A narrowband tactical ratio for the VHF and UHF frequency bands

The development of an ultra-narrowband tactical mobile radio communications system that uses linear modulation, speech bandwidth reduction, and digital signal processing for the VHF and UHF frequency bands is discussed. The speech bandwidth reduction technique, called dynamic frequency band extraction, is performed in the frequency domain, where approximately only 1/3 of the original speech bandwidth is dynamically extracted for transmission. Data information (required for finding compensation, control information. etc.) is interlaced with this discrete-time. continuous-amplitude, frequency-domain voice signal. Once modulated, using quadrature amplitude modulation (QAM) and ultralinear RF conversion and amplification, the occupied (70 dB) RF bandwidth is about 2.4 kHz, representing a more than tenfold increase in the number of available frequency allocations, compared with actual 25 kHz terrestrial land mobile FM radios. >