Efficient Digital Communication over the Time Continuous Rayleigh Fading Channel

by Dr. Tor M. Aulin,Fellow of the IEEE, Highly Cited; ISI Web of Knowledge Chalmers University of Technology, Sweden

 :  15 Dec 2004 (Wed)
 :  11:00am - 12:00noon
Venue  :  Rm 1401, 1/F (Lift 25/26), HKUST

Frequency flat, fast Rayleigh fading may be considered the most critical disturbance in a wireless communication system. In its most general form, it is modelled as a multiplicative time continuous random process (zero mean complex Gaussian) distortion of the transmitted signal. In order to achieve an efficient communication here, each part of the communication link must be carefully designed based on the properties of the time continuous channel. Previous works have used strategies developed for the additive white Gaussian noise channel(AWGN)as starting points. This is not a good strategy. It is important to deal with the deep fades. To reduce the influence of the deep fades on the error probability, diversity techniques must be used. Coded interleaved modulation can be regarded one such strategy, where the diversity effect arises as a result of nearby encoder output symbols being subjected to statistically independent fading. Central in achieving this independence is the interleaver, which spreads the symbols in time. A higher diversity order is obtained if the encoder output bits, instead of symbols, are interleaved. To avoid bandwidth expansion here, the channel symbol constellation must be expanded accordingly. The resulting system is referred to as bit-interleaved channel symbol expansion diversity (CSED). On the fast fading channel, coding is only part of the solution, however. Here, matched filter detectors originally developed for AWGN are unable to efficiently handle the rapid (compared with the signalling rate) fluctuations of the received signal power. More sophisticated solutions are needed. It is essential to make the transition from the time continuous received signal to a discrete representation in the receiver, without losing too much accuracy.

Tor M. Aulin was born in Malmo, Sweden, on September 12, 1948. He received the M.S. degree in electrical engineering from the University of Lund, Lund, Sweden in 1974, and the Dr. Techn. (Ph.D.) degree from the Institute of Telecommunication Theory, University of Lund, in November 1979.

He became a Docent at the University of Lund in 1981 and worked at this institute as a Postdoctoral Fellow. During this period, he was also a Visiting Scientist at the ECSE Department at Rensselaer Polytechnic Institute, Troy, NY. Following this, he spent one year at the European Space Agency (ESA), the European Space Research and Technology Centre (ESTEC) in Noordwijk, The Netherlands, as an ESA Research Fellow. In 1983, he became a Research Professor (Docent) in Information Theory at Chalmers University of Technology, Goteborg, Sweden. In 1991, he formed the Telecommunication Theory Group there and also became a Docent in Computer Engineering in 1995. During the fall of 1995, he was a Visiting Fellow at the telecommunications Engineering Department, Australian National University, Canberra, ACT, Australia. Some of his research interests include communication theory, combined modulation/coding strategies (such as CPM and TCM), analysis of general sequence detection strategies, digital radio channel characterization, digital satellite communication systems, and information theory. His company, AUCOM, has performed several advanced theoretical studies as a consultant to some of the major international organizations that deal with developing and operating satellite communication systems, e.g., INTELSAT and ESA. He has also performed theoretical study contracts for Saab and Volvo. He has served as an internal lecturer for Nokia, and has performed numerous studies for Ericsson in the area of digital radio transmission, the latter resulting in a patent. He has authored and published some 100 technical papers, and has authored the book, "Digital Phase Modulation" (New York: Plenum, 1986). He has organized and chaired several sessions at international symposia/conferences organized by, e.g., IEEE, and is an EAMEC representative with the IEEE Communications Society. He was an Associate Editor for the IEEE Transactions on Communications from 1993 to 2001.

Dr. Aulin has two papers among the best (Best of the Best) published during the first 50 years of the IEEE COMSOC, selected in connection with their 50th anniversary. In December, 1997, he was awarded the Senior Individual Grant from SSF, handed over at a special ceremony by the Prime Minister of Sweden.


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