OFDM Parameters Design in the DFM System

The paper proposes a mode-adaptive OFDM parameters design method for Digital Frequency Modulation (DFM) radio used in the VHF-FM, and designes two transmission modes according to the Doppler shift range under different channel profiles. In order to effectively counteract frequency-selective fading, it is necessary to set the length-ratio between cyclic prefix and useful part of the OFDM symbol; reasonably choosing the length of the useful part, makes more sub-carriers acquired within the limited bandwidth and the sensitivity to Doppler shift decreased; considering the influence to engineering complexity and data transmission efficiency brought by the number of available sub-carriers, the suitable choice of the number can realize a good trade off. Contrast to the existing parameter suggestions in the DRM-Plus system which has the same channel circumstances, the proposed method can not only counteract frequency-selective fading, but also have advantages of lower sensitivity to Doppler shift, lower engineering complexity and higher data transmission efficiency. Simulated with the existing synchronization acquisition algorithms in time domain, the results show that the proposed parameters can be used in the DFM system.