DoD Dreams of Efficient Spectra
Details on the XG Communications Program are still sketchy. However, a spokesperson for the agency said that it is looking at systems that can redistribute existing wireless capacity on the fly. This would enable more efficient use of currently available bandwidth as devices could "share" spectrum more efficiently.
"This is a program to develop a radio frequency system to dynamically assign existing spectrum," DARPA spokesperson Jan Walker told Unstrung.
The eventual aim, she says, is to create technology that will allow individual wireless devices to "listen" and grab chunks of existing bandwidth that weren't being used by other devices.
This approach is quite different from conventional third-generation (3G) cellular systems, which take what might be termed a 'scattergun' approach to delivering bandwidth to users. Conventional cellular systems transmit signals in all directions to all the users in the range of a particular cell. In other words, along with the right signals hitting the user, the system is also pumping lots of “noise” or “electro-smog” into the radio frequency environment.
The DARPA project, on the other hand, seems like it might have some commonality with systems like those developed by ArrayComm Inc. The ArrayComm system uses software and an array of antennas to continually map the RF environment, allowing it to create a “personal cell” link with each user (see ArrayComm Has Its Chips). The difference is that the DARPA technology would be mapping the environment from the device side rather than from the base station, seeking chunks of available spectrum to use.
Also, Arraycomm is interested in using time-division duplex (TDD) or "unpaired" spectrum, whereas the DARPA project is intended for use over standard “paired” spectrum, which is also called frequency-division duplex (FDD) spectrum.
Walker says that any technology resulting from the XG Communications program could have commercial as well as military applications. However, she stresses that DARPA is currently merely interested in developing technology.
"We want to look at the technology and see what's possible," Walker says. "That will allow the policy makers to decide what they want to do and commercial operators to see if they're interested."
We tried to link to the blurb about this program on the DARPA site, but the URL doesn't work, so we've excerpted it here:
The XG Communications Program is intended to demonstrate enabling technologies and system concepts to improve spectral utilization of military radio frequency emitters by a factor of 20. These demonstrations will include demonstrating a low power/wideband spectrum sensor, time/frequency agile waveforms, and dynamic spectrum access and control. At its completion, the Program will have developed and demonstrated an appliqu? [sic] for legacy and future emitter systems for joint service utility. The Program will develop enabling technologies and system concepts to provide assured military communications and sensors in support of worldwide, short notice deployments through the dynamic redistribution of allocated spectrum. This research will have significant impact on a wide variety of existing and future communications and sensors systems in DoD and commercial environments. This research is also expected to provide a common technical architecture that can meet the needs of both military and civilian future (beyond 3G) mobile communications systems. This Program will require the involvement of a variety of Government (Joint and Service Laboratories) and commercial technology development centers.
— Dan Jones, Senior Editor, Unstrung