The technology for sustainable future mobile TV

Scalable Video Coding and Differentiated Error Protection The technology for sustainable future mobile TV

Authors: Alberto Morello (Rai) & Thomas Wiegand (Fraunhofer HHI) (Coverage estimations by Paolo Forni - Rai)

SINCE 60 YEARS...

• Broadcast systems/networks have always been service-specific • • • • •

PAL/SECAM/NTSC for analogue video FM/AM for analogue radio DAB/DMB/DRM/IBOC/HDRadio/.... for Digital Radio DVB-S-T-C / ATSC /ISDB-S-T-C/,..... for Digital TV DVB-H-SH/MediaFlo/..... for Mobile-TV

• MANY TECHNOLOGIES= MANY NETWORKS= HIGHER COST

THE DVB SECOND GENERATION REVOLUTION With DVB SECOND GENERATION technologies: • Near-Shannon Physical layers • Scalable Video Coding • Very high flexibility • ... can we dream of a single technology and a single terrestrial broadcast network for TV, HDTV, MobileTV, Radio, ...?????

• Can this offer a new paradigm for successful mobile media services in the future?

Where does current divergence come from?

• Answer 1: different business scenarios / ecosystems: • • •

TV / HDTV: a Broadcasters' business (PSB, commercial or pay) Mobile TV: so-far a shared Mobile-Telco/Broadcaster business (or flop?)

Radio: large national stations (sometimes owned by TV broadcasters), medium Regional stations and a galaxy of local stations: different needs & business models

• .. but for national broadcasters, integrated multiservice broadcast networks may be very cost effective

Where does current divergence come from?

• Answer 2: different technical/functional requirements: • •

TV/HDTV fixed reception = high capacity & efficiency mobile reception = maximum ruggedness & synchronization speed

• Answer 3: The terrestrial transmission physics: huge SNR difference between outdoor reception with directive antennas and mobile & indoor reception with omni-antennas

The terrestrial physics E=85 dBÂľV/m at 10 m Band V

SNR@ 95% =48 dB

SNR@99% =11 dB rural -6 dB urban

In car

SNR@ 95% =-5 dB at ground floor (5 dB @ 70%)

SNR@ 99% =24 dB rural 7 dB urban

SNR@ 95% =11 dB urban (17 dB @ 70%)

The figures are confirmed by real tests EREMO TRANSMITTER (300W) 100%

99%

17

E=95 dBÂľV/m,

16

98%

100 % 99%

12

15 13

100% 7

11

74%

98%

100 %

90% 14

5

10

82%

100%

98%

3

9

98%

8

100%

Rai DVB-H test campaing: Torino-Eremo transmitter, UHF channel 29, ERP=4 kW 3500 indoor test points at ground floor, 500 locations

1

DVB-H Measured average Coverage Probability = 96%, in line with predictions (indoor SNR@ 95%=5 dB)

99%

6 4

2

97%

To achieve deep-indoor in every zone (3,10,11) at least 5 dB more are required – cellular network

A practical coverage example: Turin area

DVB-H urban portable outdoor & car antenna Broadcast DVB-H light-indoor (85%)

Torino - Eremo high power Transmitter (h=428 m above city level) Antenna mast: 50 m Tx=1 KW; ERP(max)=6 kW. UHF ch. 66

30Km E=85 dBµV/m 20Km E=90 dBµV/m Downtown

Cellular DVB-H urban deep-indoor (30-40 cells)

DVB-T Fixed

40Km E=80 dBµV/m

A single system for any application An impossible dream?

No unique broadcast system will ever cope with a 43-53 dB SNR difference: it's impossible to achieve from the same transmitter the same coverage area, for fixed HDTV reception with directive (outdoor) antennas and for handheld mobile-TV deep-indoor reception ...... but we have good weapons now to shoot against this problem, provided that .....:

ďƒ˜ we abandon the expensive "deep-indoor" (true >95% location) coverage criteria for a more reasonable "lightindoor" target (90% locations) ďƒ˜ we use second generation DVB technologies

The "second generation" DVB weapons  Second generation DVB systems (T2, NGH,...) (will) allow NearShannon FEC and differentiated error protection, based on the Physical Layer Pipe (PLP) concept  MIMO techniques provides important means to improve mobile/portable reception  SVC (Scalable Video Coding) provides layered video bitstreams:  a base layer fully MPEG-4 AVC compliant  one or more enhancement layers (better spacial res, temporal res. or quality) 10

1

Second Generation (T2) Physical Layer Capacity Performance (Portable channel P1) 5.0000

DVB-T2 (and NGH) (QPSK 1/2) offers Vz DVB-H: • 3.5 dB SNR gain • the use of a double tuner/antenna (MaxRatioComb.) offers additional: 3-3.5 dB SNR gain

Effective bits per Cell

3.7500

2.5000

DVB-T2 DVB-T2 1.2500

0

• TOTAL=7 dB gain • With code rate 1/4: additional 3 dB

-5.0

-3.1

-1.2 3.5 dB0.7

2.6

4.5

6.5 DVB- 8.4

3.5 dBSNR [dB]

10.3

12.2

14.1

16.0

Perspectives of MIMO 2 techniques

Low X-polar discrimination for hand-helds (indoor: around 3 dB; out-door: around 7 dB): • for low-to-medium efficiencies (0.5 to 4 bit/s/Hz) (suitable for mobile applications) the use of Alamouti is considered (cross-polar MIMO 2x2 or SIMO 1x2): 3-4 dB SNR Gains over DVB-T2

DVB-T2 SIMO or Alamouti MIMO

• Spacial multiplexing (Goldencode,...): large gains for efficiencies larger than 4 bit/ s/Hz (high capacity, dense networks) but may give

3

Potential advantage of differentiated protection + Multi-layer video coding

 It may be useful for very critical channels (e.g. large SNR variations in time or space), where it is difficult to ensure large service continuity (e.g. 99% of time and locations) and high picture quality:  mobile terrestrial (or satellite) channels (heavy shadowing attenuations; deep- indoor building penetration loss...)

 Therefore it may be reasonable to reduce network cost or increase efficiency (more programs) by offering:  high quality signals (e.g. CIF resolution) + high spectrum efficiency for fair percentages (e.g. 70-90%) of time and locations  lower quality signals (e.g. QCIF resolution) + high protection for large 13 service continuity (e.g. from 90% to 99% of time and locations)

Differentiated protection: DVB-T2 PLP approach Capacity Performance Portable

PLP2 DVBT2 TX

6.0000

Effective bits per Cell

PLP1 DVBT2PLP2 RX

8.0000

Spectrum efficiency

PLP1

channel

Each Physical Layer Pipe provides independent LDPC coding, time interleaving and mapping to constellation

4.0000

2 Tuner/Antenna

2.0000

DVB-T2

0 -5.0

PLPn

PLPn n < 256

0

5.0

10.0 SNR

15.0

1 Tuner/Antenna

20.0

SNR

For each PLP, a different "point" on the Capacity/SNR plane can be selected: 2 x tuners: from -5 dB SNR (0.5 bit/s/Hz) to 19.5 dB SNR (6 bit/s/Hz)

SVC: Scalability of Video Scalability: a functionality for removal of parts of the bitstream while achieving a performance comparable to single-layer H.264/AVC coding at that particular resolution.

Temporal: change of frame rate

30 fps 15 fps 7.5 fps

Fidelity: change of quality (e.g. SNR)

Spatial: change of frame size (i.e., resolution)

QCIF

CIF

TV

Temporal Scalability with H.264/AVC N=1 Temporal Scalability

I P P P P P P P P Base-layer

N=2 I S0 P S0 P S0 P S0 P

N=4 I S1 S0 S1 P S1 S0 S1 P

N=8 I S2 S1 S2 S0 S2 S1 S2 P

• • •

S stands for P or B picture Works for mobile TV General rule: Layers with higher temporal resolution shall not be used for prediction of layers with lower temporal resolution

Spatial (resolution) Scalability: Typical Encoding

Hierarchical MCP & Intra prediction

Spatial decimation

texture motion

Base layer coding

Multiplex

Inter-layer prediction: • Intra • Motion • Residual

H.264/AVC MCP & Intra prediction

texture motion

Base layer coding H.264/AVC compatible encoder

H.264/AVC-compatible base layer bit-stream

Scalable bit-stream

SVC Loss Typical SVC loss (vz single layer AVC) =10% at baselayer and at enhancement layer

It is possible to trade-off base-layer and enhanced-layer losses:  same loss (Δ< 10%)  no loss in the base-layer, larger loss in the upper layer

COMBINING DIFFERENTIATED PROTECTION AND VIDEO SERVICES Two independently-coded AVC video streams (Multi-layer simulcasting) at two different quality levels R

1

E1

Coder 1 (base layer)

MODULATOR

Coder 2 R

2

E2

(enhanced layer)

SIMULCAST

Problems • synchronization: "quasi-seamless" stream switching during fading • efficiency loss: since the "scene" is the same in the two layers, the base-layer information is "duplicated"

DIFFERENTIATED PROTECTION OF VIDEO SERVICES: SVC To solve the above problems of Multi-layer simulcasting, a single R1' scalable codec (SVC) may be adopted: Base layer

SVC

R1'

Coder (e.g. 10% loss compared to single coding)

E1 MODULATOR

R2'

E2

SVC R1'+R2' Enhanced layer

SVC BW GAIN VERSUS SYMULCASTING R2

R2/E2

R1

High efficiency

R1 E

Coder 1

Low Efficiency

1

T2/NGH

(base layer)

MODULATOR

Coder 2 (enhanced

R1/E1

E

R2

2

layer) SIMULCAST

BW= (R / E )+( R / E ) 1

1

2

2

Loss Δ=1.1 (=10%) R'1

SVC

E

Coder (e.g. 10% loss compared to single coding) SVC

1

T2/NGH

E

R'2

MODULATOR 2

GAIN

GAIN BW'= (R ' / E )+( R ' / E ) 1

1.1(R2-R1)

1.1R1

1

2

2

1.1(y-x)/E2

1.1R1/E1

Limits and opportunities of SVC What's the formula (R2/R1) + (E2/E1) = [1- (G Δ)-1 ]-1 Examples:

To achieve G=21% : To achieve G=13%: To achieve G=9% :

saying?

(R2/R1) + (E2/E1)=4 (R2/R1) + (E2/E1)=5 (R2/R1) + (E2/E1)=6

SVC gains if: the two streams are not be too different in bit-rate and protection : • Of course, same protection or same bit-rate are nonsense • But there are interesting use cases where SVC can offer reasonable bandwidth gains (10% to 20%) over simulcasting •

For extreme cases (very critical channels), where very large SNR differences 22 between layers are needed, SVC offers marginal gain over simulcasting

Examples of NGH potential How effective may NGH be to achieve mobile-TV / multimedia from purely broadcast networks?

Example 1 NGH with scalable video coding:  DVB-H: 11 programs (CIF) at SNR=5.5 dB  DVB-NGH: 18 programs at SNR=- 1.5 dB (QCIF) and at SNR=7 dB (CIF)

SVC gain=16%

Simulated coverage example 1: Turin area If we accept to target indoor at reduced quality (QCIF), the overall system capacity increases significantly: DVB-H: BW=500 KHz/channel --> 11 mob-TV programs DVB-NGH + AVC: BW= 378 KHz / channel --> 18 mob-TV prog.

30Km E=85 dBµV/m

Light-indoor QCIF 90% prob.

Deep-indoor

20Km E=90 dBµV/m

QCIF quality, 97% probability Downtown CIF quality, 65% probability

40Km E=80 dBµV/m

Example 2 (maximum protection) NGH with FEC 1/4 and video simulcasting DVB-H: 11 programs (CIF) at SNR=5.5 dB DVB-NGH: 11 programs at SNR=- 4.5 dB (QCIF) and at SNR=7 dB (CIF)

SVC not used

Simulated coverage example 2: Turin area Further increase of NGH protection (LDPC rate 1/4) DVB-NGH: 11 mob-TV programs as for DVB-H

30Km E=85 dBµV/m

20Km E=90 dBµV/m

Deep Indoor QCIF quality, 95% probability Downtown CIF quality, 65% probability

40Km E=80 dBµV/m

Example 3 (HDTV & Mobile-TV Coexistence) HDTV: 3 programs (10.5 Mbit/s each) at SNR=23 dB DVB-NGH (in Future Extension Frames) : 4 programs at SNR=- 1.5 dB (QCIF) and at SNR=7 dB (CIF)

SVC applied to Mobile-TV only gain=16%

Simulated coverage example 3: Turin area 3 HDTV programs using DVB-T2 4 mobile-TV programs using DVB-NGH+SVC

HDTV Mob-TV: HH Urban outdoor Rural in car

30Km light indoorE=85 QCIF dBµV/m 90% prob.

20Km E=90 dBµV/m

Deep-indoor QCIF , 96% probability Downtown CIF, 65% probability

40Km E=80 dBµV/m

Conclusions (1) "Gain budget" of DVB-NGH Vs DVB-H Tool

Gain (rough estimation from examples)

comment

DVB-2 physical layer

3.5 dB SNR (QPSK 1/2) 6.5 dB SNR (QPSK 1/4)

(OFDM, LDPC FEC , time interleaving and rot.constell.)

Double receive tuners/ antennas

3.5 dB SNR

(SIMO or Alamouti MIMO)

Layered video coding & error protection

SVC: 30% BW (or same BW but 3 dB SNR *)

loss: QCIF instead of CIF in critical locations (indoor/incar)

TOTAL

7 dB SNR + 30% BW

"light-indoor" coverage * Note: QPSK + LDPC 1/4

(or 10 dB SNR and same BW *) 90% of locations: 3 dB SNR

instead of 95% deep-indoor

Conclusions (2): How to transform the SNR gain into € saving budget

 First generation Mobile-TV was unsuccessful:  requiring very expensive cellular networks to reach "deep-indoor" broadcast coverage in towns  based on a mixed Mobile-Telco / Broadcaster business concept:  only pay-content may justify network investments  people is not ready to pay for broadcast-type content  people may be ready to pay for specific content and services, but occasionally

 Why not changing the business/cost paradigm of mobile media?

Broadcast & Premium services

Broadcast services DVB-T2 / DVB-NGH Free broadcast networks (cheap, light-indoor&cars) or low-cost

DVB-H Cellular & Broadcast networks Pay First generation

Premium services

UMTS / HSDPA/LTE cellular networks (expensive, deep-indoor)

Second generation

Mainly Pay

Thank you for attention

The capacity gain of SVC PLP Spectrum effic. ratio (E1/E2)

2.0000 Same protection

G

1.5000 1.2500

1.5 2 2.5 3 4 5

1.0000 1.0

Ideal SVC (no coding loss) E1/ E2=1

Increasing Î&#x201D; protection

1

1.7500

1.6

2.3

2.9

3.5

=R2/R1 bit-rate ratio

K

33 The two streams must not be too different in bit-rate and protection