Thesis Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH

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1. Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH Author: José Mª Llorca Beltrán Director: David Gómez Barquero Tutor: Narcís Cardona Marcet Start Date: 1/04/2010 Workplace: Mobile Communications Group of iTEAM
2. Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH 1 Objectives — This Master of Science degree thesis aims at investigating, studying and developing the new physical layer for the new handled generation of terrestrial TV standard DVB-NGH. This new physical layer is based on the DVB-T2 physical layer specification, but it introduces several advanced mechanisms to allow the transmission of high definition TV services in mobile environments. The main objective of this thesis work is focused on illustrating the benefits of the new physical layer when compared to T2 physical layer. Methodology —A comparison study between the new standard and the previous DVB-T2 is carried out, focusing on the adopted mechanisms and robustness enhancement techniques. Such study is performed by simulating both DVB-T2 and DVB-NGH physical transmission chains in typical deployment scenarios. Theoretical developments —The theoretical developments have been carried out following the standardization process of DVB-NGH, where several proposals have been admitted and studied for enhancing the NGH physical layer in different aspects, i.e. increasing the robustness, signaling capacity and overhead reduction in comparison to the DVB-T2 physical layer. Prototypes and lab tests — The DVB-T2 physical layer simulator has been developed according to the standard and the DVB-NGH physical layer simulator has been programmed following the standardization process, including all the approved proposals. Both simulators perform all the physical transmission chains for DVB-T2 and DVB-NGH. Results — The results shown in this work include performance curves, focusing on signaling robustness, signaling capacity and overhead reduction. The DVB-NGH results have been compared to SAMSUNG‘s (South Korea) in order to validate the robustness mechanisms in the standardization process of DVB-NGH. The simulation results show a gain in robustness when adopting the DVB-NGH physical layer techniques instead of DVB-T2. In addition, DVB-NGH improves signaling capacity and reduces the overhead. Future work —The future work may be done by studying the effect of the signaling physical layer at MIMO and SIMO environments. In addition, once the standardization process finalizes, another possible line of investigation may be to study the most suitable configuration of L1 signaling for different mobile transmission environments. Publications — The contents and results of this thesis has been included in two technical reports on DVB- NGH at the European R&D project ―ENGINES: Enabling Next GeneratIon NEtworks for broadcasting Services‖:  Task Force TF1 ―System concept refinements for DVB-NGH‖- Technical Report TR 1.1 Intermediate Report on DVB-NGH Concept Studies. Section 3.1.2 L1 signaling robustness improvement techniques, pp 36-48.  Task Force TF4 ―Hybrid access technologies‖ - Technical report TR4.1 Interim Report on Hybrid Access Technologies. Section 4.5 L1 Signaling for the Hybrid Profile, pp 84-88.
3. 2 Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH Moreover, the enhancement studies of the physical layer signaling in DVB-T2 have been included in the Implementation Guidelines of DVB-T2 in an updated version. This new version includes all the developments since the Implementation Guidelines of DVB-T2 were published (i.e. T2-Lite). Our contribution focused on the signaling path performance for different robustness types and modulations. The study has been evaluated in different environments, SISO and SIMO, using the TU6 channel model with Doppler frequency of 10 and 80 Hz.  ETSI TS 102 831 V1.3.1:―Digital Video Broadcasting (DVB); Implementation guidelines for a second generation digital terrestrial television broadcasting system (DVB-T2)‖, section 14.7. In addition, the contents and results of this thesis work, in conjunction with SAMSUNG contribution, have been included in the signaling chapter of DVB-NGH standard:  "Handbook of Mobile Broadcasting", CRC Press. Second Edition. Finally, a brief summary of DVB-NGH signaling has been included at ―Jornadas Telecom I+D 2011‖ paper:  ―DVB-NGH, la Nueva Generación de Televisión Digital Móvil‖. Abstract — The next generation mobile broadcasting standard DVB-NGH (Next Generation Handheld) has enhanced the physical layer signaling of DVB-T2 (Second Generation Terrestrial) in several aspects: higher signaling capacity, improved transmission robustness, reduced signaling overhead, and reduced peak- to-average-power ratio (PAPR). The physical layer signaling of DVB-T2 and DVB-NGH is transmitted in preamble OFDM symbols at the beginning of each frame. The preamble provides a means for fast signal detection, enabling fast signal scanning, and it carries a limited amount of signaling data in a robust way that allows accessing the physical layer pipes within the frame. This thesis provides an overview of the physical layer signaling in DVB-NGH. Results are compared with DVB-T2. Author: Llorca Beltrán, José María: [email protected] Director: Gómez Barquero, David: [email protected] Tutor: Cardona Marcet, Narcís: [email protected] Valencia, 09-12-2011
4. Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH 3 Index I. INTRODUCTION .............................................................................................................................. 5 I. 1 DIGITAL VIDEO BROADCASTING – NEW GENERATION HANDLED (DVB-NGH) .......................... 5 I. 2 MOTIVATION ................................................................................................................................ 5 II. AN OVERVIEW OF THE PHYSICAL LAYER SIGNALING IN DVB-T2 ........................... 6 III. IMPROVED PHYSICAL LAYER SIGNALING FOR DVB-NGH .......................................... 9 III.1. INCREASED SIGNALING CAPACITY IN DVB-NGH ......................................................................... 10 III.2. IMPROVED L1 SIGNALING ROBUSTNESS IN DVB-NGH ................................................................. 11 III.3. INCREASED L1 SIGNALING OVERHEAD REDUCTION IN DVB-NGH............................................... 17 III.4. REDUCED PAPR FOR L1 SIGNALING IN DVB-NGH ...................................................................... 21 IV. RESULTS AND DISCUSSIONS ................................................................................................ 22 IV.1. CAPACITY IMPROVEMENTS RESULTS ............................................................................................ 22 IV.2. ROBUSTNESS IMPROVEMENTS RESULTS ........................................................................................ 24 IV.3. OVERHEAD IMPROVEMENTS RESULTS ........................................................................................... 33 V. OPTIMIZATION OF THE PHYSICAL LAYER SIGNALING CONFIGURATION FOR THE DATA PATH CONFIGURATION .................................................................................................... 36 VI. CONCLUSIONS .......................................................................................................................... 38 ACKNOWLEDGMENTS ....................................................................................................................... 39 REFERENCES ........................................................................................................................................ 39
5. 4 Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH
6. Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH 5 I. INTRODUCTION I. 1 Digital Video Broadcasting – New Generation Handled (DVB-NGH) The DVB-NGH (Next Generation Handheld) standard is the mobile evolution of the European standard Digital Terrestrial Television (DTT) for the second generation DVB-T2 (Terrestrial 2nd generation). The DVB-T2 was submitted to ETSI in 2008, and will be taken into operative use during 2010. This second generation system provides about 50% increase of physical layer capacity compared to the previous standards. DVB-T2 is in its first stage targeting for fixed reception. Providing the same or better capacity increase for portable, mobile and handheld broadcasts (DVB- NGH), require new technical concepts. For this reason, DVB-NGH has been thought to be the mobile broadcasting standard reference worldwide, with better performance in terms of capacity and coverage to the existing mobile technologies, such as, the first mobile DTV generation standard DVB-H (Handled), the hybrid terrestrial-satellite mobile DTV standard DVB-SH (Satellite to Handhelds), or cell broadcast standard MBMS (Multimedia Broadcast Multimedia Services). One of the main advantages of DVB-NGH will be the possibility to transmit DVB-T2 and DVB-NGH in the same multiplex (channel RF), reusing the existing network infrastructure without the need to deploy on new dedicated networks. This can significantly reduce the investment needed to start providing mobile services. NGH services would be transmitted in frames FEFs (Future Extension Frames) within a DVB-T2 multiplex, illustrated on figure 1. Thus, it would be possible to transmit high definition services or 3D TV for fixed terminals in T2 frames and mobile services in a very robust transmission way in the NGH frames over FEF frames [6]. Fig. 1. T2 Multiplex with NGH frames over FEFs frames. I. 2 Motivation DVB-NGH is based on DVB-T2 physical layer specification, but introduces several advanced mechanisms and techniques that allow the transmission of high definition TV services. This thesis aims to investigate study and develop the new physical layer for the new handled generation of terrestrial TV standard. The main objective of this thesis is focus on how these mechanisms enhance the new physical layer in compare to T2 physical layer.
7. 6 Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH This thesis provides an overview of the physical layer signaling in the new generation mobile broadcasting DVB-NGH standard. The rest of the thesis is structured as follows. Section II briefly reviews the physical layer signaling in DVB-T2. Section III describes the signaling capacity improvements, focuses on the robustness enhancements, the signaling overhead, and finally the PAPR improvement of the L1 transmission in DVB-NGH. Section IV deals with the performance of the L1 signaling and the data path in DVB-NGH. Finally, the thesis is concluded with Section V. II. AN OVERVIEW OF THE PHYSICAL LAYER SIGNALING IN DVB-T2 The physical layer signaling in the second generation digital terrestrial TV standard DVB-T2 (Second Generation Terrestrial) has two main functions. First of all, it provides a means for fast signal detection, enabling fast signal scanning. Secondly, it provides the required information for accessing the Layer-2 (L2) signaling and the services themselves. The purpose of the L2 signaling is to associate the services with the physical layer pipes (PLPs) and with the network information. As the physical layer signaling enables the reception of the actual data, it should naturally be more robust against channel impairments than the data itself. Furthermore, in order to maximize the system capacity, it should introduce as little overhead as possible. The physical layer signaling of DVB-T2 is transmitted in preamble OFDM symbols at the beginning of each frame, known as P1 and P2 symbol(s), see figure 2. The preamble carries a limited amount of signaling data in a robust way. The frames begin with a preamble consisting of one P1 symbol and one or several P2 symbols. The number of P2 symbols in the frame depends on the FFT size of the transmission mode (e.g., two symbols for 8K FFT). The preamble is followed by a configurable number of data symbols. The maximum length of a T2 frame is 250 ms. Fig. 2. Physical layer signaling in DVB-T2 transmitted in preamble P1 and P2 OFDM symbols. The physical layer signaling is structured in three different parts which are sequentially received: the P1 signaling carried in the P1 symbol, and the L1 pre and L1 post Layer-1 (L1) signaling carried in the P2 symbol(s). The P1 symbol is used in the initial scan for detecting the presence of DVB-T2 signals on the current frequency. It carries some basic transmission
8. Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH 7 parameters, such as the frame type (e.g., T2, T2-Lite, or NGH), and it enables the reception of the P2 symbol(s). The L1 signaling transmitted in the P2 symbol(s) is divided into two parts: L1 pre and L1 post-signaling. The L1 pre-signaling provides information on the current super frame, relating to the network topology, configuration and to the transmission protocols used within the super frame (e.g., TS or GSE). The L1 pre enables the reception and decoding of the L1 post- signaling, which contains the information needed for extracting and decoding the data PLPs from the frames. The physical layer signaling of DVB-T2 was designed such that it can always be made more robust than the data path. The most robust transmission mode for the data is QPSK modulation with code rate 1/2. The P1 symbol consists of a 1k OFDM symbol, which is DBPSK (Differential Binary Phase Shift Keying) modulated in the frequency direction with a higher power than the data OFDM symbols. The P1 carriers are boosted to normalize the power between the P1 and the data OFDM symbols. The L1 pre information is BPSK (Binary Phase Shift Keying) modulated and protected with a code rate 1/5. The amount of L1 pre-signaling data is fixed and equal to 200 bits, and the size of the LDPC codeword is 16200 bits (16K). Thus, the LPDC codeword needs to be shortened (i.e., the codeword shall be padded with zeros following a shortening pattern in order to fulfill the LDPC information codeword) and punctured (i.e., not all the generated parity bits are transmitted) to be able to transmit this small amount of data. These two mechanisms decrease the outperformance of the system. The L1 post information is encoded with a 16K LDPC with a code rate 4/9. The amount of the L1 post information in DVB-T2 depends on the transmission system parameters (mainly the number of PLPs used in the system). Fig. 3. Modulation and error coding for L1 signaling.
9. 8 Physical Layer Signaling for the Next Generation Mobile TV Standard DVB-NGH The T2 specification defines an optimized puncturing and shortening scheme with a variable code rate depending on the size of the L1-post information. The effective code rate decreases as the signaling information decreases (the minimum value is 1/4 and the maximum 4/9). This rate- control compensates the performance degradation of LDPC decoding due to padding and puncturing, and it ensures the preservation of the coverage area. The modulation order of the L1- post is the only parameter of the signaling preamble that can be chosen by the broadcast network operator. The possible schemes are: BPSK, QPSK, 16-QAM, and 64-QAM. It is recommended to use one modulation order lower than the data (e.g., 64 QAM in case of 256QAM for data). This way, it is possible to assure that the signaling is more robust than the data, and the signaling overhead is minimized [1][2]. The transmission and detection of the preamble P1 symbol is very robust, and it can be correctly received even at negative signal-to-noise ratios (SNR) under mobility conditions [4]. The transmission of the rest of the physical layer signaling in the P2 symbol(s) can be configured sufficiently robust in rather static reception conditions. However, in mobile reception conditions the robustness of the L1 signaling may not be high enough due to the lack of time diversity. DVB- T2 implements a flexible time interleaver at the physical layer in order to improve the robustness of the signal against impulse noise and exploit the time diversity in mobile channels [4][5]. Since the L1 signaling is only spread in one or few OFDM symbols, it can be less robust than the data in mobile channels despite of having a lower modulation order. The L1 signaling can be optionally transmitted in-band together with the data, such that it has the same robustness. However, the full signaling from the preamble needs to be received at least when beginning the reception or changing between services. One possibility to increase the robustness of the L1 post-signaling is to further reduce the modulation order, such that it can be received in all circumstances. This increases the signaling overhead, and reduces the number of PLPs that can be used in the system. Moreover, this approach is not valid for the most robust data transmission mode (QPSK 1/2), since the L1 pre cannot reduce the modulation more than BPSK. Another possibility to increase the robustness of the L1 signaling transmission and improve the time diversity consists of transmitting information in the preamble of each frame about the current frame and the next frame. This is called repetition of L1 post- signaling, and it increases the probability of correctly receiving the L1 signaling information after receiving two frames at the expense of increased signaling overhead[2].