portant meeting, or in a classroom. A Time-of-day information enables time division CR could learn to classify its situation into "user multiplexing on a coarsegrained basis, or even a fine- interruptible" and "user non-interruptible." The radio grained basis if the quality of the time is sufficiently ac- accepting aural inputs can classify a long-running ex- curate. Time-of-day information may gate policies in and change in which only one person is speaking at a time as out. Additionally, very fine knowledge of time may be a meeting or classroom and autonomously put itself into used in geolocation applications. vibration-only mode. If the radio senses its primary user Cognitive radio: The technologies required CHAPTER 2.4b is speaking continuously or even 50 percent of the time, language framework is needed to express policy. For ex- it may autonomously turn off the vibration mode. ample, if an established policy rule is constructed in the presence of other rules, the union of all policies is ap- 2.4b.5.6 Software technology plicable. This enables hierarchal policies and policy by exception. As an example, suppose the emission level in Software technology is a key component for CR de- band A is X dBm, except for a sub-band A' for which the velopment. This section discusses key software technol- emission-level constraint is Y dBm if a Z KHz guard band logies that are enabling CR. These topics include policy is allowed around legacy signals. Even this simple struc- engines, artificial intelligence (AI) techniques, advanced ture is multi-dimensional. Layers of exceptions are signal processing, networking protocols, and the Joint complex. The policy engine must be able to constrain Tactical Radio System (JTRS) Software Communica- behavior according to the intent of the machine-readable tions Architecture (SCA). policy. An inference capability is needed to interpret multiple rules simultaneously. Policy engines In the case of spectrum subleasing, policies must be Radios are a regulated technology. A major intent of d