Modelling direct sequence pseudonoise(dspn) satellite reception with directional antennas in the dense scatterer mobile environment

A geometric propagation model is developed for simulating the reception of direct sequence pseudonoise (DSPN) satellite signals by a directional or omni antenna in the dense scatterer mobile environment. The model is first validated for narrowband signals by a direct comparison of both simulated cumulative signal strength statistics and simulated diffuse Doppler spectra with classical theory. The model is then used to predict fading statistics for DSPN signaling, either with omni or directional antennas. As expected, the mitigation of fading is closely related to the ratio of DSPN chip duration to delay spread of the scatterer medium for both the omni and directional antennas.     

Improved method for calculating mitigation bandwidth of DSPN signals

In a previous work the author (see ibid., vol.29, no.8, p.661-2, 1993) has defined the mitigation bandwidth of direct sequence pseudonoise (DSPN) as employed to combat fading over the dense scatterer mobile digital link. Now he gives a simple, elegant method for computing mitigation bandwidth. No sacrifice of precision is conceded, and closed-form expressions are given for BPSK and MSK chip modulation.<>     

Investigation of signal variance,bit error rates and pulse dispersion for DSPN signalling in A mobile dense scatterer ray tracing model

The canonical ray tracing model of R. H. Clarke is used to validate the concept of mitigation bandwidth as used to predict DSPN spread spectrum signal variability at a mobile receiving antenna in dense scatterers. Illustrative examples of chip pulse dispersion are presented, and bit error rate performance is explored under the assumption of slow fading. The pulse dispersion is seen to pose potential obstacles to any eventual chip timing extraction and radio-location ranging functions. Serendipitously, the performance of a DSPN embodiment of a 180° DPSK data link is seen to approximate closely that of a corresponding narrowband Rician fading link, even though no specular signal component is available to the DSPN link. The parameters of the equivalent Rician link are easily predicted from those of the DSPN link.     

Effective bandwidth of DSPN signalling for mitigation of fading in dense scatterers

The use of direct sequence pseudonoise (DSPN) signalling to mitigate the fading caused by very dense scatterers in the mobile communication environment is explored for the specific case of a rectangular signal spectrum. A very simple and revealing relationship emerges between the variability of the signal strength and the signal bandwidth.<>     

Fading correlation and its effect on the capacity of multielementantenna systems

We investigate the effects of fading correlations in multielement antenna (MEA) communication systems. Pioneering studies showed that if the fades connecting pairs of transmit and receive antenna elements are independently, identically distributed, MEAs offer a large increase in capacity compared to single-antenna systems. An MEA system can be described in terms of spatial eigenmodes, which are single-input single-output subchannels. The channel capacity of an MEA is the sum of capacities of these subchannels. We show that the fading correlation affects the MEA capacity by modifying the distributions of the gains of these subchannels. The fading correlation depends on the physical parameters of MEA and the scatterer characteristics. In this paper, to characterize the fading correlation, we employ an abstract model, which is appropriate for modeling narrow-band Rayleigh fading in fixed wireless systems     

Fading model for antenna array receiver for a ring-type cluster of scatterers

This correspondence presents an alternate method for simulating the time-varying flat fading wireless channels for the antenna array receivers, in which the discrete ring of scatterers is incorporated around the mobile transmitter to model the spreading of azimuth. The ring-type cluster of scatterers continuously changes due to the movement of the mobile unit. Under this time-varying environment, each scatterer, at successive stages of the ring, is correlated with the scatterers at preceding stages of the ring using the second-order Markov modelling. The correlation of fading waveforms generated with the proposed paradigm is compared with the expected analytical correlation, which clearly depicts that the simulation results are consistent with the findings based on Jakes’ model.     

Multiuser detection in fast-fading multipath environments

We propose a new framework for multiuser detection in fast-fading channels that are encountered in many mobile communication scenarios. Existing multiuser RAKE receivers, developed to combat multipath fading and multiuser interference in slow fading, suffer substantial degradation in performance under fast fading due to errors in channel state estimation. The detectors proposed in this paper employ a novel receiver structure based on time-frequency (TF) processing that is dictated by a canonical representation of the wide-sense stationary uncorrelated scatterer (WSSUS) channel model. The workhorse of the framework is a TF generalization of the RAKE receiver that exploits joint multipath-Doppler diversity. Analytical and simulated results based on realistic fast-fading assumptions demonstrate that the proposed multiuser detectors promise substantially improved performance compared to existing systems due to the inherently higher level of diversity afforded by multipath-Doppler processing     

Wireless Fading Paradigm for Antenna Array Receiver for a Disk-Type Cluster of Scatterers

This correspondence presents a signal processing based alternate approach for simulating the flat fading narrowband wireless channels for the antenna array receivers under the time-varying environment, in which the discrete disk of scatterers is incorporated around the mobile wireless transmitter to model the spreading of azimuth. The disk-type cluster of scatterers continuously changes due to the movement of the mobile wireless transmitter. Under this time-varying environment, each scatterer, at the successive stages of the disk, is correlated with the scatterers at the preceding stages of the disk using the second-order autoregressive process AR(2). At the receiver, one signal waveform is associated with each element of the antenna array taking into account the spread in azimuth of the received signal. The correlation of the fading waveforms generated by using the presented paradigm is compared with the expected analytical correlation results, which clearly manifests that the simulation results are consistent with the findings based on Jakes’ model. Moreover, the presented discrete disk-type cluster of scatterers fading model may be used to generate/simulate the variable diameter ring-type cluster of scatterers fading paradigm. The proposed channel model may play a significant role in the emerging field of wireless signal processing for the latest mobile communication systems.     

The Impact of Antenna Directivity on the Small-Scale Fading in Indoor Environments

Results obtained from using a geometrically based, single-bounce propagation model are presented to characterize small-scale fading in indoor propagation channels when directional antennas are used. The model is verified by comparing simulated results to measured results. The model is then used to obtain, via simulation, fading statistics for an indoor, line-of-sight channel. The results show that when directive antennas are used, the parameters of the Nakagami- or Rician-distributed small-scale fading vary with separation between the transmit and receive antennas. Furthermore, the strength of the variation depends on antenna directivity. Some physical mechanisms for this effect are discussed     

基于4mm电磁型微马达的管道检测微机器人系统研究

介绍了一种基于 4mm微型马达的微小机器人系统的设计及制作。新颖的电磁型微马达的设计使得微机器人具有较强的驱动能力和一定的负载能力 ;全方位的结构设计使得微机器人具有高机动性 ;同时 ,利用视觉实现机器人与外部环境相互感知 ,并在其基础上对整个机器人系统的控制结构设计进行了探索     

无线覆盖与网络优化

对网络优化中不同环境下的覆盖问题进行了阐述，重点对基站延伸覆盖系统、基站全向天线改定向的问题进行了分析，最后对小区覆盖、高速公路隧道覆盖、室内覆盖的建设思路提出了建议。     

Geometrical-based statistical macrocell channel model for mobileenvironments

We develop a statistical geometric propagation model for a macrocell mobile environment that provides the statistics of angle-of-arrival (AOA) of the multipath components, which are required to test adaptive array algorithms for cellular applications. This channel model assumes that each multipath component of the propagating signal undergoes only one bounce traveling from the transmitter to the receiver and that scattering objects are located uniformly within a circle around the mobile. This geometrically based single bounce macrocell (GBSBM) channel model provides three important parameters that characterize a channel: the power of the multipath components, the time-of-arrival (TOA) of the components, and the AOA of the components. Using the GBSBM model, we analyze the effect of directional antennas at the base station on the fading envelopes. The level crossing rate of the fading envelope is reduced and the envelope correlation increases significantly if a directional antenna is employed at the base station     

Modelling a standard broadcast directional array with the numericalelectromagnetics code

The numerical electromagnetics code (NEC) is a general-purpose wire-antenna-analysis computer program capable of modelling both a standard-broadcast directional array (DA) and a scatterer such as a power line. The starting point for such a study is a NEC model of the directional array itself. The DA's admittance matrix could be used to choose voltage excitations for the NEC model such that NEC's tower-base currents agree in magnitude and phase with those of the array's design. However, this choice of excitation is unsatisfactory because NEC's azimuth pattern differs from the theoretical azimuth pattern which is computed using sinusoidal current distributions on the DA towers. The difference is accounted for by the phase of the tower currents: in the NEC model the phase varies with height above the ground on each tower, but in the sinusoidal current approximation, the phase of the tower current is constant. In the present study the NEC model of the DA is regarded as being out of adjustment, and the objective is to adjust the excitation of the NEC model such that its azimuth pattern matches the array's theoretical pattern     

深亚微米CMOS IC全芯片ESD保护技术

CMOS工艺发展到深亚微米阶段,芯片的静电放电(ESD)保护能力受到了更大的限制。因此,需要采取更加有效而且可靠的ESD保护措施。基于改进的SCR器件和STFOD结构,本文提出了一种新颖的全芯片ESD保护架构,这种架构提高了整个芯片的抗ESD能力,节省了芯片面积,达到了对整个芯片提供全方位ESD保护的目的。     

Land vehicular propagation channel characterization of BGAN system

This paper summarizes the results of a measurement campaign, which set out to characterize Inmarsat's broadband global area network extension (BGAN‐X) L‐band land vehicular (LV) channels as a function of elevation angle and candidate antenna systems. Measurements were conducted with three types of directional antennas on motorway routes around London using Inmarsat's Indian Ocean Region (IOR), Atlantic Ocean Region‐East (AOR‐E) and Atlantic Ocean Region‐West (AOR‐W) satellite transmissions, corresponding to elevation angles of, respectively, ～7.5°, ～13° and ～30°. Simultaneous recordings of data on two types of directive receivers enabled correlation of several channel parameters. Statistics were used to refine a baseline model that derived BGAN‐X LV channel parameters by scaling the statistics obtained from an omni‐directional antenna receiver. The measurements demonstrate that Ricean mean and Ricean factor vary significantly over the chosen routes at elevation angles below ～13°. Further, the Doppler shift of the direct path can be predicted accurately. A qualitative analysis indicates that the multi‐path Doppler spread is generally (not always) caused by uniform scattering around the vehicle over short distances and undergoes spatial filtering due to the receiver antenna. A technique was established to derive statistics of a two‐state Markovian channel model at any specified fading threshold by gathering tracking system state, thereby allowing one to ascertain service expectations and operational parameters such as connection time‐out of a packet‐switched system or reliability threshold of a circuit‐switched system. The technique was used to identify and select appropriate routes, particularly for the IOR and the AOR‐W regions. Data analysis is in progress to establish the reason for the slow variations of signal mean at low‐elevation angles in Ricean conditions and to derive appropriate statistical models. Furthermore, image processing of the video recordings is expected to reveal the extent of optical and RF fades correlation. Copyright © 2008 John Wiley & Sons, Ltd.     

Planar DVB‐T Antenna Using a Patterned Helical Line and Matching Circuit

A miniaturized planar digital video broadcasting terrestrial (DVB‐T) antenna, which is composed of a patterned helical line, an open stub, and an impedance matching circuit on an FR4 (?_r=4.4) substrate for portable media player applications, is presented in this letter. The antenna has monopole‐like, omni‐directional radiation characteristics and a wide impedance bandwidth (VSWR<3) in the DVB‐T band from 174 MHz to 230 MHz at the VHF band.     

An Approach for Modestly Directional Communications in Mobile Ad Hoc Networks

Directional antennas are a promising technology for use in mobile ad hoc environments. By consuming smaller volumes than omni directional antennas, directional antennas enable significant increases in network capacity by allowing more simultaneous transmissions to occur within a multihop wireless network. In this paper, we present some of the challenges that face asynchronous directional channel access schemes and describe how these problems can be avoided by taking a synchronous approach. We describe a communications system architecture that enables modestly directional sectored antennas to be effectively exploited in a mobile ad hoc environment. A key part of this architecture is the Directional Synchronous Unscheduled Multiple Access (DSUMA) protocol. By making intelligent decisions regarding the enabling/disabling of sector antennas, DSUMA provides an increased density of transmissions while insuring that collisions do not occur. Our results indicate how the number of sectors per node affects performance in terms of spatial reuse, the likelihood of collisions, and overall network capacity.     

Angular MAC: a framework for directional antennas in wireless mesh networks

Capacity of wireless mesh networks can be enhanced through the use of smart directional antennas, which not only enable nodes to have high quality links but also increase network throughput by allowing spatial reuse. This paper proposes a new MAC protocol and framework, called Angular MAC (ANMAC) that enables directional antennas in wireless mesh networks. The protocols and algorithms of the ANMAC framework fit well with the requirements of mesh networks such as neighbor discovery and self-configuration, while providing significant throughput enhancements. The throughput enhancements are proven by comprehensive simulations with realistic antenna patterns, including performance comparisons of ANMAC with directional schemes using a similar node architecture and omni 802.11. Also, the effect of contention window size is analyzed and a dynamic contention window adaptation algorithm is proposed to maximize the throughput of the self-configuring mesh network, by taking instantaneous traffic conditions into account.     

LOFAR浮标定位算法的仿真研究

LOFAR浮标是一种被动全向浮标,主要用于对潜搜索初始阶段.常用的定位算法很多,这些方法的基本思想是最大限度地利用LOFAR和CODAR分析得到的目标信息,通过粗测和细测交替进行的方法,最终精确得到目标参数.针对Doppler-CPA、LOFIX和HYFIX定位算法进行分析和仿真,结果表明这三种算法能够很好地实现对目标的检测,最终精确得到目标参数.     

紫外光通信系统现状及发展趋势分析

紫外光通信系统作为一种新型的军事通信系统,具有抗干扰能力强、保密性好、非视距通信以及全方位通信等优点。它可作为一种专用局域军事保密通信手段,或在特定条件下作为其它通信手段的一种补充,可广泛应用于海陆空三军,对未来战争、现代化国防具有特殊的使用价值和实际意义。文中主要介绍了国内外紫外光通信系统的发展现状,并分析了其未来发展趋势。