Recognition Of Complex Signal Modulation Based On Receiver And FPGA Implementation

Modulation identification means that the receiver automatically discriminates the modulation mode recognition of received signals.It is a procedure of signal processing between signal detection and demodulation.With the development of software radio,adaptive modulation and cognitive radio technology,the future trend of civil and military communication systems is to send and receive information in a more flexible manner.Modulation identification is a key technology for implementing intelligent communication systems.In recent years,the recognition of two-leveled multi-carrier signals has also received more attention.In the current modulation recognition method,the signals are usually assumed to be pre-processed and the parameters of the received signals are known.There are some certain limitations in practical engineering applications.At the same time,for two-leveled multi-carrier signals with unknown signal parameters,the modulation recognition system is not fully studied.According to the different signal sets used in the actual project engineering,this thesis has obtained the following research achievements:Aiming at the existing problems of low recognition rate,large computation and difficulty of real-time recognition in the current modulation recognition methods when identifying the set{BPSK,QPSK,AM-FM,MTONE-FM} of narrow wideband mixed signal,a recognition method based on all digital PLL is proposed to extract the modulation information of signals.The Fourier Transformation(FFT)is used to estimate initial frequency and bandwidth,and narrowband signals and wideband signals are distinguished according to the bandwidth.Carrier recovery and modulation demodulation are completed after down conversion,cascaded integrator comb(CIC)extraction and low-pass filtering.The wide-band signals are identified by demodulated I and Q information sequences.The narrow-band FM signal with composite modulation is identified according to the number of impulse components in FFT spectrum of frequency information tracked by PLL.Aiming at the problems of the small signal samples and the bad recognition performance in the mixed set of direct modulation signal and two-leveled multi-carrier signal {BPSK,QPSK,BPSK-FM,QPSK-FM},a modulation recognition method based on dual all digital receiver and goodness of fit test is proposed in this paper.The algorithm based on the goodness of fit test starts directly from the statistical distribution function,the information carried by the data is mined thoroughly,and better results can be obtained in the condition of small samples.In the proposed algorithm,the all digital receiver is firstly used to complete bit synchronization and carrier synchronization for the received blind signal,the baseband signal is demodulated accurately.BPSK,QPSK and PSK-FM signals are distinguished by goodness of fit test according to the baseband information demodulated by the first PLL.Then,the FM signals are identified in the class.The phase discrimination signal output by the PLL is down converted and filtered as the input signal of the second PLL,The phase difference of baseband signal demodulated by PLL is used to realize the intra class discrimination of FM signal of compound modulation.The proposed modulation recognition method based on dual all digital receiver and goodness of fit test has the characteristics of low computational complexity and small sample number.