STU-III secure bearer service option invocation reliability over enhanced IS-136 TDMA digital cellular ACELP IS-641 vocoder

The U.S. Government is working with cellular/PCS standard bodies to develop bearer service option modes that will enable secure end-to-end digital voice between cellular handsets and existing STU-III (Secure Terminal Unit, 3rd generation) phones. A requirement is that handsets be able to reliably detect brief analog "go-secure" signaling sent by a STU-III as it attempts to transition from plain voice to encrypted voice mode, especially under conditions of fading errors. A simulation experiment is designed and conducted, demonstrating the feasibility of detecting such a proposed bearer option request under many environmental conditions.