Quantifying the Interference Gray Zone in Wireless Networks: A Measurement Study

In wireless networks where communications are made over a shared medium, interference and collisions are the primary causes of packet drops. In multi-hop networks such as wireless mesh networks, due to the hidden terminal problem, limiting the effects of collisions and interference is a key in achieving high performance. Typical wireless medium access control protocols perform carrier sensing to avoid collisions. Most research efforts so far has used the binary model when studying carrier sensing and interference; a node is either carrier sensed or not, and a link is either interfered or not. In reality however, there exists a gray zone. Carrier sensing and interference should be represented in continuous values. Using the measurement data from our 802.11a wireless mesh network test-bed, we propose metrics that represent the levels of carrier sensing and interference. Using our metrics, we also propose methods to estimate broadcast throughput and goodput. We evaluate the accuracy of our methods by comparing our models with the measured data. In addition, we investigate the impact of the capture effect on interference.