COMMAND RADIO LINK DIGITAL MODEM

FIELD: radio engineering, communication.SUBSTANCE: invention relates to receiving-transmitting devices and can be used in command radio links to transmit command information from a base station to on-board (and in the reverse direction). In a command radio link digital modem during transmission, a signal from the output of a modulator is subjected to spectrum spreading with multiplication using a first multiplier of a low-speed information signal coming from the output of the modulator, with a pseudo-random sequence of bipolar pulses, which is transmitted from a pseudo-random sequence generator. During reception, samples of the complex envelope of the received signal from ADC modules with frequency arrive at a digital down-converter (DDC), which provides filtration in the working frequency band and multiplies the signal with reference oscillation from a digital synthesizer (DDS) in order to compensate for Doppler shift. Further, the signal arrives at a device for searching for a noise-type signal based on delay and frequency, which enables detection of a noise-type signal. Once a noise-type signal is detected, the device for searching for a noise-type signal based on delay and frequency re-launches the means of tracking delay of the noise-type signal to provide initial synchronisation of the reference pseudo-random sequence with the pseudo-random sequence of the received noise-type signal. The system for tracking delay clocks the pseudo-random sequence generator to maintain clock synchronisation of the reference pseudo-random sequence and the pseudo-random sequence of the received noise-type signal (tracking the noise-type signal on delay). The reference pseudo-random sequence is multiplied by the multiplier with the complex envelope of the received noise-type signal and transmitted to a coherent demodulator. The coherent demodulator provides elimination of residual offset on frequency and phase of the received signal and the local reference oscillation generator, signal accumulation over the duration of the noise-type signal and a relaxed solution on the transmitted bit. The relaxed solutions are further transmitted to a noise-immune code decoder. The decoded data are transmitted through a switch to the output of the digital modem. If the encoding mode is turned off, the data from the output of the modulator are immediately transmitted to the output of the digital modem.EFFECT: maintaining working capacity and main characteristics in the presence of Doppl