LECTURE 12: SIGNAL MODULATION AND DEMODULATION

Slides:



Advertisements
Similar presentations
Signal Encoding Techniques
Advertisements

ECE 8443 – Pattern Recognition EE 3512 – Signals: Continuous and Discrete Objectives: Response to a Sinusoidal Input Frequency Analysis of an RC Circuit.
ECE 8443 – Pattern Recognition EE 3512 – Signals: Continuous and Discrete Objectives: Generalized Fourier Transform Analog Modulation Amplitude Modulation.
Department of Electronics and CommunicationsEngineeringYANSAHAN UNIVERSITY Department of Electronics and Communications Engineering YANSAHAN UNIVERSITY.
Lecture 7 AM and FM Signal Demodulation
Amplitude Modulation Wei Li CSULB May 22, 2006.
Principles of analogue modulation
1 Single Side Band Suppressed Carrier Professor Z Ghassemlooy Electronics and IT Division School of Engineering Sheffield Hallam University U.K.
Angle Modulation Objectives
MODULATION.
C H A P T E R 4 AMPLITUDE MODULATIONS AND DEMODULATIONS
Standard Amplitude Modulation (AM)
COMMUNICATION SYSTEMS- CONTINUOUS
IT-101 Section 001 Lecture #15 Introduction to Information Technology.
Chapter 4 Amplitude Modulation. Baseband vs Passband Transmission  Baseband signals: Voice (0-4kHz) TV (0-6 MHz)  A signal may be sent in its baseband.
… Representation of a CT Signal Using Impulse Functions
ELEC ENG 4035 Communications IV1 School of Electrical & Electronic Engineering 1 Section 2: Frequency Domain Analysis Contents 2.1 Fourier Series 2.2 Fourier.
Lecture 1. References In no particular order Modern Digital and Analog Communication Systems, B. P. Lathi, 3 rd edition, 1998 Communication Systems Engineering,
Prof. Brian L. Evans Dept. of Electrical and Computer Engineering The University of Texas at Austin EE345S Real-Time Digital Signal Processing Lab Spring.
Prof. Brian L. Evans Dept. of Electrical and Computer Engineering The University of Texas at Austin EE345S Real-Time Digital Signal Processing Lab Fall.
Signal and Systems Prof. H. Sameti Chapter 8: Complex Exponential Amplitude Modulation Sinusoidal AM Demodulation of Sinusoidal AM Single-Sideband (SSB)
Multiplexing.
Prof. Brian L. Evans Dept. of Electrical and Computer Engineering The University of Texas at Austin EE445S Real-Time Digital Signal Processing Lab Fall.
Signals and Systems Fall 2003 Lecture #15 28 October Complex Exponential Amplitude Modulation 2. Sinusoidal AM 3. Demodulation of Sinusoidal AM.
Course Outline (Tentative)
8.0 Communication Systems Modulation: embedding an information-bearing signal into a second signal e.g. – purposes : locate the signal on the right band.
Lecture 18-19: Linear Modulations Aliazam Abbasfar.
Wireless PHY: Modulation and Demodulation Y. Richard Yang 09/6/2012.
Introduction to Communication Prepared By Dr. Hany Taher Modified by: Dr. Mouaaz Nahas.
ECE 8443 – Pattern Recognition EE 3512 – Signals: Continuous and Discrete Objectives: Linearity Time Shift and Time Reversal Multiplication Integration.
ECE 8443 – Pattern Recognition ECE 3163 – Signals and Systems Objectives: Derivation Transform Pairs Response of LTI Systems Transforms of Periodic Signals.
ECE 8443 – Pattern Recognition EE 3512 – Signals: Continuous and Discrete Objectives: Review Resources: Wiki: Superheterodyne Receivers RE: Superheterodyne.
Eeng Chapter 4 Bandpass Circuits   Limiters   Mixers, Upconverters and Downconverters   Detectors, Envelope Detector, Product Detector  
ECE 4710: Lecture #22 1 Frequency Modulation  FM spectrum is very difficult to calculate in general  Useful to develop simple approximations when the.
CHAPTER4: CONTINUOUS-WAVE (CW) MODULATION First semester King Saud University College of Applied studies and Community Service 1301CT.
Chapter 6. Effect of Noise on Analog Communication Systems
ECE 8443 – Pattern Recognition ECE 3163 – Signals and Systems Objectives: Demultiplexing and Demodulation Superheterodyne Receivers Review Resources: Wiki:
Demodulation of DSB-SC AM Signals
ECE 8443 – Pattern Recognition EE 3512 – Signals: Continuous and Discrete Objectives: Causality Linearity Time Invariance Temporal Models Response to Periodic.
ECE 4710: Lecture #19 1 Bandpass Review  Modulated bandpass signal  where g (t) is complex envelope of baseband signal  Desired modulated signal, s.
© 2010 The McGraw-Hill Companies Communication Systems, 5e Chapter 4: Linear CW Modulation A. Bruce Carlson Paul B. Crilly (W.J. Song and J. H. Cho)
Communication Systems
Amplitude/Phase Modulation
Cape Electrical and Electronic Technology Topic: Electromagnetic Waves By: Tahvorn George & Charles,J.
8.0 Communication Systems Modulation: embedding an information-bearing signal into a second signal e.g. – purposes : locate the signal on the right band.
Modulation and Multiplexing ICS 620. Overview Frequency Spectrum Modulation techniques Multiplexing--TDM vs FDM Multiple Access Signal formats.
Analog Communication Systems Amplitude Modulation By Dr. Eng. Omar Abdel-Gaber M. Aly Assistant Professor Electrical Engineering Department.
Eeng Chapter 4 Bandpass Circuits   Limiters   Mixers, Upconverters and Downconverters   Detectors, Envelope Detector, Product Detector  
IT-101 Section 001 Lecture #15 Introduction to Information Technology.
Analog Communications
AMPLITUDE MODULATION.
Communications Engineering 1
LECTURE 11: FOURIER TRANSFORM PROPERTIES
Overview Communication is the transfer of information from one place to another. This should be done - as efficiently as possible - with as much fidelity/reliability.
Analog Operating Modes
Amplitude Modulation.
Signal Encoding Techniques
Fourier Transform Analysis of Signals and Systems
ANALOG COMMUNICATION SYSTEMS
Signal and Systems Chapter 8: Modulation
Introduction to Communications
Modulation Modulation => Converts from digital to analog signal.
Lecture 5: DSB-SC AM Modulation 1st semester
LECTURE 18: FOURIER ANALYSIS OF CT SYSTEMS
Lesson Week 8 Fourier Transform of Time Functions (DC Signal, Periodic Signals, and Pulsed Cosine)
AMPLITUDE MODULATION (AM)
LECTURE 11: FOURIER TRANSFORM PROPERTIES
8. Communication Systems
SIGNALS & SYSTEMS (ENT 281)
Presentation transcript:

LECTURE 12: SIGNAL MODULATION AND DEMODULATION Objectives: Generalized Fourier Transform Analog Modulation Amplitude Modulation Angle Modulation Demodulation and Demultiplexing Resources: Wiki: The Fourier Transform Celier: Generalized Fourier Transform MIT 6.003: Lecture 15 Wiki: Amplitude Modulation RE: AM Demodulation Wiki: Electromagnetic Spectrum Wiki: 700 MHz Auction MS Equation 3.0 was used with settings of: 18, 12, 8, 18, 12. URL: Audio:

Generalized Fourier Transform Consider a DC or constant signal: Compute its Fourier Transform: Unfortunately, the limit is not finite, and the integral does not converge. Consider an alternate approach based on an impulse function: Apply the duality property: This is known as the Generalized Fourier transform. It allows us to extend the Fourier transform to some additional useful signals such as periodic signals: The Fourier transform of a periodic signal is a train of impulse functions (and is a line spectrum).

The Concept of Modulation The electromagnetic spectrum is the most expensive “real estate” in the world. Hence, we would like to make as efficient use of it as possible (e.g., time and frequency domain multiplexing). It is more efficient (e.g., less power for a given SNR) to transmit signals at higher frequencies. Modulation: send multiple signals through the same medium (e.g. air, cables, fibers) by simply shifting them to different places in the spectrum. Amplitude Modulation: carry the information in the amplitude of the signal; use a sinusoidal carrier, c(t). Angle Modulation: alternate approach in which the signal is carried in the frequency or phase of the carrier signal (frequency and phase modulation). Many other forms of modulation including pulse-amplitude modulation (PAM), pulse-width modulation (PWM), code division multiple access (CDMA) and spread spectrum. These techniques are typically studied in an introductory course in communications theory.

Amplitude Modulation Using a Complex Exponential ]i=k, Demodulation:

Amplitude Modulation Using a Sinusoid ]i=k,

Synchronous Demodulation of Sinusoidal AM Assumptions:  = 0 (for now), Local oscillator is synchronized with the carrier. In practice, synchronization is achieved using a phase- locked loop (PLL). ]i=k,

Synchronous Demodulation in the Time Domain We can easily derive the properties of the demodulated signal: The low-pass filter removes the high-frequency replica of x(t), leaving only the “baseband” component. Suppose there is a phase difference between the transmitter and the receiver: The mismatch in phase appears as a scale factor that can be ignored. If there is a time-varying phase difference (due to drift): If the phase difference varies slowly in time, the net result is simply a time- varying amplitude change, which distorts the signal (slightly). What happens if the receiver is exactly 90 out of phase? ]i=k,

Asynchronous Demodulation Consider the spectrum of our modulation signal: Problems if the transmitter and receiver are exactly 90 out of phase. Alternative: Asynchronous modulation includes the carrier in the output and ensures the envelope of the modulated carrier contains the information. The carrier must be much higher in frequency than the signal: ]i=k,

Implementation of an Asynchronous Demodulator AM modulation was popular because of the ease with which it could be demodulated: However, for this to work, the envelope function must be positive (A+x(t) > 0). We pay a price in efficiency: more power must be used to guarantee this condition is true. ]i=k,

Double-Sideband Vs. Single-Sideband Modulation Since x(t) and y(t) are real, from conjugate symmetry, both lower sideband (LSB) and upper sideband (USB) signals carry exactly the same information. Double-sideband (DSB) occupies 2M bandwidth in  > 0, even though all the information is contained in M. Single-sideband (SSB) occupies M bandwidth in  > 0. Of course, SSB requires slightly more complicated hardware, so it was originally only used in applications where bandwidth was very limited (e.g., transcontinental telephone lines). Analog television signals, which are being obsoleted in February 2009, use a variant of SSB. ]i=k,

Single-Sideband Modulation ]i=k,

Frequency Division Multiplexing Used in many communications systems including broadcast radio and cell phones. ]i=k,

Summary Introduced the Generalized Fourier transform. Demonstrated its use on periodic signals (e.g., Fourier series). Introduced the concept of modulation. Discussed amplitude and angle modulation. Discussed modulation and demodulation of AM signals. Introduced both a synchronous and asynchronous approach to demodulation. Introduced techniques used in a variety of common communications systems including single-sideband and double-sideband modulation, and frequency division multiplexing.