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Data and Computer Communications Eighth Edition by William Stallings Lecture slides by Lawrie Brown Chapter 5 – Signal Encoding Techniques.

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Presentasi berjudul: "Data and Computer Communications Eighth Edition by William Stallings Lecture slides by Lawrie Brown Chapter 5 – Signal Encoding Techniques."— Transcript presentasi:

1 Data and Computer Communications Eighth Edition by William Stallings Lecture slides by Lawrie Brown Chapter 5 – Signal Encoding Techniques

2 Signal Encoding Techniques Even the natives have difficulty mastering this peculiar vocabulary —The Golden Bough, Sir James George Frazer

3 PENGODEAN DATA  Karakter data yang akan dikirim dari suatu titik ke titik yang lain tidak dapat dikirim secara langsung.  Karakter-karakter data tersebut harus dikodekan terlebih dahulu dengan kode yang dikenal oleh setiap terminal yang ada  Ttujuan dari pengodean adalah menjadikan setiap karakter dalam sebuah informasi digital ke dalam bentuk biner agar dapat ditransmisikan.

4 KODE-KODE  Kode yang digunakan pada komunikasi data : 1.BCD (Binary Coded Decimal) 2.SBCDIC (Standard Binary Coded Decimal Interchange Code) Interchange Code) 3. EBCDIC (Extended Binary Coded Decimal Interchange Code) Interchange Code) 4. BOUDDOT 5.ASCII (American Satndard Code for Information Interchange) Interchange)

5 KODE BCD : Binary Coded Decimal Kode biner yang mewakili 0 – 9, yang merupakan kombinasi 4 bit, Kombinasi kode maksimal 16, tapi yang digunakan hanya 0-9 dan tidak bisa untuk huruf. BCD 4 Bit Decimal

6 KODE SBCDIC: Standard Binary Coded Decimal Interchange Code Kombinasi 6 bit, kombinasi maksimal 64 kode, 10 kode untuk angka, 26 kode untuk huruf, sisanya untuk kode yang lain. BA8421KARAK TER BA8421KARAK TER BA8421KARAK TER BA8421KARAK TER ABCDEFGHIJABCDEFGHIJ KLMNOPQRSTKLMNOPQRST UVWXYZUVWXYZ

7 KODE EBCDIC :Extended Binary Coded Decimal Interchange Code Kode 8 bit, maksimal karakter 256 Pada EBCDIC, hight –order bits atau 4 bit pertama disebut zone bit dan low-order bits atau 4 bit kedua disebut dengan numeric bit. Merupakan pengembangan dari kode 6 bit yang dipakai untuk kartu berlubang. Dipakai pada komputer generasi ketiga, seperti pada IBM

8 KODE BOUDOT Terdiri dari 5 bit yang digunakan pada terminal teletype dan teleprinter Terdiri dari 25 sampai 32 kombinasi dengan kode huruf dan gambar yang berbeda. KodeHurufFigureKodeHurufFigureKodeHurufFigure ABCDEFGHIJKLMNOPABCDEFGHIJKLMNOP -?:$3!‘().,90-?:$3!‘()., Q R S T U V W X Y Z LTRS FIGS SPC CR LF NULL 1 4 BELL 5 7 ; 2 / 6 = LTRS FIGS SPC CR LF NULL

9 KODE ASCII:American Standard Code for Information Interchange ASCII 7 Bit standar alfabet no. 5 berdasarkan ISO Kode ini menggunakan 7 bit dan bit yang kedelapan digunakan untuk posisi pengecekan bit secara even atau odd parity. Memiliki 128 kombinasi yang selalu digunakan. 32 kode untuk fungsi kendali, yang lain untuk alphanumeric dan karakter khusus. KODE ASCII

10 Dari 128 kode ASCII, 34 untuk keperluan khusus seperti : Null = Null SOH = Start Of Heading STX = Start Of Text ETX = End Of Text EOT = End of Transmission ENQ = ENQuiry ACK = ACKnowledge BEL = Audible signal (Bell) DLE = Data Link Escape DC1 = Device Control 1 DC2 = Device Control 2 DC3 = Device Control 3 DC4 = Device Control 4 NAK = Negative Acknowledge SYN = SYNchronous idle ETB =End Transmissin Block BS = Backspace HT = Horizontal Tab LF = Line Feed VT = Vertical Tab FF = Form Feed CR = Carriage Return SO = Shift Out SI = Shift In DEL = Delete CAN = Cancel EM = End of Medium SUB =Subtitute ESC = Escape FS = File Separation GS = Group Separator RS = Record Separator US = Unit Separator SP = Space Kode ASCII terdiri dari karakter kontrol dan karakter informasi. Karakter kontrol untuk mengontrol pengiriman data, sedangkan karakter informasi merupakan karakter2 yang mewakili data itu sendiri

11 Kode ASCII 8 bit, mempunyai kombinasi bit yang lebih banyak, sehingga karakter-karakter yang tidak dapat diwakili 7 bit, dapat dibuat dengan kode ASCII 8 bit UNICODE Digunakan untuk menuliskan kata-kata sesuai dengan bahasa ibu. Dengan kata lain, negara-negara yang berbeda menggunakan karakter berbeda.

12 Signal Encoding Techniques

13 Macam-macam Teknik Pengkodean 1. Digital data, digital signals: simplest form of digital encoding of digital data (Data digital, sinyal digital) 2. Digital data, analog signal: A modem converts digital data to an analog signal so that it can be transmitted over an analog (Data digital, sinyal analog) 3. Analog data, digital signals: Analog data, such as voice and video, are often digitized to be able to use digital transmission facilities (Data analog, sinyal digital) 4. Analog data, analog signals: Analog data are modulated by a carrier frequency to produce an analog signal in a different frequency band, which can be utilized on an analog transmission system (Data analog,sinyal analog)

14 1.Data digital, sinyal digital: Pengkodean digital untuk data digital adalah menugaskan satu tingkat tegangan ke biner 1 atau sedangkan lainnya ke biner 0.Sedangkan untuk yang lebih kompleks memerlukan sustu sinkronisasi data. 2.Data digital,sinyal analog:Sebuah modem mengubah data digital menjadi sinyal analog sehingga dapat ditransmisikan melalaui jalur analog. Teknik dasar yang digunakan adalah amplitude shift keying(ASK), frequency shift keying (FSK), dan phase shift keying (PSK). 3.Data analog,sinyal digital:Seperti suara dan video didigtalkan supaya dapat ditransmisikan pada fasilitas transmisi digital.Salah satu teknik yang digunalan adalah pulse code modulation, yang mencakup sampling data analog secara periodeik dan menguantifikasikan sampel-sampel tersebut. 4.Data analog, sinyal analog: Data analog dimodulasi oleh sebuah frekuensi pembawa untuk menghasilkan sinyal analog dengan band frekuensi yang berbeda yang dapat digunakan pada sistem transmisi analog. Teknik yang dipergunakan adalah AM, FM, PM (phase modulation). Macam-macam Teknik Pengkodean

15 Digital Data, Digital Signal  Digital signal discrete, discontinuous voltage pulses discrete, discontinuous voltage pulses each pulse is a signal element each pulse is a signal element binary data encoded into signal elements binary data encoded into signal elements

16 1.Data Digital, Sinyal Digital Data digital merupakan data yang memiliki deretan nilai yang berbeda dan memiliki ciri-ciri tersendiri.Salah satu contoh data digital adalah teks, bilangan bulat dan karakter yang lain. permasalahannya adalah data tersebut

17 Some Terms  unipolar  polar  data rate  duration or length of a bit  modulation rate  mark and space

18 Istilah-istilah yang berhubungan dengan data digital-sinyal digital: 1.Elemen sinyal adalah tiap pulsa dari sinyal digital, data biner ditransmisikan dengan meng-encode-kan tiap bit data menjadi elemen-elemen sinyal. 2.Sinyal unipolar adalah semua elemen sinyal yang mempunyai tanda yang sama, yaitu positif semua atau negatif semua. 3.Sinyal polar adalah elemen-elemen sinyal di mana salah satu kondisi logik diwakili oleh level tegangan positif dan yang lainnya oleh level tegangan negatif. 4.Durasi atau lebar suatu bit adalah waktu yang diperlukan oleh pemancar untuk memancarkan bit tersebut. 5.Modulation rate adalah kecepatan di mana level sinyal berubah, dimana dinyatakan dalam bauds atau elemen sinyal perdetik 6.Mark dan space menyatakan digit biner 1 dan 0

19 Tugas pesawat penerima dalam mengartikan sinyal digital : 1.RX harus mengetahui timing tiap bit 2.RX harus menentukan apakah level sinyal dalam posisi bit high(1) atau Low(0) Proses diatas dilakuak dengan proses Sampling Faktor yang menetukan kesuksesan RX : 1.Data rate (kecepatan data) : peningkatan kecepatan data akan meningkatkan BIT ERROR RATE /BER ( kecepatan kesalahan bit) 2.S/N : peningkatan S/N akan menurunkan kecepatan bit 3.Bandwidth : peningkatan bandwidth dapat meningkatkan kecepatan data

20 Interpreting Signals  need to know timing of bits - when they start and end timing of bits - when they start and end signal levels signal levels  factors affecting signal interpretation signal to noise ratio signal to noise ratio data rate data rate bandwidth bandwidth encoding scheme encoding scheme

21 Comparison of Encoding Schemes  signal spectrum  clocking  error detection  signal interference and noise immunity  cost and complexity

22 Encoding Schemes

23 Nonreturn to Zero-Level (NRZ-L)  two different voltages for 0 and 1 bits  voltage constant during bit interval no transition I.e. no return to zero voltage no transition I.e. no return to zero voltage such as absence of voltage for zero, constant positive voltage for one such as absence of voltage for zero, constant positive voltage for one more often, negative voltage for one value and positive for the other more often, negative voltage for one value and positive for the other

24 Nonreturn to Zero Inverted  nonreturn to zero inverted on ones  constant voltage pulse for duration of bit  data encoded as presence or absence of signal transition at beginning of bit time transition (low to high or high to low) denotes binary 1 transition (low to high or high to low) denotes binary 1 no transition denotes binary 0 no transition denotes binary 0  example of differential encoding since have data represented by changes rather than levels data represented by changes rather than levels more reliable detection of transition rather than level more reliable detection of transition rather than level easy to lose sense of polarity easy to lose sense of polarity

25 NRZ Pros & Cons  Pros easy to engineer easy to engineer make good use of bandwidth make good use of bandwidth  Cons dc component dc component lack of synchronization capability lack of synchronization capability  used for magnetic recording  not often used for signal transmission

26 Multilevel Binary Bipolar-AMI  Use more than two levels  Bipolar-AMI zero represented by no line signal zero represented by no line signal one represented by positive or negative pulse one represented by positive or negative pulse one pulses alternate in polarity one pulses alternate in polarity no loss of sync if a long string of ones no loss of sync if a long string of ones long runs of zeros still a problem long runs of zeros still a problem no net dc component no net dc component lower bandwidth lower bandwidth easy error detection easy error detection

27 Multilevel Binary Pseudoternary  one represented by absence of line signal  zero represented by alternating positive and negative  no advantage or disadvantage over bipolar-AMI  each used in some applications

28 Multilevel Binary Issues  synchronization with long runs of 0’s or 1’s can insert additional bits, cf ISDN can insert additional bits, cf ISDN scramble data (later) scramble data (later)  not as efficient as NRZ each signal element only represents one bit each signal element only represents one bit receiver distinguishes between three levels: +A, -A, 0receiver distinguishes between three levels: +A, -A, 0 a 3 level system could represent log 2 3 = 1.58 bits a 3 level system could represent log 2 3 = 1.58 bits requires approx. 3dB more signal power for same probability of bit error requires approx. 3dB more signal power for same probability of bit error

29 Manchester Encoding  has transition in middle of each bit period  transition serves as clock and data  low to high represents one  high to low represents zero  used by IEEE 802.

30 Differential Manchester Encoding  midbit transition is clocking only  transition at start of bit period representing 0  no transition at start of bit period representing 1 this is a differential encoding scheme this is a differential encoding scheme  used by IEEE 802.5

31 Biphase Pros and Cons  Con at least one transition per bit time and possibly two at least one transition per bit time and possibly two maximum modulation rate is twice NRZ maximum modulation rate is twice NRZ requires more bandwidth requires more bandwidth  Pros synchronization on mid bit transition (self clocking) synchronization on mid bit transition (self clocking) has no dc component has no dc component has error detection has error detection

32 Modulation Rate

33 Scrambling  use scrambling to replace sequences that would produce constant voltage  these filling sequences must produce enough transitions to sync produce enough transitions to sync be recognized by receiver & replaced with original be recognized by receiver & replaced with original be same length as original be same length as original  design goals have no dc component have no dc component have no long sequences of zero level line signal have no long sequences of zero level line signal have no reduction in data rate have no reduction in data rate give error detection capability give error detection capability

34 B8ZS and HDB3

35 Digital Data, Analog Signal  main use is public telephone system has freq range of 300Hz to 3400Hz has freq range of 300Hz to 3400Hz use modem (modulator-demodulator) use modem (modulator-demodulator)  encoding techniques Amplitude shift keying (ASK) Amplitude shift keying (ASK) Frequency shift keying (FSK) Frequency shift keying (FSK) Phase shift keying (PK) Phase shift keying (PK)

36 Data digital, Sinyal Analog Contoh umum transmisi data digital dengan menggunakan sinyal analog adalah Public Telephone Network. Perangkat yang dipakai adalah MODEM (modulator-demodulator) yang mengubah data digital ke sinyal analog (modulator) dan sebaliknya mengubah sinyal analog menjadi sinyal digital (demodulator). Teknik-teknik Penyandian: Tiga teknik penyandian untuk mengubah data digital menjadi sinyal analog : 1.Amplitudo Shift Keying (ASK) 2.Frequency Shift Keying (FSK) 3.Phase Shift Keying (PSK)

37 Modulation Techniques

38 Amplitude Shift Keying  encode 0/1 by different carrier amplitudes usually have one amplitude zero usually have one amplitude zero  susceptible to sudden gain changes  inefficient  used for up to 1200bps on voice grade lines up to 1200bps on voice grade lines very high speeds over optical fiber very high speeds over optical fiber

39 Amplitudo Shift Keying (ASK) Dua biner diwakilkan dengan dua amplitudo frekuensi pembawa yang berbeda. Salah satu dari amplitudo adalah nol; satu digit biner yang ditunjukkan mellaui keberadaan sinyal paad amplitudo yang konstan dari suatu sinyal pembawa. Dapat dinyatakan sebagai berikut : A cos (2Π f1t + Θc ) biner 1 S(t) = 0 biner 0

40 Binary Frequency Shift Keying  most common is binary FSK (BFSK)  two binary values represented by two different frequencies (near carrier)  less susceptible to error than ASK  used for up to 1200bps on voice grade lines up to 1200bps on voice grade lines high frequency radio high frequency radio even higher frequency on LANs using co-ax even higher frequency on LANs using co-ax

41 Frequency Shift Keying (FSK) Dua biner diwakili oleh dua frekuensi berbeda yang dekat dengan pembawa frekuensi atau dinyatakan sebagai A cos (2Π f1t + Θc ) biner 1 S(t) = A cos (2Π f2t + Θc ) biner 0 Kecepatan data dapat mencapai 1200 bps pada voice grade line, dipakai untuk transmisi radio frekuensi tinggi dan juga jaringan lokal dengan frekuensi tinggi yang memakai kabel koaksial.

42 Multiple FSK  each signalling element represents more than one bit  more than two frequencies used  more bandwidth efficient  more prone to error

43 Phase Shift Keying  phase of carrier signal is shifted to represent data  binary PSK two phases represent two binary digits two phases represent two binary digits  differential PSK phase shifted relative to previous transmission rather than some reference signal phase shifted relative to previous transmission rather than some reference signal

44 Phase Shift Keying (PSK) Biner 0 diwakilkan dengan mengirim suatu sinyal dengan fase yang sama terhadap fase sebelumnya dan biner 1 diwakilkan dengan mengirim suatu sinyal dengan fase berlawanan dengan sinyal yang dikirim sebelumnya, atau dinyatakan sebagai berikut : A cos (2Π f1t + Π ) biner 1 S(t) = A cos (2Π f2t ) biner 0

45 Quadrature PSK  get more efficient use if each signal element represents more than one bit eg. shifts of  /2 (90 o ) eg. shifts of  /2 (90 o ) each element represents two bits each element represents two bits split input data stream in two & modulate onto carrier & phase shifted carrier split input data stream in two & modulate onto carrier & phase shifted carrier  can use 8 phase angles & more than one amplitude 9600bps modem uses 12 angles, four of which have two amplitudes 9600bps modem uses 12 angles, four of which have two amplitudes

46 QPSK and OQPSK Modulators

47 Performance of Digital to Analog Modulation Schemes  bandwidth ASK/PSK bandwidth directly relates to bit rate ASK/PSK bandwidth directly relates to bit rate multilevel PSK gives significant improvements multilevel PSK gives significant improvements  in presence of noise: bit error rate of PSK and QPSK are about 3dB superior to ASK and FSK bit error rate of PSK and QPSK are about 3dB superior to ASK and FSK for MFSK & MPSK have tradeoff between bandwidth efficiency and error performance for MFSK & MPSK have tradeoff between bandwidth efficiency and error performance

48 Quadrature Amplitude Modulation  QAM used on asymmetric digital subscriber line (ADSL) and some wireless  combination of ASK and PSK  logical extension of QPSK  send two different signals simultaneously on same carrier frequency use two copies of carrier, one shifted 90 ° use two copies of carrier, one shifted 90 ° each carrier is ASK modulated each carrier is ASK modulated two independent signals over same medium two independent signals over same medium demodulate and combine for original binary output demodulate and combine for original binary output

49 QAM Modulator

50 QAM Variants  two level ASK each of two streams in one of two states each of two streams in one of two states four state system four state system essentially QPSK essentially QPSK  four level ASK combined stream in one of 16 states combined stream in one of 16 states  have 64 and 256 state systems  improved data rate for given bandwidth but increased potential error rate but increased potential error rate

51 Analog Data, Digital Signal  digitization is conversion of analog data into digital data which can then: be transmitted using NRZ-L be transmitted using NRZ-L be transmitted using code other than NRZ-L be transmitted using code other than NRZ-L be converted to analog signal be converted to analog signal  analog to digital conversion done using a codec pulse code modulation pulse code modulation delta modulation delta modulation

52 Digitizing Analog Data

53 Pulse Code Modulation (PCM)  sampling theorem: “If a signal is sampled at regular intervals at a rate higher than twice the highest signal frequency, the samples contain all information in original signal” “If a signal is sampled at regular intervals at a rate higher than twice the highest signal frequency, the samples contain all information in original signal” eg. 4000Hz voice data, requires 8000 sample per sec eg. 4000Hz voice data, requires 8000 sample per sec  strictly have analog samples Pulse Amplitude Modulation (PAM) Pulse Amplitude Modulation (PAM)  so assign each a digital value

54 PCM Example

55 PCM Block Diagram

56 Non-Linear Coding

57 Companding

58 Delta Modulation  analog input is approximated by a staircase function can move up or down one level (  ) at each sample interval can move up or down one level (  ) at each sample interval  has binary behavior since function only moves up or down at each sample interval since function only moves up or down at each sample interval hence can encode each sample as single bit hence can encode each sample as single bit 1 for up or 0 for down 1 for up or 0 for down

59 Delta Modulation Example

60 Delta Modulation Operation

61 PCM verses Delta Modulation  DM has simplicity compared to PCM  but has worse SNR  issue of bandwidth used eg. for good voice reproduction with PCM eg. for good voice reproduction with PCM want 128 levels (7 bit) & voice bandwidth 4khzwant 128 levels (7 bit) & voice bandwidth 4khz need 8000 x 7 = 56kbpsneed 8000 x 7 = 56kbps  data compression can improve on this  still growing demand for digital signals use of repeaters, TDM, efficient switching use of repeaters, TDM, efficient switching  PCM preferred to DM for analog signals

62 Analog Data, Analog Signals  modulate carrier frequency with analog data  why modulate analog signals? higher frequency can give more efficient transmission higher frequency can give more efficient transmission permits frequency division multiplexing (chapter 8) permits frequency division multiplexing (chapter 8)  types of modulation Amplitude Amplitude Frequency Frequency Phase Phase

63 Analog Modulation Techniques  Amplitude Modulation  Frequency Modulation  Phase Modulation

64 Summary  looked at signal encoding techniques digital data, digital signal digital data, digital signal analog data, digital signal analog data, digital signal digital data, analog signal digital data, analog signal analog data, analog signal analog data, analog signal


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