The impact of FFT size on the performance of a combined OFDM-equalization radio modem

Conventional OFDM systems employ a guard interval to combat delay spread distortion of transmitted data. This reduces the efficiency of the OFDM transmission. A combined OFDM-equalization transmission strategy is presented in this paper. This strategy employs an adaptive equalizer to combat delay spread distortion instead of a guard interval. This facilitates the use of very short guard intervals and thus the efficiency of the OFDM transmission is improved. This paper presents the combined OFDM-equalization techique and demonstrates the efficiency improvement that it offers over conventional OFDM. The performance of the pre-FFT equalizer is sensitive to time variation of the mobile radio channel's impulse response. Software simulation is employed to analyze this sensitivity and a relationship is determined between performance and FFT size. The results are considered in the context of application to existing and future mobile radio systems.