Low-Weight Wireless Sensor Node With Sensor-Data-Enhanced Dual-Frequency RSSI-Based Distance Estimation

In wireless sensor networks, it can be important to determine the distance of sensor nodes between each other. At the same time, many applications have strict requirements on the weight and size of a sensor node. For example, animal monitoring requires low weight and size to minimize the impact on the animal. A distance estimator based on the received signal strength indicator (RSSI) in combination with free-space loss can efficiently be implemented but is prone to errors and inaccuracy, especially when using antennas with high directivity. In this article, a new approach using two separate antennas in two different frequency bands on ultrasmall systems is proposed. It is shown how the antenna gain directivity can be compensated. In this way, a more precise measurement of the free-space loss, and thus of the distance between the nodes, becomes possible.