Defense Advanced Research Projects Agency (DARPA) researchers have conducted a successful mobile demonstration of an ad-hoc-networking technology that lets multiple users occupy the same time and frequency slot to enhance data throughput.

During the demonstration of DARPA Interference Multiple Access (DIMA), five mobile transmitters delivered signals over 5 MHz of spectrum to a single transmitter with all of the nodes moving at speeds as great as 60 miles per hour while having less than a 1% bit-error rate, said Bruce Fette, program manager in DARPA’s strategic technology office. Previously, DIMA had been used at speeds of 15 miles per hour with a bit-error rate of 3%.

“We demonstrated that the system could work under the real-time artifacts of mobility, even with multiple vehicles in motion in an urban environment-multipath and all — that the DIMA system could track all of that and still receive multiple signals at the same time on the same frequencies and sort it all out," Fette said.

"We actually had a system that was displaying five screens worth of [VGA-quality-resolution] video while we did this demonstration. On a second screen, we were displaying five graphs — one was vehicular speed of each vehicle involved in the demonstration, on was demonstrating the signal-to-noise ratio, and one graph was demonstrating the bit-error rate."

Fette said DARPA officials are confident that DIMA would work with the network nodes traveling at even greater speeds. Whether the maximum data-throughput rates of 5.2 Mbps achieved during the demonstration can be increased is something that Fette would like to explore.

“I honestly do not know how much headroom there is in the signal processing and dynamic range,” he said. “It is one of the questions I have asked the team.”

Fette said attendees at the demonstration were “overwhelmedly excited and thrilled to see what was possible.” From a technical perspective, DARPA officials have said DIMA perhaps could be integrated into the Wireless Network after Next (WNaN) radios being developed for the U.S. Army, but military officials would need to approve such a project.

WNaN features ad-hoc networking between cognitive radios — projected to cost less than $500 each, when built in quantities of 100,000 or more — that automatically find usable spectrum and act as nodes to route voice and data information to each other via multiple hops with sub-100-millisecond latency.

Last October, a 10-node network using handheld WNaN radios integrated with voice, data and positioning capabilities worked without disruption while avoiding non-cooperative signals, despite the absence of preplanned frequencies, time slots or routes. Another feature of the WNaN project demonstrated during the event was disruption tolerant networking (DTN), which is designed to ensure that packets are not lost.

This month, DARPA will conduct another WNaN demonstration using 50 network nodes, Fette said.

"In some early scientific literature … there was a concern that these radios might have difficulties supporting a large number of users,” he said. “However, the assumptions that were in that early literature are end run by the architecture that DARPA has designed into the WNaN radio. Therefore, the expectation is that we will be able to exceed the predictions in the scientific literature about the scale factor of networks."

For the military, technologies such as DIMA and WNaN are designed to provide reliable, robust communications between troops in even hostile spectral environments with no fixed infrastructure and minimal spectral planning. Domestic first-responder agencies often have similar needs, and there have been discussions about the adaptability of such technologies outside of the military uses, Fette said.

"We're getting a lot of interest from the defense community,” he said. “I have also had interest from communities outside of defense ... but there have been some really excellent, far-sighted recognition about the value of the technology."