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FIT 1005 Networks & Data Communications

FIT 1005 Networks & Data Communications. Lecture 4 – Signal Encoding Techniques Reference: Chapter 5 Data and Computer Communications Eighth Edition by William Stallings Lecture slides by Lawrie Brown Modified Slides: http://users.monash.edu.au/~amkhan/fit1005. Digital Data to

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FIT 1005 Networks & Data Communications

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  1. FIT 1005 Networks & Data Communications Lecture 4 – Signal Encoding Techniques Reference: Chapter 5 Data and Computer Communications Eighth Edition by William Stallings Lecture slides by Lawrie Brown Modified Slides: http://users.monash.edu.au/~amkhan/fit1005

  2. Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Type of • Data • digital • analog • Signal • digital • analog • Data Encoding (Schemes) • digital to digital • digital to analog • analog to digital • analog to analog

  3. Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Type of • Data • digital • analog • Signal • digital • analog • Data Encoding (converted into) • Converting source data  into communication signal • digital to digital • digital to  analog • analog to  digital • analog to  analog

  4. Analog Data Voice (sound waves) Telephone Analog Signal Digital Data Binary Voltage pulses Analog Signal (Carrier frequency) Modem • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Data can be encoded in either form of signals Analog Signals

  5. Analog Data Digital Signal CODEC Analog data Digital Data Digital Transmitter Digital Signal Digital data • Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Data can be encoded in either form of signals Digital Signals

  6. Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Signal Encoding Techniques (1) • Digital signaling: For digital signaling, a data source g(t), which may be either digital or analog, is encoded into a digital signal x(t). • Analog signaling: The basis for analog signaling is a continuous constant-frequency fc signal known as the Carrier signal. E.g. AM or FM • Baseband signal: The input signal may be analog or digital and is called the modulating signal or baseband signal. • Baseband signals are the fundamental group of frequencies in an analog or digital waveform that may be transmitted along a channel. Examples of a digital baseband signal may be Ethernet signals operating over a LAN

  7. Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Encoding is required because • Signals are carried by the physical medium • The performance of medium will vary depending on the kind of signal, with varying characteristics in terms of • Attenuation • Error rate • Distance • etc….

  8. Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Encoding signal

  9. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Modulation signal

  10. Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Signal Encoding Techniques (2) • The electromagnetic signal is generated at the physicallayer • The electromagnetic signal could be analog or digital signals that must carry the data(message). • The data must be encoded into signals: • Data Encoding is done to produce a analog or digital signal • Modulation of a analog/digital data is used to produce an analog signal • This analog signal can then be transmitted over a network/communication link.

  11. Digital Data • to • Digital Signal • Summary • Analog Data • to • Analog Signal • Data Types • Signal Encoding • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Which one of the 4 combinations to choose? • Digital data/Digital signal • Equipment for encoding is less complex • Digital transmission has less errors • Analog data/Digital signal • Digital transmission can be done on the existing analog medium – good return on investment (ROI) • Digital transmission has less errors • Digital data/Analog signal • Some high data rate mediums are analog (e.g. optical fiber) • most of the unguided media are analog (e.g. Wireless) • Analog data/Analog signal • Can be transmitted easily and cheaply; different position on the spectrum can be shared on the same media (e.g. Frequency-division multiplexing)

  12. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Data to Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Data Encoding

  13. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Data Encoding • digital data to digital signal • analog data to analog signal • digital data to analog signal • analog data to digital signal

  14. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Digital Data, Digital Signal • Digital signal • discrete, discontinuous voltage pulses • each pulse is a signal element • binary data encoded into signal elements

  15. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Propertiesthat need to be considered while encoding • At least 5 properties need to be considered when encoding any form of data to any signals • Signal spectrum requirement • Signal synchronization capability • Signal error-detecting capability • Signal interference and noise immunity • Cost and complexity of the encoding/decoding equipment.

  16. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Property 1 • Signal spectrum • digital signal can contain infinite frequencies  high bandwidth is required • Conversely lack of high frequency component means less bandwidth required for transmission (cheaper) • No DC component - otherwise the decoding equipment can be expensive

  17. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal What is DC Component? • A non-zero constant value of the Fourier series transformation of a signal is the value of the DC component • If the signal varies between positive and negative voltages, then a non-zero difference in the area above and below the zero voltage line implies that the signal has a DC component

  18. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal What is DC Component? 0 0 + dc component 0 - dc component 0 0

  19. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Property 2 • Signal synchronization capability • Need to determine the beginning and end of each bit position. • Not an easy task • May need a separate clock between sender and receiver to synchronize themor • embedded

  20. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Property 3 • Signal Error-detecting capability • can the encoding technique identify (and correct) errors when the signal is corrupted? • Parity or CRC

  21. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Property 4 • Signal interference and noise immunity • Certain encoded signals can be decoded correctly when the signal is corrupted due to interferences or inducement of noise.

  22. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Encoding • Unfortunately we will not be able to achieve all the first four properties at the cheapest cost by a single encoding technique. • Hence cost is an last important factor that needs to be considered as well • Each encoding technique will satisfy (either fully or partially) only a sub-set of the properties.

  23. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Signal element versus data element Encoding requires to distinguish between Signal element and data element Ratio r is defined as number of data elements carried by each signal elements

  24. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Some Popular Encoding Schemes of Digital data to Digital signals

  25. Some Terms used w.r.t Digital data to  Digital signals Unipolar all signal elements have either +ve or –ve voltage (same sign) Bipolar one logic state is represented by a +ve voltage and the other by a –ve voltage data rate rate of data transmission in bits per second duration or length of a bit time taken for the transmitter to emit a bit = 1/data rate modulation rate rate at which the signal level changes, measured in baud = number of signal elements per second mark and space another term for binary 1 and binary 0 • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal

  26. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Encoding Schemes Has more desirable properties

  27. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Nonreturn to Zero-Level (NRZ-L) • two different voltages for 0 and 1 bits • 0 bit  0 / +vevoltage • 1 bit  -vevoltage • voltage constant during bit interval • no mid-bit transition - i.e. no return to zero voltage • one can use absence of voltage for 0, constant positive voltage for 1 but becomes a DC component problem • more often, negative voltage for 1 (mark) and positive voltage for 0 (space) • NRZ-L is typically the code used to generate or interpret digital data by terminals and other devices Zero / positive volts Presence of -vevoltage

  28. Nonreturn to Zero Invert on ones (NRZI) 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 no transition denotes binary 0 • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal

  29. Nonreturn to Zero Invert on ones (NRZI) 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 no transition denotes binary 0 example of differential encoding since we have data represented by changes rather than levels more reliable detection of transition rather than level easy to lose sense of polarity & synchronization • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal

  30. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal NRZ Pros & Cons • Pros • easy to design encoder and decoder • make good use of bandwidth • Cons • dc component • lack of synchronization capability • used for magnetic recording • not often used for signal transmission

  31. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Multilevel Binary Bipolar-AMI • Use more than two levels • Bipolar-AMI • zero represented by no line signal • one represented by positive or negative pulse • one pulses alternate in polarity • no loss of sync if a long string of ones • long runs of zeros still a problem • no net dc component • lower bandwidth • easy error detection because of the alternation of the polarity • Used on a T-carrier communication links

  32. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Multilevel Binary Pseudoternary • one represented by absence of line signal • zero represented by alternating positive and negative • no advantage or disadvantage over Multilevel binary bipolar

  33. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Multilevel Binary Issues • synchronization with long runs of 0’s (in the case Bipolar-AMI) or 1’s (in the case of pseudoternary) • can insert additional bits to force transitions, ( as in ISDN ) • Insertion causes  wasted bit transmission  leads to reduced transmission rate • not as efficient as NRZ • each signal element only represents one bit • receiver distinguishes between three levels: +A, 0, -A • a 3 voltage level system could represent log23 = 1.58 bits • requires approx. 3dB more signal power for same probability of bit error

  34. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Manchester Encoding • has transition in the middle of each bit period • transition serves as clock and data (property 2) • low to high represents one • high to low represents zero • An example of a bipolar encoding method • Specified for the IEEE 802 –Ethernet standards

  35. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Differential Manchester Encoding • Mid-bit transition can be used for clocking • transition at start of bit period representing 0 • no transition at start of bit period representing 1 • this is a differential encoding scheme • used by IEEE 802.5 - token ring LANs 1

  36. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal What does differential encoding mean? • In differential encoding, the signal is decoded by • comparing the polarity of adjacent signal elements • rather than determining the absolute value of a signal element. • In other words it looks for a transition rather than the absolute value. • The above would require synchronisation with respect to the sender.

  37. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Differential Manchester Encoding • At least 4 properties need to considered when encoding digital data to digital signals • 1. Signal spectrum requirement - less DC component and less frequency spectrum  • 2. Signal synchronization capability – by the mid-bit transition  • 3. Signal error-detecting capability  • 4. Signal interference and noise immunity –signal is decoded by comparing the polarity of adjacent signal elements rather then the absolute value of the signal element  • 5. Cost and complexity of the encoding/decoding equipment.  - partially met

  38. Biphase Pros and Cons Con at least one transition per bit time and possibly two maximum modulation rate is twice NRZ requires more bandwidth Pros synchronization on mid bit transition (self clocking) has no dc component has error detection • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal

  39. Scrambling Scrambling replaces long sequences of 0..0’s that would produce constant voltage by a special codes. these filling sequences must produce enough transitions to provide synchronization Should be recognized by receiver & replaced with original data be of same length as original sequence and hence no date rate reduction design goals have no dc component have no long sequences of zero level line signal have no reduction in data rate give error detection capability • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal

  40. B8ZS and HDB3 • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal B8ZS (Bipolar with 8-zeros substitution) If an octet of all zeros occurs last voltage pulse is positive, Encoded as 000+–0–+ If an octet of all zeros occurs Last voltage pulse is negative, Encoded as 000–+0+– - ve 0 0 0 - + 0 + - HDB3 (High-Density Bipolar 3-zeros) If string of Four zeros sequences occurs The fourth zero(0) is replaced with a code violation(+- or -+ pulses). Successive violations are replaced with alternate polarity.

  41. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Data Encoding •  digital data to digital signal • analog data to analog signal • digital data to analog signal • analog data to digital signal

  42. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Analog data, Analog Signal • By modulating the data (baseband) with a high carrier signal fc. • Why? • higher frequency fc can give more efficient transmission & BW • permits frequency division multiplexing (chapter 8)

  43. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Modulation • is a process of encoding an analog (or digital) data on to an analog carrier signal whose frequency, say is f c Where f c is a high frequency • Input – analog (digital) data – called baseband or modulating signal m(t) • Output - analog signal - carried modulated signal s(t) Amplitude Modulated Signal M(t) ʘ Fc(t) Analog Data modulating Signal m(t) High Frequency Signal Fc(t) Communication channel

  44. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Modulation Techniques • is to vary one of the following three aspects of the carrier signal • Amplitude of the carrier (Amplitude modulation (AM)) • Frequency of the carrier (Frequency modulation (FM)) • Phase of the carrier (Phase modulation(PM)) • Example – AM and FM radio stations for the first two respectively

  45. Analog ModulationTechniques • Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Amplitude Modulation Phase Modulation Frequency Modulation

  46. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Data Encoding • digital to digital • analog to analog • digital to analog • analog to digital

  47. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Digital Data, Analog Signal • Use the same modulation techniques discussed for analog data, analog signals • main use is public telephone system • has freq range of 300Hz to 3400Hz • use modem (modulator-demodulator) • encoding techniques • Amplitude shift keying (ASK) • Frequency shift keying (FSK) • Phase shift keying (PK)

  48. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Digital Data, Analog Signal – Modulation Techniques Digital Data Amplitude Shift keying Frequency Shift keying Phase Shift keying

  49. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal Amplitude Shift Keying • encode 0/1 by different carrier amplitudes • usually have one amplitude zero • susceptible to sudden gain changes • inefficient • used for • up to 1200bps on voice grade lines • very high speeds over optical fiber s(t) = A * Sin (2π f t + θ) A = Amplitude f = carrier frequency θ = Phase Angle “0” = 0 * Sin (2πf t + 0) “1” = A * Sin (2πf t + 0)

  50. Digital Data • to • Digital Signal • Summary • Data Types • Signal Encoding • Analog Data • to • Analog Signal • Analog Signal & • Digital Signals • Signal Encoding • Digital Data • to • Analog Signal • Analog Data • To • Digital Signal 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 • high frequency radio • even higher frequency on LANs using co-axial cable s(t) = A * Sin (2π f t + θ) A = Amplitude f = carrier frequency θ = Phase Angle “0” = A * Sin (2πf1 t + 0) “1” = A * Sin (2πf2 t + 0)

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