수중 센서 네트워크에서 저전력 통신을 위한 변조 기법의 적용성 연구

Abstract

Underwater sensor network has challenges to be overcome such in long propagation delay resulting from low speed of sound propagation, severely limited range-dependent bandwidth, attenuation and time-varying multipath propagation. All the above distinct features make the performance degradation by generating ISI(Inter Symbol Interference). Also in case of underwater sensor network considers the low power transmission because of environmental limitations.

In this thesis, the performances of PSSK(Phase Silence Shift keying) modulation technique for low-power commu nication in underwater sensor network were evaluated. PSSK is a kind of PSK(Phase Shift Keying) schemes, thus it is more bandwidth efficient than the orthogonal modulations, such as PPM, FSK. In addition, PSSK can achieve power efficiency because every symbol of PSSK has a silence period like PPM technique. In the case of M-ary PSSK, one bit determines the silence position of symbol and ()bits determine the phase of the symbol. It is improvement of the combination either of PSK and PPM techniques. Instead of traditional PPM, where some bits determine the position of the pulse, PSSK uses one bit to determine the absence that is the position of silence period of the symbol. Because the transmitter of PSSK transmits the only half energy of a symbol for a symbol period, it can save the transmit power by 3 dB. And 180° phase shift probability is lower than QPSK because of this feature will cause back-off gain. It can also save the transmit power by 1.5 dB. The result of experiment, BER(Bit Error rate) of QPSK modulation method is 2.29×10^-1 and BER of PSSK modulation method is 2.36×10^-1.