MELPe TSVCIS Vocoder Software

Tactical Secure Voice Cryptographic Interoperability Specification (TSVCIS) was developed to provide interoperability between Waveforms utilizing different vocoder rates, levels of encryption and forward error correction.

TSVCIS specifies both Narrowband (NB) and Wideband (WB) Waveforms, which provides the framework for improved speech intelligibility, security, and robustness of defense radio communications. The NB Waveform implements MELPe at the standard data rates (2400, 1200 and 600 bps). In the WB Waveform the bit rates of MELPe have been extended to include data rates of 8000, 12000 and 16000 bps. This allows for the radio users to selectively determine the characteristics of the radio communication. If the radio communication is noisy, a lower MELPe rate can be selected and the number of parity bits used for the FEC can be increased. On the other hand, a higher MELPe bit rate can be selected to improve the intelligibility of the speech, if the channel’s error rate is low. TSVCIS was designed to be inter-operable to with SCIP, so the MELPe bit rate extensions were designed to easily switch back to using standard Narrowband MELPe. 

VOCAL Technologies, Ltd. provides software solutions for core TSVCIS requirements:

• VOCAL’s enhanced Mixed-Excitation Linear Predictive (MELPe) vocoder based on STANAG 4591
• VOCAL’s implementation of Naval Research Laboratory (NRL) Variable Data Rate (VDR) vocoder. Floating point and
  optimized Fixed Point variations available.
• Forward Error Correction (FEC) software, both BCH and Hamming codes as specified by TSVCIS
• Unclassified Advanced Encryption Standard (AES) cryptography

Our TSVCIS software is available either standalone, as an embedded software library, with a VoIP stack or as part of a complete design. 

TSVCIS Narrowband Data Modes

The foundation of the speech coding for TSVCIS is the (MELPe) vocoder, which is commonly known in the U.S. as MIL-STD-3005 and in NATO as STANAG 4591. There are five main Narrowband(NB) Data Modes, in which TSVCIS utilizes all three rates of MELPe (2400 bps, 1200 bps and 600 bps). It is recommended to utilize the noise pre-processor (NPP) of MELPe. The NPP adaptively estimates the noise spectrum of the input speech signal and attenuates the noise components and enhances the speech.
All NB data modes encrypt the MELPe bits. Two of the modes use Bose-Chaudhuri-Hocquenghem (BCH) Forward Error Correction (FEC) to provide better protection against channel errors.