Performance of Outdoor Wireless Internet Micro-Hubs

Abstract

An experimental node-based wireless 802.11 b/g/n mesh network providing Internet access to users in Cambridge, Massachusetts, was developed at the Massachusetts Institute of Technology while complementary thermal modeling was conducted at the University of North Texas. Netgear WGT634U 108-megabyte-per-second wireless storage routers mounted within environmental enclosures at outdoor and indoor locations across the Cambridge coverage area serve as signal repeater nodes for the network. Denton, Texas, is a promising site to deploy a wireless network similar to the one in Cambridge. However, the ambient outdoor conditions in Denton differ from those in Cambridge and may exceed the operating envelope of the repeater nodes if not mitigated by well-designed environmental enclosures. By instrumenting a sacrificial node with thermocouples and baking it in a furnace, we determined that the node’s built-in safety shut-off temperature is 130 ± 3 °C and that the temperature at which irreversible damage occurs is in the range of 135 °C to 145 °C. By synthesizing this data with historic regional ambient temperatures through heat transfer modeling, we conclude that node thermal failure cannot be induced by high ambient temperature, provided that the node enclosure is designed with sensible thermal management precautions. Additionally, we measured the maximum viable distance between a node and a receiver. Beyond this maximum separation distance, low signal fidelity yields high packet losses (50% packets lost) and data transfer rates inferior to those of dial-up Internet (less than 56 kilobytes per second). Using a global positioning satellite system, we found maximum ranges for inter node communication both via a line of sight and through a building wall. These ranges were 183 ± 4 meters and 49 ± 4 meters, respectively. These shut-off temperature data and signal range data guide the design of future outdoor node enclosures and indicate the inter node spacing necessary to assure fast, reliable WiFi Internet coverage in Denton.