Impact of Inexpensive Oscillator in Wireless Sensor Node on Packet-Level Index Modulation Method under Real Environment

Packet-Level Index Modulation (PLIM) used in the Internet of Things (IoT) system has been proposed as a communication method that can transmit additional data bits added to the normal data transmitted in packets. PLIM has the feature of being able to increase the number of bits that can be transmitted more or less in low data rate LPWA (Low Power Wide Area) systems, while satisfying the constraints of the transmission time, called duty cycle. The additional information is allocated to the indexes of the time slot and channel to improve the transmission rate when the packet is transmitted. The demodulation performance of the indexes in PLIM depends on the accuracy of the oscillator. In particular, when time-slot indexes are used, the effect of clock drift of inexpensive oscillators that IoT wireless node equipped with is particularly noticeable. In this paper, the effect of the oscillator accuracy of the node that depends on the temperature variations occurring in realword environments is clarified through results obtained from experiments using actual equipments, and the impact on PLIM is discussed.