ATSC RF, Modulation, and Transmission - Servidor TIJBC · 2009-12-02 · ATSC RF, Modulation, and Transmission WAYNE BRETL, SENIOR MEMBER, IEEE, WILLIAM R. MEINTEL, GARY SGRIGNOLI,

ATSC RF, Modulation, and Transmission

WAYNE BRETL, SENIOR MEMBER, IEEE, WILLIAM R. MEINTEL, GARY SGRIGNOLI,XIANBIN WANG, MEMBER, IEEE, S. MERRILL WEISS, AND KHALIL SALEHIAN

Invited Paper

The developmental aspects and technical characteristics of theATSC RF transmission standard (“8-VSB”) are presented. An ex-position is given of the planning and allocation methods that weredeveloped, which are generally applicable to the introduction of asimulcast DTV service independent of the type of modulation used.Additional modulation enhancements (E-VSB) are explained. Tech-niques for implementation of distributed networks of on-channeltransmitters are introduced along with references to some specificapplications of these techniques.

Keywords—Advanced Television Systems Committee (ATSC),digital television broadcasting, distributed transmission networks,spectrum planning.

I. INTRODUCTION

On 13 February 1987, a petition was filed with the U.S.Federal Communications Commission (FCC) requestingthat the FCC initiate an inquiry to explore the impact ofadvanced technologies on existing television broadcastingand the FCC’s spectrum allocation policies relating to tele-vision. In response to that petition the FCC, on July 16,1987, adopted a Notice of Inquiry (NOI) covering a broadrange of issues relating to over-the-air television service [1].

At the time of the NOI and in the three years to follow,numerous ideas to improve broadcast television were putforward. The proposals ranged from modest to major im-provements and from fully backward compatible systems tocompletely incompatible new designs. Some proposed theuse of new spectrum while others focused on using the spec-trum already allocated for broadcast use.

Manuscript received June 28, 2005; revised September 19, 2005.W. Bretl is with the Zenith Electronics Corp., Lincolnshire, IL 60069

USA (e-mail: [email protected]).W. R. Meintel is at P.O. Box 907, Warrenton, VA 20188 USA.G. Sgrignoli is at 1139 Juniper Lane, Mount Prospect, IL 60056 USA.X. Wang and K. Salehian are with the Communications Research Centre,

Ottawa, ON K2H 8S2, Canada.S. M. Weiss is with the Merrill Weiss Group LLC, Metuchen, NJ

08840–1242 USA.

Digital Object Identifier 10.1109/JPROC.2005.861018

In 1990 the FCC made the decision that the implementa-tion of an advanced television system (ATV) in the UnitedStates would be accomplished within the existing televisionbands and that ATV channels would have the same 6-MHzbandwidth as the existing analog National Television Sys-tems Committee (NTSC) channels. Unlike the introductionof color television in the 1950s, it was decided that it was notpractical to design an ATV system that allows for transmis-sion of analog and ATV on the same channel. In view of thisdecision, it became necessary to find an additional channelfor each existing NTSC station so they would be able to begintransmission of ATV while continuing to provide NTSC ser-vice during a transition period.

This paper details the development of planning tools forimplementation of a digital DTV system that is simulcastwith existing analog transmissions. It then presents thefeatures and characteristics of the ATSC 8-level vestigalsideband (8-VSB) transmission standard, and the mostrecent developments regarding that standard, includingenhanced compatible modulation methods (E-VSB) and theuse and implementation of single-channel multiple trans-mitter networks.

II. CHANNEL ALLOTMENT PLANNING

The goal of the allotment planning was to providing asecond channel for each of the approximately 1700 full ser-vice television stations within the United States. However,at the time this work was being carried out, there were stillseveral competing ATV system proposals, and each systemhad a different set of allotment planning factors that had tobe accommodated by the computer modeling.

The first efforts to determine the feasibility of developing aplan to implement ATV were carried out by Robert Eckert atthe FCC. Soon thereafter a group of broadcast organizationsundertook the funding of a project, coordinated by the Asso-ciation for Maximum Service Television (MSTV), to developcomputer modeling to assess the availability of spectrum forATV.

The initial work of this project was an expansion of theFCC efforts whereby channel assignments were made on the

0018-9219/$20.00 © 2006 IEEE

44 PROCEEDINGS OF THE IEEE, VOL. 94, NO. 1, JANUARY 2006

basis of desired separation distance between stations. Im-provements to the FCC’s Assignment Model were made toallow the study of various separation criteria as well as theconsideration of adjacent and UHF taboo1 channels, plusspecial criteria for colocated stations. Although this methodcreated plans and allowed the determination of the numberof existing analog stations that could be accommodated witha second ATV channel, it did not provide any informationconcerning expected coverage and interference.

Because a nationwide plan for the implementation of ATVwould have such a profound effect on the broadcast industrywell into the next century, it was imperative that its designemploy the best possible methods. In view of that require-ment, efforts were undertaken to improve on the Assign-ment Model software to address the issues of coverage andinterference.

1) Model Development: To determine the spectrumrequirements for implementation of the ATV system, twocomputer models were developed and integrated. TheAssignment Model generated spectrum-efficient channelassignment plans based on minimum separation distances;while the Coverage and Interference Model (CIM) evaluatedthe performance of plans generated by the AssignmentModel. The evaluation provided the expected coverage andservice lost due to interference based on a set of user sup-plied system parameters. In addition, the CIM also had thecapability to perform channel substitutions when its analysisindicates that such a change would yield an improved plan.

2) Assignment Model: The Assignment Model usedminimum separation distances to determine the numberof existing stations that could be accommodated with anadditional ATV channel under different cochannel, adjacentchannel, and taboo channel distance separation criteria.Specifically, the model used a heuristic approach to deter-mine the “best” ATV accommodation statistics for a givenset of input conditions. This was accomplished by first or-dering the existing analog stations for a given area accordingto the apparent difficulty of finding a channel for themand then using a mathematical optimization method to findthe largest number of stations that can be accommodatedwithin that area. The output of the model was an assignmenttable that paired existing NTSC stations with specific ATVchannel assignments.

Two basic modules are used within the Assignment Model.The first module, the constraint generator, determines foreach existing NTSC station all possible ATV channels thatcould be assigned to that station based on the user suppliedseparation criteria. The second module, the optimizer/evalu-ator, used a number of mathematical algorithms to iterativelysearch for the lowest number of ATV channels that could beassigned to accommodate the entire set of NTSC stations.

Two different techniques were used to investigate the ATVassignment problem. The first technique employed an al-

1The channel relationships commonly referred to as the UHF taboo chan-nels include the channels �2, 3, 4, 5, 7, 8, +14, and +15 with respect tothe desired channel. Although they are usually discussed separately, the firstadjacent channels are also technically referenced in the FCC’s Rules as partof this group.

gorithm developed by Frank Box [2]. This technique is aheuristic assignment approach that operates on the principlethat stations should be assigned channels in descending orderof assignment difficulty. Through an iterative process, sta-tions that repeatedly fail to be assigned channels, rise towardthe top of the list of requirements for channels and are accom-modated first. The successive reordering of stations by orderof difficulty tends to improve accommodation statistics of aresulting solution or plan.

The second technique, developed by Robert Eckert atthe FCC, uses a general algorithm, known as simulatedannealing [3]. This method attempts to solve the assignmentproblem by starting with a random solution and repeatedlyproposing small changes to the solution, then replacing thesolution each time an improved accommodation is obtained.Both of these techniques were used to investigate the as-signment question, and Eckert indicated that the simulatedannealing approach yielded somewhat better results.

A. Coverage and Interference Model

Initially, software was developed that provided coverageand interference area determinations for a single station withan option to graphically display the results. Computationswere made using the FCC R-66022 propagation curvesand user-specified station data. From this basic concept, ahighly sophisticated computer model evolved. The enhancedmodel provided the capability to analyze nationwide ATVassignment plans, with flexibility to vary station and systemparameters, select from any of three propagation models,and furnish statistics on population density within coverageand interference areas for individual stations and for theentire country. The model also was improved to employactual station data from the FCC’s Television Engineeringand Directional Antenna databases as well as the ability touse three-arc-second terrain data as needed for propagationmodeling. In addition to the many computational featuresprovided, the software also incorporated capabilities foroptimization of ATV assignment plans.

1) Coverage and Interference Computation Procedure(Initial Model Options): The extent of the noise-limitedservice contour of a station is determined using the FCCpropagation curves. The F(50,50) curves are used whencomputing NTSC service, and at the user’s option eitherF(50,50) or F(50,90) curves can be used for ATV com-putations. (The F(50,90) curves are preferable for digitalATV planning because of the all-or-nothing nature of digitalreception compared to analog’s “graceful degradation.”)The desired value of the noise limited contour (specified

2The FCC R-6602 propagation curves are contained in the FCC RulesSection 73.699. They are a family of curves that provide estimates of fieldstrength exceeded for either 50% of the time or 10% of the time at 50% ofthe potential receiver locations. The curves are based on a receive antennaheight of 9 m and provide estimates for various average heights aboveaverage terrain (height above the average terrain (HAAT) between 3.2 and16.1 km from the transmit location) for the transmit antenna. They arecommonly referred to as the F(50,50) or F(50,10) curves. The F(50,90)curves used to predict field strengths for 50% of the potential receiverlocations 90% of the time can be derived by the following formula: F(50,90)= F(50,50)�[F(50,10)�F(50,50)].

BRETL et al.: ATSC RF, MODULATION, AND TRANSMISSION 45

in decibels above 1.0 V/m, dB ) is a user-specified valuewith different values permitted for each system (NTSC orATV) and TV band.3 If the user selects the FCC curvesas the propagation model, then it is assumed that fieldstrength values will equal or exceed the noise limited valueeverywhere within the computed contour. However, if eitherof the optional propagation models (Longley–Rice [4] orTIREM [5]) is selected, then a further analysis is made topredict within the contour where noise-limited service willexist. This is required since predicted signal level using thesealternative propagation models takes into consideration theterrain features along the entire path between the transmitterand the point being evaluated, whereas use of the FCCpropagation curves assumes an average height above thesurrounding terrain in all directions (see note 5).

Included in the computations are transmit power and an-tenna height above the surrounding terrain, and at the user’soption, the specific horizontal4 antenna patterns associatedwith each station. Power and height are either that found inthe FCC data base or set to a fixed value for each band andsystem. When analyzing ATV assignments contained in anassignment plan, the user can optionally set the power andheight or have the station power computed so that the ATVnoise limited service contour will match that of its pairedNTSC station, using the paired station’s parameters.

Interference calculations are made using the same stationparameters and propagation model criteria used to determinenoise-limited service. If the FCC curves are selected as thepropagation model then the F(50/10) curves are used to com-pute interfering signal levels. If either the Longley–Rice orthe TIREM model is selected then the user is requested tospecify the desired location and time probabilities, and in thecase of the Longley–Rice model, the level of confidence. Theinterference computations also include a standard receive an-tenna pattern that is assumed to have its main lobe pointed inthe direction of the desired station.

When determining the existence of interference, the useralso can specify the channel relationships to be considered.Relationships that can be included are cochannel, upperand/or lower adjacent channels and the UHF taboo channels.Different channel relationship considerations can be spec-ified for NTSC-to-NTSC, NTSC-to-ATV, ATV-to-NTSC,and ATV-to-ATV interference computations. Likewise, theuser can specify the acceptable ratio of desired-to-undesired(D/U) field strength levels for each channel relationshipthat is to be considered when predicting the existence ofinterference.

In order to evaluate the impact of interference fromindividual stations as well as overall interference, and toassess the amount of new interference caused to NTSCstations by the introduction of ATV service, a service matrixconcept is employed. This concept divides the area within

3In the United States three bands are allocated for television broadcasting:low VHF (54–72 MHz and 76–88 MHz), high VHF (174–216 MHz), andUHF (470–806 MHz).

4Since no antenna vertical plane data is contained in the FCC’s database,a set of typical standard vertical antenna patterns was developed for eachtype station and band.

the service contour of a station into a matrix of cells. Adetermination is then made of the cells within the servicearea where interference is present. The total area within thecontour receiving interference is then determined by addingup the area of the cells where interference is found to exist.By overlaying the matrices that define the areas of interfer-ence caused by individual stations it is possible to determinethe overall area of interference. Likewise, by determiningthe difference between a matrix of the interference caused byother NTSC stations and a matrix of ATV-only interferenceto an NTSC station it is possible to determine the amount ofnew interference that would be caused by the introductionof ATV stations. Similarly, it is possible to show the extentof interference that will be received by an ATV station whenNTSC stations are no longer operating.

The same matrix concept is used to determine noise lim-ited service when either the Longley–Rice or TIREM prop-agation model is selected. The area of the cells where thecomputed signal level is below the noise limited threshold issubtracted from the total area within the noise limited con-tour to determine noise limited service area.

2) Determination of Population Densities: To be ableto ascertain the population within service and interferenceareas, a database of the 1990 U.S. census at the block levelwas established. This database contains the population andreference coordinates of each census block in the UnitedStates. After the service contour of a station is established,the population within each matrix cell within the contouris computed by determining the total of the population ofthe census blocks that fall within the cell. Once this pop-ulation matrix has been established, it is then used in thesame manner as the area matrix to compute the populationstatistics.

3) Optimization Software: In addition to providing thecapability to determine coverage and interference statisticsfor an ATV assignment plan, the model also has two dif-ferent options that attempt to optimize channel assignmentsby matching ATV interference areas with interference areasof the paired NTSC station. The first option attempts to de-termine the “best” assignment scheme for stations located ata common site. A common site can be defined as a singlelocation or locations that are within a specified distance ofeach other. The second option attempts to improve the planby substituting other channels when such channels are deter-mined to provide improved interference matching.

The first option analyzes all channels assigned at a colo-cated site for each of the stations at the site and creates a ma-trix of the mismatch between the existing NTSC interferencearea and ATV interference area. The reason to analyze eachchannel for each station is that this option assumes that theATV assignment service contours are to duplicate those ofthe paired NTSC stations; therefore, the coverage and inter-ference of each ATV station will depend on that of the pairedNTSC facility. After all the stations and channels have beenexamined, the matrix is then analyzed. The NTSC stationwith the poorest overall interference area match (includingall channels) is assigned the ATV channel that has the bestmatch. That station and channel are then removed from the


matrix and the process is repeated until all NTSC stationshave been assigned an ATV channel. This system attemptsto insure that matching is evenly distributed among the sta-tions at the common site.

The second optimization option analyzes other availablechannels in an attempt to find an ATV channel that eitherdoes not receive any interference or whose interference areabetter matches that of its paired NTSC station.

When an ATV assignment plan is created based on speci-fied separation distances, many of the locations may still haveother channels that could have been assigned. This optionfirst analyzes the planned ATV channel assignment to deter-mine the amount of interference it receives from other ATVstations and existing NTSC stations. If no interference is re-ceived, then no further analysis of the ATV assignment ismade. However, if interference is found, then the area wherethe interference occurs is compared to the interference areaof the paired NTSC station. If the interference areas matchexactly (no interference is caused to the ATV station outsidethe area where the paired NTSC station received interfer-ence), no further analysis is performed; otherwise, each ofthe other available channels is analyzed searching for eithera channel that receives no interference or one where the inter-ference area better matches that of the paired NTSC station.If an improvement is found, that channel is substituted forthe channel originally assigned. The lists of additional chan-nels available at other sites not yet analyzed are then checkedto determine if this assignment would conflict with them. Ifa conflict is found, the list for the other sites is modified toeliminate the conflict. Conflicts are determined on the basisof the spacing requirements used to create the assignmentplan. It should be noted that, before the available channels areanalyzed by the model, the channels are ranked by distanceto the nearest cochannel NTSC station or ATV assignmentand those with the greatest distance separation are analyzedfirst.

4) Modifications to the Initial Model Options: In additionto the originally planned model options discussed above, itbecame necessary to create several others to study the effectof certain planning concepts not originally anticipated.Ultimately it was decided that the methodology based onthe Longley–Rice propagation model was the best approach.This decision was based on the capability to take into con-sideration the specific terrain characteristics of each path,which was expected to provide a much more realistic predic-tion of service and interference than a methodology that onlyconsidered the terrain near the transmitter (FCC propagationcurve model). A comparison of the results produced bythe Longley–Rice model to that of a specific version of theTIREM model indicated that the overall differences werenot significant. However, due to the fact that at the timethere were numerous versions of the TIREM model, andonly one documented and widely accepted version of theLongley–Rice model, the Longley–Rice model was adopted.

Although the CIM model, as discussed above, was orig-inally developed by the broadcast industry, it was eventu-ally adopted by the FCC with some minor variation in the

methodology used to define the cells used for the coverageand interference matrices.

The industry model used wedge shaped cells centered onevenly spaced radials whereas the FCC model used essen-tially square cells. The FCC used this concept to initiallyallow the use of the same matrix grid for several stationswithin a market. However, the FCC later abandoned that con-cept in favor of using a specific matrix for each station basedon the station’s location. The only other deviation was theevaluation point within each cell. In the FCC model, the eval-uation point was determined by the centroid of the populationwithin the cell rather than the center of the cell as used by theindustry model.

Once developed, the CIM was used both to analyze theefficiencies of various channel allotment plans and to refinethe plans, and played a major part in the final allotment planadopted by the FCC [6], [7]. In addition, the CIM was used tocompare the competing system proposals as well as to assistthe Grand Alliance later in their efforts to achieve consensuson a single method for the transmission of ATV. (The dig-ital HDTV Grand Alliance was a consortium of all remaningsystem proponents formed toward the end of the selectionprocess.)

After adoption of the final transition allotment plan theFCC adopted the CIM methodology to process the applica-tions for the newly allotted channels. The CIM has becomeknown as the FCC OET-69 methodology, which is detailedin FCC OET Bulletin 69 [8]. This bulletin provides the finalset of planning factors that are to be used to analyze coverageand interference in the United States. This methodologywas necessitated because the FCC has permitted individualstations to deviate from the parameters in the transitionallotment plan, including changing channels and increasingpower, provided that any new predicted interference isless than a specific percentage referred to as de minimusinterference.

B. Longley–Rice Propagation Model

The official name of the Longley–Rice model is the ITSIrregular Terrain Model. The model computes path loss ad-justment to free space signal propagation and is a general-purpose model covering 20 MHz to 20 GHz. The modelwas developed in the 1960s and is semiempirical, using the-oretical treatment of reflection, refraction, diffraction, andscatter with the theory adjusted to fit measured data. It is notintended to predict short-term variations, as it is based onyearly medians. The data used to develop the model camefrom VHF land mobile service measurement in Coloradoand northern Ohio and from the VHF and UHF televisionmeasurements from the Television Allocations Study Organ-ization (TASO) and also includes some climatic data fromCCIR.

C. Final FCC Transition Planning Criteria

The final ATV allotment plan adopted by the FCC pro-vided a companion channel for each authorized full-servicetelevision within the United States. The facility authorized


for the companion channel provided an ATV noise-limitedcontour5 that replicated the Grade B contour6 of the station’spaired analog channel. However, if the ATV facility requiredto replicate the analog contour was below the minimumpower level (1.0 kW for low VHF, 3.2 kW for high VHF,and 50.0 kW for UHF) the power was set to the minimumvalue. Likewise if the power on a UHF channel exceeded1000 kW, the power was set to that level. It is also noted thata dipole factor adjustment7 was applied to the normal GradeB or ATV noise limited contour values when determiningthe replication that involved a UHF channel. The otherparameters used in developing the final allotment plan canbe found in the FCC OET Bulletin 69 discussed above.

D. Spectrum Issues Then and Now

As noted previously, the initial goal was to provide eachexisting full service television station with a second channelfor ATV transition operation. However, no consideration wasgiven to either protecting the more than 7000 existing lowpower television stations, booster stations, and translators(collectively referred to as LPTV) or providing them with atransition companion channel.

In addition, midway through the process it was decidedby the FCC, acting on legislation passed by the U.S. Con-gress, that the number of television channels at the end ofthe transition would be reduced from 67 to 49.8 Since theposttransition television band would include only channels2–51 instead of 2–69, the final planning process attempted toavoid the use of channels above 51. This constraint made iteven more important to use the techniques of the CIM to de-velop an efficient plan that avoided unnecessary interferenceto the greatest extent possible. In the end it was not possibleto totally avoid use of the channels above 51.

At the time of this writing (August 2005), the FCC wasin the process of developing a final posttransition DTV9

allotment plan and is making extensive use of the CIM tocreate that plan. Once again, the need for the best planningmethodology has taken on new importance in that it has beendetermined that low VHF channels (2–6) may not be suitablefor DTV operation in many areas due to excessive manmadenoise. Furthermore, since the frequencies above channel51 will be used for nonbroadcast purposes, broadcastersare likely to try to avoid use of channel 51 due to potentialinterference issues that could arise both from and to thoseother services. In the end, it is expected that use of some

5ATV (DTV) noise limited contours are 28 dB� for low VHF, 36 dB� forhigh VHF, and 41 dB� for UHF, and are computed using the FCC F(50,90)propagation curves.

6Analog Grade B contours are 47 dB� for low VHF, 56 dB� for high VHF,and 64 dB� for UHF, and are computed using the FCC F(50,50) propagationcurves.

7The dipole factor adjusted value is computed by the following formula:64–20 log[615/(channel midfrequency in megahertz)] for analog and 41–20log[615/(channel midfrequency in megahertz)] for ATV (DTV).

8The number of available television channels is reduced by one becausechannel 37 (608–614 MHz) is reserved exclusively for the radio astronomyservice.

9During the course of this process, ATV has become DTV. Initially all theproposed ATV systems were analog, but since the eventual system is digital,it was appropriate to refer to the new system as DTV.

Fig. 1. VSB and NTSC spectral comparison in 6 MHz.

low VHF channels as well as channel 51 will be required toprovide a channel to every station in the congested areas.

The FCC has also adopted regulations that permit LPTVstations an opportunity to convert to digital (flash cut) or toobtain a companion digital channel and adopted use of theCIM methodology to process those requests.

III. THE ATSC VSB TRANSMISSION SYSTEM

An in-depth description of the digital VSB transmissionsystem has been published in ATSC documents [9], [10]. TheATSC-standardized version was adopted in the United Statesby a series of FCC “Report and Order” documents and pub-lished in the FCC Rules [11]–[14]. The following is a briefoverview of the digital VSB transmission system and its per-formance.

A. ATSC VSB Transmission Description

The VSB and NTSC spectra in a 6-MHz channel arecompared in Fig. 1. The analog NTSC vestigial-sidebandspectrum has the familiar three carriers (visual, chroma,and aural) that carry most of the energy in the channel. Itspower is described in terms of the peak envelope power ofthe large, constant-amplitude horizontal and vertical syncpulses. Compared to digital modulation, the analog televi-sion signal is not efficient in terms of either bandwidth orpower.

In contrast, the digital VSB spectrum is flat throughoutmost of the channel due to the noise-like attributes of ran-domized data. Its power is described as the average powerin the channel bandwidth. Its peaks can only be described interms of a statistical cumulative distribution function [15],with the RF envelope peaks remaining 99.9% of the timewithin 6.3 dB of the total in-band average power. Two steeptransition regions (each 620 kHz wide) exist at each end ofthe band. The half-power frequencies of the VSB signal are5.381 MHz apart, and represent both the Nyquist bandwidth(smallest ideal bandwidth that can sustain the desired ATSCsymbol rate) and the equivalent noise bandwidth. Therefore,the 6-MHz channel uses only 11.5% excess RF channelbandwidth, making it a very efficient system in terms ofbandwidth. A low-level constant RF pilot carrier (whichadds only 0.3 dB to the total average power) is added to thenoise-like data signal at the lower band edge. (The small


Fig. 2. Data segment and segment sync definition.

Fig. 3. Frame sync definition.

in-phase pilot is created by adding a dc component equalto 1.25 constellation units to the eight equi-probable levelsprior to modulation.) These attributes make the digital VSBsignal very efficient in terms of both power and bandwidth.

The baseband data-segment format for terrestrial broad-casts is illustrated in Fig. 2 for the trellis-coded 8-VSB signal.Note that there are eight discrete equi-probable data levelsexcept for the four-symbol binary data segment syncs thatdelineate each 832-symbol data segment. Therefore, each ofthe 828 data payload symbols carries 3 b of information ata 10.762-MHz symbol rate. However, only two of these bitsare payload data; the third bit is a parity bit resulting fromtrellis-coded modulation.

The syncs are not trellis-coded. These segment syncs takethe place of the MPEG sync byte that occurs at thebeginning of every fixed-length 188-byte MPEG packet.Thus, the swap of MPEG-sync for segment sync causes noloss of data throughput, since the MPEG-sync is reinsertedat the VSB demodulator’s output. In the 8-VSB system,each data segment carries one 188-B MPEG packet plus20 B of Reed–Solomon (RS) error correction parity for atotal of 208 B/segment.

Fig. 3 depicts a DTV binary data frame sync, which is onesegment long (832 symbols) and repeats every 313 segments.The data efficiency is reduced by only 0.32% (1/313) due tothe insertion of data frame syncs. The data frame allows dataframe synchronization in the receiver. The same binary framesync (particularly the 511-symbol and three 63-symbol PNsequences) can also be used as a known reference-trainingsignal for the receiver equalizer, which allows initializingthe equalizer as well as stable operation regardless of dataeye closure. The frame sync can also act as a means of de-termining received RF signal conditions (such as S/N ratio).The middle 63 PN sequence alternates from one frame to thenext, providing two unique frame syncs.

The VSB transmission system was developed includingfive modes (2, 4, 8, 8-trellis, and 16), all of which appearin ITU-T Recommendations J.83 and J.84 [16], [17] Thesemodes provide a tradeoff between data rate and robustnessof reception by means of different numbers of constella-tion levels and/or the use of trellis coding. The 24-symbolVSB mode section in the binary frame sync reliably in-forms receivers which of the modes is being transmitted.The Grand Alliance and the Advisory Committee on Ad-


Fig. 4. 8-VSB transmitter block diagram.

Fig. 5. 8-VSB receiver block diagram.

vanced Television Service (ACATS) selected trellis-coded8-VSB (19.39-Mb/s payload) for terrestrial broadcast andnontrellis-coded 16-VSB (38.78-Mb/s payload) for cabletransmission. Note that the symbol rate is 10.762 MHz forall of the various VSB modes, with a varying number ofbits/symbol determining the data rate for each mode to tradeoff against reception performance.

The trellis-coded 8-VSB-transmitter block diagram isshown in Fig. 4. The transmitter, which includes the channelencoder and exciter, receives the incoming data packets(188 B/packet of interspersed video, audio, and ancillarydata), and thoroughly randomizes the data so that the trans-mitted signal has a flat, noise-like spectrum. Random datais important for all the receiver recovery loops to work op-timally, and minimizes interference into analog NTSC. TheReed–Solomon encoding, known for its good burst noisecorrection capability and data overhead efficiency, addsthe 20 parity bytes to the end of each MPEG data packetbefore data bytes are convolutionally interleaved (spreadout) over 52 data segments, to a depth of 1/6 of a data frame(4 ms). Segment and frame syncs are not interleaved. Databyte interleaving helps protect against the effects of burstnoise/interference that occurs during transmission. In thetrellis-coded 8-VSB terrestrial system, the trellis encoderadds additional redundancy to the signal in the form of more(than four) data levels, creating the multilevel (eight-level)data symbols for transmission. The added redundancy allowsfurther error correction in the receiver through the cascadedforward error correction made up of Reed–Solomon blockcoding and convolutionally coded trellis-coded modulation(2/3 rate, four-state Ungerboeck code). In 16-VSB cableapplications, there is no trellis encoding, and a mappercreates the multilevel (16-level) data symbols instead of atrellis-coder.

The segment and frame syncs are then multiplexed withthe multilevel data symbols before the dc offset is added forcreation of the low-level, in-phase pilot. The VSB modulatorprovides a (root-raised cosine) filtered IF signal (typicallycentered on 44 MHz in the United States), with most of onesideband removed. Finally, the RF upconverter accuratelytranslates the IF signal to the desired RF channel with aslittle phase noise as possible before amplification by a high-power amplifier (HPA) and emission mask filtering that sig-nificantly reduces any adjacent channel energy splatter due tothird-order and fifth-order nonlinear intermodulation. The re-quired adjacent channel emission mask details can be foundin FCC documents [18] and other documents [19]–[21]. Anoptional feedback signal from the emission mask filter outputcan be fed back through a processor to precorrect the trans-mitter for any linear distortion caused by the mask filter (e.g.,nonflat amplitude or group delay response) or any nonlineardistortion caused by the HPA, such as amplitude clipping orincidental carrier phase modulation.

The VSB receiver block diagram is illustrated in Fig. 5.The DTV signal, using the existing 6-MHz RF channelallocations, is converted by the VSB receiver’s tuner tothe IF frequency (typically 44 MHz) prior to channel de-coding. After appropriate IF filtering (root-raised cosine)and automatic gain control (AGC), the pilot signal canbe used to synchronously detect the VSB signal while si-multaneously removing FM sidebands and low-frequencyphase noise inherent in low-cost consumer tuners. The clocksynchronizer recovers the 10.762-MHz symbol clock fromthe received signal as well as synchronizes the variousfollowing loops (interleaver, trellis and Reed–Solomondecoders, and randomizer) so that further VSB processingcan be accomplished. The equalizer is the workhorse ofthe DTV receiver removing any linear distortion due to


Table 1VSB Transmission System Performance Parameters

Fig. 6. Probability of error versus C/N for 8-VSB and 16-VSB systems.

multipath propagation or imperfect filtering. Any remaininghigh-frequency tuner phase noise is removed by the phasetracker. The remaining data processing circuits performthe concatenated forward error correction (short four-statetrellis decoding with minimal error propagation followed bya Reed–Solomon decoder that can correct up to tenbyte errors/MPEG packet). A convolutional deinterleaverreassembles the interleaved (dispersed) data bytes while dis-persing (spreading out) contiguous burst errors to maximizeReed–Solomon error correction. Finally, the derandomizerrecreates the original data bytes for the transport multiplexerto deliver to the video and audio decoders.

The 16-VSB-cable mode is very similar to the terrestrialmode except there is no trellis-coded modulation, and thedata rate is doubled (using the same symbol rate) by sendingfour data bits per symbol rather than two data bits per symbol.Further details can be found in [22].

B. ATSC VSB System Performance and Compliance

VSB performance has been extensively evaluated in simu-lation and measured in the laboratory [22], [23]. Table 1 con-

tains the primary system performance parameters and theirvalues. Note the similarities (common parameters) and dif-ferences among the various VSB modes as lower data ratesachieve more robust DTV reception.

Fig. 6 is an illustration of the probability of error versussignal-to-noise ratio for both the 8-VSB terrestrial and16-VSB cable modes. Both curves exhibit a very steep risein error rate around their respective 15- and 28-dB SNRthreshold of visible errors (TOV) or threshold of audibleerrors (TOA). The TOV and TOA values are identicallydefined as 2.5 MPEG packet errors per second, which isthe experimentally determined point where the prototypereceiver would just begin to show visible decoding errorsdue to transmission errors. As the SNR value at the inputto the ATSC receiver decreases from high to low, the DTVreceiver will change from an error-free, perfect picture (andsound) to an all-error, frozen picture (and muted sound) inless than 1 dB. This is the well-known “digital cliff effect”that all digital systems exhibit.

Finally, ATSC and others provide recommendations forboth transmitter [20], [21], [24] and receiver [25], [26] per-


Fig. 7. E-VSB preprocessor and multiplexer.

formance parameters as guidelines for both manufacturersand broadcasters. The recommendations are reasonable toachieve and allow the objectives of good DTV reception overvaried conditions such as urban, suburban, and rural, whetherusing either indoor or outdoor antennas, and with minimalantenna adjustment.

IV. ENHANCED VSB (E-VSB) SYSTEM

E-VSB [9], [27] is fundamentally a method of addingfurther error protection coding to part of the 8-VSB signal.It is required to simultaneously provide a performanceincrease for the E-VSB coded portion, while not degradingthe “normal” or “main” portion used by legacy ATSC re-ceivers. Secondarily, but importantly, E-VSB applicationsrequire additions to the ATSC transport and PSIP standardsto support functions such as synchronization of separate butrelated source material in the main and enhanced streams.

The basic technical advantage of the E-VSB stream is animprovement of at least 6 dB in SNR and interference thresh-olds. This is obtained in exchange for heavier forward errorcorrection coding, and therefore at the expense of payloaddata rate for the enhanced part of the transmission. Naturally,designating a portion of the transmitted symbols as enhancedreduces the bandwidth of the main stream, just as in the caseof multicasting, where each program uses only part of the19.39-Mb/s ATSC stream.

Applications envisioned for E-VSB include streams unre-lated to the main stream, related streams, and synchronizedrelated streams such as fallback audio and/or video.

Unrelated streams are envisioned for use in carryingsecondary channels or data that can be used by portable orPC-based devices with nonoptimum antennas, for example,a “subchannel” carrying stock market information, news,and weather.

Fallback audio is defined as a duplicate of the main audiothat can be switched to in the receiver when the main signal ismomentarily lost. The aim is to make this switch as seamlessand unnoticeable as possible. This is the most demanding ap-plication envisioned, involving all primary and secondary as-pects of E-VSB: the physical layer, synchronization of timestamps for the main and fallback, and enhanced PSIP that an-

nounces the availability of fallback to the enhanced-capablereceiver.

A. E-VSB Coding Details

Because the reaction of legacy receivers to deliberatecoding errors cannot be predicted, the E-VSB coding isarranged to be effectively cascaded with the normal 8-VSBcoding. As a result, legacy receivers detect a correctly codedsignal (although they do not recognize the payload contents).The coding is done in two stages. First, an RS code is appliedto the enhanced data, before it is encapsulated in normallyformed MPEG packets and processed by 8-VSB coding.These packets are transmitted with an MPEG null-packetheader, and therefore are ignored by legacy receivers. The“preprocessing” to this point is shown in Fig. 7. (N/E infigures refers to normal/enhanced data or processing-stateflags.)

Second, an enhanced convolutional code is applied, effec-tively preceding the 8-VSB convolutional code. This resultsin a signal that is indistinguishable in all physical character-istics from a normal 8-VSB signal. It has eight equally prob-able symbol levels and the same spectral characteristics andpower as standard 8-VSB. Fig. 8 shows a block diagram ofa complete E-VSB channel encoder. The blocks in the upperrow are the same as a standard 8-VSB encoder. The blocks inthe lower row are those added for E-VSB coding, includingthe preprocessing shown in detail in Fig. 7

There are several details to the processing that are requiredto maintain compatibility. In particular, since the enhancedconvolutional code changes the sequence of transmittedsymbols from what it would be for 8-VSB, it invalidatesthe 8-VSB RS coding. The E-VSB transmitter thereforerecalculates the RS code to satisfy legacy receivers. Also,since the 8-VSB convolutional coder is 12-phase, operatingas 12 separate interleaved coders, the E-VSB coder is also12-phase, and operates in synchronism with the 8-VSBcoder. Fig. 9 shows the concatenation of coders. The inputsmarked N/E are normal/enhanced flags that control thecoding on a symbol-by-symbol basis. When the flags at setto “N,” normal or “main” data is bypassed around the en-hanced coding. When the flags are set to “E,” the equivalentenhanced coder is as shown in Fig. 10.


Fig. 8. Complete E-VSB channel encoder.

Fig. 9. Concatenated enhanced and standard encoders.

Note that the enhanced portion of the coder contains a“precoder bypass,” which operates upon the enhanced data.This effectively removes the interference filter precoding ofthe standard coder for enhanced data. This precoder is in thestandard encoder to allow use of an optional comb filter inthe legacy 8-VSB receivers to reduce analog cochannel in-terference. However, it doubles the number of trellis statesthat must be decoded when it is used. The precoder bypassprevents this expansion in the enhanced trellis decoder. How-ever, because the precoder bypass circuit has two possiblestates depending on the history of normal data, the enhanced

trellis decoder in new enhanced receivers must determine theprecoder bypass state for each received enhanced symbol.

An added requirement to maintain compatibility withlegacy 8-VSB receivers occurs due to the time multiplexingof the main and enhanced data. The multiplexing introducesshifts in the time of emission of the main data packets ascompared to a pure 8-VSB system. This requires compensa-tion of the MPEG program clock references (PCRs) in theemitted signal, and also some care to maintain adherence tothe MPEG buffer models in the main channel elementarystreams.


Fig. 10. Equivalent encoder for enhanced data.

B. E-VSB Features

E-VSB provides two coding rates designated as “1/2-rate”and “1/4-rate,” referring to a choice of two convolutionalcodes. (The payload is additionally reduced by the ratio164/188 due to the added RS coding.) This additionalcoding provides an SNR threshold advantage of 6 or 9 dB,respectively, as compared to normal 8-VSB. The arrange-ment supports applications similar to those of hierarchicaltransmission, but because the different types of data areactually time multiplexed, they do not interact, and theperformance of legacy receivers on the main data is notaffected by the presence of enhanced data.

C. E-VSB Signaling

Because the enhanced data is identical to 8-VSB data inall physical respects, a means is required for the enhancedreceiver to identify it readily. It would be conceivable toidentify enhanced data by attempting to decode all the dataand accepting successfully decoded data only. This wouldresult in an unacceptably long decode/decision process andwould preclude using the data to enhance receiver perfor-mance in other areas such as the channel equalizer. There-fore, the amount and placement of the enhanced data in aVSB data field is signaled by “map” data transmitted in thefield sync segment (Fig. 11).

Twelve bits are carried as a 64-bit Kerdock code, whichalternates polarity from field to field, both as protection fromfixed ghost patterns and so that it can be distinguished easilyfrom a legacy 8-VSB broadcast, which will contain a fixeddata pattern. Nine map bits indicate the proportion of main,1/2-rate, and 1/4-rate data. Two bits in each data field indi-cate a 16-field countdown until the next map change. One bitindicates a choice of two patterns for packing the enhanceddata in a data field.

A particular map number indicates the number of data seg-ments in a data field devoted to 1/2-rate data, the number de-voted to 1/4-rate data, and the enhanced segment positionsin the field. However, the enhanced data of both rates passesthrough a single “enhanced” byte interleaver and is cut into164-B chunks, then has the enhanced RS code appended,then is placed among the main packets, and finally undergoesthe 8-VSB interleaving. Therefore, there is no place in the

Fig. 11. Data field with E-VSB map data.

system where the data is neatly confined to a packet intervalexcept at the transmitter transport stream input and receivertransport stream output. The main and enhanced symbols arethoroughly interleaved on the channel, and the detailed pat-tern of interleaving must be reconstructed in the receiver inorder to recover the enhanced data.

V. MULTIPLE TRANSMITTER NETWORKS

The conventional approach to covering a large televisionservice area involves the placement of a single high-powertransmitter at a central location. Under certain conditions,however, the conventional method may face economical andtechnical challenges that require careful considerations andengineering solutions.

With the single-transmitter configuration, signal levels arenot uniform throughout the service area. The radiated powerof the transmitter is usually calculated so as to provide suf-ficient signal strength at the edges of the coverage area. Inlocations closer to the transmitter, the signal is stronger andmay be considerably more than required for a satisfactoryreception.

The high cost of extending the coverage area of a trans-mitter by increasing its radiated power is another potentialproblem with the single transmitter approach. Serving thelast kilometer of coverage is far more expensive than the firstkilometer. For example, for a UHF digital TV signal at about


80 km from a transmitter whose antenna is 300 m above av-erage terrain, approximately a 3 dB (or 100%) increase intransmitted power would be required to increase coverage by5 km. Thus, increasing coverage with raw transmitter powercan be expensive to accomplish [28]. Another issue is inter-ference into neighboring service areas. Based on calculationsfor the location and time availability of F(50, 10) for interfer-ence and F(50, 90) for coverage using FCC curves, it can beshown that cochannel interference from a digital UHF trans-mitter will extend on the order of three times the distanceover which it can provide coverage. So, extending by 1 kmthe coverage area of a single transmitter by increasing itsoutput power would add 3 km more to its cochannel inter-ference zone.

In situations such as those detailed above, one possible so-lution is to construct a multiple transmitter network and dis-tribute the signal across the coverage area by using a numberof lower power transmitters instead of a single central trans-mitter. Among the potential benefits of this approach are[28]:

• more uniform and higher average signal levelsthroughout the service area;

• more reliable outdoor and indoor reception as a resultof higher average signal levels;

• less overall effective radiated power (ERP) and/or an-tenna height requirements, resulting in less interference;

• stronger signals at the edges of the service area withoutincreasing interference to neighboring stations.

A multiple transmitter approach of sorts is used for analogTV systems in the form of translators. Such systems aremostly used to fill coverage gaps, or to extend the cov-erage area. They are not usually intended to work with themain transmitter to uniformly distribute the signal acrossthe service area. Instead, there is typically a master/slaverelationship between the higher power central transmitterand the lower power translators. A primary limitation is thenumber of RF channels that must be used for an analog net-work. Usually, for transmitters, channels are required.

A. Distributed Transmission Networks (DTxN)

Distributed transmission can be regarded as a way ofcovering a service area with a network of two or moretransmitters, all synchronized and emitting exactly the sameprogram, and operating according to technical guidelinesand standards specifically developed for this type of system[9], [28]. The number of channels used can be far less thanthe number of the transmitters that constitute the network.

Application of DTxN is not limited to filling coverage gapsor extending the coverage area, which is usually the case inanalog TV translators. It can also be used for creating a moreuniform distribution of the transmitted signal in the mainparts of the service area, as well as enhancing the signal inother parts by illuminating the area from different directions.

1) Single-Frequency DTx Networks: If all the transmittersconstituting a DTx network are synchronized and use thesame channel for transmission, they form a single-frequencynetwork (SFN). SFN is one of the interesting possibilities

provided by DTV transmission systems. It is not feasiblewith analog TV due to the creation of harmful ghosts.

SFNs for single-carrier signals such as 8-VSB have be-come possible because of the use of adaptive equalizers inreceivers. When signals from a number of synchronized SFNtransmitters arrive at a receiver, the adaptive equalizer cantreat those signals as echoes of one another and extract thedata they carry. This assumes, of course, that the relative am-plitude and delay of the signals fall within the capabilitiesof the adaptive equalizer. This is a serious implementationissue because it must take into account the capabilities of al-ready-deployed receivers.

2) Multiple-Frequency DTx Networks: A multiple-fre-quency DTx network uses more than one channel for itssynchronized transmitters. Such a network may be com-posed of a group of smaller embedded SFNs, or a hybridof SFNs and individual transmitters operating on channelsother than those of the SFNs.

B. Limitations of DTx Networks

As a tradeoff for their benefits, DTx networks may have todeal with certain operational restrictions under specific con-ditions. Such limiting conditions could exist if a single-fre-quency DTx network and a single transmitter operating onthe adjacent channel coexist in the same market area. Underthese conditions, implementation of the SFN should be basedon a very careful and subtle design to minimize interferenceto the single transmitter.

Within-market DTV adjacent channel operation was al-lowed in DTV planning under the condition of colocating thecorresponding transmitters, or at most separating them by adistance not more than a specific value (5 km in the UnitedStates). In an SFN environment, only one of the networktransmitters can be colocated with the adjacent channeltransmitter, and for other SFN transmitters, limiting theoutput power—or taking other appropriate measures—maybe necessary to avoid unacceptable interference to the adja-cent channel transmitter [28].

In the presence of an NTSC adjacent channel, the limita-tion on operation of an SFN is more serious and may makethe implementation of the network very challenging in thetransition period from NTSC to DTV because of the muchhigher protection ratios demanded by NTSC (as comparedto DTV).

ATSC Recommended Practice A/111 [28] provides manyguidelines for designing a DTx network and managing inter-ference under various conditions, including the presence ofDTV or NTSC adjacent channel signals.

The limitations of multiple-frequency DTx networks arisemainly from any embedded SFNs, which can be designedaccording to the same principles as any SFN.

C. Configurations of DTx Networks

ATSC A/111 [28] proposes three methods or structures (orany of their combinations) for implementing a DTx network.These structures, however, have their pros and cons, and anyof them can be considered more suitable depending on the


specific situation and the conditions under which they areused.

1) Distributed-Transmitter Network: In this method, acentral studio sends a baseband signal or video/audio datastream to the DTxN transmitters via studio-transmitter-links(STL), which can be fiber optic, microwave, satellite, etc.Frequency and time synchronization of different transmit-ters constituting the network is based on ATSC A/110, “Syn-chronization Standard for Distributed Transmission” [29]. Adistributed transmitter network is a single-frequency DTxnetwork.

2) Distributed-Translator Network: In this method, thetransmitters constituting the network are coherent transla-tors, all operating on the same channel, and translating thefrequency of an over-the-air signal received from a mainDTV transmitter to a second RF channel. This eliminates theneed for an STL and makes frequency and time synchroniza-tion of different network transmitters quite simple. In thismethod, however, two channels are used, one for the coherenttranslator output, and one for the main transmitter feedingthem. One may consider this as a sort of frequency diver-sity in the overlapping coverage area of the main transmitterand the translators. A distributed translator network is a mul-tiple-frequency DTx network.

3) Digital On-Channel Repeater (DOCR): Like themethod described in Section V-C2, the transmitters con-stituting this network pick up their inputs from a maintransmitter, eliminating the need for an STL, but transmiton the same channel as they receive. With this approach,two limiting factors exist in the operation of the network.First, depending on the relative locations of the repeatersand the main transmitter, long “preechoes” may be createdby the main transmitter in the overlapping coverage areas.Second, depending on the amount of feedback from theDOCR transmitting antenna to its receiving antenna, therewill be a power limitation on the repeater output. A networkconsisting of DOCRs and a main transmitter is a single-fre-quency DTx network.

D. Applications of DTx Networks

There are a number of potential applications for DTx net-works; some are detailed below, grouped by complexity andsize.

In its simplest form, a single-frequency DTx network canbe formed by simply adding a second transmitter—whichmay be an on-channel repeater—to a main transmitter forfilling a gap or extending coverage to include a town thatis beyond the reach of the main transmitter [30]. With thissimple application, no additional channel is used by the net-work.

In a more complex case, an SFN may be used to improveservice and enhance reception in areas that are alreadywithin the coverage of the main transmitter. For example, indowntown canyons with shadow areas caused by high-risebuildings, it may be desirable to construct a network ofdistributed transmitters or DOCRs, or a distributed translatornetwork operating on a second channel, to provide a morereliable portable or indoor reception environment [31],

[32]. Different transmitters in such a supplementary DTxnetwork can illuminate a common target area from differentdirections, giving receivers a better chance of successfulreception.

A DTx network can also be used to replace an operationalor a planned single (central) high-power transmitter with anSFN comprised of lower power transmitters operating on thesame channel, and possibly some DOCRs. Under these con-ditions, the operation of the SFN should be within the pro-tected contour, limited by the specifications of the originaltransmitter to be replaced by the network. A DTx networkalso may be a hybrid of different configurations operatingon more that one channel [33]. Such a hybrid network maycontain many transmitters with different output powers andcovering a very large service area.

E. DTx Design Considerations

The use of DTx networks leads to a range of potential com-plications that must be addressed in the design process. Keyamong the issues to consider is the interference environment,which comprises two types of interference: external and “net-work internal” interference.

1) External and Internal Interference in a DTx Network:For a transmitter in a DTx network, external interferencemay be generated by sources such as cochannel NTSC andcochannel DTV stations that do not belong to the network,adjacent channel NTSC and DTV stations, and other sourcesthat are usually involved in creating interference to conven-tional single (central) transmitters. A single-frequency DTxenvironment may also include network internal interference,which does not exist in the case of the single transmitter con-figuration.

As there is more than one DTx transmitter emitting thesame signal on the same channel in the service area of asingle-frequency DTx network, a receiver in the overlappingcoverage area may receive signals from different SFN trans-mitters. The receiver considers the strongest signal as themain signal and the others as echoes. There should be a dis-tinction between these signals and natural echoes, which arereflections from stationary and moving objects, and are alsopresent in a single (central) transmitter environment. In orderto be distinguishable from natural echoes, they may be re-ferred to as “SFN signals.” There is usually no control overnatural echoes but the DTx network designer has control overthe amplitude and time delay of the SFN signals.

In parts of the service area of an SFN that can receivesignal from multiple transmitters, the amplitude and/or delayspread of the SFN signals may fall beyond the capabilityof the receiver equalizer range, and create network internalinterference. Minimizing the creation of such areas, or pre-venting them from falling over populated areas, is an impor-tant design criterion for a single-frequency DTx network.

It is important to note that under many circumstances, cre-ation of multiple SFN signals in specific areas may be a de-sired and deliberately planned, and can be quite helpful ifthe network is operating on the basis of proper design cri-teria. For example, to enable more reliable portable or in-door reception in a downtown canyon, multiple SFN signals


(under the right conditions) from different directions may bea matter of choice [32]. A correctly designed network willminimize the possibility that the multiple transmitter signalswill result in harmful interference.

2) Managing Interference in DTx Networks: Variousdesign methods can be applied to managing both externaland network-internal interference in a DTx network. Forexample, selecting a specific network configuration that fitswell with the topography of the service area and benefitsfrom terrain shielding may minimize one or both types ofinterference. Antenna directivity may be applied to bothcases, and delay adjustment of the transmitters may also beapplied to mitigate network-internal interference. All suchtechniques should be considered when designing a DTxnetwork [9].

It should be noted, however, that mutual external interfer-ence problems in a DTx network can be similar to those ofthe single (central) transmitter architecture, and resolved bythe same techniques. As far as network internal interferenceis concerned, the most important issues to consider are [9]:

• proper selections of the radiated powers;• separation distance between the SFN transmitters;• time adjustment by applying appropriate relative delays.

Incorrect choices for these parameters can make the relativeamplitude and delay of the SFN signals in some parts of theoverlapping coverage areas fall beyond the receiver’s adap-tive equalizer capabilities, and can cause reception failure inthose areas.

3) Receiver Constraints: Another important issue af-fecting the design of a DTx network is receiver performancewith respect to echo handling capabilities. Better receivers,capable of handling stronger pre- and postechoes, over awider range of delays, make DTx network design moreflexible and simpler. On the other hand, receivers withweaker capabilities put more restrictions on the design andimplementation of DTx networks. As the technology ofadaptive equalizers improves over time, this considerationwill become less stringent, allowing more flexible SFNdesigns while maintaining a particular level of reliability.

F. Implementation of Distributed Transmission Networks

A generalized DTx network may include differentcombinations of distributed transmitters, distributed trans-lators, and DOCRs. Each of these structures can be im-plemented by using a number of methods that differ intheir degree of complexity, mostly related to the achievingsynchronization between different network transmitters.For example, the synchronized translators used in a DTxnetwork can operate on the basis of RF-RF, or RF-IF-RFconversion, or the signal can be brought down to base-bandand decoded, error corrected, and then reencoded and up-converted to RF. Selection of each of these approachesis determined by the existing conditions. For example, ifthe input signals received by the translators are strong andstable, RF-RF operation may be adequate. Under these con-ditions, two translators could be frequency synchronized byphase-locking their local oscillators using global positioning

system (GPS) signals. Time adjustment can be achievedby applying appropriate delays to the signals when passedthrough the translators [32]. This RF-RF approach is thesimplest and most cost-effective method of implementingparts of a DTx network consisting of distributed translatorsor DOCRs. Synchronization of RF-IF-RF translators orDOCRs, however, should be based on more sophisticatedmethods [33].

In other circumstances, such as when translator signalsare brought down to base-band or when a number of STLsare used to bring the base-band signal to the transmitters,achieving frequency and time synchronization becomesmore complex. Under these conditions, the synchronizationprocess should be based on the methods specified in A/110[29].

1) Transmitter Identification: As of August 2005, therewere more than 1500 DTV transmitters in operation inthe United States and Canada. As the number of DTVtransmitters grows, there is an increasing need to iden-tify the origin of each DTV signal received at differentlocations. ATSC A/110 [29] includes specifications for aspread spectrum sequence, embedded as a RF watermark,for transmitter identification (TxID) purposes. Transmitteridentification techniques (or transmitter fingerprinting) areused to detect, diagnose, and classify the operating statusof radio transmitters. Transmitter identification also enablesbroadcast authorities and operators to identify the source(s)of interference, if any. More importantly, TxID can be usedto tune various transmitters in an SFN to minimize theeffects of multipath interference caused by the destructiveinterference of several different transmissions and/or by thereflection of transmissions.

To allow identification of individual transmitters in a net-work, provision is made to assign specific, identifiable codesto particular transmitters [29]. The transmitter identificationcodes are combined and used to generate a symbol sequencethat is modulated synchronously with the host 8-VSB sym-bols in such a way that ordinary receivers cannot detect theirpresence but special monitoring and measuring instrumentscan [34], [35]. The ATSC RF watermark additionally can beused for robust data transmission and positioning applica-tions [36]–[39].

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Wayne Bretl (Senior Member, IEEE) receivedthe BSEE from Illinois Institute of Technology in1966.

He joined Zenith Electronics in 1975. He isa Principal Engineer in the R&D Department,Zenith Electronics, Lincolnshire, IL. He holdsover 15 patents in television technology andrelated areas.

Mr. Bretl is a member of the Society of Mo-tion Picture and Television Engineers, the AudioEngineering Society, and the Society for Informa-

tion Display, and represents Zenith in ATSC and a number of professionaland industry associations.

William R. Meintel received the B.S.E.E. degreefrom the West Virginia Institute of Technology,Montgomery, in 1969.

He has 35 years’ experience in the commu-nications field. He was a Field Engineer for theFederal Communications Commission (FCC),Buffalo, NY, and later was Senior Field Engineerin the Chicago, IL, field office before joining theFCC’s Media Bureau Policy and Rules Division.During his tenure in the Media Bureau, he wasextensively involved in a number of complex

domestic and international spectrum planning matters and was a member ofthe U.S. delegation to a number of international conferences. Since enteringprivate practice, he has been heavily involved in technical consultingand spectrum planning for the broadcast industry. During that period hecoauthored a report for the NAB on spectrum requirements for digital audiobroadcasting (DAB), created a plan for independent television broadcastingfor Romania, and has been extensively involved in spectrum planning fordigital television (DTV) in both the United States and internationally. Hisinvolvement in DTV planning has included a wide variety of activitiesincluding computer modeling, engineering consulting, and field measure-ments programs used to validate the proposed systems. More recently hehas been providing considerable engineering support for various clients


in a number of system design and implementation projects. He has alsoauthored a number of papers and articles and made numerous presentationson subjects related to spectrum planning.

Gary Sgrignoli received the B.S. and M.S. de-grees in electrical engineering from the Univer-sity of Illinois, Champaign-Urbana, in 1975 and1977, respectively.

He joined Zenith Electronics Corporation inJanuary 1977, where he worked as an engineerin the Research and Development departmentfor 27 years. In March 2004, he set up SgrignoliConsulting, a DTV-transmission consultingfirm, and in April 2005 he merged his practicewith those of W. Meintel (Techware, Inc.) and

D. Wallace (Wallace and Associates) to create Meintel, Sgrignoli, andWallace (MSW), Waldorf, MD. Further information can be found athttp://www.MSWdtv.com. He has worked in the R&D design area ontelevision “ghost” canceling, cable TV scrambling, and cable TV two-waydata systems before turning to digital television transmission systems. Since1991, Gary has been extensively involved in the VSB transmission systemdesign, its prototype implementation, the ATTC lab tests in Alexandria, VA,and both ACATS field tests in Charlotte, NC. He was also involved withthe DTV Station Project in Washington, DC, helping to develop DTV RFtest plans. He has also been involved with numerous television broadcaststations around the country, training them for DTV field testing and dataanalysis, and participated in numerous DTV over-the-air demonstrationswith the Grand Alliance and the ATSC, both in the United States andabroad. In addition to publishing technical papers and giving presentationsat various conferences, he has held numerous digital VSB transmissionsystem seminars around the country. He holds 35 U.S. patents.

Xianbin Wang (Member, IEEE) received thePh.D. degree in electrical and computer engi-neering from National University of Singapore,Singapore, in 2000.

He was with Institute for Infocomm Research,Singapore (formerly known as Centre for Wire-less Communications), as a Senior R&D Engi-neer in 2000. From December 2000 to July 2002,he was a System Designer at STMicroelectronics,Inc., Ottawa, ON, Canada. Since July 2002, hehas been with Communications Research Centre

Canada, Ottawa, where he is currently a Senior Research Scientist. He isalso an Adjunct Associate Professor of Laval University, QC, Canada. Hiscurrent research interests include digital signal processing, broad-band wire-less system, and communication theory.

S. Merrill Weiss is a graduate of the WhartonSchool, University of Pennsylvania, Philadel-phia.

He is a consultant in electronic mediatechnology, technology management, and man-agement. He conducted the experiments thatled to the very first digital television standard(CCIR Recommendation 601) in 1981. He wasa major contributor to the work of the FCCAdvisory Committee on Advanced TelevisionService, doing the bulk of the work on imple-

mentation. He currently participates in the Advanced Television SystemsCommittee’s (ATSC’s) efforts. In the original ATSC standard for 8-VSB,there was no method available for synchronizing transmitters as neededfor single-frequency networks; he invented a synchronization method thatis now embodied in the recently adopted ATSC standard on transmittersynchronization. He has one issued patent and one pending.

Mr. Weiss has been recognized by the Society of Motion Picture and Tele-vision Engineers by elevation to the rank of Fellow and was the 1995 recip-ient of its David Sarnoff Gold Medal and the 2005 recipient of its ProgressMedal. He was also nominated for a technical Emmy Award for his concep-tion of serial digital interfaces for television systems. He has been certifiedby the Society of Broadcast Engineers at the level of Professional BroadcastEngineer. He is a member of the IEEE Broadcast Technology Society.

Khalil Salehian received the B.Sc. and M.Sc.degrees in electrical engineering from PahlaviUniversity, Tehran, Iran, in 1971 and 1974,respectively, and completed graduate studiesin computer science at Concordia University,Montreal, QC, Canada, in 1999.

He spent about 20 years working with NationalIranian Radio and Television (NIRT) in the fieldsof radio and TV network expansion, frequencyplanning, and coordintaion and compatibilitywith other services. Since 2000, he has been with

the Communications Research Centre Canada (CRC), Ottawa, ON. He iscurrently working with the Television Systems and Transmission groupof CRC. His previous fields of interest included radio and TV networkexpansion, frequency planning, and coordination and compatibility withother services. His current fields of interest include computer simulationsand coverage predictions of DTV systems, distributed transmission, andsingle-frequency networks for DTV broadcasting services. His work ondistributed transmission systems earned him the 2003 IEEE Scott Heltmemorial award.


Documents

ATSC RF, Modulation, and Transmission - Servidor TIJBC · 2009-12-02 · ATSC RF, Modulation, and Transmission WAYNE BRETL, SENIOR MEMBER, IEEE, WILLIAM R. MEINTEL, GARY SGRIGNOLI,