Situation awareness issues in tactical cognitive radio

Cognitive radios (CR) are capable of sensing their radio environment and adjusting their transmit/receive frequencies and other radio parameters intelligently. Software-defined radios (SDR) implement the radio functionality in software using a general-purpose digital signal processor and reloadable software. SDR has proven to be an ideal platform to implement CR applications. While the recently adopted IEEE 802.22 WRAN standard currently leads the civilian applications of CR technology, we point out that there are far more potentials and challenges for military applications of CR in the tactical arena. We consider the example of a team of soldiers who need to slip into enemy territory individually and make mutual contact using CR equipment by forming an ad hoc network. The situation awareness problem here is exacerbated by the likely lack of accurate knowledge of usage patterns of the radio spectrum in the alien territory. This is in sharp contrast with the civilian (e.g. 802.22) case where the frequencies and bandwidth allocations and user activity patterns in the bands of interest (e.g. VHF/UHF TV broadcast bands) are known in advance. The paper reviews the radio environment situation awareness issues in tactical military communications, points out specific problems, and proposes approaches to robust solutions for network establishment and management using CR technology in unknown radio environments. Simulation studies are presented. Two key contributions are a new channel sensing method and a novel technique for frequency rendezvous.