| In some special situations,such as rescue environment communication for earthquake relief,communication in remote mountainous areas,communication of special arms,forest fire etc.,other communication networks cannot communicate reliably.At that moment,the preferred communication technology is short-wave communication,which can be used as the last communication guarantee for reliable transmission of signals.In wireless communication,the signal to be transmitted is inevitably disturbed,as is short-wave communication.The adaptive communication techniques are employed in a short-wave communication system,and various parameters in the communication system,such as a transmission information rate of the communication system,a carrier frequency,a modulation mode,etc.,are adaptively changed according to a channel environment.Therefore,comprehensive consideration of various parameters suitable for channel characteristics has significance for the communication system to reliably transmit information.In this paper,a set of short-waveband adaptive modulation communication system can be implemented based on the Field-Programmable Gate Array(FPGA)design.The modulation and demodulation modes are adaptively adjusted according to channel environment in this system.At the same time,the switching of two modulation modes and the switching of two transmission information rates are also realized.When the channel noise is strong,the low-density modulation mode is adopted to ensure the reliability of the transmission;on the contrary,the high-order modulation mode is adopted to enhance the information rate of the transmission.The entire adaptive communication system mainly includes two parts: the physical layer and the data link layer.The system can simulates the channel communication environment by superimposing noise signals of different powers in the channel,estimating the signal-to-noise ratio(SNR)of the channel in real time at the physical layer,and sending the SNR value to the data link layer for decision,and choosing the appropriate modulation mode with the reference of SNR value.The specific research contents are as follows:Firstly,the point-to-point communication between Binary Differential Phase Shift Keying(BDPSK)and Quadrature Differential Phase Shift Keying(QDPSK)modulation is realized,including modulation,synchronization,demodulation and other parts.Secondly,the coherent demodulated envelope signal is sampled,processed in the demodulation part circuit to complete the signal to noise ratio estimation operation.A new data buffering and computing method is proposed.The data stream is continuously sent to the computing module continuously,and the value of the signal-to-noise ratio SNR is output in real time,which effectively improves the processing speed and saves the buffer space.Thirdly,the data link layer is mainly responsible for data and command processing,transceiver,and modulation switching.It consists of four modules: data control module,Cyclic Redundancy Check(CRC)module,modulation mode control module and data processing module.The four modules cooperate with each other to realize the data processing and the switching mechanism of the modulation mode. |
