# KOMUNIKASI SATELIT DIGITAL Sukiswo sukiswokyahoo com Komunikasi Satelit

• Slides: 40

KOMUNIKASI SATELIT DIGITAL Sukiswo sukiswok@yahoo. com Komunikasi Satelit, Sukiswo, ST, MT 1

Outline 4 Channel Coding & The Power Bandwidth Trade-Off 4 Coded Modulation 4 End to End Error Control 4 Digital Video Broadcasting via Satellite (DVB-S) 4 Second Generation DVB-S Komunikasi Satelit, Sukiswo, ST, MT 2

Channel Coding & The Power Bandwidth Trade-Off Komunikasi Satelit, Sukiswo, ST, MT 3

Coding with variable bandwidth 4 Coding allows bandwidth to be exchanged for power, so the link performance can be optimised with respect to cost. This is paramount in the design of a link. 4 Consider a satellite link which conveys an information bit rate Rb= 2, 048 Mbit/s using BPSK with spectral efficiency = 0, 7 bit s-1 Hz -1 The objective bit error rate is BER=10 -6. (a) Without coding =1 The transmitted bit rate is Rc =Rb=2, 048 Mbit/s The bandwidth used is Bnocod=Rc/ =2, 048/0, 7=2, 9 MHz The theoretical required value for Eb/N 0 (not taking into account implementation degradation) : Komunikasi Satelit, Sukiswo, ST, MT 4

Coding with variable bandwidth (b) Without coding <1 Assume for instance =7/8 The transmitted bit rate is Rc =Rb/ =2, 048/(7/8)=2, 34 Mbit/s The bandwidth used is Bcod=Rc/ = 2, 34 /0, 7=3, 34 MHz The theoretical required value for Eb/N 0 (not taking into account implementation degradation) : Komunikasi Satelit, Sukiswo, ST, MT 5

Coding with variable bandwidth The reduction C/N 0 is equal to the decoding gain: Komunikasi Satelit, Sukiswo, ST, MT 6

Coding with constant bandwidth 4 Coding with constant bandwidth is performed when a given bandwidth is allocated to a given link. 4 Coding is introduced without changing the carrier bandwidth B and therefore at a constant transmitted rate Rc. Consequently, the information bit rate Rb must be reduced. Komunikasi Satelit, Sukiswo, ST, MT 7

Coded Modulation Komunikasi Satelit, Sukiswo, ST, MT 8

Coded modulation 4 Coded modulation is a technique where FEC and modulation, instead of being performed in two separate steps, are merged into one process. 4 Redundancy is achieved not by adding redundant bits as in the schemes described above, but by expanding the alphabet of the modulation with respect to common schemes such as BPSK and QPSK. 4 Thus, to transmit n information bits per symbol duration Ts, a modulation based on an enlarged alphabet of M =2 m = 2 n+1 symbols is used Komunikasi Satelit, Sukiswo, ST, MT 9

Coded modulation 4 Therefore n =m-1 bits are transmitted per symbol instead of m and this technique results in a modulated carrier with slightly less spectral efficiency than M-PSK modulation, but a significant reduction in Eb/N 0 for the required bit error rate (BER). 4 For instance, coded 8 -PSK can offer up to 6 d. B reduction in Eb/N 0 compared to uncoded QPSK, for the same theoretical spectral efficiency (2 bit s-1 Hz-1) 4 There are two main classes of coded modulation: – trellis coded modulation (TCM) where convolutional encoding is implemented; – block coded modulation (BCM) using block encoding. Komunikasi Satelit, Sukiswo, ST, MT 10

TCM 8 PSK Komunikasi Satelit, Sukiswo, ST, MT 11

TCM Encoder Komunikasi Satelit, Sukiswo, ST, MT 12

Coded modulation 4 Coded modulation conveys a sequence {sk} where sk is a symbol from an M-ary alphabet at instant k. Ts. 4 All sequences are part of a specific set designed so that the minimum distance between all pairs of two sequences, called the free distance dfree, is as large as possible in order to reduce the error probability; dfree is defined by: 4 Best performance in terms of asymptotic coding gain Gcod ( ) (coding gain when Eb/N 0 ) is achieved with maximum dfree and the smallest average number Nfree of sequences at this distance. Komunikasi Satelit, Sukiswo, ST, MT 13

Coded modulation 4 The asymptotic coding gain is usually calculated with reference to an uncoded modulation which transmits the same average number of information bits per symbol duration Ts. 4 Denoting by dunc the minimum distance between all pairs of two symbols of the uncoded modulation, the asymptotic coding gain is given by: where Ecod and Eunc are the average signal energies of the coded and the uncoded schemes respectively. Komunikasi Satelit, Sukiswo, ST, MT 14

Performance of coded modulations Komunikasi Satelit, Sukiswo, ST, MT 15

End to End Error Control Komunikasi Satelit, Sukiswo, ST, MT 16

End to End Error Control 4 The above techniques for error control offer quasi-error- free (QEF) transmission (BER < 10 -10) at the expense of power or bandwidth. 4 QEF transmission can also be achieved by using a different technique based on end-to-end error control, implying retransmission of information identified as being corrupted at the receiving end at the expense of a variable delivery delay. This is called automatic repeat request (ARQ). Komunikasi Satelit, Sukiswo, ST, MT 17

End to End Error Control 4 Due to the variable delay, this technique applies particularly to data packet transmission. 4 The decoder detects errors but does not correct them: a retransmission request is sent to the transmitter. 4 It is, therefore, necessary to provide a return channel. This can be a satellite or terrestrial channel 4 Three basic techniques are employed : – retransmission with stop and wait or reception acknowledgement (ARQ Stop-and-wait); – continuous retransmission (Go-Back-N ARQ); – selective retransmission (Selective-repeat ARQ). Komunikasi Satelit, Sukiswo, ST, MT 18

End to End Error Control 4 The performance is measured in terms of efficiency, expressed as the ratio of the mean number of information bits transmitted in a given time interval to the total number of bits which could be transmitted during the same time. 4 Consider a digital satellite link with a capacity of R=48 kbit/s. The round-trip return time is taken to be TRT =600 ms. The bit error rate is BER =10 -4. Transmission is in blocks of n=1000 bits. Komunikasi Satelit, Sukiswo, ST, MT 19

End to End Error Control 4 The block error probability is PB=1 -(1 -BEP)n =1 -exp(- n. BEP) for n. BEP <<1, hence PB =0, 1. 4 Assuming that any error is detected: – efficiency in ARQ-SW: = n(1 -PB)/RTRT = 0, 03 – efficiency in ARQ-GB (N): =n(1 -PB)/[n(1 -PB)+ RTRTPB] =0, 2 – efficiency in ARQ-SR: =1 -PB = 0, 9 4 The increase in efficiency from one technique to another is accompanied by an increase in the complexity of the equipment. Komunikasi Satelit, Sukiswo, ST, MT 20

Error detection with retransmission (a) ARQ Stop-and-wait, (b) Go-Back-N ARQ and (c) Selective-repeat ARQ. Komunikasi Satelit, Sukiswo, ST, MT 21

Digital Video Broadcasting Via Satellite (DVB-S) Komunikasi Satelit, Sukiswo, ST, MT 22

DVB-S 4 Broadcasters, service providers, operators, equipment and chips manufacturers, etc. worked together at the end of the 1980 s to define a digital video broadcasting (DVB) standard. 4 This standard has been broken down into different versions depending on the specific properties of the transmission channel which conditions the physical layer characteristics: DVB-T for terrestrial digital TV, DVB-C for cable, DVB-S for satellite. 4 Later standards have been introduced: DVB-RCS for the return channel, DVB-S 2 (the second generation of DVBS), DVB-H for handheld terminals, DVB-SH for satellite handheld terminals, etc. Komunikasi Satelit, Sukiswo, ST, MT 23

DVB-S 4 The DVB-S system provides direct-to-home (DTH) services for consumer integrated receiver decoders (IRD), as well as collective antenna systems (satellite master antenna television—SMATV) and cable television headend stations. 4 The overview covers the physical layer that comprises adaptation, framing, coding, interleaving and modulation, and discusses error performance requirements to achieve quality of service (Qo. S) targets. Komunikasi Satelit, Sukiswo, ST, MT 24

DVB-S : Transmission system 4 The transmission system consists of the functional block of equipment to transport baseband TV signals in the format of the MPEG-2 transport stream over the satellite channel. The transmission system carries out the following processes on the data stream: – transport multiplex adaptation and randomisation for energy dispersal; – outer coding (i. e. Reed–Solomon); – convolutional interleaving; – inner coding (i. e. punctured convolutional code); – baseband shaping for modulation; – modulation Komunikasi Satelit, Sukiswo, ST, MT 25

DVB-S 4 Digital satellite TV services have to be delivered to home terminals with rather small antennas (around 0. 6 m) which translate typically into a power-limited downlink. 4 To achieve a high power efficiency without excessively penalising the spectrum efficiency, the DVB-S uses QPSK modulation and the concatenation of convolutional and RS codes. 4 The convolutional code can be configured flexibly, allowing the optimisation of the system performance for a given satellite transponder bandwidth. Komunikasi Satelit, Sukiswo, ST, MT 26

DVB-S 4 DVB-S is directly compatible with MPEG-2 coded TV signals (defined by ISO/IEC DIS 13818 -1). 4 The modem transmission frame is synchronous with the MPEG-2 multiplex transport packets. 4 If the received signal is above the considered threshold for the carrier-to-noise power ratio, C/N, the FEC technique can provide a quasi-error-free (QEF) quality target. 4 The QEF means BER less than 10 -10 to 10 -11 at the input of the MPEG-2 demultiplexer. Komunikasi Satelit, Sukiswo, ST, MT 27

DVB-S : Input stream scrambling 4 The DVB-S input stream is the MPEG-2 transport stream (MPEG-TS) from the transport multiplexer. 4 The packet length of the MPEG-TS is 188 bytes. This includes one sync-word byte (i. e. 47 HEX). 4 The processing order at the transmitting side starts from the most significant bit (MSB). 4 The polynomial for the pseudorandom binary sequence (PRBS) generator is defined as: Komunikasi Satelit, Sukiswo, ST, MT 28

DVB-S : Input stream scrambling Komunikasi Satelit, Sukiswo, ST, MT 29

Reed–Solomon outer coding 4 Reed–Solomon is applied to the packet sync byte, either noninverted (i. e. 47 HEX) or inverted (i. e. B 8 HEX). 4 The code generator polynomial is: 4 The Reed–Solomon RS(204, 188, T¼ 8) shortened code, from the original RS(255, 239, T¼ 8) code, is applied to each randomised transport packet (188 bytes) Komunikasi Satelit, Sukiswo, ST, MT 30

DVB-S : Frame Structure Komunikasi Satelit, Sukiswo, ST, MT 31

DVB-S : Frame Structure Komunikasi Satelit, Sukiswo, ST, MT 32

DVB-S : Transmission system Komunikasi Satelit, Sukiswo, ST, MT 33

DVB-S 2 4 The DVB-S standard uses QPSK modulation and concatenated convolutional and Reed–Solomon channel coding. 4 It has been adopted by most satellite operators worldwide for television and data broadcasting services. 4 Digital satellite transmission technology has evolved significantly in several areas since the first publication of the DVB-S standard in 1994. 4 Without going into too many details of the standard, this section provides a brief summary of DVB-S 2’s new technology, transmission system architecture and performance. Komunikasi Satelit, Sukiswo, ST, MT 34

New technology in DVB-S 2 4 DVB-S 2 makes use of the new developments in technology and future applications of broadband satellite applications. 4 The main features can be summarised as the following: – new channel coding schemes to achieve a capacity gain in the order of 30%; – variable coding and modulation (VCM) to provide different levels of error protection to different service components (e. g. SDTV and HDTV, audio, multimedia); – extended flexibility to cope with other input data formats (such as multiple transport streams or generic data formats in addition to the single MPEG transport stream (MPEG-TS) in DVB-S) without significant complexity increase. Komunikasi Satelit, Sukiswo, ST, MT 35

Transmission system architecture 4 The DVB-S 2 system consists of a number of functional blocks of equipment performing the adaptation of the baseband digital signals from the output of one or more MPEG transport stream multiplexers (ISO/IEC 13818 -1) or one or more generic data sources to the satellite channel characteristics. 4 Data services may be transported in transport stream format according to (EN-301 -192) (e. g. using multi-protocol encapsulation (MPE)) or generic stream (GS) format. 4 DVB-S 2 provides a QEF quality target of ‘less than one uncorrected error event per transmission hour at the level of a 5 Mbit/s single TV service decoder’, approximately corresponding to a transport stream packet error ratio (PER) of less than 10 -7 before de-multiplexer. Komunikasi Satelit, Sukiswo, ST, MT 36

DVB-S 2 Komunikasi Satelit, Sukiswo, ST, MT 37

Error performance 4 The error performance is described to meet the QEF requirements. 4 Table illustrates the error performance provided in the DVB-S 2 standard, as a function of the ratio of the average energy per transmitted symbol, Es, to the noise power spectral density N 0 (Es/N 0, expressed in d. B) 4 Eb/N 0=Es/N 0 -10 log( tot). tot =Spectral efficiency Komunikasi Satelit, Sukiswo, ST, MT 38

Es/N 0 quasi-error-free performance (PER=10 -7) Komunikasi Satelit, Sukiswo, ST, MT 39

Transmisi Telepon & video broadcasting 4 Perhitungan Transmisi Telepon & video broadcasting (lihat buku referensi) Komunikasi Satelit, Sukiswo, ST, MT 40