Radio transmission improvement with wavelets

Despite their popularity in signal processing, few wavelets applications were found for data transmission. Most of the data transmission systems nowadays use Orthogonal Frequency Division Multiplexing (OFDM) or some versions of it: WiFi (IEEE 802.11), WiMAX (IEEE 802.16), LTE (3GPP rel.8) or ADSL. The idea that gathers wavelet theory and data transmission is to use wavelet signals as carriers in a multi-carrier communication. Recent research has shown that, by associating the multi-carrier concept and the wavelet signals, some of the OFDM's classical drawbacks can be counteracted. Thus, some wavelet based multi-carrier schemes may provide significant out-of-band side-lobes rejection, by comparison to OFDM. Furthermore, WOFDM proved to be more robust to the time variability of the radio channel. Due to their time-scale nature and to their finite duration, wavelet carriers provide a better "time-frequency" compromise than OFDM's complex exponentials, which must be windowed by a time gate in order to be localized on the time axis. In some particular channels, this may lead to significant BER improvements. Since wavelets obey Nyquist's criterion for ISI-less transmission, there is no need for pulse shaping filters in a wavelet modulation scheme. Furthermore, the implementation complexity may be kept at the same level that in OFDM, due to the signal processing based modulator and demodulator, using Mallat's algorithm for the Discrete Wavelet Transform computation.

(a) Wavelets satisfy Nyquist criterion for ISI-less transmission.
(b) WOFDM relies on the orthogonal nature of wavelet families. The symbol transmitted on each branch may be estimated due to the orthogonality of the wavelet "carriers".
(c) WOFDM is less affected by the time variability of the channel than OFDM.

Selected Publications

• M. Oltean, "A study of the multi-scale WOFDM transmission in time variant channels", International Journal of Communications, NAUN, pp. Issue 1, Vol. 2, Dec.2008,ISSN: 1998-4480 pp. 96-105.
• M. Oltean, M. Kovaci, H. Balta, A. Campeanu "Multi Binary Turbo Coded WOFDM Performance in Flat Rayleigh Fading Channels", Acta Technica Napocensis - Electronics and Telecommunications, Volum 29, Nr.3/2008, ISSN: 1221-6542, pp.11-16.
• M. Oltean, M. Nafornita, "Errors per Scale Statistics for a Wavelet OFDM Tansmission in Flat Fading Channels", Proceedings of WISP'09, Budapesta, August 2009, pp. 119-124.
• M. Oltean, A. Isar, "On the time-frequency localization of the wavelet signals, with application to orthogonal modulations", Proceedings of ISSCS'09, Iasi, Iulie 2009, pag.173-177.
• M. Oltean, M. Nafornita, "Efficient Pulse Shaping and Robust Data Transmission Using Wavelets", Proceedings of 2007 IEEE International Symposium on Intelligent Signal Processing, Alcala de Henares, Spain, October 3-5, pp. 43-48, ISBN: 1-4244-0829-6.