Deterministic channel modeling and performance simulation of microcellular wide-band communication systems

To evaluate the performance of future microcellular IMT-2000 modems, simple physical models are required, so that a number of system characteristics, such as the signal bandwidth, the antenna beamwidth, or the base station height can be accounted for at a limited computational cost. This paper describes a deterministic three-dimensional electromagnetic model, which allows simulation of the radiowave propagation for microcellular wide-band communication systems in urban areas. The model is based on a UTD ray-tracing tool and makes use of an improved mirror method. Simulated power-delay profiles are plotted against measured power-delay profiles recorded at 1.87 GHz in a street of Louvain-la-Neuve, Belgium, by means of an 80-MHz channel sounder. Despite several discrepancies, a satisfying matching is found considering three orders of reflection and single diffraction. Predictions of rms delay-spread accounting for the sounder limited bandwidth are presented. Finally, simulated and measured channels are also compared through the resulting performance of a typical IMT-2000 service in the presence of multiple access interference.     

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。     

Reducing location update and paging costs in a PCS network

Mobility tracking operations in a personal communication service (PCS) system are signaling consuming. Several strategies have been proposed in the literature to reduce both the location update (LU) and the paging (PG) costs. In this paper, we propose a location-tracking algorithm called three-location area (TrLA), combined with selective paging. In TrLA, the mobile terminal (MT) allocates the identification of three neighboring location areas (LAs) in its local memory. We call this set of three LAs, a big-location area (BLA). Each time the MT exits the BLA, it triggers an LU message to the system databases via a base station, in order to maintain the databases up to date. The MT also updates its cache memory. A two-step selective PG is also considered and compared with the single-step (or nonselective PG). An analytical model based on a semi-Markov process has been used to evaluate our proposal. This scheme is compared with the classical Global System for Mobile Communications (GSM) standard and the two-location algorithm proposal. As a result, this new scheme outperforms the cited strategies, and in our opinion, it can easily be implemented in existing standard cellular and personal communication systems     

Indoor geolocation science and technology

This article presents an overview of the technical aspects of the existing technologies for wireless indoor location systems. The two major challenges for accurate location finding in indoor areas are the complexity of radio propagation and the ad hoc nature of the deployed infrastructure in these areas. Because of these difficulties a variety of signaling techniques, overall system architectures, and location finding algorithms are emerging for this application. This article provides a fundamental understanding of the issues related to indoor geolocation science that are needed for design and performance evaluation of emerging indoor geolocation systems     

Reuse efficiency in urban microcellular networks

We study how efficiently radio channel resources can be reused in microcellular networks. Our focus is on dense urban networks in which cell-site antennas are located well below the rooftops of surrounding buildings. Compared with conventional cellular networks, this kind of microcellular system introduces a markedly different propagation environment, characterized by a mix of strong line-of-sight (LOS) propagation and much weaker non-LOS propagation. We address a number of important issues associated with site layout and reuse planning in such microcellular networks (rectilinear street environments) and present numerical results showing the influence of frequency, cell size, link quality requirements, shadow-fading statistics, and power control on the reuse efficiency. For 900-MHz systems, orthogonal multiple-access schemes (e.g., time division), and a typical set of system parameters, we estimate that the reuse efficiency in urban microcellular networks could be up to 50% higher than that in conventional cellular networks with three-sector antennas     

Adaptive Antennas for Microcellular and Mixed Cell Environments with DS-CDMA

Adaptive antenna technology is now regarded as one of the key system components in future generation cellular networks. This paper considers the performance of a DS-CDMA system which employs adaptive antennas at the base station sites of both microcell and mixed micro/umbrella cell operational environments. A microcellular ray tracing propagation tool has been employed in order to ascertain site specific propagation data. Results for a typical small cell environment highlight both the propagation characteristics and the behaviour of the adaptive antenna, as well as the sensitivity of the system upon parameters such as the mutual coupling effect. This work does not assume idealised propagation conditions or antenna radiation patterns for the small cell analysis.In summary, the results indicate that microcellular base stations employing adaptive antenna signal processing can offer a significant capacity enhancement and improved channel characteristics when compared with their omnidirectional counterparts. In addition, it is shown that umbrella cells overlaying microcells within the same RF bandwidth allocation, do not impact upon system capacity providing that adaptive antenna technology is employed at the umbrella cell site.     

Effect of anisotropic propagation modeling on microcellular systemdesign

Microcells for wireless communications can be realized with low base station antennas operating at low power. The low base station antennas expected for microcells make the propagation characteristics dependent on the direction relative to the street grid. Due to this anisotropic propagation, the shape of microcells is no longer circular, as is typically assumed so for macrocellular system planning. Therefore the infrastructure of the microcells should be implemented with a different approach from that for macrocells. This paper aims at finding the effect of microcellular wave propagation on the development of cellular design for channelized systems in residential/commercial environments by examining key aspects of cell layout. Using a measurement-based anisotropic propagation model, cell shape and frequency reuse patterns are investigated for the downlink, and a methodology for frequency planning is presented     

Sensitivity of the System Performance to the Propagation Parameters in LOS Microcellular Environments

Propagation loss is a fundamental phenomenon that affects the performance of any wireless network. Although propagation characteristics in line-of-sight (LOS) microcellular systems are well known, so far, only a few papers have investigated its effect on system performance in a comprehensive manner. In this paper, the impact of both system parameters (i.e., cell size, antenna height, operating frequency, and reuse factor) and propagation loss parameters (i.e., breakpoint distance, path loss exponents, standard deviation of the shadowing component, signals correlation, and effective road height) on the performance of both time-division multiple access (TDMA)- and code-division multiple access (CDMA)-based LOS microcellular networks is studied. Performance is evaluated in terms of outage probability in TDMA-based systems and in terms of the other-cell interference factor in CDMA-based systems. This paper includes substantial numerical results and new insights into the behavior of wireless system performance. For instance, novel insights into the impact of both distance-dependent shadowing and the effective road height on system performance are provided. In particular, nontypical fluctuational and discontinuous behavior on performance metrics are observed, and at microwave frequencies, the spectral efficiency is greater for heavy vehicular traffic conditions (i.e., during daytime) than for light vehicular traffic conditions (i.e., during nighttime). Such an understanding of interference engineering issues is vital for the planning, designing, dimensioning, and the optimization of mobile LOS microcellular networks for present and future wireless systems beyond third generation.      

一种适应微蜂窝的移动性管理策略

在微蜂窝系统中,移动性管理是一个很重要的课题。如果采用传播蜂窝的位置登记的管理方式将会产生大量的系统资源浪费,降低系统的效率。本文提出一种基于用户移动特性（例如呼叫到达率、移动速度和移动位置等特点）的动态位置区的管理方案。在论文中对方案的寻呼代价和位置区修改代价进行分析和讨论,并与传统位置区管理方式〖１〗〖２〗做了比较。     

A flexibly configurable spatial model for mobile radio channels

The application of multiple directive antennas, i.e., directional diversity, may lead to significant capacity benefits in cellular mobile radio systems. A flexibly configurable statistical channel model for mobile radio systems using directional diversity is presented. The parameters of this model, which is available as a FORTRAN77 program, can be easily adjusted to various propagation areas such as, for example, rural, urban, microcellular, and picocellular environments. Therefore, the model is well suited to perform simulations, evaluations, and comparisons of mobile radio systems. Simulation results concerning a code-division multiple-access (CDMA) mobile radio system which uses multiple directive base station (BS) antennas in combination with joint detection illustrate the application of the presented channel model     

Derivation of antenna pattern shaping criteria for urban base stations using ray tracing

A novel method for the derivation of the optimum base station (BS) antenna radiation pattern in urban microcellular systems or wireless systems in general is presented. The multipath radio channel is sounded with a ray-tracing (RT) tool; then the BS antenna pattern is optimized in order to minimize channel dispersion and maximize field strength in the selected service area. The procedure can be performed for the different classes of microcellular BS sites, allowing the derivation of useful criteria for the shaping of the corresponding antenna patterns. The aim of the paper is to demonstrate the possibility of using the RT in combination with an optimization procedure to derive interesting antenna design indications.     

Modeling and analysis of the dynamic location registration andpaging in microcellular systems

A 0-1 integer programming model is considered to determine the most appropriate dynamic location registration (LR) area of each subscriber in microcellular systems. The minimization model of the LR area updating and paging signal costs is examined. The model is based on the subscriber characteristics, such as the call arrival rate and the velocity, as well as the regional information. The control channel blocking probabilities are considered as constraints to meet the service level of subscribers. A dynamic scheme which adaptively updates the size and shape of the LR area is developed by solving the minimization problem. Paging and location updating procedures are presented based on the dynamic procedure. The superiority of the proposed scheme is demonstrated with various computational results     

Radio propagation characteristics for line-of-sight microcellularand personal communications

To acquire a knowledge of radio propagation characteristics in the microcellular environments for personal communications services (PCS), a comprehensive measurement program was conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three base station antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies at 900 MHz and 1900 MHz. Five test settings were chosen in urban, suburban, and rural areas in order to study propagation in a variety of environments. This paper reports the LOS measurements in different environments, all of which show variations of signal strength with distance that have distinct near and far regions separated by a break point. It was also found that the location of the break point for different frequencies and antenna heights can be calculated based on first Fresnel zone clearance. The regression analysis reveals a slope that is less than two before the break point, while it is greater than two after the break point. This break distance can be used to define the size of microcell and to design for fast hand-off. Beyond the first Fresnel zone break distance the base station antenna height gain was observed to approximately follow the square power law of antenna height     

A system plan for a 900-MHz portable radio telephone

The system concepts for a high capacity personal radio telephone system are described. Previous systems for mobile radio telephone service have been based on a rigid assignment of frequencies to specific small geographic areas within the total coverage area. This approach has led to conservative geographic frequency reuse constraints and the requirement for accurate location techniques in the system. Through the utilization of the power imbalance that exists in the proposed portable radio telephone system between base and portable unit transmitters these constraints are eliminated. It will be shown how this power imbalance allows the selection of the optimum signal for the portable unit and relaxed requirements on location and reuse of frequencies. The required signal-to-interference ratios must be obtained within a design reliability level over the coverage area. Computer simulation of the frequency reuse plan and the propagation variability over the area indicates the nominal repeat intervals necessary as a function of this reliability level. A reuse plan that obtains the required repeat intervals with a high degree of spectral efficiency, through the combined use of geographic and frequency separation, will be presented. This system called tertiary offset, achieves a significant increase in interference protection by splitting each channel into a group of three channels and utilizing each subgroup in a different pattern of reuse over the area. The improvement due to this plan will be shown.     

Microwave path-loss modeling in urban line-of-sight environments

To model the path-loss characteristics in microwave urban line-of-sight (LOS) propagation, we performed measurements in metropolitan Tokyo at frequencies of 3.35, 8.45, and 15.75 GHz. The actual breakpoint distance was shorter than the theoretical one because of the influence of vehicles, pedestrians, and other objects on the road. This effect has been referred to as effective road height. We found that the breakpoint disappeared when the mobile-antenna height approached the effective road height. Based on these breakpoint characteristics, we propose new upper- and lower-bound formulas for LOS path loss in urban microcellular environments. They will be useful for the system and cell design of fourth-generation multimedia mobile communication systems using microwave bands.     

Prediction of beam tilting effects using an enhanced ray launchingmodel in the urban area

This paper presents an effective propagation area method that enhances the computation efficiency of the existing ray launching model. Using the effective propagation area method, the effective propagation region to be considered can be constructed from a given geographical database, and buildings that have a substantial effect on the total received power can be considered in a very efficient manner. In order to verify the predicted accuracy of the proposed model, the received power has been predicted for the real microcellular environment and compared with the published measurement. It is observed from the prediction results that the proposed model shows considerable improvement in computation speed and good agreement with the measurements. In addition, the effect of beam tilting on the path loss in an urban area is analyzed using the proposed model. It has been observed that beam downtilting can effectively confine the signal to the desirable home cell with reduced transmitting power, narrow half-power beam width (HPBW), and suitable fixed antenna height     

Teletraffic performance of GSM900/DCS1800 in street microcells

Studies the teletraffic issues of the Global System of Mobile Communications at 900 MHz (GSM900), and its sister, the Digital Communication System at 1800 MHz (DCS1800). The teletraffic simulations have the essential elements of GSM900 and DCS1800, but they are not be exact simulations of these two systems. The approach is to site microcellular base stations, using the microcellular prediction tool MIDAS, into a fictitious city and into parts of two real cities. The radio coverage plots are then imported into a teletraffic simulator TELSIM. The simulator is loaded with the basic GSM900 and DCS1800 parameters to give an indication of the teletraffic performance of these systems in the three environments     

城市微蜂窝的快捷精确传播预测方法

基于路测数据和统计模式,提出了针对城市微蜂窝的模式修正场强传播损耗预测方法.依据路测数据的分布和蒙特卡罗模拟的结果,将预测区域划分为若干个子区域,运用基于最小均方误差的自适应算法,从路测数据中提取每个子区域的传播损耗参数,经线性方程计算子区域内场强分布,得出整个区域的场强二维覆盖.实验结果表明,所给方法具有传统确定性模式和统计模式各自的优点,其预测精度接近确定性模式,而计算时间与统计模式相当,具有高的工程应用价值.     

Digital audio broadcasting (DAB) over non‐stationary satellite systems

Non‐stationary broadcast (BC) satellite systems can provide a continuous, direct‐to‐user, and worldwide BC service. Owing to the improved radio link margin of LEO/MEO systems, one can overcome the problems of blockage and foliage attenuation, which are significant in the alternative GEO/HEO systems. A basic analysis also reveals that the specifications of the standardized ITU A (EUREKA 147) DAB signal are adequate to cope with range and range rate effects due to the satellite motion. It is shown that a continuous, area‐wide high‐quality BC service can be provided by overlapping cellular service areas. Each cell may have an individual uplink station for feeding the BC signal. A system concept is discussed which is based on the exploitation of range, range rate, and angular information onboard the satellites with respect to each individual uplink station in order to compensate for Doppler frequency shifts and for variable signal propagation delay. Copyright © 2000 John Wiley & Sons, Ltd.