Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network

This is referred to as the "global harmonization standard." It was ratified in 2001. 802.11d defines Physical Layer requirements that conform to international regulatory requirements. As such it promotes worldwide use of Wi-Fi.

When the original 802.11 standard first became available, only a handful of regulatory domains, i.e. U.S., Europe, and Japan, had rules in place for the operation of wireless LANs based on the 802.11 series of standards. To support a widespread adoption of Wi-Fi, the 802.11d Task Group's crafted a definition of PHY requirements that would satisfy the unique regulatory requirements for channelization demanded by various local regulatory bodies throughout the world.

Making new use of existing spectrum always requires testing and assurances that new users won't interfere with legacy users and new applications won't affect adjacent spectrum bands. In some regions, the spectrum used by Wi-Fi equipment is adjacent to commercial radar systems. In other areas, Wi-Fi devices are thought to be prone to interference from cordless phones or microwaves.

The 802.11d Task Group has an ongoing charter to define PHY requirements that satisfy various regulatory needs as they develop. This is especially important for operation in the 5 GHz bands because the use of those frequencies differ widely from one country to another.