Improvement And Implementation Of MPPSK Modem

With the continuous development of wireless communication technology, more and more television channels, network programs and high-definition audio-visual products bring people unparalleled visual enjoyment and mental satisfaction but at the cost of occupying more and more spectrum bandwidth. Ultra Narrow Band (UNB) modulation provides high spectrum efficiency, which can be used to solve the problem of spectrum shortage. Based on Software Defined Radio (SDR) platform implementation, this thesis improved and realized a prototype of the M-ary Position Phase Shift Keying (MPPSK) modem by transplanting the platform design to our own hardware. Combined with a VHF transceiver, an image transmission system demonstrated via this MPPSK modem has been built, and relevant performances are tested.Firstly, the MPPSK transmitter is introduced. The principle of MPPSK modulation is described and improved after which Plus One Modulation is proposed. The digital and analog-digital hybrid implementation is discussed. Then the MPPSK transmitter block diagram is presented along with the design principle and main function of the upper computer software. In the order of the signal flow, each module is analyzed in detail and implemented, and then the block diagram and pin description are presented.Secondly, the MPPSK receiver is introduced. The MPPSK demodulation method based on impacting filter is described. The expression of digital impacting filter is presented and its frequency selection feature near its carrier frequency is revealed from its amplitude-frequency response curve. Then the judgment module is analyzed and improved by replacing the amplitude threshold with the slope detection, and the discrimination based on location information is discussed. At last the block diagram of the MPPSK receiver is presented and each module of it is designed and implemented.Thirdly, the hardware design of MPPSK communication system is introduced. The FPGA structure diagram based on the Xilinx Spartan-6 series chip as the core processor is presented. After analyzing power supplies of this design, each voltage is implemented and the design circuits and anti-jamming circuits are presented. Then the minimum FPGA system is introduced whose clock need is analyzed. After explaining JTAG and SPI Flash two configuration modes, the circuits of serial interface and LED, are presented. The modulator is introduced by describing the work process of the amplifiers and RF switches. At last the circuits of ADC clock generator and configuration are presented.In the end, the test of MPPSK communication system is introduced. The measured spectrum figure of air MPPSK modulated signal is presented and shows that-60dB bandwidth of the signal is about 33.33Hz. After calculation the bandwidth efficiency is about 1423.3bps/Hz. By analyzing the test data the performance improvement of bringing in RS channel coding to the communication system is about 3dB. Then the formula of calculating Eb/n0 using signal power and noise power spectral density is derived and how to measure them using spectrum analyzer is described too. This paper explores the anti-frequency-shift capacity of the MPPSK communication system by testing BERs at 7 frequency points and 9 attenuation values. After mapping and analyzing the BER curve, a preliminary conclusion is that the communication system can reach 10-5 BER in a range of 3 kHz if SNR is permitted.