Characteristics of ETX Link Quality Estimator Under High Traffic Load in Wireless Networks

Effective link quality estimation is a vital issue for reliable routing in wireless networks. This paper studies the performance of ETX (Expected Transmission Count) under different traffic loads. Although ETX shows the good performance under light load, its performance gets significantly worse as traffic load is increased. Broadcast route request packet storm due to new route discoveries affects severely the calculation of link ETX values under high traffic load, which makes it difficult to find a good path. This paper presents the design and implementation of a variation of ETX called HETX(High load -Expected Transmission Count), which reduces the impact of route request packets to the link ETX values under high load. We conduct the evaluation of the performance of three metrics - HETX, ETX and minimum hop-count. The simulation results showed that HETX improves the average route throughput by up to 25% over ETX under high traffic. Minimum hop-count has the poor performance compared with both HETX and ETX at all different traffic loads. Under light load, HETX and ETX show the same performance.