Research On Parameter Estimation Algorithms Of Data Link-11

Link-11 tactical data link has now served nearly half a century since the 1970 s put into use,it is a high-security,duplex digital communication system.Currently,in addition to the use of the United States,Australia and other countries are also using Link-11,and the Link-22 which is studing by the NATO is also an upgraded version of Link-11.Therefore,the study of Link-11 has a certain practical value.This article first introduces the Link-11 data link in detail.Link-11 uses 16 tone signals to transmit information,which is similar to the multi-carrier transmission data link system.OFDM is a special multi-carrier transmission system,since the sub-channels of each channel are orthogonal to each other,so the spectrum between the sub-channels are allowed to overlap with each other.In order to make the following discussion of the Link-11 signal carrier estimation performance easier,the OFDM system is also introduced in this paper.Secondly,because the high-order cyclic cumulant can suppress the Gaussian noise in theory,this paper analyzes the mold value of the fourth-order cyclic cumulant of the OFDM signals with 8QAM and 4PSK modulation in the background of general channel noise is not equal to zero only at the subcarrier,so the carrier estimation can be achieved by detecting the fourth-order cyclic cumulant modulus curve.The performance of the algorithm is analyzed under several common window functions.The results show that the algorithm is not affected by the change of window function and has good robustness.Because the communication environment of the battlefield is relatively complex,it is not the ideal channel,so it is necessary to discuss the effectiveness of the algorithm under the frequency selective fading channel.The simulation results show that the algorithm is also applicable to the frequency selective fading channel.Finally,carrier estimation of the OFDM signal with ?/4 DQPSK modulation is carried out by eight-order cyclic cumulants and squared reductions respectively by four-order cyclic cumulants.After the simulation analysis,both of these methods can accurately realize the carrier estimation of the signal,but the square reduction method is at the expense of the reduction with signal to noise ratio.In order to extract the frequency characteristic information of the Link-11 signal,it is necessary to perform the Hilbert transform on the intercepted signal,and then analyze the intercepted signal which transform by the Hilbert with the eighth-order cyclic cumulant and realize the accurate estimation of the carrier of the Link-11 signal by detecting the eight-order cyclic cumulant modulus curve.The simulation results show that the proposed algorithm can realize the blind estimation of Link-11 signal subcarriers,which helps the communication reconnaissance side to obtain more useful information for the signal.