Methods and systems for presenting an alert when leaving a direct-mode coverage area

Abstract

At least one embodiment takes the form of a process carried out by a given mobile radio in a group of mobile radios. The process includes broadcasting heartbeat messages in accordance with a group-wide symmetric-timing protocol and maintaining an in-range list of mobile radios. The in-range list is maintained at least in part by (i) adding mobile radios that are not already on the in-range list to the in-range list upon detecting transmissions from such mobile radios; (ii) maintaining, for each mobile radio on the in-range list, a respective keepalive timer in accordance with the group-wide symmetric-timing protocol; and (iii) removing mobile radios from the in-range list upon expiration of the respective keepalive timers. The process further includes presenting an alert via a user interface when a count of mobile radios on the in-range list falls below a notification threshold.

Dependencies are inferred from the claim text.