A cognitive radio that military officials believe can be sold for less than $500 per unit has passed its initial testing phase, and the project remains on track for realizing its goal of completing development of the devices in late 2010, according to an official for the Defense Advanced Research Projects Agency.

In November, DARPA conducted what project manager Preston Marshall a “very, very successful” demonstration using the first 12 nodes — though not packaged in the ultimate radio form factor, the cards have been reduced to the proper size — built in the project.

“The tests went very well — normally, something goes wrong, but nothing went wrong,” Marshall said. “It satisfied me that we don't have any insurmountable problem that we didn't see and that there's nothing but engineering issues between here and there. I'm sure we'll have a few [challenges], but there's no question that what we needed to have clearly is there.”

Key features demonstrated in the test included dynamic spectrum access, a fundamental characteristic of cognitive radios that allows all communicating radios to locate available spectrum and switch to open frequencies if they encounter interference — something previously demonstrated in DARPA's XG program.

In addition to operating in traditional peer-to-peer mode for voice communications, each radio served as a node in an ad-hoc data network. This ability enables the radios to extend their effective range if even one radio in the ad hoc network is connected to the Internet, with the IP network acting as a “trunking system, Marshall said.

“Today, we think of push-to-talk radios as having the range of the radio,” he said. “With IP, we now have the ability to say that its range is essentially worldwide — any one of us who are connected to IP can get to these radios, and they're completely interoperable.”

For voice communications, this system is effective because tests demonstrate that push-to-talk voice can be transmitted over three intermediate hops before reaching an IP network, while adding less than 100 milliseconds of latency to the transmission, Marshall said.

On the data side of the equation, a new technology called disruptive-tolerant networking (DTN) ensures that no packets in a transmission are lost, even if a connection is interrupted for a period of time because a user moved into an area where the radio is outside of the signal range. Each radio is expected to include several gigabytes of memory so it can store all information it may need to relay, Marshall said.

“It's one of the features we wanted, because people walk behind buildings, or they walk behind metal vehicles — there's always some disruption on the battlefields or in [public-safety] rescue scenarios,” he said. “You want the system to keep working despite those.”

With a first-phase demonstration planned for April or May, Marshall said he believes DARPA is on track to meet the project goal of developing a cognitive radio by late 2010 that vendors can profitably sell for less than $500 — if the vendor is confident the market will buy at least 100,000 units. DARPA is hopeful public-safety entities will adopt the technology, which would increase the size of the market and lead to a decrease in the cost of the equipment, he said.

“We benefit if there's a broader market for this equipment,” Marshall said.

Eventually, these radios also may include DARPA Interference Multiple Access (DIMA) technology, which is a set of algorithms that enables greater throughput by allowing multiple users to occupy the same time slot and frequency slot, said Brian Pierce, DIMA program manager.

“We embrace interference, not seek to avoid it,” Pierce said. “In the case of DIMA, we will allow simultaneous occupation of the same channel, which would normally be considered interfering with each other, but the algorithms allow the radio to separate out the signals and thereby increase throughput.”

A demonstration a year ago showed that DIMA would enable a single fixed node to receive transmissions from five other nodes simultaneously, resulting in 3.6 times the data throughput of 802.11g with a packet-error rate of less than 1%, Pierce said. Currently, DARPA is adapting DIMA to a mobile environment, something it hopes to demonstrate in February 2010, he said.

Portable use of DIMA would be the subject of another project, Pierce said.

DIMA and XG technologies should complement each other, with XG finding available spectrum in any environment and DIMA allowing those frequencies to be used to their maximum capacity by allowing simultaneous utilization, Pierce said. With DIMA, the military hopes to enable higher-capacity communications, suppress co-channel interference and avoid bottlenecks in very congested areas of the network — features that should be attractive to public safety, as well, he said.

“The whole trend is toward a much more dense RF environment in general,” Pierce said, noting potential interference problems. “Certainly in public safety — I can imagine in acute emergencies — that can be an issue. The bottom line is that DIMA and XG technologies are so fundamental that they will benefit public safety. I see that very clearly.”