| In military communications,frequency hopping communication greatly improving the antijamming performance and improve the reliability of communications because of its hidden features.Today,with the increasing demands on communication quality,and the increasing complexity of interference,ordinary frequency hopping communication system has been unable to meet the requirements of military communications.Cognitive frequency hopping communication apply the cognitive radio technology to frequency hopping communication.It can reduce the influence of interference and improve the reliability of communications by constantly sensing the spectrum environment and analyzing all kinds of interference in the environment in real time.In order to achieve more efficient and reliable cognitive frequency hopping communication,the efficient and high-performance receiving technology is used to deal with the received signal.It can improve the bit error performance of the system,so as to improve the reliability of communication system.This paper focuses on the study of the receiving technology for GMSK and TCM-8PSK in cognitive frequency hopping system.The main research works are listed as follows:1.This paper first introduces the design scheme of cognitive frequency hopping communication system.At the same time,it introduces the whole structure of cognitive frequency hopping communication system using GMSK and TCM-8PSK respectively.Also proposes a scheme of frequency hopping frame for these two modulation methods.2.QC-LDPC code has been studied.A method of constructing QC-LDPC code parity check matrix is introduced,and the performance analysis is carried out for different decoding algorithms.Combined with simulation results and computational complexity,the modified min sum algorithm has more advantages in hardware implementation.3.Focus on the study of the joint demodulation and decoding method of GMSK signal,in which the inner iteration adopts Max-Log-MAP algorithm,and the outer iteration is the modified min sum decoding algorithm of QC-LDPC code.The simulation analysis of the joint demodulation and decoding scheme and other demodulation methods of GMSK is carried out separately.It shows that the joint scheme has certain advantages in bit error rate performance.4.It focuses on the study of Viterbi decoding which is used to the demodulation of TCM-8PSK.And the performance simulation is carried out.It shows that TCM-8PSK can obtain a certain coding gain without change the communication bandwidth and the information transmission rate.5.It proposes an FPGA implementation method of joint demodulation and decoding scheme of GMSK.Also an FPGA implementation method of Viterbi decoding which is used to the demodulation of TCM-8PSK is carried out.The receiving part is debugged and verified respectively based on project’s hardware platform. |
