Low-Power, Low-Cost LoRaWAN Gateway Buoy for use with Wireless Underwater Sensor Networks

The use of gateway buoy technologies to facilitate the gathering of data from underwater sensor networks (USN) can be challenging given the remote and unpredictable nature of our oceans. Factors such as transmission range, data-rate, reliability, cost and power consumption are just some of the consideration taken when choosing a suitable gateway buoy technology. This paper presents a custom built low power/cost gateway buoy based on LoRaWAN. LoRaWAN is a chirp spread spectrum wireless modulation technique which has many positive attruibutes such as long range communication and low power consumption. The developed gateway buoy was deployed in long term field trials in the North Sea as part on a USN. Using the custom written gateway algorithm, results have shown a message delivery reliability of 99.97%. The field trials show the capturing of USN data in near real time utilising LoRa based message streaming from gateway to shore. The developed system also enables users to control a USN from shore. Power consumption in a fully transparent two way link was measured at 43.02mW with a shore controllable sleep mode measured at 3.06mW. This allows the user to save power during periods of inactivity on the gateway. The usable range was investigated with very reliable communication between the shore and the gateway at distance up to 10km. The LoRaWAN gateway and mooring system were purposefully cost engineered to be deployable from very small vessels such as a RHIB. In conclusion the developed gateway buoy has been tested in the harsh waters of the North sea and has demonstrated high reliability and low power consumption. The developed technology has been successfully used as part of a USN and gathered actual acoustic measurement data in near real time. Future work includes further investigation into the range capabilities of the LoRAWAN system by testing variations of the Spreading Factor (SF), Bandwidth (BW) and Coding Rate (CR).