便携式点对点可见光通信终端的实验研究

利用开关键控-非归零码(OOK-NRZ)调制编码技术,设计并实现了一对基于ARM7处理器(LPC2148)的便携式点对点可见光通信(VLC)收/发终端。发送端由编码器、光源驱动器及单个白色发光二极管(WLED)构成,接收端由可见光探测器、信号处理电路及解码器构成。实验研究了WLED的发射谱和可见光探测器的响应谱,测试分析了VLC信道的时域和频域的电-光-电(EOE)响应。阐述了系统结构和原理,编写了通信软件并制定了相关协议,实现了系统的软、硬件集成。利用研制出的通信装置,建立了点对点通信链路,并开展了数据通信实验。结果表明,在发送端,为了最大化地降低误码率(BER),WLED的调制系数应设置为0.68~1.00,即在一定的交流调制信号幅度下,需要向WLED提供合适的直流偏置电压;在接收端,在一定的阈值判决门限电压下,VLC传输呈带通特性。在所优化选择的系统参数下,系统的通信距离为0.5m,可达到的最快信息传输速率约为4 Mbps,BER小于10-6。利用多个WLED构成阵列光源,系统可进一步满足更长距离的通信需求,从而在室内、外短途通信方面具有潜在的应用价值。     

测试设备对高精度光纤陀螺误差的影响及抑制方法研究

分析了影响光纤陀螺仪测试精度的主要误差因素,详细研究了速率转台、测试工装、时间基准源等常见测试设备对光纤陀螺误差的影响。提出了基于高精度计数器对于转台精度评价结合长周期、转台固定周数的测试等抑制方法。实验结果表明,采取抑制措施后,测试工装误差引起的零偏测试误差减小了66.7%,速率转台误差引起的标度因数绝对误差以及时间基准误差引起的标度因数重复性误差均减小了一个数量级。研究结果对高精度光纤陀螺仪精度的提升以及测试设备的改进具有指导意义。     

Performance of orthogonal frequency division multiplexing based M-ary quadrature amplitude modulation in asymmetrical dual-hop mixed RF-FSO transmission system

This paper investigates the performance of a dual-hop mixed relay system with radio frequency (RF) and free-space optics (FSO) communication under the effect of pointing error (PE) and atmospheric turbulence (AT). This paper considers a system where RF and FSO links are cascaded. The RF link is modeled by Nakagami-m fading, and the FSO link is modeled as gamma–gamma (G-G) fading channel. Both the channel models use orthogonal frequency division multiplexing (OFDM) with M-ary quadrature amplitude modulation (QAM). The expressions for probability density function, cumulative distribution function, signal-to-noise ratio, and ergodic capacity are derived. The moment generating function (MGF) of fading and the bit error rate (BER) of the OFDM-based M-ary QAM scheme is derived in terms of Meijer's G-function. It has been observed that, in fixed gain relay systems, the modulation scheme's BER is dominated by the SNR of the RF link. While in a variable gain relay system, the turbulence conditions of the FSO system affect the SNR and the BER of the modulation method. The feasibility of heterodyne detection and intensity modulation direct detection (IM/DD) is analyzed in terms of outage probability and ergodic capacity. The results can be used to choose the optimal modulation order and relay system for QAM-OFDM-based optical wireless systems.     

Improved aquila optimization-based parameter evaluation framework and meta-heuristic algorithm in radio-over-fiber SpatialMux multi-input multi-output long-term evolution system

In heterogeneous access network, Multiple-Input Multiple-Output (MIMO) radio-over-fiber (RoF) system is an efficient approach for multiple signal transmission with low cost and complexity. The performance of RoF fronthaul system in MIMO system will be varied with different nonlinear effects. By adjusting various transmission parameters, such as the input signal power or the laser bias current, the nonlinear impacts produced by the RoF system can be reduced. In this paper, a novel algorithm Improved Aquila Optimization (IAO) is proposed to optimize transmission circumstances of MIMO RoF system. It determines the appropriate bias current for both lasers and Radio Frequency (RF) signal power in a short period. The input signals are wavelength multiplexed with Intensity Modulation and Direct Detection (IM/DD) applied. The carrier as well as transmission frequency is governed by the MIMO-Long-Term Evolution (LTE) standard. The proposed system is implemented in MATLAB, and the performance is evaluated. The experimental results show that fast convergence and trade-off between noise and nonlinearity are obtained with varying bandwidth. In the experimental scenario, the maximum Error Vector Magnitude (EVM) of 1.88, 3.14, and signal-to-noise ratio (SNR) of 3.204, and 2.698 was attained for both quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM) modulation. [Correction added on 24 April 2023, after first online publication: the SNR values were corrected in the preceding sentence.] For 100 iterations, the processing time was reduced to 0.137 s. When compared with the conventional state-of-the-art approaches, the accuracy and computational complexity of the proposed approach are improved.     

批量Excel校准曲线文件自动加密解密的软件设计

随着我国航空技术的不断发展,飞机结构越来越复杂,被测试的参数数量剧增,校准曲线文件数量也随之剧增。因此,手动设置Excel校准曲线文件密码的工作效率已经影响到了试飞任务的执行。为了提高Excel校准曲线文件加密解密的效率,深入研究了Excel COM组件的接口和使用方法,采用VC++开发软件,利用Windows API函数设计和实现对批量校准曲线文件的自动加密解密。通过对软件进行测试,软件运行稳定可靠。     

雾和气溶胶的光学特性对前向散射和总散射能见度仪性能的影响

建立了完整的散射式能见度仪（SVM）探测方程,搜集整理了典型天气条件下雾和气溶胶的观测资料,在此基础上,运用米散射理论计算并分析了雾和气溶胶的光散射特性及其对前向散射能见度仪（FSVM）和总散射能见度仪（TSVM）探测性能的影响。结果表明:大气散射特性显著影响SVM 的探测误差,且FSVM 受影响程度超过TSVM;雾天气下FSVM 与TSVM 的探测误差基本相当,而气溶胶天气下FSVM 探测误差比TSVM 约大6%;相同天气条件下,TSVM 接收的光通量约为FSVM 的7倍,但TSVM 泄露的散射光仍不能忽略,否则将导致较大的系统误差;若不计光通量测量误差,雾天气下FSVM 与TSVM 的探测误差分别为4.06%、5.54%,气溶胶天气下分别为35.80%、30.33%。所得结果可为SVM 的光路设计、误差分析和比对试验等提供支持。     

机载双站SAR频率同步与误差补偿

机载双站SAR系统中，收发平台是分置的，收发载机本振频率源的不同步，将会引起回波信号相位误差的积累，其积累时间长度为整个合成孔径时间．本文给出了“GPS＋独立高稳定频率源”实现双站SAR收发频率同步的方法，并对该同步方法引起的同步相位误差进行了分析，提出了一种基于收发平台视距通信的频率同步误差补偿方法．最后给出了对几种典型频率同步误差的补偿仿真，仿真结果表明，该频率同步误差补偿方法能够有效地补偿由收发不同步引起的误差项．     

便携式红外热像仪外场测温误差分析及修正

红外测温成像技术精度的影响因素较多。尤其在实验外场的复杂环境下,有时难以达到预期指标。为了有效提高便携式红外热像仪的外场测温精度,利用红外测温理论模型梳理和总结了外场测温的主要影响因子,然后利用外场实测数据对其进行了统计分析,并提出了相应的修正方法。结果表明,修正后的数据标准差由0.89 K降至0.3 K,有效提高了测温精度。     

卫星激光通信中基于Zig-Zag结构的原模图QC-LDPC码构造方法

为应对卫星激光通信信道的时变性、改善传输的可靠性,提出一种基于Zig-Zag结构的原模图QC-LDPC码构造方法.该方法将原模图与Zig-Zag结构的移位系数设计方法相结合,构造校验矩阵围长至少为8且码长码率可灵活选择的ZZ-QC-LDPC码.仿真结果表明:该方法所构造的ZZ-QC-LDPC码在误码率为10-6时,与同码率下基于等差数列和原模图构造的QC-LDPC码和基于最大公约数构造的QC-LDPC码以及具有大围长快速编码特性的QC-LDPC码相比,其净编码增益分别提高了约0.2,0.1和0.64 dB,且在较大码率范围内均具有良好的纠错性能.     

惯性/卫星导航系统实际导航性能评估算法

针对惯性/卫星组合导航进行实际导航性能(Actual Navigation Performance,ANP)评估,是保证飞机所需导航性能(Required Navigation Performance,RNP)及航空运行安全的关键.提出了惯性/卫星组合导航系统实际导航性能评估算法,从卡尔曼滤波器位置协方差矩阵开展分析,...