uplink downlink 20 mhz 36 mhz - angelfire · date / place e. nemer - 3 • the digital video...
TRANSCRIPT
Date / Place E. Nemer - 1
BPF Pre-amp TWTABPA
LOnoise density Ns
Satellite Rx ant GSR Ts PWN
Satellite Tx ant GST
Single transponder
36 MHz
20 MHz uplink downlink
36 MHz
Freq converter AGC
Date / Place E. Nemer - 2
Direct Video Broadcast (DVB) Systems
Date / Place E. Nemer - 3
• The Digital Video Broadcasting (DVB) specifications cover digital
services delivered via cable, satellite and terrestrial transmitters.
• The satellite flavor is DVB-S :
It’s intended to provide Direct-To-Home(DTH) broadcast.
Provides also collective antenna systems and cable television head-
end stations.
Designed to fit different satellite transponder bandwidths and is
compatible with Moving Pictures Experts Group 2 (MPEG 2) coded TV
services.
Enables the transmission capacity to be used for a variety of TV
service
DVB-S Introduction
Date / Place E. Nemer - 4
MPEG-2 Multiplexers
Video Coder
Audio Coder
Data Coder1
2
n
Program Multiplexer
Transport
Multiplexer
Packetizer
Packetizer
Packetizer
Packetized
Elementary
Streams
Transport
Stream
Date / Place E. Nemer - 5
The MPEG Transport Stream
•First byte of each PES packet must be the first byte of the transport packet payload
•Each transport packet must contain data from only one PES packet
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Transport Stream Role
• Transport of all programming information
– All information that a particular provider transmits (on a particular
frequency)
• Minimize processing required for:
– Retrieval of coded data from one stream
– Extraction of transport stream packets of one or more transports and
the output of a new transport stream
– Enabling the transport and recovery of a stream over a lossy
environment
Date / Place E. Nemer - 7
Two Types of Transport Streams
• Simple Program Transport
Stream (SPTS)
– Different PES share a
common time base
– The different PES could
carry video, audio and
data
– Example would be a movie
transmitted with multiple
languages
• Multiple Program
Transport Stream (MPTS)
– Carries multiple SPTS
Multi Program TS
Carrying Single Program
TS
1. MPTS 2. MPTS 3. MPTS
1. SPTS 2. SPTS 3.SPTS
1. PES 2. PES 3.PES
ES
Network
Single Program TS
Carrying Packetized ES
Packetized ES Forming
Elementary Stream
Date / Place E. Nemer - 8
MPEG-2 Transport Packet Header
Transport
Scrambling Control
(2 bits)
Transport Packet
Header
(4 Bytes)
Sync Byte
(8 bits)
Transport Error
Indicator
(1 bit)
Payload Unit
Start Indicator
(1 bit)
Transport
Priority
(1 bit)
PID(13 bits)
Adaptation
Field
(variable Size)
Data Bytes
(variable Size)
Adaptation Field
Control
(2 bits)
Continuity
Counter
(4bits)
MPEG-2 Systems Transport Packet (188 Bytes)
Transport Packet Header (4 Bytes)
Transport packets are 188 bytes because MPEG-2 required these packets to be carried across ATM (188 bytes = 4 ATM cells)
Date / Place E. Nemer - 9
MPEG Program Streams
• A group of tightly coupled PES packets referenced to a
common time base
• Intended for transmission in a relatively error-free
environment
– Enable easy software processing of the received data
• Used for video playback and some network applications
Date / Place E. Nemer - 10
Transport Layer PIDs
Date / Place E. Nemer - 11
MPEG Signaling Tables
• PAT - Program Association Table
– Lists the PIDs of tables describing each program. The PAT is sent with the PID value of 0x000.
• CAT - Conditional Access Table
– Defines type of scrambling used and PID values of transport streams which contain the conditional access management and entitlement information (EMM). The CAT is sent with the PID value of 0x001.
• PMT - Program Map Table
– Defines the set of PIDs associated with a program, e.g. audio, video…,
• NIT - Network Information Table
– PID=10, contains details of the bearer network used to transmit the MPEG multiplex, including the carrier frequency
• DSM-CC - Digital Storage Media Command and Control
– messages to the receivers
Date / Place E. Nemer - 12
DVB Signaling Tables
• BAT- Bouquet Association Table
– Groups services into logical groups
• SDT- Service Description Table
– Describes the name and other details of services
• TDT - Time and Date Table
– PID=14, provides present time and date
• RST - Running Status Table
– PID=13, provides status of a programmed transmission, allows
for automatic event switching
• EIT - Event Information Table
– PID=12, provides details of a programmed transmission
Date / Place E. Nemer - 13
Transport multiplex adaptation and randomization for energy dispersal
Outer coding(i.e. Reed-Solomon)
Convolutional interleaving
Basebandshaping formodulation
Modulation.
DVB-S Transmitter
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DVB-S Transmitter
Date / Place E. Nemer - 15
Transport Packet
Date / Place E. Nemer - 16
Transport Stream Multiplexer
Date / Place E. Nemer - 17
DVB Scrambler/Descrambler
p(n-14) +p(n-15)
x(n) y(n)
y(n) = x(n) + p(n-14) + p(n-15)
Self descrambling:
y(n) = x(n) + p(n-14) + p(n-15) + p(n-14) + p(n-15)
= y(n)
Date / Place E. Nemer - 18
• It facilitates the work of a timing recovery circuit, by
eliminating long sequences consisting of '0' or '1' only.
• It eliminates the dependence of a signal's power spectrum
upon the actual transmitted data,
– Making it more dispersed to meet maximum power spectral density
requirements
– If the power is concentrated in a narrow frequency band, it can
interfere with adjacent channels caused by non-linearities of the
receiving tract).
Purposes of Scrambling
Date / Place E. Nemer - 19
19
Randomized Transport Packets
Date / Place E. Nemer - 20
Reed-Solomon Encoding
• The code is specified as an RS(n,k) with m-bit symbols.
– E.g. the DVB code is RS(204,188) using 8-bit symbols.
– n refers to the number of encoded symbols in a block,
– k refers to the number of original message symbols.
• The difference n-k ( called 2t) is the number of parity
symbols that have been appended to make the encoded
block.
Date / Place E. Nemer - 21
Reed Solomon RS(204,188,t=8) error protected packet.
Date / Place E. Nemer - 22
R-S Performance
• An RS decoder can correct up to (n-k)/2 or t symbols,
• Any t symbols can be corrupted in any way, and the original
symbols can be recovered.
• The DVB code
– splits the message into blocks 188 symbols long.
– 16 parity symbols (2t = 204-188 = 16) are then appended to produce the
full 204 symbol long code.
• Up to 8 (t = 16/2) symbol errors can then be corrected
Date / Place E. Nemer - 23
R-S Performance
• With the DVB code, a sequence of up to 56 consecutive bits could be
corrupted affecting at most 8 symbols, and the original message could
still be recovered.
– However it does mean that RS codes are relatively sensitive to evenly spaced
errors
– i.e. in the DVB code if 9 symbols have a single bit error then no corrections
can be made.
– Therefore the RS encoded block is further encoded in a Convolutional code to
try and cope with both burst and random errors.
Date / Place E. Nemer - 24
Framing Structure
Date / Place E. Nemer - 25
Interleaved Frames (Interleaving depth I=12).
Date / Place E. Nemer - 26
Convolutional Interleaver
A convolutional interleaver consists of a set of shift registers, each with afixed delay. In a typical convolutional interleaver, the delays arenonnegative integer multiples of a fixed integer (although a generalmultiplexed interleaver allows arbitrary delay values). Each new symbolfrom the input signal feeds into the next shift register and the oldestsymbol in that register becomes part of the output signal. The schematicbelow depicts the structure of a convolutional interleaver by showing theset of shift registers and their delay values D(1), D(2),...,D(N). The blocks inthis library have mask parameters that indicate the delay for each shiftregister. The delay is measured in samples.
Date / Place E. Nemer - 27
Interleaver
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Interleaving Operation
120091106810357024001
Columnsby Readout :
1296300
0118520
0010741
:
delay)Clock (2Register Third Input to
delay)Clock (1Register Second Input to
delay) (noRegister First Input to
12963
11852
10741
:
121110987654321
o
BS
B
S
Output
S
Shifting
S
Blocking
S
Date / Place E. Nemer - 29
De-Interleaving Operation
121110987654321000000
Columnsby Readout :
1296300
1185200
1074100
:
delay)Clock (0Register Third Input to
delay)Clock (1Register Second Input to
Clock) (2Register First Input to
1296300
0118520
0010741
:
120091106810357024001
o
BS
B
o
S
Output
S
Shifting
S
Blocking
S
Date / Place E. Nemer - 30
Convolutional Encoder
Input Bit Stream
To Q Channel
To I Channel
Date / Place E. Nemer - 31
Convolutional Code Definition
Punctured Code Definition
Date / Place E. Nemer - 32
Punctured Code
Date / Place E. Nemer - 33
Puncturing Pattern & Transmission Sequence
Code Rates Puncturing patternTransmitted sequence
(after parallel-to-serial conversion)
1/2 X: 1
Y: 1 X 1Y1
2/3 X: 1 0
Y: 1 1 X1 Y1 Y2
3/4 X: 1 0 1
Y: 1 1 0 X1 Y1 Y2 X3
5/6 X: 1 0 1 0 1
Y: 1 1 0 1 0 X1 Y1 Y2 X3 Y4 X5
7/8 X: 1 0 0 0 1 0 1
Y: 1 1 1 1 0 1 0 X1 Y1 Y2 Y3 Y4 X5 Y6 X7
Date / Place E. Nemer - 34
Punctured Convolutional Code Block Diagram
Date / Place E. Nemer - 35
Baseband Shaping
for
for
where:
is the Nyquist frequency and = 0.35 (roll-off).
Date / Place E. Nemer - 36
QPSK and OQPSK Modulators
Date / Place E. Nemer - 37
• The 2-dimensional QPSK modulation
is used to create 4 or 8 symbols.
• The modulated signal can be
expressed in a polar form as
)2
2cos()()(M
itftpsAtS eei
• We can use M quantized levels of , to create a variety of PSK modulation.
• M=2, makes this a BPSK, M=4 is QPSK, M=8, 8PSK and so on.
• In DVB-S the modulation required is QPSK.
• In DVB-S2 the modulation possible are QPSK, 8QPSK, 16APSK, 32 APSK
2
DVB-S Modulation
Date / Place E. Nemer - 38
DVB-S - Bit rates versus transponder bandwidth
• The transmission symbol rate Rs can be matched to given transponder
characteristics
• Achieving the maximum transmission capacity compatible with the acceptable
signal degradation due to transponder bandwidth limitations
• The following table gives examples of the useful bit rate capacity Ru
achievable on a satellite transponder with bandwidth BW corresponding to
BW/Rs = 1,28.
Date / Place E. Nemer - 39
BPF Pre-amp TWTABPA
LOnoise density Ns
Satellite Rx ant GSR Ts PWN
Satellite Tx ant GST
QAM modulator Earth
Station 1
BW = B1 < W
ERP P1
GT
i
iP
Other sources destined to the same transponder (TWTA)
Single transponder
Interfering sources
36 MHz
20 MHz uplink downlink
36 MHz
Freq converter
LNB
noise density Ng
Tuner
12 GHz
Demod
~1 GHz
GR
I, Q
Total path loss
AGC
Total gain gP
WNWNPPP gSTsatr
STgsat GPP
Antennadist. net
Date / Place E. Nemer - 40
Non-linearity AM-AM and AM-PM curves are
given by TWTA specs. Distortion
is function of input backoff
(IBO), which can be as low as 0
dB.
Optus data sheet suggest
that when 2 carriers are
used per TWTA, the backoff
is > 20 dB, which makes
non-linearity very minor.
I/Q imbalance +/- 1.5 dB amplitude;
+/- 3 deg in phase
Tuner data sheets
(Broadcomm, Infineon,
Maxim).
Frequency Error - From transponder frequency
translation : +/- 25 kHz
- From LNB at user site
- From crystals at Rx (50 ppm)
Intelsat restriction for 1st
Doppler shift +/- 2kHz worst case
Tuner Phase noise -55 dBc/Hz @ 1 kHz
-75 dBc/Hz @ 10 kHz
-90 dBc/Hz @ 100 kHz
Tuner data sheets
(Broadcomm, Infineon,
Maxim).
LNB Phase noise Same order as Tuner’s LNB sheets
(CaliforniaAmplifiers,
GOSPELL).
Multipath profile -10 dBc @ 26 – 30 nsec.
-15 dBc @ 51 – 55 nsec
-20 dBc @ 76 – 80 nsec
-25 dBc @ 11 – 115 nsec
(std docs)
Date / Place E. Nemer - 41
Maximum Power 37 dBW typical Satellite specs (eg :
OPTUS)
Output backoff [0: 20] dB depending on nb
carriers / TWTA
Satellite specs
Path loss attenuation * 206 dB free space loss;
* 0.8 dB receive antenna loss
Weather-induced
attenuation
An additional degradation of 3 to
6 dB in signal strength
An additional degradation of 3 to
15 dB in C/N
Satellite specs (eg : IESS
308)
Delay variation 175 nsec per sec Intelsat VA and VI
Adjacent satellite (Co-
chan)
40 dB Optus data sheets
Intermod noise [ 24 : 14] dB , depending on
output backoff points of TWTA
(14 dB for 1 dB OBO, and 24 dB
for 6 dB OBO)
TWTA data sheet
dBN
Eb 5.7:5.40
Date / Place E. Nemer - 42
TWTAdistortion
Microreflections
I / Q Imbalance
Weatherattenuat
Freq Err
Timingjitter
TWTAPhase Noise
Intermodproducts
Inband QAMinterference(adj satellites)
AWGN Antenna Temperaturenoise
LNBPhase Noise
AdjacentChannelInterf
Tx Nyq
Tx(I+jQ) symbols
Rx Nyq
Rx
(I+jQ) symbols
Modeling
TunerPhase Noise
Date / Place E. Nemer - 43
Tuner
AGCAFCNCO
I / Qbalancing
TimingRecovery
FFE
PLL
FBE
SlicerEqualizer
De-RandomizerA rsdecA
De-interleaverconv_dec
Channel De-coding
MPEG sync
SymbTo
bits
bits
bytes
1 samp/symb
2->4Samples/symbol Behavioral algorithmic
AFCestim
LPFADC
ADC
(I + j Q)
Baseband I & Q
Date / Place E. Nemer - 44
ADC
EnergyEstimate/correction
AGC
Functions : estimate and correct energy on I, Q inputs thru tuner feedback
Input is I and Q from tuner Sampling rate is [2 : 4] samples / symbolsCorrection : variable current output to the Tuner (only IF gain control)
AnalogGain
H(z)
gain
EnergyEstimate/correction
AGC
digitalGain
H(z)
ADC gain
6-8 bits 6 - 8 bits
Real System Model
Tuner
Date / Place E. Nemer - 45
digitalGain
6 bits
5 - 10 bits
Nominal Energy
11 z
Integrator
abs
abs
S1.411
1
z
S2.7S2.7
Parameter Format Bits
Input, Output
S1.4 S2.7
6
10
Constants S0.9 10
Tuner gain fct
10 bits
Output (10 bits)
Q
I
16 bits
S2.7
Date / Place E. Nemer - 46
AGC gain
Mag
Acquisition
Time (samples)
Date / Place E. Nemer - 47
I / Qcorrection
2.5 to 4Samples/symbol
2.5 to 4Samples/symbol
Q’
H(z)
1
1
EstimateMag Err
Estimatephs Err
I’T_I’
T_Q’
(I + j Q)
CorrectPhase
H(z)
Date / Place E. Nemer - 48
Equalizer out
Equalizer out
with IQ balancing
without IQ balancing
Rx Input with IQ imbalance
Date / Place E. Nemer - 49
NCOError
Detector
12-20 taps Tsym/2
ResamplerLoopFilter
Nyquist Filter
Output symbols
error
S2.7
S2.7
10 bits
20 bits
})5.0()]1()(Re{[
)(
nxnxnx
ne
S3.16
10 bits
Timing error
Notes• N : Nyquist taps, typically 12 to 20• Resampler, Nyquist filter and error detector operate at
2*Fsym.• Loop filter operates at Fsym.• NCO operates at Fsamp, typically Fsam=2.5*Fsym
Date / Place E. Nemer - 50
• Number of iterations to reach steady state decreases when first order loop gain increases.
• AWGN variance does not affect significantly the number of iterations to reach steady state.
Acquisition Time
Date / Place E. Nemer - 51
FFE
PLL
FBE
Slicer
Equalizer
• CMA : • Opens the eye ; QPSK : gain control • Blind : error criteria based on preset radius
• CMA / PLL • Stops the rotating constellation (due to freq / phase offset)• Uses CMA to update the FFE filter
3 stages…enabled sequencially
(I + j Q) (I + j Q)
1 samp/symb 1 samp/symb
• LMS / PLL • Decision-directed• Uses the CMA taps as a starting FFE• Continues a locked-on phase
Date / Place E. Nemer - 52
FFE filter
-
2S
grad
16 bits
S1.14
R
16 bits
S2.7
10 bits
S2.7
10 bits
W
16 taps
S0.20(16 effect)
Input symbols
22)( Rnyn *)()()( knxnnynGradk
)()()1( nGradnwnw kkk
Date / Place E. Nemer - 53
AWGN : Eb/No = 7.5
FreqOff: Fs/400
Date / Place E. Nemer - 54
FFE filerSlicer
-
2S
*je
grad
10 bits
S0.11
S2.7
10 bits
R
15 bits
16 bits
10 bits16 taps
Input symbols
LoopFilter
VCOPhase Detector
PLL
12 bits
next page
Date / Place E. Nemer - 55
11 z
1z
Loop filter
S0.5
12 bits
VCO
gainS0.12
6 bits
LoopFilter
VCOPhase Detector
2
*
d
dr
y
yyimerr
Phase detector
slicer in
slicer out
PLL
15 bits
Date / Place E. Nemer - 56
FFE filer
Phase Detector
Slicer
11 z
1z
*jeLoop filter
LMS
S0.5
15 bits
12 bits
S0.11
16 bits
S1.14
VCO
gainS0.12
FBE filer
LMS
Output symbols
*je
Error16 bits
Error16 bits
10 -12 bits
16 taps
6 bits
Input symbols
15 bits
12 bits
Nf
Nb
Date / Place E. Nemer - 57
FreqOff: Fs/400
4 Reflections : @ 36, 55, 85, 155 nsec
Date / Place E. Nemer - 58
FreqOff: Fs/400
4 Reflections : @ 36, 55, 85, 155 nsec
Date / Place E. Nemer - 59
• DVB-S2 is the second-generation specification for satellite broadcasting – developed
by the DVB (Digital Video Broadcasting) Project in 2003.
• Use a powerful FEC system based on LDPC (Low-Density Parity Check) codes
concatenated with BCH codes.
• Take advantage for combined with a variety of modulation formats (QPSK, 8PSK,
16APSK and 32APSK).
• For interactive applications, such as Internet navigation, it may implement Adaptive
Coding & Modulation (ACM), thus optimizing the transmission parameters for each
individual user.
• The DVB-S2 system has been designed for several satellite broadband applications
- Broadcast services for SDTV and HDTV
- Interactive services, including Internet access
- Digital TV contribution and News Gathering.
- Data content distribution and Internet trunking.
DVB-S2 – Overview
Date / Place E. Nemer - 60
• Broadcast Services- digital multi-programme Television (TV) / High
Definition Television (HDTV) broadcasting services to be used for
primary and secondary distribution in Fixed Satellite Service (FSS)
and Broadcast Satellite Service (BSS) bands.
(Including compatibility to MPEG-4)
• Digital TV Contribution and Satellite News Gathering (DTVC/DSNG)
• Interactive Services- Interactive data services including Internet
access (only the forward broadband channel)
• Data content distribution/trunking and other professional
applications (only the forward broadband channel)
DVB-S2 – Overview
Date / Place E. Nemer - 61
Performance Comparison
0
0.5
1
1.5
2
2.5
3
3.5
0 2 4 6 8 10 12
Eb / No
Bit
s/S
ec
/Hz
DVB-S and DSNG DVB-S2
2.5dB = 33% more useful data rate, or 2.5m Vs. 4.5m antenna
2.5 dB margin gain
signal-to-noise ratio
DVB-S2 – Overview
Date / Place E. Nemer - 62
13 SDTV MPEG2
26 SDTV h.264
10 SDTV MPEG2
20 SDTV h.264
10 SDTV MPEG2
21 SDTV h.264
7 SDTV MPEG2
15 SDTV h.264
3 HD MPEG2
6 HD h.264
2 HD MPEG2
5 HD h.264
2 HD MPEG2
5 HD h.264
1 HD MPEG2
3 HD h.264
58.8 Mbps (+32%)44.4 Mbps46 Mbps (+36%)33.8 Mbps
8PSK 23QPSK 7/8QPSK 3/4QPSK 2/3
29.7 Mbauds
(ROF 0.25)
27.5 Mbauds
(ROF 0.35)
30.9 Mbauds
(ROF 0.20)
27.5 Mbauds
(ROF 0.35)
DVB-S2DVB-SDVB-S2DVB-S
SATELLITE EIRP 53.7 dBWSATELLITE EIRP 51 dBW
Typical 36MHz transponder usage with DVB-S and DVB-S2:
Number of HD channels
Number of SD channels
Bit rate
Modulation
Symbol Rate
Roll-Off factor
DVB- S - S2 – Evolution
Date / Place E. Nemer - 63
Subject DVB-S DVB-DSNG DVB-S2
FEC Reed-Solomon &
Viterbi
Reed-Solomon &
Viterbi
LDPC
FEC rates 0.46 – 0.81 0.46 – 0.81 0.25 - 0.9
FEC Performance 2-2.5 dB better
Modulation BPSK, QPSK QPSK,8PSK,16QAM QPSK,8PSK,16APSK,32A
PSK
Max Spectral Efficiency 1.61 3.22 4.44
Block size ~ 32Kbit ~ 32Kbit 64Kbit , 16Kbit
Roll-off 0.35 0.35, 0.25 0.35, 0.25, 0.20
CCM/VCM/ACM CCM CCM VCM/ACM (for IP data)
Implementation
Complexity
Low Medium Very High
Stream adaptation MPEG MPEG MPEG & programmable
DVB- S - S2 – Evolution
Date / Place E. Nemer - 64
• Powerful FEC system based on LDPC (Low-Density Parity Check) codes
• Wide range of code rates (from 1/4 up to 9/10)
• New Modulation schemes ranging from 2 to 5 bit/second/Hz spectrum
efficiency - QPSK, 8PSK, 16APSK, 32APSK
• Set of three spectrum shapes with roll-off factors 0.35, 0.25 and 0.20
• Flexible stream adapter, suitable to operate with single and multiple TS on
the same carrier with different modulation and FEC
• Variable & Adaptive Coding and Modulation (VCM/ACM) functionality,
allowing to optimise channel coding and modulation on a frame-by-frame
basis.
DVB-S2 – Overview
Date / Place E. Nemer - 65
-3dB
35%
25%
-26dB
20%
DVB-S2 – Spectral Shape
Date / Place E. Nemer - 66
Non-uniform 8PSK constellationHierarchical QPSK
Sending, on a single Satellite channel, two Transport Streams - Hierarchical QPSK
• HP (High Priority) DVB-S (QPSK) – modulate for DVB-S
• LP (Low Priority) DVB-S2 (BPSK) ) – modulate for DVB-S2
Example: At QPSK ¾ it can add up to 17Mbps for new programs in DVB-S2. (36Mhz TP)
DVB-S2 – Hierarchical Modulation
Date / Place E. Nemer - 67
00
I
Q
10
11 01
Q=LSB I=MSB
000
I
Q
011
111
001
LSB
MSB
101
010
110
100
text
1100
1101 1111
1110
0000
0100
0101
0001
1001 1011
0011
0111
0110
0010
1010 1000
I
Q
= R2 / R1
LSB
MSB
R1
R2
text
10001
10011 10111
10101
00000
10000
10010
00010
00011 00111
00110
10110
10100
00100
00101 00001
I
Q
=R2 / R1
=R3 / R1
LSB
MSB
R1
R2
R3
11000
01000
11001
01001 01101
11101
01100
11100
11110
01110
11111
01111 01011
11011
01010
11010
QPSK2 bits/symbol
8PSK3 bits/symbol
16APSK4 bits/symbol
32APSK5 bits/symbol
DVB-S2 – Constellations
Date / Place E. Nemer - 68
• The System is defined as the functional block of equipment performing the
adaptation of the baseband digital signals.
• The System is designed to support source coding MPEG delivered directly
over IP protocols.
• If the received signal is above the C/N+I threshold, the Forward Error
Correction (FEC) technique adopted in the System is designed to provide
"less than one uncorrected error-event per transmission hour at the level of
a 5 Mbit/s single TV service decoder.
DVB-S2 – System Definition
Date / Place E. Nemer - 69
• Mode Adaptation Block
- It shall provide input stream interfacing, Input Stream Synchronization (optional), null-packet deletion (for ACM and Transport Stream input format only), CRC-8 coding for error detection at packet level in the receiver.
• Scrambler Block.
- Provide padding to complete a Base-Band Frame and Base-Band Scrambling.
• BCH Codes Block.
- In technical terms a BCH code is a multilevel cyclic variable-length digital error-correcting code used to correct multiple random error patterns.
- The principal advantage of BCH codes is the ease with which they can be decoded, via an elegant algebraic method known as syndrome decoding.
• LDPC Code Block.
- LDPC codes are a type of error-correcting code invented in the early 60's
- Low-density parity check codes are codes specified by a matrix.
DVB-S2 – Operations
Date / Place E. Nemer - 70
• Encoding shall be carried out by the concatenation of BCH outer codes and LDPC (Low Density Parity Check) inner codes (rates 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10) .
• This sub-system shall perform outer coding (BCH), Inner Coding (LDPC) and Bit interleaving .
• Input stream shall be composed of BBFRAMEs and the output stream of FECFRAME, each BBFRAME (Kbch bits) shall be processed by the FEC coding subsystem, to generate a FECFRAME
• The parity check bits (BCHFEC) of the systematic BCH outer code shall be appendedafter the BBFRAME, and the parity check bits (LDPCFEC) of the inner LDPC encodershall be appended after the BCHFEC field
DVB-S2 – FEC, Forward Error Correction
Date / Place E. Nemer - 71
Table Coding parameters for normal FECFRAME 64800ldpcn
Table Coding parameters (for normal FECFRAME 16200ldpcn
DVB-S2 – System Definition
Date / Place E. Nemer - 72
CCM Constant Coding and Modulation
All frames use the same (fixed) parameters
VCM Variable Coding and Modulation
Different streams/services are coded with different (fixed)
parameters on the same carrier
ACM Adaptive Coding and Modulation
Each frame is coded with its own set of parameters. Parameters
are modified dynamically according to the reception conditions for
each receiver
DVB-S2 Operation Mode
Date / Place E. Nemer - 73
• QPSK, 8PSK, 16APSK and 32APSK
constellations shall be applied, depending on
the application area
• Shall be applied, to shape the signal spectrum
(squared-root raised cosine, roll-off factors
0,35 or 0,25 or 0,20) and to generate the RF
signal..
• The roll-off factor, , is a measure of the excess
bandwidth of the filter.
• The graph shows the amplitude response as
is varied between 0 and 1, and the
corresponding effect on the impulse response.