Some Key Techniques About Modulation And Coding In UAV Communication

The UAV (unmanned air vehicle) is playing an more and more important role in modern wars. It is featured by long endurance,large cruise range,heavy overload capability as well as attitude alteration limitless and casualty avoid when flying in hostile territory compared to manned air vehicle. Compared to satellites it has low altitude,controllable movement,convenient arrangement and low cost. New types of UAV are under development in many countries as preponderant battle platforms. With greateroperation radius,UAV communication scope has ranged beyond eyesight. This resulting new problems. Some critical coding and modulation techniques in UAV communication have been discussed in this thesis,including differential phase keying (DPSK),modulation multiple symbol detection (MSD),adaptive trellis coded modulation (ATCM),and space-time coding. This work was supported by the National Defense 973 project.UAV communication has many sophisticated technologies. Several topics on coding and modulation theories of UAV communication were discussed in this thesis. By analyzing features of UAV communication,difference on three aspect between UAV and satellite/civil mobile communication were pointed out,i.e. rapidity of the channel state parameters changing when low-altitude flying,wide range of the signal to noise ratio(SNR) in receiver,and demand on transmission delay. Some applicable approaches were brought forward in this thesis. During the course of research,many analysis and simulation were conducted for various channel states and coding types in order to balance between performance enhancement and reliability. Five parts made up the whole thesis:In the first part,we analyzed characteristics and requirements of UAV communication. Based on modern digital communication technology we gave a solution scheme on UAV communication. We pointed out three critical techniques,which will be discussed in latter parts.In the second part,the necessity of employing differential demodulation in rapid changing channel was explained,performance of multiple symbol detection of MDPSK and decision feed back multiple symbol detection were analyzed. Then we present a new differential demodulation algorithm.The decision data is used to recoverthe carry phase. Given the same observation intervals,this demodulation algorithm has almost the same performance,but the receiver is much more simplified.In the third part,a new adaptive trellis coded modulation (ATCM) solution was presented. We analysis the best coding scheme in different channel modes,different SNR and different demodulation solution. The ATCM solutions in many references are constructed by first choosing a specified code,such as Coset code or multi dimension TCM,then change the information rate by adopting different modulation constellation collection and different way to divide the modulation constellation collection. The approach in this thesis first design the best performance channel code in different channels and different SNR,then design the adaptive coder/decoder. The receiver continually estimates the fading and noise of the channel and transmits them to the transmitter by reverse channel. Then the transmitter use these information to choose the best channel code adaptive the current channel. It is convenient to construct,and can get better performance.The fourth part considered how to improve system performance by adopting transmission diversity in flat fading channels. In the traditional space-time trellis code design,the space diversity,time diversity and channel code are concerned together to get best space diversity,time diversity and code gain. But for the same reason,it haven't the same diversity feature as space-time block code,as well as it haven't the same error correction capability as convolutional code or trellis code modulation. Space-time block code use linear combination to combine the modulo of received signal vectors from different antenna to obtain the same performance as receive diversity. While the space-time trellis code directly combine the...