NASA tests WiFi mesh networks

NASA is testing mesh networks in a Mars-like Arizona setting.

Courtesy of Tropos Networks Inc.

Mars has no data networks yet, so NASA engineers are investigating IEEE 802.11b wireless fidelity as a low-cost alternative.

But before they can equip future Mars rovers with WiFi cards, engineers at the space agency must devise a way to make the short-range cards communicate with base stations miles away.

To do that, NASA recently tested a mesh networking architecture for wireless communications at a remote Arizona site, said Marc Seibert, senior research engineer for the NASA Glenn Research Center in Cleveland.

Although the testing is not for any specific mission, the agency foresees future missions by astronauts or multiple data collection devices such as roaming rovers or stationary sensors.

Today, NASA transmitters largely use protocols designed by the Consultative Committee for Space Data Systems, a coalition of international space agencies and industry. The protocols were developed for high-latency space communications, where hops between nodes can span millions of miles. There is little commercial use for such protocols, so space communications equipment must be custom-built, which is costly.

For the past five years, Glenn and NASA's Ames Research Center in Moffett Field, Calif., have been testing WiFi to relay data and voice over short distances. Researchers have tested commercial products from vendors such as Cisco Systems Inc. and NetGear Inc. of Santa Clara, Calif.

One difficulty with WiFi is that the end clients need access points to route data back to base stations. The access points are potential points of failure, especially in inhospitable climates and rocky terrains.

A mesh topology does not rely on a single gateway to direct traffic. Instead, each access point, or node, can forward packets from clients or from other nodes.

By having each access point automatically discover its neighbors and potentially act as a relay, the traffic can be dynamically rerouted around equipment failures.

'In a diverse terrain, the ability to take out a node and have the nodes figure out how to get data back to the base station is very appealing,' Seibert said.

In September, he and other Glenn researchers completed the agency's first test of a WiFi mesh network, using ruggedized WiFi access points from Tropos Networks Inc. of San Mateo, Calif.

The Tropos 5110 WiFi access point's proprietary routing algorithm establishes relationships with other access points to form ad hoc networks, said Bert Williams, Tropos' marketing vice president. The gateways route packets by standard Internet Protocol.

Here on Earth

The test took place at the sparsely populated Meteor Crater area of Arizona, which closely resembles the harsh terrain of the red planet.

One access point was set up at a base camp and a second access point on a nearby hilltop. The testers then drove around the area with a notebook PC equipped with an 802.11b card, sending data back to the base camp through the hilltop access point'in effect sending data through two nodes.

Using Iperf open-source software that measures IP bandwidth between two points, the NASA engineers racked up a steady throughput of 1 Mbps at up to 1.3 miles. They found each hop cut total throughput by about half.

Although the test was successful, much work remains to ready Marsbots for WiFi, and vice versa. The Tropos equipment was built for terrestrial communications, such as city-run networks. The wireless equipment is waterproof and can withstand extreme temperatures but is not radiation-hardened.

'I can see robots deploying a WiFi mesh on a planet,' Seibert said. 'You could deploy a mesh each day, depending on where your team is going. You'd figure out where the mesh should be, and robots would go out and test the links before the humans got there.'

About the Author

Joab Jackson is the senior technology editor for Government Computer News.

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