Research On Technology Of High-efficiency Ground-to-air Direct Sequence Spread Spectrum Communication For Low-altitude Networked Ammunition

Networked ammunition is a new concept intelligent weapon with functions of intelligent detection,target identification,coordinated attack,damage assessment,etc.According to application environment,networked ammunition can be divided into ground network ammunition,network guidance ammunition and cruising missile.Cruising missile is a typical low-altitude networked ammunition which is the combination of unmanned aerial vehicle(UAV)and ammunition.Compared with conventional ammunition,cruising missile can fly over the designated area and update target.Compared with UAV,cruising missile can attack the target at the same time it discover the presupposed target.Then cruising missile has the advantages of fast response and precise attack,depending on secure and stable communication link.Therefore,it makes sense to research ground-to-air communication link of low-altitude networked ammunition.In view of the complex electromagnetic environment and high dynamic characteristics,how to improve the secrecy and anti-interference of communication systems has become an important topic in the research of ground-to-air data communication link.Direct sequence spread spectrum(DSSS)is an important anti-jamming technology for low altitude network ammunition with its advantages of high spectrum efficiency,good security and strong anti-interference performance.However,when DSSS is applied to low-altitude networked ammunition,there are some limitations.For example,rapid Doppler changes and multipath interference caused by low-altitude flight will have a serious effect on the performance of synchronization loop,complex electromagnetic environment will degrade the adaptability of adaptive threshold,potential application of binary offset carrier(BOC)signal in ground-to-air communication link will pose a challenge to signal acquisition,and the rapid development of reconnaissance technique and electronic equipment will put forward new challenges to the anti-interception of the system.Therefore,considering the unique characteristics of low-altitude networked ammunition,the key technologies of ground-to-air communication link are studied.(1)The pseudo-random sequence of ground-to-air communication link determines the performance of anti-interference,ant-interception and acquisition probability.A pseudo-random sequence optimization strategy is established to satisfy the high dynamic characteristics of the low-altitude carrier platform.Based on the restraints between Doppler frequency shift,multipath interference and data modulation,the evaluation system of pseudo-random sequence is established according to the index of the performance measurement of the low-altitude networked ammunition communication link.Based on the results of comprehsensive evaluation,a pseudo-random sequence family suitable for low altitude networked ammunition communication links is selected to improve the anti-interference and anti-interception performance of spread spectrum signals in complex electromagnetic environment.(2)In low-altitude flight,complex terrain will cause severe multipath fading and affect the setting of synchronous threshold,which is the key factor determining the average acquisition time.In order to reduce the impact of complex battlefield environment,satisfy the timeliness of low-altitude networked ammunition communication and optimize the average acquisition time,an adaptive threshold analysis model based on noncoherent accumulation and average acquisition time is established.Based on in-depth analysis of the relationship between incoherent accumulation and false alarm probability,detection probability and average acquisition time,this model realizes adaptive threshold by adjusting the noncoherent accumulation.Then the average acquisition time of the system is optimized.(3)In view of the peculiar characteristics of binary offset carrier(BOC)signal,such as restraining multipath interference,improving tracking accurary and expanding channel capacity,it has become a potential application of ground-to-air data communication link.In order to remove the multi peaks of the autocorrelation function of CBOC signal,a new fuzzy suppression algorithm named SSCM is proposed.According to correlation functions can be superposed by triangle functions,local auxiliary signals for suppressing side-peaks are constructed.The two local auxiliary signals are processed separately with the CBOC signal,and the results are accumulated.This algorithm can improve the acquisition probability,ensure the tracking accuracy and suppress zeros of cross-correlation.This method can achieve unambiguity acquisition and further improve the acquisition probability of ground-to-air DSSS signals.(4)The rapid development of electronic reconnaissance equipment seriously threatens the application of DSSS in Networked ammunition.In order to improve the anti-interception and anti-interference performance of low altitude network ammunition communication uplink and improve the engineering feasibility of code hopping technology,differential self-encoding spectrum system(DSESS)is proposed.DSESS uses G function to establish the mapping relationship between pseudo-random sequence and data information,so that the spread spectrum sequence jump randomly.Then the data information is hidden in a hopping code with good randomness and uniformity to achieve secure transmission.On the basis of maintaining the anti-multipath interference characteristics,DSESS enhances the ability of anti-interception and anti-interference,and improves the engineering feasibility of the self-code system.