The development and deployment of DFS-based 5 GHz spectrum-sharing technology has arguably been largely successful, though achieving this success has required considerable use of government resources on an ongoing basis. As spectrum sharing between radars and non-radar systems are considered in other bands, the lessons described above ought to be heeded. Fundamentally, substantial resources will likely be needed to support sharing in new bands. These resources will be needed on both the front end (in design and development phases of sharing technologies) and at the back end, on an ongoing basis after such technologies have been deployed. It is unlikely that complex spectrum-sharing schemes between radars and non-radar systems will ever be fire-and-forget in the sense that they can be deployed without the need for ongoing work by engineers and spectrum managers to keep them functional.

Chapter Contents:

• 4.1 Introduction
• 4.2 Early radar development
• 4.2.1 The reason behind higher radar frequencies
• 4.2.2 Radar spectrum band development
• 4.2.3 Radars need quiet spectrum to work well
• 4.2.4 Why frequency bands allocated to radars require large bandwidths
• 4.2.5 Why radars have tended to have their own spectrum allocations
• 4.3 Regulation of radar spectrum in the United States and worldwide
• 4.4 The advent of radar band sharing
• 4.5 Radar 101: essential knowledge for spectrum sharing
• 4.5.1 Specification of what the radar must do
• 4.5.2 Radar receiver inherent internal thermal noise and other losses
• 4.5.3 The radar antenna
• 4.5.4 Radar wave propagation to and from a target
• 4.5.5 Peak power the radar must transmit
• 4.5.6 Radar pulse repetition rate
• 4.5.7 Radar pulse echo integration for effective detection
• 4.5.8 Radar beam-scanning interval
• 4.6 Radar receiver susceptibility to interference in spectrum-sharing scenarios
• 4.7 Detecting our hypothetical radar for DFS purposes
• 4.7.1 The DFS spectrum-sharing concept
• 4.7.2 Uniqueness of DFS for real-world spectrum sharing
• 4.7.3 Timeline of international (ITU-R) and U.S. national development of DFS
• 4.7.4 DFS introductory efforts, 1996
• 4.7.5 Initial FCC R1998
• 4.7.6 WRC-03 and Recommendation M. 1652, Circa 2003
• 4.7.7 Determination of protection criteria, late 1990s through mid-2000s
• 4.7.8 First DFS implementation steps in the United States, 2003–2004
• 4.7.9 DFS certification testbed development, 2005–2006
• 4.7.10 DFS certification requirements developed, 2005–2006
• 4.7.11 DFS compliance testbed constructed and early testing, 2005–2006
• 4.7.12 Initial DFS deployment experience, 2006–2009
• 4.7.13 Ongoing DFS deployment experience, 2010–present
• 4.8 Technical assumptions of DFS
• 4.8.1 Assumption: radars can be detected while U-NII message traffic is occurring
• 4.8.2 Assumption: detection of radar signals by APs protects radars from all network transmissions
• 4.8.3 Assumption: radar-detection thresholds are adequate to protect radars from harmful interference
• 4.8.4 Assumption: radar waveform testing is sufficiently robust
• 4.8.5 Assumption: firmware updates installed in DFS units after initial certification will not cause DFS to be impaired or disabled
• 4.8.6 Assumption: DFS-equipped U-NIIs will be properly installed and operated
• 4.8.7 Ongoing need for enforcement in DFS bands
• 4.9 More lessons learned
• 4.10 Challenges for manufacturers and vendors
• 4.10.1 Challenges to the communications community in understanding radar systems
• 4.10.2 Difficulty of detecting general, not specific, radar waveforms
• 4.10.3 Lack of industry testbeds for DFS
• 4.10.4 Development of the NTIA testbed and its use by industry and FCC
• 4.11 Challenges for development of DFS test-and-certification protocols
• 4.11.1 Advantages: working from a blank slate
• 4.11.2 Disadvantages: areas of developmental doubt and uncertainty
• 4.12 Interference cases after initial DFS deployment
• 4.12.1 Identification of interfering DFS-equipped devices at San Juan
• 4.13 Ongoing DFS spectrum sharing maintenance
• 4.13.1 Continuing monitoring of DFS devices
• 4.13.2 Consideration of more complex future radar waveforms
• 4.14 Looking forward to future spectrum sharing
• References

Inspec keywords: radar; frequency allocation

Other keywords: spectrum managers; radar spectrum sharing; nonradar systems; frequency 5 GHz; DFS-based spectrum-sharing technology; government resources; dynamic frequency selection

Subjects: Radar and radionavigation; Legislation, frequency allocation and spectrum pollution