HF Modem Evaluations for the Advanced Narrowband Digital Voice Terminal (ANDVT).

摘要

During this program, the specifications for the ANDVT HF modem have been refined and detailed evaluation and simulation of the new technical features within this modem have been conducted. These include a multiple-tone signal detection format with an adaptive threshold, a multiple-tone/multiple-stage Doppler estimation algorithm, a matched filter frame estimation algorithm utilizing PN correlation properties, a low-rate error-correction coding approach for protection of the KG sync sequences, an error-correction coding approach specifically designed to protect the critical speech parameters, use of soft-decision (channel measurement) information obtained from the demodulator, and decision-directed Doppler tracking utilizing information from all data tones. The analytical and simulation results provide the desirable result that the preamble can be successfully received at a lower SNR than is required for the reception of high-quality 2400-b/s digitized voice.