Transcript DVB-H

MOBILE TV
-Narendranath Kanukolanu
Topics
 Introduction
 DVB-T
 DVB-H
 Issues and Solutions
 Conclusion
 References
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
DVB-T


DVB-T stands for Digital Video Broadcasting Terrestrial and it is the DVB European consortium
standard for the broadcast transmission of digital
terrestrial television.
This system transmits an MPEG-2 family digital
audio/video stream, using OFDM modulation with
concatenated channel coding
DVB-T
 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
 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 multi-carrier 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: convolution 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
World Standards
 DAB and E-DMB-in Europe and China
 DVB-H- USA/Europe and any where there is digital TV
spectrum
 HD Radio-USA
 Media FLO (Qualcomm)-USA
 T-DMB-Korea and Possibly Europe and China
 ISDB-T- Japan
Comparison Charts
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
MobileTV
What Is Mobile TV
Mobile TV = DVB-H


On-line video services

Mobile Broadcast
A Small digital TV, set top box receiver
Watch and record TV programs, interact with programs and other
viewers
Other Rich Media experiences
On-line video services

Access on-line services to rent or buy TV shows, videos, and movies;
download them to mobile device
Video to-go
Video to-go


Store videos to mobile format and manage them with Nokia PC
Suite
Transfer and syncronize recorded, downloaded or ripped videos
from PC/Mac or home media devices
DVB-H 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
 Standardized in the first quarter of 2004
DVB-H
 The DVB-H system is largely compatible to the DVB-T
standard, which means that the modulator and RF circuits
can be reused with only slight additions. It is possible to
have both DVB-T services and DVB-H services broadcast
by a single transmitter
Contd..
 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 are the challenges
 Re-uses basically the well-known DVB-T transmission
parameters
 Inheriting the DVB-T flexibility & performance,
 Offering additional delivery methods to extend the
traditional tradeoff bit rate capacity & ruggedness & cell
size to a new dimension: the “nomad city”.
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
Timesliced:
Not timesliced:
•Service 1
•Service 4
•Service 2
•Service 3
4
Time
 MPE-FEC for performance
 4k mode was chosen to provide mobility inMPEmedium
SFNs
= Multiprotocoll encapsulation
FEC= Forward Error Correction
 Extended TPS bits for efficient signaling SFN= Single Frequency Network
Drivers for Mobile TV




TV application missing from Mobile Phone
TV is bigger application than telephone globally
Daily amount of time spent on multimedia is more
Digital convergence happening in Mobile Handsets
Mobile reception of DVB-T
 DVB-T includes hierarchical modes where two transport
streams can be sent simultaneously
 Low capacity, high capacity
 A separate network for DVB-H is desired
 Optimization of speed, coverage and capacity
What the Consumer expect?
.
Good picture
and sound
quality
Service
availability
Value for
money
Single Device
to carry
(phone)
Simplicity of
use
Right selection
of channels
Multimedia
Device
DVB-H System overview
.
OPTIONAL:
DVB-T
SERVICES
DVB-H
SERVICES
ERROR
PROTECTION
(MPE-FEC)
IP
ENCAPSULATION
TIME
SLICING
TRANSPORT STREAM MULTIPLEXER
DVB-T CODER/MODULATOR
4k-MODE
SIGNALLING
When will it be used?
System Architecture
For Collaboration Between Mobile and
Broadcast Operators
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
 Cost efficient delivery of broadcast content to a large
audience
 Low time to market and complexity
 Flexible transport stream sharing between DVB-T and
DVB-H possible
 Based on DVB-T with minimal changes
 Only IP based services possible
 Reduced power saving when total bit rate for DVB-H
services is very low (no big “bursts” possible)
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
IP Datacast (IPDC)
 “IP data casting is a service where digital content formats,
software applications, programming interfaces and
multimedia services are combined through IP (Internet
Protocol) with digital broadcasting.” All content delivered as
IP packets
 Connectivity layer convergence
 DVB-H combined with IP data casting enables distribution
of many kinds of digital content
 TV broadcast, music, games etc.
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)
Mobile Terminal
 FE = Front End, contains radio receiver and demultiplexer
FE
WLAN
Cellular
Link
CPU
Media
decoder
Display
ISSUES
 Battery Power
 Loss Free Handover for IP Data Cast
 Continuous Transmission
ISSUE1:Battery Power
 TIME SLICING is the mechanism DVB-H uses to transmit data in
periodic bursts with significant and higher instantaneous bit rates
 Using TDM significant power savings can be achieved
 TDM (Time Division Multiplexing) is the technology used in Time
Slicing.
 TDM combines data streams by assigning each stream a different time
slice in a set .
 TDM repeatedly transmits a fixed sequence of time slices over a single
transmission channel.
TIME SLICING TECHNIQUE
S
E
R
VI
C
E
SERVICE 1
SERVICE 2
SERVICE 3
DVB-H
SERVICE 4
DVB-T
REGULAR DVB-T MULTIPLEX
S
E
R
VI
C
E
1
1
SERVICE 4 TV
DVB-H Time Slices
“always on-not used data is skipped”
SLEEP
MODE
Contd…
 Time slicing enables a receiver to stay active only a fraction
of time while receiving bursts of a requested service saving
battery power.
 When the receiver is tuned to receive one of the programs it
has to receive the other unwanted programs at the same time
consuming a lot of battery.
 The High bit rate signals are buffered in the time slicing
memory of the DVB-H capable receiver.
Contd…
 The DVB-H receiver will receive its intended high bit rate
service in one time slice and make the front end sleep during
the other slices,
 The High end Bit rate service received will be buffered in
the receiver memory and played out continuously to provide
the desired QoS.
Time Slicing
Contd…
1536kbps_DVBH
Content
Provider
1536kbps_DVBH
DVB-H TOWER
1536kbps_DVBH
1536kbps_DVBH
Ethernet
Switch
ISSUE2:Continuous Transmission
 A DVB-H receiver is expected to usually be a single antenna
terminal.
 As the DVB-H cell becomes smaller up to several
kilometers radius, handover between different cells will
happen.
 When the receiver works in time slicing mode, it can
measure the signal SNR value In the off burst time and
eventually perform soft handover.
 Thus the time slicing mode makes seamless soft handover
possible for single antenna DVB-H reception.
Calculation
 If a service has an average bite rate of ravg is transmitted in
bursts with the bit rate rburst and the time between two bursts
of the same service (cycle time) is called t, the burst
duration tburst that may be calculated from the other values
using…
tburst = ravg/ rburst *
t
Contd..
 As the off time toff is the difference between the cycle time
and the burst time,

toff 1- ravg/ rburst *
=
t
TIME SLICING TECHNIQUE
 Continuous Transmission
C
a
p
a
c
it
y
SERVICE 1
SERVICE 2
SERVICE 3
SERVICE 4
Time
Continuous Transmission
.
384kbps_DVBH
Content
Provider
384kbps_DVBH
DVB-H TOWER
384kbps_DVBH
384kbps_DVBH
Ethernet
Switch
Contd…
 Each receiver will receive an effective bit
rate of 384 Kbps and the the other 1152
Kbps of unwanted traffic. Thus each receiver
will receive 1536 Kbps in total of which
three quarters is unwanted traffic.
ISSUE3:Loss Free Handover for
IP Data Cast
 Mobility is the most important feature of handheld devices
and uninterrupted service has to be provided when there is
movement.
 A technology called “Phase shifting” is proposed for
Loss free handover.
Contd…
 The main challenge in today's field of communication is to
offer high data rates while having a error-prone
communication channel and only a small battery power
budget Additionally, seamless mobility is a strong demand.
 An Algorithm for synchronizing adjacent cells in order to
ensure seamless handovers is proposed.
 Time slicing is also important for handover.
Handover in Broadcast Systems
 The Technique used is PHASE SHIFTING.
 Different from cellular Telecommunication systems as no
return channel exists.
 Emphasis on how the signals of neighboring DVB-H cells
may be synchronized and under which conditions seamless
handover themselves may actually be one.
Contd..
 The network's infrastructure has no feedback about who is
using the services and possibly moving from one cell to
another. All the information for performing handovers has to
be deployed to the terminals which will perform the
handovers on their own.
 The term cell in this context is used for a subsystem that
may consist of one or more several transmitters sending
entirely identical content on the same frequency.
 A Cell Handover in this context is the change of frequency
and data stream in order to receive the same service
continued within another cell.
Example Scenario
Phase Shifting Algorithm
 When a terminal changes from one DVB-H cell to another,
ideally it should be able to seamlessly continue receiving the
current service in the new cell without any packet loss,
assuming that the service is available in both cells.
 The Phase shifting should be big enough so that there is no
overlapping between the time slices of the adjacent cell and
the necessary synchronization time for the terminal to
change from one signal to another.
Algorithm
IP PACKET
.
IP FEEDING
STREAM TO
CELL 1
4 5
6
SIGNAL OF
CELL 1
IP FEEDING
STREAM TO
CELL 2
SIGNAL OF
CELL 2
7
8
6
7
8
1 1
1 2
DVB-H TIME
SLICE
123456
4 5
1
0
9
9
123
1
6
1
0
111
789
012
1 1
1 2
456789
PHASE SHIFT
1 1 1
3 4 5
1 1 1
3 4 5
1
6
Contd..
 There is an overlapping of IP packets between two
consecutive time slices of two different cells. This ensures,
even with significant tolerance towards IP feeding stream
delays, seamless loss-free handovers.
 More than two cells have common borders, so more than
two different phase shifts are needed.
4 -Coloring Graph Problem
 The various phase shifts that are necessary for n adjacent
cells can be interpreted mathematically as colors in a graph
coloring problem, never allowing twice the same color in
adjacent nodes.
 With four different phase shifts loss-free handover between
any two cells will be possible, no matter how the shape of
the cells might be. (Ideally Hexagonal)
Quantitative Analysis
tburst = ravg/ rburst *
toff 1- ravg/ rburst *
=
 From Equation 1 and 2
t
(1)
t
(2)
Contd..
 To simplify the equation the sum of tsync and tsafety is defined
as being tsetup
Contd..
 From Eq 1,2,4
Contd..
 The result is that the ratio between the average data rate of a
service and the whole data rate that can be used for a service
supporting soft handover must be smaller than 25%reduced
by the ratio of the setup time and t.
 At is also dependent of ravg as the memory of the terminal
mbuf is limited.
 For the consumption of a service, only half of the terminal
buffer size mbuf can be used, as the other half is needed to
monitor the same service of an adjacent cell, at least in
handover status.
Contd..
Conclusion
 Traditional broadcasting is undergoing a process of change
as a consequence of the move towards an all-digital
broadcasting environment. New technology, such as DVBH, streaming technology and personal video recorders
(PVRs) can complement traditional broadcasting.
References



Loss-free handover for IP datacast over DVB-H networks
May, G.; Consumer Electronics, 2005. (ISCE 2005). Proceedings of
the Ninth International Symposium on 14-16 June 2005
Performance analysis of time slicing in DVB-H
Yang, X.D.; Song, Y.H.; Owens, T.J.; Cosmas, J.; Itagaki, T.; Mobile
Future, 2004 and the Symposium on Trends in Communications.
Sympo TIC '04. Joint IST Workshop on 24-26 Oct. 2004
Digital Video Broadcast - Handheld (DVB-H)-A Mobile Last-Mile
Tactical Broadcast Solution
Bennett, B.; Hemmings, P.; Holt, C.; Military Communications
Conference, 2005. MILCOM 2005. IEEE 17-20 Oct. 2005
 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
 DVB <http://www.dvb.org/index.php?id=20>