Novel RF direct under-sampling technique and its application to OFDM systems

A novel RF direct under-sampling technique, which is equivalent to RF Nyquist-sampling, has been developed. The technique enables higher-order modulations such as a 16-QAM signal to be demodulated without losing vector information despite under-sampling being used. The only drawback of the technique is that it requires a precise sampling frequency to be synchronized with the input RF carrier frequency. Therefore, we also developed a new frequency comparator that makes carrier regeneration implementable even when 16-QAM signals are demodulated. To prove the validity of the new under-sampling technique, we report experimental results of the OFDM receiver fabricated using FPGA devices.