Terrestrial Mobile TV

Yan Binfeng Zhang Zhijiang

（China Unicom Co. Ltd.， Beijing 100032， China）

Abstra c t:Mobile TV services can be offered by the cellular communication network and the terrestria l/sate llite d ig ital b roadcasting network.There are four technologies for imp lem enting m obile TV.They are respectively based on the cellu lar mobile network,terrestria l d igital b roadcasting TV network,satellite,and app lication layer.Digital Video Broadcasting-Handhe ld（DVB-H）and Terrestria l-Digital Multimed ia Broadcasting（T-DMB）are two typical terrestrial d igital TV broadcasting standards.The form er is spec ified by the DVB Pro ject for delivering m ultim ed ia services to handheld term inals through the terrestria l d igital b roadcasting network,and the latter was launched in Korea on the basis of the Eureka-147 Digita l Aud io Broadcasting（DAB）standard.The developm ent ofm obile TV currently faces the p rob lem s concerning standards,frequency resources,regu lation and term inals.Mobile TV can be independently operated by the m obile operator or the b roadcasting and TV operator,or jointly operated by the two.Mobile TV is an im portant attemp t of integ rating these two networks.Moreover,the coord ination of supervision departments and the estab lishment of technical standards will d irec tly affect the p rog ress of d igital convergence in the future.

M obile TV is a service thatallows mobile subscribers to receive b roadcastd igitalaud io/video

content through channels by using intelligentmobile term inalsw ith operating system and videofunctions.

Mobile TV is imp lemented chiefly in two ways:one is to use the cellular mobile networks,through which China Mobile and China Unicom have rolled out theirmobile TV services,and the other is to use terrestrialor satellite digital b roadcasting,via which the handset equipped w ith a d igitalTV receiving module can d irectly receive d igitalTV signals.The latter is currently a p referred choice foroffering mobile TV service.

As an emerging multimed ia service,mobile TVhas aroused w idesp read concern in the industry.There have been heated researches on this service around the world.Over ten related technologies have been introduced,and they can be c lassified into the follow ing four types:

（1）Technologies Based on Mobile Networks These technologies use the spec trum bands occup ied by themobile communications system,and p rovide usersw ith downlink b roadcastchannels through imp roved mobile communications networks.The typical technologies inc lude Multimed ia BroadcastMulticastService（MBMS）and Broadcastand MulticastService（BCMCS）.

（2）Technologies Based on Terrestrial DigitalBroadcasting Networks

These technologies use the b roadcasting TV spec trum bands and are designed for terrestriald igital b roadcasting TV.Some aremobile TV technologies thatmake enhancements on the terrestrialdigitalb roadcasting TV technologies,such as DigitalVideo Broadcasting-Handheld（DVB-H）and Med iaFLO,while others are stillused for terrestrialdigitalb roadcasting TV systems,inc lud ing Korea's Terrestrial-DigitalMultimedia Broadcasting（T-DMB）,Japan's Integrated Services Digital Broadcasting-Terrestrial（ISDB-T）,DigitalMultimedia Broadcasting-Terrestrial（DMB-T）launched by Tsinghua University and Advanced DigitalTelevision Broadcasting-Terrestrial（ADTB-T）developed by ShanghaiJiao Tong University.

（3）Technologies Based on Satellite Broadcasting Networks

These technologies p rovide downlink transm ission via satellite.Typ ical technologies inc lude Europe's Satellite-DigitalMultimed ia Broadcasting（S-DMB）,as wellas Japan's and Korea's S-DMB.

（4）Technologies Based on App lication Layer Rep resented by the Open Mobile Alliance Broadcastservice group（OMA BCAST）,these technologies define the im p lementation ofmobile TV service in terms of the app lication layer.

This artic le introduces two typical terrestriald igitalb roadcasting TV technologies:DVB-H and Korea's T-DMB,and d iscusses themain p rob lem s in the developmentof mobile TV.

1 DVB-H Standard

1.1 DVB-H Network Architecture

DVB-H uses the digitalterrestrial network fordownlink transm ission of mobile TV content.Itadop ts the cellular mobile network foron-demand services,userauthorization and accounting,customerservice and interactive backhaul.Its network architecture consists of the d igitalterrestrialnetwork and cellularmobile network,as shown in Figure 1.

▲Figure 1. DVB-H network architecture.

1.2 DVB-H Key Technologies

The DigitalVideo Broadcasting（DVB）standard fam ily was firstput forward by the DVBProject in the early 1990s.Digital Video Broadcasting-Terrestrial（DVB-T）was developed during them id 1990s and was accep ted as a European DVB standard by the European

Telecommunications Standard Institute（ETSI）in Feb ruary 1997.The DVB-T standard has been adop ted in 59 countries and regions around the world inc lud ing Australia,New Zealand,Brazil and Singapore,in add ition to European countries.From the overallapp lication perspective,the DVB-T technologies have been quitemature.

DVB-H is based on DVB-Tand full backward compatib le.DVB-H services can share the DVB-Tmultip lexerw ith Moving Pic ture Experts Group phase 2（MPEG-2）services.DVB-H was app roved by the ETSIin 2004 as a Europeanmobile TV standard.DVB-H networks have been builtand tried for commercialuse inmore than 20 countries worldw ide.

DVB-H allows simultaneous transm ission ofmultip le channels of television,rad io and video tomobile handheld devices inc ludingmobile phones.Ituses time slicing to reduce power consum p tion of receiving devices,and adds Cell Identifiers（Cell IDs）to support fastscanning ofsignals and frequency handoff.Moreover,itimp roves the intensity ofsignals received inmobile environments,thus supporting indoor,outdoor,portab le and mobile scenarios.

Compared to DVB-T,DVB-H adds the follow ing technologies:

（1）Introduction of time slicing to reduce power consum p tion

In order to reduce the receiver's power consump tion,DVB-H sends data in burstmode,i.e.,one service exc lusively occupies allbandw id th of the system to send data fora certain time（such as 200ms）,and then the next service is sent.Afterallservices are sent（such as after4 s）,the firstservice w illbe retransferred.The receiveronly needs to receive signals ata specified time,and can be c losed atanother time.As data are transferred ata high rate,the duration ofeach time segmentw illbe very short.Therefore,the receiver is in a dormantor c losed statemostof the time,saving a maximum of90%of the power consum p tion.

（2）Introduction of4Kmode to achieve w ide area coverage while supporting mobility

The 4Kmode in DVB-H uses 3 409 carriers.Each subcarrierhas three modulationmodes:Quad rature Phase ShiftKeying（QPSK）,16Quad rature Amp litude Modulation（QAM）and 64QAM.

（3）Introduc tion ofMultiProtocol Encapsulation-Forward ErrorCorrec tion（MPE-FEC）to deliver IP-based services and to enhance anti-interference capability

The MPE-FEC technology adds Reed-Solomon（RS）error correction codes in IP packets.The MPE-FEC frames are arranged in amatrix w ith 255 columns.The numberof thematrix rows can vary from 1 to a given value（the maximum value is 1 024）.Therefore,the maximum MPE-FEC frame occupies 2 megabits.

DVB-H has the following advantages:

·Low term inalpower consump tion:The receiver is open to receive IP-based packets foronly 10%of the whole transfer time.

·Seam less handover:Only one receiver is used to com p lete the handoff and ensure the service continuity.

·Enhanced mobile and portab le receiving capability:MPE-FEC enhances the recep tion ofweak signals,imp roves anti-interference competence and supports transferofhigh-speed mobile data.

·Large capacity:Itcan transfer40 to 50 TV channels w ithin the 8MHz bandw id th.

·High flexibility:Itallows flexib le capacity selection and cellsize by using mobile signalrecep tion of individual antenna inm idd le-to large-sized Sing le Frequency Networks（SFN）.

·Com patib le w ith DVB-T:DVB-H and DVB-Tare based on the same physical layer；thus,they can use the samemodulatorand transm itter.

In the DVB-H technicalsolution,IP Datacast（IPDC）fulfills the authentication of its users through themobile network.Moreover,concerning the billing and accounting,customer care and customer managementofmobile TV services,as wellas other services such as Video on Demand（VoD）,downloading and web b rowsing,are also im p lemented through themobile network.The IPDC solution p rovides the standard Sim p le Network ManagementProtocol（SNMP）interface to enab le interoperabilityw ith the operator's existing networkmanagement system.

▲Figure 3. T-DMB transport structure based on the Eureka-147 DAB.

The p rocess ofuserauthentication im p lemented in the IPDC solution is as follows:

（1）Amobile term inaluser sends a request fora p rog ram to the IPDC core app lication system in the form ofa short message；and then,the core app lication system authenticates the userafter receiving the request.

（2）After the authentication,the core app lication system w illsend the Rights Ob ject（RO）in the Open Mobile Alliance（OMA）DigitalRights Management standard（DRM）.

（3）After receiving the RO in the OMA DRM,themobile term inalcan open the related security file and use the key to decryp tand d isp lay the enc ryp ted video p rogram.

The IPDC solution imp lements billing formobile TV services based on the mobile operator's existing billing system.The related CallDetailRecords（CDRs）are generated in the IPDC core app lication system,and are then transferred to the billing system forbilling and accounting.

The IPDC solution p rovides a managementsystem specially designed for configuration and monitoring of the IP Encapsulator（IPE）.The operator can also use the existing network managementsystem to im p lement centralized monitoring of the alarms sent from the IPDC core app lication system and IPE.The faultmanagementinterface is based on the standard SNMP.

2 Korea's T-DMB Standard

2.1 T-DMB Network Architecture

The T-DMB network architec ture is shown in Figure 2.The T-DMB transportstructure based on the Eureka-147 DAB is shown in Figure 3.

The T-DMB transfer frame consists of three channels,namely,the Synchronous Channel（SC）,the Fast Information Channel（FIC）and the Main Service Channel（MSC）,as shown in Figure 4.

FIC consists ofseveralFast Information Blocks（FIBs）thatare responsib le for transferring the control information necessary for interp retation of the MSC configuration.The core of the controlinformation is the Multip lexer Configuration Information（MCI）,which contains themultip lexerstruc ture information and necessarymultip lexer reconfiguration information.Other information inc luded in the FIC indicates Service Information（SI）,Cond itional Access（CA）managementinformation and Fast Information Data Channel（FIDC）.In order to respond to the MCIin a fastand securemanner,the FIC is neither interleaved in time nor transferred by adop ting high-levelerror p rotection mechanism.

The MSC contains a series of Common Interleaved Frames（CIFs）.ACIF is transm itted every 24m s and contains 55 296 bits.ACapacity Unit（CU）is the smallestadd ressab le unitofa CIFand contains 64 bits.An integ ral numberofCUs can form the basic transferunitof the MSC,also called the sub-channel.These sub-channels are multip lexed in the MSC.

Figure 4. ►T-DMB transfer framestructure.

▲Figure 2. T-DMB network architecture.

▲Figure 5. Schematic diagram of T-DMB video multiplexer.

Two transportmodes are defined for service com ponents in the MSC:the stream mode and the packetmode.In the stream mode,service components are transferred ata fixed bit rate in a given sub-channel.The packetmode may be defined for the purpose of conveying severaldata service com ponents into a sing le sub-channel.Each sub-channelmay carry one or more service com ponents.

T-DMB,based on the Eureka-147 DAB,supports Korean language and enhances the ability ofusing a stream-mode data channelto transfer video,aud io and data services.Formore details,p lease refer to the ETSIEN 300 401 standard.

When using a stream mode data channelto transm itvideo,aud io and data services,T-DMB has an additionalvideo multip lexer.Figure 5 shows a schematic d iag ram of the videomultip lexer.

The relative functionalmodules in Figure 5 are described as follows:

·The InitialOb jec tDescrip tor（IOD）generator creates an IOD conform ing to the ISO/IEC 14496-1 standard.

·The Ob jec tDescrip tor（OD）/Binary Format for Scenes（BIFS）generator creates an OD/BIFS stream conform ing to the ISO/IEC 14496-1 standard.

·The AVC video encoder transform s the inputvideo signals into the regulated bitstreams following H.264/AVC standard.

·The Bit-Sliced Aud io Coding（BSAC）audio encoder transforms the inputaud io signals into the bitstream s follow ing ISO/IEC 14496-3 BSAC standard.

·The Synchronization Layer（SL）packetizergenerates an SL packet from the inputdata stream s accord ing to the ISO/IEC 14496-1 standard.

·The section generator creates a section inc lud ing an IOD/OD/BIFS accord ing to the ISO/IEC 13818-1 standard.

·The Packetized Elementary Stream（PES）packetizer transforms the inputSL packetinto a PES packet follow ing ISO/IEC 13818-1 standard.

·The TransportStream（TS）multip lexer can encapsulate the input section and PES packetinto MPEG-2 TS stream.

·Themultip lexed MPEG-2 TS is errorp rotec ted by the outerencoder RS（204,188）.

·Ifa data stream has errorp rotection im p lemented by the outerencoder RS（204,188）,itis interleaved into a video service stream in the convolutional interleaver.

2.2 T-DMB Key Technologies

T-DMB adop ts key technologies such as OrthogonalFrequency Division Multip lexing（OFDM）modulation,frequency/time interleaving,convolution encod ing,RS encoding,convolution interleaving and Sing le Frequency Network（SFN）.Each of these technologies is d iscussed furtherbelow.

（1）OFDM Modulation

OFDM is a high-speed transm ission technology in w ireless conditions.OFDM divides a given channelinto several orthogonalsub-channels in the frequency domain,each sub-channel uses one sub-carrier formodulation,and allsub-carriers are transm itted parallelly.In this way,each sub-channelis relatively flat,although radio channels are not flatand are frequency selective.The signalbandw id th is less than the correspond ing channelbandw id th,that is,the signalis narrowband transported through each sub-channel.Therefore the Inter-Symbol Interference（ISI）is significantly reduced.Allsub-channelcarriers in the OFDM system aremutually orthogonaland theirspectrums are overlapping,which notonly reduces inter-carrier interference butalso im p roves spectrum efficiency.Tab le 1 shows themain OFDM modulation parameters adop ted by T-DMB.

▼Table 1. Main OFDM modulation parameters adopted by T-DMB

◄Figure 6.Convolution encoder.

（2）Frequency/Time Interleaving The purpose of interleaving is to rearrange data in the time or frequency domain to p rotectagainstsignal fad ing and error transm ission.T-DMB adop ts the time and frequency interleaver,and p rovides d ifferentparameters for d ifferentsend ingmodes.Furthermore,the time interleaving is app licab le for outputs ofvarious convolutional encoders.Itis app licab le for the sub-channelsignals ofMSC,butnot for those of FIC（see the ETSIEN 300 401 standard）.

（3）ConvolutionalEncod ing

Channelcod ing is based on the punctured convolutionalencoding,and it can im p lementboth EqualError Protection（EEP）and UnequalError Protection（UEP）,depend ing on the bit errorsensitivity（see the ETSIEN 300 401 standard）.

Convolutionalencod ing parameters vary in transported service type,netbit rate and errorp rotection level.The error p rotec tionmethods inc lude UEP and EEP.The UEP scheme is basically designed foraud io,but itcan also be app licab le fordata.However,the alternative EEP app roach is app licab le forboth data and aud io.

The octalpolynom ials generated by the four symbolic vectors are 133,171,145,and 133.The structure of the convolution encoder is shown in Figure 6.

（4）RSEncoder

The specifications forRS outer encoder comp lyw ith the ETSIEN 300 744 standard,in which a shortened RS（204,188,t=8）encoder derived from the RS（255,239,t=8）is defined.

（5）Convolutional Interleaving

The specifications for convolutional interleaving com p ly w ith the ETSIEN 300 744 standard.Figure 7 illustrates a concep tualdiagram of the outer interleaverbased on the Forney app roachwhich follows the Ramsey type IIIapp roach,w ith I=12.

（6）SFN

In order to achieve reliab le coverage for certain service areas,SFN uses multip le rad io transm itters,which are synchronous but located in d ifferent p laces,to simultaneously send the same signalover the same frequency channel.

SFN hasmany attrac tions.Firstly,it facilitates frequency p lanning,b rings a g reatsaving ofvaluab le frequency resources and imp roves spectrum efficiency.Second ly,due to the inherent nature of the rad io signal,whateverhigh transm itting powera sing le d igitalTV transm ittermay p rovide,there are always areas notcovered by any signalin a city w ith towering skyscrapers.These areas are called b lind areas orb lind spots.SFN can solve the p rob lem ofb lind areas coverage and achieve better coverage bymeans ofmulti-pointco-channel transm itting.Third ly,the SFN technology can reduce the transm itter cost.By op tim izing and ad justing the sing le-frequency transm itting network（inc lud ing the quantity and distribution of BTSs,heightof the transm itting antenna,and transm itting power）,several low-power transm itters can be used to rep lace one high-power transm itterso as to reduce signal rad iation and elec tromagnetic pollution,enhance coverage evenness,and change the coverage intention as required atany time.T-DMB adop ts the SFN technology to imp lementan effective and reliab le coverage forservice areas.

▲Figure 7. Schematic diagram of convolutional interleaver.

3 Feasibility Analysis of Dep loying Mobile TV Service

3.1 Problem s

The follow ing p rob lem s are faced while dep loying mobile TV service:

（1）Standard Prob lem

China is now stipulating its own DTV terrestrialtransm ission standard and w ill p robab ly release the related mobile TV standards.

（2）Frequency Resource Prob lem

When analog TV is comp letely c losed,the vacanthund reds of megabytes frequency resource（VHF,UHF）w illeffec tively alleviate the spectrum scarcity.However,in the transition period,the coexistence of analog and d igitalb roadcasting will worsen the already existing shortage of frequency resource.

（3）Regulation Prob lem

Generally,the b roadcasting and communications fields in each country have d ifferent requirements,and they are alsomanaged by d ifferentgovernment departments.Each country p laces strict restric tions on the enterp rises in the related fields.

（4）Term inalProb lem

Itis necessary to solve the term inal p rob lems such as low network transm ission rate,shortbattery life and small-sized design.

3.2 Operation Modes

Mobile TV servicemay havemultip le operationmodes.Based on China's cond itions,itcan be operated in three modes:independentoperation bymobile operators,independentoperation by broadcasting and TVoperators,and joint operation by the above two.The following is a b riefanalysis of the three modes.

（1）IndependentOperation by Mobile Operators

Mobile operators invest in build ing mobile digitalb roadcasting and TV networks.However,this casemay occupy partof the frequency bands availab le foranalog TV,which needs to getapp rovalof the State Adm inistration ofRad io,Film and Television（SARFT）.However,the app rovalis difficult to obtain,and it's also d ifficult to get the operation license forb roadcasting and TV services.

（2）IndependentOperation by Broadcasting and TVOperators

Benefiting from related policies of the Chinese government,broadcasting and TV operators are superior in running mobile TV service.Itcan build a digital broadcasting network oriented tomobile devices to delivermobile TV services to mobile subscribers.Add itionally,itcan comp lete contentmaking,editing and channelintegration.As current b roadcasting and TV networks only p rovide downlink paths,they can neither supportuserauthentication and accounting,noroffer personalized services such as custom ized and interactive p rograms.

（3）JointOperation

Broadcasting and TV operators actas the downlink network supp lierand contentp roviderofmobile TV services whilemobile operators p rovide the up link network and are responsib le for operations inc luding userauthentication,accounting,service custom ization and p rog ram interaction.Besides,mobile operators can use the BCMCS/MBMS technologies to p rovide on-demand services as a supp lement to b roadcasting services through the mobile network.

4 Conclusions

The g row ing technologiesmake the boundary of the broadcasting and TV and communications industries b lurrier.Themobile operator is the controller of term inals and telecom pathswhile the broadcasting and TVoperator is the aud io/video contentp rovider.Both of them are necessary formobile TV service.

In fac t,both the stream ing TV based onmobile networks and the b roadcasting mobile TV based on w ireless d igitalTV technology need the cooperation of the two operators.

In term s ofpolicies,the broadcasting and TV operatorowns both the license to runmobile TV services and themobile TV p rogram copyrightwhile themobile operator controls themobile network to carrymobile TV services.Presently,only through the jointcooperation of the two,canmobile TV service be dep loyed.

In terms ofservices,themobile operator dep loys stream ing TV services thatneed the contentsupport from the broadcasting and TV operator；the b roadcasting and TV operator rolls out the b roadcasting mobile TV thatneeds the handsetusermanagementsystem supp lied by themobile operator to comp lete service accounting and customerafter-sales service.

In terms ofsubscribers,low p riced buthigh quality broadcastservices,as wellas personalized interactive services,are desired.Therefore,there exists the basis and necessity for the two operators to cooperate,and the related departments shallstreng then communication to jointly work towards feasib le cooperative solutions.Mobile TV is an im portantattem p t for the convergence of communications and b roadcasting and TV industries.The coord ination ofsupervision departments and the estab lishmentof technical standardsw illd irectly affec t the p rog ress of trip le p lay in the future.