To help achieve universal secure communications interoperability in the Department of Defense (DoD), one intermediate goal has been the development of a universal voice encoder (vocoder) that can seamlessly encode speech at a wide range of variable and fixed data rates to suit a wide range of DoD communication equipment. This report describes the most recent advancements in achieving this goal. Four of the most important areas of improvements presented are: (1) Significant improvements were made to the variable data rate (VDR) vocoder that make it much more robust in less than ideal environments. (2) Error control coding is now extended to all VDR modes. (3) Fixed rate vocoding modes based directly on the VDR encoding method were designed so that transcoding between these options can be done directly and with very little degradation in voice quality. (4) Heavily error protected, fixed rate modes were designed. These modes can be used as fail-safe modes to ensure communicability when channels deteriorate to previously unusable levels.

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To meet beyond line of sight (BLOS) communications requirements, a novel software defined radio relay method for power conservation is proposed. This method is able to achieve approximately 7.5 watt per relay node power savings for SNR challenged links (probability = 1/3), adjacent interference links (probability = 1/3), and 33% clear links (probability = 1/3). This is accomplished by dynamically adjusting the relay methodology between a low power amplifyand-forward (AF) relay method, a compress-and-forward (CF) relay method, and a power intensive decode-and-forward (DF) relay method. To demonstrate the novel architecture the following models were developed in MATLAB/Simulink and tested on an Avnet Zynq-7000 software defined radio (SDR) with Military RT 1439A radios: an audio FM transmitter model, an audio FM receiver model, an AF relay model, a CF relay model, a DF relay model, and the novel SDR relay model.

One intermediate goal towards achieving universal secure voice interoperability in the Department of Defense (DoD) has been the development of a universal voice encoder (vocoder). This vocoder would seamlessly encode speech at a wide range of interoperable variable and fixed data rates to suit a wide range of DoD communication equipment. This paper describes the most important features of such a vocoder and recent advancements in achieving this goal. Specifically this paper will describe three main areas: 1) Summary of the variable data rate (VDR) algorithm and the most recent improvements to the vocoder. 2) Methods for transcoding between fixed rate and variable data rate vocoding modes. 3) Summary of heavily bit error protected, fixed-rate modes.

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