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EE350: Communication Systems

EE350: Communication Systems. Modulation (AM, FM, PAM), Demodulation and Noise Fairfield University: School of Engineering DoctorD: Jeffrey N. Denenberg jeffrey.denenberg@ieee.org http://doctord.webhop.net. The Communication Problem. Get information from here to there Channel challenges

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EE350: Communication Systems

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  1. EE350: Communication Systems Modulation (AM, FM, PAM), Demodulation and NoiseFairfield University:School of Engineering DoctorD: Jeffrey N. Denenbergjeffrey.denenberg@ieee.orghttp://doctord.webhop.net EE350

  2. The Communication Problem • Get information from here to there • Channel challenges • Additive noise: “white”, Gaussian noise here • Non-linear distortion and time variation: only touched on here(but used and analyzed in xmitter/receiver implementations) • Frequency response: Gain & Phase “Distortion” EE350

  3. Some Terminology • Information source: supplies an analog signal in the form of a time-varying voltage or current that directly corresponds to the information. (baseband signal) • Audio • Telephone: 300Hz to 3.3kHz • AM broadcast: 100Hz to 5kHz • FM Broadcast: 50Hz to 15kHz • CD Audio: 20Hz to 20kHz • Scanned Video(Philo Farnsworth, electron beam, 1921) • NTSC: 6MHz EE350

  4. Terminology (2) • Transmitter: Puts the signal into a form that can traverse the channel . • Carrier: a simple waveform that is compatible with the channel. • Usually a sine wave • Transmission line: Coaxial cable, Twisted Pair • Free space: Electromagnetic Wave • Can be a light beam (or ultrasound) • Free Space: Laser • Fiber Optics: What keeps the light inside the fiber? EE350

  5. Terminology (3) • Modulation: vary a parameter of the carrier in proportion to the baseband information signal. • AM: amplitude modulation • FM: frequency modulation (Colonel Edwin Armstrong)(closely related to phase modulation) • Receiver: recovers an estimate of the original information baseband signal from the corrupted (by the channel) transmitted signal. • Demodulation: the inverse of the modulation process, sometimes called detection. Armstrong with an early superhetrodyne receiver EE350

  6. Terminology (4) • Channel: The medium through which the signal travels. • Additive noise: Interferes with the desired signal • “White noise”: Random (unpredictable) signal with equal energy at all frequencies • Gaussian noise: values distributed according to the “bell” curve • Non-linear distortion: Usually ignored in schoolwork, not here • Time variation: Variations in transmission delay and gain, not dealt with here • Frequency response: sometimes due to “reflections” or echoes • Gain variation with frequency • Phase variation with frequency: • Linear phase: just a fixed delay • Phase distortion: different propagation delay at different frequencies EE350

  7. Terminology (5) • Multiplexing:The sharing of a high capacity channel • Time-Division Multiplexing • Fast channel; Slow signals • Sampling: Represent a continuous signal as a sequence of narrow pulses (PAM) • Frequency-Division Multiplexing • Wide bandwidth channel; Narrow bandwidth signals • Modulation: move each signal to a different frequency range • Demodulation: recover a particular baseband signal EE350

  8. Course Description • DoctorD’s Web Site: http://doctord.webhop.net • Syllabus • Schedule (updated often) • Texts: cover both EE350 and EE352: Digital Communications • Haykin, “Communication Systems”, Wiley, 2001 • Hsu, “Analog and Digital Communications”, Schaums Outlines, 2003 • References: Web • Class Contact List • Learnlinc: http://learnlinc2.ffldusoe.edu/learnlinc/ EE350

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