Research On Key Communication Technologies Of DS-UWB Micro Uavs

In modern battlefield, the unmanned aerial vehicles (UAV) play an important role. Especially beyond-the-horizon communications relay role of UAV will become increasingly prominent. In order to communicate in the serious complex hash environment, the information transmission with high symbol rate between UAVs must have a strong anti-jamming capability. The direct sequence ultra-wideband (DS-UWB) technology has the characteristics of low power, high data transmission speed, wide bandwidth, high multi-path resolution and good penetrability, and it can satisfy the requirements of UAV communication links. In this dissertation, some key technologies of the UWB will be discussed.Firstly, the history of UWB will be introduced briefly, and the challenges of applying the UWB to the UAV communication will be discussed. Then the problem of the selection of monocycle which is suitable for UWB communication system of UAV is discussed. In the case of limited payload, the mathematical model of propagation characteristics of DS-UWB UAV communications is analyzed and established in free space and frequency dependent two-ray path channel. In two-ray path model, Rake receiver is employed, which uses maximum ratio combing technology. The model reveals the relations among the propagation parameters, such as the bit error rate (BER), transmission distance and data transmission rates, different orders of Gaussian pulse and transmission power. Simulation results show that: in the same situation of the BER, transmission distance and data transmission rate, the first order Gaussian pulse has the minimum transmission power. Due to UAV's limit of payload, the first order DS-UWB should be employed as the carrier waveform. In the situation of BER equals to 10-6Secondly, a direct sequence ultra-wideband (DS-UWB) channel estimation method using Maximum Likelihood algorithm for the indoor dense multi-path UWB channel of preamble structure is suggested in the proposal of IEEE P802.15.TG3a. The Normalized Mean Square Channel Estimation Error (NMSCEE) is employed to measure the , theSNR of two-ray path model is 3.01dB lower than free space model. The transmission power of the two-ray path model is about 50% lower than free space propagation model, and the BER performance of two-ray model is better than free space model. All of those provide a basis for the signal chosen of DS-UWB UAV communication links. performance of the estimation method. The effect of the estimation performance influenced by different assisted-pilot numbers and the different Gaussian waveforms as UWB monocycle is discussed in different SNR conditions. Due to Federal Communications Commission (FCC)'s limits, the order of the derivative Gaussian pulse should be 5 of more. The simulation results show that the estimation algorithm can achieve satisfying performance with 60 as the pilot number. And when the pilot number is less than 50, the fifth order Gaussian pulse is the best choice. If the pilot number is more than 50, the ninth order Gaussian pulse is suitable. The results can be as the references and the basis for the practical UWB system.Finally, the problem of UWB synchronization acquisition is analyzed. In order to solve this problem, the TR-UWB system is proposed. In the first place, the reason that the two level signaling can largely reduce the search space is described. And then, the two stage acquisition scheme is proposed. According to simulation results, the TR-UWB can achieve good probability of detection with less time consumption, comparing with the traditional method.