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RAWCLI vocoder
Robust Advanced Low Complexity Waveform Interpolation (RALCWI) technology uses
proprietary signal decomposition and parameter encoding methods to provide high voice
quality at high compression ratios. The voice quality of RALCWI-class vocoders, as
estimated by independent listeners, is similar to that provided by standard vocoders running
at bit rates above 4000 bit/s. The Mean Opinion Score (MOS) of voice quality for this
Vocoder is about 3.5-3.6. This value was determined by a paired comparison method,
performing listening tests of developed and standard voice Vocoders
The RALCWI vocoder operates on a “frame-by-frame” basis. The 20ms source voice frame
consists of 160 samples of linear 16-bit PCM sampled at 8 kHz. The Voice Encoder performs
voice analysis at the high time resolution (8 times per frame) and forms a set of estimated
parameters for each voice segment. All of the estimated parameters are quantized to produce
41-, 48- or 55-bit frames, using vector quantization (VQ) of different types. All of the vector
quantizers were trained on a mixed multi-language voice base, which contains voice samples
in both Eastern and Western languages.
Waveform-Interpolative (WI) vocoder was developed in AT&T Bell Laboratories around
1995 by W.B. Kleijn, and subsequently a low- complexity version was developed by AT&T
for the DoD secure vocoder competition. Notable enhancements to the WI coder were made
at the University of California, Santa Barbara. AT&T holds the core patents related to WI,
and other institutes hold additional patents. Using these patents as a part of WI coder
implementation requires licensing from all IPR holders.
The product is the result of a co-operation between CML Microcircuits and SPIRIT DSP. The
co-operation combines CML’s 39-year history of developing mixed-signal semiconductors
for professional and leisure communication applications, with SPIRIT’s experience
in embedded voice products.
Regenerative repeater
Introduction of on-board regeneration alleviates the conflict between enhanced traffic
capacity and moderate system cost by reducing the requirements of the radio front-ends, by
simplifying the ground station digital equipment and the satellite communication payload in
TDMA and Satellite-Switched-TDMA systems. Regenerative satellite repeaters can be
introduced in an existing system with only minor changes at the ground stations. In cases
where one repeater can be dedicated to each station a more favorable arrangement of the
information data than in SS-TDMA can be conceived, which eliminates burst transmission
while retaining full interconnectivity among spot-beam areas.
ADVANCEMENTS IN DIGITAL COMMUNICATIONS
Novel Robust, Narrow-band PSK Modes for HF Digital Communications
Some items that I wrote that may be of general interest: