HF Modem Design for the Advanced Narrowband Digital Voice Terminal (ANDVT)
NAVAL ELECTRONICS SYSTEMS COMMAND HYATTSVILLE MD
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A major part of this study is the specification of a modem optimized for transmission of digitized speech over a HF channel. A tenth-order linear predictive coder LPC-10, yielding a data rate of 2400 bs, is used as the speech processor and a HF channel with an available bandwidth of 2.4 kHz is assumed. A modulation format which is frame synchronous to that of the speech processor allows coding to be applied to critical bits generated by the LPC-10 speech analyzer. In addition to the specification of modems for digitizing speech, an equally important part of this study is the development of new preambles which can operate at low signal-to-noise ratios in the presence of time-varying multipath profiles typical of HF channels. This task includes the specification of a waveform for signal presence detection, Doppler estimation, frame estimation, and the decoding of a KG synchronizing sequence. Complexity estimates, based on an implementation by a programmable processor, are obtained for the preamble and digitized speech modem specified in this study.
- Electrical and Electronic Equipment
- Radio Communications