Systems Seminar
Exploiting Time and Frequency Selectivity in
MC-CDMA Communications Systems
Tamer A. Kadous
UW ECE Department
Abstract
The combination of Code Division Multiple Access (CDMA) and MultiCarrier (MC)
modulation has been proposed to develop high data-rate wireless communication
systems. The performance of MC-CDMA systems is significantly limited by a
number of imperfections, including Doppler spreading (due to temporal channel
variations) as well as phase noise and frequency offsets (due to local
oscillators). In this talk, I introduce two schemes that, in contrast to
existing designs, deliver improved performance under fast fading by exploiting
Doppler diversity. Moreover, the schemes fully compensate for frequency
offsets as well as phase noise. The first scheme is aimed at the receiver and
exploits a canonical signal model that efficiently captures the effects of all
impairments. In this receiver the information transmitted on a particular
subcarrier is decoded by processing a small subset of subcarriers
surrounding the desired subcarrier. The second scheme is aimed at fully
exploiting time and frequency selectivity at both the transmitter and
receiver. It uses a signaling and reception scheme that approximately
diagonalizes the time-varying frequency selective channel.
The main idea is to transmit the information on a set of signaling waveforms
each of which encounters at fading in time and frequency. Necessary
conditions for the scheme to hold and the optimal choice of basis waveforms
is discussed.
Time and Place: Wed., Apr. 18, 3:30-4:30 pm in 4610 Engr. Hall.
SYSTEMS SEMINAR WEB PAGE:
http://www.cae.wisc.edu/~gubner/seminar/