Download presentation

1
**Information Sources and Signals**

Asst. Prof. Chaiporn Jaikaeo, Ph.D. Computer Engineering Department Kasetsart University, Bangkok, Thailand Adapted from the notes by Lami Kaya, © 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.

2
**Analog vs. Digital Data Analog data Digital data**

Data take on continuous values E.g., human voice, your weights, temperature reading Numerical representation: real numbers Digital data Data take on discrete values E.g., number of students in class, text data Numerical representation: integers

3
**Analog vs. Digital Signals**

To be transmitted, data must be transformed to electromagnetic signals Analog signals have an infinite number of values in a range Digital signals Have a limited number of values

4
**Data and Signals Analog Data Analog Signal Digital Data Analog Signal**

Telephone Analog Data Analog Signal Modem Digital Data Analog Signal Codec Analog Data Digital Signal Digital Transmitter/ Line Coder Digital Data Digital Signal

5
**x(t) = x(t+T) - < t < **

Periodic Signals A periodic signal completes a pattern within a timeframe, called a period A signal x(t) is periodic if and only if x(t) = x(t+T) - < t < value period time

6
**Sine Waves Simplest form of periodic signal**

General form: x(t) = A×sin(2ft + ) period T = 1/f peak amplitude time signal strength phase / phase shift

7
**Sine Signal Characteristics**

Frequency ( f ): the number of oscillations per unit time (usually seconds) Amplitude ( A ): the difference between the maximum and minimum signal heights Phase ( ): how far the start of the sine wave is shifted from a reference time 7

8
**Varying Sine Waves A = 1, f = 1, = 0 A = 2, f = 1, = 0**

9
**Sine Signal Characteristics**

The frequency can be calculated as the inverse of the time required for one cycle, which is known as the period Examples: period T = 1 seconds frequency is 1 / T or 1 Hertz period T = 0.5 seconds frequency is 2 Hertz 9

10
**Time and Frequency Units**

11
Composite Signals Consider the signal + =

12
**Composite Signals A mathematician named Fourier discovered that**

Joseph Fourier ( ) Composite Signals A mathematician named Fourier discovered that It is possible to decompose a composite signal into series of sine functions Each with different frequency, amplitude, and phase = +

13
**Time vs. Frequency Domains**

1 -1 2 4 time signal level 1 -1 2 4 signal level frequency Time Domain Representation plots amplitude as a function of time Frequency Domain Representation plots each sine wave’s peak amplitude against its frequency Frequency domain representation is much easier for analysis

14
Bandwidth of Signal Bandwidth of a signal is the difference between the highest and lowest frequencies of the signal 14

15
**Digital Signals and Signal Levels**

Two-level signal Each level represents 1 bit Four-level signal Each level represents 2 bits 15

16
Example How many different levels are required if we want each level to represent n bits?

17
**Baud and Bit Rate Baud How many times a signal changes per second**

Bit rate How many bits can be sent per time unit (usually per second) Bit rate is controlled by baud and number of signal levels 1 sec 1 00 11 10 01 1 sec Baud = 10 Bit rate = 10 bps Baud = 10 Bit rate = 20 bps

18
Baud and Bit Rate Relationship between baud, signal levels, and bit rate is: Example: What is the bit rate (in bps) of a 16-level signal transmitted at 20 baud

19
**Transmission Latency Composed of Propagation time Transmission time**

Queuing time Processing time Entire message propagation time transmission time

20
**Transmission Latency Sender Receiver First bit leaves Data bits**

Propagation time First bit arrives Transmission time Last bit leaves Last bit arrives Time Time

21
**Fourier Analysis of Digital Signals**

Digital signals consist of infinite set of sine waves What is the bandwidth? + + + + …

22
**Bandwidth of a Medium Most transmission media have bandwidth limit f f**

1 (low-pass channel) gain freq f0 3f0 5f0 7f0 ... 9f0 f f0 3f0 5f0 f Transmission medium t t

23
**Line Coding The process of encoding digital data into digital signal**

Example: Manchester encoding (used in Ethernet LAN)

24
Synchronization The electronics at both ends of a medium must have circuitry to measure time precisely Easy at low bit rate Much more difficult at high bit rate

25
Synchronization Good line coding schemes allow receiver to synchronize its timing to match the sender's 1 1 1 1 1 1 1 Bad Good

26
Line Coding Schemes

27
**Converting Analog to Digital**

Common technique: Pulse Code Modulation (PCM)

28
**PCM: Sampling and Quantizing**

quantizing (rounding to nearest integer) Sampling points

29
PCM: The Whole Picture * *PAM: Pulse Amplitude Modulation

30
**Minimum Sampling Rate Nyquist Theorem:**

Ex. Find the maximum sampling interval for recording human voice (freq. range 300Hz – 3000Hz) t sampling interval

31
**Nyquist’s Sampling Theorem**

See also: Wagon-wheel effect

32
Example Calculate the minimum bit rate for recoding human voice, if each sample requires 60 levels of precision (Human voice has range of 300Hz – 3000Hz)

33
Data Compression Data compression refers to a technique that reduces the number of bits required to represent data Lossy - some information is lost during compression (e.g, JPG, MP3) Lossless - all information is retained in the compressed version (e.g., PNG, PCM)

34
**Summary Data and signals Signal as series of sine waves Bandwidth**

Fourier analysis Bandwidth Line coding Analog to digital conversion PCM Data compression

Similar presentations

OK

Lifecycle from Sound to Digital to Sound. Characteristics of Sound Amplitude Wavelength (w) Frequency ( ) Timbre Hearing: [20Hz – 20KHz] Speech: [200Hz.

Lifecycle from Sound to Digital to Sound. Characteristics of Sound Amplitude Wavelength (w) Frequency ( ) Timbre Hearing: [20Hz – 20KHz] Speech: [200Hz.

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Download ppt on conservation of biodiversity Ppt on marketing download Export pdf to ppt online free Free download ppt on autonomous car What does appt only meant Ppt on ac and dc motors Ppt on diffusion of solid in liquid Ppt on global warming for students free download Ppt on ms word 2007 tutorial Ppt on leadership skills download