Method of selecting and determining the transmission priority of Voice Grants on an active Channel

By Michael P. McMahon

This document details a method that can be used to determine the transmission order and priority of voice grant updates on an active channels based on Subscriber Unit (SU) affiliation and current channel assignment.  This method is used to advertise voice grants on an active channel in a timely manner and in a way that will minimize the impact on the primary function of the channel. Advertising call activity at the site on an active channel permits monitoring radio units to determine if they should remain on the current channel or depart the current channel to join a higher priority call in progress on a different channel. 

Existing trunked systems utilize a PMG (Priority Monitor Group) flag to determine if a voice grant LC’s should be sent out on all active channels at a site with an SU affiliation. The PMG flag is set on a Talk Group (TG) basis at the Zone Controller (ZC). This works well in most cases, but can lead to the unnecessary transmission of voice grant updates on an active channel. It is also possible to miss desired call updates based on incorrect system configuration.

The functionality of the method is covered in the following paragraphs.

Upon receiving a voice grant from the ZC, the site, in addition to current tasks, will determine if a voice grant update is required for transmission on a channel. In order to determine if a voice grant update is required, the site will compare the group affiliation of SU’s assigned to an active channel  to the TG specified in the voice grant update.

If no SU affiliation is located, the site will specify the transmi...