS-250C Short-haul SMPTE 259M SMPTE 310M DVB-ASI
Input/Output Impedance 75 Ohm 75 Ohm 75 Ohm 75 Ohm
Data Rate N/A 270 Mb/s 19.4 to 40 Mb/s 270 Mb/s
Rise/Fall Times N/A 0.4 to 1.5 ns 0.4 to 5.0 ns 0.4 to 1.5 ns
MPEG-2 Data Capacity N/A 214 Mb/s 19.4 to 40 Mb/s 214 Mb/s
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Desirable System Features

Broadcasters and cable operators require additional system features to create a fail-safe network as well as a network that is flexible and easily upgradeable. Modular technology is beginning to dominate fiber optic system design, allowing unprecedented system flexibility and reliability. By isolating the power supply and various A/V modules from the optical transport chassis, a broadcaster or cable operator could specify any combination of digitized RS-250C, SMPTE 259M, SMPTE 310M, or DVB-ASI in a single chassis. Hot-swappable power supplies allow end users to quickly replace a defective power supply without removing power from the system or replacing the entire video transport unit, reducing cost and system down-time. Another desirable feature for future-proof broadcast networks involves the ability to multiplex multiple video and audio signals into a single optical stream. This allows the capacity of the optical fiber to increase without installing additional optical fibers. CWDM and DWDM, operating in the 1400-1600 nm wavelength window allows a number of signals at different wavelengths to be combined. Additionally, incorporating erbium-doped fiber amplifiers, which operate in the 1550 nm window, could greatly extend the transmission range of the broadcast or cable operator, allowing them to reach a wider audience. While many solutions exist for both analog and digital video transmission, broadcasters and cable operators would most benefit from a transport platform that supports both, providing a migration path to implement FCC mandated DTV transmission while still allowing current analog equipment to be utilized. This system would offer a number of network configurations, V/A channel counts, and transmission distance options. See Multi-format Analog and Digital V/A Network Configurations for details on various analog and digital video/audio transport platforms and applications.