As a prelude to proposing rules, the FCC is seeking comment on many issues related to dynamic spectrum access technologies, including how they can increase spectrum capacity and what the Commission can do to promote their use.
A basic idea in these systems is to take advantage of the time a user is not transmitting, and let someone else use that spectrum until the original user needs it again. If the second user is in the middle of something when the first user needs it back, the second user identifies another piece of spectrum to move to. Both users, ideally, notice no degradation of performance. Overall spectrum capacity is increased.
For the purpose of the FCC’s inquiry, dynamic spectrum access is a broad term that includes cognitive radio; radio that is aware of the RF environment and uses that information to make decisions based on its objectives. The term Software Defined Radio (SDR) is sometimes used in this context, but an SDR device may be used for other purposes.
The following issues are some of those identified in a Notice of Inquiry (NOI) that the Commission adopted at its November 30 meeting:
- Technical advances. The Commission wants information on the state of the art of spectrum sensing, interference suppression, propagation models, and policy-based radios, whose emissions are governed by a set of rules. Information is sought on how radios could be tested as part of the equipment authorization process. A related issue is how the Commission should police interference complaints in an increasingly-dynamic radio environment.
- Development and deployment. The Commission looks for opportunities to progress dynamic radio systems. It wants comment on how its database and Spectrum Dashboard can be made more useful. It asks how existing secondary-spectrum market rules might be revised to accommodate dynamic radios. (Existing rules are described as providing “wide latitude” for flexible spectrum use and spectrum leasing, and there’s a suggestion that the public doesn’t fully realize that.) The Commission asks which bands are most appropriate for dynamic spectrum access techniques, discusses the opportunity to aggregate “scraps” of narrower-band spectrum into something more useful, and asks about the feasibility of using spectrum in the 40 GHz range and higher.
- Test-beds. A test-bed would be an area in which certain frequencies are set aside, and guidelines established, for dynamic radio experimentation beyond that contemplated by the experimental licensing rules. The Commission looks for opportunities to fund such a test-bed and encourage participation.
- Real-time databases. It’s possible to take the database model used for TV white spaces and apply it to other bands. Dynamic radio systems could use such databases to determine current spectrum availability. The experience with TV white space operation can inform this and subsequent dynamic spectrum access proceedings.
- Real-time spectrum monitoring. The Commission has a vision of deploying spectrum monitoring equipment throughout the country, in a manner similar to weather monitoring stations seen along highways and atop some schools. A dynamic radio system could query the monitoring equipment for a specific area, and would then have current information on the RF environment. The Commission asks if such a system is practical, and who should run it.
- Public safety. The Commission asks about the potential use of dynamic radios by the public safety community to address ongoing interoperability problems.
The Commission does not address the issues of the definition of harmful interference, the rights of incumbent spectrum users, and receiver standards, except to say that they are matters of general spectrum policy that might be addressed in future proceedings.
Some of the issues in the NOI are interrelated. When a dynamic radio system queries a spectrum database, the information received is processed and an appropriate message is sent to the radio. This introduces latency, and the messaging over the air interface can consume a substantial portion of the data capacity one had hoped to gain. One way to relieve this, depending on the state of the art, is to add functionality to the radio that allows it to make more decisions on its own. This increased processing, however, reduces battery life. These and other tradeoffs are being explored by system developers. It would help them, and the FCC’s goal of promoting these systems, if the rules eventually adopted give them sufficient freedom to innovate.