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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

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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

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 s 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 s 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.[^1] 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.[^2] 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.[^3] 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.[^4]
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.[^5] That system operated with 1705 subcarriers and 64
QAM, and provided a useable data rate of 18.66 Mbps.[^6] More detailed
descriptions of both COFDM and 8-VSB are provided in the attached
Appendix.

[History of COFDM]{.underline}

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.[^7] 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.[^8]
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.[^9] 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.[^10]

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.[^11] 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.[^12] 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.[^13]

Sinclair invited broadcasters, equipment manufacturers, the press and
others to observe its demonstration. Engineers from OET attended the
demonstration on June 29, 1999.[^14] 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.[^15]
The bandwidth occupancy was 5.7 MHz for COFDM and 5.38 MHz for
8-VSB.[^16] 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.[^17]
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.[^18] 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.[^19] 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 11^th^ 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.[^20] The report documents reception results at 40 sites in the
Baltimore area.[^21] 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.[^22] 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 s and --29 dB at +1.5 s.[^23] 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 s, -25 dB at +1.5 s, and --29 dB at +2 s. 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 s, -14 dB at +0.5 s,
-16 dB at +0.8 s, -25 dB at +9.5 s, with additional multipath components
from --25 to --30 dB at +2 to +5 s and at about --30 dB at +10 to +13s.
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 s, -4 dB at +3.5 s, -7 dB at +4.4
s, -15 dB at +9.5 s, -22 dB at 12.7 s 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.[^24]

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.[^25] 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            | C  | Out  |      |      | In   |      |      |
|                 | ha | door |      |      | door |      |      |
|                 | n. | S    |      |      | S    |      |      |
|                 |    | ites |      |      | ites |      |      |
+=================+====+======+======+======+======+======+======+
|                 |    | No.  | P    | Av   | No.  | P    | Av   |
|                 |    | S    | ctg. | ail. | S    | ctg. | ail. |
|                 |    | ites | \>   | P    | ites | \>   | P    |
|                 |    |      |      | ctg. |      | T    | ctg. |
|                 |    |      | T    |      |      | hres |      |
|                 |    |      | hres |      |      | hld. |      |
|                 |    |      | hld. |      |      |      |      |
+-----------------+----+------+------+------+------+------+------+
| 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,     | 30 | 333  | 89.9 | 78.7 | 67   | 82.9 | 40.6 |
| D.C. (I)        |    |      |      |      |      |      |      |
+-----------------+----+------+------+------+------+------+------+
| Washington,     | 34 | 279  | 65.3 | 63.0 | 67   | 56.2 | 31.2 |
| D.C. (II)       |    |      |      |      |      |      |      |
+-----------------+----+------+------+------+------+------+------+
| 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.[^26]

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.[^27] 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). [^28] 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.[^29] 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.[^30]

## 

## **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.[^31]

[General Views on the Transmission Standard Issue]{.underline}

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]{.underline}

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]{.underline} 

## 

## 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]{.underline}

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 s 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 s.[^32] The Motorola chip is said to be
able to correct ghosts of - 2.9 to + 41 s.[^33]

###### 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."[^34] In our
opinion, that conclusion is still valid today.

## [Evaluation of 8-VSB and COFDM]{.underline} 

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.[^35] The COFDM system may
also offer advantages for single frequency networks and mobile
reception.[^36]

### *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       | VSB    | Urban  | COFDM  | VSB    | Net.   | P      |
|            | Total  | Center | Urban  | Fringe | Adv    | ercent |
| \(1\)      | Pop.   | Pop.   | Adv    | Adv    | antage | G      |
|            |        |        | antage | antage |        | ain/(L |
|            | \(2\)  | \(3\)  |        |        | \(6\)  | oss)w/ |
|            |        |        | \(4\)  | \(5\)  |        | COFDM  |
|            |        |        |        |        |        |        |
|            |        |        |        |        |        | \(7\)  |
+============+========+========+========+========+========+========+
| New York   | 18,1   | 1,4    | 5      | 3      | \(C\)  | 0.83   |
|            | 99,417 | 66,538 | 86,615 | 10,132 | 1      |        |
|            |        |        |        |        | 50,971 |        |
+------------+--------+--------+--------+--------+--------+--------+
| Los        | 14,3   | 1      | 71,232 | 1      | \(V\)  | (0.45) |
| Angeles    | 32,652 | 78,304 |        | 36,273 | 65,041 |        |
+------------+--------+--------+--------+--------+--------+--------+
| Chicago    | 8,3    | 1      | 70,918 | 94,939 | \(V\)  | (0.29) |
|            | 95,277 | 77,294 |        |        | 24,021 |        |
+------------+--------+--------+--------+--------+--------+--------+
| Ph         | 8,0    | 4      | 1      | 3      | \(V\)  | (1.60) |
| iladelphia | 11,757 | 69,872 | 87,949 | 15,846 | 1      |        |
|            |        |        |        |        | 27,897 |        |
+------------+--------+--------+--------+--------+--------+--------+
| Boston     | 6,4    | 2      | 84,588 | 1      | \(V\)  | (0.77) |
|            | 85,082 | 11,469 |        | 34,438 | 49,850 |        |
+------------+--------+--------+--------+--------+--------+--------+
| San        | 6,2    | 1      | 58,146 | 1      | \(V\)  | (1.09) |
| Francisco  | 07,475 | 45,364 |        | 25,618 | 67,472 |        |
+------------+--------+--------+--------+--------+--------+--------+
| W          | 6,1    | 1      | 45,105 | 1      | \(V\)  | (1.13) |
| ashington, | 83,756 | 12,763 |        | 14,849 | 69,744 |        |
| D.C.       |        |        |        |        |        |        |
+------------+--------+--------+--------+--------+--------+--------+
| Detroit    | 5,0    | 1      | 84,892 | 1      | \(V\)  | (0.89) |
|            | 89,907 | 69,784 |        | 30,002 | 45,110 |        |
+------------+--------+--------+--------+--------+--------+--------+
| Dallas/Ft. | 4,1    | 4      | 1      | 40,542 | \(C\)  | 3.69   |
| Worth      | 57,223 | 84,778 | 93,911 |        | 1      |        |
|            |        |        |        |        | 53,369 |        |
+------------+--------+--------+--------+--------+--------+--------+
| Atlanta    | 3,2    | 3      | 1      | 67,005 | \(C\)  | 2.63   |
|            | 82,147 | 83,239 | 53,296 |        | 86,291 |        |
+------------+--------+--------+--------+--------+--------+--------+

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.[^37] 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.[^38] 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. [^39]

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.[^40] 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.[^41] 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 s and about +23 s. The guard interval for the DVB-T COFDM system used in the Sinclair test was about 37 s. 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 s 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 s or less. This appears to be a reasonable
explanation for the relatively poor performance of the 8-VSB receivers
in the Sinclair test. [^42]

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 s 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.[^43] 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.[^44] 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.[^45]

*[Mobile and Single Frequency Network Operation]{.underline}*. 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.[^46]

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.[^47]

*[Data Rate]{.underline}*. 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.[^48]
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.[^49] 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]{.underline}

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.

[^1]: The ATSC 8-VSB system provides " equalizer training sequences"
    every 24 milliseconds (ms) to assist the adaptive equalizer in the
    receiver to correct for fading and multipath. See Section 10.3,
    "Guide to the Use of the ATSC Television Standard," Doc. A/54, 4Oct
    95.

[^2]: Ensuring that the subcarriers are orthogonal to one another allows
    the signals to be separated at the receiver using correlation
    techniques. In general, rather than using arrays of oscillators and
    demodulators to create and decode the many subchannels, modern
    OFDM/COFDM systems employ the Discrete Fourier Transform as part of
    the modulation and demodulation process. Using this technique, both
    transmitter and receiver can be implemented using special purpose
    Fast Fourier Transform (FFT) hardware.

[^3]: "COFDM: An Overview," William Y. Zou, Public Broadcasting Service,
    Alexandria, VA and Yiyan Wu, Communications Research Centre, Ottawa,
    Canada, IEEE Transactions on Broadcasting, Vol. 41, No. 1, March
    1995.

[^4]: Multipath echoes generally arrive within a few tens of
    microseconds (s) of the main signal.

[^5]: The DVB Project is a consortium of public and private sector
    organizations. The European Telecommunications Standards Institute
    (ETSI) has adopted the formats developed by DVB as a European
    standard (ETSI EN 300 744 V1.2.1 (1999-07)).

[^6]: The DVB standard provides for two modes of operation, a 2K mode
    with 1705 subcarriers, and an 8K mode with 6817 subcarriers. The 2K
    mode is suitable for single transmitter operation and for small
    single frequency networks with limited transmitter distances. The 8K
    mode can be used for both single transmitter operation and for both
    small and large single frequency networks. ETSI EN 300 744 V1.2.1
    (1999-07), p. 9.

[^7]: A U.S. patent was issued for OFDM in 1970. [See]{.underline}, U.S.
    Patent 3,488,445, issued January 6, 1970.

[^8]: Under this concept, rather than a single high power transmitter, a
    number of lower power transmitters arranged in a cellular-like
    manner and operating on the same frequency is used to provide
    equivalent area coverage. See, for example, "Distributed
    Transmission Concept for ATV," Gerald Chouinard, Communications
    Research Centre, Communications Canada, Ottawa, Ontario, Canada,
    presented at MIT Workshop on Broadband Data Broadcasting, October
    26-27, 1992; and "New Coverage Concepts for Digital Terrestrial
    Television Broadcasting," Gerald Chouinard, Communications Research
    Centre, Communications Canada, Ottawa, Ontario, Canada, presented at
    the 18^th^ International Television Symposium, Montreaux,
    Switzerland, June 10-15, 1993.

[^9]: "Orthogonal Frequency Division Multiplexing: An Application to
    High Definition Television," George A. Hufford, NTIA Report 94-316,
    August, 1994.

[^10]: DVB is a consortium of public and private sector organizations.
    The European Telecommunications Standards Institute (ETSI) has
    adopted the formats developed by DVB as a European standard (ETSI EN
    300 744 V1.2.1(1999)).

[^11]: "Advisory Committee Final Report and Recommendations," FCC
    Advisory Committee on Advance Television Service, November 28, 1995.

[^12]: "Sinclair Launches Tests to Determine Viability of Current
    Digital Television Transmission Standard,"
    [http://www.sbgi.net](http://www.sbgi.net/) (August 16, 1999).

[^13]: Sinclair had previously conducted indoor reception tests in the
    Philadelphia, Pennsylvania area.

[^14]: Bruce Franca, Robert Bromery, and Robert Eckert of the FCC's OET
    attended the demonstration.

[^15]: *HDTV News Online*, article by Ed Williams of PBS,
    <http://web-star.com/hdtv/edwill.html> (August 16, 1999).

[^16]: Neither the COFDM nor the 8-VSB signals used for the
    demonstration complied with the out of band requirements contained
    in the FCC rules.

[^17]: Sinclair indicated that high definition program material was not
    available at the time for the format used by the COFDM receiver. For
    the purposes of the demonstration, additional random bits were
    transmitted to exercise the COFDM system and provide for full data
    payload of the system.

[^18]: A third location was not visited due to time constraints.

[^19]: At this location, the COFDM system did appear to contain some
    visual impairments or artifacts to at least one of the FCC engineers
    although it could not be determined whether this was due to the
    transmission or in the program material.

[^20]: "Comparative Reception Testing of 8VSB and COFDM In Baltimore,"
    Nat Ostroff and Mark Aitken, Sinclair Broadcast Group,
    [www.sbgi.net/DTV](http://www.sbgi.net/DTV), September 24, 1999.

[^21]: The Sinclair Report also notes that a number of additional sites
    were investigated and that while these sites were not documented the
    results at those sites are consistent with the 40 documented sites.

[^22]: "Report on Data Captured from Sinclair Broadcast Transmissions in
    the Area of Baltimore, USA," Jonathan Parker, Mat Collins, and Doug
    Pulley, Oak Technology Ltd., Bristol, U.K., July, 1999.

[^23]: Values are relative to 0 dB for the main path.

[^24]: Oak states that this is anecdotal information since the
    laboratory COFDM receiver was not used to verify reception of the
    signal.

[^25]: "Preliminary DTV Field Test Results and Their Effects on VSB
    Receiver Design," Gary Sgrinoli, Zenith Radio Electronics
    Corporation (Preliminary ICCE '99 Conference Paper). DTV field tests
    have been performed in nine cities, including Charlotte, Washington,
    D.C., Raleigh, Chicago, Seattle, New York, San Jose, Cincinnati, and
    Dallas.

[^26]: For indoor tests, the test location was chosen to be at an
    existing NTSC set with an indoor antenna within the home. If such a
    site was not present, then another site within the home was
    selected, typically in a corner of the living or family rooms, on in
    a bedroom.

[^27]: It can be inferred that the differences between the percentage of
    sites above threshold and the availability percentage generally
    indicate that reception was impaired by multipath, noise, and/or
    other propagation phenomena,

    since adequate signal strength was available for reception. We
    further note that the results in the Table reflect DTV testing that
    is in some instances based on transmitter powers and antenna heights
    that are substantially lower than would be used in providing
    permanent service. Accordingly, the Table results may underestimate
    the actual availability of DTV reception in those markets.

[^28]: *See* "Broadcaster Seeks Change in Digital TV Format," Joel
    Brinkley, *New York Times*, July 12, 1999.

[^29]: *See* "Back to the Future, " *Broadcasting &Cable*, August 2,
    1999.

[^30]: *See* "8-VSB -- Can It Be Fixed," *HDTV News Online*, July 16,
    1999; "Fallout From Sinclair Gambit On U.S. DTV Standard Lands On
    Receiver Makers," *Digital Technology Reports*, July 26, 1999;
    "8-VSB vs. COFDM: Debate Refuses to Go Away (but Should)," *TV
    Technology*, March 24, 1999 "Sinclair Re-examines COFDM Capability,"
    *TV Technology*, June 16, 1999; and "You Have to Receive to
    Believe," Bear, Stearns, & Co. Report, August 3, 1999.

[^31]: We wish to thank the following individuals for their assistance
    in providing information for this report: Bruce Allen (Harris
    Communications), Lynn Claudy (National Association of Broadcasters),
    Dave Converse (Owned TV Station Group of ABC, Inc.), Greg DePriest
    (Toshiba), Peter Fannon (Panasonic/Matshushita Electric), George
    Hanover and Ralph Justus (Consumer Electronics Manufacturers
    Association), John Henderson (Hitachi), Frank Kott (North American
    Philips Corporation), Wayne Luplow (Zenith Electronics Corporation),
    Ian Matthews (Sony), Andy Setos (Fox Television Stations, Inc.),
    Saul Shapiro (ABC, Inc.), David Smith, Nat Ostroff and Harvey Arnold
    (Sinclair Broadcast Group), Victor Tawil (Association for Maximum
    Service Television, Inc.), Michael Tsinberg (Toshiba), and Ed
    Milbourn (Thomson Consumer Electronics, Inc.).

[^32]: "VSB/QAM Receiver Cracks the Code to Indoor and Mobile
    Reception," Patrick Mannion, *Electronic Design*, August 23, 1999.

[^33]: "New Chips Said to Fix DTV Reception Flaws," *Communications
    Daily*, August 23, 1999.

[^34]: "COFDM: An Overview," William Y. Zou, Public Broadcasting
    Service, Alexandria, VA and Yiyan Wu, Communications Research
    Centre, Ottawa, Canada, IEEE Transactions on Broadcasting, Vol. 41,
    No. 1, March 1995.

[^35]: "Performance Comparison of ATSB 8-VSB and DVB-T COFDM
    Transmission Systems for Digital Television Terrestrial
    Broadcasting", Dr. Yiyan Wu, Communications Research Centre, ICCE
    '99. "Guide for the Use of Digital Television Terrestrial Broadcast
    Systems Based on Performance Comparison of ATSC 8-VSB and DVB-T
    COFDM Transmission Systems, Document 11A/65-E, 11 May 1999, Special
    Rapporteur's Group, Study Group 11 of the Radiocommunication Study
    Groups of the International Telecommunications Union.

[^36]: Wu and others, however, suggest that mobile operation and HDTV
    reception cannot be achieved concurrently at this time with COFDM.

[^37]: The urban centers were determined from examinations of city maps.
    Census tract data was then aggregated for the area defined as the
    urban centers.

[^38]: The COFDM urban center service estimates were developed based on
    the "worst-case" indoor test data reported by Sgrignoli. This data
    showed signal availability of about 80 percent and reception at
    about 50 percent of the sites where the threshold signal level was
    available. The estimates also assume that all reception failures
    above threshold are due to multipath and can be corrected with
    COFDM.

[^39]: This analysis assumes that the same transmitters are used for
    both COFDM and 8-VSB. The 4 dB power advantage for 8-VSB is based on
    an assumption that a COFDM transmitter operates with a 2.5 dB higher
    peak-to-average ratio and that the COFDM receiver requires at least
    a 1.5 dB higher threshold signal or C/N ratio. We believe that this
    assumption is conservative. We note that others have suggested that
    the 8-VSB power advantage is 6 dB or more. For example, according to
    Harris and others, the ATSC 8-VSB system has at present a 6 dB
    performance advantage over DVB-T COFDM system from a transmitter
    power implementation point of view. This results from a 3.5 dB
    difference in C/N performance and a 2.5 dB higher peak to average
    power ratio for the DVB-T COFDM system. However, Wu postulates that
    improvements in COFDM technology may reduce this difference to 4 dB
    in the future. He notes that about 1.5 dB of the difference in C/N
    is due to the fact that the DVB-T coding was chosen to provide
    compatibility with the DVB-S (satellite) and DVB-C (cable) standards
    and can correct 8-byte transmission errors. The ATSC system uses a
    more powerful code that can correct up to 10-byte errors. This 1.5
    dB difference is unlikely to be reduced with technical advances or
    system improvements, according to Wu. We also believe that the
    assumption that only 50 percent of households will be able to
    receive 8-VSB service in this "4 dB fringe area" is also
    conservative.

[^40]: This estimate is based on a Longley-Rice analysis of service
    areas defined by the DTV Table of Allotments adopted in the *Second
    Memorandum Opinion and Order* in Docket No. MMB 87-268, 14 FCC Rcd
    1348 (1998).

[^41]: The ATSC 8-VSB system employs a training sequence to help
    determine what multipath echoes are present. This training sequence
    is a burst of pseudo-random data of approximately 48 s that occurs
    every 24.2 ms. In theory, echoes of up to about 48 s can be
    corrected by using this training sequence. Other methods may also be
    applied to cancel echoes.

[^42]: While these receivers exhibited poor indoor reception performance
    using a simple bow-tie antenna, we do not intend to imply that these
    receivers are inadequate for DTV service. Many engineering and
    design choices go into making acceptable consumer products. Since
    these receivers are intended to be used with large screen television
    displays, reception with simple indoor antennas may not have been a
    design consideration taken into account. According to Sinclair,
    these receivers did provide satisfactory reception with an
    appropriate outdoor antenna.

[^43]: The availability of a threshold signal is affected by transmitter
    power, antenna height, building height, the materials of which the
    building is constructed, window size, the location of the antenna
    and receiver within the building.

[^44]: "Performance Comparison of ATSB 8-VSB and DVB-T COFDM
    Transmission Systems for Digital Television Terrestrial
    Broadcasting", Dr. Yiyan Wu, Communications Research Centre, ICCE
    '99.

[^45]: Electronically steerable antennas work by electronically changing
    the orientation of the receiving elements. Unlike the traditional
    "UHF loop" or "rabbit ears" antennas, the receiving elements of such
    antennas will remain in a fixed position at all times. Thus, the
    antenna pointing will be transparent to the user.

[^46]: For example, all stations associated with a particular television
    network would have to be assigned the same channel or frequency.
    This means that any change in affiliation by a station would require
    a change in the station's channel assignment.

[^47]: For example, DTV service area is defined using an outdoor antenna
    with a gain of about 10 dB mounted at 30 feet above the ground.
    Mobile operation would use receivers with much less gain and at
    lower heights and therefore the service area would be considerably
    less at the same data rate.

[^48]: COFDM generally does not require channel-limiting filters at the
    transmitter. Rather, to meet an emission mask requirement, a COFDM
    system may simply not use carriers near the band edges.

[^49]: See, for example, Conclusions of W.F. Schrieber, Report on OFDM
    Meeting at MIT, 26-27 October 1992.
    <http://wb-star.com/hdtv/cofdmschr.html> (August 18, 1999).