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S32-3: AHG on Waveform
Generation and Framing
Nejib Ammar,
S32-3 Chairman
Zenith
Outline
• S32-3 Work Area
• Waveform Parameters
– BW, FFT
– Guard Interval
– Pilots
– PAPR Reduction
• Layer Division Multiplexing (LDM)
• Bootstrap
• Framing
• Summary
Broadband PHY
uplink
Physical Layer Architecture
Output
(Broadband)
User Data
Unicast IP
(IP is desired)
Access Ch Gen
Scrambler Framer
Output
(Broadcast)
User Data
OFDM Gen Framer
Broadcast PHY
downlink
Control
DFT
BICM
1. Timestamp to measure Time
Advance
2. Reserved timeslot in real time
PLP for interactivity in a frame with
unfixed length
Scrambler Framer
CMD: PHY
Assignments
QoS
(L2)
Formatting
Freq Int’l
BICM / LDM
Preamble
Output
(SISO)
Scheduler
D/A
Encapsulated
packets
(L2)
Framer
PLP
Scrambler FEC
SFN Interface (STL)
Carries Baseband Description
PHY (Studio)
Bit Int’l Mapper LDM
Time
Int’l
MIMO OFDM Freq Int’l Pilot /
Tone
Framer /
Reserve
Preamble
PHY
MISO
/ STR
IFFT
PAPR
GI Bootstrap /
Spectrum
Shaping
Output
(MIXO)
Structure and Waveform Blocks
Signaling
LDM
Injection
Combines
multiple
layers of data
streams with
different
BICM
OFDM
Framer
Combines
multiple
inputs into
single stream
and formats it
in frames
Structure
Waveform Generator
Pilots
Insertion
Inserts pilots
and reserved
tones for
channel
estimation,
synchronization
IFFT
Generates
OFDM
waveform
PAPR
Guard Int.
Insertion
Reduces
peak-toaverage
power ratio
Inserts GI to
combat
multipath
effects
Bootstrap
Insertion
Inserts the
bootstrap for
service discovery,
initial
synchronization
and core
signaling
Key Considerations
•
•
•
•
•
•
•
Flexibility to support a variety of network types, network sizes and service types
– Different combinations of FFT sizes, guard intervals , scattered pilot patterns, different frame types
Robustness
– Increased signaling data robustness
Reduced overhead to increase payload
– Optimized pilots patterns for channel BW and propagation conditions
Power savings
– Time Division Multiplexing (TDM) of data frames
Reduced complexity for fast deployment
– H/W implementation and Testing
World standard
– Support for different channel BWs
Extensibility to support future needs
– Future extension frame parts
Waveform Parameters
•
•
•
Baseline supports three channel BWs
– 6MHz (e.g. US, South America)
– 7MHz (Typical VHF band)
– 8MHz (Typical UHF band)
FFT sizes
Higher Mobility
Higher Payload
8K
16K
32K
Carriers Spacing (Hz)*
837.1
418.5
209.3
Symbol Duration Tu (µs)*
1194.7
2389.3
4778.7
Adjustable Number of Carriers (NoC)
– Maximum capacity under various Masks
– Adaptable to RF environment changes
(*) 6 MHz Channel
Guard Interval (GI)
GI
GI
6 HMz
7 MHz
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
#11
#12
28
56
75
112
149
224
299
355
448
532
597
709
24
48
64
96
128
192
256
304
384
456
512
608
8 MHz Dx Basis
21
42
56
84
112
168
224
266
336
399
448
532
4
4
3
4
3
4
3
3
4
4
3
3
FFT
8K
X
X
X
X
X
X
X
16K
X
X
X
X
X
X
X
X
X
X
X
#
32K
X
X
X
X
X
X
X
X
X
X
X
X
Samples
192
384
512
768
1024
1536
2048
2432
3072
3648
4096
4864
• Flexible set to support different networks from pure MFN to
large SFN sizes
• Balanced and optimized for 6, 7 & 8 MHz channel bandwidths
• Optimized overhead based on channel estimation extent
Pilots (1/2)
Sub-carrier (frequency)
Dx
OFDM symbol (time)
Dy
Data cell
SP cell
CP cell
Reserved cell
• Scattered Pilots (SP)
–
–
–
Used mainly for channel estimation
Flexibility of choices with respect to echo range and
mobile speed
Dx values trade-off echo range and overhead


–
–
Basic set for max GI utilization (75%~90%)
Extended set for post-GI equalization (38%~45%)
Dy=2 optimized for high mobility (~200km/h@695MHz)
Dy=4 optimized for fixed service
GI
Samples
8K
192
384
Pilot Pattern
Separation of
pilot bearing
carriers (Dx)
Number of symbols
forming
one SP sequence (Dy)
SP1
3
2
SP2
3
4
SP3
4
2
SP4
4
4
SP5
6
2
SP6
6
4
SP7
8
2
SP8
8
4
SP9
12
2
SP10
12
4
SP11
16
2
SP12
16
4
SP13
24
2
SP14
24
4
SP15
32
2
SP16
32
4
16K
32K
SP15, SP16, SP11, SP12
SP15, SP16
SP15
SP11, SP12, SP7, SP8
SP15, SP16, SP11, SP12
SP15
512
SP9, SP10, SP5, SP6
SP13, SP14, SP9, SP10
SP13
768
SP7, SP8, SP3, SP4
SP11, SP12, SP7, SP8
SP15, SP11
1024
SP5, SP6, SP1, SP2
SP9, SP10, SP5, SP6
SP13, SP9
1536
SP3, SP4
SP7, SP8, SP3, SP4
SP11, SP7
2048
SP1, SP2
SP5, SP6, SP1, SP2
SP9, SP5
2432
NA
SP5, SP6, SP1, SP2
SP9, SP5
3072
NA
SP4, SP4
SP7, SP3
3648
NA
SP4, SP4
SP7, SP3
4096
NA
SP1, SP2
SP5, SP1
4864
NA
NA
SP5, SP1
Pilots (2/2)
•
Continual Pilots (CP)
– Used for estimation, compensation and tracking of carrier frequency and timing offsets
– CP reference indices
•
•
•
Random and evenly distributed for robust synchronization under frequency selective fading
Reduced capacity overhead ( ~0.7%)
Nested CP tables for different FFT modes to reduced memory requirements
Peak-to-Average Power Ratio (PAPR)
Reduction Techniques
•
•
•
PAPR reduction techniques used to reduce high
peaks of OFDM signal
– Two complementary (optional) techniques
are recommended for ATSC3.0 baseline
Tone Reservation (TR): dedicated tones
(subcarriers) are modulated and utilized to
cancel peaks in time domain
– Small capacity overhead (~1%) is required
– Good performance especially for high
constellation order
Active Constellation Extension (ACE): Boundary
constellation points are extended to predefined
sectors (mask) to reduce peaks in time domain
– Good performance especially for low
constellation order
ACE: Extension Mask of 64-QAM
2D-NUC
Layered Division Multiplexing (LDM)
•
•
•
LDM is a new transmission technology to super-impose
two (or more) PHY data streams with different power
levels, channel coding and modulation types
– Upper Layer (UL): Very robust. well suited for HD
portable, indoor, mobile reception
– Lower Layer (LL): High data rates. Well suited for
multiple-HD and 4k-UHD high data rate fixed
reception
Injection Level parameter determines the distribution of
total power among two layers
– Can be varied between 3dB and 10dB is steps of
0.5 dB
– Example: 5 dB injection level allocates 24%
transmission power to LL and 76% to UL
Receiver decodes UL first, cancels it from the receive
signal to get LL
Total Power
(Upper Lower + Layers)
Upper Layer
Lower Layer
Example of LDM Transmission
6 MHz RF Channel (-4 dB Lower Layer
Injection)
LDM System
Upper
Data rate
SNR
layer
2.0 Mbps
-2.0
(robust-mod)
QPSK 3/15
dB
Upper layer
2.7 Mbps
-0.3
(mid-rate)
QPSK 4/15
dB
Upper layer
4.1 Mbps
2.7
(high-rate)
QPSK 6/15
dB
Low layer with -4 dB injection
14.3 Mbps
Low-rate
14.6 dB
64Q 7/15
20.5 Mbps
Mid-rate1
18.5 dB
64Q 10/15
24.6 Mbps
Mid-rate2
21.2 dB
256Q 9/15
30.1 Mbps
24.4
High-rate
256Q 11/15
dB
Bootstrap
Frequency
Bootstrap Signal
Post-Bootstrap Waveform
...
Time
• Quick and robust detection of ATSC signal
• Fast initial synchronization and channel estimation
• Signaling of system versioning, EAS wake-up and core L1 signaling
Bootstrap: Time Domain Signal
A: IFFT of frequency structure
B: cyclic prefix (postfix) with phase shift
C: cyclic prefix
Frequency
Bootstrap Signal
Post-Bootstrap Waveform
...
CAB, BCA, BCA…
Time
• Mixing C-A-B and B-C-A structures
– Resilience to interference and adverse channel effects
– Ease of estimation of fractional frequency offsets
– Robust detection performance
Bootstrap: Frequency Domain Signal
Root
ZC
Subcarrier
mapping
and zero
padding
Seed
I
F
F
T
PN
Sequence Generator
•
•
Frequency domain signal (A portion in time domain) is a Zadoff-Chu (ZF) sequence, modulated by a PN
sequence and mapped to 2K symbol
– Sync detection/service discovery based on correlation of ZC sequence with one among prescribed
sequences
– Channel estimation based on cross correlation with detected PN sequence
Four bootstrap symbols carry 22 signaling bits using cyclic shifts of the detected root sequence.
Signaling fields include
– EAS wake-up
– Core system parameters such as BW, BSR, preamble structure
Signaling config. for
•
•
…
Payload symbol Y
Payload symbol 0
.. ..
Preamble symbol X
(L1-Dynamic)
Bootstrap symbol 3
Preamble symbol 0
(L1-Static)
Bootstrap symbol 2
Bootstrap symbol 1
Bootstrap symbol 0
Frame Structure
Signaling config. for
Recommendation of general framing and L1 structure
– Bootstrap: four symbols to provide ATSC signal versioning and preamble configuration
– Preamble: variable number of symbols to deliver L1 signaling (static + dynamic) indicating payload configuration
– Data symbols carry arranged PLP payload
Work is ongoing to define details of PHY signaling and PLP mapping with provision for
– Flexibility to support a variety service rates, multiplexing, resource allocation etc.
– Extensibility to enable new needs in the future
– Maximum layer independence
– Enable power saving for mobile devices
– Enable management of change time between services
Summary
•
•
•
The baseline waveform parameters offer broadcasters a rich toolset to enable their specific
network and service needs
– Large set of GI to optimize their network set-up
– Different FFT sizes to enable static and nomadic services
– Rich and efficient sets of pilots to deal with different reception environments
Bootstrap provides a robust and quick entry to ATSC signal
– Quick synchronization
– Fast and reliable EAS wake-up
– Delivery of core signaling and system versioning for extensibility
Framing structure is being defined to enable delivery of mobile and fixed services within a
single RF channel
– Flexibility to support resource allocations for different types of services
– Power savings for mobile receivers
– Extensibility to support future and changing RF environments
ATSC 3.0,
Technology
Marches On
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