Summary

IEICE Information and Communication Technology Forum

2015

Session Number:SESSION7

Session:

Number:SESSION7-2

DSSS System with OQPSK-Spread FSK: Study on Characteristics of Low Envelope Fluctuation and Bit Error Rate Due to Narrow-Band Interference

Yusuke Akiyoshi,  Mai Ohta,  Makoto Taromaru,  

pp.-

Publication Date:2015-08-31

Online ISSN:2188-5079

DOI:10.34385/proc.22.SESSION7-2

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Summary:
This paper proposes a transmission system suitable for short range radio systems of small wireless devices using direct sequence (DS) spread spectrum (SS) modulation. FSK and OQPSK are employed as the primary and spreading modulations respectively. FSK, π/4-DQPSK, or OQPSK modulations having constant or low-fluctuation envelope are favourable because small wireless terminals/devices, such as sensor nodes, require high efficiency of power amplifiers and simplicity of circuits due to limited power sources. SS modulation is a promising technique for the use of ISM bands because SS transmission can mitigate interference from the other radio systems that are asynchronous to each other. However, BPSK or QPSK, which has conventionally been used for spreading modulations, makes high envelope fluctuations no matter what the primary modulation is. On the other hand, the transmitted signal of the proposed system has low envelope fluctuation since OQPSK is employed to spread the primary-modulated signal with constant envelope. Therefore, the transmitter and the receiver can employ high efficiency RF (radio frequency) power amplifiers and limiter amplifiers respectively. Because OQPSK spreading is a linear modulation, high capability of immunity against interference can be maintained in the same manner of common DS-SS systems. Simulation studies show the basic properties: good eye patterns in condition without interference or noise, low envelope fluctuation, and sufficient bit error rate performance due to narrowband interference.