基于概率模型的无线传感器网络优化覆盖算法

为了更好地解决无线传感器网络在覆盖过程中出现大量冗余信息及节点能量消耗不均衡等现象,提出了一种节点能量均衡的最优覆盖算法。该算法利用监测区域内传感器节点与目标节点的从属关系建立网络模型,给出传感器节点与目标节点之间的从属关系;通过从属关系和概率理论,求解传感器节点对目标节点的覆盖期望值,然后计算出覆盖监测区域所需最少传感器节点数量。实验结果表明,该算法不仅可以使用最少传感器节点完成对监测区域的有效覆盖,而且抵制了冗余信息数据的产生,提高了网络生存周期。     

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     

A geometrical-based microcell mobile radio channel model

In this paper we present a geometric multipath propagation model for a microcell mobile environment. The proposed model provides the statistics for the direction-of-arrival (DOA) of multipath components. These statistics are required to test adaptive array algorithms for cellular applications. The proposed model assumes that (1) a line-of-sight (LOS) path exists between the transmitter and the receiver, (2) the scatterers lie within a circle of radius R around the mobile station, and (3) the base station lies within this circle. The distances between the scatterers and the mobile station are subject statistically to a hyperbolic distribution. The model also provides the multipath power delay profiles (PDP), which are used to evaluate the bit error rate (BER) and the signal to interference ratio (SIR) for the direct-sequence code division multiple access (DS-CDMA). We derive and simulate the joint probability density functions (pdfs) of the power—DOA and the power—Doppler shift. Further we determine expressions for the BER performance and for the SIR of a DS-CDMA system over the proposed channel model. A simplified expression based on the improved Gaussian approximation (SEIGA) is used to evaluate the BER and the SIR in a wideband multipath channel. Although the proposed model is applicable for downlink as well, in this paper we will analyze the uplink environment only.     

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     

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     

TD-LTE小基站回传承载方案

TD-LTE小基站的部署场景、覆盖策略与传统宏基站不同,站址的规划也与宏基站有较大区别,采用传统宏基站PTN回传网络承载TD-LTE小基站将面临三大难题:网络效能低、安全性差、智能性低.对如何建设高效、安全、智能的小基站回传网络进行了研究,结合中国移动网络现状,提出PON+CMNet、PTN+CMNet、PON+PTN 、PTN端到端4种小基站回传承载方案,并对这4种方案进行了现网测试验证.验证表明,4种承载方案均满足小基站通信业务需求,采用PON+CMNet承载方案在安全性、智能性、高效性上优于另外3种承载方案.     

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     

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     

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.     

Capacity analysis for underlaying CDMA microcell/macrocell systems

The CDMA system can provide more capacity than the conventional AMPS system and the hierarchical layer of cells is required for system design in the future. However, the problem is whether the same RF channels used in a CDMA underlaying macrocell/microcell structure also obtain high capacity as in the homogeneous structure. This paper investigates the interference of uplink and downlink from both the microcell and macrocell in a hierarchical structure. Downlink power control is also considered. The results show that the capacity of microcell in a hierarchical structure is 23 per cent less than in homogeneous cells. The capacity of macrocell in a hierarchical structure decreases dramatically in proportion to the number of microcells. The capacities of the microcell and macrocell are limited in downlink, and uplink, respectively. In addition, more efforts for microcell should be made, such as more power is transmitted by microcell basestation if the same RF channel is used in a hierarchical structure. The results suggest that different RF channels are used in a two‐tier cellular environment. Copyright © 2001 John Wiley & Sons, Ltd.     

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     

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     

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     

Adjacent channel interference in a macrocell/microcell WCDMA system

This paper studies the impacts of adjacent channel interference (ACI) on uplink capacity in a multi‐macrocell/multi‐microcell wideband code‐division multiple access (WCDMA) system. A method is presented for computing ACI and deriving capacity limitation. This method is based on an interference analysis that accounts for shadow fading, and random distribution of mobile users. The results indicate that both the base station (BS) separation and adjacent channel interference power ratio (ACIR) strongly affect system capacity reduction. The proposed method in this paper is useful for measuring the impacts of ACI on uplink capacity. Copyright © 2008 John Wiley & Sons, Ltd.