空间飞行器DS-UWB通信多用户检测与频谱共存技术研究
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摘要
随着卫星、小型无人机等空间飞行器技术的快速发展,空间飞行器的编队飞行技术越来越受到人们的重视。在这方面,DS-UWB(Direct Sequence Ultra Wideband,直接序列超宽带)通信系统拥有信息传输速率高、易于实现多址通信等一系列优点,适合于搭建编队空间飞行器的通信链路。编队空间飞行器DS-UWB通信属多址系统,与传统UWB通信有两方面不同。一方面,一般通信距离在300m~10km范围内,大大超出地面室内UWB的通信距离,因此发射功率必定突破FCC(Federal Communication Committee,联邦通信委员会)对室内UWB通信的限制。另一方面, DS-UWB通信要与现行USB(Unified S-band,统一S波段)窄带测控系统信号共存,且由于UWB占用带宽较宽,会覆盖USB传输频段,两种通信体制势必相互干扰,研究二者的频谱共存势在必行。
针对DS-UWB多用户检测技术,本文建立了一种基于匹配滤波和误码识别的联合多用户检测方法,将多用户检测问题归纳为匹配滤波检测判决之后的误码识别与筛选的过程,通过构造基于最优多用户法则的映射函数,将匹配滤波的判决码元映射到特征空间,并通过K均值聚类的方法对码元进行识别,筛选出误码,并通过符号判决法则来纠正误判,从而有效降低误码率。在实验仿真过程中分别对误码率、计算复杂度、抗多址干扰能力以及误码识别率四个主要性能指标进行仿真。实验结果表明,联合多用户检测算法的误码性能逼近最优多用户检测器,其计算复杂度随用户数而线性增长,具有良好的实时处理能力;此外,该联合算法随着用户数量的增加,能够保持良好的检测性能,非常适合于多用户、大容量通信条件下的检测。
针对于频谱共存技术,本文分析了USB窄带信号对于DS-UWB系统的干扰模型,提出了干扰阈值的概念,并且在实验仿真中得出了联合多用户检测对于USB窄带干扰有较好的抑制效果这一结论。此外,本文重点研究了存在编队飞行器DS-UWB通信干扰的情况下USB接收机性能问题。我们分析了在不同的DS-UWB脉冲重复频率与USB基带码速率比值的情况下对于USB接收机接收误码率的影响。实验结果表明,当比值小于1时,主要的干扰形式为脉冲干扰;而当比值远远大于1时,所形成的为高斯白噪声干扰。为了降低和消除脉冲干扰,增加判决采样速率是一个好的方法,因为该方法可以减小DS-UWB信号能量进入USB窄带接收机的机会,实现USB测控信号的可靠传输。
With the rapid development of space craft technology, people make a claim for higher requirement to the communication and control ability of the space craft and begin to focus on the craft formation flying technology. The key to make the formation flying come true is to build the inter-craft link between each two crafts, and the direct sequence ultra-wideband (DS-UWB) communication system is a right choice based on its high transmission rate, large message capacity, high interference resistance and confidentiality and easy to accomplish multi-access communication. Space craft DS-UWB communication system belongs to the multi-access system which can embrace a certain number of transmitters working simultaneously. Compared to the traditional UWB communication system, there are two main differences. On one hand, the communication power will break through the restraint designated by Federal Communication Committee (FCC). On the other hand, the DS-UWB signal will co-exist with the unified S-band (USB) signal in the condition of formation flying, and due to the wide range of frequency band of DS-UWB system that will overlap the transmission band of USB, there must be some interference between two systems, so it is meaningful and useful to ensure the coexistence between DS-UWB and USB.
As for the multi-user detetion technique of DS-UWB system, in this dissertation, we propose a hybrid multi-user detector based on matched filter and error-bit recognizer and regard the multi-user detection as a error-bit recognition and filtering process after the detection of the matched filter. In this detector, we construct a mapping function and map the output codes from matched filter into a one-dimensional feature space to get the amplitude information. After that, set an initial value and classify the codes into right codes and wrong ones by K-means clustering. Finally, make the sign judgment to prevent some right codes being picked out as the wrong codes and correct the wrong codes to reduce the bit error rate (BER) of the system. The simulation results show that the hybrid multi-user detector can improve the BER performance of the system because of high recognition probability of the wrong codes in K-means clustering, especially along with the narrowband interference made by USB. What’s more, the proposed hybrid MUD is not sensitive to the user number. It can achieve good BER performance when there are 20 UWB transmitters in the channel, which is fit for the signal detection in the condition of a number of transmitters and enormous communication capacity.
As for the spectrum coexistence, in this dissertation, we emphasize on the bit-error performance of USB receiver along with the interference created by the formation craft DS-UWB transmitters. We analyze the impact on the bit error rate of USB receiver with different proportion between pulse repetition frequency (PRF) of DS-UWB signal and the baseband transmission rate of USB signal. The simulation results demonstrate that when PRF of DS-UWB signal is approximately equivalent to the baseband transmission rate of USB signal, the main type of interference is pulse interference which creates a intense immediate impulse to the USB signal; when the PRF of DS-UWB signal is much greater than the baseband transmission rate of USB signal, the output of DS-UWB signal passing through RF filter of USB receiver can be seen as the white Gaussian noise. In order to decrease and eliminate the interference to the USB system, it is a better way to increase the rate of judgment impulse which is can decrease the opportunity that the energy of DS-UWB signals enters the receiver of USB system.
针对DS-UWB多用户检测技术,本文建立了一种基于匹配滤波和误码识别的联合多用户检测方法,将多用户检测问题归纳为匹配滤波检测判决之后的误码识别与筛选的过程,通过构造基于最优多用户法则的映射函数,将匹配滤波的判决码元映射到特征空间,并通过K均值聚类的方法对码元进行识别,筛选出误码,并通过符号判决法则来纠正误判,从而有效降低误码率。在实验仿真过程中分别对误码率、计算复杂度、抗多址干扰能力以及误码识别率四个主要性能指标进行仿真。实验结果表明,联合多用户检测算法的误码性能逼近最优多用户检测器,其计算复杂度随用户数而线性增长,具有良好的实时处理能力;此外,该联合算法随着用户数量的增加,能够保持良好的检测性能,非常适合于多用户、大容量通信条件下的检测。
针对于频谱共存技术,本文分析了USB窄带信号对于DS-UWB系统的干扰模型,提出了干扰阈值的概念,并且在实验仿真中得出了联合多用户检测对于USB窄带干扰有较好的抑制效果这一结论。此外,本文重点研究了存在编队飞行器DS-UWB通信干扰的情况下USB接收机性能问题。我们分析了在不同的DS-UWB脉冲重复频率与USB基带码速率比值的情况下对于USB接收机接收误码率的影响。实验结果表明,当比值小于1时,主要的干扰形式为脉冲干扰;而当比值远远大于1时,所形成的为高斯白噪声干扰。为了降低和消除脉冲干扰,增加判决采样速率是一个好的方法,因为该方法可以减小DS-UWB信号能量进入USB窄带接收机的机会,实现USB测控信号的可靠传输。
With the rapid development of space craft technology, people make a claim for higher requirement to the communication and control ability of the space craft and begin to focus on the craft formation flying technology. The key to make the formation flying come true is to build the inter-craft link between each two crafts, and the direct sequence ultra-wideband (DS-UWB) communication system is a right choice based on its high transmission rate, large message capacity, high interference resistance and confidentiality and easy to accomplish multi-access communication. Space craft DS-UWB communication system belongs to the multi-access system which can embrace a certain number of transmitters working simultaneously. Compared to the traditional UWB communication system, there are two main differences. On one hand, the communication power will break through the restraint designated by Federal Communication Committee (FCC). On the other hand, the DS-UWB signal will co-exist with the unified S-band (USB) signal in the condition of formation flying, and due to the wide range of frequency band of DS-UWB system that will overlap the transmission band of USB, there must be some interference between two systems, so it is meaningful and useful to ensure the coexistence between DS-UWB and USB.
As for the multi-user detetion technique of DS-UWB system, in this dissertation, we propose a hybrid multi-user detector based on matched filter and error-bit recognizer and regard the multi-user detection as a error-bit recognition and filtering process after the detection of the matched filter. In this detector, we construct a mapping function and map the output codes from matched filter into a one-dimensional feature space to get the amplitude information. After that, set an initial value and classify the codes into right codes and wrong ones by K-means clustering. Finally, make the sign judgment to prevent some right codes being picked out as the wrong codes and correct the wrong codes to reduce the bit error rate (BER) of the system. The simulation results show that the hybrid multi-user detector can improve the BER performance of the system because of high recognition probability of the wrong codes in K-means clustering, especially along with the narrowband interference made by USB. What’s more, the proposed hybrid MUD is not sensitive to the user number. It can achieve good BER performance when there are 20 UWB transmitters in the channel, which is fit for the signal detection in the condition of a number of transmitters and enormous communication capacity.
As for the spectrum coexistence, in this dissertation, we emphasize on the bit-error performance of USB receiver along with the interference created by the formation craft DS-UWB transmitters. We analyze the impact on the bit error rate of USB receiver with different proportion between pulse repetition frequency (PRF) of DS-UWB signal and the baseband transmission rate of USB signal. The simulation results demonstrate that when PRF of DS-UWB signal is approximately equivalent to the baseband transmission rate of USB signal, the main type of interference is pulse interference which creates a intense immediate impulse to the USB signal; when the PRF of DS-UWB signal is much greater than the baseband transmission rate of USB signal, the output of DS-UWB signal passing through RF filter of USB receiver can be seen as the white Gaussian noise. In order to decrease and eliminate the interference to the USB system, it is a better way to increase the rate of judgment impulse which is can decrease the opportunity that the energy of DS-UWB signals enters the receiver of USB system.
引文
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