Fading and carrier frequency offset robustness for different pulse shaping filters in OFDM

Abstract

A carrier frequency offset (CFO) or a time varying (fading/Doppler spread) channel in an orthogonal frequency division multiplexed (OFDM) system will create interbin interference (IBI). IBI causes decreased SNR and increased symbol error rate (SER). The amount of CFO or Doppler spread which creates a given performance degradation depends on the number of channels, the SNR and the pulse shaping. The common OFDM scheme, with M-QAM and square pulses, are compared with an OFDM scheme with M-offset QAM (M-OQAM) and pulses of finite duration. The comparison is made both for stationary and flat fading channels. For flat fading channels, analytical methods have been developed for calculation of the SER caused both by IBI due to CFO and by IBI due to Doppler spread. The models show a good agreement with simulations. Comparison of the two different OFDM systems show that for stationary channels the system with pulse shaping allows a higher CFO than the system using square pulses. For a flat fading channel the two systems have similar Doppler spread and CFO robustness.