Multistate phase diversity microcell antenna

The authors introduce a multistate phase diversity scheme to reduce fading problems at the base station end in a microcellular environment. The results obtained show that the phase diversity scheme provides a considerable improvement at the receiving end with a compact antenna configuration     

Application of some theoretical models for coverage prediction inmacrocell urban environments

The implementation of cellular mobile radio (CMR) systems in urban environments has been the main reason for the development of theoretical models to predict coverage. This paper reports the results obtained on comparing the estimates of several models with measurements made in two distinct types of urban environment. The models used for the final diffraction loss calculation produced very similar results in most cases, with almost identical computational costs. Nevertheless, for multiple diffraction loss, the advantages of using a regular or an irregular building profile modeling depend on the degree of regularity of building height and spacing in the area under study, as well as on the computation times desired for the calculations     

Effective models in evaluating radio coverage on single floors ofmultifloor buildings

An effective site-specific hybrid model is developed to predict the path loss and the effective radio coverage on single floors. The hybrid model, combined with a two-dimensional (2-D) model and an easy-to-use direct-transmitted ray (DTR) model, is incorporated with the building blueprint in usage. Both effects of the interior walls and the metallic objects such as whiteboards, bookcases, and standing air conditioners on radio propagation are considered. It is found that inclusion of metallic objects will enhance the performance of the model     

Capacity losses in sector and microcell cellular systems

Cellular system capacity calculations are based on the assumption that traffic is uniformly distributed. A simple analysis of hourly cellular cell site usage statistics is performed to assess the validity of this assertion. The data shows that call traffic is not uniform across geography or time of day. For the particular data set used there is a 9% capacity penalty incurred by reducing the geographic size of the service areas by a factor of three. Smaller service areas show a greater variability in demand and a greater ratio of peak to average demand     

Sizing up the microcell for mobile radio communications

Within cellular mobile radio communication systems large cells have been widely deployed, with cell sizes decreasing as the number of subscribers increase. This has lead to the possibility of using very small cells, or microcells. However, the term microcell has been used to mean different things to different organisations. With much work being performed on propagation within microcells and on infrastructure issues for microcells there is now a sufficient base of knowledge to allow the introduction of these small cells. The paper defines the microcell, examines propagation modelling methods and tools, and looks at problematic areas such handover and the complexity of the infrastructure required. Finally, the future of microcells for mobile radio use is considered     

Vapour microcell for chip scale atomic frequency standard

Reported is the original implementation of a microcell (1 mm³ ) in which a stable cesium vapour is generated after the cell is sealed. This new type of microcell is suitable for chip scale atomic clocks (CSACs) and can be realised at the industrial scale in an economic way     

Fiber-optic microcell radio systems with a spectrum delivery scheme

The authors examine microcell radio systems that use subcarrier transmission and spectrum delivery switch (SDS) techniques to meet traffic demands for a large number of portable phones. Radio signals are transmitted over fibre between base stations (BS) and a central station (CS). Relationships between blocking probability and offered traffic are described as a parameter of SDS ports. Optical link performances, such as link gain and carrier-to-noise ratio (CNR), are presented. Moreover, it is found that using FM techniques can improve the dynamic range by 20 dB compared to conventional methods for the uplink from BS to CS. The proposed technique can also increase the number of transmittable carriers compared to conventional methods for the downlink from CS to BS. This network strategy results in more flexible transmission     

Effectiveness of four-branch height and polarization diversityconfiguration for street microcell

This paper proposes a four-branch height and polarization diversity configuration that achieves almost constant received signal power over any terminal inclination in a street microcell communication environment. An example of the four-branch diversity antenna is also presented. Our measurement results in cell-size comparison among height diversity, polarization diversity, and height and polarization diversity configurations confirm the effectiveness of the proposed diversity configuration     

Comparison of MIMO antenna configurations in picocell and microcell environments

This paper presents the results achieved with a dual-polarized multiple-input multiple-output (MIMO) measurement system in the 2 GHz range. Results from continuous measurement routes were used in evaluating and comparing different MIMO antenna configurations. Different pattern and polarization diversity possibilities were studied using two methods: elements were selected from the antenna arrays used in measurements, and as another option, in the mobile station the incident waves were estimated and used in different dipole antenna arrays. The capacity limit seems to be higher in an indoor picocell than in an outdoor microcell environment. At the mobile station, directive elements result in 35% higher average capacities than those of the omnidirectional elements; however, the capacity of the directive elements also depends on the azimuth direction of arrival of the incident field. Dual-polarized antenna configurations have approximately 14% higher capacities than copolarized configurations. Increasing the number of mobile antenna elements increases the capacity in those environments where the angular spread of the incident field is large. Increasing the distance between elements at the fixed station increases the capacity - especially in microcells where signals arrive from specific directions.     

Channel management in microcell/macrocell cellular radio systems

In this paper, we study spectrum management in a two-tier microcell/macrocell cellular system. Two issues are studied: micro-macro cell selection and frequency spectrum partitioning between microcells and macrocells. To keep the handoff rate in a two-tier cellular system at an acceptable level, low mobility users (with speed υ0 ) should undergo handoffs at microcell boundaries, and high mobility users (with speed υ>V₀) should undergo handoffs at macrocell boundaries. The mobile determines user mobility from microcell sojourn times and uses it for channel assignment at call origination and handoff. The probability of erroneous assignment of a mobile to a microcell or macrocell is shown to be significantly lower than previous approaches. We investigate the optimal velocity threshold, V₀, and propose that it may be dynamically adjusted according to traffic load. Finally, we propose a systematic way for finding an optimal partition of frequency spectrum between microcells and macrocells. This partitioning is based on the traffic load and velocity distribution of mobiles in the system     

Maximal connected sets—application to microcell CDMA

Current trends in personal and data communication networks favour code division multiple access (CDMA) as a solution to spectral congestion. This is because of enhanced capacity, security, network flexibility, simplified protocol, and relative immunity to propagation induced errors such as multipath and interference, as compared with traditional frequency division multiple access (FDMA). Various CDMA schemes have been proposed and described in relation to VSAT systems, local area microcells,² and cellular telephones. Additionally, numerous product applications have emerged in the areas of modems, voice links and wireless local exchanges. These systems require inter- and intra-cell control. By contrast, the scheme presented in this paper places no reliance on intercell protocol. It enables new cells to be added to the network without any impact on the hardware. Network reconfiguration requires software changes only. Therefore, the scheme is appropriate to systems which demand flexibility with minimum overheads.     

Coherence bandwidth measurements in an indoor microcell at 62.4 GHz

Results of experiments made at 62.4 GHz in a long narrow corridor to measure the coherence bandwidth are presented. The correlation coefficients between envelopes separated in frequency are measured and expressed as functions of distance between terminals. They are found to be highly variable with the location of the terminals in the microcell. From these data the frequency correlation function is computed and used to calculate the coherence bandwidth. The coherence bandwidths for correlation levels of 0.5, 0.7, and 0.9 are given for 90% of the time     

Coherence bandwidth measurements in a suburban microcell at 62.4GHz

Results of experiments made at 62.4 GHz to measure the coherence bandwidth in a suburban mobile radio environment are presented. The correlation coefficients between envelopes separated in frequency are measured and expressed as functions of distance from the base station. They are found to be highly variable with the location of the receiver in the microcell. From these data, the frequency correlation function is computed and used to calculate the coherence bandwidth. Values of the coherence bandwidth for correlation levels of 0.5, 0.7 and 0.9 are given for 90% of the time     

Call admission control in the microcell/macrocell overlaying system

Call admission control can significantly affect the performance of a cellular system by adding additional bandwidth to a wireless network. In this paper, we show how call admission control can be used to optimize the performance of a hierarchical cellular system. The hierarchical system we study is based on a novel frequency planning scheme, whereby both the micro and macro layers can share the same spectrum and a hard partition of the frequency spectrum is not needed. The original analysis of the hierarchical system showed that a significant capacity gain can be achieved by the scheme. However, this capacity is gained at the expense of the carrier-to-interference ratio (C/I) performance of the macrocells. In this paper, we show that call admission control can be used in hierarchical cellular systems to achieve a capacity gain without sacrificing the C/I performance of the macrocells     

Measurements of path loss at 910 MHz for proposed microcell urbanmobile systems

Measurements of propagation path loss at 910 MHz were made in an urban area (Ottawa, Canada), using transmission from an antenna at street-lamp height (8.5 m) to a mobile receiving antenna at a height of 3.65 m. The received power was sampled about once per meter. On the same street as the transmitter, the received power was found to approximate the free-space value, with occasional 10 dB fades. On other streets, the signal was in most places less than the free-space value by 20 dB or more. The received power was found to depend in a detailed way on the distribution of buildings and the open areas between them     

Performance study for a microcell hot spot embedded in CDMAmacrocell systems

The code-division multiple-access (CDMA) system can provide more capacity than other systems, and the hierarchical layer of cells is required for system design. However, the problem is whether the same radio frequency (RF) channels used in a CDMA overlayed/underlayed macrocell and microcell structure also obtain a high capacity as in the homogeneous structure. We investigate the interference of uplink and downlink from both the microcell and macrocell under a hierarchical structure. A downlink power control scheme and two power control methods for the uplink are also considered. Performance measures such as blocking probability, C/I, capacity, and service hole area are also obtained by computer simulation. Besides, some extra efforts for a microcell are also noted, such as more power need to be transmitted by a microcell base station (BS) if the same RF channels are used in the hierarchical structure. The capacities of macrocell and microcell in the overlaying/underlaying structure are limited by the uplink and downlink, respectively. With downlink power control, the microcellular capacity can be increased. However, the combination of downlink power control for the microcell and C/I uplink power control for the macrocell causes the overall system capacity to significantly increase     

A microcell/macrocell cellular architecture for low- andhigh-mobility wireless users

Th authors explore the use of a wireless network having a two-tier architecture to serve both conventional mobile subscribers and quasi-stationary (e.g., PCN (personal communications network)) subscribers. The latter are served by microcells which are embedded within macrocells that serve the mobile users. This provides a balance between maximizing the number of users per unit area (which favors small cells) and minimizing the network control associated with handoff (which favors large cells). Four approaches to sharing the spectrum between the two tiers, using per-cell capacity as the measure, are evaluated. The first two feature spread-spectrum sharing, i.e., they use TDMA (time-division multiple access) among microcell users and CDMA (code-division multiple access) among macrocell users (System I), or vice versa (System II). The other two approaches feature orthogonal sharing, i.e., they use TDMA in both tiers, with time slots (System III) or frequency channels (System IV) partitioned so there is no overlap between tiers. Analysis shows that the capacity tradeoffs are poor for Systems I and II because of the large amounts of cross-tier interference: and that System IV gives the best capacity tradeoffs     

室内覆盖信号概述及隧道覆盖设计

随着人们对网络通信质量的要求越来越高,在城市建设过程中,一些未覆盖地区的网络信号设计成为重点课题。为了提高室内覆盖信号以及隧道覆盖信号质量,文章对当前常用的隧道内无缝覆盖方法进行分析,旨在为信号传输提供支持。     

一种基本概率赋值转换为概率的最优化方法

将基本概率赋值转换为概率在不确定性决策中有重要作用,本文提出了一种基于证据关联系数的最优化转换方法.主要思想是:转换后所得到的概率分布可以视为一个特殊的基本概率赋值函数,从命题的上下概率之间寻优使得被转换的基本概率赋值与转换所得概率之间的证据关联系数最大.将提出的最优化转换方法与常用的Pignistic概率转换方法通过...