SMPTE/SBE Dallas Ft. Worth Mar 31 2011 meeting notes

1. ATSC Mobile TV: A Practical Look
(How it Works)
March 31, 2011
Mike Simon
Advanced Technology Manager
Rohde & Schwarz, Inc

2. Topics
• ATSC DTV Standards Timeline
• The Challenges:
• Mitigate Mobile Fading
• Backward Compatibility (BC) Legacy Receivers
• Dual Stream System (HDTV/SDTV + Mobile)
• Introducing ATSC Mobile’s Cross Layer Design
• How to Add Enhancements to Mitigate Mobile Fading and enable BC
• New M/H FEC and Interleaving (Channel Coding)
• New M/H Training Signals
• New M/H Signaling
• Basic Blocks of M/H Transmitter and M/H Receiver
• The operating constraints of ATSC Mobile Systems
• Questions

3. ATSC DTV Standard Timeline
The ATSC began work on Mobile in 2007 and
adopted Mobile DTV Standard (A/153) in October 2009

4. The ATSC M/H Protocol layers
Out Of Scope
This Paper
Focus on Physical Layer the “Real Challenge”

5. ATSC (A/53) Propagation Environment
Optimized Coverage 15 dB C/N TOV = AWGN

6. Challenge Mobile Fading Environment
Fast Fading
Long Deep Fades

7. Multipath (Fading) in Mobile Environment
Small Mobile Antenna Omni and low receive Height
results in the instantaneous receive level
being the Vector Sum of all received paths this is termed Fading
(See Next Slide Fading Phenomena)
When instantaneous receive level below receiver threshold C/N
Bit Errors will result Unless Mitigated

8. Mobile Fading Simulation
Fading Phenomena Occurs Resulting Voltage Receive Antenna
Independent of Transmit Power (Un-modulated Carrier Shown)

9. Simulation Handheld Pedestrian Fading
C Long deep Fades will Occur
A
F
D
B
Transmitter E
Amplitude
A: Free Space (LOS)
B: Reflection
(object is large compared to wavelength)
C: Diffraction
D: Scattering
(object is small or its surface irregular)
E: Shadowing (birth death) Time
F: Doppler Delay
Delay Spread

10. Major Technical Barriers Prohibiting Mobile
#3 Constraint Signaling
#2 Constraint Training
Viterbi Decoding
Good for AWGN Not Fading Channel
#1 Constraint Type FEC

11. A/53 VSB Data Field
Training Sequences
Designed Fixed Service
~ every 24 ms
(Need More M/H)

12. Adding New Technologies ATSC Mobile DTV
While Maintaining ATSC Legacy Compatibility

13. A/153 Dual Stream System Block
*
All M/H Data PID 0x1FF6
Like Null Packet to
Legacy
Discarded

14. Simplified Emitted VSB Data Field (A/153)
Note: Mapping of M/H Data, Training, Signaling
Note: Important
Location of Data in
VSB Field is Key
To be Explained

15. ATSC Legacy and M/H Receiver Paradigms
• Receives 100% of Symbols
• Identify Content TS Layer
• Receives Only Selected Symbols
• Identify Content Physical Layer

16. M/H Cross Layer Design
• OSI Layer Model: The model is ATSC M/H “Cross Layer Design”
comprised of a set of “layers,” each of
which are responsible for specific
functionalities, Interaction of non-
adjacent layers is never allowed
• ATSC M/H knowledge of the lower
physical 8-VSB layer is given to upper
layers to enable Synchronous (pre-
processing) of M/H data at upper
layer and (post-processed) at
physical layer with a known VSB Re-Assembling Pieces
frame mapping to Add Value
• WHY ? Enables Optimal insertion of
Turbo Codes, Training Signals,
Signaling in a backward
compatible manner

17. Simplified ATSC M/H Cross Layer Design
A/53 ~ 15 dB C/N
M/H ~ 4 dB C/N
M/H TS Packets PID (0x1FF6)
Discarded by A/53 Receivers

18. M/H Receiver’s Turbo Decoder
A/153 M/H prototype receiver CRC lab test : (½) rate C/N (7.1 dB) and (¼) rate C/N (3.2 dB) in AWGN
The (¼) rate turbo code in dynamic multipath (TU 6) 331 km/hr @ 17 dB C/N

19. RS/ CRC (M/H Frame Encoder) OUTER FEC
Outer FEC

20. Time Diversity M/H frame

21. RS/ CRC M/H Frame Encode/Decode
Erasure Decoding = Correct up to 48 rows

22. Trellis State Initialization (Training Signal)
(1 of 12) Modified Trellis Coders (Exciter) Shown
1. All Trellis States Initialized to Zero (Yellow)
2. Pre-calculated Training Data Introduced (Grey)
3. Produces known M/H Training Symbols at Known Locations VSB Field

23. Closer to Actual Format (M/H) VSB Field

24. A/153 Receiver (Parade Reception)

25. Timing References Required M/H
Studio Transmitter
GPS/
NTP
Stratum 1
Server GPS
ATSC
(Normal) MPEG2 Encoding 10 MHz 1PPS
Services and Service NTP
Multiplexer
M/H M/H
STL
Multiplexer Exciter
M/H IP Services
(ATSC Time Aware)
A/153 requires that both the TS rate (TSrate) and the Symbol rate (Fsym) is to be derived from the GPS 10 MHz reference:
TSrate = 433998/223797 x 107 Hz = 19392658 bps
Fsym = 313/564 x TS rate = 10762238 Hz
Null Packet ADD/Drop Not Permitted (Synchronous Link STL) Mux to Exciter

26. Measuring Units of Time TS Bit Periods
ATSC Tick
M/H frame 1 M/H Frame = 18,769,920 Bits
M/H sub-frame M/H sub-frame M/H sub-frame M/H sub-frame M/H sub-frame 1 M/H Sub Frame = 3753984 Bits
#0 #1 #2 #3 #4
M/H M/H M/H M/H M/H M/H M/H M/H M/H M/H M/H M/H M/H M/H M/H M/H
slot slot slot slot slot slot slot slot slot slot slot slot slot slot slot slot
#0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14 #15
156 Packets 1 M/H Slot = 234634 Bits
188 Bytes 1 Packet = 1504 Bits
8 Bits 1 Byte = 8 Bits

27. A/153 ATSC Time Defined
1 Sec
GPS (Ticks)
1 M/H Frame
0.968 Sec
ATSC (Ticks)
Jan. 6, 1980 00:00:00 UTC
GPS / ATSC Epoch
ATSC Time Equation:
# GPS Second Ticks x (4809375/ 4654936) = # ATSC Ticks
Every M/H Station Emits (Antenna) Start M/H Frame at Same Time
• Benefits
• Better Channel Change Station to Station
• Improved Handoff Regional Content

28. Typical M/H In Operation
ATSC
(Tick)
M/H Frame Period
Time
MAX Delay (Time)
Release Time Start M/H Frame into STL =
GPS seconds (ATSC Tick) – Max Delay
Transport Delay (time)
Tx
M/H Sub- M/H Sub- M/H Sub- M/H Sub- M/H Sub-
Frame #4 Frame #3 Frame #2 Frame #1 Frame #0 Dly
1 MH Frame = 20 VSB Frames ~ 0.968 sec
Transmitter to Antenna Delay (Time)
F
MPEG2 TS A/153 I A/153
M/H Mux STL F M/H Exciter
IP M/H M/H Signaling O
GPS
GPS/ (ATSC Time) 10 Mhz
NTP Cadence 1PPS
Server Generator
ATSC Ticks M/H Frame Period

29. Thank You
Mike Simon
Advanced Technology Manager
Rohde & Schwarz, Inc.
Mike.Simon@rsa.rohde-schwarz.com