An Additive Model as a Physical Basis for Shadow Fading

Received signal power in mobile wireless communications is typically modeled as a product of three factors: distance-dependent average path loss law, variation in the local mean power (shadow fading), and small-scale fading. Of these three factors, the least investigated is the shadow fading, which is usually explained as a result of multiplication of large number of random attenuating factors in the radio channel. In this paper, the authors propose an additive model as an alternative physical basis for shadow fading within an "extended local area" where path loss is constant. Starting from a sum-of-sinusoids signal model, they show that under mild statistical assumptions on the powers of the sinusoids, the resulting signal power will have approximately Gaussian distribution in logarithmic scale. A cluster-based model for shadow fading emerges as a special instance of the general result. They present simulation and measurement results that support their theoretical findings. The new physical basis for shadow fading also provides insights into simulation and modeling of radio channels     

Macroscopic Diversity in Frequency Reuse Radio Systems

Macroscopic diversity is a technique that can facilitate high quality and ubiquitous communications between low-power portable radiotelephones and data terminals, and radio base stations (ports) that are connected to the local network. It uses radio signals from several base stations to mitigate the effect of shadow fading, a variation of signal strength over space created by the presence of buildings, foliage, and terrain variations. With a path loss exponent of four and a shadow fading standard deviation of 10 dB, four-branch macroscopic diversity results in a 13 dB improvement in signal strength and a 15 dB improvement in signal to cochannel interference ratio for high user capacity interference-limited operation. (Both figures are for 99 percent statistical coverge of the service area.) The improvement in signal to cochannel interference ratio is equivalent to a factor-of-five savings of spectrum.     

Quantifying short-range surface-to-surface communications links

As wirelessly connected embedded systems become ubiquitous, previously undocumented propagation environments must be explored to support their design. This paper describes the results of a study of such an environment: short-range wireless propagation outdoors, near the ground. In the study, frequencies were considered within three industrial, scientific, and medical (ISM) bands: 902-928 MHz, 2400-2426 MHz, and 5725-5752 MHz. Experimental propagation loss was summarized based on measurements in eighteen environments, at varying heights, distances, and polarizations. Based on the data collected, the appropriateness of a simple design guideline, based on a two-ray propagation model, is discussed. Summaries of the path loss, fading, and the influences of antenna height, antenna separation, and surrounding clutter in highly variable environments are given. Additionally, limited numerical modeling of the impact of surface roughness is provided. Particular focus was given in the study to heights and distances appropriate for randomly deployed wireless sensor networks, such as autonomous unattended ground-sensor systems.     

The Ratio of Antenna Heights as a Parameter to Characterize Path Loss: A Millimeter Wave Desktop Propagation Study

This paper contains measured data for desktop propagation path loss at millimeter wave band. Different ratios between transmitting antenna height and receiving antenna height were studied based on a vector network analyzer system. Transmitting and receiving antenna were separated by distances ranging from 5 to 300 cm on a wooden desktop, and the antenna heights were varied from 5 to 25 cm. Average path loss data are coupled with the path loss exponents and the breakpoint locations of piecewise model to provide insight into large scale propagation characteristics of desktop millimeter wave communication systems. These measurement results may aid in the development of future short range wireless propagation in millimeter wave bands.     

分布式天线系统中的系统下行误符号率分析

首先建立了包含快衰落、阴影衰落和路径损耗的复合衰落信道模型,对分布式天线采用覆盖式（BT）传输策略,推导出给定移动台位置的小区下行点对点链路误符号率表达式.并在高信噪比条件下,通过给出移动台在小区的任意分布图,推导出小区下行平均误符号率的近似闭合表达式.仿真结果表明,所推导的近似表达式可很好地反应系统的实际性能.     

一种深度残差网络构建的5G无线智能传播模型

为建立更为准确的全覆盖、全应用、全频谱的5G无线信道模型,提出通过认知无线电与深度神经网络相结合的方法研究无线电波传播特性。根据传统无线传播模型并考虑到不同传播环境,根据信道大尺度衰落特性(包括路径损耗、阴影衰落和小尺度衰落特性)的统计结果,通过BP算法提取特征,并应用FeatureTools进行深度特征综合建立特征方程,计算特征变量与传播损耗的相关系数,进行相关系数的置信区间及变量独立性检验,最终筛选出22个特征并排序。基于深度残差网络建立传播路径损耗的回归模型,结合批正则化过拟合测算平均接收功率,为建立更精确的无线信道模型提供了量化依据,并最终在测试数据集上取得均方根误差8.36(本地)和10.03(云端)的成绩,对工程实践具有较强的参考价值。     

分布式MIMO系统小区平均遍历容量分析

针对分布式MIMO系统的圆形小区平均遍历容量展开研究.文章首先建立了包含快衰落、阴影衰落和路径损耗的复合衰落信道模型;然后,对分布式天线采用覆盖式（BT）传输策略,并在高信噪比条件下,导出给定移动台位置时,区上、下行点对点链路遍历容量表达式.最后,考虑移动台在小区内任意分布特点,进一步推导出小区平均遍历容量闭合近似表达式.仿真结果表明,所推导的近似表达式可很好的反应系统的实际性能.导的近似表达式可很好的反应系统的实际性能.     

Propagation analysis of signal fading for basic exchange radios

Although empirical multipath fading models are available for microwave links above 2 GHz, these models are not directly applicable to basic exchange radio (BEXR) links because of the substantial differences in frequency, antenna beamwidth, and radio path clearance. A method for obtaining a scaling factor which accounts for the differences between BEXR and microwave links is presented. First, the terrain scattering is studied using a rough surface model, and the atmospheric refraction is studied using a ray tracing approach. Then, the received signal powers of a microwave link and two BEXR links on the same path under the same propagation condition are calculated. The signal characteristics are investigated and used to simulate the fading distributions for all three links. From the simulation results, a scaling factor is derived and used to modify the existing microwave multipath fading models for BEXR application. The predictions of the modified model agree well with measured BEXR data. This study shows that the probability distribution of signal fading on BEXR links is a strong function of antenna height and beamwidth     

一种分布式多入多出(MIMO)信道的容量研究

分布式MIMO系统结合了点对点MIMO信道与分布式天线系统两者的特点，能改善链路的质量，提高覆盖面积。本文提出了一种包含路径损耗、阴影衰落与小尺度衰落的分布式MIMO信道模型，分析推导了采用该模型时的分布式MIMO信道容量。通过计算机仿真，研究分析了阴影衰落、Rice信道因子K等因素对分布式MIMO上行信道容量的影响，得出了分布式MIMO信道容量空间分布的特点。     

On the performance of single frequency networks in correlatedshadow fading

All transmitters in a single frequency network (SFN) simultaneously transmit the same information within the same frequency block. Simulcasting provides a diversity gain which has been shown to yield good coverage. In traditional analysis uncorrelated shadow fading is used. In some cases this assumption does not capture the behaviour of the shadow fading, e.g., when several transmitters are shadowed by a large obstacle. We investigate the changes in coverage due to correlation among the received signals field strength from different transmitters. A spatial shadow fading correlation model is proposed and validated using the Blomquist-Ladell (1974) prediction method on a digital terrain data base. Results for both wide area and local SFN show that the coverage properties depends on the correlation in the shadow fading. This will affect the planning process since strong correlation, due to the structure of the terrain, yields better coverage for high transmitter powers (interference limited systems) and worse coverage for low transmitter powers (noise limited systems)     

Path loss model for wireless narrowband communication above flat phantom

A new empirical path loss model for wireless communication at 2.4 GHz above a flat, lossy medium, representing human tissue, is presented. The model is valid for dipole antennas for heights up to 5 cm above the phantom and for distances up to 40 cm, and was applied to muscle and brain simulating media. For antennas placed close to the lossy medium, it was found that antenna height has a major influence on path loss. The model has been validated by measurements and simulations, which show excellent agreement     

Propagation measurements for fixed wireless loops (FWL) in asuburban region with foliage and terrain blockages

We present the results of propagation measurements at 2.485 GHz for fixed wireless loops. Path loss measurements were performed and characterized at 43 subscriber locations around a base station antenna located on top of Crawford Hill in Holmdel, NJ. This suburban location is characterized by rolling hills, foliage, and terrain blockages. Temporal and horizontal motion path loss fluctuations were found to be uncorrelated, each characterized by a different Ricean distribution. Lower r.m.s. delay spreads were obtained with directive subscriber antennas than with omni-directional antennas. No substantial gain loss (less than 2 dB) of subscribers' directive antennas was observed. The effects of trees, with foliage, surrounding the base station upon the path loss and the ratio of scattered power to specular power are also examined. The distance exponent of path loss versus distance (about 1.5) was observed to be less than free-space. Diffraction loss from hilltop trees, shadowing the base station, are suspected to be the cause. This loss decreases as the remote moves further away and comes out of the shadow. Scattered power from directions other than line-of-sight was observed to be as high as one half of the specular contribution when tree scattering near the base station was significant     

Radio Channel Characterization for Moderate Antenna Heights in Forest Areas

This paper describes the results achieved by an experimental campaign whose goal was to characterize the directional propagation channel at 1.9 GHz in forested areas for moderate antenna heights. These experimental results are useful in the context of pedestrian radio-localization systems relying on cellphone signals. Wideband experimental results, which are recorded with transmit-to-receive distances ranging from 40 to 110 m, indicate that the path loss is well modeled by ITU-R Recommendation 833-4. The temporal fading and multipath dispersion are also analyzed. The delay spread, which ranges from 60 to 120 ns, is strongly anticorrelated with the temporal coherence and increases with transmit-to-receive distance. The azimuth spread remains limited, with average values of about 15deg.     

Propagation characteristics for wideband outdoor mobilecommunications at 5.3 GHz

In this paper, empirical channel models and parameters are derived from the wideband measured data at 5.3 GHz in outdoor mobile communications. The path loss exponents and intercepts are obtained by using the least square method. The mean excess delay and mean root-mean-square (rms) delay spread are within 29-102 ns and 22-88 ns, respectively. The correlation distances and bandwidths are within 1-11 λ and 1.2-11.5 MHz, respectively, when the envelope correlation coefficients equal 0.7 in line-of-sight cases. These correlation values depend strongly on the base station antenna heights. The window length for averaging out the fast fading components is about 1-2 m for microcells and picocells. The multipath number distributions follow both Poisson's and Gao's distributions, but Gao's distribution is better in the high probability region. Large excess delays up to 1.2 μs and rms delay spread about 0.42 μs are found in the urban rotation measurements, where the receiver is close to a large open square     

室内分布发射天线STBC系统的发射天线位置优化

该文针对室内环境下分布发射天线STBC系统,在考虑了路径损耗、阴影衰落和莱斯衰落的基础上推导了室内的平均误符号率(AASER),通过使室内的平均误符号率最小得到了优化的发射天线位置。理论分析表明最优的发射天线位置与房间的长、宽、高以及移动台的高度有关。仿真结果验证了理论分析的正确性。     

Towards a more accurate method of predicting the distribution of multipath fading on terrestrial microwave links

Initial work is described towards the development of a more accurate asymptotic prediction method for the high fade depth range of the fading distribution on line-of-sight terrestrial microwave links. The influence of parameters such as path length, frequency, terrain roughness, path inclination, antenna beamwidth and path clearance is analysed using multipath fading data from a large number of links in the UK.     

Adaptive Empirical Path Loss Prediction Models for Indoor WLAN

This paper presents robust empirical path loss models to characterize indoor propagation for access point (AP) deployed at different heights. The proposed models are developed with wireless local area network infrastructure at 2.4 GHz. The models are backed by extensive received signal strength (RSS) measurements acquired in line of sight and obstructed line of sight regions. The models are developed for two conditions, viz; quasi realistic and realistic RSS measurements. The quasi realistic measurements are taken after suppressing human intervention and electrical interferences to minimum. While the realistic RSS measurements are made in presence of all the human interventions and electrical interferences. The shadow fading component for both quasi realistic and realistic conditions is statistically modeled with the dependency on AP height. The proposed technique can be applied with higher confidence level to the buildings with similar construction features where RSS measurements are made upon. The results reveal that the performance of the proposed propagation models is significantly higher than the existing International Telecommunication Union-path loss model. The results also demonstrate that the realistic path loss model is more robust than the quasi realistic model.     

An empirical result for the height gain in forest medium

Radio path loss measurements were conducted in various tropical rain forests of India at frequencies from 50 to 800 MHz, antenna heights from 1.5 m to 16.5 m above ground with both horizontally and vertically polarized emissions, and at a large variety of path ranges. The results from a series of antenna height-gain measurements in the forest vegetation are presented. Based on the data thus collected, an empirical model is suggested to assess quantitatively the antenna height gain as a function of frequency and antenna heights.     

Path-loss model for broadcasting applications and outdoor communication systems in the VHF and UHF bands

A simple propagation model for the VHF and UHF bands is presented. The model is a computational form of the data provided by the FCC F(50,50) propagation curves, and it is aimed to be used by practicing engineers. It allows the estimation of median path loss, received power or electrical field strength which usually is sufficient in many practical applications. The model is independent of frequency and is applicable to outdoor environments in a range of distances from 0.5 miles (800 m) up to 40 miles (64.36 km) and transmitting antenna heights from 100 ft (30.48 m) up to 2000 ft (609.6 m), and is based on a receiving antenna height of 30 ft (9 m).     

A New Empirical Formula for Handover Rate in Microcellular Systems

In this paper, we propose a new empirical formula for handover rate as a function of base stations separation, standard deviation of shadow fading, path loss exponent, averaging distance, and correlation distance. The handover initiation algorithm is based on averaged signal strength measurements using relative signal strength with hysteresis margin approach. We generate the data through computer simulations for the average number of handovers referred to as handover rate, for the practical range of path loss exponent and standard deviation of shadow fading. The proposed formula provides for a practical design tool to optimize the handover initiation performance under varied propagation environments.