ATSC M/HMobile Broadcast for Portable Services
Thomson/Micronas Joint Technology Proposal
April 12 2008April 12 2008
ATSC M/H Needs and System Overview
Rich Citta
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 )
Flexibility with Efficiency
Allows for Wide Range of Operating Points– Light mobile channels
Low rate single channel videoData services
– Heavy mobile channelsMulti-channel mobile video servicesHigh resolution mobile video services
– Dynamically changing mobile channelsVarying mixes according to changing programming block
Maximum Efficiency of Spectrum UsedAllows for a wide variety of business models
Receiver Market
Cell-phone
Car TV
Smart-phone
Lap Top
ATSC HDTV
Receiver Markets
Cell-phones QVGA Car – TV QVGA-VGA Smart-phones VGA Lap Tops SDTV All ATSC receivers HDTV
Multi resolution system needed
Receiver Environment
Receiver Environment
Receiver Environment
Receiver Environment
Receiver Environment
Rayleigh Fading Channel
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
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
Diversity
Receiver Diversity For cars For laptop computers Time Diversity For Handheld ReceiversTransmitter Spatial Diversity S F N
Transmitter Frequency Diversity Maximum over lapping coverage M F N
Transmitter Frequency & Spatial Diversity For shadowing due to hills
Transmitter Spatial Diversity
S F N
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
Time
Mobile Bursts
Receiver Off
Time Coded Diversity
Physical Layer Combiner
Delay Buffer
8-10 Seconds!!
R = 1/2Robust time-diverse output
Each Burst independently decodable for deep fades
together they provide maximum threshold performance
Redundancy
Burst coder
Data
Block Coding Provides Maximum Diversity Capability
BurstEncoder
R=1/2DELAY10 sec.
Tx A
Tx B
BurstEncoder
R=1/2
DELAY10 sec.
Station A
Station B
Provides Maximum Diversity CapabilityCoded Cooperative Transmitter Diversity
M F N
A Total Diversity Solution
Receiver 1
Tx A
Tx B
Time Frequency Space
Receiver 2
Receiver / Transmitter Diversity
Channel 51 Sear Tower
Channel 52 Sear Tower
Channel 53 Hancock Tower
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
Design Objectives for Mobile System
Spectrum is a limited asset with increasing valueEfficiency throughout the system
Flexibility– Broadcasters have diverse requirements and
business models will vary considerablyDiversity
– Time > 8 sec. To address pedestrian modes– Frequency For overlapping coverage
Upper Layer Innovations:SVC and StaggerCasting
David Campana
Management Layer –Layers (S4-2)
Physical Layer –Layers (S4-1)
Presentation Layer - Media Formats (S4-3)
Legacy Transport
RF
FEC
ATSC M/H Layers
Transport-M
Streaming Delivery File Delivery
Application FrameworkCAS DRM
Signaling Announcement
Video Codec(s) &Parameters
Audio Codec(s) &Parameters
Captioning
Image Formats
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
Scalable Video Coding – Motivation
QVGA15 Hz
SD 30 Hz
HD 60 HzWidescreen
SVCEncoder
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)
SVC – Encoder structure
SDSourceVideo
Spatial Scaling
AVCEncoding
AVC-LikeEncoding
Packetizer
Inter-layer prediction
Bitstream
CIF AVCLayer
SD SVClayer
CIF source
Extended Spatial Scalability
This example shows the use of SVC for
•Upscaling to higher resolution
•Cropping (narrow to widescreen adaptation)
Base Layer
Enhancement Layer
Additional Use Cases
SVC elegantly supports several interesting use cases which are difficult or impractical using traditional video compression
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
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.
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.
StaggerCast
Redundant stream sent in advance of the original stream
Adds significant time diversity (seconds) Introduces no channel change delayOperates at application level (ie. RTP in ATSC
M/H)
StaggerCast - Illustration
c d e f i j k l
A B C D G H I J
Lost packets
“c” = “C”
time
A B C D G H I Je f
Stagger
Base
Recovered
output(RTP stream)
Source(RTP stream)
TerminalBroadcast
Stagger = original
StaggerCast –Block Diagram
Delay
Stream Combiner
Delay
Base = Delayed original
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.
Channel Change Illustration
c d e f r s t u v w
A B C D P Q R S T U
Stagger stream protects from this point forward
Channel change
Terminal immediately plays new channel. Playback is not yet protected by stagger stream.
time
Base
Stagger
StaggerCast Summary
Adds time diversity at application levelDoesn’t impact channel changeOptional tool for both receiver and broadcaster
StaggerCast with SVC
StaggerCast and SVC benefit from each otherSVC improvement over AVC is more dramatic
when base layer is protected more stronglyMinimized StaggerCast overhead by protecting
only the critical elements of the stream– SVC base layer only
– Audio
SVC and StaggerCast Demo
Video:– 384x224 (widescreen)
– 24 fps
– IDR every 24 framesChannel:
– ATSC M/H approximation
– 1 second burst losses
– 10% packet loss
SVC and StaggerCast Demo - Video
AVC
SVC and StaggerCast
PHY Architecture
Wen Gao
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
ATSC MH Transmitter Proposal
ModulationPilot
InsertionSync
Insertion12-1 Trellis
EncoderByte
Interleaver
ReedSolomonEncoder
DataRandomizer
ATSC A53 (legacy)
LegacyMPEG TS
Source
PreamblePacketsInsertion
Virtual TSHeaderModifier
PacketDeinterleaver
GF(256)SCBC
Packetizationand
Interleaver
ATSC M/H
Mobile DataSource
MUX
Common Timing
Legacy ATSC Encoding – RS code
Defined on a Galois Field GF(256)– (K=187, N=207)
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
187 bytes 207 bytes R = 2/3
TSR S
encoderTrellis
EncoderInterleaver
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
187 bytes 207 bytes R = 2/3
TSR S
EncoderTrellis
EncoderInterleaverSCBC
Encoder
187 bytes
Rate 1/2 Byte Code
(N=2, K=1) 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) fieldExample:
m=(12), C= (12) (1, 2) = (12,24)
m=(154), C= (154)(1,2) = (154, 41)
Rate 2/3 Byte code
(N=3, K=2) byte code (GF(256) code)– The Generator matrix is
Example:
210
201G
)49,154,12(210
201(12,154)mGC
154) , (12m
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
Z1
Z2
+3
+1
-1
-3
Z2 Z1
1 1
1 0
0 1
0 0
4PAM
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
Z1
Z2
+3
+1
-1
-3
Z2 Z1
1 1
1 0
0 1
0 0
4PAM
Rate 12/26 SCBC Code
Serial Concatenation of two 2/3 byte codes and byte interleaver
Encoding is done across packets
12 TS packets
187 bytes
12 TS packets
14 parity packets
187 bytes12/26 SCBC
ByteEncoderR=2/3
BytePunctureR=27/26
ByteEncoderR=2/3
18 ByteInterleaver
12 Bytes 18 Bytes 18 Bytes 27 Bytes 26 Bytes
Rate 12/52 SCBC Code
Serial Concatenation of ½ byte code and 12/26 SCBC code with byte inter-leaver
1st 12Bytes
2nd 12Bytes
Byte
EncoderR=1/2
24 Byte
Interleaver
12 Bytes
2nd 26 Bytes
ByteEncoderR=2/3
BytePuncture
R=27/26
ByteEncoderR=2/3
18 Byte
Interleaver
1st 26 Bytes
ByteEncoder
R=2/3
BytePuncture
R=27/26
ByteEncoder
R=2/3
18 ByteInterleaver
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
12 MH packets
187 bytes
12 MH packets
14 parity packets
187 bytesSCBC
Encoder 12 MH packets
14 parity packets
187 bytesRS
Encoder
20 bytes
RS Parity Byte
RS Parity byte
ATSC MH Receiver
Soft symbols from Trellis decoder are fed back to equalizer
Iterative decoding process
Trellisdecoder
SCBCdecoder
InterleaverR S
decoder
Equalizer
DeInterleaver
Interleaver
The 12/26 Rate: AWGN Threshold 7.0 dB at 9-th iteration
The 12/52 Rate: AWGN Threshold 3.5 dB at 13th iteration
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
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
12 MH packets
187 bytes
187 bytes 12 MH packets
187 bytes
½ Byte code
12/26 Encoder
12 Parity packets 12/26 Encoder
26 packets
26 packets
Stream A
Stream B
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
Network N
Network C
CH 6
CH 13
City A
City B
Time
Network A CH 3
CH 5Network A
Backup Slides
12/26 SCBC Code decoder: Iterative decoder
12/52 SCBC Code decoder: Iterative decoder
ATSC MH data frame
Data Block 0
Data Block 1
Data Block 11
Data Block 12
Data Block 13
Data Block 23
Preamble block
Preamble blockVirtual positionwhere field sync
occurs
Virtual positionwhere field sync
occurs
Note: 1 block contains 26 TS packets
Convolutional Byte Inter leaver
0 Packet 0 Packet 0 Packet 0 Packet 1
2
51 Packet
207bytes
After convolution interleaver, 52 TS packets appear as following:
Convolutional Byte Inter leaver
Byte0
Byte26
Byte 51
ByteByte104
Byte156
5253
Byte206
Convolutional Interleaver byte locations with a contiguous
codeword
Byte 17
Byte 18
Byte 19
Byte 20
Byte 21
Byte 22
Byte 23
Byte 24
Byte 25
Byte 26
Byte27
Byte 28 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
13 12 11 10 9 8 7 6 5 4 3 2 1 0Byte 13
Byte 14
Byte 15
Byte 16
Convolutional Byte Inter leaver
Byte0
Byte
26
Byte 51
ByteByte104
Byte156
Byte 51
Byte
0
5253
For 12/26 or 12/52 SCBC code, gray regions contains complete 12/26 SCBC coded codeword
ATSC Trellis coded Modulation (TCM)
