Fiber transmission seeks all-digital pathways at NAB 96

Fiber transmission seeks all-digital pathways at NAB `96

BOB PAULSON

For the television industry, signal transmission over optical fiber is still a technology in search of a widespread application, according to fiber-optic communications companies at the National Association of Broadcasters `96 show. More than 93,000 attendees and 1000 exhibitors set attendance records in Las Vegas last April.

Part of the delay in this quest for a pace-setting application stems from the fact that coaxial cable for analog video, and shielded twisted-pair cable for audio, are technically adequate to transport digital video and audio signals inside existing production, postproduction, broadcasting and cablecasting facilities. For interfacility signal transport over the public network, both analog and digital television and audio signals are compressed and carried at multiplexed DS-3 speeds of 44.736 megabits per second and lower rates over fiber-optic networks.

Copper-based transmission, however, presents noise problems. For example, inadequate compression techniques in telephone company codecs create irreversible artifacts. These artifacts become objectionable, both visibly and audibly, because the encode/decode process is independently repeated at downstream facilities, during further digital signal processing and compression. Moreover, they also appear before broadcasting, during the creation of the Federal Communications Commission-prescribed 4.2-megahert¥composite analog video and 20-kilohert¥stereo audio signals.

Broadcasters and cablecasters tolerate the artifact penalties of DS-3 compression because the artifacts are not generally visible in the home-received signal. During production and postproduction, however, compression of digital video and audio signals is unacceptable. It is tolerated during telephone company transportation only because the cost of uncompressed transmission, if circuits are available at all, is generally unjustifiable except to make deadlines.

The market for systems to transport digital signals inside the plant is expected to open up after the expected FCC blessing of a compressed digital broadcast emission standard. It authorizes broadcasting of many streams of digital standard-definition signals or one stream of digital high-definition signals on the 6-MH¥ultrahigh-frequency channels to be assigned to all current television broadcasters. Every future in-plant signal transportation circuit will, therefore, have to accept serial digital signals at bit rates from 1.5 to at least 360 Mbits/sec.

Fiber pioneers reappear

NAB `96 saw several television-industry fiber-optic pioneering companies reappear with new names, and different product offerings. For example, Meret Communications in San Diego, CA, is now the conglomerate name for three leaders in fiber-optic applications development whose fiber roots date back 20 years: Meret Optical Communications, Dynair Electronics and Catel Telecommunications.

Meret`s products fall into three groups: headend, switching and transmission products. The AM, FM and digital fiber-transmission systems transport high-quality video, audio and data for broadcast standard and high-definition television production, computer graphics, imaging and closed-circuit TV applications.

Artel Video Systems Inc. in Marlborough, MA, demonstrated two digital systems: The Digilink family transports one or two analog composite video channels at 12-bit resolution and associated analog audio channels at 18-bit resolution. The Megalink system transports 270-Mbit/sec digital component video and four multiplexed digital audio channels (Society of Motion Picture Television Engineers [SMPTE] Standard 259M) at 1310- and 1550- nanometer windows. The system accommodates user-defined video and data signals over a range of bit rates.

Lighthouse Digital Systems, Grass Valley, CA, demonstrated a line of digital fiber-transmission systems and baseband switching matrices. Featured were the Lighthouse Navigator Control System, which replaces or enhances existing control systems, and a family of fiber-optic/coaxial-cable/two-wire converter, distribution amplifier, reclocker and custom modules that can be mixed and matched in 2-RU rack frames. Digital signals accommodated include Fiber Distributed Data Interface, high-definition television, Synchronous Optical Network, SMPTE 259M digital video and AES/EBU digital audio.

Telecast Fiber Systems, Worcester, MA, showed turnkey hybrid fiber/coaxial-cable field production cabling systems. Complementing its electronic news gathering and field production systems--Sidewinder, Viper and Adder--Telecast debuted the Cobra Fiber Optic Triax Interface.

This interface extends or replaces triaxial cable in mobile sports production such as golf, skiing and auto racing. Designed for compatibility with Sony and Ikegami triaxial-cable-configured cameras, the Cobra system increases the unrepeatered head/camera control unit separation by three to five times (50,000 feet/80 kilometers), without repeatering or cable equalization. Each 600-meter length of nonmetallic four-strand military-specification tactical fiber cable lightens the triaxial-cable load by half a ton.

All camera signals, communications and control functions are carried on fiber, and component program video transmission enables artifact-free chroma keying. Specific power and special signal requirements of the camera head are supplied from the field-located Cobra, which is powered from 12-volt batteries or a generator. q

Bob Paulson is founder of Omnimedia Communication in Westborough, MA, and an industry consultant.

Future-proofing the Next Generation of Fiber Transmission Systems

Several committees of the Society of Motion Picture Television Engineers (SMPTE) are feverishly researching and writing video and audio interface standards for the next generation of products. Will the products exhibited at NAB `96 satisfy emerging television-industry needs? To meet these needs, several factors must be taken into consideration:

Future-proof design

Systems on display at the show, except for telecast field production systems, serve point-to-point past needs of telecommunications industry digital outside-plant and the present needs of television industry analog inside-plant infrastructures.

Telecommunications products in television-industry applications are over-featured and over-priced. They won`t accommodate future all-digital, plant-signal transportation needs. Additionally, they don`t exploit new SMPTE standards 292M and 297M, which define optical-fiber interfaces for high- and standard-definition equipment (SMPTE 259M), such as equipment-mounted PC board modules, with SMPTE standard-specified SC/PC connectors, powered internally.

All-digital plant signal-transportation needs

Future television production and broadcasting plant design may become all digital. Bit rates to be accommodated by video and audio-signal routing and distribution systems may range from 1.5-megabit-per-second DS-1 (MPEG-1, a single channel of AES/EBU audio, or the highest MPEG-2 compression level--i.gif., the lowest MPEG-2 bit rate), through a dozen or more discrete numerical steps still being defined, to 360 Mbits/sec. The latter is under consideration as the sole standard bit rate for "lightly compressed" high-definition video, which was originally designated as the wide screen 525/60 bit rate.

Distribution infrastructure design

Developments include Tektronix, Hewlett-Packard, Avid, Panasonic and Silicon Graphics driving Fibre Channel networking in professional quality video applications. This Fibre Channel support stems from these companies` commitment to open solutions for broadcast and postproduction industries.

A proposed standard with a 1-Gbit/sec peak operating bandwidth is already under consideration by the American National Standards Institute, SMPTE and the Fibre Channel Association. Rex Ferbrache, vice president of strategy for Tektronix` video and networking division, emphasizes, "Customers in both broadcast and postproduction segments have been asking for open solutions that allow them to choose components from different vendors to solve their needs."

This freedom allows customers to augment their traditional routing switches with a flexible, high-speed network interconnect. Networking in the computer and data-transmission industries, where Fibre Channel was born and flourished, is not the X-Y switching matrix architecture of the television industry. Therefore, there are ring, tree, and branch networks in future television plant signal transportation systems. The architecture might include high-speed digital fiber circulating rings, interconnected via gateways by full duplex digital fiber-optic backbones. Each ring could have appropriately located add-on/drop-off access nodes, serving as load/unload stations for 1.5- through 360-Mbit/sec bit streams, each with its own "header and descriptor" data. (An SMPTE standard is in process.) Connections from the switching/multiplexing node to source and destination equipment should be made with fiber.

Inside- and outside-plant fiber interfaces

Current interface locations and practices are embedded in regulations drawn up 62 years ago years by the Federal Communications Commission and Public Utilities Commissions of various states and territories, and framed by the Telecommunications Act of 1934.

The demarcation point is a "closet" located close to the customer`s property line. Fibers entering the premises terminate in codecs that transform and deliver the customers` signals in the electrical domain, most often as analog baseband video and audio. If signals need translating back into digital optical for inside-plant delivery, the cost is incurred by the customer.

Today, most telecommunications carriers cannot or will not splice their fibers to customers` inside-plant fibers to allow the customer to extend circuits to its own terminating equipment. With the passage of the Telecommunications Act of 1996, a few imaginative telecommunications companies may begin to offer this option. The impetus for change will probably come from telecommunications companies demanding that more of the 50% to 90% dark, or inactive, fibers now entering broadcast and postproduction facilities be activated and revenue-producing.

U.S. telecom exports jump 26% in 1995

U.S. exports of telecommunications equipment grew to $16.3 billion in 1995, an increase of 26% over 1994, according to the Telecommunications Industry Association (TIA). The top two export markets for the year were Canada at $1.9 billion, up 22%, and Japan at $1.8 billion, up 25%, based on figures from the U.S. Department of Commerce. Emerging markets represented 4 of the top 10 largest export markets, accounting for 21% of total exports.

Exports to Hong Kong jumped 119% in 1995 to $890 million, making it the fastest-growing export market for the year, the next fastest being China, with exports up 36% to $870 million. The opening of the Chinese market has accounted for a substantial rise in U.S. telecommunications equipment exports to the region. Other emerging markets in the top 10 include Mexico at $1 billion and Brazil, up 29% to $655 million.

Two of the larger sectors of telecommunications exports in 1995 were modems, up 44% to $744 million, and radio transceivers, up 35% to $1 billion.

More in High-Speed Networks