Some New Results of Propagation Measurements and Their Application for Planning Transmitter Networks

To improve the coverage with medium frequency (MF) transmitters, new results of propagation measurements have to be recognized. Experiments were made to draw ground conductivity maps and to evaluate new propagation curves. Further measurements were begun to get information about the propagation with different polarization at MF. Great interest exists in preparing new frequency ranges for practical application. First experiments were made in the 11-12 GHz area to study the influence of terrain and the troposphere on propagation. On a 56-kin beyond line-of-sight path, field strength was recorded over a one-year period and the first results of mobile measurements in terrain were compared with propagation curves.     

Computer prediction of service areas for VHF and UHF land mobile radio services

A computer program written to predict the effective service area of a transmitter in a VHF or UHF mobile radio network is described. The computed results enable field strength contours to be determined, and hence provide more useful information than is possible by reference to standard statistical curves. Present manual methods of calculating the attenuation to be expected over transmission paths rely on the laborious extraction of essential ground profile information along the path joining the transmitter to the receiver. This difficulty may be overcome by using a topographical data base in a computerized method of service area prediction. With this scheme each data base entry represents the effective terrain height above sea level within each 0.5-km square. A high-speed computer can access the necessary information from the data base to reconstruct a close approximation of the radio path profile. The reconstructed profile is then processed to calculate the transmission loss. These computations are repeated for numerous points throughout the area and enable field strength contours to be deduced. The propagation model described forms part of a fully automated frequency assignment procedure for the private land mobile radio services in operation in the Directorate of Radio Technology, Home Office, UK.     

Propagation measurements for UHF spread spectrum mobile communications

The U.S. Army is currently developing a number of spread spectrum radio systems to support its needs for more survivable and efficient mobile UHF data distribution on the tactical battlefield of the 1990's and beyond. The analysis and prediction of the performance of these systems in mobile tactical environments has been met with a great deal of uncertainty relating to the applicability of narrow-band propagation models and the effects of terrain irregularity and vegetation on broad-band signals. An overview is presented of an ongoing Army program utilizing wide-band pulse response measurements to characterize ground mobile tactical UHF spread spectrum propagation channels. Recently acquired experimental data are used to demonstrate the potential of this program for improving available tools for prediction and analysis of tactical UHF spread spectrum systems employing bandwidths of hundreds of MHz.     

A SPATIAL PREDICTION THEORY FOR LONG-TERM FADING IN MOBILE RADIO COMMUNICATIONS

There have been traditional approaches to model radio propagation path loss mechanism both theoretically and empirically. Theoretical approach is simple to explain and effective in certain cases. Empirical approach accommodates the terrain configuration and distance between base station and mobile unit along the propagation path only. In other words, it does not accommodate natural terrain configuration over a specific area. In this paper, we propose a spatial prediction technique for the mobile radio propagation path loss accommodating complete natural terrain configuration over a specific area. Statistical uncertainty analysis is also considered.     

Propagation factors controlling mean field strength on urban streets

Calculation of mean field strength for urban mobile radio has been made on a ray-theoretical basis assuming an ideal city structure with uniform building heights. The result shows that building height, street width, and street orientation as well as mobile station antenna height are controlling propagation parameters in addition to the ordinary factors. The major theoretical characteristics agree approximately with experimental data including conventional empirical predictions. This suggests a way of theoretically predicting mean field strength in an urban area.     

Spread-Spectrum Mobile Radio with Variable-Bit-Rate Speech Transmission

We describe a digital mobile radio system in which users experiencing poor transmission reduce the number of bits per second used for speech coding from 32000 to 28000. They do so in a manner that greatly reduces the binary error rate. The reduced error rate more than compensates for increased quantization noise. We predict two statistics of user satisfaction in a mobile radio service area: POW, the percentage of users experiencing poor or worse transmission, and GOB, the percentage good or better. In a typical environment the maximum number of users that can operate within a 20 MHz band with POW ≤ 5 percent is 137, compared to 91 users when everyone transmits 32 kbits/s. The modulation technique is FH-FSK (frequency hopped, frequency shift keying) and the digital code is embedded ADPCM (adaptive differential pulse code modulation), in the mobile radio service area, signal strength depends on distance from mobile unit to a central base station. There is slow (shadow) fading due to terrain and building variations and rapid (Rayleigh) fading due to multipath propagation. To predict user satisfaction we have combined three different analyses: 1) a theory of FH-FSK, 2) a theory of the signal-to-noise ratio statistics in mobile radio service areas, and 3) a model, based on computer simulations and subjective testing data, of the dependence of subjective speech quality on ADPCM transmission rate and binary error rate.     

Three-Dimensional Urban EM Wave Propagation Model for Radio Network Planning and Optimization Over Large Areas

A new 3-D urban electromagnetic wave propagation model is presented. It provides fast 3-D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input–multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3-D modeling compared with the vertical-plane approach or 2-D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area.      

Method of calculation of parameters of wireless access channel for mobile terminals in millimeter wavelength band

It is proposed a number of new technical solutions to implement the delivery of multimedia signals 4G services with data transfer rate for each subscriber 6–12 Mb/s, which move at a speed of 300–350 km/h with a total capacity of the network over a thousand subscribers. The block diagram (architecture) of transfer network in the millimeter wavelength band is developed. We derived balance equation for the network radio energy, which is the basis of the method for calculating the radio channel parameters. Examples of calculation of radio wireless access parameters to mobile terminals in the millimeter range are presented.     

Short-term phase stability of audio signals in mobile radio vehicle-base links

An investigation into the phase perturbation of an audio tone transmitted over conventional frequency-modulated mobile radio links at frequencies of 72, 170, and 462 MHz is described. Data from stationary and moving vehicles in a variety of urban routes and in mountainous terrain are presented. The effects of noise and of multi-path propagation are identified. The results are interpreted in light of the requirements of a particular automatic vehicle monitoring (AVM) system, which is described briefly, but should be of interest to others concerned with the transmission of phase-sensitive data.     

Flat suburban area propagation at 820 MHz

The results of a comprehensive mesurement program at 820 MHz designed to determine propagation characterstics in flat suburban terrain are presented. The data are organized to separate the effects of surface features, mobile antenna gain, and land-site antenna height, gain, and type (omnidirective and directive). The data have been collected using a digital data acquisition system to sample each of 18 variables once every three milliseconds. The mobile traveled over 500 route miles in the suburban Philadelphia/Camden, NJ area while probing an 11-square-mile measurement area in collecting these data. The results show propagation characteristics and relative antenna comparisons in flat suburban terrain. These results are compared to earlier urban data and show an environmental advantage of 11 dB for flat open suburban terrain.     

Performance evaluation of COFDM for digital audio broadcasting. I.Parametric study

This paper describes the performance of COFDM (coded orthogonal frequency division multiplexing) for digital audio broadcasting (DAB) over various multipath mobile radio channels. COFDM is a channel coding and modulation scheme which mitigates the adverse effects of fading by using wideband multicarrier modulation combined with time interleaving and a convolutional error correcting code. A guard interval is inserted at the transition between successive symbols to absorb the intersymbol interference created by the time domain spread of the mobile radio channel. The decoding process is performed using differential demodulation in conjunction with a soft decision Viterbi decoder. The COFDM evaluation is done by means of computer simulations. A parametric study of the proposed COFDM system is done in this first of a series of papers to determine the optimal system parameter values for operation at a radio frequency of 1.5 GHz. The results show that the parameter values proposed in the standard are indeed well suited for operation at 1.5 GHz. Using the set of optimal parameter values found, the COFDM performance is then evaluated in mobile radio channels typical of different geographical environments. Simulation results confirm the benefit that the system gains from frequency diversity found in the urban and hilly terrain areas     

Choice of a suitable method for the prediction of the field strength in planning land mobile radio systems

Aiming at the choice of a method for the field strength prediction over irregular terrain in land mobile radio service which could be adopted as the most suitable for engineering purposes, six out of the known methods have been analyzed. To verify their prediction accuracy, complex field tests have been carried out. With the moving vehicle, the field strength has been measured along well defined path profiles. Statistical processing of the recorded data has yielded the median field strength levels in a number of points of the path serving as reference for the accuracy assessment. Other features of the compared methods, such as their operativeness, complexity, suitability for the computer application, influence of subjective factors, and tolerances in determining the initial data, have been discussed. The "clearance angle" method, recently proposed and experimentally verified in detail during the field test described in this paper, has been chosen, after an argued analysis, as the most suitable field strength prediction method for engineering purposes.     

Computer prediction of field strength in the planning of radio systems

The application of a method of predicting the field strengths from mobile radio base station transmitters and in radio links is presented, and the extension of the method to facilitate frequency assignment is outlined. The topographic data for a country are stored in a computer and programs are provided which predict the signal levels produced by a specific transmitter at points spaced 0.5 km apart. A further program enables a plotter to be used to derive signal level contours which can be overlaid on a map. The field strength prediction method is proving valuable in the siting of VHF base stations, in the reduction of field testing required for mobile systems, and in the study of possible areas of cochannel interference. It has also been extended to effect path calculations for point-to-point radio links. An extension of the cochannel interference study in which channel assignments are made by a logical procedure so as to maintain co-channel interference below some chosen level while making the minimum demands on the spectrum is outlined. The method described has potential applications in national frequency planning.     

Application of the fast far-field approximation to the computationof UHF pathloss over irregular terrain

The availability of fast numerical methods has rendered the integral-equation approach suitable for practical application to radio planning and site optimization for UHF mobile radio systems. In this paper, we describe a conceptually simple scheme for the efficient computation of UHF radial propagation loss over irregular terrain, which is based on the fast far-field approximation. The method is substantially faster than conventional integral-equation (IE) solution techniques. The technique is improved by incorporating the Green's function perturbation method and we outline a way in which the formulation can be made more exact. Computational issues such as terrain profile truncation and the effect of small-scale roughness are addressed. The method has been applied to gently undulating terrain and compared to published experimental results in the 900-MHz band. It has also been successfully applied to more hilly terrain and to surfaces with buildings added     

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.     

基于地理位置变化的5G小基站传播特性研究

移动互联网和物联网时代来临,高数据业务需求推动着5G网络的致密化建设,加速部署小基站更适应5G网络的建设需求。有效地提供5G网络规划需要准确了解3.5 GHz传播特性,在半径为0.5 km的微蜂窝环境中,通过实测模拟信号与三维射线跟踪模拟结果的比较分析传播特性,推导出反映位置特性的最佳5G小基站传播模型。     

UTD multiple-edge transition zone diffraction

The uniform theory of diffraction (UTD) is applied to multiple absorbing screens, which are in the transition zones near shadow boundaries. The theory includes the application of slope diffraction, which is a first-order effect in transition zone diffraction. By choosing length parameters independently for amplitude and slope diffraction, it is ensured that the solution has continuity of amplitude and slope at each point. The solution is compared with known solutions with good results except when two screens are very near each other. The study is of particular interest to radio propagation over terrain in mobile radio systems     

Comments on the performance of selected low-power HF radio sets in the tropics

The performance of five low-power HF radio sets was measured at 3.6 MHz under field conditions in Thailand. Variations in performance were noted for CW and voice transmissions as a function of type of set, type of antenna, time of day, and communication range (5-100 mi) in tropical forest (jungle), mountain, and delta terrain. Radio teletype (RTTY) tests over longer paths (out to 1320 km) were made using a jeep-mounted set. The results showed that relatively good communications can be achieved in the tropics on short and intermediate length paths with low-power sets--especially when the proper antenna is used and when the operating frequency is properly chosen.     

Propagation through an elevated duct: Tradewinds III

In July and August of 1960, a joint Naval Research Laboratory-Naval Electronics Laboratory radio-meteorological program (Project Tradewinds III) was carried out between San Diego, Calif., and Opana, Hawaii. The purpose of this project was to evaluate the propagation characteristics of the duct formed by the tradewinds inversion which is generally found in this region. Two frequencies, 220 Mc and 445 Mc, were used and data concerning signal strength vs range from each terminal, height gain data at several points in the path, as well as the gross meteorological conditions which prevailed over the path were taken. This report attempts both to correlate the radio propagation data with the observed meteorology and to formulate a mechanism to explain the presence in the duct of signal power transmitted from a point well below the duct. In general, cloud heights and types serve as indicators of the stability of the tradewinds inversion and can be correlated with the altitude and strength of the inversion and consequently of the duct. By using both ray and scatter theories, a relation is developed which may be used to determine the signal losses expected in transmission through an elevated duct in which either or both terminals are well below the duct.     

A comparison of prediction methods for 800 MHz mobile radio propagation

The design and installation of a mobile radio system involves the evaluation or prediction of the propagation characteristics associated with the geographical area of interest. A wide variety of prediction techniques has been developed for different mobile environments, so that the task of selecting an appropriate propagation prediction method can be difficult and complex. This is especially true for systems operating in the upper-UHF band of 800-950 MHz, where mobile radio services are rapidly growing. A practical comparison is given of current prediction techniques available in the literature (for slow lognormal fading rather than multipath Rayleigh fading), with an emphasis on three essential criteria to consider in the selection process: the type of terrain or geography covered by each method, the form of prediction provided (e.g., transmission loss estimates, field strength contour maps, etc.), and the implementation difficulty and degree of sophistication.