Hi Luigi,
Before you can truly set up RF Grouping each WLC must have at least one AP installed that can hear another AP that is associated with the other WLC;
Given all controllers share the same RF Group Name, in order to form an RF Group, a WLC needs to only have a single AP hear one AP from another WLC
Workflow involved when an RRM system collaborates to form an RF Grouping. It is also imperative to understand where RF computations happen. This is an outline of the steps that the Cisco Unified Solution goes through in order to learn, group, and compute all RRM features:
Controllers, whose APs must have an RF configuration computed as a single group, are provisioned with the same RF Group Name. An RF Group Name is an ASCII string each AP uses in order to determine if the other APs they hear are a part of the same system.
APs periodically send out neighbor messages that share information about themselves, their controllers, and their RF Group Name. These neighbor messages can then be authenticated by other APs that share the same RF Group Name.
APs that can hear these neighbor messages and authenticate the messages based on the shared RF Group Name, pass this information up to their connected controllers. The neighbor messages consist primarily of controller IP addresses and information on the AP that transmits the message.
The controllers, which can now identify the other controllers that are part of the RF Group, form a logical group to share the RF information. Subsequently, the controllers elect a Group Leader.
Equipped with detailed information about the RF environment for every AP in the RF Group, a series of RRM algorithms are run at the RF Group Leader. The algorithms are designed to optimize AP configurations related to these functions (with the exception of the Coverage Hole Detection and Correction Algorithm, which are run at the local controller to the APs):
Dynamic Channel Assignment (DCA)
Transmit Power Control (TPC)
From this good doc;
http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008072c759.shtml#overview
Hope this helps!
Rob
