SIR based interference modeling for wireless mesh networks: A detailed measurement study

Spatial reuse is a central aspect in the efficiency of wireless mesh networks. Accurate inter-link interference measurement and estimation is necessary for such spatial reuse. In this work, we explore in depth Signal to Interference Ratio (SIR) based interference modeling. We take a measurement centric approach, characterizing the SIR versus PDR (Packet Delivery Ratio) relationship in outdoor mesh network settings. Our significant findings are the following. (1) In outdoor environment there is a range of SIR values (intermediate SIR region), wherein it is difficult to predict the PDR accurately. (2) Fortunately, the width of this intermediate SIR region is small: about 4-5dB for most data rates. (3) The SIR vs PDR relationship depends significantly on the modulations used by transmitter as well as the interferer: we characterize this dependence. The use of an outdoor 802.11g-based testbed is a significant aspect of our measurements. The above findings have important implications for the design of interference measurement and prediction schemes. We quantify the accuracy of our SIR-based technique by applying an offline prediction model in our outdoor mesh testbed and observe that of the 44 pairs of links the SIR technique predicts performance with less than 10% error for over 85% of the links for which the SIR values lie outside the intermediate SIR region. An evaluation of existing interference modeling techniques reveals that these make certain incorrect assumptions which make them perform significantly worse than our proposed technique.