Maximizing signal strength for OFDM inside buildings

Propagation inside buildings suffer from large shadowing and high multipath effects. This is a serious problem for wireless local area network (WLAN) systems. This paper shows that shadowing and path loss can be minimized by exploiting the multipath tolerance of orthogonal frequency-division multiplexing (OFDM). This can be achieved by using multiple transmission antennas spread over the area of a WLAN cell. These antennas act as repeaters, transmitting and receiving the same signal at the same time. This decreases the average path loss, but increases the multipath delay spread. Using OFDM allows the advantage of reduced path loss to be utilized without detrimental effects of inter-symbol interference caused by the increased delay spread. The reduced path loss allows an increased system capacity, quality of service, or a decrease in intercellular interference in a cellular WLAN     

A summary of the transmitting and receiving properties of antennas

An expression for the electric field radiated by an arbitrary current distribution is given, which leads to a straightforward characterization of an antenna by a complex vector called the equivalent length. All classical transmitting parameters-such as the radiated power density, power intensity, radiation resistance, directional gain, and gain-are simple functions of the equivalent length. The same is true for the receiving parameters: induced voltage, available power, equivalent surface, and antenna factor. Eliminating the equivalent length between the gain and an equivalent surface provides a simple, direct, and general proof of the fundamental relation for antennas     

空间光DPSK发射与自相干接收系统实验

搭建通信速率为10 Gbps的光DPSK调制发射、自相干接收单元实验测试平台。采用光相位调制和自相干接收技术实现光DPSK系统设计。为稳定输出信号解决相位漂移,发射单元设计出自适应增益控制单元和交叉点自适应控制单元。在系统测试平台上,完成差分编码模块、发射单元和自相干接收单元及系统性能测试。实验室环境条件下,测得系统接收单元灵敏度为-48 dBm,通信系统误码率优于1×10-7;误差矢量幅度为7 %,通信性能较好,满足系统设计指标要求。     

A comparison of time delay spread and signal level measurements within two dissimilar office buildings

A detailed analysis of time delay spread and signal level measurements at 850 MHz was performed within a large office building. The results were compared with studies of a much smaller and dissimilar office building. The results were found to be substantially the same, despite the physical differences of the buildings themselves. This may be due to external geographical features. Overall worst-case root mean square (rms) time delay spreads in the buildings were 250 ns and 218 ns in the larger and smaller building, respectively. However, these values improved to under 100 ns when there was a good direct path between the antennas. Time delay spread was also shown to be independent of relative antenna polarizations of the transmitter and receiver, even on line-of-sight paths. Received signal levels were below -90 dB with reference to the level at 0.3 m separation, in the worst cases.     

Deterioration of average evoked potential waveform due toasynchronous averaging and its compensation

In order to improve the signal-to-noise ratio of evoked potentials, the responses to repetitive stimuli are usually recorded, and the averaging method is applied to them. If each starting point of the averaging varies with respect to the response because of asynchronous sampling of the measurement data, the average waveform of the evoked potential signal is distorted by the averaging. We analyzed the asynchronous averaging in the frequency domain and derived a relationship between the fluctuating time and the degree of the deterioration. By using this relationship, a required sampling rate was derived to ensure the accuracy of the averaging. Furthermore, we also deduced a compensation procedure for the asynchronous averaging in case of coarse sampling.     

On the relationship between the transmitting and receiving properties of an antenna

The response of a linear, passive antenna in free space to an incident plane wave is related to its far-field radiation in the reverse direction bybar{h}^{r}=bar{h}^{t}. The vector effective heightbar{h}^{r}characterizes the voltage across the open-circuit antenna terminals induced by an incident plane-wave field, and the correspondingbar{h}^{t}characterizes the far-field radiation of the antenna when driven by a current injected into the same terminals. This relationship, which is shown to follow from the well-known reciprocity principle, both includes phase and makes mathematically explicit the polarization relation involved in the identity of the transmit and receive patterns of an antenna.     

谈大功率短波宽带天线的收发开关

本文首先研究和探讨了大功率短波宽带天线和大功率短波宽带天线收发开关设计的意义和价值,并对一种大功率短波宽带天线收发开关的设计展开研究和探讨,为大功率短波宽带天线收发开关的研究和设计提供资料参考.     

一种无人机视频信号的收发电路设计

为了提高无人机在恶劣环境下的工作能力,将从遥感系统中采集的视频信号转换为数字信号,设计了基于CPLD系统的FSK调制解调收发电路,用VHDL语言实现了FSK调制解调的设计;同时将CMOS反向器应用于接收电路,构成模拟放大器将信号放大。整个设计基于ALTERA公司的Quartus Ⅱ开发平台,使用MAXⅡ系列的CPLD芯片实现,并用OrCAD PSpice软件对放大电路进行仿真分析。实验结果表明无线收发电路能够保证图像传输质量,达到预期设计的无线传输要求。     

无线激光图像传输收发电路的设计与实现

设计并实现了激光发射与接收电路模块,每个模块主要由激光收发电路、数据处理器、存储器和视频转换电路等4部分组成,具有体积小、使用灵活的特点.重点介绍了622 Mbit/s高速激光收发电路的设计.研究并实现了对视频数据流的时序控制,如有效图像数据的提取与重新组合、存储等,采用曼彻斯特编码保证了激光信号接收与时钟恢复的稳定.在使用一组简易光学天线的情况下,理论通信距离大于6 km,并成功地完成了距离大于100 m的实验.结果表明:该系统可以稳定地传输图像,适合地面短距离高速接入等应用,为进一步研究无线激光通信技术提供了实验平台.     

Prediction models and measurements of microwave signals scatteredfrom buildings

The planning of urban microwave communication systems must consider the harmful interference these systems cause to existing links, and vice versa. Site shielding is an interference reduction technique wherein a building is used deliberately to shield a radio terminal from interfering signal. The site-shielding factor (SSF) is, however, influenced by the arrival of interference on paths caused by reflection and scatter from nearby buildings. Prediction models are needed to estimate the effects arising from the scatter. The paper develops prediction models based on a plane reflector and discusses experimental measurements aimed at the validation of these models. The paper describes the results of the initial stage of a continuing investigation into building scatter aimed at the formulation of a prediction procedure for site shielding suitable for radio system planning and coordination     

GPS spoofer countermeasure effectiveness based on signal strength,noise power,and C/N0 measurements

Spoofing sources can effectively disrupt a GPS receiver during the acquisition phase by generating multiple false correlation peaks and increasing the noise floor. Such deceptive correlation peaks can mislead the GPS receiver into acquiring the spoofer generated signals rather than the authentic signals. Also, the spoofer can increase the receiver noise floor to bury the authentic signals in the noise and at the same time generate correlation peaks with amplitudes commensurate with reasonable C/N₀ expectations. The main focus of this paper is on assessment of the reduced effectiveness of the GPS spoofer countermeasure during acquisition where the GPS receiver utilizes C/N₀ discrimination. As shown, whereas the C/N₀ discrimination is of limited effectiveness, with a modest circuit modification, the receiver can measure the absolute power of the correlation peaks, which is an effective means of detecting and discriminating spoofer sources. It will be shown that employing absolute power monitoring technique considerably reduces the vulnerability region of the receiver compared with the C/N₀ monitoring techniques. Copyright © 2012 John Wiley & Sons, Ltd.     

收发光波长差异产生的反常声光偏转器指向偏差

从求解描述反常声光相互作用几何关系的Dixon方程出发,得到了具体参数下的一组较优的入射角和衍射角.根据实际应用系统的需求,分析了包括TeO2晶体在PAT系统光路中的放置方向及其端面切割角度等在内的参数,设计了一种收发光波长均为800nm的反常AOD模型结构.基于此结构,分析了发射光波长取800～830nm时,由收发光...     

Measurements of the transmitting and the receiving patterns of a dipole antenna for an electron plasma wave

The transmitting and the receiving patterns of a dipole antenna for an electron plasma wave have been measured by using the interference method. The results agree fairly well with the theoretical patterns that were predicted from the fluid model analysis and also experimentally prove the reciprocity relationship between the transmitting and the receiving patterns, which is theoretically found to be valid in the plasma wave approximation. The characteristics of the transmitting and the receiving efficiencies versus the dc bias voltage applied to the dipole antenna have been also experimentally investigated.     

一种测量平均小信号增益及饱和光强方法

探讨了一种测量激光器平均小信号增益及饱和光强的方法.通过改变光学谐振腔出光镜的透射率适测得三组出光功率,然后由所测功率值和相应的透射率,根据所给出的数学模型求解出结果.这种方法的优点是不需要专门的探测光源.因此,对于不方便找到适合探测光源的情况,如对某种化学激光器的测试诊断有一定的可行性.同时,为了更加清楚地说明这种方法,还给出了一种改变透过率的光路结构的方案.     

Improvements in near-field discrimination for radar or sonar systems by the use of separate transmitting and receiving arrays

A recent letter described how the near-field discrimination of a radar or sonar could be improved by the use of multiplicative signal processing. This letter shows that similar improvements can be obtained by the use of a much simpler technique employing separate transmitting and receiving arrays.     

Measurement of magnetic fields inside single- and double-Layer reinforced concrete buildings during Simulated lightning currents

This paper presents measurements of the voltages, the magnetic fields and the magnetic-field derivatives inside a structure simulating reinforced concrete buildings. The test structure comprises a cubic cage of 2-m side length with single- or double-layer reinforced grids. The injected lightning currents simulate the positive, the negative first and the negative subsequent return strokes with amplitudes of /spl sim/ 77, 16, and 4.8 kA, respectively. Three distinct points of the lightning stroke impact to the structure roof are considered, namely, the center, the mid-edge and the corner. In the case of a single-layer cage, the results reveal that slow-rising magnetic-field components are generated inside the structure for various lightning currents. This effect becomes dominant for the case of the double-layer cage. For all the simulated currents, striking to the structure corner induces the lowest voltage across it, but gives the highest values for both the resultant magnetic fields and the magnetic-field derivatives. For all striking points, the magnetic fields have the highest values for positive strokes, while the negative subsequent strokes give the highest amplitude of the resultant magnetic-field derivatives and roof-to-floor voltages. Compared to the case of a single-layer cage for the negative subsequent strokes, the use of a double-layer cage shows a considerable mitigation of the voltage across the structure, and a moderate mitigation of both the resultant magnetic fields and the magnetic-field derivatives.     

N-delta and differential average signal processors:detailing of their signal and noise response

A detailed and complete derivation of the impulse response (and transfer function) for the most commonly used charge-coupled-device (CCD) output signal processing techniques is presented. A basic mathematical model is discussed for 2-δ double sampling and is then generalized to n-sample systems. The method is adapted to show how the impulse response for the differential averaging technique is derived. The relationship between n-δ and differential average is illustrated mathematically. Simple signal gain derivations using the previously derived impulse responses are given. White, 1/f , and 1/f² noise power are discussed in light of the derivation. Graphs illustrating the noise dependence of both n-δ and differential average processor types are included     

蒸发波导激光雷达的原理与信号接收系统设计

从海洋大气相对湿度的角度出发建立了大气折射率变化与气溶胶激光散射特性的理论联系,着重对蒸发波导激光雷达的信号接收系统进行了设计。针对微弱光信号接收、光电转换与电压放大的难点,前端信号调理电路采用雪崩光电二极管和宽带低噪声放大器对所述高速瞬态微弱光信号进行接收和二级放大,同时保证了系统的高增益、宽宽带及低噪声性能。采用波长为1.064μm的激光雷达对半径范围为0.1~20μm的气溶胶粒子群进行探测实验,进一步验证了信号接收系统的分辨率和灵敏度。     

采用单片机发送并接收红外遥控信号的方法

以HS0038作为红外接收头，介绍了红外遥控信号的单片机软件编码解码方法，包括编码、调制和解码的原理，以及硬件电路和程序实现。经实验测试，该方法能使红外遥控信号可靠发送和接收。     

一种宽窄波束、软硬件结合的相控天线阵设计

就高频地波雷达海洋环境监测的一种新颖宽窄波束、软硬件技术相 的收发共同相控天线阵的设计,选用将Ｈａｌｌｅｎ方程与电流分布函数的殆全域多面式展开相结合的矩量法,分析了比较了相控天线阵在不同设计参数下的电磁性能,重点分析互耦伯影响以及实施“收发共用”对阻抗的匹配的苛匹配的要求和现有设计在该问题上的技术缺陷,得一了关于该天线阵工程设计的若干结论。