Wireless Systems Design

Wi-Fi Passes Space Evaluation

Recently, Wi-Fi networks have been popping up in more and more places. From airports and coffee shops, they've made their way into bookstores, fast-food restaurants, and more. As prevalent as these networks are becoming, however, they seemed fated to remain Earthbound. Then, Tropos Networks, Inc. (www.tropos.com) announced that NASA has successfully tested its 5110 Wi-Fi cells.

The tests were conducted at NASA's on-site field trial at Meteor Crater in Arizona. According to Tropos Networks, this is the first time that NASA used outdoor cellular Wi-Fi technology as the communications network for potential interplanetary exploration. The Tropos equipment was evaluated because it enables the quick and economical deployment of highly reliable, large-scale wireless hot zones. These outdoor Wi-Fi hot zones complement and ubiquitously extend the ability to communicate from traditional Wi-Fi hot-spot equipment. Such equipment is already in use within the program.

Specifically, NASA evaluated two- and three-node Tropos Wi-Fi cells. The cells covered a 1-to-2-square-mile hot zone. The purpose was to simulate the area of an interplanetary exploration mission (see photo). The simulation included a base camp and the operating area surrounding it. Communications were then tested between a base-camp server and a mobile test computer, which was running an IEEE 802.11b client.

During the demonstration, NASA tested the network using Iperf performance-monitoring tools. It conducted trials using a roaming client device. Iperf is one of several software tools that provide a "goodput" measurement of the effective data throughput—both between two nodes and through a diverse network.

At a range of 1.3 miles from the base camp, NASA communications engineers measured a reliable 1 Mbps. They used a simple laptop inside a moving vehicle with no external antenna. As a result of the successful evaluation of this cellular Wi-Fi technology, NASA plans to pursue the use of the Tropos equipment in its production network for future field testing.

In the future, NASA is interested in connecting multiple nodes in a Wi-Fi mesh network. This network will include the following: a personal computer installed with a Wi-Fi client adapter that's embedded in two space suits; an extra-vehicular-activity robotic assistant with multiple computers connected via Wi-Fi; a science trailer and lunar planetary science module with multiple Wi-Fi nodes; and other sensor webs of cameras, microphones, and science equipment on the simulated planet surface.

In this simulation, communications were tested between a Wi-Fi-enabled PC that was embedded into the space suit, a Wi-Fi-enabled PC on the robotic assistant, and the surface command center. A Wi-Fi network could eventually be used during the collection of geologic samples, the testing of those samples, and the command and control of additional robotic "explorers."

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