Synchronization and Noise Immunity of Communication Systems Using Signals with Multi-position Modulation

Abstract

The presented report describes the results of the development of a digital communication system designed for use in a complex noise environment or in a counteraction. The system is designed to transmit video messages in real time.Mechanisms for providing increased protection against interference are implemented by selecting a spread spectrum signal with data transmission in a cyclic delay of pseudo-random sequence. Demodulation and synchronization algorithms for receiving signals are described in detail.Working prototype of the system transmitting video messages was created. Radio channel based on the AD9361 transceiver (Analog Devices). The layout works in the frequency range 3 – 4 GHz. Video reception is performed when the signal/noise ratio at the input of the receiver is minus 9 dB.The selected signal and synchronization method made it possible to implement protection against interference having a spectrum width commensurate with the width of the signal spectrum (about 100 MHz) using the pseudo-random frequency hopping. The frequency hopping is possible in a cyclic form or in the form of rapid frequency tuning in the event of damage to the selected frequency channel.The noise immunity of the developed system is compared with a system using a signal with a multi-position quadrature modulation 256 QAM. The developed system has a higher noise immunity at the same speed of information transmission.