Factors Affecting the Performance of Sub-1 GHz IoT Wireless Networks

Table 4

Checklist of factors affecting the performance of Sub-1 GHz IoT wireless networks.

Category	Factor	Description
Path	Line of sight	The line of sight affects the extent of interference to the wireless signal. The more complex the line, the more it affects wireless performance. The performance variability is highest in indoor environments.
Path	Distance	Wireless signal attenuates when its energy disperses around the transmitter’s antenna, which takes effect even in free space or line of sight. In our experiments, RSSI values decrease as the distance increases, regardless of the environment.
Path	Fresnel zone	When a wireless signal travels in the Fresnel ellipsoid region, the less obstacle in the ellipsoid zone, the better the signal travels.
Configuration	Transmit power level	The hardware configuration parameters can significantly affect signal strength. A higher power level results in higher signal strength, but it costs higher power consumption. A trade-off between signal strength and power consumption should be considered. Other configurable parameters may have similar influences.
Weather	Precipitation	Precipitation forms such as rain, hail, snow, sleet, or thunderstorm have significant impacts on wireless signals because they could be absorbed and interfered with. In our experiments, the mean RSSI value is much lower on a rainy day than on a sunny day. Similar effects are expected for other forms of precipitation.
Weather	Humidity	Humidity affects wireless performance more in long-range communication than in short-range. With the same setup of the D2D experiment, the standard deviation of the RSSI values on a foggy day at a distance of 500 m was much higher than at the range of 100 m.
Weather	Temperature	Hardware operation is presumably affected by temperature, particularly when the hardware runs outside its nominal operating temperature range. From our experiments, we conclude that the influence of temperature depends on the operating temperature range and the durability of the battery. Similar effects may exist in other pieces of hardware equipment.
Installation	Mobility	According to the Doppler shift effect, the movement of the wireless modules will affect the signal propagation. The frequency of the received signal may be changing as the modules move. As shown in Table 2, the moving receiver has a lower RSSI value than a stationary receiver.
Installation	Module position	The installed position of hardware components subtly affects wireless signal propagation. As shown in Table 2, modules installed on top of the drone perform slightly worse than those installed below it.
Installation	Antenna direction	2.1 dBi omnidirectional antennas are used for our experiments. Antenna direction should not affect the omnidirectional antennas’ signal strength, but practically the experiments result in different mean RSSI values. This difference may be caused by other metal objects in the vicinity of the antennas.
Installation	Hardware component	Other than the temperature, which affects hardware pieces, the hardware components might have their own influences. As discussed in Subsection 4.4, the battery charge status and its durability would affect the emitted signal and influence the wireless performance.