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)
TS bitrate
1 2 3 1 2 3 1 2 3 1 2 4
Time
Timesliced: •Service 1 •Service 2 •Service 3 Not timesliced: •Service 4 • MPE-FEC for performance • 4k mode was chosen to provide mobility in medium SFNs • Extended TPS bits for efficient signaling MPE = Multiprotocoll encapsulation 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.”
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 DVB-T Broadcasters DVB-H Broadcasters Mobile Operator UTMS Core Base station Mux DVB-H transmitter Broadcast operator
DVB-H features/pros
• 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
• 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.”
• • • • • • • • •
References
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
DVB
Cable & Satellite International
Sonera medialab
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 ,