SkyEdge I I Outbound Overview
Agenda DVB-S2 Introduction Modulation Schemes FEC MODCODs Operation Modes ACM Benefits Framing Process Test your knowledge
2
DVB-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
3
DVB-S2 Introduction Modulation Schemes Advanced Modulation Schemes QPSK, 8PSK, 16APSK and 32APSK 2, 3, 4, or 5 bits per symbol
Q
Q
10
00
000
I QPSK 11
I 8PSK
01
2 bits per symbol
3 bits per symbol 111
Q 16APSK
Q
32APSK 5 bits per symbol
4 bits per symbol 0000
00000
I
I
1111 11111
4
DVB-S2 Introduction Forward 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
5
Spectral Efficiency of DVB-S2
6
DVB-S2 Introduction Operation 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 – C o m b i n a t io n o f m o d u l at i o n a n d c o d i n g
7
DVB-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
8
DVB-S2 Introduction MODCOD
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).
9
System Architecture MODCOD 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.
10
MODCOD Algorithm Flow Diagram VSAT reports Es/No value every 1 sec
Update new Es/No value in the HSP table
No
New Es/No value requires MODCOD change ? yes HSP send new MODCOD To DPS and NMS
DPS stamps new MODCOD in the packets
DPS stores new MODCOD value 11
MODCOD Algorithm ACM System Margin 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
12
System ACM Margin Es /No Regions per Active MODCOD Es/No (dB)
+12.65 8PSK 9/10
Clear Sky
+11 +9.5 8PSK 9/10 +7.9 +8.0 8PSK 3/4 +6.4 +4.75 QPSK 9/10 +3.1 +2.65
QPSK 2/3
+1.0 -0.7 QPSK 1/2 -2.35 QPSK 1/4
Deep Fade VSAT Es/No Better weather
ACM Marg in (1.65 dB)
condition
Worsen weather
T (Sec)
13
DVB-S2 Introduction DVB-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
14
DVB-S2 Introduction DVB-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.
15
DVB-S2 Introduction Transport 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
16
SkyEdge II OB Frames Pilot Insertion – Short Frames MODCOD
Spectral Efficiency
Pilot Insertion
MODCOD
Spectral Efficiency
Pilot Insertion
QPSK 1/4
0.357467
YES
8PSK 3/4
2.077885
YES
QPSK 1/3
0.615532
YES
8PSK 5/6
2.33512
YES
QPSK 2/5
0.744564
YES
8PSK 8/9
2.577778
NO
QPSK 1/2
0.830585
YES
16APSK 2/3
2.505223
YES
QPSK 3/5
1.156532
NO
16APSK 3/4
2.809662
NO
QPSK 2/3
1.2884
NO
16APSK 4/5
2.983575
NO
QPSK 3/4
1.420269
NO
16APSK 5/6
3.157488
NO
QPSK 4/5
1.508181
NO
16APSK 8/9
3.418357
NO
QPSK 5/6
1.596093
NO
32APSK 3/4
3.419165
YES
QPSK 8/9
1.727961
NO
32APSK 4/5
3.630805
YES
8PSK 3/5
1.692033
YES
32APSK 5/6
3.842446
YES
8PSK 2/3
1.884959
YES
32APSK 8/9
4.159906
YES 17
SkyEdge II OB Frames Pilot Insertion – Normal Frames MODCOD
Spectral Efficiency
Pilot Insertion
MODCOD
Spectral Efficiency
Pilot Insertion
QPSK 1/4
0.478577
YES
8PSK 5/6
2.422276
YES
QPSK 1/3
0.640827
YES
8PSK 8/9
2.646012
NO
QPSK 2/5
0.770627
YES
8PSK 9/10
2.679207
NO
QPSK 1/2
0.965327
YES
16APSK 2/3
2.574613
YES
QPSK 3/5
1.188304
NO
16APSK 3/4
2.966728
NO
QPSK 2/3
1.322253
NO
16APSK 4/5
3.165623
NO
QPSK 3/4
1.487473
NO
16APSK 5/6
3.300184
NO
QPSK 4/5
1.587196
NO
16APSK 8/9
3.523143
NO
QPSK 5/6
1.654663
NO
16APSK 9/10
3.567342
NO
QPSK 8/9
1.766451
NO
32APSK 3/4
3.623332
YES
QPSK 9/10
1.788612
NO
32APSK 4/5
3.866247
YES
8PSK 3/5
1.739569
YES
32APSK 5/6
4.030589
YES
8PSK 2/3
1.935658
YES
32APSK 8/9
4.302894
YES
8PSK 3/4
2.177525
YES
32APSK 9/10
4.356875
YES
18
DVB-S2 Framing Process Block Diagram IPlex
Input
BaseBand Signaling
CRC
1
Scrambler
Bit Mapping QPSK 8PSK 16APSK 32APSK
I Q
PL Signaling Pilot Insertion
BCH
LDPC
Outer Code Block code
I n n er C o d e Turbo code
2
FEC Frame Interleaver
PL Frame
XFEC Frame FEC Frame
FEC ¼, 1/3, 2/5, ½, ….9/10
BB Frame
3
PL Scrambler
BB Filter & Quadrature Modulator
RF L-Band Output
Shaping (α=0.2) 19
DVB-S2 Framing Process
1
TS H
2
3
PLHeader
20
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 it’s Es/No value? _____________________________________________________________
4.
How many active MODCODs are in the OB Channel? _____________________________________________________________
5.
What are the benefits of using DVB-S2 ACM? _____________________________________________________________
21
The En d
22
