Author: aqd500

This week I focused on narrowing down the design of the wireless sensor network. After having spoken to Prof. Mukherjee, we pivoted to a time-division multiplexing approach rather than an asynchronous medium access control method to optimize power consumption even further. Furthermore, to reduce maintenance cost, we want our network to be resilient to link failures (e.g. if multipath effects caused by inclement weather degrades the quality of the channel between two nodes). Since a forest fire is not a frequent occurrence, and since the time before spreading to an open fire is 60 minutes, we would like to detect node failures (or critical link failure) within a timeframe of 15-30 minutes of the actual event. After having read a paper on TDM MAC for wireless sensor networks by Koutsonikolas and Salonidis, I decided to base our forest fire WSN’s MAC algorithm off their approach. Now, we have a good method for ensuring that sensor data can be transmitted and forwarded across the network from any node in the mesh network to the gateway. The clock synchronization method described in the paper enables each node to correct their clock drift in regular intervals, and to match up to a global transmission and reception schedule. I also soldered pin headers to the gas sensor and plan to test whether it can detect a match being lit next to it by interfacing it with an STM32 via SPI by Monday.

Due to the pivot to a new project idea, we have only had a few days to plan out the design of this new idea: WSN for early wildfire detection. Nevertheless, I have been researching medium-access protocols that we could use to minimize power in the WSN. The most promising one would be an asynchronous B-MAC protocol where the sender would have some notion of the designated receiver’s wakeup period, allowing it to send a much slower preamble. The preamble would ensure that the receiver and the transmitter are in the “awake” state before the actual sensor data is sent. However, this would mean that the sensor node cannot be fully turned off during the off state, as it would still need to receive the preamble. Fortunately, the STM32 has a low-power mode where UART is still enabled, so the board could still receive data from the LoRa transceiver in this lower power state. Conversely, we could implement a synchronous MAC protocol (much like TDMA) which would allow the STM32 to go into an even lower power state mode, but this requires regular beacons to account for RTC clock drift among the sensor nodes, which sounds much trickier to implement. I do believe we are behind because we chose an idea so late, but I believe we can catchup promptly by the end of next week with other teams. My goal is to get LoRa communication up and running between a pair of STM nodes, and finalize the MAC protocol design.