DIGITAL CONVERSION AND
HDTV PLANT DESIGN ISSUES
The television industry
witnessed many technological advances in its short history; transitioning to digital
television and eventually on to HDTV may prove to be most significant of all. This change
distorts traditional business models used to measure success. Familiar tenets become variables; years of
accumulative experience yield to a new learning curve, indeed the industry braces for a
paradigm shift. Many engineering notions and disciplines give way or at least merge with
yet to be defined concepts. For certain, the
broadcast industry is undergoing a dramatic evolution.
High Definition Television has arrived, broadcasters and viewers alike will
experience the impact, and no one is likely to escape its affect. In the early
1960’s, transition from black and white television to color was a significant change
in technology, but it was a compatible change. Viewers with black and white TVs were not
forced to purchase new color sets to continue watching their favorite programs. The
monochrome image was unaffected by adding the new color sub-carrier, the system was
compatible. So too, with the introduction of stereo FM radio. Listeners need not purchase
new stereo receivers for continued listening to monaural programming. This compatibility
was important, perhaps critical to the success and timely roll-out of these new
technologies. With the dawning of digital television (DTV) and the companion High Definition Television (HDTV) technology, compatibility is no longer possible. From inception, all new equipment is required for the transmission and decoding of terrestrial digital signals. Older television sets will need a new outboard set-top decoder just to convert the signal for displaying less than true high definition. It should be noted however, the displayed picture will far exceed the quality of present-day NTSC images. All new digital television receivers are a must for decoding and displaying true High Definition signals. Compatibility is no longer possible.
Rulemaking concluded in 1997 with adoption of the 5th and 6th Report and Order affecting HDTV. The Commission announced a Memorandum of Understanding with Mexico and later with Canada. Stations were instructed to notify the FCC if not in agreement with initial modifications concerning replication of their NTSC signal. Issues affecting channels 60-69 and "Must-Carry" were introduced. The FCC identified 1997 through 2003 as the construction phase for digital (HDTV) television. Stations were to evaluate their channel, power and antenna height assignments. They were to review tower needs (including stress analysis), co-location of antennae, and possibly the re-negotiation of existing lease agreements affecting ancillary appurtenances. Other issues exist as well, including government, landlord, state and local zoning approval for new tower construction, higher levels of radio frequency radiation and FAA compliance. Stations need to apply for construction permits (CP) to begin tower construction, purchase new broadcast equipment, and modify existing infrastructure. If deemed necessary, stations could request extensions to the build-out schedule. By November 1998, DTV construction was to be completed by 24 stations in the top 10 markets. May 1999 would see DTV construction completed for affiliates of ABC, CBS, NBC, and FOX in the top 10 markets and by November 1999 for stations in the top 30 markets (nearly all these targeted deadlines have been met). May 2002 defines completion of DTV construction for all remaining commercial stations. A year later, DTV construction must be completed for all (PBS) Public Broadcasting Stations. By 2003, simulcasting
(transmission of both NTSC and HDTV signals) will be required for half the broadcast day. In 2004, it will increase to 75% and for the
entire broadcast day by 2005. In the year 2006, contingent upon 85% market penetration,
stations will relinquish one of two 6Mhz channels for auctioning by the FCC. At that time,
transition to DTV will be complete and pending FCC deadline extensions, NTSC will go dark. This most aggressive
timeline for implementation is complicated by the relatively few broadcast facilities
prepared for conversion. Typically NTSC
plants have limited resources to handle digital formats.
Since conversion to a digital infrastructure is necessary to support HDTV,
broadcast facilities are faced with the dilemma of rapid technological rollout, aging
infrastructure and limited manpower. The
engineering staff faces challenges not only for digital conversion, but also the on-going
responsibility of maintaining the legacy plant. Not one, but two
separate formats are necessary for digital (HDTV) conversion. The first is digital, the
second a change in the aspect ratio from 4:3 to 16:9. The displayed digital image with its
clarity and detail is most impressive, but the introduction of the 16:9 format will likely
capture the attention of viewers as never before. Manipulating
video images in dual display formats further complicates the conversion plan. A
staged approach to these and other concerns defines the "Scope of Work" at each
facility. Establishing a realistic time-line
and remaining flexible toward problem solving is necessary for successful conversion.
There is justifiable concern over meeting the deadline, as the issues are many and varied.
Time to seek assistance toward full digital conversion will quickly disappear for as
someone once said, “dates on the calendar are closer than they appear.” Unlike other schemes
for conversion, HDTV appears backward in its implementation. The accepted starting point is the last link in
the chain—the transmitter. Addressing
concerns at the transmitter site will likely involve the existing tower. A stress analysis
may be required to determine structural integrity. Towers
are often populated with multiple antennae in support of paging, microwave, two-way radio
and PCS communication services. These
appurtenances create additional wind loading further stressing the structure. It may be necessary to modify leases and arrange
for relocating these contract services. Adding
a second antenna (HDTV) will likely require additional guying and tensioning. This creates a substantial increase in downward
thrust (measured in multiple tons) affecting not only the tower, but also the tower
support platform structure as well. Installation of a HDTV antenna weighing several
thousand pounds is no small task. Crews capable of safely rigging towers in excess of 1500
feet are limited, remember a qualified steeplejack is a must, personal safety cannot be
compromised. There is also concern
over RF radiation caused by the additional transmitted signals from the top or
side-mounted antenna. The affect will likely be minimal, but be aware EPA and FCC
regulations governing Radio Frequency Radiation and Human Exposure may apply. Testing may
be necessary. Should the overall antenna
height change, it will be necessary to file proper variance forms with the FAA. If a new tower is necessary, local zoning issues
and regulations will also come into play. Just
a reminder, be certain the tower registration number is prominently displayed in
compliance with FCC regulations. Often overlooked in the
planning process is the ability of surface energy providers to deliver sufficient capacity
to handle the increased load. Check with your utility company confirming if adequate
supply is available. If not, a new build-out
may be necessary. DTV transmitters
require not only additional space but additional cooling as well. This new demand on your HVAC system could require
modifications to duct work and capacity. Many
installations will add UHF transmitters. UHF rigs often require a “closed”
cooling systems. Provisions for
accommodating this style system will need additional space planning.
Water or coolant
plumbing is one thing but RF plumbing is quite another.
A good deal of copper piping is required to combine and diplex the RF. Radio frequency combiners, diplexers and band
traps are space hogs. Locating these copper
mazes will likely challenge the already overcrowded workspace. Be sure there is sufficient
ceiling clearance to allow change out of the high power tube(s). Before we leave the
transmitter site another issue needs consideration. The Studio-to-Transmitter (STL) link
will likely require modification or replacement. If you are considering a separate (new)
frequency for the digital STL link, it is strongly recommended you contact your local SBE
(Society of Broadcast Engineers) frequency coordinator.
Most broadcast auxiliary services (BAS) STL bands (typically 6/7GHz. and 13GHz) are
fully occupied making additional interference-free channels difficult if not impossible to
secure. Fortunately, microwave technology,
has evolved allowing simultaneous transmission of a dual carrier (digital and analog) over
a common frequency. This hybrid technique
should find wide acceptance in the industry. Alternate
paths for carrying digital signals are also available and should be explored. The cost of fiber optics, a long established
method of carriage, is now within budgetary reach. Contracting
with your local fiber provider may prove to be a viable solution to frequency congestion. In contrast to a
seemingly controlled environment at the transmitter site, the studio has its own
personality with unique issues for consideration. Aside
from the occasional squirrel shunted across the service feed line, the transmitter site is
mostly a “hands-off” situation. Major
repair will gather one or two engineers, but that's about it. The studio on the other hand is quite another
matter, for it includes multiple users with multiple demands. Selecting an in-house
“native” format (480p/i, 720p, 1080p/I, 1080/24) and selecting a transmission
scheme from the 18 ATSC compression formats can be a formidable task. The format(s)
selected will likely coincide with that of the program provider (network) but if it does
not, additional high-end format conversion equipment will be required. Whatever scheme is selected, more equipment, rack
space and ancillary support gear will inevitably follow.
With racks already loaded to capacity, new gear could infringe upon the workspace
of others. Creative use of available space
might require substantial modification to floor plans. A staged approach to conversion
will require reusing existing space; keeping in mind displacement of personnel and
personal workspace can have a domino effect. Planning
is critical and care should be taken to insure that maximum efficiency is maintained.
Master control is a
mission critical workspace for any broadcast facility and taking great care to insure
uninterrupted operation of this legacy point-of-control is paramount. Introducing new equipment, functionality and
ergonomic workspace to accommodate the switching and monitoring of multicast programs
(multi-casting) is a sizable challenge. The ability to program and transmit multiple
standard definition signals simultaneously defines a new ere for the broadcaster. Point-of-control for these multiple streams of
data redefines functionality of master control. The
most significant physical and operational changes will likely occur at master control. (Extensive modification to workload in the Traffic
Department will run a close second.) If multi-casting is
planned, MC automation for simultaneous switching and machine control will be a necessity. Typically, an increase in workload is not matched
with an increase in workforce. The likelihood of adding personnel to manage the additional
programming channels is remote. If an
entirely new control room were anticipated, the broadcaster would do well to plan for easy
access to both control locations ergonomically merged where possible. If new building construction is required, the
Americans with Disabilities Act (ADA) will require specific compliance. Typically, and
especially with older facilities, new technology and new equipment is introduced and
placed on-line with little regard for power line load balancing or for that matter proper
grounding techniques. This invariably leads
to "hot" breakers or just plain outages in delivered power. Either case is unacceptable and, by new design,
needs to be remedied. Proper grounding
technique(s) is critical in managing the higher bit rate signals. Proper grounding
techniques are truly a defined science.
Having considered floor plans and equipment elevations you can now focus on integrating new with old technologies. As mentioned earlier, a typical studio facility is analog with limited interface to digital formats. Graphics, Non-Linear Editing and Media Composing are good examples of isolated digital “islands” currently existing in an NTSC plant. Legacy digital-to-analog (D/A) conversion, treated as the exception rather than the rule, was limited in functionality. Little if any long-range plans in place for digital integration of the entire plant. Since these digital islands will live on throughout the transition to digital, issues of Analog-to-Digital, Digital-to-Analog conversion, Up and Down conversion and aspect ratio conversion, providing anamorphic proportioning will need to be considered. These disciplines are required to integrate legacy “islands” to newly installed digital platforms. Up-conversion provides a path to merge standard definition (SD) with high definition (HD). The down-converter manages the High Definition stream for integration to the present NTSC signal. Unfortunately, all conversion processing degrades overall quality. An integral part of any
station is signal routing. Great care should
be taken in selecting the correct signal routing characteristics to support advances in
technology and future build-out. Ability to
handle bit rate streams of 270 Mb/s, 360Mb/s or greater may be inadequate for continued
growth. A router supporting 1.5Gb/s (albeit
expensive) may be the better initial choice. Whatever
selection is made requires careful planning to properly interface the formats. As with additions to master control adding a whole
house routing system is a formidable task. Traditional thinking
affirms, bigger is better. Typically, whole
house routers are configured with 144, 256 or a greater number of cross points. Perhaps a different approach is in order, one that
supports careful tie-line management and "distributed intelligence" in router
planning. The new system should consider
pre-existing digital islands and address routing signals locally rather than globally. It may be more cost-effective to manage multiple
smaller routers, say 32 or 64 squared, rather than the giants of past. As a side note, history supports the
in-house routing system as “king of the hill”. Perhaps now, the “king”
has been displaced by another team player. Considering
multicasting, opportunistic datacasting and management of HD bit streaming the new center
of the universe is really AUTOMATION/ASSENT MANAGEMENT. Some digital
distribution amplifiers provide analog outputs utilized for signal monitoring. This allows
re-use of some existing monitors, but with an aspect ratio change to 16:9, source
monitoring is no longer a straightforward process. Considering
cost it is unlikely stations will replace all 4:3 monitors with 16:9 capability. In the interim a compromise in aspect ratio will
be noticed when adapting old monitors for displaying the new image. Patching, cabling and
termination take on a whole new meaning. No
longer will a hastily installed BNC connector suffice. New digital signals are unforgiving
to improper termination or connectorization and in most cases demand selection of special
higher (bit rate) digital cabling. Re-use of
old NTSC patch bays may provide unacceptable performance. In the digital domain,
termination must be correct and specific to the application, 75 ohms for video, 110 ohms
for audio. When you think about it the new
digital signal, at a 1.5 Gb/s bit rate, approximates RF characteristics and as such must
follow the rules dictated for handling RF energy. Even
tight cinching of cable ties could compromise system performance. When using video and
fiber optic cording, care must be taken not to radius too tightly. Manipulation of the
MPEG-2 compression scheme requires careful thought and judicious use of encoding.
Dissimilar compression algorithms result in concatenation.
This phenomenon, caused by cascading multiple and different encoders/re-encoders creates
blocking in video detail and although undesirable, is likely unavoidable. Additionally, latency, or the finite time required to process
video/audio, will be of real concern. This one concept alone represents a challenge to
“timing” within a plant, as it is a cumulative delay through each piece of
equipment and unique to the video path. Adjusting
for latency gives a whole new meaning to the phrase, “joining network on time.”
Encoders and decoders converting composite to 4:2:2 and conversely, also contribute
artifacts to the processed video. Minimizing the number of times these conversions occur
will help maintain signal integrity. Video processing, audio delay and noise reduction
management will become staples for the new digital plant.
Proper timing,
processing and distribution of the AES/EBU digital audio signal is critical, as latency is
a concern here as well. “Breaking out” (disembedding) audio from the video data
stream allowing concurrent processing creates a phasing/timing issue affecting overall
performance. Some issues of embedded versus
discrete handling of the data stream are still unresolved.
The AC-3 ATSC standard requires multiplexing and de-multiplexing 5.1 (actually 6)
channels of audio. Of all new technologies
involved in digital conversion, proper and successful manipulation of the digital audio
data stream remains a significant challenge. Great strides have been gained in digital
audio processing technologies and it is anticipated that 12 channels of AES/EBU of digital
audio could be routed throughout a broadcast facility. If that weren’t
enough, consider these issues in search of resolve: PSIP, Closed-Captioning, Lip Sync,
Conditional Access, Interactive TV, Datacasting, Copyright Protection, Encryption, Must
Carry, DTV Receiver Issues, Cable Compatibility Issues, Grade B Replication, Conditional
Access, DASE ATVEF (Advanced TV Enhancement Forum) iTV tools to mention but a few. Live news presentation
and Electronic Newsgathering (ENG) continue as a most significant service provided by the
local broadcaster. The ability to have
multiple remote news crews canvassing the marketplace collecting and reporting news
stories is a major service to the viewing public. Conversion in this area of operation
must be done carefully, avoiding interruption to service.
Digital conversion involves outfitting several news vehicles with
video/audio/editing and RF equipment necessary for digital remote pick-up (RPU) microwave
transmission. Fixed inter-city relays (ICR)
microwave links back to the studio, will also need replacement/modification. It is
impractical from an operational standpoint and far too costly from a budgetary standpoint
to replace all legacy equipment at one time. A
staged approach may prove the wise choice.
Recording of news
acquisition and sustaining programming will eventually involve tape-less disc storage and
file server technology. Programs of varying
lengths will be captured on hard drive and made available for instant access and playback. File server technology may eventually replace the
videotape format altogether, but when you consider cost-effectiveness of storing massive
amounts of data, tape is still viable. For
the foreseeable future, field acquisition will remain on tape with content transferred to
the in-house file server. Making use of LAN
(Local Area Network) topologies and server technology will enhance desktop editing. Browsing and transfer of video files will
revolutionize the way news stories are prepared. No
longer will tapes arrive at the back door only to be rushed to editing, crash edited and
readied for hand delivery to the point of playback. Video from the ENG van will be
downloaded, faster than real time, to disk and presented for multiple user editing. Server
technology allows for multiple users to access a common database while simultaneously
delivering program material for presentation-to-air.
Video streaming to the Internet and VOD (Video on Demand) will redefine the
broadcaster/viewer relationship. Maybe we
should bring back 16mm film processing? Change in job
description will create a culture shock for some in the industry. Soon, a reporter, writer and editor will be the
same individual performing all tasks from their desktop. New methods for performing old
tasks will exist for some time to come. Care must be taken to remain sensitive to the
established methodology, for nearly every employee will experience the impact of digital
conversion. Merging new technologies with old, relocation and co-location of work areas
deserves your full consideration.
Networking is central
to all issues discussed for accomplishing the task at hand. Networking is the backbone for
the entire system. Use of Ethernet, File
Transfer, Digibus, Fibre Channel, TCP/IP, 10BaseT, 100BaseT, FDDI, FITD, and/or ATM to
name but a few, are network disciplines commensurate with achieving desired results. The systems design engineer must be familiar with
network topologies as well as asset management disciplines.
Care should be exercised to properly design the distribution, hub orientation and
patching plot of the network backbone. Some will say, correctly installed networks will
have the capacity to replace today’s traditional video/audio whole-house routing
systems. Time will tell.
Thus far we have
considered but a few of the technical issues surrounding analog-to-digital-to HDTV
conversion. This is by no means a complete
compilation of the conversion process issues but should serve as a guide to the careful
coordination necessary to complete the task. Pulling all these changes together into a
single orchestrated project requires Project Management.
You may feel confident about tackling the entire project with your existing staff
of engineers and construction personnel. Depending
on the size of your facility, this may be possible, but in many facilities, manpower and
resources are limited. Your staff is already occupied with day-to-day maintenance routines
and the operational concerns for keeping the legacy NTSC plant alive and well. To
extricate enough staff members, from their daily tasks, to address digital conversion
issues may be a greater challenge than you anticipate. If outsourcing some or all of the work is your preference, consider the following: A consulting firm needs to evaluate your specific conversion goals when developing the design criteria. These defined goals should include architectural, interior design and system electronics. Facilities design is a focused concern for any Project Management team defining space parameters, acoustics, lighting, floor plans, electrical loads, heating, ventilation/air conditioning, radio frequency interference and other related areas. The consulting team should develop a comprehensive equipment package to support your application and budgetary constraints. If your station is like most, accurate systems documentation is nearly non-existent or should it exist is likely outdated and incomplete. The design service provider you select should include comprehensive CAD (computer aided drawings) of equipment elevations, rack layouts, console design, block drawings and interconnection wiring diagrams. Likewise, a complete equipment list, vendor recommendations, bid evaluation, vendor negotiations and system proof-of-performance tests should be included in the total package of services provided. The consulting team
(Integrator) must remain amenable and sensitive to your requests adjusting to your
specific requirements. Ability to oversee all aspects of the project and deliver a
“turnkey” service can be very desirable. The
“design/build” approach typically insures timesaving, economy of scale and
associated cost-saving results. If total overseeing is not required, consider a consultant
in the role of Area Manager, working in concert corporate directives, contractor(s) and
local management teams. A competent design
group should be capable of working side-by-side with a third party installer representing
your best interest.
|
|||||||||||
