Radio communications device incorporating channel guard decode and

Abstract

A significantly improved scanning method and apparatus is disclosed which allows tone channel guard decode and scan to optimally coexist on the priority channel. In an exemplary embodiment of the present invention, tone channel guard decoding processing is divided into three processing windows. The first window (hereinafter referred to as SHORTLOOK) serves to indicate whether channel guard might be present. If the SHORTLOOK window processing indicates that the correct channel guard might be present, then a further processing window, hereinafter referred to as SECONDLOOK, is initiated. If at anytime during the SECONDLOOK time period, a second predetermined threshold is exceeded, the system is informed that the correct channel guard tone pattern is most probably present. The audio is then unmuted, even though the SECONDLOOK time period expires before the channel guard tone pattern is capable of being reliably detected in accordance with conventional standards. A LASTLOOK window is utilized when the SECONDLOOK window has detected a tone and opens the audio. During the LASTLOOK window, a further tone channel guard detect threshold is monitored. If this threshold is exceeded, then the priority channel audio is allowed to remain active, thereby serving as a check on the determinations made in the SHORTLOOK and SECONDLOOK windows.