They are commonly used today in their 802.11a, 802.11b, 802.11g and 802.11n versions to provide wireless connectivity in the home, office and some commercial establishments.
The 802.11j standard "Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: [4.9–5.0 GHz] Operation in Japan" is designed specially for the Japanese market.
Finalized in 2004, the standard works in the 4.9–5.0 GHz band to conform to the Japanese rules for radio operation for indoor, outdoor and mobile applications.
802.11j defines uniform methods that let APs move to new frequencies or change channel width for better performance or capacity—for example, to avoid interference with other wireless applications.
[1][2] In the United States, the 4.9 GHz band is reserved for use by public safety wireless applications.