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DVB-S2 BENEFITS FOR MILITARY BROADCAST SYSTEMS Bruce Bennett Defense Information Systems Agency Arlington, VA ABSTRACT The Digital Video Broadcast - Satellite, Second Generation (DVB-S2) protocol has been developed and standardized as an evolution of the Digital Video Broadcast- Satellite (DVB-S) waveform for European satellite broadcasting by the European Telecommunications Standards Institute (ETSI), and is a candidate for use in US military systems that employ DVB-S. This paper will describe the evolutionary efficiencies of DVB-S2 over DVB-S, increases in performance, capacity, and effectiveness, and draw some conclusions about how military broadcast systems could benefit from this waveform in the future. The Global Broadcast Service, a DVB-based, one-way, high- capacity, Department of Defense (DoD) satellite system that is used for transfer of classified and unclassified video, imagery, and other information, will be presented in a case study to illustrate the potential impacts of migrating a DVB-S based system to the DVB-S2 standard. The paper focuses on the technology and waveform efficiency of the DVB-S2 standard in military satellite communication (MILSATCOM) applications and provides a clear description of the status and authority of this evolving standard. INTRODUCTION A second-generation standard for Digital Video Broadcast over Satellite (DVB-S), denoted DVB-S, Second Generation (DVB-S2) was ratified by the European Telecommunications Standards Institute (ETSI) in March 2005. DVB-S2 combines DVB-S and DVB-Digital Satellite News Gathering (DVB-DSNG) with advancements in coding technology and interactive services to provide capacity and reliability enhancements for a variety of applications. The enhanced features of the DVB-S2 standard will provide immediate and future capacity and availability benefits that can improve the performance and reduce cost for systems that currently implement DVB standards for media broadcast. DVB-S2 OVERVIEW AND FEATURES The DVB-S2 standard, described in ETSI document EN 302 307, builds upon the proven DVB-S and DVB- and Christopher Holt Michael Skowrunski Edwin Summers Booz Allen Hamilton McLean, VA DSNG standards through a feature set that combines the functions of both standards while incorporating advances in modulation and coding technologies. In addition, DVB-S2 includes advanced modes of operation such as Variable Coding and Modulation (VCM) and Adaptive Coding and Modulation (ACM) that enable dynamic, variable modulation and coding on a per-stream or per- user basis. In contrast to Constant Coding and Modulation (CCM) these advanced modes allow carrier adaptation to terminal characteristics and link conditions and improve system throughput and availability. This section will briefly introduce the features in DVB-S2 and describe the benefits over the current DVB-S standard. Table 1 provides a brief comparison of the feature set of each standard. Table 1. Comparison of DVB-S and DVB-S2 Features II~~~~~~~ Ii Modulation QPSK QPSK, 8PSK, 16APSK, 32APSK Coding Viterbi and Reed LDPC and BCH Scheme Solomon 1/4, 1/3, 215, 1/2, Coding Rates 1/2,213,314,516,7/8 315,213,314,415, 516, 819, 9/10 VCM and ACM* Coding No (CCM only) (*Requires return channel) Roll-Off 0.35 0.20, 0.25, 0.35 Spectral 1.0 - 1.75 bits/Hz 0.5 - 4.5 bits/Hz Efficiency MODULATION AND CODING DVB-S relies on a single modulation mode, Quadrature Phase-Shift Keying (QPSK). Four modulation modes are available in DVB-S2, as pictured in Figure 1. Two lower-order modes, QPSK and 8 Phase-Shift Keying (8PSK), exhibit nearly constant modulation envelopes and are well-suited for broadcast operations over satellite transponders in saturation.' QPSK is a robust mode that can operate even under poor link conditions, down to C/N > -2.4 dB with appropriate coding. When operating near or below the noise floor, optional pilot symbols can I "DVB-S2 - Ready for Lift Off' Morello and Mignone, 2. Page 1 of 7

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Page 1: [IEEE MILCOM 2005 - 2005 IEEE Military Communications Conference - Atlantic City, NJ, USA (17-20 Oct. 2005)] MILCOM 2005 - 2005 IEEE Military Communications Conference - DVB-S2 Benefits

DVB-S2 BENEFITS FOR MILITARY BROADCAST SYSTEMS

Bruce BennettDefense Information Systems Agency

Arlington, VA

ABSTRACT

The Digital Video Broadcast - Satellite, SecondGeneration (DVB-S2) protocol has been developed andstandardized as an evolution of the Digital VideoBroadcast- Satellite (DVB-S) waveform for Europeansatellite broadcasting by the EuropeanTelecommunications Standards Institute (ETSI), and is acandidate for use in US military systems that employDVB-S. This paper will describe the evolutionaryefficiencies of DVB-S2 over DVB-S, increases inperformance, capacity, and effectiveness, and drawsome conclusions about how military broadcast systemscould benefit from this waveform in the future. TheGlobal Broadcast Service, a DVB-based, one-way, high-capacity, Department ofDefense (DoD) satellite systemthat is used for transfer of classified and unclassifiedvideo, imagery, and other information, will be presentedin a case study to illustrate the potential impacts ofmigrating a DVB-S based system to the DVB-S2standard. The paper focuses on the technology andwaveform efficiency of the DVB-S2 standard in militarysatellite communication (MILSATCOM) applicationsand provides a clear description of the status andauthority ofthis evolving standard.

INTRODUCTION

A second-generation standard for Digital VideoBroadcast over Satellite (DVB-S), denoted DVB-S,Second Generation (DVB-S2) was ratified by theEuropean Telecommunications Standards Institute(ETSI) in March 2005. DVB-S2 combines DVB-S andDVB-Digital Satellite News Gathering (DVB-DSNG)with advancements in coding technology and interactiveservices to provide capacity and reliability enhancementsfor a variety of applications. The enhanced features ofthe DVB-S2 standard will provide immediate and futurecapacity and availability benefits that can improve theperformance and reduce cost for systems that currentlyimplement DVB standards for media broadcast.

DVB-S2 OVERVIEW AND FEATURES

The DVB-S2 standard, described in ETSI document EN302 307, builds upon the proven DVB-S and DVB-

and

Christopher HoltMichael SkowrunskiEdwin Summers

Booz Allen HamiltonMcLean, VA

DSNG standards through a feature set that combines thefunctions of both standards while incorporating advancesin modulation and coding technologies. In addition,DVB-S2 includes advanced modes of operation such asVariable Coding and Modulation (VCM) and AdaptiveCoding and Modulation (ACM) that enable dynamic,variable modulation and coding on a per-stream or per-user basis. In contrast to Constant Coding andModulation (CCM) these advanced modes allow carrieradaptation to terminal characteristics and link conditionsand improve system throughput and availability. Thissection will briefly introduce the features in DVB-S2and describe the benefits over the current DVB-Sstandard. Table 1 provides a brief comparison of thefeature set of each standard.

Table 1. Comparison ofDVB-S and DVB-S2 FeaturesII~~~~~~~Ii

Modulation QPSK QPSK, 8PSK,16APSK, 32APSK

Coding Viterbi and Reed LDPC and BCHScheme Solomon

1/4, 1/3, 215, 1/2,Coding Rates 1/2,213,314,516,7/8 315,213,314,415,

516, 819, 9/10VCM and ACM*

Coding No (CCM only) (*Requires returnchannel)

Roll-Off 0.35 0.20, 0.25, 0.35Spectral 1.0 - 1.75 bits/Hz 0.5 - 4.5 bits/HzEfficiency

MODULATION AND CODING

DVB-S relies on a single modulation mode, QuadraturePhase-Shift Keying (QPSK). Four modulation modes areavailable in DVB-S2, as pictured in Figure 1. Twolower-order modes, QPSK and 8 Phase-Shift Keying(8PSK), exhibit nearly constant modulation envelopesand are well-suited for broadcast operations over satellitetransponders in saturation.' QPSK is a robust mode thatcan operate even under poor link conditions, down toC/N > -2.4 dB with appropriate coding. When operatingnear or below the noise floor, optional pilot symbols can

I"DVB-S2 - Ready for Lift Off' Morello and Mignone, 2.

Page 1 of 7

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be included in the physical layer framing structure of thetransmitted signal to assist the receiver with carrierrecovery. The spectral efficiency of QPSK isapproximately 2 bits per Hertz (bits/Hz). 8PSK providesan improvement in spectral efficiency, -3 bits/Hz, whereimproved link conditions exist (5.5 < C/N < 11 dB)2.

Figure 1. DVB-S2 Modulation Modes

Two higher-order modulation modes, 16-ary AmplitudePhase-Shift Keying (16APSK) and 32APSK, tradepower efficiency for higher throughput when semi-linearsatellite transponders are available. As shown in Figure1, the constellation points for 16APSK and 32APSKreside on circles, which provides compensation fortransponder non-linearity. Pre-distortion methods canalso be employed at the uplink to mitigate the effects oftransponder non-linearity on higher-order modulationbroadcasts.3 With appropriate channel conditions andcode rate selection, spectral efficiency as high as 4.5bits/Hz can be realized with 32APSK. Higher-ordermodes require larger output back-off (OBO) at the TS toavoid saturation of the satellite transponder, and aretargeted at professional applications requiring higherthroughput. Carrier output can be shaped using one ofthree roll-off factors: uc=0.20, 0.25, and 0.35. Lower roll-off factors can accommodate tighter bandwidthrestrictions, although there is an increased risk of non-linear degradations in the carrier.4 High-ordermodulations and tighter roll-off factors can be used,individually or combined, to provide more throughputfor a given channel. Greater throughput is increasingly

2 "DVB-S2 - Ready for Lift Off' Morello and Mignone, 4.3"DVB-S2 - Ready for Lift Off' Morello and Mignone, 2.4 "DVB-S2 - Ready for Lift Off' Morello and Mignone, 5.

important for MILSATCOM systems to satisfy userdemands for high-definition video (MPEG-4, AdvancedVideo Coding [AVC]) and other bandwidth-intensiveapplications.

In addition to the availability of a variety of lower andhigher-order modulation modes, recent advancements inmanufacturing and processor technology also allowcommercial implementation of new forward errorcorrection (FEC) schemes that were once too complex tophysically implement.5 The DVB-S2 FEC system isbased on Bose-Chaudhuri-Hocquenghem (BCH) outercoding concatenated with Low Density Parity Check(LDPC) inner coding using normal (64800 bit) and short(16200 bit) block codes. LDPC coding rates range from1/4 to 9/10, enabling operations over seriously degradedlink conditions and increased capacity on clear channels.The new coding scheme combined with availablemodulation modes in DVB-S2 allow operation within0.7 - 1.2 dB of the theoretical Shannon limit.6 Figure 2illustrates the useful bit rate (Ru) over the range ofLDPC code rates and modulation modes available inDVB-S2.

819

0,2 0,3 0,4 0,5 06

LDPC code rate

0 7 O,R 0,9

Figure 2. Useful Bit Rates Versus LDPC Code Rate7

The increased coding efficiency of the LDPC block codewill provide an immediate improvement over theconvolutional code specified in the DVB-S standard.When modeled on an additive white Gaussian noise(AWGN) channel, the use of DVB-S2 with LDPCcoding and the same transmission conditions as a typicalDVB-S link will result in capacity gains of 25-30% (or

5"The DVB-S2 Satellite Standard Revealed" Newtec, 3.6 "DVB-S2 - Ready for Lift Off' Morello and Mignone, 5.7EN 302 307, ETSI, 64.

Page 2 of 7

Q Q

* 0 0

QPSK 8PSK

A~~~~~~~~~~~

0* 0- --* 0* 0 .0 0.

@00~~. .00._ 0-0000- 0 . 0, \ 000-

0 0**_l* 0

16APSK 0 0

32APSK

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2-2.5dB more link margin for the same spectralefficiency).8 Figure 3 depicts the theoretical spectrumefficiency over the C/N operating range of DVB-S2,with comparison to the current DVB-S efficiency.Additional capacity gains can be realized even onsaturated transponders by using 8PSK modulation wherelink conditions permit, though greater link margins arerequired. Large aperture terminals with very good linkconditions could take advantage of the significantspectral efficiency offered by 1 6APSK and 32APSK.While these modes will provide high capacities, carefulplanning should be employed to ensure link availabilityis maintained due to the high C/N requirements of thesemodes.

Spectrumefficiencyversus required C2fi1 on AWGN channel

4,5 -- r-

,D--'Dottedlirs~modulatiGncoznstaed. Shaon limit L_____m__+zI

3,......

3,....---1-r--l--0-_1sPI2,5

=3 =2=1= 1 2 :3 4 6 7 9 9 I0 11 12 13 1411i5=ri=

9 ,D -____ _ _ -_ 2__C_ND[dB]in_R.

Figure 3. DVB-S2 Spectral Efficiency versus C/N9

While current systems could realize an immediateperformance benefit by employing DVB-S2 with QPSKmodulation and the more efficient LDPC block codes,the diverse group of receive terminals and varying linkconditions in a system will likely make a full-scaleswitch to a higher-order modulation impractical.Effective use of the new operating modes will require amethod to target those modes to specific terminals orgroups of terminals. The next section describes howDVB-S2 enables this capability.

ADVANCED OPERATING MODES

The DVB-S system accepts a single input data streamand provides a single modulation and protection level forthis stream on the channel output. This CCM schemeresults in a simple broadcast mechanism that requires theprotection level of the output to be set based on the linkto the worst-case user. In this case the limiting factor ofthe broadcast channel capacity is usually the worst-caseuser, resulting in under-utilized capacity margins thatwould otherwise be available to large aperture terminalsor terminals in more ideal operating conditions. DVB-S2addresses this deficiency by offering a VCM mode and a

8 "DVB-S2 - Ready for Lift Off' Morello and Mignone, 5.9EN 302 307, ETSI, 64.

more advanced ACM mode that will allow systemplanners to make better use of available channelcapacity.

Variable Coding and Modulation

Figure 4 illustrates the DVB-S2 encoding andmodulation process, which consists of a layered framingstructure that can process and multiplex data from asingle or multiple MPEG-2 streams onto a single carrier.Data from individual streams is sliced into data packetsof a size determined by the LDPC block code length.The FEC system processes these data packets intoFECFRAMES which are bit-mapped to formXFECFRAMEs. Since each FECFRAME is composedof data from a single input stream, the protection leveland modulation of each stream can be set independentlyusing VCM. The ability to employ multiple modes on asingle carrier requires the receiver to determine the modeused prior to demodulation and decoding. DVB-S2specifies a physical layer frame (PLFRAME) thatencapsulates each FECFRAME and providesdemodulation and decoding instructions to the receivervia the PLFRAME header. The PLFRAME includes asingle FECFRAME and a physical layer header thatcontains the modulation and coding informationnecessary for synchronization and data recovery. Headerinformation is Binary Phase-Shift Keyed (BPSK) andencoded using a 7/64 block code. This provides a robustheader in a common mode that all receivers can decodeand process.

System planners could utilize VCM by assigningcategories based on terminal characteristics or typicallink conditions and designating separate input streams toeach category. The stream protection and modulationcould be adapted to the parameters of the terminalcategory based on the availability required for thoseservices or users. In a possible system scenariocontaining small and large terminals, small terminalswould be assigned to a highly-protected QPSK streamwhile large terminals received a less-protected, higher-order modulation stream to receive higher-data rateservices. Assuming operation on the same transponderbandwidth and with the same level of availability for allusers, overall system capacity could be significantlyimproved. Similarly, the total system capacity could bebaselined and the protection level lowered to reducebandwidth required for large aperture terminals. In bothcases, total system cost is reduced when compared to aDVB-S system by either eliminating the need to procurebandwidth for additional services, or by reducing thetotal system bandwidth required. A third option wouldbe to take advantage of the improved BCH/LDPCcoding efficiencies by reducing the size of the receive

Page 3 of 7

....r,I1I+

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terminals. In this case the coding efficiency gainsrealized by DVB-S2 would be applied to reducing thesize of the receiving antenna while keeping bandwidthand throughput constant. Smaller antennas will greatlyreduce logistical burdens and better supportdisadvantaged units in tactical operating environments.

Figure 4. DVB-S2 Encapsulation Process

Adaptive Coding and Modulation

DVB-S2's ACM feature allows interactive servicesystems that employ a return channel such as DVB-Return Channel Satellite (RCS) to dynamically setindividual stream modulation and protection parametersin real-time. In a typical ACM-enabled system, eachreceiver will measure the signal quality of thedownstream link and report the value and a preferredmodulation and coding level back to the hub through thereturn channel. The hub evaluates the report and can

change the modulation and coding parameters tosuccessive frames addressed to that user accordingly.Modulation and coding can be changed in this manner

on a frame-by-frame basis. Successful implementationof ACM will require careful analysis of the feedbackloop delay to ensure that link adaptations can beprocessed in a timely manner to maintain serviceavailability through periods of fast fading. In addition,variable bit rate (VBR) codecs or other payloadthrottling techniques may be required to adjust theincoming stream rate when the link capacity has beenreduced due to fading. Availability of critical servicesthrough fading periods will also require development ofquality of service (QoS) factors to distinguish criticalservices from low-priority or routine data.

Dynamic signal protection with ACM will allow systemplanners to significantly reduce the fade margin that iscurrently built-in to link budgets as overhead, resultingin significant improvements in capacity whilemaintaining the same level of availability. The benefitsof ACM are realized on a per-user basis, allowing a

system of diverse terminals and link conditions tooperate with even greater efficiency than VCM alone. Asystem employing ACM can realize capacity gains up to200% compared to systems using CCM.10By taking advantage of innovations in manufacturingtechnology and advancement in modulation and codingschemes, DVB-S2 presents a scalable and efficientfeature set that will be suited for a variety ofapplications. Integration of DVB-S2 into MILSATCOMarchitectures will allow realization of significant gains insystem flexibility, bandwidth efficiency and availability.

DVB-S2 GBS TECHNOLOGY INSERTION

Open standards such as DVB are appropriate for militaryapplications where interoperability among systems is a

prime concern. For this reason current and future DoDprograms are strongly encouraged or required to adoptopen standard systems to ensure joint interoperabilityamong United States' (US), North Atlantic TreatyOrganization (NATO), and allied systems. As an

example, the DoD IP Modem Working Group draftspecification for the Joint Network-Centric InternetProtocol Modem System (JNIMS), which describes theIP modem system that will transform MILSATCOMnetworks to a net-centric model, specifies DVB-S2 as

the forward-link protocol citing the benefits of an

established, open standard that is available in COTSequipment. This section describes how a current DVB-based MILSATCOM system, the Global BroadcastService (GBS), could transition to DVB-S2 and realizeimmediate performance benefits.

The GBS was launched in 1999 as a worldwide, high-capacity, one-way transmission system that providesbroadcast of classified and unclassified video, imagery,and other information to joint military forces in garrison,in transit, and in theater. GBS enables real-timeinformation product delivery to the warfighter byproviding a combination of leased commercial andgovernment owned satellite communications payloadsthat are shared based on combatant commanders'/JointTheater Planning (JTP) commanders' priorities,operational locations, and the platform capabilities of thedeployed users. The system's significant role inOperation Enduring Freedom (OEF) demonstrated theimportance of real-time broadband content distribution

1o EN 302 307, ETSI, 6.

Page 4 of 7

DVB-S.2 System Resulting FrameStage

User Data Mode(MPEG-2 TS)] Adaptation

BBHEADER USER DATA PADDING(opt~ionl

Encoding

BBHEADER USER DATA BCH LDPC PADDING

Bit Mapping

XFECFRAME

PhysicalLayer

Framing

PLHEADER XFECFRAME

ModulatedSignal Modulation

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over previously used low-speed terrestrial networks andmail delivery services for broadband informationproducts such as broadcast video and large imageryfiles."

Initially the GBS system was designed around aproprietary, ATM-based technology that was difficult tomanage and scale. As commercial technologies andstandards matured, the GBS Joint Program Office (JPO)and the Defense Information Systems Agency (DISA)led a technology refresh effort to transform thearchitecture to open standards communicationstechnology using commercial DVB and IP products.This technology refresh effort has significantly enhancedthe capabilities and real-time IP-based services that GBSprovides to theater- deployed warfighters, whilereducing cost, size, and complexity of TS and RSequipment.

GBS Transmit Suites (TS), currently located in Norfolk(VA), Sigonella (Italy), and Wahiawa (HI), collect datato be disseminated to end-users and transmit it tosatellite uplinks. The current architecture enables thesystem to ingest IP content directly from customernetworks as well as from sources that are staged locallyto the TS, as illustrated in Figure 5. Packets destined forbroadcast are statistically multiplexed and encapsulatedusing Multiprotocol Encapsulation (MPE)'2 at the IPgateway. The resulting Moving Pictures Expert Group -

2 Transport Stream (MPEG-2 TS) is delivered by to theDVB-S modulator and broadcast to end-user ReceiveSuites (RS) which receive, decode, process, and deliverthe data to backend communication networks.

Figure 5. GBS Architecture Content Flow

Inserting the DVB-S2 technology into the GBS systemwill require an equipment refresh to implement the newstandard while maintaining the integrity of existing data

1 "GBS Next Generation Architecture", Bennett, Holt, et al, 1.12 EN 301 192, ETSI, 14.

interfaces. While this would not be a trivial task in thelegacy, proprietary-based GBS architecture, the currentarchitecture based on IP and DVB standards enablesrapid integration of commercial-off-the-shelf (COTS)technologies. With the possible exception of a minorsoftware upgrade, replacement of the DVB-S modulatorsand integrated receiver decoders (IRD) with DVB-S2versions as shown in Figure 6 will be the only actionrequired to complete the effort.

Figure 6. GBS Upgrades to support DVB-S2

At the GBS TS, existing DVB-S modulators will bereplaced with modulators conforming to the DVB-S2standard. Interfaces for data ingress and RF egress willremain unchanged, allowing for a simple replacementwith COTS equipment. Full execution of the refresh mayalso require an upgrade of the IP gateway to supportUnidirectional Lightweight Encapsulation (ULE), whichcan be accomplished with a software upgrade.

The GBS system currently uses MPE to package IP datainto the MPEG-2 TS format. This process, described inthe DVB Specification for Data Broadcasting13, allowsfor transport of private data on MPEG-2 transportstreams using the Digital Storage Media Command andControl (DSM-CC) datagram section structure. DSM-CC sections were developed to generically support arange of applications and therefore are not optimized fortransporting IP packets. MPE appends a 17 byte headerto each IP(v4) datagram prior to fragmenting it intoMPEG-2 TS packets. The large header reducesefficiency of the logical channel and creates excessprocessing overhead at the sending and receivingstations.

ULE has been proposed as a more efficientencapsulation protocol to address the problemsassociated with MPE. The ULE process encapsulates theprotocol data unit (PDU) with a header to form asubnetwork data unit (SNDU) and places it directly into

13EN 301 192 v1.4.1, ETSI, 14.

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the MPEG-2 TS packet through a process called datapiping. A completed SNDU header ranges from 8 bytesto 15 bytes in length, depending on the inclusion of theNetwork Point of Attachment (NPA) address, and isindependent of the IP version being transported (IPv4 orIPv6). The smaller encapsulation header size in ULEwill result in improved channel efficiency and reducedprocessing latency at sending and receiving stations.

In the GBS RS, the IRD performs all functions relatingto demodulation and de-encapsulation of the incomingsignal, hence Receive Suites must be updated with IRDsthat comply with DVB-S2 and ULE standards. Thischange will likely not affect the IRD physical interfacesand will therefore be transparent to the remainder of theRS architecture.

Scheduling must be carefully considered whenundertaking an upgrade of a critical portion of thebroadcast system architecture. Intermediary measuresmust be taken to ensure continuity of service throughoutthe transition period. Some COTS vendors are helping tomitigate interoperability issues between legacy andDVB-S2 equipment by including DVB-S capabilities inDVB-S2 modulators. This would allow a GBS TS to beupgraded for DVB-S2 yet continue to support the userpopulation with the legacy protocol until all ReceiveSuites can be updated to support the new protocol.

GBS DVB-S2 CASE STUDY

A case study using the GBS architecture, currently basedon DVB-S, will illustrate the potentially significantbenefits that can be realized by refreshing thearchitecture with the DVB-S2 standard. This case studywill examine notional Wideband Gapfiller System(WGS) satellite links in the GBS system to show howthe improved coding efficiency and VCM modeavailable in DVB-S2 can improve system throughput.Some features introduced by DVB-S2, such as additionalroll-off factors and ACM, will not be studied in thefollowing examples though it is understood that their usemay allow improved performance and efficiency abovethese cases.

The WGS system will initially consist of three satellitesthat will provide expanded Ka-band coverage for theGBS system. Each satellite could augment the currentGBS transport capacity by providing four transponderseach carrying 45 megabits per second (Mbps) ofinformation for a total capacity augmentation of540Mbps.

Table 2 lists some parameters from a notional linkbudget calculation for the WGS system that will be usedin the following examples. Although the 2 meter (m)terminal exhibits a higher link margin and could support

higher data rates, DVB-S supports only one coding andmodulation scheme for the carrier therefore the linkbudget must support the worst-case terminal at the costof reduced potential throughput for the entire system.

Table 2. Example GBS Link ParametersI'1

DVB-S TXParameters

QPSK w 36.6Msps (o=0.35), 2/3Convolutional, Reed Solomon

Antenna Size 0.9m 2.OmPredicted Eb/N0 6.4dB 10.4dBRequired Eb/N0 4.7dB 4.7dB

Margin 1.7dB 5.7dBThroughput 45Mbps

The immediate benefit that DVB-S2 could provide to thesystem described above is coding efficiency. Comparedto the Reed Solomon (204,188) outer coding in DVB-S,the BCH outer coding in DVB-S2 uses larger block sizesyielding efficiency improvements on the order of 3-8%.However, the LDPC inner coding provides the mostsignificant benefit, allowing the use of a more aggressiveFEC scheme on a specific link. In the example above, aDVB-S2 system could support QPSK at 8/9 FEC(required Eb/N0=4. 1dB14) yielding a throughput of65Mbps as shown in Table 3. When factored across thesystem the total augmented capacity increases 44% to780Mbps, or the equivalent throughput of approximately5 transponders. The calculations assume the use ofnormal FECFRAMES.

Table 3. Encoding Comparison for GBS ExampleIi1M ITi.

Modulation QPSK a 36.6Msps QPSK V36.6Msps

Inner Coding Convolutional @ 2/3 LDPC @ 8/9Outer Coding Reed Solomon BCHThroughput 45Mbps 65Mbps

System Capacity 540Mbps 780Mbps

While the example in Table 3 illustrates the benefitsprovided by improved coding efficiency in DVB-S2, itdoes not address the fact that the link must be designedfor the worst-case terminal. Although throughput hasbeen significantly improved, the link budget for the largeterminal contains excessive margin, which translates tounderutilization of the transponder. Using DVB-S itwould be possible to service small and large terminalpopulations on separate, independently-modulatedcarriers at the expense of a second transmitter chain.DVB-S2 provides a more elegant solution throughVCM, which allows both terminal populations to be

14 SkyPHY Receiver DVB-S2 Evaluation Platform ProductBrief, Efficient Channel Coding, Inc., 1.

Page 6 of 7

:

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serviced from a single carrier that is variably modulatedand encoded. This solution essentially "simulcasts"separate data streams to large and small apertureantennas.

A potential DVB-S2 VCM solution can be formed bybuilding on the example above, continuing to use theterminal populations described in Table 2. The smallterminal population will realize a performance gainthrough the benefit of DVB-S2's coding efficiency. Thelink margin for the large terminal population will beutilized by employing a higher-order modulation andappropriate coding. In this case, 8PSK with 5/6 LDPCcoding was chosen to illustrate the improved throughputwith the higher-order modulation that will be achievedwhile maintaining a reliable link margin. The parametersand resulting throughput estimates are shown in Table 4.

Table 4. GBS Example with VCM

Modulation QPSK QPSK 8PSKInner Convolutional LDPC @ 8/9 LDPC @ 5/6

oding 2/3__OuterCoding Reed Solomon BCH BCH

Throughput 45Mbps 38.3Mbps 3 7. 4Mbps(combined) 75.7MbpsSystem 540Mbps 908Mbps

By effectively reclaiming the portion of link margin thatwas unusable in a CCM system, total system throughputfor the VCM example increased 68%, the equivalent ofapproximately 8 transponders. A system planner couldallocate carrier bandwidth as needed to satisfy thechannel requirements of each terminal population, withthe overall result of an increase in transponderutilization. Allowing the system planner to takeadvantage of link margin that was previously unusedtranslates to considerable savings on transponder costs.

A final example demonstrates how the DVB-S2efficiency can be used to reduce the size of the receivingterminal. The sample link parameters in Table 2 includea 0.9m antenna similar to that found in the NextGeneration Receive Terminal (NGRT). Reducing thesize of the antenna would provide many benefits for thewarfighter, including reduced size and weight of thesuite and shorter setup time. Table 5 lists the results of acomparison between DVB-S and DVB-S2 with the 0.9mantenna, and DVB-S2 over a 0.7m antenna (QPSKmodulation with 2/3 encoding). DVB-S2 requiresapproximately 2.3dB less link margin to maintain the

signal, which the example shows can be used to reducethe antenna size by 28%.

Table 5. GBS Receive Antenna Size Comparison

I EmmoMiI I MII-Antenna Size 0.9m 0.9m 0.7mThroughput 45Mbps 48.6Mbps 48.6MbpsDelivered 6.4dB 6.4dB 4.3dB

/N o_

Required 4.7dB 2.4dB 15 2.4dBEb/No 1. 7dB 4._OB_1_9dMargmin 1.7dB 4.0OdB 1.9dB

The previous examples provided simple predictions tothe benefits of integrating DVB-S2 into the GBS system.Actual improvements in bandwidth utilization andthroughput will depend on link budgets for the entireterminal population, the margin necessary to maintainrequired system reliability, and the parameters of theactual transponders used in the system. The examplespresented do not account for other DVB-S2 features thatwill provide further, potentially substantial benefits.Future completion of a planned upgrade to incorporatethe DVB-RCS standard will enable use of DVB-S2'sACM functionality, which will allow further reclamationof link margin for providing data on a real-time basis asconditions allow.

CONCLUSIONS

This paper has summarized the features presented in theDVB-S2 standard, described the improvements inchannel efficiency over DVB-S, and presented examplesdemonstrating the immediate and future benefits ofincorporating DVB-S2 in MILSATCOM systems. DVB-S2 can provide significant improvements in capacity,receive suite size, and long-term operational costs.Benefits of a GBS migration to DVB-S2 will likely beincremental as the standard is incorporated and systemplanning evolves to adopt new features. The long-termintegration of the DVB-S2 standard into GBS willimprove the system's high-capacity broadcasts to thejoint warfighting community and position GBS to realizefuture gains as it migrates to a two-way, interactiveservices-based architecture.

The authors wish to thank the following individuals fortheir invaluable contributions both to the GBStechnology refresh effort and to this publication: RoseThomas, Dr. Robert Sims, Mike Difrancisco,Christopher Ellis, Joseph Tolley, James Obi, DaveBeliveau, Mark Snellings, Keith Dyson, Mike Mulcahy,Kensing Quock, and Mathew Schuck.

15 SkyPHY Receiver DVB-S2 Evaluation Platform ProductBrief, Efficient Channel Coding, Inc., 1.

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