Reliability through modulation diversity: can combining multiple IEEE 802.15.4-2015 SUN modulations improve PDR?

The IEEE 802.15.4-2015 standard includes the SUN (Smart Utility Networks) modulations, i.e., SUN-FSK, SUN-OQPSK and SUN-OFDM, which provide long range communications that allow to trade data rate and occupied bandwidth depending on the aplication reliability requirements. However, given the constraints of low-power devices and the challenges of the wireless channel, communication reliability cannot still meet the PDR (Packet Delivery Ratio) requirements of industrial applications, i.e., PDR>99%. Hence, in this paper we evaluate the benefits of improving communication reliability by combining packet replication with modulation diversity using multiple IEEE 802.15.4g SUN modulations. The results derived from a real-world deployment show that going from 1 to 3 packet transmissions with the same SUN modulation can increase PDR from 85.0/84.6/71.3% to 94.2/94.1/86.0% using SUN-FSK, SUN-OQPSK and SUN-OFDM, respectively. Combining the same number of packet transmissions with modulation diversity, i.e., using different modulation for each packet transmission, allows to further increase the average PDR to 97.1%, representing a relative increase of 3.1/3.2/12.9%, respectively. These results indicate the potential of using modulation diversity as a tool to increase the reliability of SUN networks for industrial applications.