ATSC Mobile TV: A Practical Look (How it Works)

March 31, 2011

Mike Simon Advanced Technology Manager

Rohde & Schwarz, Inc

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

ATSC DTV Standard Timeline

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

Out Of Scope This Paper

The ATSC M/H Protocol layers

Focus on Physical Layer the “Real Challenge”

ATSC (A/53) Propagation Environment

Optimized Coverage 15 dB C/N TOV = AWGN

Challenge Mobile Fading Environment

Fast Fading

Long Deep Fades

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

Mobile Fading Simulation

Fading Phenomena Occurs Independent of Transmit Power

Resulting Voltage Receive Antenna (Un-modulated Carrier Shown)

Transmitter

Amplitude

Time Delay

A: Free Space (LOS)

A

Delay Spread

B: Reflection (object is large compared to wavelength) C: Diffraction D: Scattering (object is small or its surface irregular) E: Shadowing (birth death) F: Doppler

C

D

B

E

F

Simulation Handheld Pedestrian Fading

Long deep Fades will Occur

Major Technical Barriers Prohibiting Mobile

Viterbi Decoding Good for AWGN Not Fading Channel

#1 Constraint Type FEC

#2 Constraint Training

#3 Constraint Signaling

A/53 VSB Data Field

Training Sequences

Designed Fixed Service

~ every 24 ms

(Need More M/H)

Adding New Technologies ATSC Mobile DTV

While Maintaining ATSC Legacy Compatibility

A/153 Dual Stream System Block

All M/H Data PID 0x1FF6

Like Null Packet to

Legacy

Discarded

*

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

ATSC Legacy and M/H Receiver Paradigms

• Receives 100% of Symbols

• Identify Content TS Layer

• Receives Only Selected Symbols

• Identify Content Physical Layer

M/H Cross Layer Design

• OSI Layer Model: The model is 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 frame mapping

• WHY ? Enables Optimal insertion of Turbo Codes, Training Signals, Signaling in a backward compatible manner

Re-Assembling Pieces

to Add Value

ATSC M/H “Cross Layer Design”

Simplified ATSC M/H Cross Layer Design

M/H TS Packets PID (0x1FF6)

Discarded by A/53 Receivers

A/53 ~ 15 dB C/N

M/H ~ 4 dB C/N

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

RS/ CRC (M/H Frame Encoder) OUTER FEC

Outer FEC

Time Diversity M/H frame

RS/ CRC M/H Frame Encode/Decode

Erasure Decoding = Correct up to 48 rows

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

Closer to Actual Format (M/H) VSB Field

A/153 Receiver (Parade Reception)

Timing References Required M/H

ATSC

Encoding

and Service

Multiplexer

M/H IP Services

NTP

Studio

STL

Transmitter

M/H

Multiplexer

M/H

Exciter

GPS/

NTP

Stratum 1

Server

10 MHz

GPS

1PPS (Normal) MPEG2

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

Measuring Units of Time TS Bit Periods

M/H

slot

#0

M/H

slot

#1

M/H

slot

#2

M/H

slot

#3

M/H

slot

#4

M/H

slot

#5

M/H

slot

#6

M/H

slot

#7

M/H

slot

#8

M/H

slot

#9

M/H

slot

#10

M/H

slot

#11

M/H

slot

#12

M/H

slot

#13

M/H

slot

#14

M/H

slot

#15

M/H sub-frame

#0

M/H sub-frame

#1

M/H sub-frame

#2

M/H sub-frame

#3

M/H frame

M/H sub-frame

#41 M/H Sub Frame = 3753984 Bits

1 Byte = 8 Bits

156 Packets

188 Bytes

8 Bits

1 M/H Slot = 234634 Bits

1 Packet = 1504 Bits

1 M/H Frame = 18,769,920 Bits

ATSC Tick

A/153 ATSC Time Defined

Jan. 6, 1980 00:00:00 UTC

GPS / ATSC Epoch

1 Sec

0.968 Sec

GPS (Ticks)

ATSC (Ticks)

1 M/H Frame

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

Typical M/H In Operation

A/153

M/H Mux

A/153

M/H Exciter

F

I

F

O

M/H Sub-Frame #0

M/H Sub-Frame #1

M/H Sub-Frame #2

M/H Sub-Frame #3

M/H Sub-Frame #4

1 MH Frame = 20 VSB Frames ~ 0.968 sec

STL

M/H Frame Period

Transmitter to Antenna Delay (Time)

M/H Signaling

MAX Delay (Time)

MPEG2 TS

IP M/H

Release Time Start M/H Frame into STL =

GPS seconds (ATSC Tick) – Max Delay

Time

Tx

Dly

Transport Delay (time)

(ATSC Time)

Cadence

Generator

GPS/

NTP

Server

GPS

10 Mhz

1PPS

ATSC

(Tick)

M/H Frame PeriodATSC Ticks

Thank You

Mike Simon

Advanced Technology Manager

Rohde & Schwarz, Inc.

Mike.Simon@rsa.rohde-schwarz.com