In general, cognitive radio system (CRS) can be viewed as a radio system using technology that allows it to obtain knowledge of its operational environment, established policies and its internal state
dynamically and autonomously adjust its operational parameters and protocols according to the obtained knowledge and predefined objectives
and to learn from the results obtained. Given such definition many use cases and business cases are possible, including heterogeneous type CRS, spectrum sharing type CRS, and dynamic spectrum assignment type CRS. As a result, several standardization activities have been performed recently to enable such use cases and exploit the corresponding business opportunities. One of such standardization has been performed within the IEEE 1900.4 Working Group (WG) on "Architecture and Enablers for Optimized Radio &amp
Spectrum Resource Usage." In February 2009, the first IEEE standard defining CRS has been published originating from the IEEE 1900.4 WG and entitled "Architectural Building Blocks Enabling Network-Device Distributed Decision Making for Optimized Radio Resource Usage in Heterogeneous Wireless Access Networks." This paper gives technical overview of this standard. Also, it describes ongoing activities in the IEEE 1900.4 WG aimed at developing two draft standards: P1900.4.1 for "Interfaces and Protocols Enabling Distributed Decision Making for Optimized Radio Resource Usage in Heterogeneous Wireless Networks" and P1900.4a for "Architecture and Interfaces for Dynamic Spectrum Access Networks in White Space Frequency Bands." ©2009 IEEE.