Mobile DTV Standards

DTV standards, first developed in 80's and 90's, have yet to meet the requirements set for servicing mobile and hand-held devices. These requirements include:

• Mobility: MDTV standards need to provide quality reception when the end point is moving at high speeds (e.g., 350Km/hour in fast trains). Here, the Doppler effect becomes significant, resulting in degradation of the SNR at the end point and must be well compensated by the transmitter and the receiver. Hand-off between two adjacent transmitters has to be done smoothly, without causing end-user interference.
• Small size antennae: Antenna(e) has to fit into the small form factor of a mobile phone or similar device, without degrading the received quality.
• Low power consumption
• Additional requirements
  
  • Built-in support for "datacasting" - delivery of different types of data (e.g., software applications, games, etc.) to different users
  • Built-in support for conditional access based on the device's ID

Several standards/technologies have been developed to meet mobile requirements:

• The Chinese homegrown, China Multimedia Mobile Broadcasting – CMMB. Siano is active member of the CMMB Workgroup.
  http://www.cbc.cn/
• The European-based standards, Digital Video Broadcasting Terrestrial (DVB-T) and Handheld (DVB-H). Siano is an active member of the DVB standardization activity, managed by the DVB organization.
  www.dvb.org
• The Japanese standard, Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) and its Brazilian flavor, Sistema Brasileiro de Televisão Digital-Terrestre (SBTVD).
  www.dibeg.org
• Digital Audio Broadcasting (DAB) and its Korean-based flavor, Terrestrial Digital Multimedia Broadcasting (T-DMB). Siano is an active member of the DMB organization, World DMB.
  www.worlddab.org
• The USA, Mobile Advanced Television Systems Committee (ATSC) and its mobile flavor – ATSC Mobile/Handheld (ATSC-M/H). Siano is an active member of ATSC.
  www.atsc.org.

CMMB

China Multimedia Mobile Broadcasting (CMMB) is an MDTV standard, developed and specified in China by the State Administration of Radio, Film, and Television (SARFT). A trial network was deployed in 37 major cities in China prior to the 2008 Olympic Games. As of 2010, the CMMB network covers over 330 cities. The CMMB network is planned to cover populated areas with broadcast transmission in the UHF band, while rural areas are planned to be covered with satellite and terrestrial 'gap-fillers' transmission using the S-Band.

The CMMB standard was designed to meet the requirements of mobile devices, including the requirement for low-power consumption, mobility at high velocities, exceptional sensitivity, etc.

CMMB - Key Features: 

• Proprietary bit stream format
• H.264 content
• Compatible with 2 and 8 MHz bandwidth system
• Time-slot mechanism for low power consumption
• Two levels of FEC (Forward Error Correction) for high level of robustness and mobility

DVB-T and DVB-H

When DVB-T was first published in 1997, it wasn't designed to target mobile receivers. Following a trial run, DVB-T mobile services have been launched in the EU and South East Asia. With the advent of diversity antenna receivers, services which target fixed reception can now largely be received on the move as well. Although this standard is not optimized for battery operated devices and for reception in extreme conditions (e.g., fast moving trains) by utilizing algorithms and other adaptations, as well the availability of lower power consuming receiver chips, DVB-T has become a mobile and portable technology in the recent years.

Taking the DVB-T concept a few steps further, the Digital Video Broadcasting for Handheld devices (DVB-H) was developed, optimized for digital TV reception on battery based handheld devices, which may move at high velocities.

DVB-H (DVB-T) Additions

• Battery saver - utilizing time-slicing schemes
• MPE - Multi Protocol Encapsulation
• Forward Error Correction (FEC) at the MPE level, for additional robustness and mobility
• 4k OFDM FFT mode for mobility and network design flexibility
• Additional minor changes, e.g., in signaling
• DVB-H is meant for IP-based services via MPE insertion; can share DVB-T multiplex with MPEG2 services

ISDB-T

Integrated Service Digital Broadcasting – Terrestrial (ISDB-T) is an advanced version of the ISDB and was first adopted for commercial transmissions in Japan in 2003.

The ISDB-T was developed to provide flexibility, expandability, and commonality for multimedia broadcasting services using terrestrial networks. ISDB-T system adopted the Band Segmented Transmission - Orthogonal Frequency Division Multiplexing (BST-OFDM), which consists of a set of 13 frequency blocks called OFDM segments. ISDB-T is suitable of receiving simultaneously several types of services like HDTV, SDTV and Mobile applications.

ISDB-T Key Features

• Provides a variety of video, sound, and data services
• Sufficiently resistant to any multipath and fading interference encountered during portable or mobile reception
• Flexible and efficient use of modulation scheme and required bit rate
• Hierarchical transmission: OFDM carrier parameters and channel coding can be independently configured for each stream (up to three streams)
• Partial Reception: ability to receive only one segment of the transmitted signal, using a narrow-band receiver

ISDB-T Related Standards

• 1-Seg - Mobile terrestrial digital audio/video and data broadcasting service which includes several characters: using a central segment among 13 segments, low coding rate, long guard interval and restrictive image and sound quality.
• Full-Seg - Specifies the reception of all 13 allocated segments,1seg uses only single segment, and the remainder can be allocated as (1) one 12-segment HDTV program, (2) three 4-segment SDTV (Standard-definition TV) programs, or (3) one 8-segment (Medium Definition) program and one 4-segment SDTV program; combination of these services (1), (2) or (3) can be changed at any time.
• SBTVD / ISDB-TB Brazil
  In 2006, the Brazilian government announced the adoption of certain changes in the Japanese standard: the Brazilian standard compression format MPEG-4 H.264 High profile is used for high definition broadcasts, along with ISDB-Tb UHF range expansion of 474-803 MHz. In 2009, the International Telecommunications Union (ITU) recognized in BDTVS – as international standard. It was adopted initially in Brazil and continued in most Latin American countries.
• ISDB-Tsb: The terrestrial digital sound broadcasting specification. The technical specification is the same as ISDB-T with VHF band usage, 1/3 segments and target for Japan.
• ISDB-Tmm: Terrestrial mobile multi-media will serve for dedicating content such as sports, movies, music channes and other with CD quality sound; targetted for mid-2012 in Japan.

ATSC

ATSC is the DTV standard used in North American. First introduced in 1995, it is optimized for fixed DTV content reception in the typical North American environment using stationary TVs and STBs. It can deliver content at either Standard Definition (SD) or High Definition (HD).

ATSC transmission is not robust enough to adequately sustain Doppler shift and fading channels in mobile environments. To overcome this problem, additional channel coding mechanisms were introduced in ATSC-M/H to protect the signal.

In 2009 ATSC-M/H was approved as official standard (A/153), similar to how DVB-H is the mobile extension to the DVB-T terrestrial digital TV standard.

ATSC M/H introduces new challenges that need to be addressed to ensure successful transmission and reception, including: 

• Bursts of data
• Encoding and multiplexing
• Transport stream
• Power saving