Mobile radio propagation in British cities at frequencies in the VHF and UHF bands

Measurements of the received signal envelope magnitude have been made in three British cities at frequencies of 85.875, 167.2, and 441.025 MHz. In all cases unmodulated carrier waves were radiated from aerials atop tall buildings or prominent terrain features and detected using a vehicle-mounted receiver. These measurements have provided the basis for an analysis of the factors affecting the transmission loss in urban/suburban areas which, in turn, has enabled a propagation prediction model to be constructed. Close agreement between measured and predicted path losses has been found for the various terrain situations investigated. The statistical prediction errors produced by the proposed model for the three British cities analyzed are shown to be similar in magnitude to those obtained using an extrapolation of the Okumura method. Because the proposed model is much less complex and procedurally simpler, it is recommended for use, in the first instance, in British cities.     

Mobile in-home UHF radio propagation for short-range devices

In-home propagation measurements, in the frequency range of 400, 860, and 2400 MHz, are evaluated for single, narrow-band applications of one-way domestic mobile alarm systems. In particular, the influence of multipath effects is investigated     

Modelling tropospheric ducting effects on VHF/UHF propagation

The application of the parabolic equation method to range-independent and range-dependent tropospheric propagation modelling problems is demonstrated. The parabolic equation is an approximation to the Helmholtz wave equation which allows progressive calculation of the propagated electromagnetic field as solution is stepped out in range. The solution method described is derived from a technique developed by R.H. Hardin and F.D. Tappert (1973) for application to underwater acoustics problems. This split step Fourier solution involves the discretization of the field with respect to height and the use of the fast Fourier transform at successive range points. The solution is stable, with errors being dependent on wavenumber, range step size, and the gradients of refractive index with respect to height and range. Advantages of this method over other methods used to evaluate the effects of ducting layers on tropospheric propagation are discussed     

Propagation of Wide-Band Signals at VHF/UHF

The experimental jam-resistant secure voice communications (JRSVC) system developed by M.I.T. Lincoln Laboratory was used to conduct a series of VHF/UHF (225-400 MHz) propagation measurements, representative of a veriety of tactical communications situations, both ground to ground and ground to low-flying aircraft. Results are unusual in two regards: they were made with the receiver in motion, covering many contiguous propagation paths, and the JRSVC system, by frequency-hopping over almost an octave and averaging the results, largely eliminated the effects of frequency-selective (multipath) fading that generally dominate VHF/UHF propagation measurements.     

VHF/UHF波段树干电磁散射特性分析

运用FDTD方法计算树干的宽带电磁散射特性.即将地面的散射场与入射场视为两个激励场作用于树干,从而得到地面背景下树干的散射场.给出了树干时域、频域、极化域和空域的电磁散射特性,并对这些特性进行了分析.     

An Integrated Voice/Data System for VHF/UHF Mobile Radio

This paper presents the basic architecture and performance of a mobile radio multiaccess voice/data system. Natural pauses in conversational speech allow bandwidth saving through interleaving of data packets and talkspurts from different voice sources. A speech detector designed specifically for the mobile environment is presented. Blocking and delay performance of the multiaccess uplink is analyzed for voice traffic, assuming no traffic effects from the low priority data packets. Performance results from simulation are then presented for two downlink strategies in a two-hop virtual circuit in which a base station acts as a relay. The results verify also that the uplink analysis is valid for low voice traffic. For the data traffic, simulation results are presented in terms of data packet transmission delay and probability of collision with talkspurts. The results indicate that data flow may be limited by the collision factor. This work concludes that relative to conventional radio telephoning in which two channels are dedicated to each transmitter/receiver pair, a bandwidth reduction of 30-35 percent can be achieved.     

VHF/UHF波段树干超宽带散射特性研究

本文用时域方法研究了树干的超宽带散射特性.由于树干及地面均为色散有耗媒质,因此树干散射特性是复杂的频率函数.时域有限差分算法(FDTD)尤其适合于此类具有色散特性的超宽带散射特性研究.运用FDTD算法建立起树干散射模型后,经过计算,可以得到整个时域过程的散射,对时域散射场进行快速傅立叶变换(FFT),则可获取全部感兴趣的超宽带频域特性.相对于矩量法(MOM)而言,FDTD能更方便快捷地为叶簇穿透(FOPEN)检测目标提供全面的时频信息.     

Mobile radio propagation in Auckland at 76 MHz

A series of field trials in Auckland at 76 MHz have confirmed that propagation path loss is normally distributed and may be characterised by a fourth-power-law distance dependency. The path loss standard deviation has been found to be dependent on the mobile terminal's environment and on frequency, but is essentially independent of base station antenna height and path length. The excess path loss over plane earth predictions and the standard deviation of path loss have been measured as 14.6, 5.0, 0.8 and 1.0 dB and 6.2, 5.2, 3.7 and 5.0 dB for urban, light urban, suburban and rural environments, respectively.     

Mobile radio propagation in Auckland at 927 MHz

Field trials in Auckland have shown that in the region 800 m to 5 km from a 50 m elevated base-station propagation loss may be characterised by a fourth-power law distance dependency and may be modelled as plane earth propagation loss plus excess loss of 45.6 dB. In the region closer to the base station, the propagation loss has a different characteristic. A `piecewise? model is proposed.     

Mobile radio propagation in Auckland at 851 MHz

A series of field trials undertaken in Auckland at 851 MHz have shown that the median propagation loss may be estimated by the plane earth propagation loss plus a clutter factor of 45.1, 27.0, 21.7 and 18.3 dB for urban, light urban, suburban and rural environments, respectively.     

Mobile radio propagation in Auckland at 465 MHz

A series of field trials in Auckland at 465 MHz have confirmed that propagation path loss may be characterised by a fourth-power-law distance dependency. The excess loss over plane earth predictions has been measured as 37.8, 26.4, 18.6 and 14.1 dB for urban, light urban, suburban and rural environments, respectively.     

A versatile wave propagation model for the VHF/UHF rangeconsidering three-dimensional terrain

A polarimetric wave propagation model for field strength forecasting and coverage prediction in the VHF/UHF frequency range is presented. The model uses a digital terrain data bank and considers multipath propagation. Based on the uniform geometrical theory of diffraction (UTD) and physical optics an approach is described for calculating the propagation effects in natural 3-D terrain, given by topological and morphographical data. The method for field strength forecasting is described and methods for the analysis of the predicted multipath signal are discussed. It is shown how the complex probability density function (PDF) for the receiver field strength and the field strength delay spectrum can be derived. Methods for further evaluation of the transmitting channel characteristics are discussed     

Statistics of motor vehicle ignition noise at VHF/UHF

Temporal sweeps of the amplitudes of electromagnetic vehicle ignition noise were made in Ottawa at six fixed frequencies in the range from 150 to 500 MHz using a 10 kHz bandwidth. Statistical analyses were performed of both the amplitude and temporal characteristics of the impulsive noise. The amplitudes approximately followed a lognormal distribution. The pulse spacings were uniformly distributed between about 5 and 15 ms and the pulse durations were about 150 μs long     

VHF/UHF波段星载SAR电离层效应研究

星载UHF／VHF波段合成孔径雷达对隐蔽目标有很强的探测能力,在军事和民用中都有重要应用前景,但其实现受到电离层效应的严重限制。文中介绍了此研究方向的现状、主要问题、以及相应的解决方法。     

UHF radio propagation characteristics in straight open-groovestructures

The imperfect waveguide method is used to study UHF radio propagation characteristics in open-groove structures with particular interest being devoted to the frequency characteristics of the propagation attenuation constant. Attenuation of propagation has been characterized by the surrounding media absorption, the roughness of the sidewall, and the sidewall tilt. Our study shows that attenuation due to the surrounding media absorption is inversely proportional to the square of the frequency, whereas that due to the roughness on the sidewall surfaces is inversely proportional to the frequency and that due to the sidewall tilt is directly proportional to the frequency. The imperfectness of the actual open groove structures will cause additional electromagnetic mode conversion, thus increasing the propagation loss. The theoretical results are in agreement with the experimental data     

Evaluation and verification of the VHF/UHF propagation channelbased on a 3-D-wave propagation model

This paper is intended to increase and improve the knowledge concerning the characterization of digital VHF/UHF communication channels. This characterization of the propagation channel is based on the field strength-delay-spectrum (FDS) of the three-dimensional (3-D) multipath wave propagation. A statistical superposition of the predicted multipath signals yields the probability density function of the narrowband signal and the averaged channel impulse response of the wideband propagation channel. Thereof, the relevant parameters, e.g., standard deviations, mean values, delay spread, and correlation coefficients, are derived both in time and frequency domain. The angles-of-arrival of the multipath signals are used to calculate the Doppler spectra of moving receivers for the characterization the time-variant properties of the propagation channel. In total, a rather complete summary of derivations, algorithms and characteristics of the VHF/UHF propagation channel is presented. Narrowband and wideband measurements are included for verification     

VHF／UHF宽带功率放大器设计

设计了一种30-520MHz功率放大器。采用传输线和集中常数相结合的阻抗匹配方式。实现了功率放大管的宽带匹配;对滤波器电子开关进行了分析并采用ADS进行仿真,插损及隔离度在全频段达到了设计要求;最后给出了测试结果,满足了指标的设计要求。该功率放大器已应用于某宽带通信设备且工作良好。     

Broadband switched parasitic arrays for portable DVB-T receiver applications in the VHF/UHF bands

The fixed active switched Parasitic array (FASPA) has been recently proposed as an attractive alternative solution to fully adaptive arrays -mainly due to cost considerations -regarding interferer cancellation and multipath-fading mitigation. in such an array, the signal source is permanently connected to a fixed element, while the state of the surrounding parasitic elements, controlled by p-i-n diodes, is either short-circuited or open-circuited. The radiation pattern is steered by employing all possible combinations of open-circuited and short-circuited elements [1].     

Hybrid image/ray-shooting UHF radio propagation predictor forpopulated indoor environments

A novel model for indoor wireless communication, based on a dual image and ray-shooting approach, is presented. The model, capable of improved site-specific indoor propagation prediction, considers multiple human bodies moving within the environment. In a modern office at 2.45 GHz, the combined effect of pedestrian traffic and a moving receiver causes rapid temporal fading of up to 30 dB     

Comparison of some path loss prediction methods with VHF/UHFmeasurements

Field strength measurements were conducted at VHF and UHF for different base station antenna heights in the south Indian coastal zones in urban, sub-urban, quasi-open and open regions. These experimentally observed values are compared with different prediction methods like Hata, ITU-R, Blonquist & Ladell, Egli, and Tbrahim & Parsons. The results showed that in sub-urban and urban regions Hata's method gave reasonable agreement with the observed values and in the open region gave better agreement at 440 MHz than at 150 MHz. All the other methods deviated appreciably from the observed values