基于CNN-SPGD算法的相干光通信像差校正方法研究

为了降低大气湍流对自由空间光通信系统传输性能的影响,建立了一套自适应光学校正系统来校正高阶像差。对该系统的混频效率,误码率和迭代次数等参数进行研究。首先,将图像的Zernike系数划分为8个大类,256个小类,通过CNN模型预测输入光斑的大类。对于每一小类的像差,取每一阶系数范围的中点作为标准点形成一个标准Zernike系数向量,按照其对应的标准电压作为初始校正电压进行校正。实验结果表明:随机并行梯度下降算法使混频效率达到0.80、0.85和0.9需要的迭代次数分别为110次、161次和280次;在使混频效率达到相同值的前提下,CNN-SPGD(Convolutional Neural Networks-Stochastic Parallelism Gradient Descent)算法所需的迭代次数分别为4次、37次和141次。而在相同的迭代次数下,CNN-SPGD算法在系统中的混频效率更高,误码率更低。CNN-SPGD算法与SPGD算法相比,像差校正速度更快。该CNN-SPGD算法可以大幅度减少传统自适应光学系统的迭代次数,满足激光通信的各种需求。

混合毫米波射频/多输入多输出-自由空间光通信中继系统

为准确评价混合毫米波射频/多输入多输出-自由空间光通信(millimeter Wave Radio Frequency/Multiple Input Multiple Output-Free Space Optical,mmW RF/MIMO-FSO)中继系统的性能,利用Meijer-G函数推导出混合mmW RF/MIMO-FSO中继系统端到端中断概率、误码率以及遍历容量的闭合解析表达式。该混合系统的中继采用固定增益方案、接收端采用等增益合并方式合并多路信号。mmW RF信道服从Nakagami-m衰落,FSO信道服从Gamma-Gamma分布。数值仿真结果显示,MIMO技术可以有效缓解由于大气湍流强度的增强而导致的混合中继系统性能降低。随着激光发射器和光电探测器相对应的收发孔径数目的增加,混合中继系统性能逐渐增强,但与此同时系统的复杂度也不断提高。综合分析可知,当激光发射器发送的激光信号束与光电探测器使用的接收孔径数相等且都为2时,MIMO-FSO链路的性能达到最佳状态。

基于室内地图推演与信号穿墙修正的定位优化方法

针对室内定位中信号穿墙非视距传播带来的测量误差问题,提出了一种穿墙测距与视距测距相混合的穿墙修正定位优化方法。在室内典型的隔墙非视距场景中,建立了近似拟合信号穿墙传播特性的测距模型,将穿墙入射角、墙体结构、介电常数、墙体厚度等因素参数化,并借助室内地图进行节点与锚点间的隔墙判定,仅根据室内地图及冗余测距信息即可进行定位求解。仿真与UWB实测实验结果表明,在考虑信号穿墙传播的多变地图场景下,所提方法的室内定位平均精度优于加权最小二乘法的平方测距定位方法。

混合RF/FSO中继系统中断性能研究

为准确评价混合射频/自由空间光通信(RF/FSO:Radio-Frequency/Free-Space Optics)中继系统性能,利用Meijer's G函数推导得到混合RF/FSO中继系统端到端中断概率闭合解析表达式。该混合RF/FSO中继系统采用放大转发中继、RF(Radio-Frequency)双天线发射技术。RF信道衰落服从Rayleigh分布,FSO(Free-Space Optics)信道衰落服从M分布。蒙特卡洛仿真验证了推导结果的准确性。

The Research of Indoor Positioning Based on Visible Light Communication

The key techniques in indoor positioning based on visible light communication and the state of the art of this research were surveyed. First, the significance of indoor positioning based on visible light communication from two aspects of the limitations of current indoor positioning technology and the advantages of visible light communication was discussed; And then, the main four technology of indoor positioning based on visible light communication were summarized and the triangulation of RSS method and the principle of image positioning were introduced in detail; Next, the performance characteristics of various typical algorithms were compared and analyzed; In the end, several suggestions on future research of indoor positioning based on visible light communication were given.

On Channel Assignment for Multicast in Multi-Radio Multi-Channel Wireless Mesh Networks:A Survey

The major challenge faced by wireless mesh networks is the capacity reduction caused by interference,and interference can be reduced or even eliminated through appropriate channel assignment.This article presents a comprehensive survey of channel assignment schemes for multicast in multi-radio multi-channel wireless mesh networks.We analyze the state-of-the-art channel assignment schemes for multicast and provide comprehensive taxonomy of the latest work.In general,we classify the channel assignment schemes for multicast into two types,that is,sequential multicast routing and channel assignment(SMRCA)and joint multicast routing and channel assignment(JMRCA).Detailed review of channel assignment schemes in each category is provided.Possible future research directions and corresponding solutions are also explored to motivate research interests in the field of channel assignment for multicast in wireless mesh networks.

Partially Overlapped Channels- and Flow-Based End-to-End Channel Assignment for Multi-Radio Multi-Channel Wireless Mesh Networks

Capacity reduction is a major problem faced by wireless mesh networks. An efficient way to alleviate this problem is proper channel assignment. Current end-toend channel assignment schemes usually focus on the case where channels in distinct frequency bands are assigned to mesh access and backbone, but actually backbone network and access network can use the same IEEE 802.11 technology. Besides, these channel assignment schemes only utilize orthogonal channels to perform channel assignment, and the resulting network interference dramatically degrades network performance. Moreover, Internet-oriented traffic is considered only, and peerto-peer traffic is omitted, or vice versa. The traffic type does not match the practical network. In this paper, we explore how to exploit partially overlapped channels to perform endto-end channel assignment in order to achieve effective end-to-end flow transmissions. The proposed flow-based end-to-end channel assignment schemes can conquer the limitations aforementioned. Simulations reveal that loadaware channel assignment can be applied to networks with stable traffic load, and it can achieve near-optimal performance; Traffic-irrelevant channel assignment is suitable for networks with frequent change of traffic load,and it can achieve good balance between performance and overhead. Also, partially overlapped channels' capability of improving network performance is situation-dependent, they should be used carefully.

Implementation and decoding method of OCC system based on MIMO

The application of high-frame-rate cameras as well as the complex image processing techniques will lead to a series of problems,such as high system cost and long transmission delay.In this paper,we introduce narrow-band filtering technology to reduce the impact of optical noise and reduce the complexity of image processing from the physical level.We also introduce multiple-input multiple-output(MIMO)technology into the optical camera communication(OCC)system to increase system transmission rate,and propose a light emitting diode(LED)array decoding algorithm based on the directional projection method to reduce the system delay.By accumulating the target pixel values in each row and column of the image,the proposed method then determines the position and boundary of the detected target to distinguish the target area from the background.Experimental results indicate that the communication distance can reach up to 5.5 m without error bits detected.When the LED array at the transmitter of this system flashes at a frequency of 12 Hz,the transmission rate can reach 126.32 bit/s.

Decoding algorithm with multiple features based on optical camera communication system

The performance of decoding algorithm is one of the important influential factors to determine the communication quality of optical camera communication(OCC) system. In this paper, we first propose a decoding algorithm with adaptive thresholding based on the captured pixel values under an ideal environment, and then we further propose a decoding algorithm with multiple features, which is more suitable under the existence of the interference of light sources. The algorithm firstly determines the light-emitting diode(LED) array profile information by removing the interfering light sources through geometric features, and then identifies the LED state by calculating two grayscale features, the average gray ratio(AGR) and the gradient radial inwardness(GRI) of the LEDs, and finally obtains the LED state matrix. The experimental results show that the bit error ratio(BER) of the decoding algorithm with multiple features decreases from 1×10^(-2) to 5×10^(-4) at 80 m.