Realizable Ideal D/C and C/D converters for OFDM signals

For real bandlimited periodic signals, the author in [2] derives the realizable ideal D/C converter that is composed of finite number of finite-duration periodic pulses. However, we can not apply the results in [2] for complex bandlimited periodic signals, such as the baseband signals in the orthogonal frequency-division multiplexing (OFDM) system. In this paper, we first derive the realizable ideal D/C converter for the complex baseband signals of the OFDM system. The proposed D/C converter is composed of only finite-number of finite-duration complex periodic pulses, and therefore is realizable within one period of the signal. Based on the orthogonality among the circularly-shifted interpolation pulses, we also propose a realizable ideal C/D converter that could implement the ideal sampling for the OFDM signals. Due to the complex interpolation pulse, the signals in the I- and Q-channels are coupled together in the ideal D/C (or C/D) converter, and we can not decouple the ideal D/C (or C/D) converter into two independent D/C (or C/D) converters in the I- and Q-channels.