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Fundamentals of Data and Signals

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งานนำเสนอเรื่อง: "Fundamentals of Data and Signals"— ใบสำเนางานนำเสนอ:

1 Fundamentals of Data and Signals
Chapter Two Fundamentals of Data and Signals

2 Objective สามารถอธิบายความแตกต่างระหว่างข้อมูลและสัญญาณ และสามารถบอกถึงประโยชน์ของข้อมูลและสัญญาณดิจิตอล ผ่านข้อมูลและสัญญาณอนาล็อก สามารถระบุองค์ประกอบพื้นฐานทั้ง 3 ของสัญญาณได้ สามารถอธิบายแบนด์วิธของสัญญาณ และความสัมพันธ์ที่เกี่ยวข้องกับความเร็วในการถ่ายโอนข้อมูล สามารถระบุความแรงและความเบาบางของสัญญาณ และมีความสัมพันธ์กันอย่างไร สามารถระบุคุณสมบัติพื้นฐานของการส่งข้อมูลอนาล็อกกับสัญญาณอนาล็อก, ข้อมูลดิจิตอลกับสัญญาณดิจิตอล, ข้อมูลดิจิตอลกับสัญญาณอนาล็อก และข้อมูลอนาล็อกกับสัญญาณดิจิตอล สามารถระบุและออกแบบแผนภาพ เทคนิคการเข้ารหัสดิจิตอลพื้นฐาน และอธิบายข้อดี/ข้อเสียของแต่ละเทคนิค สามารถแยกแยะเทคนิคการมอดูเลชั่นในรูปแบบต่างๆ รวมถึงสามารถอธิบายข้อดี ข้อเสีย และการนำไปใช้ได้อย่างถูกต้อง สามารถบอกถึงเทคนิคดิจิไทซ์เซชั่น ทั้ง 2 เทคนิคที่นิยมใช้ และอธิบายข้อดีข้อเสียของแต่ละเทคนิค สามารถอธิบายความแตกต่างของรหัสข้อมูล และนำไปประยุกต์ใช้ในระบบการสื่อสารได้

3 Introduction – Data and Signals
Chapter Two - Fundamentals of Data and Signals Introduction – Data and Signals Data are entities that convey meaning (computer file, music on CD, results from a blood gas analysis machine) Signals are the electric or electromagnetic encoding of data (telephone conversation, we page download) Computer networks and data/voice communication systems transmit signals Data and signals can be analog or digital

4 Four Combinations of Data and Signals
Chapter Two - Fundamentals of Data and Signals Four Combinations of Data and Signals

5 Analog versus Digital Analog is a continuous waveform, with examples
Chapter Two - Fundamentals of Data and Signals Analog versus Digital Analog is a continuous waveform, with examples such as (naturally occurring) music and voice

6 Analog versus Digital Chapter Two - Fundamentals of Data and Signals
It is harder to separate noise from an analog signal than it is to separate noise from a digital signal (imagine the following waveform is a symphony with noise embedded)

7 Analog versus Digital Chapter Two - Fundamentals of Data and Signals
Digital is a discrete or non-continuous waveform with examples such as computer 1s and 0s

8 Chapter Two - Fundamentals of Data and Signals
Analog versus Digital Noise in a digital signal. You can still discern a high voltage from a low voltage

9 Analog versus Digital Chapter Two - Fundamentals of Data and Signals
Noise in a digital signal. Too much noise – you cannot discern a high voltage from a low voltage

10 All Signals Have Three Components
Chapter Two - Fundamentals of Data and Signals All Signals Have Three Components Amplitude Frequency Phase

11 Amplitude Chapter Two - Fundamentals of Data and Signals
The amplitude of a signal is the height of the wave above or below a given reference point

12 Chapter Two - Fundamentals of Data and Signals
Frequency The frequency is the number of times a signal makes a complete cycle within a given time frame; frequency is measured in Hertz (Hz), or cycles per second Spectrum – the range of frequencies that a signal spans from minimum to maximum Bandwidth – the absolute value of the difference between the lowest and highest frequencies of a signal

13 Chapter Two - Fundamentals of Data and Signals

14 Frequency For example, consider an average voice
Chapter Two - Fundamentals of Data and Signals Frequency For example, consider an average voice The average voice has a frequency range of roughly 300 Hz to 3100 Hz The spectrum would be 300 – 3100 Hz The bandwidth would be 2800 Hz

15 Chapter Two - Fundamentals of Data and Signals
Phase The phase of a signal is the position of the waveform relative to a given moment of time or relative to time zero A change in phase can be any number of angles between 0 and 360 degrees Phase changes often occur on common angles, such as 45, 90, 135, etc.

16 Chapter Two - Fundamentals of Data and Signals

17 Signal Strength Chapter Two - Fundamentals of Data and Signals
All signals experience loss (attenuation) Attenuation is denoted as a decibel (dB) loss Decibel losses (and gains) are additive

18 Signal Strength So if a signal loses 3 dB, is that a lot?
Chapter Two - Fundamentals of Data and Signals Signal Strength So if a signal loses 3 dB, is that a lot? A 3 dB loss indicates the signal lost half of its power dB = 10 log10 (P2 / P1) -3 dB = 10 log10 (X / 100) -0.3 = log10 (X / 100) = X / 100 0.50 = X / 100 X = 50

19 Converting Analog Data into Analog Signals
Chapter Two - Fundamentals of Data and Signals Converting Analog Data into Analog Signals In order to transmit analog data, you can modulate the data onto a set of analog signals Broadcast radio and television are two very common examples of this

20 Amplitude modulation (e.g. AM radio)
Chapter Two - Fundamentals of Data and Signals Amplitude modulation (e.g. AM radio)

21 Converting Digital Data into Digital Signals
Chapter Two - Fundamentals of Data and Signals Converting Digital Data into Digital Signals There are numerous techniques available to convert digital data into digital signals. Let’s examine five: NRZ-L NRZ-I Manchester Differential Manchester Bipolar AMI

22

23 Chapter Two - Fundamentals of Data and Signals
Note how with a Differential Manchester code, every bit has at least one significant change. Some bits have two signal changes per bit (baud rate = twice bps)

24 Chapter Two - Fundamentals of Data and Signals
4B/5B Digital Encoding Yet another encoding technique that converts four bits of data into five-bit quantities The five-bit quantities are unique in that no five-bit code has more than 2 consecutive zeroes The five-bit code is then transmitted using an NRZ-I encoded signal

25 Chapter Two - Fundamentals of Data and Signals

26 Converting Digital Data into Analog Signals
Chapter Two - Fundamentals of Data and Signals Converting Digital Data into Analog Signals Three basic techniques: Amplitude shift keying Frequency shift keying Phase shift keying

27 Amplitude Shift Keying
Chapter Two - Fundamentals of Data and Signals Amplitude Shift Keying One amplitude encodes a 0 while another amplitude encodes a 1 (a form of amplitude modulation)

28 Amplitude Shift Keying
Chapter Two - Fundamentals of Data and Signals Amplitude Shift Keying Some systems use multiple amplitudes

29 Multiple Signal Levels
Chapter Two - Fundamentals of Data and Signals Multiple Signal Levels Why use multiple signal levels? We can represent two levels with a single bit, 0 or 1 We can represent four levels with two bits: 00, 01, 10, 11 We can represent eight levels with three bits: 000, 001, 010, 011, 100, 101, 110, 111 Note that the number of levels is always a power of 2

30 Frequency Shift Keying
Chapter Two - Fundamentals of Data and Signals Frequency Shift Keying One frequency encodes a 0 while another frequency encodes a 1 (a form of frequency modulation)

31 Chapter Two - Fundamentals of Data and Signals
Phase Shift Keying One phase change encodes a 0 while another phase change encodes a 1 (a form of phase modulation)

32 Quadrature Phase Shift Keying
Chapter Two - Fundamentals of Data and Signals Quadrature Phase Shift Keying Four different phase angles used 45 degrees 135 degrees 225 degrees 315 degrees

33 Chapter Two - Fundamentals of Data and Signals

34 Quadrature Amplitude Modulation
Chapter Two - Fundamentals of Data and Signals Quadrature Amplitude Modulation As an example of QAM, 12 different phases are combined with two different amplitudes Since only 4 phase angles have 2 different amplitudes, there are a total of 16 combinations With 16 signal combinations, each baud equals 4 bits of information (2 ^ 4 = 16)

35 Chapter Two - Fundamentals of Data and Signals

36 Higher Data Transfer Rates
Chapter Two - Fundamentals of Data and Signals Higher Data Transfer Rates How do you send data faster? Use a higher frequency signal (make sure the medium can handle the higher frequency Use a higher number of signal levels In both cases, noise can be a problem

37 Maximum Data Transfer Rates
Chapter Two - Fundamentals of Data and Signals Maximum Data Transfer Rates How do you calculate a maximum data rate? Use Shannon’s equation S(f) = f x log2 (1 + S/N) Where f = signal frequency (bandwidth), S is the signal power in watts, and N is the noise power in watts

38 Maximum Data Transfer Rates
Chapter Two - Fundamentals of Data and Signals Maximum Data Transfer Rates For example, what is the data rate of a 3400 Hz signal with 0.2 watts of pwer and watts of noise? S(f) = 3400 x log2 ( /0.0002) = 3400 x log2 (1001) = 3400 x 9.97 = bps

39 Converting Analog Data into Digital Signals
Chapter Two - Fundamentals of Data and Signals Converting Analog Data into Digital Signals To convert analog data into a digital signal, there are two techniques: Pulse code modulation (the more common) Delta modulation

40 Pulse Code Modulation Chapter Two - Fundamentals of Data and Signals
The analog waveform is sampled at specific intervals and the “snapshots” are converted to binary values

41 Pulse Code Modulation Chapter Two - Fundamentals of Data and Signals
When the binary values are later converted to an analog signal, a waveform similar to the original results

42 Pulse Code Modulation Chapter Two - Fundamentals of Data and Signals
The more snapshots taken in the same amount of time, or the more quantization levels, the better the resolution

43 Chapter Two - Fundamentals of Data and Signals
Pulse Code Modulation Since telephone systems digitize human voice, and since the human voice has a fairly narrow bandwidth, telephone systems can digitize voice into either 128 or 256 levels These are called quantization levels If 128 levels, then each sample is 7 bits (2 ^ 7 = 128) If 256 levels, then each sample is 8 bits (2 ^ 8 = 256)

44 Chapter Two - Fundamentals of Data and Signals
Pulse Code Modulation How fast do you have to sample an input source to get a fairly accurate representation? Nyquist says 2 times the highest frequency Thus, if you want to digitize voice (4000 Hz), you need to sample at 8000 samples per second

45 Chapter Two - Fundamentals of Data and Signals
Delta Modulation An analog waveform is tracked, using a binary 1 to represent a rise in voltage, and a 0 to represent a drop

46 Chapter Two - Fundamentals of Data and Signals
Data Codes The set of all textual characters or symbols and their corresponding binary patterns is called a data code There are three common data code sets: EBCDIC ASCII Unicode

47 Data and Signal Conversions in Action
Chapter Two - Fundamentals of Data and Signals Data and Signal Conversions in Action Let us transmit the message “Sam, what time is the meeting with accounting? Hannah.” This message leaves Hannah’s workstation and travels across a local area network

48 Chapter Two - Fundamentals of Data and Signals
EBCDIC

49 Chapter Two - Fundamentals of Data and Signals
ASCII

50 Unicode Each character is 16 bits
Chapter Two - Fundamentals of Data and Signals Unicode Each character is 16 bits A large number of languages / character sets For example: T equals r equals a equals

51 Data and Signal Conversions in Action
Chapter Two - Fundamentals of Data and Signals Data and Signal Conversions in Action

52 Data and Signal Conversions in Action
Chapter Two - Fundamentals of Data and Signals Data and Signal Conversions in Action

53 Workshop จงอธิบายคำศัพท์ต่อไปนี้ data, signals, spectrum, bandwidth, bit rate, baud rate, sampling rate จงคำนวณหาแบนด์วิธที่มีการเปลี่ยนแปลงความถี่จาก50เฮิร์ต เป็น500 เฮิร์ต จงวาดรูปแสดงภาพของแรงดัน(Voltage) เพื่อนำเสนอในรูปแบบของบิต“ ” เพื่อเข้ารหัสดังต่อไปนี้ NRZ-L, NRCI, Manchester, Differential Manchester และ Bipolar-AMI ดังรูปที่ 2-12 จงวาดภาพคลื่นอนาล็อกของข้อความบิต “ ” โดยใช้การมอดูเลชันเชิงเลขทางขนาด(ASK), การมอดูเลชันเชิงเลขทางความถี่ (FSK) และการมอดูเลชันเชิงเลขทางเฟส (PSK)


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