TSVCIS Narrowband and Wideband Waveform Forward Error Correction
Tactical Secure Voice Cryptographic Interoperability Specification (TSVCIS) was developed to provide a flexible, secure and adaptive over-the-air communication framework. TSVCIS established both narrowband (NB) and wideband (WB) waveforms. Both NB and WB waveforms utilize the Enhanced Mixed Excitation Linear Predictive (MELPe) based on STANAG 4591. To improve the error resiliency of the communication channel each waveform offers different modes with varying levels of forward error correction (FEC). This allows operators to switch modes based on the noise conditions of the channel.
Table 1 shows the MELPe and FEC bit allocation for each NB voice mode. In NB 1200/2400 mode, MELPe 1200 is used to encode the speech signal, and a Bose-Chaudhuri-Hocquenghem (BCH) code is used for FEC. Together MELPe and FEC bits add up to 2400 bps. On a noisy channel this mode could provide superior voice quality as MELPe 2400 does not always have great resiliency to bit errors. Similarly, for NB 600/2400, MELPe 600 is used to encode the speech signal and multiple BCH codes are used for further bit error correction.
|NB Modes||MELPe Bits||Frame Length(ms)||Forward Error Correction Bits|
In Wideband Modes, the data rate and level of FEC is variable. All modes use MELPe 2400 as a baseline to encode the speech data. Appendix E & F modes use additional bits for the Variable Data Rate (VDR) vocoder. Appendix F uses both BCH and Hamming codes for FEC. Appendices G, H and I implement BCH codes.
|Appendix||Mode||MELPe Bits||MELPe VDR Bits||Forward Error Correction Bits|
|E||WB Voice 16 without FEC||54||280||0|
|F||WB Voice 16 with FEC||54||120||165|
|G||WB Voice 16 Gateway||54||0||110|
|H||WB Voice 12||54||0||180|
|I||WB Voice 8||54||0||110|
VOCAL Technologies, Ltd. TSVCIS software includes BCH and Hamming FEC, along with MELPe and VDR vocoder software. Please contact us to learn more about our TSVCIS and RoIP software solutions.