05559401

504 IEEE TRANSACTIONS ON BROADCASTING, VOL. 56, NO. 4, DECEMBER 2010

Embedded Transmission of Multi-Service OverDTMB System

Xiaoqing Wang, Jintao Wang, Jun Wang, Yangang Li, Shigang Tang, and Jian Song

Abstract—To efficiently support the transmission of terrestrialand mobile services within the same spectrum over the DigitalTelevision Terrestrial Multimedia Broadcasting (DTMB) system,a flexible multi-service datacasting scheme in a backward com-patible manner is proposed. Using this scheme, the conventionalDTMB receivers work as usual by simply selecting the specificterrestrial DTV programs on the basis of the package identifier(PID) checking, while only the desired mobile service data areprocessed by the mobile receivers via the designed control signals.Both theoretical analysis and computer simulation show that,at acceptable spectral efficiency penalty, the proposed methodnot only supports the embedded transmission of multi-serviceswith no reception performance degradation for the traditionalterrestrial broadcasting service, but also flexibly provides muchbetter mobile reception performance.

Index Terms—Backward compatibility, datacasting, digitaltelevision terrestrial multimedia broadcasting (DTMB), multi-ser-vices, package identifier (PID).

I. INTRODUCTION

D IGITAL Television (DTV) services can be broadcastedvia terrestrial, satellite and cable networks, among which

the digital television terrestrial broadcasting (DTTB) is themost important. In the past ten years, several DTTB standardshave been announced and implemented in different regionsof the world, and they are the USA-based ATSC (AdvancedTelevision System Committee) standard, the Europe-basedDVB-T (Digital Video Broadcasting-Terrestrial) standard,the Japan-based ISDB-T (Integrated Services Digital Broad-casting-Terrestrial) standard [1], and the China-based DTMB(Digital Television Terrestrial Multimedia Broadcasting) stan-dard [2], [3]. Recently, with the proliferation of mobile devicessuch as mobile phones and PDAs (personal digital assistants),there is an increasing demand for mobile-specific services

Manuscript received January 15, 2010; revised March 31, 2010; acceptedApril 06, 2010. Date of publication August 30, 2010; date of current versionNovember 19, 2010. This work was supported in part by the Ph.D. ProgramFoundation from Ministry of Education of China under Grant 20090002120026,the Chinese NSFC (National Natural Science Foundation of China) Projectunder Grant 20091300779 and the Chinese AQSIQ (Administration of QualitySupervision, Inspection and Quarantine) Project under Grant 200910244.

X. Wang, J. Wang, J. Wang, and J. Song are with the State Key Labo-ratory on Microwave and Digital Communications, the Tsinghua NationalLaboratory for Information Science and Technology (TNList), Department ofElectronics Engineering, Tsinghua University, Beijing 100084, China (e-mail:[email protected]; [email protected]; [email protected]; [email protected]).

Y. Li and S. Tang are with the Applied Science and Technology Research In-stitute Company Ltd., Hong Kong (e-mail: [email protected]; [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TBC.2010.2067550

beyond the reception of the terrestrial broadcasting services.For example, numbers of competing standards for mobile TVhave emerged, such as MediaFLO (Media-Forward Link Only)[4], T-DMB (Terrestrial-Digital Multimedia Broadcasting) [5],DVB-H (digital video broadcasting transmission system forhandheld terminals) [6], ATSC-M/H (Advanced TelevisionSystem Committee-Mobile/Handheld) and CMMB (ChinaMobile Multimedia Broadcasting) [7], and they all use thededicated spectrum of UHF with the frequency range from470 MHz to 862 MHz.

To revive the lack of spectral resource and provide flex-ible mobile services, there is an interest in extending theconventional DTTB systems to include the newly-introducedmobile services as well, which takes advantage of the residualthroughput setting aside for traditional terrestrial broadcastingservices, namely datacasting. For example, some improvedATSC systems were discussed in [8] and [9]. More recently,compatible transmission of terrestrial DTV and mobile serviceshas been introduced into the DVB-T2 standard [10]. However,all the above systems have to modify the original receiversto some extent, which will be uneconomic if conventionalreceivers have been widely used. To realize thorough backwardcompatibility with lots of existing receivers, improving originalDTTB systems by modifying merely the transmitter subsystemsis highly preferred and has attracted increasing attention fromboth academia and industry [11], [12].

The DTMB standard is capable to support both terrestrialand mobile applications, as a result, it would be convenient totransmit mobile services along with the terrestrial DTV pro-grams over the same spectrum. However, it is not clearly statedhow to effectively accommodate both terrestrial and mobile ser-vices simultaneously within the same band. As demonstrated in[2], when DTMB is applied to the multi-service transmissionscenario, the time division multiplexing (TDM) can be used,where all services have to accommodate to the fixed broad-casting method of the terrestrial DTV service. As a result, theTDM scheme does not perform well for mobile services. Thereasonable explanation is that, on one hand, the mobile environ-ment is very error-prone, as it presents more severe multipathfading and faster time variation. On the other hand, since mo-bile services are received at slow or high speed, the mobile datahave different quality of service (QoS) requirement, includinghigher receiving sensitivity and larger coverage area. Therefore,there is a need to flexibly provide lower SNR threshold than thefixed terrestrial DTV service. Besides that, the handheld termi-nals for mobile services have a number of features in common:small size, light weight, and battery operation, which all requirelower power consumption. Therefore, there is a need for im-proved methods to realize flexible multi-service transmissionbased on different QoS requirement.

0018-9316/$26.00 © 2010 IEEE

WANG et al.: EMBEDDED TRANSMISSION OF MULTI-SERVICE OVER DTMB SYSTEM 505

Fig. 1. Transmitter model of DTMB.

Fig. 2. Receiver model of DTMB.

Aiming at the above problems, a flexible multi-service data-casting scheme over DTMB is proposed, which transmits bothterrestrial and mobile services within the same spectrum. At thereceiver side, the DTMB standard receivers remain unchanged,and work as usual by discarding the unwanted data packets afterchecking the package identifier (PID) in the transport stream(TS). In contrast, the mobile receivers are designed to only se-lect and further process the desired mobile service data. Thewhole enhanced DTMB system not only efficiently facilitatesthe multi-service transmission but also flexibly provides muchlower signal to noise ratio (SNR) margin for the new mobileservices.

The outline of this paper is as follows. Section II reviewsthe conventional DTMB system. The equivalent QAM mappingmethod for mobile services are presented in Section III. The en-hanced DTMB multi-service datacasting scheme, together withthe newly-designed transmitter and mobile receiver, is proposedin Section IV. Section V shows simulation results to verify thefeasibility and the system performance of the proposed scheme,before conclusions are drawn in Section VI.

II. REVIEW OF CONVENTIONAL DTMB SYSTEM

Fig. 1 shows the transmitter diagram of DTMB [2]. At first,the input MPEG-2 (standard moving pictures experts group-2)TS packets are scrambled with an m-sequence of bitlong. And then, the forward error correction (FEC) code is used,which consists of a BCH (762, 752) outer code and a low den-sity parity check (LDPC) inner code with 3 optional rates, i.e.,LDPC0.4 (7488, 3048), LDPC0.6 (7488, 4572) and LDPC0.8(7488, 6096). After that, the output binary sequence is mappedto M-QAM symbols ( ,16,32, and 64), before the convolu-tional interleaving is adopted, which offers 2 interleaving modeswith corresponding time delay of 170 and 510 data blocks re-spectively. 36 transmission parameters signaling (TPS) symbolsare added to transmit necessary terrestrial encoding and modula-tion information, before the signal frame is constructed by boththe frame body and the pseudo random noise (PN) sequencewith the length of 420, 595, and 945 symbols. It is worth noting

that, in the “frame body processing’’ module, the frame body isoperated by the inverse fast Fourier transform (IFFT) for multi-carrier modulation, and in contrast, the frame body is unchangedfor single-carrier modulation. Finally, the baseband processingand the up-converting are carried out. In DTMB, 8 MHz is as-signed to transmit the radio frequency (RF) signals at a symbolrate of 7.56 MSps. At the receiver side, as shown in Fig. 2, withthe channel state information obtained via the synchronizationand channel estimation, the frame body can be equalized, andthen processed by the corresponding inverse operations to thetransmitter.

III. MODIFIED EQUIVALENT QAM MAPPING SCHEME

As demonstrated in [13], the higher-order QAM results in theworse bit error rate (BER) performance at the same receivedSNR, which hinders the mobile applications.

In the set partitioning theory [14], the equivalent QAM(E-QAM) mapping can be derived by only occupying a subsetof the standard QAM constellation, where the order of theoriginal higher-order QAM is lowered. In this section, 2 kindsof E-QAM mapping schemes will be described to provideperformance advantage over the standard QAMs.

A. Regular E-QAM

Without loss of generality, the regular equivalent 4QAMs(E-4QAMs) that are derived from the standard 16QAMare taken as an example. Denote 2 consecutive input bitsbefore mapping as , and any 16QAM symbol com-posed of 4 bits is expressed as . Atfirst, the 2 bits are doubly extended with fixed padding,that is, “ ” or ‘ ”or “ ” or ‘ ”. Andthen, the 4 extended bits are modulated via the standard16QAM. Fig. 3 depicts the location of the symbol sets of

, , and withinthe standard 16QAM constellation, which are labeled as“rectangle points” ,namely E-4QAM(1), “upper triangular points”


Fig. 3. DTMB standard 16QAM constellation and the illustration of regularE-QAM concept.


, namely E-4QAM(2), “lower tri-angular points” ,namely E-4QAM(3), and “ellipse points”

, namely E-4QAM(4), respectively.Similarly, as shown in Fig. 4, 4 more examples of

regular E-4QAMs are derived from the standard 64QAM,which are E-4QAM(5) labeled as “rectangular points”

, E-4QAM(6) labeled as“ellipse points” ,E-4QAM(7) labeled as “upper triangle point”

and E-4QAM(8) labeledas “shadow points” ,respectively. Moreover, 3 typical examples of equivalent16QAMs (E-16QAMs) have been derived from the stan-dard 64QAM, i.e., E-16QAM(1) surrounded by circles,E-16QAM(2) surrounded by squares and E-16QAM(3)surrounded by rectangles. Regular E-4QAMs and regularE-16QAMs are also derived from the standard 32QAM inFig. 5, which are not described in detail here. It is noted that,


all E-QAM schemes are not limited to the above examples inthis paper.

A simplified soft-output demapping algorithm is used here[15], which applies the Bayes rule to calculate log-likelihoodratio (LLR) of the individual -th bit corresponding topossible values “0”, “1” as

(1)

where is the subset comprising the complex symbolwith “0” in position while is complementary, and ,

and are the received signal, channel state information andthe output of one-tap equalizer given by , respectively.

B. Offset and Rotated E-QAM

Again taking advantage of the standard 16QAM, Fig. 6illustrates two examples of the offset E-4QAM and rotatedE-4QAM. The 2 consecutive input bits before mapping aredenoted as . The offset E-4QAM symbols are derivedthrough the extension “ ”, and labeledas “ellipse points” . Therotated E-4QAM symbols are derived through the extension“ ” and “ ”, and labeled as“rectangle points” .

As studied above, since these E-QAMs improve the mobileperformance, all of them can be taken advantage of to facili-tate the mobile service scenario. However, as discussed in [16]and [17], the demapping complexity of the offset or the rotatedE-QAM increases a lot due to the implementation of the biasadjustment or the 2-dimension demapping, which makes themobile receivers to consume more power. In the following, the


Fig. 6. DTMB standard 16QAM constellation and the illustration of non-reg-ular E-QAM concept.

offset and rotated E-QAM schemes will not be discussed, andthe E-QAM specializes the regular E-QAM for simplicity.

From Figs. 3–5, we can see that, the average energy of someE-QAMs, such as E-4QAM(1) and E-4QAM(2), is different asthey use a subset of the standard QAM constellations. There-fore, the average energy of the multiplexed symbol stream isdifferent from the original standard stream. Based on this ob-servation, E-QAMs with larger average energy result in the av-erage transmit power increment at the same time interval, whichis expressed as

(2)where is the average energy of lower-order E-QAM,

is referred as the average energy of standard higher-order QAM and is the occupancy-ratio of E-QAM symbolsin the multiplexed signal stream. For example, when ,the average transmit power increment due to the embedding ofE-QAM(1) is around 0.8 dB, whereas E-QAM(2) consumes lessaverage transmit power of 1 dB.

At the receiver side, the so-called mapping margin, which ispurely from using E-QAMs with different average energy at thesame time interval, is given by

(3)

where is the noise power density. For example, also as shownin Fig. 3, when transmitting the signals multiplexed with bothE-4QAM and standard 16QAM symbols at the occupancy-ratioof 25%, 16QAM symbols have unit average energy after nor-malization, whereas E-4QAM(1) symbols have larger averageenergy equal to 0.8 dB and E-4QAM(2) symbols have smalleraverage energy equal to 1 dB. According to (3), at the re-ceiving end, the mapping margin for E-4QAM(1) is as much as2.6 dB, that is, at the cost of the average transmit power incre-ment of 0.8 dB, E-4QAM(1) can provide a receiving SNR gainof 2.6 dB. While the mapping margin for E-4QAM(2) is 7 dB,

TABLE IMAPPING MARGIN AND TRANSMIT POWER INCREMENT FOR TYPICAL MODES

UNDER AWGN CHANNEL ��

that is, although E-QAM(2) saves average transmit power of1 dB, its SNR degradation at the receiver side is 7 dB.

In conclusion, by applying (2) and (3), Table I summarizesboth the mapping margin and the average transmit power in-crement of some typical E-QAM modes by using the standard16QAM and 64QAM. It is indicated that, E-QAMs with largeraverage energy can be used for mobile services in need of largerreceiving SNR margin and larger service coverage. Here, thetransmit or receiving signal to noise ratio (SNR) margin meansthat the difference between the required SNRs of mobile andterrestrial services. As a result, the E-QAM scheme involves atradeoff between the reception performance and the transmitpower consumption. By flexibly choosing different E-QAMmodes according to the QoS requirement, the embedded trans-mission of multi-services is efficiently achieved.

IV. PROPOSED DTMB MULTI-SERVICE SYSTEM

The transmitter diagram of the enhanced DTMB multi-ser-vice system is depicted in Fig. 7. For the simplicity purpose,we focus on analyzing the dual-service case, which includesthe original terrestrial DTV programs and the newly-introducedmobile service. Besides the modules defined in DTMB [2],there are additional blocks in shadow to merely process the mo-bile service. In addition, there is also a need for control signalsto support the compatibility and the flexibility of dual-servicetransmission, which are generated in the “control module” withthe pre-defined parameters for the mobile service.

At First, in the data-path of terrestrial DTV service, onlyterrestrial DTV bits are scrambled in the “standard scram-bling” module, which is reset at the beginning of each signalframe. The polynomial generator with the initial state of“100101010000000” is [2]

(4)

Meanwhile, in the data-path of mobile service, the mobilestream is sent to the “enhanced pre-processing” module, whichconsists of 3 blocks: “first-level channel encoding”, “enhancedfixed extension” and “enhanced packet formatting”. Theseblocks all pass the terrestrial DTV bits unchanged. As anenhanced encoder for the mobile service, the new first-levelchannel encoding is carried out to increase the noise immunitycapability of the mobile data service. Since the FEC codesthat are concatenated with BCH and LDPC codes are used intraditional DTMB systems, and the flexible multi-rate decoderhas also been studied in [18] and [19], reusing the existing


Fig. 7. Transmitter model of the enhanced DTMB multi-service system.

Fig. 8. Receiver model of mobile service.

FEC codes in DTMB is a good choice for simplifying thedesign. After that, taking advantage of the E-QAM scheme inSection III, the pre-encoded mobile bits are further extended,before being prepared for the format of MPEG-2 TS packetin DTMB. It is worth noting that, according to [20], every TSpacket has the packet header (PH) of 4 bytes, 13 bits of whichare adopted as the PID to identify the specific programs inDTMB standard receivers. As a result, the formatting shouldinclude adding the mobile PID (M-PID).

Following the format matching, PH bytes including M-PIDother than valid mobile data are scrambled according to (4). ThePH bytes are scrambled so that the existing DTMB receivers,which include a descrambler, can correctly recover the M-PIDfrom the mobile service data. The mobile data are not requiredto be scrambled by avoiding the cost of descrambling, as a re-sult, the complexity of the mobile receiver is reduced and thepower consumption of the mobile receiver is lowered. Based onthe pre-defined parameters obtained from the control signals,both terrestrial and mobile service data are flexibly multiplexedin time domain. With no further change in the rest modules ofDTMB standard transmitter subsystem, the output of the multi-plexed bits then undergo the “post-processing”, which consistsof standard FEC, standard QAM mapping, interleaving, TPS in-sertion, frame construction, baseband processing and up-con-verting to turn to RF emission signals.

At the receiver side, conventional DTMB receivers are con-tinued to be used for the backward compatibility. The conven-tional DTMB receivers receive and decode every data packetsin the multiplexed stream, and then discard the mobile data byidentifying the specific PID for the specific terrestrial DTV pro-grams. In contrast, a newly-designed receiver as shown in Fig. 8is used to simply deal with the mobile service data in need afterthe de-interleaving. Details of the proposed procedure go asfollows.

TABLE IIPARAMETERS AND THEIR DEFINITIONS

1) Control Module: As established in DTMB, for PN420,PN595 and PN945 modes, every 225, 216, and 200 signalframes are used to form a group called a super-frame lasting125 ms, respectively. The first signal frame of the super-frameis named as the control frame, which is reserved to carry pre-de-fined parameters in demand [2]. In this paper, the control frameis exploited to indicate the parameters for the mobile serviceas shown in Table II, including the enhanced first-level FECrate, the selected E-QAM mode, the interleaving mode, themultiplexing mode and the occupancy-ratio. The architectureof the control frame is also schematically depicted in Fig. 9.

It is necessary to pointed out that, the multiplexing mode isreferred as the flexible position of the mobile service framesin a super-frame, which are distinguished from the terrestrialframes by the M-PID in the PH. Since there are 224/215/199signal frames following each control frame, at most of4-bytes are used. According to different applications of the mo-bile services, their M-PIDs are differently defined. If the M-PIDin the -th 4-bytes is for the specific mobile service, that means


Fig. 9. Proposed control frame structure.

the corresponding signal frame is allocated for the mobile ser-vice. Otherwise, the corresponding -th signal frame belongsto the terrestrial service or other mobile applications. AlthoughM-PIDs are different from PIDs of terrestrial DTV programs,they still have to be valid ones from the PID family to makesure to be correctly identified. Moreover, the system throughputand spectral efficiency are both closely related to the occupancy-ratio, which will be further described in the following.

To increase the transmission reliability of the mobile param-eters in the control frame, error-correcting techniques could beadopted for the control frame data, such as encoded by FEC withhigh error-correction performance and modulated by low-orderconstellations like BPSK, which are not limited to the enhancedtechniques used for the mobile service data. Perfect knowledgeof the mobile parameters are assumed to be obtained at the mo-bile receiver.

2) Enhanced Pre-Processing Module: Referring to Fig. 7,before multiplexing two streams of terrestrial and mobile ser-vices, the “enhanced pre-processing” module is only used topre-process the mobile service data.

To help the mobile service have better noise immunity andhigher receiving sensitivity, the input mobile bits are firstly pre-encoded by the enhanced first-level FEC encoder according tothe control signal. Any kind of error correcting codes, includingthe code rate, the error correction capability, the complexity ofencoding and decoding, can be selected depending on the QoSrequirement.

It is necessary to point out that, when considering the schemeassociated with the E-QAM, if the mapping margin purely fromthe E-QAM can provide the mobile service with the requiredsystem performance according to the QoS requirement, the en-hanced channel encoder can be turned off.

Once the modulation mode for the mobile service is selected,as mentioned above, the pre-coded mobile bits are then fur-ther extended with fixed bits padding. It is worth noting that,after processed by the fixed extension, the mobile bits are onlyprepared for the format of E-QAM constellation requirement,rather than modulated to QAM symbols. The standard QAMmapping in the “post-processing” module are actually used tocarry out the QAM modulation.

After that, 4 PH bytes including M-PID bits are firstly added.When considering specific lengths of the information bits for dif-ferent FEC rates, matching bits are padded into the mobile ser-vice data to make the length of mobile frames compatible withDTMB,as theformatmatchedframeswillbeencodedbythestan-dard second-level FEC. These additional padding bits can be re-served for the parity bits for M-PID when using error correctingcodes such as repetition codes, or even be completely irrelevant.Furthermore, the numbers of padding bits in need are different

according to the standard FEC modes, which results in differentpayload penalty in the multi-service datacasting design.

Taking mobile E-4QAM(1)/LDPC0.4 and terrestrial16QAM/LDPC0.8 mode as an example, Fig. 10 schemati-cally depicts how exactly the “enhanced packet formatting”works here. 3008 information bits are firstly encoded by thefirst-level FEC code, i.e., BCH(762, 752)&LDPC0.4, and turnto a pre-encoded block with 7488 bits. After that, by using thefixed extension method of E-4QAM(1) with bit “0” padded,the length of the mobile pre-encoded block is thus doubled andturns to 2 blocks of 7488 bits. And then, in order to well matchthe format of the following standard FEC code, which consistsof BCH(762, 752) and LDPC0.8, the 2 blocks including addi-tional padding bits, are divided into 3 groups to form equivalentstandard FEC blocks, each of which has the length of 6016bits. Under this scheme, 1024 padding bits are inserted in everyequivalent standard FEC block, including the M-PID of 13bits for each TS packet. In DTMB, every 16QAM/LDPC0.8frame should contain 2 FEC blocks of 6016 bits, where eachFEC block is composed of 4 TS packets with 188 byte long.Therefore, in order to form integral frames, another 3008mobile bits experience the same process. Finally, 6 equivalentFEC blocks are buffered to form 3 standard 16QAM/LDPC0.8signal frames, where 2048 padding bits in total are inserted forevery 16QAM/LDPC0.8 frame.

Denote variables as Table III, the payload rates of both ter-restrial DTV and mobile services are given by

(5)

(6)

respectively. Also, due to the extension and padding bits, thespectral efficiency penalty compared to traditional terrestrialservice transmission is approximately calculated as

(7)

By applying (5)–(7), take the mobile E-4QAM/LDPC0.4 andterrestrial 16QAM/LDPC0.8 mode as an example. Accordingto [7], the mobile TV service requires data throughput of 384


Fig. 10. Packet formatting flow.

TABLE IIIDENOTATIONS

Kbps at least. When the occupancy-ratio is 25% and PN lengthis 945, at the cost of 6% spectral efficiency, the enhanced systemhas a terrestrial DTV payload of 14.4 Mbps plus a mobile pay-load of 798 Kbps. Similarly, when the occupancy-ratio is 15%,at the spectral efficiency penalty of 4%, the mobile E-16QAM/LDPC0.4 and terrestrial 64QAM/LDPC0.6-mode has provideda terrestrial DTV payload of 16.3 Mbps plus a mobile payload of479 Kbps. It is indicated that, for small occupancy-ratio of mo-bile service data, the spectral efficiency penalty is negligible. Asthe occupancy-ratio increases, mobile throughput increases lin-early while terrestrial throughput decreases, which would offerinherent flexibility in terms of carrying multiple services withdifferent QoS requirement.

TABLE IVPARAMETERS AND THEIR DEFINITION

3) Mobile Receiver Design: Fig. 8 shows the newly-designedmobile receiver. At the mobile receiver, post-processing is car-ried out similarly to the conventional DTMB receivers. After theconvolutional interleaving in DTMB, the specific M-PID in thecontrol frame is checked to determine the mobile frame positions,and then the frames which belong to the desired mobile serviceare selected for the further processing. After that, the parity bitsrelated to thesecond-levelFECencodingaswell as the4PHbytesand the formatting bits are removed. By carrying out the removaloperation, we make sure that the mobile valid bits can be directlydemapped using the lower-order E-QAM constellation. Takinga careful look at the above procedure, we can see that, by onlydemapping their own service data using the lower-order E-QAMconstellation as well as only decoding the mobile bits, the mobilereceivers have much lower power consumption.


TABLE VBRAZIL A CHANNEL PROFILE

Fig. 11. BER versus transmit SNR performance comparison under Brazil Achannel with Doppler spread of 20 Hz.

V. SIMULATION RESULTS

In this section, simulation results are presented to evaluate theperformance of the proposed DTMB datacasting scheme. Themajor simulation parameters are listed in Table IV. Two mainparameters for performance evaluation, including both the re-ceiving SNR margin and the transmit SNR margin, have been in-vestigated under AWGN channel and mobile multipath channel,respectively. The profile of the multipath channel, namely BrazilA, is shown in Table V.

In China, the two most widely used modes for DTMBsystems are 16QAM/LDPC0.8 and 64QAM/LDPC0.6. Here,4 kinds of E-4QAMs derived from 64QAM, i.e., E-4QAM(5),E-4QAM(6), E-4QAM(7) and E-4QAM(8) are used.

With the fraction behind “/” denoted as the LDPC rate,Fig. 11 shows the BER versus the transmit SNR performanceof the enhanced DTMB multi-service system under Brazil Achannel with Doppler spread of 20 Hz. The occupancy-ratio is25% here. The mobile E-4QAM(5)/0.8-mode provides a totaltransmit SNR margin of overthat of terrestrial 64QAM/LDPC0.6-mode, which includesthe mapping margin at the cost of the increasing averagetransmit power. Similarly, E-4QAM(6)/0.8-mode provides atotal transmit SNR margin of .On the contrary, due to the mapping margin decline ofE-4QAM(7), E-4QAM(7)/0.8-mode saves the average transmitpower, which results in a smaller transmit SNR margin of

. E-4QAM(8) has so much perfor-mance degradation that it is not suitable for practical mobileapplications, and thus not considered here.

By applying (5) and (6), the data throughput of the 4 mo-bile E-4QAM/0.8-modes and terrestrial 64QAM/0.6-mode canbe calculated, with a payload of 1.2 Mbps to support 3 mobileTV services of 384 Kbps, plus the payload of 16.2 Mbps to sat-

TABLE VIRECEIVING SNR � �� FOR DIFFERENT MODES

UNDER AWGN CHANNEL � � � ��

E-QAM MODES DERIVED FROM THE OUTEST CORNER OF THE

HIGHER-ORDER QAMS ARE USED.

TABLE VIITHROUGHPUT FOR DIFFERENT MODES � � � ��

isfy multiple SDTV (standard definition TV) services. Since ad-justing the occupancy-ratio could offer inherent flexibility of theterrestrial and the mobile throughput, the occupancy-ratio couldbe reduced when an HDTV (high definition TV) program needsto be transmitted.

In summary, Tables VI and VII compare the receiving SNRmargins under AWGN channel and throughput comparisonsof typical compatible modes in the enhanced DTMB system.Different occupancy-ratio would provided inherent tradeoff be-tween the terrestrial and mobile throughput, which all guaranteethe feasibility of the proposed DTMB multi-service transmis-sion scheme. It is expected that similar comparison results canbe obtained in mobile multipath environment. It is indicatedthat, with the tradeoff between the reception performance andthe transmit power consumption, the enhanced DTMB servicesystem can not only maintain the original terrestrial receptionperformance but also support the mobile services at satisfactoryreception performance.

VI. CONCLUSION AND FUTURE WORK

A flexible DTMB multi-service datacasting system is pro-posed to support both terrestrial and mobile services in a back-ward compatible manner. The multiplexed stream is receivedand decoded at the conventional DTMB receivers, and the de-sired terrestrial service data are selected via the PID checking.At the mobile DTMB receivers, the mobile service data out ofthe multiplexed stream are separated via control frames. Simu-lation results indicate that the proposed scheme provides signifi-cant transmit and receiving SNR margin as well as inherent flex-ibility. Compared with the conventional DTMB broadcasting


system, although the total payload is slightly reduced due to thepadding and the formatting bits, the improved DTMB multi-ser-vice system not only achieves the purpose of multi-service trans-mission with no reception performance degradation for conven-tional terrestrial DTV service but also provides flexible modesto realize different embedded transmission of mobile servicesover the DTMB system.

Finally, the work in this paper can be extended in severaldirections. For example, firstly, the average transmit power in-creases due to the E-QAMs with larger average energy, as a re-sult, the peak to average power ratio (PAPR) is larger and the la-tent nonlinear distortion impact in high power amplifier (HPA)is not negligible. The PAPR reduction and high power ampli-fier (HPA) linearization techniques should be further consid-ered [21]. Secondly, mobile parameters are currently obtainedvia the control frame in this paper, yet it makes the spectralefficiency slightly suffered. The system throughput can be fur-ther improved by redefining the TPS symbols or using the phaseknowledge of the PN sequences.

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Xiaoqing Wang was born in Shandong, China.She received the B.S. degree in 2007 from theDepartment of Electronic Information Engineeringin Tianjin University. She has been pursuing thePh.D. degree at the DTV Technology R&D Center,Tsinghua University since 2007.

Her main research interests are in the areas ofbroadband wireless transmission technologies, dig-ital TV broadcasting and powerline communications.

Jintao Wang received the B.Eng and Phd.D. degreesin electrical engineering both from Tsinghua Univer-sity, Beijing, China in 2001 and 2006, respectively.

Since 2006, he has been an assistant professorof Tsinghua’s DTV Technology R&D center. Heis the standard committee member for the Chinesenational digital terrestrial television broadcastingstandard. His current research interest is in the areaof the broadband wireless transmission, especiallythe channel estimation and space-time coding tech-niques.

Jun Wang was born in Henan, P. R. China, on Oc-tober 5, 1975. He received the B. Eng. and Ph.D de-grees from the Department of Electronic Engineeringin Tsinghua University, Beijing, China, in 1999 and2003 respectively.

He is an assistant professor and member of DigitalTV R&D center of Tsinghua University since 2000.His main research interests focus on broadband wire-less transmission techniques, especially synchroniza-tion and channel estimation. He is actively involvedin the Chinese national standard on the Digital Ter-

restrial Television Broadcasting technical activities, and is selected by the Stan-dardization Administration of China as the Standard committee member fordrafting.

Yangang Li received the masters degree in electricalengineering.

He is a Senior Manager at Hong Kong Applied Sci-ence and Technology Research Institute (ASTRI) andthe co-director of the ASTRI-Tsinghua MultimediaBroadcasting and Communications (MBC) Joint Re-search Lab. He is responsible for the research and de-velopment activities and commercialization of tech-nologies in the general area of DTMB, the DTTBstandard in China. Before joining ASTRI, he was aSenior Advisor at ZTE, San Diego. Prior to that, he

had been with Navini Networks (acquired by Cisco) and Cwill Telecommunica-tions. His primary research interests include wireless communication systems,DTV systems, DSP algorithms, and baseband chipsets design.


Shigang Tang received the B.Eng degree withdistinction from University of Electronic Scienceand Technology of China in July 2003, and the Ph.D.in electrical engineering from Tsinghua University,China.

He then joined Hong Kong Applied Science andTechnology Research Institute Company Limited(ASTRI) as a senior engineer in Aug. 2008. Hisresearch interests are in the area of signal processingfor wireless communications and broadcasting, inparticular, receiver algorithm design for the Chinese

digital terrestrial television broadcasting systems.

Jian Song received the B.Eng and Ph.D. degrees inelectrical engineering both from Tsinghua Univer-sity, Beijing, China in 1990 and 1995, respectivelyand worked for the same university upon his gradu-ation.

He has worked at The Chinese University ofHong Kong and University of Waterloo, Canadain 1996 and 1997, respectively. He has been withHughes Network Systems in USA for 7 years beforejoining the faculty team in Tsinghua in 2005 asa professor. He is now the director of Tsinghua’s

DTV Technology R&D center. His primary research interest is in physicallayer and has been working in quite different areas of fiber-optic, satelliteand wireless communications, as well as the powerline communications. Hiscurrent research interest is in the area of digital TV broadcasting. Dr. Song haspublished more than 50 journal and conference papers and holds one US patent.

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