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Proposal of OFDM system with data repetition

This paper proposes a novel method for orthogonal frequency division multiplexing (OFDM) systems, which can keep the user's objective performance even under very low carrier to noise power ratio (CNR) and severe frequency selective fading conditions at the cost of a reduction in the information transmission speed. A salient feature of the proposed method is that the process of coherent summation of the repeated data during demodulation is carried out by downsampling the received signal with a sampling interval that does not satisfy the sampling theorem. The ratio of downsampling is selected purposely at the receiver with a value larger than the maximum sampling interval indicated by the sampling theorem so as the subcarriers containing repeated data in the frequency domain would fold over coherently as many times as the number of data repetitions. The proposed OFDM system makes it possible to reduce the size of the FFT processor used at the demodulator, and can be realized on the basis of conventional OFDM modulator and demodulator.