ATSC MH Mobile Broadcast for Portable Services

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ATSC M/HMobile Broadcast for Portable Services
April 12 2008

• Thomson/Micronas Joint Technology Proposal

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ATSC M/H Needs and System OverviewRich Citta
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Broadcaster Requirements

• True Mobile service
• Handheld device service
• Backward compatible
• Top 5 broadcasters in market
• Program Full HDTV (14 mbits/s )
• New services ( 5 mbits/s
  )
• Bottom 5 broadcasters in market
• Program SDTV ( 3 mbits/s )
• New services (16 mbits/s )

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Flexibility with Efficiency

• Allows for Wide Range of Operating Points
• Light mobile channels
• Low rate single channel video
• Data services
• Heavy mobile channels
• Multi-channel mobile video services
• High resolution mobile video services
• Dynamically changing mobile channels
• Varying mixes according to changing programming
  block
• Maximum Efficiency of Spectrum Used
• Allows for a wide variety of business models

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Receiver Market
Cell-phone
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Car TV
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Smart-phone
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Lap Top
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ATSC HDTV
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Receiver Markets

• Cell-phones QVGA
• Car TV QVGA-VGA
• Smart-phones VGA
• Lap Tops SDTV
• All ATSC receivers HDTV
• Multi resolution system needed

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Receiver Environment
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Receiver Environment
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Receiver Environment
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Receiver Environment
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Receiver Environment
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Rayleigh Fading Channel
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Worse cast Cellphone

• Cellphone Antenna 10-15dB lost
• Height 1.5m 5-10dB lost
• In car speed 3-5dB lost
• In building 5-30dB lost
• Pedestrian waking into deep null
• 
  10-40dB lost

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Lower Data Rates Needed

• R 1/2 Th. 15dB ? 7.5 dB
• R 1/3 Th. ? 5.0 dB
• R 1/4 Th. ? 3.5 dB
• R 1/6 Th ? 2.0 dB
• More improvement needed for worst
• case environment

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Diversity

• Receiver Diversity
• For cars
• For laptop computers
• Time Diversity
• For Handheld Receivers
• Transmitter Spatial Diversity S F N
• Transmitter Frequency Diversity
• Maximum over lapping coverage M F N
• Transmitter Frequency Spatial Diversity
• For shadowing due to hills

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Transmitter Spatial Diversity
S F N
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Burst Mode Transmission

• Allows for power efficient receivers
• Power off receiver while waiting for data of
  interest
• Multiple service tiers/power requirements in the
  same multiplex
• Seamless MFN operation
• Maximizes coverage throughout operating area
• Supports current and future SFN and MFN operation

Mobile Bursts
Time
Receiver Off
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Time Coded Diversity
Block Coding Provides Maximum
Diversity Capability
R 1/2

• Robust time-diverse
• output
• Each Burst
• independently
• decodable for
• deep fades
• together they provide
• maximum threshold
• performance

Data
Physical Layer Combiner
Burst coder
Delay Buffer 8-10 Seconds!!
Redundancy
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Coded Cooperative Transmitter Diversity
M F N
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A Total Diversity Solution
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Receiver / Transmitter Diversity
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Channel 51 Sear Tower
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Channel 52 Sear Tower
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Channel 53 Hancock Tower
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Coded Cooperative Transmitter Diversity

• 2nd Channel Frequency Diversity
• 2 Independently Fading Signals
• Mitigates Deep Nulls Fades
• Improve Quality of Service or
• Boost Data Rate by more than 2

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Design Objectives for Mobile System

• Spectrum is a limited asset
• with increasing value
• Efficiency throughout the system
• Flexibility
• Broadcasters have diverse requirements and
  business models will vary considerably
• Diversity
• Time 8 sec. To address pedestrian modes
• Frequency For overlapping coverage

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Upper Layer InnovationsSVC and
StaggerCastingDavid Campana
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Management Layer Layers (S4-2)
ATSC M/H Layers
Presentation Layer - Media Formats (S4-3)
Physical Layer Layers (S4-1)
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Robustness in the Upper Layer

• Technologies to improve the robustness (coverage
  and user experience) that are independent of the
  physical layer
• S4-3 Presentation Layer
• Scalable Video Coding
• S4-2 Management Layer
• StaggerCasting

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Scalable Video Coding Motivation
QVGA15 Hz
SD 30 Hz
SVC Encoder
HD 60 Hz Widescreen
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Scalable Video Coding (SVC)

• Scalable Video Coding Extensions to H.264 AVC
• Adds an enhancement layer to the base H.264 AVC
  stream
• Backward compatible with H.264 AVC
• SVC base layer is playable by legacy H.264 player
• Three types of scalability
• Spatial (resolution) most applicable to ATSC
  M/H
• Temporal (time)
• Fidelity (SNR)

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SVC Encoder structure
CIF AVCLayer
CIF source
SDSourceVideo
Spatial Scaling
AVCEncoding
Packetizer
Inter-layer prediction
Bitstream
SD SVClayer
AVC-LikeEncoding
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Extended Spatial Scalability
Base Layer
Enhancement Layer

• This example shows the use of SVC for
• Upscaling to higher resolution
• Cropping (narrow to widescreen adaptation)

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Additional Use Cases

• SVC elegantly supports several interesting use
  cases which are difficult or impractical using
  traditional video compression

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Fast Channel Change

• Encoder selects different GOP length for the base
  and enhancement layers
• Short GOP in base layer for fast channel change
• Long GOP in enhancement layer for bit rate
  efficiency

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SVC Value Proposition to ATSC M/H

• Standard Evolution
• Standard can evolve to higher resolution and
  quality without obsoleting current generation AVC
  only devices.
• Graceful Degradation of Video Quality
• If enhancement layer is lost, SVC decoder can
  decode base layer and upsample to conceal loss.
• Efficient Simulcast
• SVC is 10-30 more efficient than H.264 AVC
  simulcast at the exact same resolutions and
  encoder video quality settings.

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StaggerCast - Motivation

• Mobile channels require significant time
  diversity for good performance
• Other methods of adding time diversity
  (interleaving, long block codes) add unacceptable
  delay to channel change for the user.

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StaggerCast

• Redundant stream sent in advance of the original
  stream
• Adds significant time diversity (seconds)
• Introduces no channel change delay
• Operates at application level (ie. RTP in ATSC
  M/H)

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StaggerCast - Illustration
Lost packets
c
d
e
f
i
j
k
l
Stagger
c C
A
B
C
D
G
H
I
J
Base
time
A
B
C
D
G
H
I
J
e
f
Recovered
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StaggerCast Block Diagram
Terminal
Broadcast
Stagger original
Delay
output (RTP stream)
Source (RTP stream)
Stream Combiner
Delay
Base Delayed original
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StaggerCast Channel Change

• StaggerCast does not add to channel change delay.
• On channel change
• The receiver plays back base stream immediately
• The receiver buffers the stagger stream.
• After stagger buffer is filled
• The receiver can use the stagger stream to
  protect against loss.

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Channel Change Illustration
Channel change
c
d
e
f
r
s
t
u
v
w
Stagger
Base
A
B
C
D
P
Q
R
S
T
U
time
Stagger stream protects from this point forward
Terminal immediately plays new channel. Playback
is not yet protected by stagger stream.
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StaggerCast Summary

• Adds time diversity at application level
• Doesnt impact channel change
• Optional tool for both receiver and broadcaster

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StaggerCast with SVC

• StaggerCast and SVC benefit from each other
• SVC improvement over AVC is more dramatic when
  base layer is protected more strongly
• Minimized StaggerCast overhead by protecting only
  the critical elements of the stream
• SVC base layer only
• Audio

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SVC and StaggerCast Demo

• Video
• 384x224 (widescreen)
• 24 fps
• IDR every 24 frames
• Channel
• ATSC M/H approximation
• 1 second burst losses
• 10 packet loss

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SVC and StaggerCast Demo - Video
AVC
SVC and StaggerCast
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PHY ArchitectureWen Gao
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Outline of Thomson/Micronas PHY Layer

• Overview of PHY proposal
• Important Features of PHY proposal
• No modification of the ATSC transmitter since all
  encoding is done at the transport level
• Serial concatenated block code (SCBC)
• Flexible training data without trellis reset
• Low latency symbols
• Burst transmission
• Transmitter diversity

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ATSC MH Transmitter Proposal
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Legacy ATSC Encoding RS code

• Defined on a Galois Field GF(256)
• (K187, N207)
• Non-binary Linear systematic block code
• Adding two code words produces a code word
• Multiplying a code word by a field element
  produces a code word

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ATSC MH Encoding SCBC code

• New non-binary linear Systematic block code
• Serial concatenation of simple byte codes with
  byte interleaver
• Byte Codes defined on same Galois Field as RS
  code
• Achieve excellent performance with short block
  length
• 26 bytes, 52 bytes
• All encoding done at Transport level. Hence no
  modification of the transmitter
• Ensure fully backward compatible

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Rate 1/2 Byte Code

• (N2, K1) byte code (GF(256) code)
• The information byte is m
• Generator matrix is G (1, 2)
• The codeword is C mG
• Note that all the operations are done in GF(256)
  field
• Example
• m(12), C (12) (1, 2) (12,24)
• m(154), C (154)(1,2) (154, 41)

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Rate 2/3 Byte code

• (N3, K2) byte code (GF(256) code)
• The Generator matrix is
• Example

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Byte Code Design Optimization

• Use 4 PAM as an example
• Un-equal noise protection of bit Z1 and Z2
• Byte codes are optimized
• One bit will appear in both noise-prone bit
  position and reliable bit position in general

• Use 4 PAM as an example
• Un-equal noise protection of bit Z1 and Z2
• Byte codes are optimized
• One bit will appear in both noise-prone bit
  position and reliable bit position in general
• Overall bit error rate is reduced

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Rate 12/26 SCBC Code

• Serial Concatenation of two 2/3 byte codes and
  byte interleaver

• Encoding is done across packets

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Rate 12/52 SCBC Code

• Serial Concatenation of ½ byte code and 12/26
  SCBC code with byte inter-leaver

2nd 26 Bytes
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Concatenation of RS and SCBC code

• Due to the concatenation, the parity bytes are
  also SCBC encoded
• For MH data, the legacy RS code will still be
  useful, rather than simply for backward
  compatibility

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ATSC MH Receiver

• Soft symbols from Trellis decoder are fed back to
  equalizer
• Iterative decoding process

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The 12/26 Rate AWGN Threshold 7.0 dB at 9-th
iteration
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The 12/52 Rate AWGN Threshold 3.5 dB at 13th
iteration
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Summary of SCBC code

• Variety of code rates for trade-off between
  robustness and data rate
• 12/26,12/52,17/26,24/208, etc
• Ensure backward compatibility with no
  modifications of the transmitters
• SCBC codes achieve significant coding gain
• TOV threshold CNR 14.9 dB ? 3.5 dB

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Code Cooperative Diversity

• SCBC code allows code cooperative diversity
• Example 12/52 SCBC encoding forms two streams
• Stream A and B are decodable separately (7 dB CNR
  threshold)
• Joint decoding of stream A and B can achieve
  lower CNR threshold (3.5dB)
• Variety of diversity can be formed using stream A
  and B
• Sent with relative delay ? code and time
  diversity
• Sent from two transmitters using different
  channels ? code and freq diversity

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System Synchronization in MFN

• Approach
• Broadcast stations are synchronized (e.g. using
  GPS)
• Burst time slots are coordinated
• Value
• Enables soft handoff with network affiliates
  broadcasting same program
• Enables a mobile receiver to obtain program
  guide from all local mobile stations without
  interrupting the current mobile program

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Backup Slides
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12/26 SCBC Code decoder Iterative decoder
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12/52 SCBC Code decoder Iterative decoder
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ATSC MH data frame
Note 1 block contains 26 TS packets
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Convolutional Byte Inter leaver

• After convolution interleaver, 52 TS packets
  appear as following

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Convolutional Byte Inter leaver
Byte 0
Byte 104
Byte 156
52 53
Byte
Byte 26
Byte 206
Byte 51
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Convolutional Interleaver byte locations with a
contiguous codeword
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Convolutional Byte Inter leaver

• For 12/26 or 12/52 SCBC code, gray regions
  contains complete 12/26 SCBC coded codeword

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ATSC Trellis coded Modulation (TCM)