Research On Key Technology Of Aeronautical Telecommunication Network Cooperative Transmission Based On L-DACS1 Data Link

Aeronautical Telecommunication Network(ATN),as the infrastructure of air traffic management,will gradually evolve into an all-IP network in the next 20 years.At the same time,the terrestrial wireless communication sub-network of ATN will use the most promising L-band Digital Aeronautical Communication System 1(L-DACS1)protocol.L-DACS1 uses orthogonal frequency division multiplexing technology,which greatly improves the channel bandwidth and information rate.However,in order to use spectrum resources efficiently,L-DACS1 usually adopts embedded deployment.i.e.,L-DACS1’s band is embedded in the middle of two adjacent Distance Measure Equipment’s(DME)bands,therefore is severely interfered by Pulse-Pairs that generated by DME.Based on the review of current research of L-DACS1 data link,and combining with the characteristics of multi-scenario communication of aeronautical channel,the physical layer of L-DACS1 is studied in this paper.A new method of aeronautical channel estimation and equalization without prior information is proposed.Additionally,taking into account that although the existing pulse interference mitigation method is applicable in a wide range,it did not make a targeted research based on the unique characteristic of DME interference waveform,we propose a new time-frequency domain DME interference mitigation method,and three new time domain DME interference mitigation methods.Our methods can effectively improve the bit error rate performance.The achievements and innovations of our paper are summarized as follows:1.The performance evaluation model of aeronautical channel is established.The performance of L-DACS1 is evaluated in different modulation modes and flight scenarios.Since the existing channel estimation methods usually rely on the autocorrelation,a new aeronautical channel estimation/equalization method based on the Legendre polynomials expansion model of multi-OFDM-symbol is proposed.Our method does not depend on a priori knowledge,and is more suitable for aeronautical channels with varied communication scenarios.2.A novel DME interference mitigation method based on pulse-blanking and unaffected sub-carriers is proposed.Our method firstly obtains the amplitude constraint according to the unaffected sub-carriers,then uses the constrained Least Squares to estimate those disturbed sub-carriers and finally reconstructs and mitigates the inter-carrier interference by an iterative manner.Experimental results show that our method can effectively mitigate DME interference and is superior to the existing time-frequency DME interference mitigation method.3.A novel DME interference mitigation method based on system identification and sparse representation is proposed.Our method assumes that the complex-valued waveform of the DME pulse-pair can be obtained by practical measurement.Then the Finite Impulse Response model is used to approximate the overall filter characteristics of L-DACS1 receiver,thus the waveform of the deformed pulse-pair in the receiver can be obtained.Finally,combining the sparse representation algorithm,each reconstructed DME pulse-pair is subtracted from the interfered signal.The performance of our method is superior to the existing DME interference mitigation method.4.A novel DME interference mitigation method based on nonlinear frequency estimation is proposed.When only real-valued waveform of DME pulse-pair can be obtained,the nonlinear carrier of the pulse-pair is approximated by a piecewise linear model and then each pulse-pair can be reconstructed.Furthermore,an automatic pulsepair detection method is proposed to enhance the practicability.The pulse-pair waveform is directly detected by an iteratively weighted average of non-overlapping pulse-pairs in the received signal,then each pulse-pair is reconstructed by a sparse representation algorithm and subtracted from the interfered signal.