DVB-SH System for Broadcasting to Handheld Devices EE 5359 Multimedia Processing, Spring 2011.

Guided by Dr. K.R. Rao

Irfan Kerawalla ID: 1000719155 [email protected]

Objective: To implement the DVB-SH (Digital Video Broadcast - Satellite Services to Handheld Devices) standard designed for transmission of video, audio and data services on mobile devices.

Motivation: Mobile TV is expected by many to become one of the next big mass media markets. Growing number of mobile phone users around the globe has triggered excessive demand for multimedia content. People are constantly on the move and want all the latest updates ranging from news to social life on their fingertips. This project is a step towards understanding the process involved in implementing and delivering quality media content to handheld devices.

Requirements of a mobile TV service: Low power consumption technology. Stable reception with mobility. High speeds and clear picture quality. Minimal loss of signal due to fading and multipath effects.

What is DVB-SH? DVB-SH [1] is the name of a transmission system standard designed to deliver video, audio and data services to vehicles and handheld devices. The key feature of DVB-SH is that it is a hybrid satellite/terrestrial system that allows the use of a satellite to achieve coverage of large regions or even a whole country. In areas where direct reception of the satellite signal is not possible, terrestrial gap filler can be used seamlessly to provide coverage. It is designed to use frequencies below 3GHz, typically around 2.2GHz. The system and waveform specifications have been published as ETSI standards. (TS 102 584, TS 102 585 and EN 302 583). [1]

System Architecture: Figure 1 shows the network architecture of the DVB-SH system

Figure 1. DVB-SH network architecture [8]

TR (a) are broadcast infrastructure transmitters that provide reception in urban areas. TR (b) are personal gap fillers. Their purpose is to provide indoor coverage. TR (c) are mobile broadcast infrastructure transmitters.

Band used for DVB-SH transmission

Figure 2. Band used in DVB-SH transmission [7]

DVB-SH seeks to exploit the less congested, higher frequency, S-band where there are opportunities for MSS (mobile satellite services) systems, operating in conjunction with CGC (complementary ground components). S-band enables small omnidirectional antennas to be used in mobile devices.

Compression in DVB-SH DVB-SH uses H.264/AVC [19] compression standard. The block diagram of H.264 encoder and decoder are given in figure 2 and figure 3 respectively.

Figure 3. H.264 encoder block diagram [10]

Figure 4. H.264 decoder block diagram [10]

Typical applications of DVB-SH may include: Broadcasting of radio and TV content. Broadcasting of audio or video content customized for mobile TV (eg. virtual TV channels, podcasts,). Data delivery (“push”), eg. for ring tones, logos. Video-on-demand services. Informative services (eg. news) including location-based services. Interactive services via an external communications channel eg. Universal Mobile Telecommunications System (UMTS).

DVB-SH transmission system:

Figure 5. Conceptual description of a DVB-SH system [11] (MPE: multiprotocol encapsulation – forward error correction, TPS: transmission parameters signaling)

Figure 5 shows the block diagram of a DVB-SH system. It consists of the following blocks: MPEG-4/WMV9 audio and video encoders DVB-H IP encapsulators. DVB-H modulators. DVB-H transmitter system. Gap fillers. SFN adapters GPS receiver system. The video is encoded using MPEG-4/ H.264 encoders which convert standard high definition TV to quarter common intermediate format (QCIF) or quarter video graphics array (QVGA) and provide an internet protocol (IP) output for further IP encapsulation. The next stage is IP encapsulation. The IP encapsulator carries out multiple functions like combining of various services, integrating the program and system information (PSI/SI) data streams, providing time-slicing control, and multiprotocol encapsulation (MPE). The radio frequency (RF) signals are then modulated to coded orthogonal frequency modulation (COFDM) signal by the modulator. The modulators can be used to set the output bandwidth to 5, 6, 7 or 8 MHz, giving flexibility in the transmission plan.

The modulated signal is up-converted by an exciter and transmitted by a high-power transmitter.

Orthogonal frequency division multiplexing: Orthogonal Frequency Division Multiplexing (OFDM) [8] is the natural choice for terrestrial modulation and is the basis of both the DVB-H and DVB-T systems. DVB-SH introduces a second scheme, a time division multiplex (TDM), leading to two reference architectures termed SH-A and SH-B: [8] • SH-A uses OFDM both on the satellite and the terrestrial link • SH-B uses TDM on the satellite link and OFDM for the terrestrial link. It is a spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” in this technique which prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion. This is useful because in a typical terrestrial broadcasting scenario there are multipath-channels (i.e. the transmitted signal arrives at the receiver using various paths of different length). Since multiple versions of the signal interfere with each other (inter symbol interference (ISI)) it becomes very hard to extract the original information. [13]

Figure 6. IP encapsulator and OFDM modulator in DVB-SH-A systems [14]

Time-slicing Time slicing is a very important aspect in DVB-H technology. The objective of time-slicing is to reduce the average power consumption of the terminal and enable smooth and seamless service handover. Time-slicing consists of sending data in bursts using significantly higher instantaneous bit rate compared to the bit rate required if the data were transmitted using traditional streaming mechanisms. [8] Time-slicing enables a receiver to stay active only a fraction of the time, while receiving bursts of a requested service. Note that the transmitter is constantly on (i.e. the transmission of the transport stream is not interrupted). Time-slicing also supports the possibility to use the receiver to monitor neighboring cells during the off-times (between bursts). By accomplishing the switching of the reception from one transport stream to another during an off period it is possible to accomplish a quasioptimum handover decision as well as seamless service handover.

DVB-SH receiver: Figure 7 shows the receiver block diagram of a DVB-SH receiver. It includes a DVB-H receiver (a DVB-T de-modulator, a time slicing module, and an optional MPE-FEC module) and a DVB-H terminal. The DVB-T demodulator recovers the MPEG-2 transport stream (TS) packets from the received DVB-T RF signal. It offers three transmission modes: 8K, 4K, and 2K with the corresponding signaling. The time-slicing module controls the receiver to decode the wanted service and shut off during the other service bits. It aims to reduce receiver power consumption while also enabling a smooth and seamless frequency handover. The MPE-FEC module, provided by DVB-H, offers in addition to the error correction in the physical layer transmission, a complementary FEC function that allows the receiver to cope with particularly difficult reception situations. The handheld terminal decodes/uses IP-services only. Note that 4K mode and the in-depth interleavers are not available, for compatibility reasons, in cases where the multiplex is shared between services intended for fixed DVB-T receivers and services for DVB-H devices. [11]

Figure 7. Conceptual description of a DVB-SH receiver [11]

Important parameters in DVB-SH systems:

Table 1. Physical layer parameter and data rates of DVB-SH system [14]

FFT size [18]: FFT sizes can be selected from 8K, 4K, 2K and 1K. A larger FFT size leads to higher tolerance to multipath propagation that is common in urban environments. However higher FFT sizes have lower carrier spacing and Doppler shifts which increase with the frequency and speed. 2K size is ideal for use in S-band. [14] Guard bands: They are used in time domain between two OFDM symbols. Higher guard bands reduce system capacity. In frequency domain, a higher guard interval results in higher subcarrier spacing. [14] Modulating scheme: The modulation scheme for individual subcarriers can be QPSK or 16QAM for DVB-SH system. [14]

Table 2 gives the OFDM symbol lengths in time domain with and without guard intervals. It is worth noting that with the longest guard interval and using 4K mode one can build single frequency networks (SFN) using up to about 33–35-km transmitter distances. The maximum distance is dictated by the transmission delay between the transmitter sites. This should be smaller than the guard interval length.

Table 2. Framing and typical data rates in an S-band DVB-SH-A system in 5 MHz spectrum slot [14]

Figure 8. Transmission mode influence in 16QAM 2/3 [11].

Testing DVB streams: DVB streams can be obtained from the website www.dvb-h.org In this project, a tool called „TS reader lite‟ version 2.8.46g [15] has been used to analyze the DVB test streams. TS reader is a transport stream analyzer, decoder, recorder and stream manipulator for MPEG-2 systems. It supports DVB, ATSC, ISDB, and Digicipher® II extensions to the base MPEG-2 specification. TS reader gives the user the big picture overview of what is being carried inside MPEG-2 transport streams and can be very useful for finding errors or inefficiencies. TS reader does not necessarily need hardware to operate and analyze DVB streams. It can run a virtual simulation by taking the transport stream file as an input. In this project, three test streams have been run in the TS reader tool.

PAT: PAT stands for Program Association Table. It lists all programs available in the transport stream. Each of the listed programs is identified by a 16-bit value called program_number. Each of the programs listed in PAT has an associated value of PID for its Program Map Table (PMT). The value 0x0000 of program_number is reserved to specify the packet ID (PID) where to look for Network Information Table (NIT). If such a program is not present in PAT the default PID value (0x0010) shall be used for NIT. TS Packets containing PAT information always have PID 0x0000. [16] PMT Program Map Tables (PMTs) contain information about programs. For each program, there is one PMT. While the MPEG-2 standard permits more than one PMT section to be transmitted on a single PID, most MPEG-2 "users" such as ATSC and SCTE require each PMT to be transmitted on a separate PID that is not used for any other packets. The PMTs provide information on each program present in the transport stream, including the program_number, and list the elementary streams that comprise the described MPEG-2 program. There are also locations for optional descriptors that describe the entire MPEG-2 program, as well as an optional descriptor for each elementary stream. Each elementary stream is labeled with a stream_type value. [16]

CAT: A conditional access table (CAT) holds information that is used by an access device (such as a set top box with a smart card) to decode programs that are part of a conditional access system (e.g. on-demand programs). If any of the programs have conditional access control, the CAT table transmitted on PID 01. The CAT table provides the packet identifier (PID) channel code that provides the entitlement management messages (EMM) to the descrambler assembly. This table is used for conditional access to the streams. This table provides association with EMM stream. When the TS is scrambled then this section contains the EMM PID. This EMM pid is encrypted using the smart card number. The PID value is 0x0001. [16]

NIT: Network information table (NIT) table provides information about the multiplexes and transport streams on a given network. Information about the current network uses table_id of 0x40, which about other networks uses table_id of 0x41. It is segmented into network information sections and is carried on PID 0x0010. [16]

SDT: The Service Description table (SDT) describes services which are part on an MPEG transport stream. There is one SDT per transport stream. The SDT may include name of the service, service identifier, service status, and whether or not the service is scrambled. The SDT uses the reserved PID 0x0011. [16]

EIT: The Event Information Table (EIT) provides schedule information about events on a service. This includes the event name, start time duration and the status of the event. [16]

Test stream 1 16QAMCR12FEC23

Figure 9. Test stream 1 [15]

Figure 10. Test stream 1 pie chart [15]

Test stream 2 16QAMCR12FEC34

Figure 11. Test stream 1 [15]

Figure 12. Test stream 2 pie chart [15]

Test Stream 3 16QAMCR12FEC56

Figure 13. Test stream 3 [15]

DVB-SH systems in the United States The United States currently follows the advanced television systems committee (ATSC) [17] standard for satellite and terrestrial transmission. The telecom operator AT&T has agreed to buy spectrum in the lower 700 MHz frequency band licensed by Qualcomm. [12] Alcatel Lucent has hosted successful trials of DVB-SH systems across the United States. [12] ICO Global Communications has successfully launched a satellite named ICO G1 specifically for mobile television. [12]

Figure 14. The ICO G1 system based on DVB-SH system [14] (ATC: ancillary terrestrial component)

Future systems using DVB-SH technology: Development of interactive TV applications. DVB-SH can be used in intelligent transport services to warn drivers of traffic congestion and alternate route planning. Statistical multiplexing can increase the number of broadcasted TV channels. Remote network monitoring.

List of acronyms: CAT: Conditional access table. CGC: Complementary ground components. DVB-SH: Digital video broadcast satellite to handheld. EIT: Event information table. FFT: Fast fourier transform. ISI: Inter-symbol interference. MPE: Multiprotocol encapsulation-forward error correction. MSS: Mobile satellite services. NIT: Network information table. OFDM: Orthogonal frequency division multiplexing. PAT: Program association table. PMT: Program map tables. QAM: Quadrature amplitude modulation. QCIF: Quarter common intermediate format. QPSK: Quadrature phase shift keying. QVGA: Quarter video graphics array. SDT: Service description table. SFN: Single frequency networks. TPS: Transmission parameters signaling. UMTS: Universal mobile telecommunications system.

References: [1] ETSI EN 301192: Digital Video Broadcasting (DVB); DVB specification for data broadcasting (DVB-DATA). [2] ETSI TS 102005: Digital Video Broadcasting (DVB); Specification for the use of video and audio coding in DVB services delivered directly over IP. [3] ETSI EN 300468: Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems (DVB-SI). References [1] [2] and [3] can be accessed from http://www.dvb-h.org [4] DVB BlueBook A079 Rev. 1: IP Datacast over DVB-H: PSI/SI. http://broadcasting.ru/pdf-standard-specifications/internet%20protocol/a079.pdf

[5] DVB BlueBook A111: Framing structure, channel coding and modulation for Satellite Services to Handheld devices (SH) below 3GHz. http://www.dvb.org/(RoxenUserID=9b5031601a81d830f6f38d9ed110cb03)/technology/standar ds/a111_DVB-SH_Specification.pdf

[6] DVB-Scene edition No. 21: A New Star in the Sky, by Prof. Dr-Ing. Ulrich Reimers. [7] P. Kelley, C. Rigal, “DVB-SH in S-band” References [6] and [7] can be accessed from http://www.ebu.ch/fr/technical/trev/trev_311-dvb_sh.pdf

[8] DVB-SH fact sheet 0409, April 2009 http://www.dvb-h.org/PDF/dvb-sh-fact-sheet.0409.pdf [9] ETSI EN 302304 V1.1.1. (2004-11): Digital Video Broadcast www.dvb-h.org [10]Block diagram for encoder and decoder of H.264 http://nuntius.com/technology3.html

[11] Proceedings of the IEEE, vol. 94, no. 1, pages 195 – 197, January 2006, G.Faria et al, “DVB-H: Digital broadcast services to handheld devices”.

[12] DVB news updates http://www.dvb.org/about_dvb/dvb_worldwide/usa/

[13] Orthogonal frequency division multiplexing http://www.wave-report.com/blog/?p=72 [14] Implementing mobile TV, second edition, 2010, Amitabh Kumar. [15] Testing tool TS reader lite http://www.tsreader.com/tsreader/index.html [16] Transport stream parameters http://en.wikipedia.org/wiki/MPEG_transport_stream [17] ATSC standards for mobile DTV http://www.atsc.org/cms/index.php/standards/published-standards/163-a153-atsc-mobile-dtvstandard-parts-1-8

[18] K.R. Rao, D.N. Kim and J.J. Hwang, “Fast fourier transform algorithms and applications”, Springer 2010. [19] Advanced video coding for generic audiovisual services http://www-ee.uta.edu/Dip/Courses/EE5359/H.264%20Standard2007.pdf