SkyEdge II

Outbound Overview

2Agenda

DVB-S2 Introduction

Modulation Schemes

FEC

MODCODs

Operation Modes

ACM Benefits

Framing Process

Test your knowledge

3DVB-S2 Introduction

SE II Outbound channel is based on DVB-S2 (EN302 307)

The DVB-S2 system has been designed for several satellite broadband

applications.

DVB-S2 offers better Spectral efficiency compared with DVB-S

Advance modulation schemes

Stronger FECs

Roll off factor of 0.2

The use of ACM

4DVB-S2 IntroductionModulation Schemes

Advanced Modulation

Schemes

QPSK, 8PSK, 16APSK

and 32APSK

2, 3, 4, or 5 bits per

symbolI

Q

I

Q

II

QQ

QPSK

16APSK 32APSK

8PSK2 bits per symbol 3 bits per symbol

5 bits per symbol4 bits per symbol

00

01

10

11

0000

1111

11111

00000

111

000

5DVB-S2 IntroductionForward Error Correction (FEC)

LDPC / BCH Forward Error Correction Codes

1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9 and 9/10

QPSK 1/4, 1/3 and 2/5 can operate under exceptionally poor link conditions,

even when the signal level is below the noise level

Offers minimum distance from the Shannon limit

Code rates depend on the selected modulation and the system requirements

6Spectral Efficiency of DVB-S2

7DVB-S2 IntroductionOperation Modes

Constant Coding and Modulation (CCM)

Single MODCOD

Similar principle to DVB-S (SE OB)

Adaptive Coding and Modulation (ACM)

Each frame can be transmitted using a different MODCOD, regardless

of its input stream.

MODCOD is selected according to reception conditions of the VSATs

MODCOD Combination of modulation and coding

8DVB-S2 Introduction

ACM - Benefits

Maximum Availability

Using robust MODCODs such as QPSK 1/4 or QPSK 1/3 to achieve almost

any availability goal

BW Utilization

By taking advantage of clear sky situations we can increase the OB effective

bit rate when using efficient MODCODs such as 8PSK 9/10

Optimizing the transmission parameters for each VSAT

MODCODs are selected based on path conditions

MODCODs are under closed-loop control via a return satellite channel

MODCOD change on a frame-by-frame basis

9DVB-S2 IntroductionMODCOD

From the 29 available MODCODs, up to 8 can be configured and be active in

the OB

Data rate vary depending of the spectral efficiency of the MODCOD used

The MODCOD used for each VSAT can change dynamically due to changes

in the VSAT reception quality

Transmission to a single VSAT may use different MODCODs in continuous

manner thanks to the PLHeader Armor- Piercing coding (BPSK).

10

System ArchitectureMODCOD Control Flow description

Each VSAT reports its Es/No value once per second.

According to the Es/No, the HSP assigns a MODCOD to each VSAT based on

the MODCODs thresholds.

If a change of MODCOD occurs, the HSP advertises the new MODCOD to the

DPS and NMS

The DPS marks each packet according to the currently selected MODCOD.

The DPS uses a TCP tunnel for all Unicast Data and separated UDP tunnels for

VoIP, Multicast and Abis

Only the Unicast Data from the DPS requires flow-control.

11

MODCOD AlgorithmFlow Diagram

VSAT reports

Es/No value every 1 sec

New

Es/No value

requires

MODCOD change

?

HSP send new MODCOD

To DPS and NMS

DPS stores new

MODCOD value

DPS stamps new MODCOD

in the packets

yes

No

Update new Es/No

value in the HSP table

12

The ACM system margin is an dB margin to support reasonable fade changes

while the process of changing MODCOD is taking place

The VSAT send its Es/No reading once per second

Fading can cause a 1dB loss per second

Taking in consideration 650 msec round trip

Worst case of 1.65 sec response time

Therefore, the system margin should be 1.65dB

MODCOD Algorithm

ACM System Margin

13

QPSK 1/4

QPSK 1/2

QPSK 2/3

QPSK 9/10

8PSK 3/4

-2.35

Es/No (dB)

T

(Sec)

+1.0

+3.1

+6.4

+7.9

+11

8PSK 9/10

8PSK 9/10

-0.7

+2.65

+4.75

+9.5

+12.65

+8.0

ACM Margin (1.65 dB)

Clear Sky

VSAT Es/No

System ACM Margin

Es/No Regions per Active MODCOD

Better weather

condition

Worsen weather

condition

Deep Fade

14

DVB-S2 IntroductionDVB-S2 Transport Stream

The DVB-S2 standard allows the use of two sizes of frames

Short Frames - 16200 bits (2KB)

Reduces latency and jitter

Used for small networks / VoIP / Abis

Normal Frames - 64800 bits (8KB)

Increase throughput

Less Over Head related to the data transmitted

Provides a gain of 0.3 to 0.5 dB over short frames

15

DVB-S2 IntroductionDVB-S2 Transport Stream

The use of Short or Normal frames affects the response time, fill factor and

the efficiency of the system. It has to be decided as part of the sizing

process.

16

DVB-S2 IntroductionTransport Stream

Pilot Insertion

In order to assist the PLFRAME synchronization recovery at the VSAT site

under low C/N conditions, DVB-S2 use the injection of pilot symbols in the

physical layer frames

Each PLFRAME has a PLHeader and several data slots (90 symbols). In this

PLHeader there is information about the MODCOD and Pilots use of the data

slots

The Pilot insertion will consist in 36 symbols (Pilot Block) each 16 slots

(inside the physical layer frame) for the MODCODs that need them

Pilots are used only for some MODCODs

17

SkyEdge II OB FramesPilot Insertion Short Frames

MODCOD Spectral

Efficiency

Pilot

Insertion

QPSK 1/4 0.357467 YES

QPSK 1/3 0.615532 YES

QPSK 2/5 0.744564 YES

QPSK 1/2 0.830585 YES

QPSK 3/5 1.156532 NO

QPSK 2/3 1.2884 NO

QPSK 3/4 1.420269 NO

QPSK 4/5 1.508181 NO

QPSK 5/6 1.596093 NO

QPSK 8/9 1.727961 NO

8PSK 3/5 1.692033 YES

8PSK 2/3 1.884959 YES

MODCOD Spectral

Efficiency

Pilot

Insertion

8PSK 3/4 2.077885 YES

8PSK 5/6 2.33512 YES

8PSK 8/9 2.577778 NO

16APSK 2/3 2.505223 YES

16APSK 3/4 2.809662 NO

16APSK 4/5 2.983575 NO

16APSK 5/6 3.157488 NO

16APSK 8/9 3.418357 NO

32APSK 3/4 3.419165 YES

32APSK 4/5 3.630805 YES

32APSK 5/6 3.842446 YES

32APSK 8/9 4.159906 YES

18

SkyEdge II OB FramesPilot Insertion Normal Frames

MODCOD Spectral

Efficiency

Pilot

Insertion

QPSK 1/4 0.478577 YES

QPSK 1/3 0.640827 YES

QPSK 2/5 0.770627 YES

QPSK 1/2 0.965327 YES

QPSK 3/5 1.188304 NO

QPSK 2/3 1.322253 NO

QPSK 3/4 1.487473 NO

QPSK 4/5 1.587196 NO

QPSK 5/6 1.654663 NO

QPSK 8/9 1.766451 NO

QPSK 9/10 1.788612 NO

8PSK 3/5 1.739569 YES

8PSK 2/3 1.935658 YES

8PSK 3/4 2.177525 YES

MODCOD Spectral

Efficiency

Pilot

Insertion

8PSK 5/6 2.422276 YES

8PSK 8/9 2.646012 NO

8PSK 9/10 2.679207 NO

16APSK 2/3 2.574613 YES

16APSK 3/4 2.966728 NO

16APSK 4/5 3.165623 NO

16APSK 5/6 3.300184 NO

16APSK 8/9 3.523143 NO

16APSK 9/10 3.567342 NO

32APSK 3/4 3.623332 YES

32APSK 4/5 3.866247 YES

32APSK 5/6 4.030589 YES

32APSK 8/9 4.302894 YES

32APSK 9/10 4.356875 YES

19

DVB-S2 Framing Process Block Diagram

CRC BaseBand

SignalingBCH LDPC Interleaver

FEC , 1/3, 2/5, , .9/10

Bit

Mapping

BB Filter &

Quadrature

Modulator

RF L-Band

Output

PL Frame

QPSK

8PSK

16APSK

32APSK

BB FrameInput FEC Frame

Outer Code

Block code

Inner Code

Turbo code

PL Scrambler

Shaping

(=0.2)

PL Signaling

Pilot Insertion

IPlex

Scrambler

I

Q

FEC Frame

XFEC Frame

1 2

3

20

DVB-S2 Framing Process

TSH

1

2

3PLHeader

21

Test Your Knowledge

1. What is the FECFRAME length?

_____________________________________________________________

2. What information is included in the BB Frame header?

_____________________________________________________________

3. How does the VSAT reports its Es/No value?

_____________________________________________________________

4. How many active MODCODs are in the OB Channel?

_____________________________________________________________

5. What are the benefits of using DVB-S2 ACM?

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22

The End