[EECS Colloquium] Seminar: Today, April 26, Faculty Candidate, 11am

[Bollmann, Paul]

Seminar: ECE Faculty Candidate   Wednesday April 26 11:00 - 11:50am Kelley 1007   Steve Thompson Postdoctoral Scholar Department of Electrical and Computer Engineering University of California, San Diego     Constant Envelope OFDM   Orthogonal frequency division multiplexing (OFDM) is a popular modulation technique for wireless digital communications. It provides a relatively straightforward way to accommodate high data rate links over harsh wireless channels characterized by severe multipath fading. OFDM has two primary drawbacks, however. The first is a high sensitivity to time variations in the channel caused by Doppler, carrier frequency offsets, and phase noise. The second, and the focus of this talk, is that the OFDM waveform has high amplitude fluctuations, a drawback known as the peak-to-average power ratio (PAPR) problem. The high PAPR makes OFDM sensitive to nonlinear distortion caused by the transmit power amplifier (PA). Without sufficient power backoff, the system suffers from spectral broadening, intermodulation distortion, and, consequently, performance degradation. High levels of backoff reduce the efficiency of the PA. For systems with limited power resources, such as mobile battery-powered devices, this problem is particularly detrimental. A new PAPR mitigation technique is presented. In constant envelope OFDM (CE-OFDM), the high PAPR OFDM signal is transformed to a constant envelope 0 dB PAPR waveform by way of angle modulation. The constant envelope signal can be efficiently amplified with nonlinear power amplifiers thus achieving greater power efficiency. In this talk, the fundamental aspects of the CE-OFDM modulation are studied, including the signal spectrum, the signal space, optimum performance, and the performance of a practical phase demodulator receiver. Performance is evaluated over a wide range of multipath fading channel models. It is shown that CE-OFDM outperforms conventional OFDM when taking into account the effects of the power amplifier. System details of a hardware implementation are also discussed.     Biography:   Steve Thompson received the BSc degree from Arizona State University (1999), and the MSc and PhD degrees from the University of California, San Diego (2001 and 2005, respectively) all in Electrical Engineering. From 1997 to 1998 he worked as an Associate Engineer at Inter-Tel, Chandler, AZ. He also worked summer internships at Los Alamos National Laboratory, Los Alamos, NM (1998); and SPAWAR Systems Center, San Diego, CA (2001 and 2004). Dr. Thompson's research interests are in the general area of digital communications. Currently, he is working on constant envelope OFDM at UCSD as a Postdoctoral Scholar.

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