Frequency offset sensitivity reduction of multicarrier transmission by waveshaping

Abstract

This paper addresses the reduction of system sensitivity to the frequency offset due to time shaping of the multicarrier (MC) signal. Rectangular and Gaussian shapes (with different spreads) are considered. For a multipath channel, degradation of the performance of the OFDM system to the frequency offset for BPSK and QPSK modulation and for these waveshapes is investigated and compared. The effect of changing the number of carriers, as well as the multipath channel delay spread, on the sensitivity reduction of OFDM with shaping is thoroughly studied. Results show that the Gaussian shaped OFDM is much less sensitive to the frequency offset than conventional (rectangular) OFDM. Reducing the time spread of the Gaussian shape reduces the sensitivity. For OFDM with both rectangular and Gaussian shapes, sensitivity to frequency offset slightly increases by increasing the number of carriers. For a waveshaped OFDM system with a fixed spread of Gaussian shapes, performance degradation due to frequency offset is higher for BPSK than QPSK. Results show that, compared with conventional OFDM with 32 carriers, the Gaussian shaped MC, with a spread width of 10% of the symbol time, reduces the sensitivity of the system to frequency offset by a factor of almost 6 dB. Results can be used in the analysis and design of high-speed digital data transmission over wireless multipath fading channels.