The neXt Generation program or XG is a technology development project sponsored by DARPA's Strategic Technology Office, with the goals to "develop both the enabling technologies and system concepts to dynamically redistribute allocated spectrum along with novel waveforms in order to provide dramatic improvements in assured military communications in support of a full range of worldwide deployments."
In the Wireless World Research Forum of 27 October 2003, Preston Marshall, program manager of DARPA XG Program, said "The primary product of the XG program is not a new radio, but a set of advanced technologies for dynamic spectrum access."
References
DARPA XG Wikipedia(Text) CC BY-SA