Front-End Design for Underwater Communication System with 25 kHz Carrier Frequency and 5 kHz Symbol Rate

J. Ocean Eng. Technol. 2010;24(1):166-171.

Kim Seung-Geun,Yun Chang-Ho,Park Jin-Young,Kim Sea-Moon,Park Jong-Won,Lim Young-Kon

Ocean System Engineering Research Department MOERI KORDI,Ocean System Engineering Research Department MOERI KORDI,Ocean System Engineering Research Department MOERI KORDI,Ocean System Engineering Research Department MOERI KORDI,Ocean System Engine

25kHz 반송파와 5kHz 심볼율을 갖는 수중통신 수신기용 전단부 설계

김승근,윤창호,박진영,김시문,박종원,임용곤

한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부,한국해양연구원 해양시스템연구부

Keywords: Frond-End, QPSK receiver, Underwater communications, Receiver design

핵심용어: 전단부, QPSK 수신기, 수중통신, 수신기 설계

Abstract

In this paper, the front-end of a digital receiver with a 25 kHz carrier frequency, 5 kHz symbol rate, and any excess-bandwidth is designed using two basic facts. The first is known as the uniform sampling theorem, which states that the sampled sequence might not suffer from aliasing even if its sampling rate is lower than the Nyquist sampling rate if the analog signal is a bandpass one. The other fact is that if the sampling rate is 4 times the center frequency of the sampled sequence, the front-end processing complexity can be dramatically reduced due to the half of the sampled sequence to be multiplied by zero in the demixing process. Furthermore, the designed front-end is simplified by introducing sub-filters and sub-sampling sequences. The designed front-end is composed of an A/D converter, which takes samples of a bandpass filtered signal at a 20 kHz rate; a serial-to-parallel converter, which converts a sampled bandpass sequence to 4 parallel sub-sample sequences; 4 sub-filter blocks, which act as a frequency shifter and lowpass filter for a complex sequence; 4 synchronized switches; and 2 adders. The designed front-end dramatically reduces the computational complexity by more than 50% for frequency shifting and lowpass filtering operations since a conventional front-end requires a frequency shifting and two lowpass filtering operations to get one lowpass complex sample, while the proposed front-end requires only four filtering operation to get four lowpass complex samples, which is equivalent to one filtering operation for one sample.