http://www.simocogroup.com http://www.etsi.org/technologies-clusters/technologies/digital-mobile-radio http://www.dmrassociation.org/dmr-standards.html http://www.dmrassociation.org/about-dmra.html https://www.fcc.gov/general/narrowbanding-overview http://wiki.radioreference.com/index.php/Trunking_Basics