1 / 10

Modulation

Modulation. Conversion of digital information to analog signals Example: Telephone lines are band-limited (300-3300Hz) Modem = mo dulator/ dem odulator Characteristics of defining sine waves: Amplitude Frequency Phase. Change one or more of them to send information. Modulation.

remy
Download Presentation

Modulation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Modulation • Conversion of digital information to analog signals • Example: Telephone lines are band-limited (300-3300Hz) • Modem = modulator/demodulator • Characteristics of defining sine waves: • Amplitude • Frequency • Phase Change one or more of them to send information ECE 766 Computer Interfacing and Protocols

  2. Modulation • Modulation Techniques • Amplitude Shift Keying (ASK) • Frequency Shift Keying (FSK) • Phase Shift Keying (PSK) • Aspects of Modulation • Bit rate vs. Baud rateBit rate ≥ Baud rate • Carrier Signal Quadrature AmplitudeModulation (QAM) ECE 766 Computer Interfacing and Protocols

  3. 1 1 0 0 Amplitude Time 1 baud 1 baud 1 baud 1 baud 1 second Amplitude Shift Keying (ASK) • Basic technique (like AM)  change the amplitude of the signal to transfer logical values • On-Off Keying (OOK) • Highly susceptible to noise • Inefficient ECE 766 Computer Interfacing and Protocols

  4. Amplitude Minimum Bandwidth = Nbaud Frequency fc fc-(Nbaud/2) fc+(Nbaud/2) Amplitude Shift Keying (ASK) • Bandwidth requirement • BW = (1+d) x Nbaud • d ≥ 0  related to the condition of the line ECE 766 Computer Interfacing and Protocols

  5. 1 1 0 0 Amplitude Time 1 baud 1 baud 1 baud 1 baud 1 second Frequency Shift Keying (FSK) • Represent each logical value with another frequency (like FM) • Not susceptible to noise as much as ASK • Limiting factor: Physical capabilities of the carrier ECE 766 Computer Interfacing and Protocols

  6. Amplitude BW=fc1--fc0+Nbaud fc1--fc0 Nbaud/2 Nbaud/2 Frequency fc0 fc1 Frequency Shift Keying (FSK) • Bandwidth requirement • How about duplex communication? ECE 766 Computer Interfacing and Protocols

  7. Reference 1 1 0 0 Amplitude Time 1 baud 1 baud 1 baud 1 baud 1 second Phase Shift Keying (PSK) • Use different phased signals to represent binary values • 0 = in phase with reference • 1 = out of phase with reference • Not practical ECE 766 Computer Interfacing and Protocols

  8. 1 1 0 0 Amplitude Time 1 baud 1 baud 1 baud 1 baud 1 second 1 0 Phase Shift Keying (PSK) • Differential PSK • 0 = same phase as last signal element • 1 = 180º shift from last signal element • Constellation Diagram: ECE 766 Computer Interfacing and Protocols

  9. 010 01 011 001 10 00 100 000 111 101 11 110 4-PSK (Q-PSK) 8-PSK Phase Shift Keying (PSK) • Quadrature Phase Shift Keying (Q-PSK):Do not only use 180º shift • Min. BW requirement: same as ASK! • Self clocking (most cases) ECE 766 Computer Interfacing and Protocols

  10. Quadrature Amplitude Modulation (QAM) • Combine ASK and PSK such that each signal corresponds to multiple bits • More phases than amplitudes • Minimum bandwidth requirement same as ASK or PSK 3 amplitudes 12 phases ECE 766 Computer Interfacing and Protocols

More Related