辐射模缝隙馈源激励的2GHz无线电波在室内的传播

本文给出了用辐射模缝隙馈源作为发射天线时，2GHz窄带和宽带无线电波在室内传播特性的测量结果。对于窄带信号，主要测量了传播过程中的衰减，测量结果表明，沿缝隙馈源方向，接收信号电平按指数规律衰减，在垂直于电缆方向上，接收信号电平的衰减较慢，损耗指数较小：在平行和垂直于馈源方向上慢衰落基本服从正态分布，而快衰落分别服从Rayleigh和Rician分布。对于宽带信号，测量了多径脉冲相应，得到了均方根时延扩展及其概率分布。     

Propagation at 2.0 GHz in an Enclosed Area Using a Coaxial Cable with Leaky Sections as the Transmitting Antenna

This paper presents the results of narrowband and wideband propagation measurements carried out at 2.0 GHz in a large enclosed area using a coaxial cable with leaky sections as the transmitting antenna. The narrowband measurements were devised to measure attenuation of radio signals and the wideband techniques to measure multipath impulse responses and their associated root mean square delay spread. Analysis of the narrowband data files shows that the received signal levels in the direction parallel to the cable generally decay and display peaks in front of leaky sections due to the specific attenuation and special structure of the cable. The received signal levels in the direction radial to the cable decrease slowly and the distance-power law exponent is found to be slightly larger than one. The slow and fast variations of the received signal levels are also examined. The results reveal that the slow variations do not follow the lognormal distribution, while the fast variations fit the Rayleigh distribution in both parallel and radial directions. Analysis of the wideband data files yields that the maximum value of the root mean square delay spread is 86.1 ns and the root mean square delay spread values are less than 55 ns 50% of the time. One therefore can conclude that the enclosed area channel excited by the coaxial cable with leaky sections has a broad coherent bandwidth and can support the data rate up to 2.3 Mb/s without equalization.     

带漏泄段同轴电缆激励的2GHz无线电波在大型封闭区域内的传播

本文给出了在大型封闭区域,用带漏泄段的同轴电缆作为发射天线时,2GHz窄带和宽带无线电波传播特性的测量结果,对于窄带信号、主要测量了传播过程中的衰减,测量结果表明,在平行于电缆方向上,接收信号的电平比垂直于电缆方向的电平大;接收信号的快衰落服从瑞利分而,而慢衰落不服从正态分布。对于宽带信号,测量了多径脉冲响应,得到了均方根时延扩展及其概率分布。     

Distributed Antennas for Indoor Radio Communications

The idea of implementing an indoor radio communications system serving an entire building from a single central antenna appears to be an attractive proposition. However, based on various indoor propagation measurements of the signal attenuation and the multipath delay spread, such a centralized approach appears to be limited to small buildings and to narrow-band FDMA-type systems with limited reliability and flexibility. In this paper, we present the results of indoor radio propagation measurements of two signal distribution approaches that improve the picture dramatically. In the first, the building is divided into many small cells, each served from an antenna located in its own center, and with adjacent cells operating in different frequency bands. In the second approach, the building is divided into one or more large cells, each served from a distributed antenna system or a "leaky feeder" that winds its way through the hallways. This approach eliminates the frequency cell handoff problem that is bound to exist in the first approach, while still preserving the dramatic reductions in multipath delay spread and signal attenuation compared to a centralized system. For example, the measurements show that, with either approach, the signal attenuation can be reduced by as much as a few tens of decibels and the rms delay spread becomes limited to 20 to 50 us, even in large buildings. This can make possible the implementation of sophisticated broad-band TDMA-type systems that are flexible, robust, and virtually building-independent.     

A microcellular ray-tracing propagation model and evaluation of itsnarrow-band and wide-band predictions

Due to the site specific nature of microcellular operational environments, propagation models are required to take into account the exact position, orientation and electrical properties of individual buildings, and hence, ray-tracing techniques have emerged as the dominant methods to predict propagation in such environments. A novel hybrid three-dimensional (3-D) ray-tracing algorithm which can evaluate scenarios incorporating many thousands of objects by utilising the concept of “illumination zones,” is presented. In order to evaluate the accuracy of the presented model, comparisons of narrow-band and wide-band predictions with measurements are performed for a variety of scenarios. First, power comparisons show that very accurate predictions can be achieved (RMS errors less than 3.7 dB). Then, wide-band analysis shows that since the RMS delay spread for systems with finite bandwidth is a function of the multipath phase, only average measured and predicted RMS delay spread values can be compared and as a result, limited averaging can produce large RMS errors. With sufficient averaging the achieved wide-band accuracy in terms of the predicted RMS delay spread, is adequate for most planning purposes     

Wideband indoor channel characterisation using microstrip patchantennas at 1.95 GHz with different antenna height configurations

Results highlighting the improvement in power loss factor n, RMS delay spread and correlation with distance of the indoor channel employing microstrip patch antennas mounted in an optimised height configuration are presented. Extensive power delay profile measurements with four different antenna height configurations in two laboratory environments were conducted using a vector network analyser at 1.95 GHz. Analysis of the measurement results shows improvement of n values from 2.9 to 2 and median RMS delay spread of 10.4 ns to 6.2 ns with changes of antenna configuration     

Natural wave propagation in mine environments

Theoretical and experimental aspects of the natural propagation of high-frequency waves in mines are presented. A narrow-band and a wide-band analysis have been carried out to determine the most important characteristics of the channel such as the longitudinal attenuation, the coherence bandwidth, and the delay spread of the impulse response in the various areas of an underground mine. The basic principle of a localization of a mobile has also been checked by determining the direction of arrival of the waves     

Improve uniformity for an indoor visible light communication system

Visible light communication (VLC) is an alternative technology to the radio frequency (RF) for different applications in the indoor and outdoor environments, it could be utilized for illumination and communication simultaneously, and it offers several advantages over contemporary RF technologies such as low power consumption, free license, large bandwidth, and being friendly to the environment. In this paper, an indoor VLC system uniformity improvement in terms of high received power, signal‐to‐noise ratio (SNR), and bit rate, with RMS delay spread reduction, is proposed. It features a novel model that utilizes a 13‐optical attocells configuration on the ceiling. Moreover, proposed model was evaluated at different semi‐angle at half power. The average received power and SNR were improved to 2.85 dBm and 75.5 dB, while achieved received power and SNR levels at the center of the room were 4.92 dBm and 79.5 dB, respectively. A minimum average RMS delay spread of 0.4749 nanoseconds is obtained, while the highest average bit rate calculated is 211 Mb/s. The proposed model provides a better communication quality and meets illumination standards requirements.     

A Statistical Model for Indoor Multipath Propagation

The results of indoor multipath propagation measurements using 10 ns, 1.5 GHz, radarlike pulses are presented for a medium-size office building. The observed channel was very slowly time varying, with the delay spread extending over a range up to about 200 ns and rms values of up to about 50 ns. The attenuation varied over a 60 dB dynamic range. A simple statistical multipath model of the indoor radio channel is also presented, which fits our measurements well, and more importantly, appears to be extendable to other buildings. With this model, the received signal rays arrive in clusters. The rays have independent uniform phases, and independent Rayleigh amplitudes with variances that decay exponentially with cluster and ray delays. The clusters, and the rays within the cluster, form Poisson arrival processes with different, but fixed, rates. The clusters are formed by the building superstructure, while the individual rays are formed by objects in the vicinities of the transmitter and the receiver.     

Delay Spread Statistics in a Two-Path Distributed Antenna System with Gamma-Lognormal Fading Channels

This letter analyzes the statistical properties of the root-mean-square (RMS) delay spread in a two-path distributed antenna system, where the received signal power from each path is subject to composite gamma fading and lognormal shadowing. The channel power delay profile considered consists of two delta functions with correlated power levels. We present analytical expressions for the probability density function of the RMS delay spread, as well as the cumulative distribution function, mean value and standard deviation. These analyses are validated through comparison with Monte-Carlo simulation results.     

Measurements and Statistical Modeling of 900 MHz Radio Propagation Channels for Microcellular and Personal Communications in Tunnels

This paper reports the results of measurements of 900 MHz narrow-band radio wave propagation in four tunnels with pedestrians and vehicles. Analysis of the measured data files shows that the power distance factor ranges from 1.87 to 4.44. The power attenation rate with distance is insensitive to the location of the transmit antenna in the cross section of a tunnel, but the transmit antenna insertion loss is. The log-normal distribution fits slow variation of the received signals. The Racian distribution closely describes fast fading in the straight sections of tunnels. However, the Rayleigh distribution does not fit the fast fading in the curved sections of tunnels, as expected.     

A novel 3-D indoor ray-tracing propagation model: the pathgenerator and evaluation of narrow-band and wide-band predictions

A novel three-dimensional (3-D) ray-tracing model capable of supporting detailed representation of the indoor environment, as well as external building structures, is presented in this paper. The developed algorithm uses a hybrid imaging technique where the two-dimensional (2-D) image generations in vertical and horizontal planes are combined to produce 3-D paths. It also employs the concept of “illumination zones” of the images which greatly simplifies the image map and allows the evaluation of complex indoor scenarios. In order to investigate the accuracy of the presented model, comparisons of predictions with narrow-band and wide-band measurements are performed in line-of-sight (LOS), non-LOS (NLOS), and deep shadow areas, both for co- and cross-polarized antennas. The analysis shows that accurate power predictions can be achieved for both antenna polarizations with rms errors less than 7 dB, even when long sections of the test route are in deep shadow areas. There is a trend agreement between the simulated and measured channel impulse responses, while the rms delay spread in NLOS areas is predicted with less than 5-ns rms error (or better than 13% normalized mean error). The paper provides an insight into the real and the modeled radio channel     

Multipath Time Delay Jitter Measured at 850 MHz in the Portable Radio Environment

Time delay jitter in digital personal communications systems, caused by moving the antenna by a few wavelengths, was studied at two office buildings and two residences at a frequency of 850 MHz. A wide-band pseudonoice code technique was used. The results indicate that peak-to-peak time delay, variations on the order of 375 ns may be encountered. The worst case jitter was not necessarily found when there was a large time delay spread. It was also found that the excess mean delay and the root mean-square (rms) time delay spread of the delay distribution profiles were approximately the same.     

Ray-optical prediction of radio-wave propagation characteristics intunnel environments. 2. Analysis and measurements

For pt.I seeibid. vol.46, no.9, p.1328, (1998).The uniform theory of diffraction (UTD) developed in part 1 is used to predict narrow- and wide-band propagation characteristics in tunnels at 900- and 1800-MHz. Narrow-band propagation characteristics is shown in the spatial domain and wide-band propagation in the time domain. In empty straight-tunnel environments, propagation exhibits a break-point phenomenon and has very short time delay spread. In empty curved or branched tunnel environments, propagation suffers higher loss. Vehicles cause additional propagation loss and larger varying time delay spread in tunnels. The measured results have validated the accuracy of the theoretical model and provided important information on narrow-band and wide-band propagation characteristics in empty, branched and obstructed tunnels     

Simultaneous wide-band four-antenna wireless channel-soundingmeasurements at 1920 MHz in a suburban environment

Simultaneous four-antenna wide-band mobile channel-sounding measurements were made in two areas at 1920 MHz. The received signal strength and transmission loss were examined. Path-loss exponents for the two sectors were found to be 4.9 and 4.1. Root mean square delay spreads for the two sectors were found to be less than 1.38 and 0.65 μs for 90% of the data and less than 3.14 and 1.35 μs for 99% of the data. Fast fading reduction using antenna diversity and increased channel bandwidth (19.6 kHz, 1.25 MHz, 5.0 MHz, and 10.0 MHz) were examined. Three signal combining methods were considered: selection diversity, equal gain combining, and maximal ratio combining. The measured results show that increasing the number of diversity antennas or the channel bandwidth significantly reduces fading. Maximal ratio combining yields the largest diversity gain, exceeding 11.0 and 17.0 dB at the 90% and 99% fast fade depth probability levels, respectively, for the 19.6-kHz narrow-band signal and 6.7 and 6.9 dB for the 10.0-MHz broad-band signal when all four channels are used     

Adaptive DFE for GMSK in indoor radio channels

We simulate the performance of an equalized Gaussian minimum shift keying (GMSK) signal in an indoor radio environment with fading, noise, imperfect carrier recovery, cochannel interference (CCI), and intersymbol interference (ISI). We show that data rates of 20 Mb/s at bit error rates (BER) ⩽10^-4 are possible with root mean square (RMS) delay spreads up to 25 ns using a simple limiter-discriminator-integrator (LDI) receiver and a (6, 4) decision feedback equalizer (DFE). In environments with larger RMS delay spreads, coherent detection is required for the same performance. We show that using a decision-directed second-order digital carrier synchronizer with time varying loop filters, frequency offsets up to 200 kHz can be corrected with negligible performance degradation. This paper utilizes a DFE structure which compensates for both modulator and channel ISI, and yet requires no power-intensive multiplication operations in the feedback section. A DFE (8, 8) with two-level switched (selection) diversity is shown to allow 20 Mb/s data transfer at a BER⩽10^-4 for RMS delay spreads under 150 ns, with CCI. A light BCH (26, 31) code allows error-free reception of over 90% of packets with RMS delay spreads under 150 ns, and up to 70% of packets with RMS delays of 150 ns     

基于低频窄带的超高性能高频宽带合成源设计

随着测试仪器的发展,高频段信号的应用越来越多,因此对高频信号测试系统的性能要求也不断提高.本文在基于高性能的低频窄带合成源的基础上,提出一种通用的超高性能高频宽带合成源设计方案.本方案采用分频锁相和混频锁相组成的双环锁相模式,在分频锁相模式下,信号进行快速锁定,实现宽频段内信号的大幅度切换;在混频锁相模式下,通过引入不同频段的窄带信号与VCO的反馈信号进行混频鉴相获得超高性能的宽带信号,最终实现宽带高频信号的稳定输出.     

Line-of-sight indoor radio communication using circular polarizedwaves

This paper presents an anti-multipath fading scheme employing a circular polarized wave for line-of-sight (LOS) indoor radio communications. The circular polarized wave transmission/reception significantly mitigates the multipath fading caused by reflections from walls, ceiling, and floor since the energies of single-bounce reflected waves do not appear at the receiver, thereby resulting in significant amplitude fade and delay spread reduction. The received signal intensity variations and delay spread are investigated numerically using a 14-path propagation model and the usefulness is confirmed by comparing with a linear polarized wave transmission/reception under a same LOS condition     

The indoor radio propagation channel

In this tutorial survey the principles of radio propagation in indoor environments are reviewed. The channel is modeled as a linear time-varying filter at each location in the three-dimensional space, and the properties of the filter's impulse response are described. Theoretical distributions of the sequences of arrival times, amplitudes and phases are presented. Other relevant concepts such as spatial and temporal variations of the channel, large-scale path losses, mean excess delay and RMS delay spread are explored. Propagation characteristics of the indoor and outdoor channels are compared and their major differences are outlined. Previous measurement and modeling efforts are surveyed, and areas for future research are suggested