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                          DTV REPORT 
                              ON 
                  COFDM AND 8-VSB PERFORMANCE




              Office of Engineering and Technology
                       September 30, 1999













OET  Report 
FCC/OET 99-2


                                
                                
                                
                                
                                
                          DTV REPORT 
                              ON 
                  COFDM AND 8-VSB PERFORMANCE




              Office of Engineering and Technology
                       September 30, 1999







OET  Report 
FCC/OET 99-2

Prepared by:                                 
Bruce Franca
Alan Stillwell
Robert Bromery
Robert Eckert
Michael Davis
                       Executive Summary

The Office of Engineering and Technology (OET) has conducted an independent assessment of
Coded Orthogonal Frequency Division Multiplex (COFDM) and 8-Level Vestigial Side-band (8-
VSB) systems for the provision of digital television (DTV) services in the United States.  This
study was initiated at the request of Commissioner Susan Ness in response to issues raised in
result of indoor reception demonstrations by the Sinclair Broadcasting Group, Inc. (Sinclair).  As
indicated below, the OET study concludes that the ATSC 8-VSB standard should be retained.

The Sinclair demonstrations consisted of an A/B comparison of 8-VSB versus COFDM reception
made at two to three locations in downtown Baltimore.  Reception was attempted using a "bow-
tie" type UHF antenna with two 8-VSB receivers and two COFDM receivers.  The antenna was
rotated 360 degrees and the range over which reception was achieved was recorded.  In general,
reception of COFDM was better than 8-VSB at the two sites visited.  Sinclair engineers indicated
that at both locations analog TV reception was either very poor or not acceptable.  Independent
measurements indicated that the reception difficulties at the Sinclair sites were due to the presence
of strong static signal reflections, or "multipath."

A review of field tests conducted in a number of cities shows good performance for 8-VSB for
outdoor reception.  These studies show outdoor service availability of 80-95 percent for cities
with a small to moderate percentage of obstructed sites and 63-79 percent for cities with a large
percentage of obstructions.  The field test data also indicate that indoor reception of DTV signals
is more challenging.  Indoor service availability ranged from 75-100 percent in cities with a small
to moderate percentage of obstructed sites and from 31-40 percent in markets with a large
percentage of obstructed sites.  The above test results indicate that DTV service availability
approaches that of NTSC service in most instances and with expected receiver improvements will
exceed it in the near future.

OET held discussions with a number of industry representatives.  Sinclair stated that its tests have
raised concerns as to the ability of  the 8-VSB standard to provide service using simple indoor
antennas.  Sinclair also indicated that it has completed additional observations in the Baltimore
area, including sites located near the edge of the demonstration's predicted DTV service area. 
Sinclair indicated that there were no indoor sites where antenna pointing was not a significant
factor in obtaining satisfactory reception of 8-VSB DTV service.  It also observed that the
necessity to re-orient the antenna to receive stations at different locations would be a significant
impediment to DTV "channel surfing."  It also stated that at their edge of service sites, there were
no locations where 8-VSB was significantly easier to receive than COFDM.  
 
In general, with the exception of Sinclair, other parties continued to support the 8-VSB system as
the DTV transmission standard.  They generally stated that all of the factors that have been
identified regarding COFDM performance in the Sinclair demonstrations were well understood
and considered at the time the DTV transmission system decision was made. They stated that the 
demonstration locations had very strong ghosts that were outside of the correction range of the 8-
VSB receivers used by Sinclair.  Most of the industry representatives stated that, in theory, 8-
VSB and COFDM should be able to perform nearly the same where there is static multipath. 
Most also stated that COFDM can generally be expected to perform better in situations where
there is dynamic multipath, e.g., in mobile operations.  A number of parties also stated that 8-VSB
offers a number of advantages over COFDM for broadcast DTV service, including superior
overall coverage, lower costs of construction and operation, and immunity to impulse noise from
household appliances.  Industry representatives also asserted that 8-VSB receivers that perform
better than the units used in the demonstration are, in fact, available now.  The consumer
electronics (CE) manufacturers all viewed multipath performance as an issue that will be worked
out in the normal process of improving new products. 

The study finds that each system has its unique advantages and disadvantages.  The 8-VSB
system, in general, has better threshold or carrier-to-noise (C/N) performance, has a higher data
rate capability, requires less transmitter power for equivalent coverage, and is more robust to
impulse and phase noise.  The COFDM system, on the other hand, has better performance in
dynamic and high level static multipath situations, and offers advantages for single frequency
networks and mobile reception.  

The study examined and estimated the difference in service availability between COFDM and 8-
VSB operation in the top-10 TV markets.  In this analysis, COFDM was assumed to have an
advantage in urban areas close to a station's transmitter and 8-VSB was assumed to have an
advantage in fringe area coverage.  These estimates appear to indicate that the relative
advantages/disadvantages of either system with regard to overall coverage are generally small and
vary by market. The study also investigated the impact on interference to existing NTSC stations
of increasing the power of DTV stations by 4 dB in order to make up for the disadvantage of
COFDM for fringe reception noted above.  This analysis indicates the overall increase in
interference to NTSC service from higher power COFDM operations would be generally small. 
OET indicated that further study is needed to examine whether COFDM could support
satisfactory service on VHF and lower UHF channels due to impulse noise concerns.

The study also finds that the adaptive equalizer performance of 8-VSB receivers is very important
for reception in multipath conditions.  It has been suggested that a value of 22 ms seems to be a
reasonable minimum equalizer range, but that longer ghost canceling ranges may be beneficial. 
While quantitative measurements on the 8-VSB DTV receivers used in the Sinclair test were not
available, it has been implied that the adaptive equalizer performance for these receivers was in
the range of about 10 ms or less.  This appears to be a reasonable explanation for the relatively
poor performance of the 8-VSB receivers in the Sinclair test, especially with regard to indoor
reception.

The study finds that the Sinclair demonstration has provided useful insight into certain indoor
reception conditions, particularly with regard to strong multipath conditions, and possible
deficiencies of some early DTV receiver designs.  However, the study concludes that the
multipath reception problems identified by Sinclair are solvable with improved adaptive equalizer
performance and that a well-designed 8-VSB receiver should be able to provide satisfactory
reception at the Sinclair locations.  It further notes that signal strength and immunity to
interference from impulse noise are also important factors in successful indoor reception and that
8-VSB may have some advantage over COFDM with regard to these factors.


The study also concludes that, as with most products, performance improvements in DTV
receivers will continue to be made over time.  From recent announcements and claims regarding
the availability of improved equalizer chips, it appears reasonable to conclude that manufacturers
are working to improve 8-VSB receivers, including the receivers' indoor reception and signal
acquisition capabilities.  In this regard, CE manufacturers indicated that improved receivers will
be available this fall and that further improvements will be introduced next year.

The study further finds that 8-VSB has about a five percent data rate advantage over COFDM.
While a 5 percent data rate difference is relatively small, it could have some impact on the ability
to provide certain high definition television programming. 

In summary, OET concludes that both 8-VSB and COFDM have certain advantages and
disadvantages, and that both systems are capable of providing viable DTV service.  OET further
concludes that, based on discussions with consumer equipment manufacturers and recent
announcements by semiconductor manufacturers Motorola and NxtWave, reasonable solutions to
the multipath issue and indoor reception problems raised by Sinclair are being developed and
should be available in the near future.  OET also finds that some of COFDM's benefits, i.e., its
advantages for single frequency network operation and mobile service, may be inconsistent with
the current structure of broadcasting in the United States.  Further, 8-VSB has some advantages
with regard to data rate, spectrum efficiency and transmitter power requirements.  Accordingly,
OET concludes that the relative benefits of changing the DTV transmission to COFDM are
unclear and would not outweigh the costs of making such a revision.  OET therefore recommends
that the ATSC 8-VSB standard be retained.
                       Table of Contents



                                                            Page

Introduction                                                         1

Technical Overview Of 8-VSB and COFDM                                     1
     8-VSB and COFDM
     History of COFDM

The Sinclair Demonstration Tests                                          4
     The Sinclair Demonstration
     Sinclair Report                                                 
     Oak Technology Report

8-VSB Field Tests                                                    8

Reports in the Press                                                      9

Information from Industry Representatives                                     11
     General Views on the Transmission Standard Issue
     Industry Views on the Sinclair Demonstration
     COFDM vs. 8-VSB
     Improvements in 8-VSB Performance
     Effects on DTV Roll-out

Evaluation and Recommendation                                       15
     Evaluation of 8-VSB and COFDM
        Threshold and Service Area/Interference Performance
        Multipath Performance
        Indoor Reception
        Mobile and Single Frequency Network Operation
        Data Rate
     Summary Recommendation

Appendix (not available in on-line version)
           DTV REPORT ON COFDM AND 8-VSB PERFORMANCE



                          Introduction

Recently, the Sinclair Broadcast Group, Inc. (Sinclair) has conducted demonstration tests 
comparing a Coded Orthogonal Frequency Division Multiplexing (COFDM) system with the 8-
Level Vestigial Side-band (8-VSB) system developed by the Advanced Television Systems
Committee (ATSC) and adopted by the Commission as the standard for digital television (DTV)
transmissions.  Based on these demonstrations, Sinclair has raised questions about the ability of
the 8-VSB system to provide satisfactory "over-the-air" service in urban areas using simple
indoor antennas. 

The Office of Engineering and Technology (OET) has been asked by Commissioner Susan Ness
to conduct its own independent assessment of these concerns based upon available engineering
information and data and consultations with outside parties.  This paper provides OET's
preliminary assessment of the problems identified by Sinclair, the efforts by industry to improve 8-
VSB reception, and whether there is any need for further action on this matter. 


             Technical Overview of 8-VSB and COFDM

8-VSB and COFDM

The ATSC 8-VSB system uses a layered digital system architecture consisting of:  1) picture layer
that supports a number of different video formats; 2) compression layer that transforms the raw
video and audio samples into a coded bit stream; 3) transport layer that "packetizes" data; and 4)
radio frequency (RF) transmission layer.  The ATSC 8-VSB transmission system is a 
single carrier frequency technology that employs vestigial sideband (VSB) modulation similar to
that used by conventional analog television.  The transmission layer modulates a serial bit stream
into a signal that can be transmitted over a 6 MHz television channel.  

The ATSC 8-VSB system transmits data in a method that uses trellis-coding with 8 discrete levels
of signal amplitude.  A pilot tone is provided to facilitate rapid acquisition of the signal by
receivers.  Complex coding techniques and adaptive equalization are used to make reception more
robust to propagation impairments such as multipath, noise and interference.  The 6 MHz ATSC
8-VSB system transmits data at a rate of 19.4 Mbps.



By contrast, the OFDM system is a multicarrier technology.  The principle of OFDM is to break a
single data stream into many parallel, lower rate data streams.  OFDM then uses many subcarriers
to transmit these lower rate streams of data simultaneously.  To ensure that the subcarriers do not
interfere with one another, the frequency spacing between subcarriers is carefully chosen so that
each subcarrier is orthogonal to one another.  The individual subcarriers are typically modulated
using a form of either quadrature amplitude modulation (QAM) or quadrature phase shift keying
(QPSK).  Coding techniques (the "C" in COFDM) can be used to improve performance.  

The multicarrier design of COFDM makes it resistant to transmission channel impairments, such
as, multipath propagation, narrowband interference and frequency selective fading.  COFDM
avoids interference from multipath echoes by increasing the length of the signal samples, so that it
is greater than the temporal spread of the multipath, and by applying a "guard interval" between
data symbols where the receiver does not look for information.  Guard intervals can be designed
so that most multipath echoes arrive within the guard period and therefore do not interfere with
the reception of data symbols.  This permits COFDM to successfully operate with echoes as large
as the main signal, i.e., 0 dB.  Further, because information is spread among many carriers, if
narrowband interference or fading occurs, only a small amount of information is lost.

The Sinclair demonstrations used a COFDM system based upon the European Terrestrial Digital
Video Broadcasting (DVB-T) standard using equipment that was modified to operate in the
traditional 6 MHz channel used in the United States.  That system operated with 1705 subcarriers
and 64 QAM, and provided a useable data rate of 18.66 Mbps.  More detailed descriptions of
both COFDM and 8-VSB are provided in the attached Appendix.
History of COFDM

The theory of orthogonal frequency division multiplexing (OFDM) has been well known for some
time.  The concept of using parallel data transmission and frequency division multiplexing was
first published in the mid-1960s, and a U.S. patent was filed and issued for this approach in 1970. 
In the early 1990s, significant technical interest was shown in the use of COFDM for terrestrial
digital television broadcasting.  In 1992, for example, the Communications Research Centre
(CRC) of Communications Canada published several papers investigating the possibility of a
distributed transmission concept for digital television using a multi-carrier modulation method,
such as COFDM.  These early studies by the CRC suggested that such systems might provide
some advantages over single-carrier systems.  In particular, these studies indicated that
multicarrier systems would allow operation of single frequency networks and could provide
improved performance under multipath distortion.  In 1994, George A. Hufford of the Institute
for Telecommunications Sciences of the National Telecommunications and Information
Administration (NTIA) also released a report on the application of OFDM technology for high
definition television.  In this report, Hufford indicates that "multicarrier modulation techniques
such as OFDM may provide a remedy for multipath and other propagation path imperfections for
over-the-air high data rate transmission systems, such as HDTV."

During this period, a number of prototype DTV systems using COFDM were also developed and
demonstrated.  These included the HD-DIVINE by the Nordic countries, DIAMOND by
Thomson-CSF, SPECTRE by NTL of the United Kingdom, HDTVT in Germany, and others.  In
addition, in 1993, the Digital Video Broadcasting (DVB) project was initiated in Europe. 

In 1994, several U.S. and Canadian broadcast organizations solicited potential bidders to build
COFDM DTV hardware for evaluation.  In 1995, this group presented a proposal for a COFDM
DTV system to the FCC's Advisory Committee on Advanced Television Service.  The Advisory
Committee, however, found that the proposed COFDM system was not ready for testing and did
not demonstrate the superiority of COFDM over 8-VSB for the majority of markets.  In making
this decision, the Advisory Committee was, among other things, concerned about the additional
transmitter power that would be required with a COFDM system.


                The Sinclair Demonstration Tests

On June 24, 1999, the Sinclair Broadcast Group (Sinclair) announced that it would begin tests to
determine the viability of the DTV standard using the transmission facilities of its station in
Baltimore, Maryland.  Sinclair stated that the purpose of this testing was to compare 8-VSB and
COFDM.  It stated that previous tests that it had conducted raised concerns as to the ability of the
8-VSB standard to provide "over-the-air" service into homes and offices using simple indoor
antennas.  

Sinclair invited broadcasters, equipment manufacturers, the press and others to observe its
demonstration.  Engineers from OET attended the demonstration on June 29, 1999.   The
following is a report of what was observed at the demonstration by OET engineers.

The demonstration was conducted using the transmitting facilities of WBFF-TV.  The DTV
signals were transmitted on channel 40 with an average effective radiated power (ERP) of about
50 kW, using a transmitting antenna mounted about 1000 feet above the ground.  The peak-to-
average power ratio was about 8.5 dB for COFDM and about 6.5 dB for 8-VSB.  The
bandwidth occupancy was 5.7 MHz for COFDM and 5.38 MHz for 8-VSB.  The COFDM
program material consisted of a 7-second clip of standard definition PAL material with an
encoded rate of about 3.5 Mbps with extra "bit stuffing" for an effective data rate of 18.66
Mbps.  A server was used to provide high definition program material for the 8-VSB signal at a
data rate of 19.39 Mbps.        

Two 8-VSB and two COFDM receivers were used in the demonstration.  The two 8-VSB
receivers were commercially available consumer DTV receivers that were purchased locally by
Sinclair.  The COFDM receivers used were a European consumer COFDM receiver modified to
operate at 6 MHz and a laboratory-type test receiver that provided data rate measurement
capability.  The demonstration viewed by the OET staff consisted of an A/B comparison of 8-
VSB versus COFDM reception made at two locations in downtown Baltimore.  Reception was
attempted using a "bow-tie" type UHF antenna mounted on a tripod approximately 5-6 feet off
the ground.  The antenna was then rotated 360 degrees and the range over which reception was
achieved was recorded.  If no reception was achieved with the bow-tie antenna, a second, small
UHF indoor reflector-type antenna was used.  Sinclair indicated that they considered service
acceptable where reception was achieved over a complete 360 degrees rotation of the antenna.  

Both locations visited during the demonstration were within about eight miles of the WBFF-TV
transmitter.  The first location was on Lombard Street.  Measurements were taken on the
sidewalk at street-level.  At this location, both COFDM and 8-VSB reception were achieved
using the bow-tie antenna.  However, reception using the COFDM system was easier to acquire
and was maintained over a full 360 rotation of the antenna.  8-VSB reception at this location
was achieved over two arcs of about 60 degrees each, or about 120 degrees.  In addition, the
antenna had to be rotated more slowly and carefully for 8-VSB reception.  The second location
visited was an 11th floor apartment located in the Baltimore Harbor area on Lee Street.  This
location faced away from the transmitter site so that only reflected signals could be received.  At
this location, only COFDM reception was achieved with the bow-tie antenna.  8-VSB reception
was only possible by placing the reflector type antenna in direct contact with the aluminum
window frame.  Those in attendance postulated that this effectively permitted the entire window
frame and surface to become part of the receiving system.  In general, reception of COFDM was
better than 8-VSB at the two sites visited.  Sinclair engineers indicated that at both locations
analog TV reception was either very poor or not acceptable with simple indoor antennas.

As a result of these demonstrations, Sinclair argued that today, DTV does not work.  They also
stated that the traditional outdoor reception model used also to predict reception for DTV service
is outdated.  They observed that a large portion of the viewing population who rely on over-the-
air broadcast service do not have outdoor antennas and instead have loop or bow-tie antennas
sitting on their receivers indoors.  They argued that there is a demonstrably better alternative in
COFDM, and that at the least manufacturers need to improve the reception capabilities of their
DTV receivers to be comparable to that available with COFDM.

Sinclair Report

On September 24, 1999, Sinclair presented a report of the results of its Baltimore reception tests
to the IEEE Broadcast Symposium in Washington, D.C.  The report documents reception
results at 40 sites in the Baltimore area.  Sinclair indicates that approximately three-quarters of
these sites were located within the "near field," i.e., less than 30 miles, of the WBFF-TV
transmitting antenna.  It reports that 8-VSB reception was successful at 10 of 31 sites with a
Panasonic receiver and at 12 sites of 31 sites with a Pioneer receiver.  For COFDM, it reports
successful reception at all 31 sites with a Nokia receiver and at 21 of 25 sites with an NDS
receiver.  Sinclair also presents "ease of reception" data showing the range in degrees of antenna
orientation at which reception was achieved.  The Sinclair data indicates that COFDM was less
sensitive to antenna orientation than 8-VSB.  Sinclair indicates that it was not possible to receive
8-VSB signals at locations with "spectrum deviations" in excess of 15 dB from a signal with
"nominal reception" characteristics.  It further indicates that COFDM reception was possible with
spectrum deviations of up to 25 dB.  Sinclair also states that 8-VSB, as compared to COFDM,
was quite intolerant to dynamic multipath conditions.  

Sinclair indicates that the purpose of its "far field," i.e., beyond 30 miles, testing was to try to
determine if a meaningful difference in performance could be observed due to the differences
between 8-VAB and COFDM in threshold carrier-to-noise (C/N) ratio needed for acquisition of
service.  It states that while there is a 4 dB difference in the theoretical C/N performance between
of the two systems in favor of 8-VSB, the average daily calibration threshold difference between
the 8-VSB and COFDM receivers was 3.28 dB and that in the field this difference shrank to 2 dB. 
Sinclair suggests that this may be due to the effect of real world impairments that add to the
theoretical "gaussian" channel values.   

In its summary comments and conclusions, Sinclair states that the need for indoor reception was
ignored during the design phase of 8-VSB and that portability and mobility was not given any
level of priority.  It argues that these factors should not be overlooked today.  Further, it states
that the results of the Baltimore tests demonstrate that the present generation of 8-VSB receivers
being offered to the public fall far short of the performance needed to make DTV a success as an
over-the-air service.  Sinclair argues that the broadcast community should demand better
performance from 8-VSB receivers or look elsewhere for a DTV transmission system.

Oak Technology Report

Oak Technology Ltd., a manufacturer of DVB-T chipsets and other semiconductors, has
published a brief report with some technical information on the demonstration.  The Oak report
contains measurement data and observations from five sites in Baltimore that were visited on June
24, 1999.  These sites included Sinclair's offices and the Lombard Street and Lee Street
Apartment sites visited by OET staff.  In addition, the Oak report contains data from two other
sites:  the "Latin Fields" School parking garage and the "Panda Mall" parking garage.  The Oak
report is important in that it "quantified" the received signals and multipath conditions present at
each of the Sinclair sites they visited.  That is, at each site, samples of both the COFDM and 8-
VSB signals were captured.

The "Latin Fields" site is described as a fairly open site about 4 miles from the station with no
direct line of sight.  The spectrum of the received signal at this location was described as "good"
with some ripple.  The channel impulse response showed significant multipath components at  18
dB at + 1 ms and  29 dB at +1.5 ms.  Both COFDM and 8-VSB reception were described as
good, with COFDM reception being more robust to antenna rotation.

At the "Panda Mall" site, the spectrum was described as highly shaped with a deep null indicating
a strong short delay echo.  The channel impulse response showed significant multipath
components at  10 dB at +0.5 ms, -25 dB at +1.5 ms, and  29 dB at +2 ms.  At this location, both
COFDM and 8-VSB reception were described as good.

The Oak report also provided some indication of the signal propagation at the two sites visited by
OET staff.  The spectrum was described as "poor" at the Lombard street site.  The channel
impulse response showed many significant multipath components.  In particular, significant
multipath components were found at  8 dB at  0.5 ms, -14 dB at +0.5 ms, -16 dB at +0.8 ms, -25
dB at +9.5 ms, with additional multipath components from  25 to  30 dB at +2 to +5 ms and at
about  30 dB at +10 to +13ms.  At this location, Oak reports no reception with the "bow tie"
antenna for 8-VSB.  (Although, as indicated above, during the OET staff visit, 8-VSB reception
was achieved.)  COFDM reception was achieved, but with artifacts on one receiver.  At the Lee
Street apartment, Oak describes the spectrum as poor with many deep nulls indicating long delay
echoes.  The channel impulse response indicated "lots of multipath" with the most significant
paths at  12 dB at +0.3 ms, -4 dB at +3.5 ms, -7 dB at +4.4 ms, -15 dB at +9.5 ms, -22 dB at 12.7
ms and  17 dB at +17.2 us.  Oak reported COFDM reception via one of the set-top boxes and no
8-VSB reception at this site.  

In summary, Oak notes that there was considerable variation in signal strength at the three
outdoor sites and that far less variation was seen at the apartment site due to its elevated location. 
Oak states that "although the channel impulse responses are quite interesting, they do not appear
to be particularly 'bad.' That is, we believe that at all locations both COFDM and VSB should be
receivable given an appropriately designed receiver."

OET staff conversations with various manufacturers seem to confirm Oak's conclusion that 8-
VSB receivers can be designed to operate in the environments found in the Sinclair
demonstration.  As indicated below, several manufacturers, e.g., Harris, Hitachi, Thompson and
Zenith, have used this data (or similar data taken in their own tests at some of the Sinclair sites) to
simulate the reception conditions of the Sinclair demonstration.  These manufacturers have stated
that their existing or future equipment would perform satisfactorily under these conditions. 
Sinclair has also stated that they may be cooperating with a chipset manufacturer in further testing
of 8-VSB reception.
 

                       8-VSB Field Tests

In addition to the Sinclair demonstration, field tests of the 8-VSB system have been conducted in
a number of cities.  These tests have been conducted by broadcasters, transmitter suppliers,
receiver manufacturers and others to gain experience with the DTV system and to provide
information for improving the performance of transmitter and receiver hardware.  As reported in a
paper by Gary Sgrignoli of Zenith, a total of 2682 outdoor sites in nine cities and 242 indoor sites
in five cities have been evaluated in these tests.  These tests provide data on 8-VSB performance
in a variety of urban, suburban and rural environments. Other tests are currently under way in
additional locations.  

A summary of these tests is presented in following table:


City
Chan.
Outdoor Sites
Indoor Sites




No. Sites
Pctg. >
Threshld.
Avail.
Pctg.
No. Sites
Pctg. >
Threshld.
Avail.
Pctg.


Charlotte (I)
53
199
95.5
91.5
32
90.6
75.0


Charlotte (II)
6
169
100
82.2





Raleigh
32
163
93.9
89.6
36
91.7
80.6


Chicago
20
112
99.1
92.9
10
100
100


San Jose
52
80
96.3
95.0





New York
56
158
91.1
80.4





Washington, D.C. (I)
30
333
89.9
78.7
67
82.9
40.6


Washington, D.C. (II)
34
279
65.3
63.0
67
56.2
31.2


Seattle (I)
38
399
88.0
68.7


                 
                 
                 
             


Seattle (II)
48
404
88.4
67.8





The above table shows the city in which each test was conducted, the TV channel used, and, for
both indoor and outdoor measurements, the number of sites where measurements were taken, the
percentage of sites with received signal-to-noise (S/N) ratio above the 15 dB 8-VSB operating
threshold, and the percentage of sites at which service was actually available.

The data in the table is grouped by those cities with a small-to-moderate percentage of obstructed
sites (less than about 25 percent), i.e., Charlotte, Raleigh, Chicago, San Jose, and New York) and
those with a large percentage of obstructed sites (38-64 percent), i.e., Washington, D.C. and
Seattle.  Stations in the first group had transmitter antenna height above average terrain (antenna
HAAT) of over 1000 feet and generally smooth terrain.  Those in group two had antenna HAAT
less than 800 feet and generally hilly terrain.

The field test data generally show good performance for 8-VSB for outdoor reception.  These
studies show outdoor service availability of 80-95 percent for cities with a small to moderate
percentage of obstructed sites and 63-79 percent for cities with a large percentage of
obstructions.

The field test data also indicate that indoor reception of DTV signals is more challenging.  Indoor
service availability ranged from 75-100 percent in cities with a small to moderate percentage of
obstructed sites and from 31-40 percent in markets with a large percentage of obstructed sites. 
Sgrignoli suggests that indoor reception problems are generally due to lower signal strength
(caused by lower antenna height, building penetration losses, and lower antenna gain), more
multipath (more reflecting objects and less directional antennas), and moving objects that obstruct
and reflect signals (people and vehicles).   

Sgrignoli concludes that the above test results indicate that 8-VSB DTV service availability will
approach that of NTSC service in most instances.  He also states that DTV receiver
implementation will continue to improve as second and third generation models become available
in the market.


                      Reports in the Press

Newspaper reports of the Sinclair demonstration and concerns were typified in an article in the
New York Times (Times article).   The Times article highlighted the problems Sinclair says it
found with indoor reception of DTV signals.  It noted that the problem with the current system is
multipath distortion from reflected signals.  The Times article described how in the demonstration
it was necessary to carefully aim the antenna to receive 8-VSB service, while it was very easy to
receive COFDM service.  The article reported that one broadcaster viewing the demonstration
stated that "You have to work to find a signal" with the 8-VSB system, "and have to work to lose
it" with the other.  It indicated that Sinclair seeks to revise the DTV standard and that if it is
successful, much of the new DTV equipment that consumers and stations have already purchased
would be rendered obsolete.  The article went on to state that Sinclair intends to ask other TV
station group owners to sign a petition to the FCC requesting that it consider the standards issue. 


The Times article also reported that supporters of the current system argued that the Sinclair
demonstration was flawed because it stressed the advantages of the COFDM system without
addressing the trade-offs and disadvantages.  It further described supporters' statements that the
demonstration used first-generation 8-VSB receivers and that manufacturers would improve the
performance of their receivers in subsequent generations.  It also noted that the 8-VSB system
had been extensively tested and found to perform "magnificently."  The Times article indicated
that Sinclair could have trouble enlisting the support of a large group of broadcasters, noting the
National Association of Broadcasters had not heard from other broadcasters indicating that they
wanted to revise the DTV standard.

The trade press published a number of articles on the 8-VSB/COFDM controversy.  An article in
Broadcasting & Cable (Broadcasting article) reported that some broadcasters, led by Sinclair,
feared loss of service to viewers unwilling or unable to mount an outdoor antenna or subscribe to
cable service.  The Broadcasting article stated that the first generation of DTV receivers do a far
worse job of receiving pictures than a "$79 black-and-white sitting on the kitchen counter."  The
article further reports that Sinclair is concerned that the reception problem threatens the
potentially lucrative business for broadcasters of transmitting data to computers, particularly
laptops and other portable devices.  It quotes David Smith, President and CEO of Sinclair, as
saying of DTV "Today, it does not work."  It further indicates that within the next 60 days,
Sinclair intends to petition the FCC to either impose DTV receiver standards to improve reception
or reconsider 8-VSB as the U.S. standard. 

The Broadcasting article next reports on the side-by-side tests in the Sinclair demonstration and
the reactions of those observing the demonstration.  Typical comments of those observers
indicated that the COFDM system "just worked better.  It was difficult or impossible to get 8-
VSB in some cases, and it was not that way with COFDM."  One of those observers stated that
while "it's impossible to draw any conclusions from the Sinclair tests, he would like to see more
research into the merits of 8-VSB and COFDM, and sooner rather than later."  The article states
that Sinclair points out that the COFDM system can also support mobile reception -something
that 8-VSB was not designed for.  In response, supporters of the 8-VSB system note that not
many people watch TV while driving along.

Reporting the general reactions of broadcast engineers, the Broadcasting article indicates that
most aren't sure if the 8-VSB standard is actually inadequate for indoor reception or whether the
Sinclair demonstration simply reflects the shortcomings of the first generation DTV receivers that
were rushed to market last fall.  Other reactions from broadcast engineers were typified in the
statements by Andy Setos of Fox that "we didn't learn much new" and "we know chips are being
developed to address those matters."  The article reports that receiver manufacturers view this as
a receiver issue, not a system issue and indicate that their second generation 8-VSB receivers,
some of which are on the market now, offer a significant improvement in their ability to handle
multipath.  The Broadcasting article also reports that most manufacturers and broadcasters
pointed out that COFDM's multipath performance comes with the trade-off that its carrier-to-
noise threshold is greater than that of 8-VSB (5 dB higher), and that this means COFDM does not
reach out as far as 8-VSB.  It reports that the engineers stated that to achieve the same reach
would require more than twice the power as 8-VSB, with larger transmitters, larger electric bills,
and perhaps an overhaul of the DTV Table of Allotments. 

The Broadcasting article indicates that Sinclair's stance seems to appeal to some smaller station
groups that aren't sure they'll get digital carriage by cable systems.  In this regard, a spokesman
for Pappas Telecasting is quoted:  "The concept we were sold was broadcast replication, and
that's based on signal strength.  But it appears you don't have replication if you can't receive the
signal at the same locations as you receive an NTSC signal you'd be willing to watch."  The
Broadcasting article says that with the exception of Fox, the major networks have been quiet on
the DTV debate.  It states that CBS and ABC are conducting indoor tests of 8-VSB reception. 
The Broadcasting article closes with a statement by Craig Tanner of the ATSC that "What
Sinclair is doing fundamentally is communicating to the world that they believe in a different set of
requirements for digital broadcasting.  It remains to be seen whether anyone agrees with them and
whether the industry as a whole can come to a consensus."

Several other articles in the trade press have reported information essentially similar to that in the
Times and Broadcasting articles.

                                
           Information from Industry Representatives

OET staff also had discussions on these matters with a number of industry representatives who
are variously knowledgeable about the DTV standard, the 8-VSB and COFDM transmission
systems, DTV receiver performance, the Sinclair demonstration, and television stations' DTV
implementation plans.  These parties included representatives of broadcast trade associations,
television networks, television stations, television station equipment manufacturers, consumer
electronics (CE) manufacturers, and others.

General Views on the Transmission Standard Issue  

With the exception of Sinclair, the industry representatives we spoke with indicated that they
continue to support the 8-VSB system as the DTV transmission standard.  These parties generally
stated that all of the factors that have been identified regarding COFDM performance in the
demonstrations conducted by Sinclair were well understood and considered at the time the DTV
transmission system decision was made.  For example, Ed Milbourn of Thomson stated that there
were no surprises in the Sinclair demonstration.  He and others stated that there were trade-offs in
the potential performance characteristics of the candidate transmission systems, and that these
tradeoffs were balanced in making the transmission system decision.  They acknowledged that the
design of the COFDM approach does have some inherent advantages over the 8-VSB design in
handling multipath, and in particular the dynamic multipath that is typically seen in mobile
operations.  However, they also stated that the performance of 8-VSB in handling static multipath
can be very close to that of COFDM.  Those supporting the 8-VSB system said that they believe
that the dramatic performance differences between 8-VSB and COFDM observed in the Sinclair
demonstrations are the result of the relatively poor multipath signal handling capabilities of the
first-generation VSB receivers used in those tests, rather than a limitation of the VSB system. 
Lynn Claudy of the NAB, Victor Tawil of MSTV, Bruce Allen of Harris Corporation and others
stated that they are comfortable that the 8-VSB system has plenty of potential to provide
satisfactory service and that manufacturers simply need to improve the multipath handling
capabilities of DTV receivers.  

In a follow-up conversation with Sinclair, Nat Ostroff discussed additional work that Sinclair had
done with its demonstration project.  He indicated that Sinclair has now completed observations
on a total of 40 sites in the Baltimore area, with 12 of these sites located near the edge of the
demonstration's predicted DTV service area.  Ostroff indicated that they found no indoor sites
where antenna pointing was not a significant factor in obtaining satisfactory reception of 8-VSB
DTV service.  He also observed that the necessity to re-orient the antenna to receive stations at
different locations would be a significant impediment to DTV "channel surfing."  Ostroff stated
that at their edge of service sites, there were no locations where 8-VSB was significantly easier to
receive than COFDM.  He therefore discounted the concern that the 8-VSB advantage in carrier-
to-noise ratio would be an important factor in the range at which service could be received. 
Rather, he stated that other impairments in the path of far reception seemed to swamp the C/N
advantage of 8-VSB.

Ostroff also indicated that Sinclair is pleased that the industry, both broadcasters and consumer
electronics manufacturers are paying more attention to the improvement of DTV receiver
performance.  He noted that in a little more than two months, the atmosphere has gone from
denial of the problem to acceptance that action is needed and to resistance to use of the outdoor
reception model for DTV.  He stated that the announcement of the Motorola and NxtWave DTV
demodulator chips with improved multipath handling performance is very encouraging.  In this
regard, he stated that he has invited NxtWave to verify the performance of their new chipset at the
sites used in the Sinclair tests this September.  Ostroff indicated that if the new chips work, we
may be beginning to see the light at the end of the tunnel on this problem.

Some broadcasters expressed the viewpoint that the important issue is that DTV receiving
equipment needs to provide satisfactory service from off-the-air signals when consumers bring it
home and place it in operation. These parties stated that broadcast DTV service has to work when
people buy equipment or else the service will fail.  One party offered the view that supporters of
COFDM have made that technology work well, so why hasn't the same happened with 8-VSB? 
He stated that broadcasters have been making their share of investments in DTV, and that CE
manufacturers need to close the gap on their side.  Dave Converse of ABC's Owned TV Station
Group indicated that his organization was not surprised by what they saw at the Sinclair
demonstration and they have not reached a position on whether any changes or actions are
needed.

Industry Views on the Sinclair Demonstration  

The industry representatives who viewed the Sinclair demonstration agreed that the performance
of the COFDM set-up was significantly better than that of the 8-VSB.  They also agreed that the
observed differences were due to the presence of multipath at the selected observation sites. 
However, many of these parties also offered explanations as to why such significant differences
were observed.  All of the industry representatives  agreed that the demonstration, while not
scientific, shows that the 8-VSB receivers currently available do not perform well in conditions of
strong multipath signals and that the available COFDM equipment is able to work in such
situations. John Henderson of Hitachi and Bruce Allen of Harris indicated that they had made
their own measurements and observations at some of the locations used for the Sinclair
demonstration.  They indicated that at the sites selected by Sinclair, the problem affecting
reception was very strong levels of multipath signals.  They stated that these locations had very
strong ghosts, both leading and trailing, that were outside of the correction range of the 8-VSB
receivers Sinclair used.  The parties also noted that NTSC service of acceptable quality was not
available at the Sinclair sites.  Several parties familiar with the performance of the available 8-
VSB receivers stated that Sinclair used models with the poorest multipath performance.

Henderson indicated that while he didn't feel that Sinclair had picked particularly "bad" locations,
he didn't see similarly strong ghosts when he used his equipment to examine the performance of
the 8-VSB signals of operating DTV stations in other markets, including New York.  Allen stated
that Harris felt that the sites chosen for the demonstration were not typical even for an urban
environment, and that in fact only a very small percentage of sites would have the strong signal
and strong multipath levels exhibited in the Sinclair sites.

Both Henderson and Allen also offered a critical analysis of various elements of the Sinclair
demonstration.  First, they stated that the COFDM system used by Sinclair had a data
transmission rate less than that of the 19.4 Mbps rate of the 8-VSB system.  They indicated that
this allows for longer guard intervals in the COFDM signal, which improves reception under
multipath conditions.  Henderson and Allen stated that a COFDM configuration with higher data
rate would not have operated as well.  Allen indicated that neither the 8-VSB signals nor the
COFDM signals met the FCC DTV emissions mask, and that the COFDM emissions exceeded the
mask by more than those of the 8-VSB signal.  He indicated that the Harris tests used a DTV
receiver with a better adaptive equalizer and tuner (second generation) than the units used by
Sinclair, and that they were able to receive 8-VSB service at all of the Sinclair sites.  However, he
indicates that Harris did have to point its antenna.

COFDM vs. 8-VSB  

Industry representatives stated that, in theory, the 8-VSB and COFDM systems should be able to
perform nearly the same in providing service where there is static multipath but that COFDM can
generally be expected to perform better in situations where there is dynamic multipath, e.g., in
mobile operations.  These parties stated that with 8-VSB, multipath reflection, or ghosting, is
processed through an adaptive equalizer and more complex equalizers are needed to handle
stronger reflections and longer intervals of reflection.  Wayne Luplow of Zenith stated that in
practice, COFDM will always perform a little better where there is a strong main signal and a
ghost that is almost as strong.  Allen similarly indicated that COFDM will perform better with
dynamic multipath and with static multipath where the reflection is less than 4 dB down from the
main signal.

As described by Allen, Tawil and others, 8-VSB offers a number of advantages over COFDM for
broadcast DTV service.  First, despite Sinclair's claim that the C/N advantage of 8-VSB is
mitigated by other factors, these parties maintained that 8-VSB offers superior overall coverage. 
Harris, for example, stated that COFDM would require substantially more power than 8-VSB (6
dB, or four times, more power than 8-VSB) to serve the same area.  These parties state that
broadcasters using COFDM would therefore be faced with losing substantial coverage, or
incurring significantly higher costs for more powerful transmitters and additional electric power
for operation.  Harris stated that the additional power is needed because COFDM has a higher
C/N threshold than 8-VSB and because it operates with a higher peak-to-average signal power
ratio than 8-VSB.
     
Harris also argued that 8-VSB operation is significantly more cost effective.  It indicated that
COFDM station construction costs would be higher because of the need for a more powerful
transmitter, heavier antenna and transmission lines, and possibly a stronger tower or tower
strengthening.  In addition, the cost of operating the station would increase, because more electric
power would be used.  Harris estimates that the cost of construction to increase from 50 kW to
200 kW operation would be $600,000, and that the annual operating costs of such a station would
increase $65,000.  As a second example, Harris estimates that the construction cost to increase
from 250 kW to 1 MW would be $950,000, and that the annual operating costs of such a station
would increase by $227,000.  In this regard, Harris specifically refuted Sinclair's claim that
converting to COFDM would only cost broadcasters the $50,000 price of a new COFDM exciter. 


A number of parties also suggested that 8-VSB is more immune to impulse noise than COFDM. 
Ed Kott of Philips indicated that there have been significant problems of interference from impulse
noise (RF noise from vacuum cleaners, hair dryers, light dimmers, power lines, etc.) to COFDM
service in Great Britain.  Allen indicated that COFDM is 8 dB more susceptible to impulse noise
commonly found in consumer homes.  He indicated that impulse noise occurs particularly in the
VHF band and the lower portion of the UHF band, and that low band VHF channels in particular
would suffer a significant loss of coverage if COFDM were used.

Harris stated that the data throughput for COFDM DTV operation in a 6 MHz channel would be
less than the 19.4 Mbps provided with 8-VSB operation.  They stated that this difference makes
8-VSB more efficient for data applications, including emerging broadband services, as well as
more suitable for HDTV programming.  Harris indicated that the higher data capacity also enables
8-VSB to provide other services, such as multichannel video and ancillary data, more efficiently. 
The Harris staff also suggested that in order to replicate existing NTSC service with COFDM it
might be necessary to revisit the DTV Table of Allotments.  

Improvements in 8-VSB Performance  

Most of the parties we spoke with asserted that 8-VSB receivers that perform better than the
units used in the demonstration are, in fact, available now.  That is, other models are already
available that can provide acceptable service at the Sinclair locations.  However, those receivers
would still need to have their antenna properly oriented to provide service at the Sinclair
locations.  The CE manufacturers we spoke with all indicated that they are working on improving
their 8-VSB receivers, particularly the adaptive equalizer section of those devices that correct for
multipath.  They stated that these improvements are part of ongoing efforts in product
development that were well underway before the current controversy arose.  In this regard, they
indicated that they were well aware of the less than optimal multipath performance characteristics
of their current products and not surprised by the observations made in Sinclair's demonstration. 
The CE manufacturers all viewed multipath performance as an issue that will be worked out in the
normal process of improving new products.  They were all very confident that they could, and
would, produce equipment that would provide satisfactory reception of 8-VSB signals in the
presence of complex multipath conditions. 

Peter Fannon of Panasonic, Ed Kott of Philips, Wayne Luplow of Zenith, Ian Matthews of Sony,
and Ed Milbourn of Thomson indicated that their second generation receivers, many of which will
be available for this Christmas sales season, will provide substantially better multipath handling
capability.  They further indicated that their third generation models, to be available in the future,
will have further improvements.  One party indicates that his firm's third generation equipment
will be able to process reflections of as much as 40 ms difference from the main signal and will
have faster processing capability for handling dynamic multipath.  Luplow indicated that in the
"concrete canyons" of central urban areas he expects there will be only a small percentage of
locations where COFDM would work better than 8-VSB.  He also indicated that he thinks it will
always be necessary to do some antenna pointing in indoor environments.  Luplow and  Milbourn
stated that manufacturers are already developing DTV antennas that are electronically steerable by
the receiver itself, so that consumers will not have to do this manually as they do with current
rabbit ear and loop antennas.

Recently, both NxtWave and Motorola announced new VSB demodulator chips that offer
improved performance.  The NxtWave chip claims to be able to cancel ghosts of  - 4.5 to + 44.6
ms.   The Motorola chip is said to be able to correct ghosts of  - 2.9 to + 41 ms.  


                 Evaluation and Recommendations

While the Sinclair demonstration has raised the debate between COFDM and 8-VSB, this issue is
not new.  In 1995, it was stated that the "   debate on COFDM versus vestigial sideband (VSB)
modulation or quadrature amplitude modulation (QAM) has been engaged in the past and there is
no sign that it will end soon.  One reason is that neither COFDM nor VSB has a clear advantage
in all of the performance aspects."  In our opinion, that conclusion is still valid today.

Evaluation of 8-VSB and COFDM 

As discussed below, our analysis finds that each system has its unique advantages and
disadvantages.  The ATSC 8-VSB system, in general, has better threshold or carrier-to-noise
(C/N) performance, has a higher data rate capability, requires less transmitter power for
equivalent coverage, and is more robust to impulse and phase noise.  The COFDM system has
better performance in both dynamic and high level (up to 0 dB), long delay static multipath
situations.   The COFDM system may also offer advantages for single frequency networks and
mobile reception.    

Threshold and Service Area /Interference Performance.  As indicated above, COFDM has an
advantage close to the transmitter with regard to strong multipath signals and 8-VSB has an
advantage with regard to service threshold and fringe area coverage.  The following table shows
estimates of the difference in service availability between COFDM and 8-VSB operation in the
top 10 TV markets:

                Service Availability Comparison


City


                              (1)
                           VSB Total
                              Pop.
                                
                              (2)
                             Urban
                          Center Pop.
                                
                              (3)
                             COFDM
                             Urban
                           Advantage
                              (4)
                           VSB Fringe
                           Advantage
                                
                              (5)
                              Net.
                           Advantage
                                
                              (6)
                            Percent
                          Gain/(Loss)
                            w/ COFDM
                              (7)
                                
                                
                            New York
                           18,199,417
                           1,466,538
                            586,615
                            310,132
                          (C)  150,971
                              0.83
                                
                                
                          Los Angeles
                           14,332,652
                            178,304
                             71,232
                            136,273
                          (V)  65,041
                             (0.45)
                                
                                
                            Chicago
                           8,395,277
                            177,294
                             70,918
                             94,939
                          (V)  24,021
                             (0.29)
                                
                                
                          Philadelphia
                           8,011,757
                            469,872
                            187,949
                            315,846
                          (V)  127,897
                             (1.60)
                                
                                
                             Boston
                           6,485,082
                            211,469
                             84,588
                            134,438
                          (V)  49,850
                             (0.77)
                                
                                
                         San Francisco
                           6,207,475
                            145,364
                             58,146
                            125,618
                          (V)  67,472
                             (1.09)
                                
                                
                        Washington, D.C.
                           6,183,756
                            112,763
                             45,105
                            114,849
                          (V)  69,744
                             (1.13)
                                
                                
                            Detroit
                           5,089,907
                            169,784
                             84,892
                            130,002
                          (V)  45,110
                             (0.89)
                                
                                
                        Dallas/Ft. Worth
                           4,157,223
                            484,778
                            193,911
                             40,542
                          (C)  153,369
                              3.69
                                
                                
                            Atlanta
                           3,282,147
                            383,239
                            153,296
                             67,005
                         (C)  86,291  
                              2.63
                                
                                
                                
The above Table compares estimated COFDM service advantages in the downtown urban centers
of the major markets and estimated  8-VSB advantages in the outer fringe service areas of those
markets.  Column (6) of the table shows the net advantage in population served for COFDM or 8-
VSB  and column (7) shows the percentage gain or loss that could be expected from COFDM
operation.  Column (2) shows the average population predicted to be served by DTV stations in
the market with 8-VSB service.  Column (3) shows the urban center population.  Column (4)
shows the COFDM urban advantage in population served.  The COFDM urban advantage is
based on an assumption that 80 percent of the urban center population would have a COFDM
signal above threshold and that 50 percent of these locations would be faced with a difficult
multipath situation where COFDM would work and it is assumed 8-VSB would not.  Column
(5) shows the 8-VSB fringe advantage in population served.  The VSB fringe advantage is based
on the assumptions that there is a 4 dB transmitter power advantage for 8-VSB that extends
coverage beyond that provided by COFDM and that 50 percent of the population in this extended
coverage area could receive service with 8-VSB but not with COFDM. 
                                
We recognize that the service area comparison estimates provide only a rough measure of the
relative performance advantages of the two systems.  Nevertheless, these estimates would appear
to indicate that the relative advantages/disadvantages of either system with regard to overall
       coverage are generally small and vary by market. 
                                
We also investigated the impact on interference to existing NTSC stations of increasing the power
of DTV stations by 4 dB in order to make up for the disadvantage of COFDM for fringe
reception noted above.  This analysis indicates that if the 1 MW cap is retained, the overall
increase in interference to NTSC service would be generally small.  Most NTSC stations would
receive 1 percent or less additional interference to their predicted service area.  However, for a
small number of NTSC stations, population service loss would be more significant.  This analysis
assumes that COFDM would have interference characteristics with respect to interference to
NTSC similar to 8-VSB, i.e., would appear like random noise.  We believe that this is a
reasonable assumption, but further study and testing is needed to confirm the interference
characteristics of COFDM.  Further study would also be needed to examine whether COFDM
could support satisfactory service on VHF and lower UHF channels due to impulse noise
concerns.  At this time, it is unclear whether any changes in the DTV Table of Allotments would
          be needed to accommodate a change to COFDM.
                                
Multipath Performance.  As noted above, COFDM systems avoid multipath interference by
having a sufficient guard interval between symbols and the 8-VSB system must have an adaptive
equalizer of sufficient length.  From the Oak report, the principal propagation phenomena at the
Sinclair demonstration was strong static multipath, with all of the significant multipath
components between  0.5 ms and about +23 ms.  The guard interval for the DVB-T COFDM
system used in the Sinclair test was about 37 ms.  Reflections within this interval should be able to
be rejected, and the demonstration showed good performance for COFDM in this regard.  
                                
With regard to 8-VSB, Sgrignoli states that the choice of equalizer length is very important for 8-
VSB receivers, and that the optimal design is still under investigation.  He indicates that the initial
estimate of 22 ms seems to be a reasonable minimum equalizer range for now, but that a longer
ghost canceling range may be beneficial.  While we do not have quantitative measurements on the
8-VSB DTV receivers used in the Sinclair test, it has been implied that these receivers did not
meet this value and that their adaptive equalizer performance was actually in the range of about
10 ms or less.  This appears to be a reasonable explanation for the relatively poor performance of
          the 8-VSB receivers in the Sinclair test.   
                                
While the Sinclair demonstration has provided some useful insight into certain indoor reception
conditions and possible deficiencies of some early DTV receiver designs, it appears that these
reception problems are readily solvable.  All of the CE manufacturers we talked to indicated that
problems in receiving service in the presence of strong static ghosts could be solved with an
improved adaptive equalizer performance.  We believe that an 8-VSB receiver designed receiver
to incorporate the 22 ms minimum equalizer range suggested by Sgrignoli should be able to
provide satisfactory reception at the Sinclair locations.  Furthermore, given the recent
announcements regarding the availability of improved chips that exceed this specification, we
believe it is reasonable to conclude that manufacturers are addressing and will solve this problem
in the near future.  We expect that, as with most products, performance improvements in DTV
        receivers will continue to be made over time.  
                                
Indoor Reception. To date, there has been only limited testing using indoor antennas.  In this
regard, there appears to be a general consensus that indoor DTV reception needs further
investigation.  The Sinclair demonstration has highlighted the effects of multipath.  However, 
signal strength and immunity to interference from impulse noise are also important factors in
                 successful indoor reception.  
                                
We note that, in general, there will always be a portion of indoor locations where a threshold
signal will not be available.  This is also the case with NTSC analog TV service.  In the limited
indoor testing reported by Sgrignoli, the percentage of sites where the field strength was below
the minimum threshold level needed for service varied across markets from 8 to 44 percent. 
Given the current 3.5 dB higher threshold signal required for successful COFDM operation, we
would expect that the overall number of locations where service was not available due to
insufficient signal strength would be higher with COFDM.  And, in effect, the overall number of
locations that would need to use outdoor antennas would increase.    
                                
 Impulse noise interference occurs predominantly in VHF and low UHF bands and is caused by
industrial equipment, home appliances such as vacuum cleaners, light dimmers, microwave ovens,
etc., and high voltage power lines.  The DVB-T system is more susceptible to impulse
interference than 8-VSB and there is some anecdotal information from the United Kingdom that
DVB-T has experienced some difficulties in this regard.  In view of these considerations and the
projected improvements in 8-VSB adaptive equalizers, we believe that, while multipath may be
the most significant factor affecting indoor reception of DTV service, further study would be
needed before it could be concluded that COFDM has a significant overall advantage over 8-VSB
                     for indoor reception.
                                
In its demonstration, Sinclair also contends that service is acceptable where reception is achieved
over a complete 360 degrees rotation of a simple bow-tie antenna, i.e., no antenna pointing is
necessary.  We disagree with this position.  While it is certainly desirable to avoid the need for
manual antenna orientation, it is also reasonable to expect viewers to perform some antenna
orientation, similar to what is done today for existing NTSC analog television.  Based on our
discussions with CE manufacturers, we believe that reasonable solutions to the indoor reception
problems are being developed.  These products will include not only receivers with improved
adaptive equalizers but also new electronically pointable, or "steerable," indoor antennas that are
           controlled automatically by the receiver.
                                
Mobile and Single Frequency Network Operation.  COFDM has an advantage in its ability to
support large single frequency network operation and mobile operation over large geographic
areas.  For example, this would allow use of a single channel to provide the same programming
concurrently over a very wide area, perhaps an entire country, and in this way could better
support mobile service.  In this regard, such an approach would avoid the problem of leaving the
service area of an individual station during a program while travelling.  This is the approach that
some European countries are pursuing.  However, to implement this approach in the United
States would necessitate a substantial change to structure of the broadcast industry and the way it
                         is regulated.
                                
COFDM may also offer an advantage with regard to mobile data operation within the service area
of a TV station.  This could be used to provide data and other communications to palm-top
computers and other hand-held devices.  However, trade-offs would have to be made between the
rate of data transmission and the range of service.  In general, a station's mobile service range
would be less than its current projected DTV service area, and at higher data rates, i.e., above 18
             Mbps, it would be substantially less. 
                                
Data Rate.  In COFDM, the spectrum of the transmitted signal is sharply confined in frequency
because it is the sum of equally spaced subchannel signals, each of which is sharply confined. 
Therefore, a COFDM system can have a higher occupied bandwidth than 8-VSB, which is limited
to an occupied bandwidth of 5.38 MHz due to the Nyquist roll-off criteria needed to fit into the 6
                    MHz channels available. 
                                
The 6 MHz DVB-T COFDM system used in the Sinclair demonstration had an occupied 
bandwidth of 5.7 MHz.  This provided an effective data rate for the system of 18.66 Mbps or 4
percent less than the 19.39 Mbps for 8-VSB.  While COFDM systems can have higher occupied
bandwidths than the 5.38 MHz of 8-VSB, we believe that the 5.7 MHz occupied bandwidth of the
equipment used by Sinclair may be overly ambitious.  Previous studies have suggested that to
provide the same adjacent channel interference performance as 8-VSB, a COFDM system would
have to limit its occupied bandwidth to 5.625 MHz or less.  This would result in a slight
reduction in the 18.66 Mbps data rate available and would suggest that ATSC 8-VSB would have
about a 5 percent data rate advantage over the DVB-T 6 MHz COFDM system used by Sinclair.  
                                
While a 5 percent data rate difference is relatively small, it could have some impact on the ability
to provide certain high definition television programming.   The DVB-T COFDM system is very
flexible and the data rate can be increased by increasing the coding rate and/or by shortening the
guard interval.  These changes, however, would affect system performance.  Specifically,
increasing the coding rate would have a C/N penalty and decreasing the guard interval would have
             a penalty in multipath performance.  
                                
Summary/Recommendation

Both 8-VSB and COFDM have certain advantages and disadvantages.  Both systems are capable
of providing viable DTV service.  We do not find that at this time the performance potential of
either system is clearly superior in all respects.  Based on our discussions with CE manufacturers
and recent announcements by semiconductor manufacturers, we believe that reasonable solutions
to the multipath issue and indoor reception problems raised by Sinclair are being developed and
should be available in the near future.  We also believe that COFDM's benefits for large single
frequency network operation and mobile service may not be important or meaningful given the
current structure of broadcasting in the United States.  Further, we believe that 8-VSB has some
advantages with regard to data rate, spectrum efficiency and transmitter power requirements. 
Accordingly, at this time, we find that the relative benefits of changing the DTV transmission to
COFDM are unclear and would not outweigh the costs of making such a revision.  We therefore
recommend that the ATSC 8-VSB standard be retained.