The Digital Video Broadcasting Next Generation Handheld (DVB-NGH) standard has adopted many advanced technologies, including overhead reduction schemes, to maximize the system capacity. However, some of the overhead reduction schemes of Layer-l (LI) signaling result in increased initial capture time delays. In order to get a more flexible trade-off between overhead reduction and initial capture time delay, a full-truncated Ll signaling scheme is proposed in DVB-NGH systems. Simulation results demonstrate the effectiveness ofthe proposed scheme.
2015 10th International Conference on Communications and Networking in China (ChinaCom) Reduction of Physical Layer Signaling Overhead in DVB-NGH Systems Weidong Wen l,2, Jinfeng Tian2 , Mingqi Li 2, Guohui Lil ISchool of Communication and Information Engineering, Shanghai University, Shanghai, China 2Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, China Email:809604228@qq.com Abstract-The Digital Video Broadcasting Next Generation Handheld (DVB-NGH) standard has adopted many advanced technologies, including overhead reduction schemes, to maximize the system capacity However, some of the overhead reduction schemes of Layer-l (LI) signaling result in increased initial capture time delays In order to get a more flexible trade-off between overhead reduction and initial capture time delay, a full-truncated Ll signaling scheme is proposed in DVB-NGH systems Simulation results demonstrate the effectiveness ofthe proposed scheme robustness [5] Overhead reduction is an effective way to improve the bandwidth usage Multiple schemes have been proposed in DVB-NGH systems to reduce the overhead of the physical layer signaling, such as the n-periodic spreading of L I-pre data and the L l-config signaling partitioning [6] etc Overhead reductions by using spreading and partitioning are achieved at the expense of a longer initial capture time, because receivers may need to wait for more than one frame to start decoding the PLPs [n order to get a more flexible trade-off between overhead reduction and initial capture time delay, a new signaling scheme is proposed in this work, by introducing the conception of full signaling and truncated signaling Keywords-DVB-NGH; LI signaling; overhead reduction I [NTRODUCTION The Digital Video Broadcasting Next Generation Handheld (DVB-NGH) standard [1] is the mobile evolution of the European standard Digital Terrestrial Television (OTT) for the second-generation digital terrestrial (DVB- T2) [2], targeting for better performance in terms of capacity and coverage to the existing mobile technologies [t introduces several advanced techniques and matching physical layer (or Layer-I, L I) signaling that enable high definition services for fixed terminals and provide improved reception for battery-powered and mobile receivers Fig I L1 signaling structure ofDVB-NGH The rest of this paper is outlined as follows Section II reviews the overhead reduction schemes for LI signaling in DVB-NGH systems In Section III, the optimized overhead reduction method is proposed Then the analysis of the simulation results is presented in Section IV Finally we conclude our work in Section V The LI signaling in the DVB-NGH system offers the required information for accessing the Layer-2 (L2) signaling and the services themselves [3] [t is divided into three categories: the PI signaling, the Ll-pre signaling, and the L I-post signaling The L I-post signaling is further split into two main parts: configurable (Ll-config) and dynamic (L I-dyn) All of these fields of L I signaling are carried in the NGH physical frame (frame for short) An overview of the Ll signaling structure and its frames is given in Fig The PI signaling indicates the transmission type and basic transmission parameters, which may be followed by an additional PI (API) signaling for supporting the Satellite profile In DVB-NGH systems, the Ll-pre signaling provides information relating to the network topology, configuration and logical channel It also enables the extraction and decoding of the Ll-post signaling, which contains the information needed to identify and decode the physical layer pipes (PLPs) within the frame For the Ll-post signaling, the configurable parameters shall always remain unchanged for the entire duration of one logical super-frame, while the values of the dynamic parameters may change for different logical frames [I] [4] II OVERHEAD REDUCTION OF LAYER SIGNALING OF DVB-NGH [t has been known that the basic scheme of L I signaling in DVB-NGH is that one frame carries PLPs and corresponding LI signaling which includes PI, Ll-pre, Ll-config, as well as Ll-dyn It is illustrated in Fig.2 with PLPs transmitted in every frame, where the L l-config signaling provides the signaling information of PLPs per frame Fig Basic scheme in DVB-NGH In order to maximize the system capacity, a system should introduce as little overhead as possible Despite more Ll-signaling contents have been added in compare of T2 contents, DVB-NGH has restructured and optimized LI Compared with DVB-T2, the Ll signaling of DVB-NGH has been optimized, in terms of overhead, capacity and 719 978-1-63190-077-8 © 2015 IEEE signaling can reach 1e-4 and the P signaling has the most robust detection performance among the LI signaling That means the L signaling can be successfully parsed from a frame at least with the possibility of 99.99% Given this consideration, robustness consideration is ignored in this paper signaling structure in order to reduce signaling overhead The first proposed method for signaling overhead reduction in DVB-NGH systems is the n-periodic Ll-pre signaling Due to the fact that the L I-pre signaling is only required for the initial capture, and seldom changes during a super frame, so it is possible to spilt L I-pre signaling fields into n frames in a single radio frequency (RF) channel scenario This spreading of quasi static signaling contents to several frames improves the time diversity and reduces the signaling overhead by a factor of n, but with a drawback of increasing initial capture time Therefore, the parameter n represents a trade-off between initial capture time and signaling overhead Fig Simplified scheme in DVB-NGH III Secondly, the conception of logical frame in DVB-NGH can be used to reduce L l-post signaling overhead One logical frame with a L I-post signaling can span several NGH frames At this case the Ll-post signaling is not transmitted in every NGH frame, which results in overhead reduction of L l-post signaling at the expense of increased initial capture times For simplification, each logical frame is exactly mapped to one NGH frame in this work OPTIMIZED OVERHEAD REDUCTION METHOD In this section, a new method for overhead reduction of Ll signaling is presented to replace the schemes of n-periodic L I-pre signaling spreading and self-decodable Ll configurable partitioning, trying to get a better tradeoff between overhead and initial capture The concept of full signaling and truncated signaling are introduced in this work, striving separately for faster initial capture and lower signaling overhead Noting that the proposed scheme can still inherit other strategies described in the previous section, including logical frame, PLP mode, and "OPTIONS FALG" The third improved scheme is to optimize the PLP signaling loop by the PLP mode conception in the L l-config signaling of DVB-NGH Instead of defining the properties of each PLP, such as the PLP identification number, modulation, code rate, time interleaving configuration etc., PLPs are associated in groups with the same settings The parameter configuration of a group of PLPs is called a PLP mode The parameters can be defined only once in a single PLP configuration if there are several PLPs with the same parameters, which results in significant overhead reduction Because the partitioning approach is abandoned in the proposed scheme, the signaling fields valid for PLP partition of Ll-config signaling can be deleted For the proposed scheme, a field of I-bit is added to the PI signaling to signify whether the proposed Ll signaling in the current frame is truncated or not Such PI signaling is called modified PI signaling for the convenience of description A further improvement for reducing the L I-config signaling overhead in DVB-NGH consists in the introduction of "OPTIONS FALG" to signal the availability of some optional features which are not commonly used There are many options in the DVB-NGH system, such as sub-slicing, auxiliary streams, reserved for future use fields etc The amount of required signaling information can be significant in some cases and the corresponding fields can be removed ifits feature is unused The full signaling of the proposed scheme comprises of the modified P signaling, Ll-pre signaling, Ll-config signaling, and L I-dyn signaling, supporting all the functions, such as initial scanning, zapping, handover, and continuous reception etc Herein, the L I-pre signaling, Ll-config signaling, and the Ll-dyn signaling are same as those of the basic scheme However, the truncated signaling, which is an abridged form of the full signaling, only supports continuous reception function For the truncated signaling, the signaling fields with constant values during a period of time (e.g super frame or logic super frame) of L I-pre and L I-config signaling are truncated The signaling fields of the truncated L l-pre signaling is presented in Table I The bits of L I-pre signaling decrease from 496 to 65 after truncating Since all the fields of L l-config signaling are invariant within a logical super frame, the bits of the truncated L l-config signaling can be reduced to zero, which means none of the configurable field is contained in the truncated L signaling Lastly, the DVB-NGH standard introduces the concept of self-decodable L I configurable partitioning for overhead reduction, which means that each logical frame carries only one partition of PLP signaling loop for a part of PLPs Each PLP has associated a repetition interval that indicates how frequently the PLP is signaled in the L I-config, while the amount of Ll-config information transmitted per frame is constant and self-decodable A simplified scheme, including n -periodic Ll-pre spreading and L I-config partitioning, is illustrated with PLPs in Fig Here, the Ll-pre data is separated into frames, and the transmitted number of PLPs in each frame is due to partitioning Therefore, only a quarter of the Ll-pre data is carried in every frame, and the Ll-config signaling only contains signaling fields of PLPs in each frame TABLE I THE SIGNALING FIELDS OF THE TRUNCATED L I-PRE SIGNALING L1 POST DELTA (24 bits) FRAME lOX (8 bits) As we know, signaling design often relates to transmission reliability In DVB-NGH, the robustness of Ll signaling has been enhanced by introducing new 4K LDPe codes, incremental redundancy (IR) and additional parity (AP) [7] The frame error rate (FER) of L I-pre and L I-post Truncated L I-pre signaling (65 bits) LC CURRENT FRAME RF lOX (3 bits) LC CURRENT FRAME RF POS (3 bits) LC NEXT FRAME RF IDX (3 bits) LC NEXT FRAME DELTA (24 bits) 720 The ratio of frame number of full signaling to that of truncated signaling, denoted by RFNFT, can be configured according to the requirements on initial capture time and overhead reduction The frames with full signaling are deployed as evenly as possible during the considered frames, to enable fast initial capture When n frames are considered, the RFNFT can be set as the value of i: n - i , where i denotes the number of frames carried with full L I signaling among total n frames Thus n - i means the number of frames carried with truncated L1 signaling No truncated signaling is configured in these frames if n-i equals o Fig 4a and Fig 4b describe the cases for n of with i = I and i = respectively where .! ;~ - Frame2 5) The value of signaling field LC_ NUM _ RF is assumed to be for multi-RF channels case, while it equals for single RF channel scenario; 6) The input stream is transport stream (TS) and the value of signaling field of NUM_STREAMS]ER]LP is assumed to be ; To evaluate the performance of overhead reduction, the number of bits of overall L signaling within n frames is counted, with respect to the number of PLPs Here, the number ofPLPs given by NumPLPs, is the number ofPLPs within a logical super frame, which is signaled by the field of NUM]LP]ER_ LSF in the Ll-config signaling In order to further analyze the overhead saving of the proposed scheme in relation to the simplified scheme in the DVB-NGH system, an overhead saving factor denoted by '7,oving is defined as Fig 4a Proposed scheme in DVB-NGH (RFNFT=l :3) .- ~ Frame1 -l.~i Frame2 ; III Frame] -~ ;~ - denotes the ceiling integer; 4) All optional functions of L I-post signaling are not enabled and the corresponding fields are removed, except for PLPs partitioning in the simplified scheme The value of the signaling field PARTITION_ NUM_ADD]LP of the simplified scheme is set to 0, and the relationship between the number of PLPs per logical frame and the number of PLPs per logical super frame in the simulation can be assumed as Note that the proposed full and truncated signaling method is suitable for both single RF channel and multi-RF channels scenarios, while the overhead reduction method for L I-pre signaling of DVB-NGH is limited to single carrier frequency scenario ~ Framel i.l Frame4 ~ iJsaving A N simp/(fied - N N proposed simpitfied (1) where NSimpli/ied and Nproposed denote the number of LI signaling bits of the simplified scheme and the proposed scheme, respectively Apart from that, the metric of average initial capture time is introduced to evaluate the average cost time to accomplish parsing a targeted frame when initial scanning or zapping occurs To simplify the calculating, the following premises are hypothesized: I) the frequency hopping time of ms in the multi-RF channels scenario is ignored, 2) the cost time for parsing a frame is assumed to be one frame length, 3) PLPs is considered, each of which has the same value of field given by PLP]ARTITION_CLUSTER_ID ClusterlD ='0 I' Therefore, the average initial capture time can be written as Fig 4b Proposed scheme in DVB-NGH (RFNFT=l:l) IV == PERFORMANCE EVALUATION Simulation Conditions and Performance Metrics In this section, three L signaling schemes, including the basic scheme, the simplified scheme, and the proposed scheme, are involved to compare the overhead performance in DVB-NGH systems Specifically, the proposed L I signaling scheme is further demonstrated with RFNFTs of I:n-l, 2:n-2, and :n-3 in the simulation As the overhead reduction method for Ll-pre signaling of DVB-NGH is limited to single carrier frequency transmission, two scenarios, i.e., single RF channel and multi-RF channels, are considered separately in the simulation Tbasic = -'0 (2a) In order to simplify the evaluation, some assumptions are made before simulation as follows (2b) 1) The aPlsignaling is not used; T = slmp/{fied _mull! RFs' 2) Logical channel type A is considered and the frames mapped from the same logical channel have the same frame length on different RF channels; (ClusterID+I)xI'r nxTF Tproposed = -2i - " +Tp 3) Overhead reduction by "PLP mode" is applied in all L I signaling schemes The number of PLP modes IS assumed to be T +J,F (2c) (2d) where ~asic' r.,'implifled _1 RF' r.,'imp/!(Ted _"utlt; RFs and Tproposed are the average initial capture time cost by the basic scheme, simplified scheme in single RF scenario, simplified scheme in multi-RF scenario, and proposed scheme, respectively 721 Tr denotes the frame length I: : : 11000, B Numerical Results 10000 9000 The number of bits of L I signaling versus the number of PLPs in the single RF channel scenario is shown in Fig 5, where the considered frames number n equals It can be seen that the overall overhead of L signaling in all signaling schemes increases as the number of PLPs is increased The basic scheme always has the most number of signaling bits for different number of PLPs, while the proposed scheme of RFNFT= 1:4 offers the best performance of overhead reduction For a given number of PLPs, the number of L signaling bits of the simplified scheme is between that of the proposed scheme of RFNFT=2:3 and RFNFT=3:2 As we have the fourth assumption in this section, the numbers of bits of the predominant Ll signaling (i.e., Ll-config signaling) for NumPLPs= j and NumPLPs = j + are equal, where j is an odd integer This results in an approximate ladder profile of the signaling overhead ofthe simplified scheme c ' 7oo0 -~~~~~~ 6oo0 , ~~~~ =~~~ ill 5000- 4oo0 ~~~~-~~~~~~ - z 3000· 1OO00~' ~ ~ ~-~ -1~0 ~12 NumPLPs Fig, 6, Bits number comparison of LI signaling in the multi-RF channels scenario (n=5) 0,7 0,6 -±7?~-= + -:f-::=~~~ ~ ~ til IIi 0.5- ~ 0.4 ~,L -+- -4 Proposed scheme,RFNFT=2:3 e- Proposed scheme,RFNFT=3:2 a;~ 7000- _~7""'+ -:oA~; ~~- 0,3 -nf -t-rr-+-, 7f7'~+ '"c o~ O.1 -1 -/-.t-I ~f'- -+- NumPLPs=3,RFNFT=2:n·2 6000· *"- NumPLPs=3,RFNFT=1:n-1 -' a r ! ~ *"- Proposed scheme,RFNFT= 1:4 ! Proposed scheme,RFNFT=1:4 I _ _ _-= &~_ _ -4 Proposed scheme,RFNFT=2:3 e Proposed scheme,RFNFT=3:2 sooo ~ e Simplified scheme en , ' -+- Basic scheme SOOO - ~ 10000.·, , -' _ _ ' -_ _-' , gOOD *"- ~:~i:;;::~eme -+- NumPLPs=3,RFNFT=3:n-3 5000- *"- NumPLPs=6,RFNFT=1 :n-1 § z 4000· -0.1 - +- hL -+- NumPLPs=6,RFNFT=2:n-2 -+- NumPLPs=6,RFNFT=3:n·3 - 02;: -: ~-~ -=========~==~~~ 3000· 2000· 1000 ' o 10 Fig, 7, 12 NumPLPs lJsaving versus n in the multi-RF channels scenario The average initial capture time versus n is shown in Fig For the basic scheme, the average cost time for initial capturing is always one and a half frame, while it costs frames for the simplified scheme in the multi-RF channels case Apart from the above two constant time delay, the average initial capture times of other cases increase with increasing n The simplified scheme in the single RF channel scenario needs the most average time, followed by the proposed scheme with RFNFT= : n -1 The smaller ratio the RFNFT is, the more average time the initial capture process costs Under the same conditions, there are some cost time values of the proposed scheme lower than those of the simplified scheme in the multi-RF scenario Fig, 5, Bits number comparison of L I signaling in the single RF channel scenario (n=5) Fig depicts the comparison of number of bits of Ll signaling in the multi-RF channels scenario We can see that the trends of curves and the conclusions obtained from Fig are close to those in Fig 5, except for the location of the overhead curve of the simplified scheme Since the n-period spreading of L I-pre signaling can't be applied in the multi-RF channels scenario for the simplified scheme, every frame must carry complete L I-pre data This increases the number of L signaling bits compared to the single RF channel scenario As the L I-config signaling partitioning is still adopted in the simplified scheme, so it has less overhead than the basic scheme 900.' In Fig 7, the overhead saving factor as a function ofn in the multi-RF channels scenario is described The value of overhead saving factor increases as n is increased Positive values indicate that the proposed scheme outperforms the simplified scheme in overhead reduction; otherwise the former is inferior to the latter Fig shows that the overhead saving factor is always positive value when RFNFT is equal to I: n -I Moreover, the less the RFNFT is, the more overhead reduction we can obtain It can be observed that the points where n is equal to in Fig 7, exactly verify the results in Fig , e Basic scheme , 800 -+- Simplified scheme,1 700 -+- RF +- Simplified scheme, multi RFS d1 e- :§ Proposed scheme, RFNFT=1:n-1 Proposed scheme, RFNFT=2:n-2 Proposed scheme, RFNFT=3:n-3 ~ 600~ -+~ ~ ~~ ~ !ro 500 ~ 400 ~ ~ 100 " Fig, 8, Average initial capture time versus n 722 V CONCLUSIONS In this paper, a new L1 signaling scheme is proposed in DVB-NGH systems, to address a better tradeoff between overhead reduction and initial capture delay The concepts of the full signaling and the truncated signaling are put forward, which can be applied in both single carrier frequency and multiple carrier frequencies scenarios The proposed scheme with a proper RFNFT may achieve significant overhead reduction, with a shorter initial capture delay Simulation results demonstrate that the proposed scheme provides a more flexible tradeoff between overhead reduction and fast initial capture VI ACKNOWLEDGEMENT This research is sponsored by the project of Chinese Academy of Sciences Key development (KGZW-EW-I 03-1); Science and Technology Commission of Shanghai Municipality (STCSM) under Grant No 130Z1511200 REFERENCES [1] Digital Video Broadcasting, Next Generation Broadcasting System to Handheld, Physical Layer Specification (DVB-NGH), DVB Doc A160, Nov 2012 [2] Digital Video Broadcasting (DVB), Frame Structure Channel Coding and Modulation for a Second Generation Digital Terrestrial Television Broadcasting System (DVB-T2), ETSI EN 302 755, VI.I.I, 2008 [3] 1.M Llorca Beltran, "Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH," Mobile Communications Group of Iteam, Jan 2010 [4] H Frank and P Mihail, Physical Layer Signalling for Digital Broadcast System, U.S Patent Application, US892940lB2, Jan 2015 [5] Zoellner, Robert, and L Stadelmeier, "Optimization of the physical layer signalling overhead of DVB-T2 and DVB-NGH," in Proceeding of IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), pp 1-5, June 2012 r61 A Mourad, I G Gonzalez, H Jeong, and S Yun, Frame Structure and Signalling for Wireless Broadcasting System, UK Patent Application, GB 2490212A, Apr 2011 P1 H Jeong and S Yun, Method and Apparatus for Transmitting and Receiving Infonnation in a Broadcasting/Communication System, US Patent Application, US20130055051, Feb 2013 723 ... the signaling overhead by a factor of n, but with a drawback of increasing initial capture time Therefore, the parameter n represents a trade-off between initial capture time and signaling overhead. .. corresponding fields can be removed ifits feature is unused The full signaling of the proposed scheme comprises of the modified P signaling, Ll-pre signaling, Ll-config signaling, and L I-dyn signaling, ... Ll-pre data is carried in every frame, and the Ll-config signaling only contains signaling fields of PLPs in each frame TABLE I THE SIGNALING FIELDS OF THE TRUNCATED L I-PRE SIGNALING L1 POST DELTA