Tactical Wireless Communications and Networks: Design Concepts and Challenges

7.1 Cognitive Radios and Spectrum Regulations

The tactical wireless arena has addressed spectrum scarcity in waveforms, such as the high-band networking waveform (HNW) previously mentioned, by using directional antennas. Unlike omnidirectional antennas, which dissipate spectrum in all directions, directional antennas' focused beams allow for more efficient spectrum reuse. In commercial cellular wireless, base stations use a similar concept, with sector/carrier planning, to aid spectrum reuse. Even with such techniques, spectrum reuse without CRs is inefficient. Studies completed by the US Federal Communications Commission (FCC) Spectrum Policy Task Force, in rural and major metropolitan³ areas, showed that the overall spectrum usage ranges from 15 to 85 percent. The FCC questioned its regulatory approach and started seeking solutions to solve this spectrum bottleneck challenge, without touching the allocations controlled by major industries (primary users such as radio and TV broadcast) that might oppose an overhaul of the current system. One possible solution is to create secondary users which can be controlled by the primary users; however, this could result in a logistical nightmare for the FCC. Another approach, referred to as “opportunistic spectrum sharing,” would allow secondary users to access primary users' spectrum (without primary user regulation) while the spectrum is not in use. As long as secondary users do not interfere with primary users in specific frequency bands, ...