Transcript Document

DVB-H
digital video broadcasting for
handheld devices
Björn Forss
Magnus Melin
Introduction
• Convergence of digital media and communication give users
possibility to consume most digital content also in mobile environment
• The emerging DVB-H standard aims to provide digital TV reception in
mobile devices
– Earlier known as DVB-X
• DVB-H is being standardized by and ad hoc group of the DVB
organization
– Expected to be standardized in the first quarter of 2004
• DVB-H combines traditional television broadcast standards with
elements specific to handheld devices; mobility, smaller screens and
antennas, indoor coverage and reliance on battery power
Motivation for creating DVB-H
• Why not use UMTS?
– Not scalable for mass content delivery
– For delivery of mass media content, broadcast networks should be
preferred over point-to-point cellular networks
• Why not use DVB-T?
– Was designed for rooftop reception
– Need for an efficient power saving mechanism
– Inadequate impulse noise protection
• Why not use DAB?
– Designed for devices with similar power constraints but too narrow
spectrum is assigned for data transmission
DAB = Digital Audio Broadcasting
DVB-T
• Terrestrial Digital Television Standard
– Used in 36 countries world wide
• One-to-many broadband wireless data
transport
– Video, audio, data and – importantly – IP packets
– Scalable: cell size up to 100km (DVB-H cell size is smaller)
– Huge capacity: 54 channels each 5-32Mbit/s
• Shut down of analog TV will free up huge
frequency capacity for DVB-T usage
DVB-T = Digital Video Broadcasting - Terrestrial
DVB-T (2)
• Developed for MPEG-2 stream distribution, but can
basically carry any data
– Flexible, has many modes, 4.98-31.67 Mbit/s @ C/N=25dB
• COFDM multicarrier modulation with 2k and 8k modes
– One DVB channel is ~8MHz
• 1705 sub carriers (spacing: 4464 Hz) - 2k mode
• 6817 sub carriers (spacing: 1116 Hz) - 8k mode
– Carrier modulation: QPSK, 16 QAM or 64 QAM
– Error correction: convolutional code and Salomon-Reed
• Basic mode in Finland:
– 64 QAM, code rate = 2/3, guard interval 1/8
– Gives 22.12 Mbits/s capacity when C/N=19.2 dB and 8 MHz channel
COFDM = Coded Orthogonal Frequency Division Multiplexing
C/N = Carrier to Noise ratio
Mobile reception of DVB-T
• DVB-T includes hierarchical modes where two
transport streams can be sent simultaneously
– Low capacity, high capacity
• DVB-T can also be used for broadcast to mobile
devices, but a suitable mode have to be selected
– 8k 64 QAM: < 50 km/h
– 2k QPSK: > 400 km/h tolerable
• A separate network for DVB-H is desired
– Optimization of speed, coverage and capacity
2k, 4k or 8k and why?
• A small number of sub-carrier provides (like in 2k):
– large inter-carrier spacing -> gives tolerance to the echoes affected
by Doppler
– short symbol duration ->limits the maximum delay of accepted
echoes
• A large number of sub-carriers (like in 8k):
– small inter-carrier spacing but a large symbol duration
• In short, the choice of the sub-carrier number has no
impact on the broadcast capacity but on the trade-of
between Doppler acceptance and maximum echo delays
DVB-H mission
• Make it “… possible to transmit in one
DVB transport stream both DVB-H and
DVB-T components in such a way that
existing DVB-T receivers which cannot
decode the DVB-H portion are not
disturbed by this DVB-H portion.”
DVB-H system elements
• Time slicing for power saving
– Time between the bursts gives the power saving (off time)
Bandwidth
TS bitrate
1 2 3 1 2 3 1 2 3 1 2
4
Timesliced:
Not timesliced:
•Service 1
•Service 4
•Service 2
•Service 3
Time
• MPE-FEC for performance
• 4k mode was chosen to provide mobility in medium SFNs
= Multiprotocoll encapsulation
• Extended TPS bits for efficient signaling MPE
FEC= Forward Error Correction
SFN= Single Frequency Network
IP Datacast (IPDC)
• “IP datacasting is a service where digital content
formats, software applications, programming
interfaces and multimedia services are combined
through IP (Internet Protocol) with digital
broadcasting.” <http://www.ipdc-forum.com/about/>
– All content delivered as IP packets
– Connectivity layer convergence
• DVB-H combined with IP datacasting enables
distribution of many kinds of digital content
– TV broadcast, music, games etc.
DVB-T and DVB-H coexistence
DVB-T RF in
DVB-T
ETS 300 744
8k, 2k, 4k, TPS
Time Slicing MPE FEC
DVB-H CODEC
IP-out
IPDC over DVB-H business
• New forms of multimedia enjoyment for
consumers
• New market opportunities for telecommunication
and broadcasting industries
• High bandwidth and high transmission speeds but
insensitive to number of recipients  attractive
from a business perspective
IPDC = IP Datacast
Network Design Flexibility &
Signaling
• Different datacast network operator and cellular network operator
• Digital broadcast infrastructure
• More transmission sites than normal broadcast networks required, but
less than normal cellular phone networks – existing masts can be
reused
• Cellular networks used for payment and administrative data
• Cellular network and broadcast network can share same core network
ISP
IP
Backbone
Mobile Operator
UTMS
Core
Base station
DVB-T
Broadcasters
DVB-H
Broadcasters
Mux
DVB-H
transmitter
Broadcast operator
DVB-H features/pros
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Cost efficient delivery of broadcast content to a large audience
Low time to market
Low complexity
Not heavily affected of peak usage (during special events etc.)
Flexible transport stream sharing between DVB-T and DVB-H possible
Based on DVB-T with minimal changes
Fulfils most commercial requirements
Allows seamless handover
No adverse effect on DVB-T
IP allows encryption
DVB-H features/cons
• Only IP based services possible
• Reduced power saving when total bit rate
for DVB-H services is very low (no big
“bursts” possible)
Mobile Terminal
• FE = Front End, contains radio receiver and
demultiplexor
FE
WLAN
Cellular
Link
CPU
Media
decoder
Display
Power consumption and handover
• IP encapsulation allows sending the data in
bursts to the mobile station and this saves
energy (battery power)
• Power consumption and handover
– 2 Mbit buffer
– Handover possible during off time (services can
be used even if the terminal has moved during
off time)
C/N Performance
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RS decoder utilizing the Time Slice buffer
Virtual time interleaver
10% TS PER tolerated
Doppler and CN improved in mobile and
portable
• Impulse interference tolerance improved
• Possibility to vary the level of robustness
Nokia’s 7700 with support for DVB-H
“The Nokia 7700 will support the Nokia Streamer SU-6 accessory, the
first mobile IP Datacast receiver designed to demonstrate the mobile
phone television experience using the DVB-H network. The Nokia
Streamer can be attached to the Nokia 7700 like a battery pack, and will
be used in pilot projects to showcase the future of digital broadcasting on
mobile devices.” <http://press.nokia.com/PR/200310/922406_5.html>
References
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DVB-H – digital TV for handhelds? Jukka Henriksson, Nokia
Content Distribution Using Wireless Broadcast and Multicast Communication
Networks. Janne Aaltonen, Thesis for Degree of Doctor, Tampere University of
Technology
IP Datacasting Technology - Bringing TV to the Mobile Phone, White Paper
<http://www.nokia.com/BaseProject/Sites/NOKIA_MAIN_18022/CDA/Categories/Abou
tNokia/Press/WhitePapers/_Content/_Static_Files/ipdatacastingtechnology.pdf>
DVB <http://www.dvb.org/index.php?id=20>
Cable & Satellite International <http://www.cable-satellite.com/main_news.htm>
Sonera medialab <http://www.medialab.sonera.fi/projects/ipdcmhp/ >
EE-Times Junko Yoshida, <http://www.eetimes.com/sys/news/OEG20030310S0049>
Performance analysis and low power VLSI implementation of DVB-T receiver
<http://www.signal.uu.se/Courses/Semabstracts/ofdm2.pdf>
DVB-T: New Operative Modes For Digital Terrestrial TV, Gerard Faria,
<http://www.broadcastpapers.com/tvtran/HarrisDVBTNewOpModes.doc>