수중통신용 버스트 QPSK 변조기 설계

Abstract

Since the underwater communication system is deployed under the water and far from the ground, it is generally operated with built-in battery. To extend the operation time, low power consumption is essential. So that, we adopt the burst transmission scheme and design the frame structure for burst QPSK transmission. Also, in the paper, we represent three design schemes of pulse-shaping filter of QPSK modulator for underwater communications; which are direct scheme, sub-filtered scheme, and look-up table based scheme. Among them, the look-up table based scheme needs the smallest number of operations for pulse-shaping filtering because it require only the same number of look-up table reading to the number of samples per symbol. Furthermore, if the symbol duration is an integer multiple of the period of carrier and the look-up table based scheme is used, the pulse-shaping filtering and digital mixing can be performed at the same time by pre-computing the results of pulse shaping and mixing according to the all combination of symbol sequence and then storing the results to the look-up table. The look-up table based scheme will be used as a key module of the digital modulator.