Research On Joint Coded Modulation Based On MIMO Technology For Data Link Of Unmanned Aerial Vehicle

With the application of new task load on unmanned aerial vehicle(UAV),such as large field of view high-resolution digital aerial camera,high-precision aerial imaging spectrometer,synthetic aperture radar,etc.,there will be a lot of real-time color,thermal images,video and other informationin the investigation process,which result in the amount of information back to increase the geometric progression.However,the low capacity of existing data link communication is one of the main reasons for the development of UAV system.At present,single antenna was mainly used to communicate UAV wih the ground control center.Its channel capacity severely restricts the maximum transmission rate,resulting in a long time to send,increasing the risk of unmanned aerial vehicles were shot down.Joint coded modulation technology is an important way to achieve bandwidth efficiency,LDPC-CPM is a special case of joint coded modulation technology,which improves power while maintaining CPM constant envelope and high spectral efficiency.Utilization rate.In order to further improve the information transmission rate,the paper combines MIMO technology with joint coded modulation technology,namely MIMO-LDPC-CPM transmission technology,which can greatly improve the channel capacity and transmission efficiency,and can obtain the coding gain and diversity gain,and(Such as MIMO-OFDM,MIMO-QPSK/QAM)can not be achieved by maintaining the constant envelope of CPM modulation and many other advantages.Therefore,the study of MIMO-LDPC-CPM transmission technology in the UAV link application has important theoretical value and promote the application prospects.This paper aims to improve the channel capacity of UAV reverse link,explore the combination of MIMO,LDPC and CPM.According to the different requirements of two typical application scene performance of line of sight and non-line of sight,LDPC-CPM transmission program,the specific research content is as follows:(1)In the line of sight scenario,a LDPC-CPM transmission scheme based on Layered Space-Time Code(LSTC)is designed——(LSTC-LDPC-CPM).According to the Rimoldi decomposition model,the CPM is decomposed into a combination of a continuous phase encoder(CPE)and a memoryless modulator,combined with external LDPC codes,random interleavers,serial-to-parallel converters established LSTC-LDPC-CPM system.Using the characteristics of soft information exchange between CPM and LDPC,the principle of Turbo detection is applied to the system,and an iterative detection receiver based on soft input soft output(SISO)algorithm is designed.The main parameters such as the number of antennas,LDPC code length and bit rate,CPM correlation length are simulated,and the influence of BST on the bit error rate performance and implementation complexity is determined.The implementation parameters of LSTC-LDPC-CPM scheme are determined.(2)In the non-line of sight scenario,an LDPC-CPM transmission scheme based on Space-Time Block Code(STBC)is designed——STBC-LDPC-CPM.According to Laurent decomposition principle,CPM is decomposed into a number of weighted sums of amplitude pulse signals,combined with differential precoding and space-time block coding,the STBC-LDPC-CPM system is constructed.The separate and demodulate of MIMO-CPM is used to the output soft information based on the minimum mean square error(MMSE),Combining LDPC Decoding to design iterative detection decoding receiver.The simulation results are based on the LDPC code length and bit rate,CPM association length,weighing BER performance and implementation complexity,determine the implementation parameters of the STBC-LDPC-CPM scheme.(3)Aiming at the positive feedback phenomenon in the iterative receiver of STBC-LDPC-CPM scheme,a weighted combined average external information exchange method is proposed.At the same time,the adjunctive iteration criterion and the weighted combined average external information processing mode Combined with dynamic iteration decoding.The improved external information processing method can effectively improve the iterative convergence of the system,combined with iterative stop criterion can reduce the average number of iterations and improve the real-time performance of the system.(4)Evaluate the performance of LSTC-LDPC-CPM scheme and STBC-LDPC-CPM scheme.The performance of the proposed scheme is evaluated in terms of reliability,transmission rate and receiver complexity.The applicability of the two schemes in the line-of-sight and non-line-of-sight scenarios is analyzed by using the single-antenna scheme with the same rate as the comparison sample.The MIMO-LDPC-CPM transmission technology provides a reference and feasibility study for the application of the new generation of UAVs in the reverse link.