Experimental investigation of radio performance in wireless sensor networks

Testing of the range and radiation pattern of wireless sensors is often not fully documented. In this paper, we perform a full characterization of the Tmote Sky motes from MoteIV Corporation. Packet yield, RSSI, and LQI are measured as a function of distance, angle, and transmit power, while taking environmental conditions into consideration. Wireless sensors have a very limited energy source, and the ability to make nodes last as long as possible can be greatly affected by their placement in the network. We aim to present a set of guidelines for setting up Wireless Sensor Networks that will enable them to achieve their QoS goals and maximum lifetime. Our results show that the radio antenna pattern on the Tmote Sky devices is not truly omnidirectional. RSSI does appear to degrade as an exponential function of distance, and LQI appears to be a very reliable indication of packet yield. The most significant result we have found is that transmitting and receiving node heights have a major impact on link performance. We have also found that under any circumstance, it is difficult to support data rates higher than 30 kbps with the current radio stack in TinyOS 1.x. Experimental data is analyzed and the importance of these results is discussed in depth.