Radio spectrum (3 kHz-300 GHz) is a finite and scarce resource. Most of today's radio systems require rigorous protection against interference from other radio devices. Such protection is often provided by exclusive use of an assigned radio spectrum. Most of the radio spectrum is therefore licensed to traditional communication system and services. However, with this approach spectrum resources are sometimes wasted for various reasons. For example, any economic failure of licensed radio services and systems may lead to unused spectrum. As another example, public safety and military radio systems often require spectrum use only occasionally. In still another example, technological progress in communication systems has resulted in the improvement in spectral efficiency. As a result, certain frequency bands, called “white space” licensed to operators may be shared by secondary users. White space refers to portions of a licensed radio spectrum that licensees do not use all of the time or in all geographic locations. This white space spectrum may be dynamically accessed by registered and/or valid secondary users in order to share the spectrum when it is not used by the licensee.