March 93 - An Object-based Direct Broadcast Satellite System
An Object-based Direct Broadcast Satellite System
G. Gordon Apple
After approximately a century of radio and a half-century of television, broadcasting
is about to enter a new era - an era of data distribution, software, compressed
video, interactive elements, distance learning, intelligent agents, and inexpensive
program origination. Reception will be available nationwide from the first day of
service and will include customized, subscription, impulse-access, proprietary, and
public programming. OOP techniques will be a fundamental component of the delivery
system, system management, user interface, and a large number of new types of
broadcast services not previously possible.
This and other processor-based communications systems will result in a fundamental
paradigm shift in the software industry from single static applications to smaller
components: standardized and custom dynamic, interactive, intelligent, and even
disposable components. Emphasis will increase on robust software and on system
design that can handle diverse and anomalous conditions.
Some of the history of this system is discussed along with the evolution that occurred
from dedicated analog hardware to object oriented software. Aspects of this particular
system are described and example software implemented in C++ MacApp is discussed.
The subsystems and techniques described here are broadly applicable to a variety of
computer-based communications systems but are primarily intended for use through
ACC's1 Direct Broadcast Satellites (DBS) within the next 24 to 36 months. DBS
service will allow reception with antennas as small as 18 in. anywhere in the nation.
With no dependence on local distribution companies, it will be the only truly national
broadcasting service. ACC's DBS will be an integrated broadcast system and will allow
reallocation of digital transmission capacity between transponders and within
different uplinks using the same transponder.
ACE's system design draws on a variety of disciplines including video compression,
dynamic multiplexing, high-speed demodulation and re-synchronization, remote
uplink synchronization techniques (similar to that used on some military satellites),
error correcting codes, live on-line object-oriented databases, encryption, indexed
indirect service access, and object oriented multimedia software. As such, it will be
able to deliver the usual compliment of cable TV video fare, digital radio, wide-screen
video, HDTV and computer file downloads, but also many new types of object-based
digital broadcast services.
Educational course broadcasting will be a major beneficiary of the OOP approach.
These combined techniques will allow course delivery to be two to three orders of
magnitude more efficient, less costly, and more service-prolific than would otherwise
be possible. For example, the two transponders being donated by ACC to the Foundation
for Educational Advancement Today will be able to simultaneously carry literally
hundreds of courses where only two would have been possible previously, and 10 to 20
using only video compression. At the same time, the provided video quality will be
vastly superior because much of it will be generated locally by the receiver processor
from received data and software objects and can be displayed on as normal or HD TV
screen or on a personal computer with a non-interlaced screen.
In addition, a new multimedia OOP element will make local interactivity possible in
the broadcast environment. Software objects used for generating screens and
animations will allow user interaction, user individualization, automated response
collection, and return link communication by telephone line modem, VSAT, cellular
systems, etc. (see Figure 1). InterBroadcast Satellite System activity can range from
a simple screen button that beeps to animated coloring books for children and medical
students (want to see my brain anatomy coloring book?) to sophisticated laboratory
experiment simulations. The persistence of these objects can be controlled absolutely
or conditionally. They can be forced to self-destruct after a specified time, be copy
controlled, or allow copying and off-line use. They can also be used in conjunction with
locally available required or optional resources such as course-specific or
general-reference CD-ROMs.
Needless to say, success of this and related systems will open vast new markets for
new types of software, software components, authoring tools, and content providers. Of
necessity, emphasis initially will be on completing development of the system,
development of authoring tools and demonstration software. However, a goal is to make
it possible for a not-terribly-computer-literate teacher or professor to be able to do
a live nationwide course broadcast without ever leaving the office. A personal
computer, pen pad, and an inexpensive TV camera should be all that is minimally
required. A LAN could connect to the campus or office-complex uplink or an ISDN link
could connect from a home office. This could totally eliminate expensive studio
facilities, equipment, and trained personnel presently required for most distance
learning.
What I hope to accomplish here is to give you a some indication of both the importance
of object oriented programming as an integral element of this system, and to indicate
the directions that I believe the software technology and markets will be going as a
result of these new interactive capabilities and distribution channels.
In the Beginning
The evolution of this broadcasting system from analog TV hardware to object oriented
software mostly follows my own career. At Purdue, several of us were working on
various aspects of digital signal processing, compression, transmission coding, and
error correction coding. We would regularly get thrown off of the campus CDC 6600
after monopolizing it for hours at a time doing transforms (precursors of JPEG) on
images. On a NASA research contract we built what I now believe to be one of the first
digital signal processors and maybe the first transform codec. We were also working
with digital transmission. But with T1-carrier becoming more available, in our
collective wisdom we agreed that there was no future in modems. (Kick, kick.)
A few years later at Bell Labs we developed for Picturephone what was probably the
first commercially-targeted video compression codec using intra-frame and frame
differential conditional replenishment techniques. Transform techniques were still out
of the question by at least several orders of magnitude in cost and capability. However,
one of the significant techniques that evolved out of this project was that of dynamic
multiplexing, a technique that would later be extremely important in OOP-based DBS.
CBS, TRW, and DBS
Skipping ahead a few years past one of the first digital telephone switching machines,
the Space Shuttle, and secure voice terminals, CBS was one of the first-round DBS
applicants. At that time and even today, virtually all video transmission was (and is)
analog. I was at TRW at the time (circa 1980) and we did a joint study to determine
the feasibility of using DBS to distribute HDTV, particularly using digital
transmission. At that time we were considering three transponders (channels) per
satellite covering one time zone and received with a 1 meter dish. A complete system
design was generated for a digitally compressed HDTV transmission system using a
mode-comparison-switching approach combining various differential compression
techniques that could be implemented at high speed and used a relatively simple
receiver decoder. Again, transform techniques were still two or three orders of
magnitude too computationally and economically expensive. Even with the simpler
approach, digital transmission was still thought to be too expensive to implement.
During the CBS project was when I started to seriously consider the ramifications of a
universal digital broadcast system and promote its utility. As part of the project, at an
oral presentation to CBS headquarters, I tried to convey my excitement for the concept
that digital broadcasting had implications that went far beyond standard television or
even HDTV. It was soundly dismissed as just being more video-text in which they had
recently taken a financial bath. I protested that we were talking about 10,000 times
the delivery capacity of the toy that had been tried, but it fell on deaf ears. The cable
and VCR boom was just beginning - and the Macintosh was yet to rise from the ashes of
the Lisa. CBS completely pulled out of DBS, leaving a vacuum that was to later pull me
in again.
Clinton Country
Back in my home town of Little Rock, a former high school class-mate had been a
second-round applicant for a DBS license under the name of Advanced Communications
Corporation and was successful partly because of the CBS pull-out. When I told him
what I had in mind, he was all ears (with apologies to Ross Perot). Although
investment money was not readily forthcoming, we filed our plans with the FCC. ACC
became the first company in the world to commit to digital broadcasting and steadily
increased its orbital holdings to where now it is one of two main DBS license holders.