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Embedded Transmission of Multi-Service Over

Embedded Transmission of Multi-Service Over
DTMB System.which can support mobile services

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  • 504 IEEE TRANSACTIONS ON BROADCASTING, VOL. 56, NO. 4, DECEMBER 2010 Embedded Transmission of Multi-Service Over DTMB System Xiaoqing Wang, Jintao Wang, Jun Wang, Yangang Li, Shigang Tang, and Jian Song Abstract—To efficiently support the transmission of terrestrial beyond the reception of the terrestrial broadcasting services.and mobile services within the same spectrum over the Digital For example, numbers of competing standards for mobile TVTelevision Terrestrial Multimedia Broadcasting (DTMB) system, have emerged, such as MediaFLO (Media-Forward Link Only)a flexible multi-service datacasting scheme in a backward com-patible manner is proposed. Using this scheme, the conventional [4], T-DMB (Terrestrial-Digital Multimedia Broadcasting) [5],DTMB receivers work as usual by simply selecting the specific DVB-H (digital video broadcasting transmission system forterrestrial DTV programs on the basis of the package identifier handheld terminals) [6], ATSC-M/H (Advanced Television(PID) checking, while only the desired mobile service data are System Committee-Mobile/Handheld) and CMMB (Chinaprocessed by the mobile receivers via the designed control signals. Mobile Multimedia Broadcasting) [7], and they all use theBoth theoretical analysis and computer simulation show that, dedicated spectrum of UHF with the frequency range fromat acceptable spectral efficiency penalty, the proposed methodnot only supports the embedded transmission of multi-services 470 MHz to 862 MHz.with no reception performance degradation for the traditional To revive the lack of spectral resource and provide flex-terrestrial broadcasting service, but also flexibly provides much ible mobile services, there is an interest in extending thebetter mobile reception performance. conventional DTTB systems to include the newly-introduced Index Terms—Backward compatibility, datacasting, digital mobile services as well, which takes advantage of the residualtelevision terrestrial multimedia broadcasting (DTMB), multi-ser- throughput setting aside for traditional terrestrial broadcastingvices, package identifier (PID). services, namely datacasting. For example, some improved ATSC systems were discussed in [8] and [9]. More recently, compatible transmission of terrestrial DTV and mobile services I. INTRODUCTION has been introduced into the DVB-T2 standard [10]. However,D IGITAL Television (DTV) services can be broadcasted via terrestrial, satellite and cable networks, among whichthe digital television terrestrial broadcasting (DTTB) is the all the above systems have to modify the original receivers to some extent, which will be uneconomic if conventional receivers have been widely used. To realize thorough backwardmost important. In the past ten years, several DTTB standards compatibility with lots of existing receivers, improving originalhave been announced and implemented in different regions DTTB systems by modifying merely the transmitter subsystemsof the world, and they are the USA-based ATSC (Advanced is highly preferred and has attracted increasing attention fromTelevision System Committee) standard, the Europe-based both academia and industry [11], [12].DVB-T (Digital Video Broadcasting-Terrestrial) standard, The DTMB standard is capable to support both terrestrialthe Japan-based ISDB-T (Integrated Services Digital Broad- and mobile applications, as a result, it would be convenient tocasting-Terrestrial) standard [1], and the China-based DTMB transmit mobile services along with the terrestrial DTV pro-(Digital Television Terrestrial Multimedia Broadcasting) stan- grams over the same spectrum. However, it is not clearly stateddard [2], [3]. Recently, with the proliferation of mobile devices how to effectively accommodate both terrestrial and mobile ser-such as mobile phones and PDAs (personal digital assistants), vices simultaneously within the same band. As demonstrated inthere is an increasing demand for mobile-specific services [2], when DTMB is applied to the multi-service transmission scenario, the time division multiplexing (TDM) can be used, where all services have to accommodate to the fixed broad- Manuscript received January 15, 2010; revised March 31, 2010; accepted casting method of the terrestrial DTV service. As a result, theApril 06, 2010. Date of publication August 30, 2010; date of current version TDM scheme does not perform well for mobile services. TheNovember 19, 2010. This work was supported in part by the Ph.D. ProgramFoundation from Ministry of Education of China under Grant 20090002120026, reasonable explanation is that, on one hand, the mobile environ-the Chinese NSFC (National Natural Science Foundation of China) Project ment is very error-prone, as it presents more severe multipathunder Grant 20091300779 and the Chinese AQSIQ (Administration of Quality fading and faster time variation. On the other hand, since mo-Supervision, Inspection and Quarantine) Project under Grant 200910244. bile services are received at slow or high speed, the mobile data X. Wang, J. Wang, J. Wang, and J. Song are with the State Key Labo-ratory on Microwave and Digital Communications, the Tsinghua National have different quality of service (QoS) requirement, includingLaboratory for Information Science and Technology (TNList), Department of higher receiving sensitivity and larger coverage area. Therefore,Electronics Engineering, Tsinghua University, Beijing 100084, China (e-mail: there is a need to flexibly provide lower SNR threshold than thewangxq07@mails.tsinghua.edu.cn; wangjintao@tsinghua.edu.cn; wjun@ts-inghua.edu.cn; jsong@tsinghua.edu.cn). fixed terrestrial DTV service. Besides that, the handheld termi- Y. Li and S. Tang are with the Applied Science and Technology Research In- nals for mobile services have a number of features in common:stitute Company Ltd., Hong Kong (e-mail: ygli@astri.org; shigangtang@astri. small size, light weight, and battery operation, which all requireorg). Color versions of one or more of the figures in this paper are available online lower power consumption. Therefore, there is a need for im-at http://ieeexplore.ieee.org. proved methods to realize flexible multi-service transmission Digital Object Identifier 10.1109/TBC.2010.2067550 based on different QoS requirement. 0018-9316/$26.00 © 2010 IEEE
  • WANG et al.: EMBEDDED TRANSMISSION OF MULTI-SERVICE OVER DTMB SYSTEM 505Fig. 1. Transmitter model of DTMB.Fig. 2. Receiver model of DTMB. Aiming at the above problems, a flexible multi-service data- that, in the “frame body processing’’ module, the frame body iscasting scheme over DTMB is proposed, which transmits both operated by the inverse fast Fourier transform (IFFT) for multi-terrestrial and mobile services within the same spectrum. At the carrier modulation, and in contrast, the frame body is unchangedreceiver side, the DTMB standard receivers remain unchanged, for single-carrier modulation. Finally, the baseband processingand work as usual by discarding the unwanted data packets after and the up-converting are carried out. In DTMB, 8 MHz is as-checking the package identifier (PID) in the transport stream signed to transmit the radio frequency (RF) signals at a symbol(TS). In contrast, the mobile receivers are designed to only se- rate of 7.56 MSps. At the receiver side, as shown in Fig. 2, withlect and further process the desired mobile service data. The the channel state information obtained via the synchronizationwhole enhanced DTMB system not only efficiently facilitates and channel estimation, the frame body can be equalized, andthe multi-service transmission but also flexibly provides much then processed by the corresponding inverse operations to thelower signal to noise ratio (SNR) margin for the new mobile transmitter.services. The outline of this paper is as follows. Section II reviews III. MODIFIED EQUIVALENT QAM MAPPING SCHEMEthe conventional DTMB system. The equivalent QAM mapping As demonstrated in [13], the higher-order QAM results in themethod for mobile services are presented in Section III. The en- worse bit error rate (BER) performance at the same receivedhanced DTMB multi-service datacasting scheme, together with SNR, which hinders the mobile applications.the newly-designed transmitter and mobile receiver, is proposed In the set partitioning theory [14], the equivalent QAMin Section IV. Section V shows simulation results to verify the (E-QAM) mapping can be derived by only occupying a subsetfeasibility and the system performance of the proposed scheme, of the standard QAM constellation, where the order of thebefore conclusions are drawn in Section VI. original higher-order QAM is lowered. In this section, 2 kinds of E-QAM mapping schemes will be described to provide II. REVIEW OF CONVENTIONAL DTMB SYSTEM performance advantage over the standard QAMs. Fig. 1 shows the transmitter diagram of DTMB [2]. At first,the input MPEG-2 (standard moving pictures experts group-2) A. Regular E-QAMTS packets are scrambled with an m-sequence of bit Without loss of generality, the regular equivalent 4QAMslong. And then, the forward error correction (FEC) code is used, (E-4QAMs) that are derived from the standard 16QAMwhich consists of a BCH (762, 752) outer code and a low den- are taken as an example. Denote 2 consecutive input bitssity parity check (LDPC) inner code with 3 optional rates, i.e., before mapping as , and any 16QAM symbol com-LDPC0.4 (7488, 3048), LDPC0.6 (7488, 4572) and LDPC0.8 posed of 4 bits is expressed as . At(7488, 6096). After that, the output binary sequence is mapped first, the 2 bits are doubly extended with fixed padding,to M-QAM symbols ( ,16,32, and 64), before the convolu- that is, “ ” or ‘ ”tional interleaving is adopted, which offers 2 interleaving modes or “ ” or ‘ ”. Andwith corresponding time delay of 170 and 510 data blocks re- then, the 4 extended bits are modulated via the standardspectively. 36 transmission parameters signaling (TPS) symbols 16QAM. Fig. 3 depicts the location of the symbol sets ofare added to transmit necessary terrestrial encoding and modula- , , and withintion information, before the signal frame is constructed by both the standard 16QAM constellation, which are labeled asthe frame body and the pseudo random noise (PN) sequence “rectangle points” ,with the length of 420, 595, and 945 symbols. It is worth noting namely E-4QAM(1), “upper triangular points”
  • 506 IEEE TRANSACTIONS ON BROADCASTING, VOL. 56, NO. 4, DECEMBER 2010Fig. 3. DTMB standard 16QAM constellation and the illustration of regularE-QAM concept. Fig. 5. DTMB standard 32QAM constellation and the illustration of regular E-QAM concept. all E-QAM schemes are not limited to the above examples in this paper. A simplified soft-output demapping algorithm is used here [15], which applies the Bayes rule to calculate log-likelihood ratio (LLR) of the individual -th bit corresponding to possible values “0”, “1” as (1)Fig. 4. DTMB standard 64QAM constellation and the illustration of regularE-QAM concept. where is the subset comprising the complex symbol with “0” in position while is complementary, and , and are the received signal, channel state information and , namely E-4QAM(2), “lower tri- the output of one-tap equalizer given by , respectively.angular points” ,namely E-4QAM(3), and “ellipse points” B. Offset and Rotated E-QAM , namely E-4QAM(4), respectively. Again taking advantage of the standard 16QAM, Fig. 6 Similarly, as shown in Fig. 4, 4 more examples of illustrates two examples of the offset E-4QAM and rotatedregular E-4QAMs are derived from the standard 64QAM, E-4QAM. The 2 consecutive input bits before mapping arewhich are E-4QAM(5) labeled as “rectangular points” denoted as . The offset E-4QAM symbols are derived , E-4QAM(6) labeled as through the extension “ ”, and labeled“ellipse points” , as “ellipse points” . TheE-4QAM(7) labeled as “upper triangle point” rotated E-4QAM symbols are derived through the extension and E-4QAM(8) labeled “ ” and “ ”, and labeled asas “shadow points” , “rectangle points” .respectively. Moreover, 3 typical examples of equivalent As studied above, since these E-QAMs improve the mobile16QAMs (E-16QAMs) have been derived from the stan- performance, all of them can be taken advantage of to facili-dard 64QAM, i.e., E-16QAM(1) surrounded by circles, tate the mobile service scenario. However, as discussed in [16]E-16QAM(2) surrounded by squares and E-16QAM(3) and [17], the demapping complexity of the offset or the rotatedsurrounded by rectangles. Regular E-4QAMs and regular E-QAM increases a lot due to the implementation of the biasE-16QAMs are also derived from the standard 32QAM in adjustment or the 2-dimension demapping, which makes theFig. 5, which are not described in detail here. It is noted that, mobile receivers to consume more power. In the following, the
  • WANG et al.: EMBEDDED TRANSMISSION OF MULTI-SERVICE OVER DTMB SYSTEM 507 TABLE I MAPPING MARGIN AND TRANSMIT POWER INCREMENT FOR TYPICAL MODES UNDER AWGN CHANNEL (O 0 = 25%) that is, although E-QAM(2) saves average transmit power of 1 dB, its SNR degradation at the receiver side is 7 dB.Fig. 6. DTMB standard 16QAM constellation and the illustration of non-reg- In conclusion, by applying (2) and (3), Table I summarizesular E-QAM concept. both the mapping margin and the average transmit power in- crement of some typical E-QAM modes by using the standard 16QAM and 64QAM. It is indicated that, E-QAMs with largeroffset and rotated E-QAM schemes will not be discussed, and average energy can be used for mobile services in need of largerthe E-QAM specializes the regular E-QAM for simplicity. receiving SNR margin and larger service coverage. Here, the From Figs. 3–5, we can see that, the average energy of some transmit or receiving signal to noise ratio (SNR) margin meansE-QAMs, such as E-4QAM(1) and E-4QAM(2), is different as that the difference between the required SNRs of mobile andthey use a subset of the standard QAM constellations. There- terrestrial services. As a result, the E-QAM scheme involves afore, the average energy of the multiplexed symbol stream is tradeoff between the reception performance and the transmitdifferent from the original standard stream. Based on this ob- power consumption. By flexibly choosing different E-QAMservation, E-QAMs with larger average energy result in the av- modes according to the QoS requirement, the embedded trans-erage transmit power increment at the same time interval, which mission of multi-services is efficiently achieved.is expressed as IV. PROPOSED DTMB MULTI-SERVICE SYSTEM The transmitter diagram of the enhanced DTMB multi-ser- (2) vice system is depicted in Fig. 7. For the simplicity purpose,where is the average energy of lower-order E-QAM, we focus on analyzing the dual-service case, which includes is referred as the average energy of standard higher- the original terrestrial DTV programs and the newly-introducedorder QAM and is the occupancy-ratio of E-QAM symbols mobile service. Besides the modules defined in DTMB [2],in the multiplexed signal stream. For example, when , there are additional blocks in shadow to merely process the mo-the average transmit power increment due to the embedding of bile service. In addition, there is also a need for control signalsE-QAM(1) is around 0.8 dB, whereas E-QAM(2) consumes less to support the compatibility and the flexibility of dual-serviceaverage transmit power of 1 dB. transmission, which are generated in the “control module” with At the receiver side, the so-called mapping margin, which is the pre-defined parameters for the mobile service.purely from using E-QAMs with different average energy at the At First, in the data-path of terrestrial DTV service, onlysame time interval, is given by terrestrial DTV bits are scrambled in the “standard scram- bling” module, which is reset at the beginning of each signal frame. The polynomial generator with the initial state of “100101010000000” is [2] (3) (4)where is the noise power density. For example, also as shown Meanwhile, in the data-path of mobile service, the mobilein Fig. 3, when transmitting the signals multiplexed with both stream is sent to the “enhanced pre-processing” module, whichE-4QAM and standard 16QAM symbols at the occupancy-ratio consists of 3 blocks: “first-level channel encoding”, “enhancedof 25%, 16QAM symbols have unit average energy after nor- fixed extension” and “enhanced packet formatting”. Thesemalization, whereas E-4QAM(1) symbols have larger average blocks all pass the terrestrial DTV bits unchanged. As anenergy equal to 0.8 dB and E-4QAM(2) symbols have smaller enhanced encoder for the mobile service, the new first-levelaverage energy equal to 1 dB. According to (3), at the re- channel encoding is carried out to increase the noise immunityceiving end, the mapping margin for E-4QAM(1) is as much as capability of the mobile data service. Since the FEC codes2.6 dB, that is, at the cost of the average transmit power incre- that are concatenated with BCH and LDPC codes are used inment of 0.8 dB, E-4QAM(1) can provide a receiving SNR gain traditional DTMB systems, and the flexible multi-rate decoderof 2.6 dB. While the mapping margin for E-4QAM(2) is 7 dB, has also been studied in [18] and [19], reusing the existing
  • 508 IEEE TRANSACTIONS ON BROADCASTING, VOL. 56, NO. 4, DECEMBER 2010Fig. 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 the TABLE IIdesign. After that, taking advantage of the E-QAM scheme in PARAMETERS AND THEIR DEFINITIONSSection 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 the 1) Control Module: As established in DTMB, for PN420,power consumption of the mobile receiver is lowered. Based on PN595 and PN945 modes, every 225, 216, and 200 signalthe pre-defined parameters obtained from the control signals, frames are used to form a group called a super-frame lastingboth terrestrial and mobile service data are flexibly multiplexed 125 ms, respectively. The first signal frame of the super-framein time domain. With no further change in the rest modules of is named as the control frame, which is reserved to carry pre-de-DTMB standard transmitter subsystem, the output of the multi- fined parameters in demand [2]. In this paper, the control frameplexed bits then undergo the “post-processing”, which consists is exploited to indicate the parameters for the mobile serviceof standard FEC, standard QAM mapping, interleaving, TPS in- as shown in Table II, including the enhanced first-level FECsertion, frame construction, baseband processing and up-con- rate, the selected E-QAM mode, the interleaving mode, theverting to turn to RF emission signals. multiplexing mode and the occupancy-ratio. The architecture At the receiver side, conventional DTMB receivers are con- of the control frame is also schematically depicted in Fig. 9.tinued to be used for the backward compatibility. The conven- It is necessary to pointed out that, the multiplexing mode istional DTMB receivers receive and decode every data packets referred as the flexible position of the mobile service framesin the multiplexed stream, and then discard the mobile data by in a super-frame, which are distinguished from the terrestrialidentifying the specific PID for the specific terrestrial DTV pro- frames by the M-PID in the PH. Since there are 224/215/199grams. In contrast, a newly-designed receiver as shown in Fig. 8 signal frames following each control frame, at most ofis used to simply deal with the mobile service data in need after 4-bytes are used. According to different applications of the mo-the de-interleaving. Details of the proposed procedure go as bile services, their M-PIDs are differently defined. If the M-PIDfollows. in the -th 4-bytes is for the specific mobile service, that means
  • WANG et al.: EMBEDDED TRANSMISSION OF MULTI-SERVICE OVER DTMB SYSTEM 509Fig. 9. Proposed control frame structure.the corresponding signal frame is allocated for the mobile ser- according to the standard FEC modes, which results in differentvice. Otherwise, the corresponding -th signal frame belongs payload penalty in the multi-service datacasting design.to the terrestrial service or other mobile applications. Although Taking mobile E-4QAM(1)/LDPC0.4 and terrestrialM-PIDs are different from PIDs of terrestrial DTV programs, 16QAM/LDPC0.8 mode as an example, Fig. 10 schemati-they still have to be valid ones from the PID family to make cally depicts how exactly the “enhanced packet formatting”sure to be correctly identified. Moreover, the system throughput works here. 3008 information bits are firstly encoded by theand spectral efficiency are both closely related to the occupancy- first-level FEC code, i.e., BCH(762, 752)&LDPC0.4, and turnratio, which will be further described in the following. to a pre-encoded block with 7488 bits. After that, by using the To increase the transmission reliability of the mobile param- fixed extension method of E-4QAM(1) with bit “0” padded,eters in the control frame, error-correcting techniques could be the length of the mobile pre-encoded block is thus doubled andadopted for the control frame data, such as encoded by FEC with turns to 2 blocks of 7488 bits. And then, in order to well matchhigh error-correction performance and modulated by low-order the format of the following standard FEC code, which consistsconstellations like BPSK, which are not limited to the enhanced of BCH(762, 752) and LDPC0.8, the 2 blocks including addi-techniques used for the mobile service data. Perfect knowledge tional padding bits, are divided into 3 groups to form equivalentof the mobile parameters are assumed to be obtained at the mo- standard FEC blocks, each of which has the length of 6016bile receiver. bits. Under this scheme, 1024 padding bits are inserted in every 2) Enhanced Pre-Processing Module: Referring to Fig. 7, equivalent standard FEC block, including the M-PID of 13before multiplexing two streams of terrestrial and mobile ser- bits for each TS packet. In DTMB, every 16QAM/LDPC0.8vices, the “enhanced pre-processing” module is only used to frame should contain 2 FEC blocks of 6016 bits, where eachpre-process the mobile service data. FEC block is composed of 4 TS packets with 188 byte long. To help the mobile service have better noise immunity and Therefore, in order to form integral frames, another 3008higher receiving sensitivity, the input mobile bits are firstly pre- mobile bits experience the same process. Finally, 6 equivalentencoded by the enhanced first-level FEC encoder according to FEC blocks are buffered to form 3 standard 16QAM/LDPC0.8the control signal. Any kind of error correcting codes, including signal frames, where 2048 padding bits in total are inserted forthe code rate, the error correction capability, the complexity of every 16QAM/LDPC0.8 frame.encoding and decoding, can be selected depending on the QoS Denote variables as Table III, the payload rates of both ter-requirement. restrial DTV and mobile services are given by 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- (5)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, (6)rather than modulated to QAM symbols. The standard QAMmapping in the “post-processing” module are actually used to respectively. Also, due to the extension and padding bits, thecarry out the QAM modulation. spectral efficiency penalty compared to traditional terrestrial After that, 4 PH bytes including M-PID bits are firstly added. service transmission is approximately calculated asWhen 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 with (7)DTMB, as the format matched frames will be encoded by the stan-dard second-level FEC. These additional padding bits can be re-served for the parity bits for M-PID when using error correcting By applying (5)–(7), take the mobile E-4QAM/LDPC0.4 andcodes such as repetition codes, or even be completely irrelevant. terrestrial 16QAM/LDPC0.8 mode as an example. AccordingFurthermore, the numbers of padding bits in need are different to [7], the mobile TV service requires data throughput of 384
  • 510 IEEE TRANSACTIONS ON BROADCASTING, VOL. 56, NO. 4, DECEMBER 2010Fig. 10. Packet formatting flow. TABLE III TABLE IV DENOTATIONS PARAMETERS AND THEIR DEFINITION 3) Mobile Receiver Design: Fig. 8 shows the newly-designed mobile receiver. At the mobile receiver, post-processing is car-Kbps at least. When the occupancy-ratio is 25% and PN length ried out similarly to the conventional DTMB receivers. After theis 945, at the cost of 6% spectral efficiency, the enhanced system convolutional interleaving in DTMB, the specific M-PID in thehas a terrestrial DTV payload of 14.4 Mbps plus a mobile pay- control frame is checked to determine the mobile frame positions,load of 798 Kbps. Similarly, when the occupancy-ratio is 15%, and then the frames which belong to the desired mobile serviceat the spectral efficiency penalty of 4%, the mobile E-16QAM/ are selected for the further processing. After that, the parity bitsLDPC0.4 and terrestrial 64QAM/LDPC0.6-mode has provided related to the second-level FEC encoding as well as the 4 PH bytesa terrestrial DTV payload of 16.3 Mbps plus a mobile payload of and the formatting bits are removed. By carrying out the removal479 Kbps. It is indicated that, for small occupancy-ratio of mo- operation, we make sure that the mobile valid bits can be directlybile service data, the spectral efficiency penalty is negligible. As demapped using the lower-order E-QAM constellation. Takingthe occupancy-ratio increases, mobile throughput increases lin- a careful look at the above procedure, we can see that, by onlyearly while terrestrial throughput decreases, which would offer demapping their own service data using the lower-order E-QAMinherent flexibility in terms of carrying multiple services with constellation as well as only decoding the mobile bits, the mobiledifferent QoS requirement. receivers have much lower power consumption.
  • WANG et al.: EMBEDDED TRANSMISSION OF MULTI-SERVICE OVER DTMB SYSTEM 511 M @BER = 2 2 10 FOR DIFFERENT MODES TABLE V TABLE VI BRAZIL A CHANNEL PROFILE RECEIVING SNR UNDER AWGN CHANNEL (O 0 = 25%) E-QAM MODES DERIVED FROM THE OUTEST CORNER OF THE HIGHER-ORDER QAMS ARE USED. TABLE VII THROUGHPUT FOR DIFFERENT MODES (O 0 = 25%)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 main isfy multiple SDTV (standard definition TV) services. Since ad-parameters for performance evaluation, including both the re- justing the occupancy-ratio could offer inherent flexibility of theceiving SNR margin and the transmit SNR margin, have been in- terrestrial and the mobile throughput, the occupancy-ratio couldvestigated under AWGN channel and mobile multipath channel, be reduced when an HDTV (high definition TV) program needsrespectively. The profile of the multipath channel, namely Brazil to be transmitted.A, is shown in Table V. In summary, Tables VI and VII compare the receiving SNR In China, the two most widely used modes for DTMB margins under AWGN channel and throughput comparisonssystems are 16QAM/LDPC0.8 and 64QAM/LDPC0.6. Here, of typical compatible modes in the enhanced DTMB system.4 kinds of E-4QAMs derived from 64QAM, i.e., E-4QAM(5), Different occupancy-ratio would provided inherent tradeoff be-E-4QAM(6), E-4QAM(7) and E-4QAM(8) are used. tween the terrestrial and mobile throughput, which all guarantee With the fraction behind “/” denoted as the LDPC rate, the feasibility of the proposed DTMB multi-service transmis-Fig. 11 shows the BER versus the transmit SNR performance sion scheme. It is expected that similar comparison results canof the enhanced DTMB multi-service system under Brazil A be obtained in mobile multipath environment. It is indicatedchannel with Doppler spread of 20 Hz. The occupancy-ratio is that, with the tradeoff between the reception performance and25% here. The mobile E-4QAM(5)/0.8-mode provides a total the transmit power consumption, the enhanced DTMB servicetransmit SNR margin of over system can not only maintain the original terrestrial receptionthat of terrestrial 64QAM/LDPC0.6-mode, which includes performance but also support the mobile services at satisfactorythe mapping margin at the cost of the increasing average reception performance.transmit power. Similarly, E-4QAM(6)/0.8-mode provides atotal transmit SNR margin of . VI. CONCLUSION AND FUTURE WORKOn the contrary, due to the mapping margin decline of A flexible DTMB multi-service datacasting system is pro-E-4QAM(7), E-4QAM(7)/0.8-mode saves the average transmit posed to support both terrestrial and mobile services in a back-power, which results in a smaller transmit SNR margin of ward compatible manner. The multiplexed stream is received . E-4QAM(8) has so much perfor- and decoded at the conventional DTMB receivers, and the de-mance degradation that it is not suitable for practical mobile sired terrestrial service data are selected via the PID checking.applications, and thus not considered here. At the mobile DTMB receivers, the mobile service data out of By applying (5) and (6), the data throughput of the 4 mo- the multiplexed stream are separated via control frames. Simu-bile E-4QAM/0.8-modes and terrestrial 64QAM/0.6-mode can lation results indicate that the proposed scheme provides signifi-be calculated, with a payload of 1.2 Mbps to support 3 mobile cant transmit and receiving SNR margin as well as inherent flex-TV services of 384 Kbps, plus the payload of 16.2 Mbps to sat- ibility. Compared with the conventional DTMB broadcasting
  • 512 IEEE TRANSACTIONS ON BROADCASTING, VOL. 56, NO. 4, DECEMBER 2010system, although the total payload is slightly reduced due to the [18] L. Zhang, L. Gui, and Y. Xu et al., “Configurable multi-rate decoder ar-padding and the formatting bits, the improved DTMB multi-ser- chitecture for QC-LDPC codes based broadband broadcasting system,” IEEE Trans. Broadcast., vol. 54, no. 2, pp. 226–235, Jun. 2008.vice system not only achieves the purpose of multi-service trans- [19] J. Song, D. Niu, and K. Peng et al., “Multi-rate ldpc decoder imple-mission with no reception performance degradation for conven- mentation for china digital television terrestrial broadcasting standard,”tional terrestrial DTV service but also provides flexible modes in Proc. IEEE Int. Conf. Commun., Circuits Syst. (ICCCAS), Xiamen, China, May 2007, pp. 24–28.to realize different embedded transmission of mobile services [20] Information technology C Generic coding of moving pictures and asso-over the DTMB system. ciated audio. International standard, ISO/IEC 13818 Std., Joint Tech- Finally, the work in this paper can be extended in several nical Committee ISO/IEC JTC1/SC29/WG11, 1995.directions. For example, firstly, the average transmit power in- [21] B. Ai, Z. Yang, and C. Pan et al., “Analysis on LUT based predistortion method for HPA with memory,” IEEE Trans. Broadcast., vol. 53, no.creases due to the E-QAMs with larger average energy, as a re- 1, pp. 127–131, Mar. 2007.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 obtained Xiaoqing Wang was born in Shandong, China. She received the B.S. degree in 2007 from thevia the control frame in this paper, yet it makes the spectral Department of Electronic Information Engineeringefficiency slightly suffered. The system throughput can be fur- in Tianjin University. She has been pursuing thether improved by redefining the TPS symbols or using the phase Ph.D. degree at the DTV Technology R&D Center, Tsinghua University since 2007.knowledge of the PN sequences. Her main research interests are in the areas of broadband wireless transmission technologies, dig- ital TV broadcasting and powerline communications. REFERENCES [1] Y. Wu, E. Pliszka, and B. Caron et al., “Comparison of terrestrial DTV transmission systems: The ATSC 8-VSB, the DVB-T COFDM, and the ISDB-T BST-OFDM,” IEEE Trans. Broadcast., vol. 46, no. 2, pp. 101–113, Jun. 2000. Jintao Wang received the B.Eng and Phd.D. degrees [2] J. Song, Z. Yang, and L. Yang et al., “Technical review on Chinese in electrical engineering both from Tsinghua Univer- digital terrestrial television broadcasting standatd and measurements sity, Beijing, China in 2001 and 2006, respectively. on some working modes,” IEEE Trans. Broadcast., vol. 53, no. 1, pp. Since 2006, he has been an assistant professor 1–7, Mar. 2007. of Tsinghua’s DTV Technology R&D center. He [3] W. Zhang, Y. Guan, and W. Liang et al., “An introdution of the Chi- is the standard committee member for the Chinese nese DTTB standard and analysis of the PN595 working modes,” IEEE national digital terrestrial television broadcasting Trans. Broadcast., vol. 53, no. 1, pp. 8–13, Mar. 2007. standard. His current research interest is in the area [4] M. Chari, F. Ling, and A. Mantravadi et al., “FLO physical layer: An of the broadband wireless transmission, especially overview,” IEEE Trans. Broadcast., vol. 53, no. 1, pp. 145–160, Mar. the channel estimation and space-time coding tech- 2007. niques. [5] S. Cho, G. Lee, and B. Bae et al., “System and services of terrestrial digital multimedia broadcasting (T-DMB),” IEEE Trans. Broadcast., vol. 53, no. 1, pp. 171–178, Mar. 2007. [6] M. Poggioni, L. Rugini, and P. Banelli, “DVB-T/H and T-DMB: Physical layer performance comparison in fast mobile channels,” Jun Wang was born in Henan, P. R. China, on Oc- IEEE Trans. Broadcast., vol. 55, no. 4, pp. 719–730, Dec. 2009. tober 5, 1975. He received the B. Eng. and Ph.D de- [7] R. T. Anders Henten and I. Windekilde, “Towards a realistic as- grees from the Department of Electronic Engineering sessment of mobile TV developments,” in Pre-Conf. Workshop Int. in Tsinghua University, Beijing, China, in 1999 and Commun. Assoc.(ICA) Conf., Chicago, IL, May 2009. 2003 respectively. [8] C. W. Rhodes, “Some recent improvements in the design of DTV re- He is an assistant professor and member of Digital ceivers for the ATSC standard,” IEEE Trans. Consumer Electron., vol. TV R&D center of Tsinghua University since 2000. 48, no. 4, pp. 938–945, Nov. 2002. His main research interests focus on broadband wire- [9] J. Meehan, “Antenna diversity for improved indoor reception of US less transmission techniques, especially synchroniza- Digital terrestrial television receivers,” IEEE Trans. Consum. Electron., tion and channel estimation. He is actively involved vol. 48, no. 4, pp. 850–853, Nov. 2002. in the Chinese national standard on the Digital Ter- [10] Implementation guidelines for a second generation digital terrestrial restrial Television Broadcasting technical activities, and is selected by the Stan- television broadcasting system (DVB-T2), ETSI Std. , Feb. 2009. dardization Administration of China as the Standard committee member for [11] V. Gaddam and D. Birru, “A newly proposed ATSC DTV system for drafting. transmitting a robust bit-stream along with the standard bit-stream,” IEEE Trans. Consum. Electron., vol. 49, no. 4, pp. 933–938, Nov. 2003. [12] S. Kim, J. Lee, and S. Kim et al., “Enhanced-xVSB system devel- opment for improving ATSC terrestrial DTV transmission standard,” Yangang Li received the masters degree in electrical IEEE Trans. Broadcast., vol. 52, no. 2, pp. 129–136, Jun. 2006. engineering. [13] A. Goldsmith, Wireless Communications. Cambridge, U.K.: Cam- He is a Senior Manager at Hong Kong Applied Sci- bridge Univ. Press, 2004. ence and Technology Research Institute (ASTRI) and [14] G. Ungerboeck, “Channel coding with multilevel/phase signals,” IEEE the co-director of the ASTRI-Tsinghua Multimedia Trans. Inform. Theory, vol. 28, pp. 55–67, 1982. Broadcasting and Communications (MBC) Joint Re- [15] F. Tosato and P. Bisaglia, “Simplified soft-output demapper for bi- search Lab. He is responsible for the research and de- nary interleaved COFDM with application to HIPERLAN/2,” IEEE Int. velopment activities and commercialization of tech- Conf. Commun. (ICC), vol. 2, no. 2, pp. 664–668, May 2002. nologies in the general area of DTMB, the DTTB [16] R. G. Gallager, Principles of Digital Communication. New York, standard in China. Before joining ASTRI, he was a U.S.: Cambridge Press, 2008. Senior Advisor at ZTE, San Diego. Prior to that, he [17] J. Boutros and E. Viterbo, “Signal space diversity: A power- and band- had been with Navini Networks (acquired by Cisco) and Cwill Telecommunica- width-efficient diversity technique for the Rayleigh fading channel,” tions. His primary research interests include wireless communication systems, IEEE Trans. Inform. Theory, vol. 44, no. 4, pp. 1453–1467, 1998. DTV systems, DSP algorithms, and baseband chipsets design.
  • WANG et al.: EMBEDDED TRANSMISSION OF MULTI-SERVICE OVER DTMB SYSTEM 513 Shigang Tang received the B.Eng degree with Jian Song received the B.Eng and Ph.D. degrees in distinction from University of Electronic Science electrical engineering both from Tsinghua Univer- and Technology of China in July 2003, and the Ph.D. sity, Beijing, China in 1990 and 1995, respectively in electrical engineering from Tsinghua University, and worked for the same university upon his gradu- China. ation. He then joined Hong Kong Applied Science and He has worked at The Chinese University of Technology Research Institute Company Limited Hong Kong and University of Waterloo, Canada (ASTRI) as a senior engineer in Aug. 2008. His in 1996 and 1997, respectively. He has been with research interests are in the area of signal processing Hughes Network Systems in USA for 7 years before for wireless communications and broadcasting, in joining the faculty team in Tsinghua in 2005 as particular, receiver algorithm design for the Chinese a professor. He is now the director of Tsinghua’sdigital terrestrial television broadcasting systems. DTV Technology R&D center. His primary research interest is in physical layer and has been working in quite different areas of fiber-optic, satellite and wireless communications, as well as the powerline communications. His current research interest is in the area of digital TV broadcasting. Dr. Song has published more than 50 journal and conference papers and holds one US patent.