Mobile Radio Environment Research Articles

Regular Data Broadcasting Plan with Grouping in Wireless Mobile Environment

Regular Data Broadcasting Plan with Grouping in Wireless Mobile Environment

A Genetic Algorithm Applied for Optimization of Antenna Arrays Used in Mobile Radio Channel Characterization Devices

This paper presents a proposed method for synthesizing scenario-dependent channel characterization system arrays that are adapted to the mobile radio environment where measurements take place. The criterion for synthesizing the array is the minimization of the angular Cramer-Rao lower bound, which is the lower bound of the mean square estimation error (MSEE) for an unbiased estimator. The core of the process is a genetic algorithm (GA) that seeks for the most advantageous array topology for each scenario. Simulation results show that the method succeeds in synthesizing feasible antenna arrays that have increased direction of arrival (DoA) estimation accuracy and are superior to the arrays typically used during actual measurement campaigns.

Microcell electric field strength prediction model based upon artificial neural networks

A new microcell prediction model for mobile radio environment is presented in this paper. The popular feedforward artificial neural networks (ANN) are used as an optimizing tool to build the model, making possible to overcome some important disadvantages of known, both deterministic and statistical prediction models. In order to build the model, extensive electric field strength measurements were carried out in the city of Belgrade, for four different test transmitter locations. The analysis of the model has shown that the proposed model is fast, accurate (on the order of the local mean measurements uncertainty), reliable and suitable for computer implementation.

QoS-Aware Service Selection Algorithms for Pervasive Service Composition in Mobile Wireless Environments

The successful application of pervasive services running in mobile wireless networks and devices relies on its ability to provide efficient and cost-effective QoS (Quality of Service) support. This paper proposes a comprehensive QoS model specifically for pervasive services. It considers not only user-perceived factors but also mobile wireless network characteristics. The corresponding formula to calculate each QoS criterion is also devised. In particular, this paper formulates the QoS-aware service selection problem for pervasive service composition and proposes some solutions to the problem, i.e., global-search-based LOSSA (local optimal service selection algorithm) and limited broadcast based LOSSA-k. The evaluation results of the algorithms have shown the effectiveness of the QoS model and the efficiency of the proposed LOSSAs.

Channel Coding for Progressive Images in a 2-D Time-Frequency OFDM Block With Channel Estimation Errors

Coding and diversity are very effective techniques for improving transmission reliability in a mobile wireless environment. The use of diversity is particularly important for multimedia communications over fading channels. In this work, we study the transmission of progressive image bitstreams using channel coding in a 2-D time-frequency resource block in an OFDM network, employing time and frequency diversities simultaneously. In particular, in the frequency domain, based on the order of diversity and the correlation of individual subcarriers, we construct symmetric n -channel FEC-based multiple descriptions using channel erasure codes combined with embedded image coding. In the time domain, a concatenation of RCPC codes and CRC codes is employed to protect individual descriptions. We consider the physical channel conditions arising from various coherence bandwidths and coherence times, leading to a range of orders of diversities available in the time and frequency domains. We investigate the effects of different error patterns on the delivered image quality due to various fade rates. We also study the tradeoffs and compare the relative effectiveness associated with the use of erasure codes in the frequency domain and convolutional codes in the time domain under different physical environments. Both the effects of intercarrier interference and channel estimation errors are included in our study. Specifically, the effects of channel estimation errors, frequency selectivity and the rate of the channel variations are taken into consideration for the construction of the 2-D time-frequency block. We provide results showing the gain that the proposed model achieves compared to a system without temporal coding. In one example, for a system experiencing flat fading, low Doppler, and imperfect CSI, we find that the increase in PSNR compared to a system without time diversity is as much as 9.4 dB.

A crash faults detection service for wireless and mobile ad hoc networks

PurposeThe purpose of this paper is to describe an adaptive approach for diagnosing faulty nodes in a wireless mobile environment.Design/methodology/approachBased on a diagnosis approach that has been previously developed for wired networks. A discussion of the novel diagnosis protocol and its correctness is also included.FindingsIn this paper, the author presents a new implementation of a failure detection service for wireless ad hoc and sensor systems that is based on an adaptation of a gossip‐style failure detection protocol and the heartbeat failure detector. The authors show that the failure detector is eventually perfect – that is, there is a time after which every faulty mobile is permanently suspected by every fault‐free host, and no host will be suspected before it crashes.Research limitations/implicationsThe main limitations of this work is the lack of simulations results. Future works will be directed at providing such performance evaluations.Practical implicationsThe work introduced in this paper aims mainly at identifying faulty nodes in a wireless mobile environment. This service has been identified as one of the basic building blocks for dependable mobile ad hoc networks (MANETs).Originality/valueThe paper is first work that adapts a previously developed failure detection service to wireless and MANETs.

An Analysis of Probability Distribution of Doppler Shift in Three-Dimensional Mobile Radio Environments

The Doppler shift (DS) distribution of the signal that is received by a mobile station in 3D mobile radio environments is closely related to the signal's power spectral density (PSD). From the relationship between the arriving angles and the DS, general equations are derived, bridging the probability density function (pdf) of the elevation angle with the pdf of the DS, its variance, and the characteristic function. These equations are then used to analyze the statistic distribution of the DS based on the semispheroid model, which has been recently proposed by Janaswamy. For this particular model, analytical expressions for the pdf and the variance of the DS have been derived, and a definite-integral expression is provided for the characteristic function. When the average strengths of the waves that are distributed on different equal-Doppler-shift surfaces are assumed to be equal, the derived pdf of the DS is equivalent to the signal's PSD, and the derived characteristic function of the DS is equivalent to the signal's autocorrelation function.

A Zipper OFDM Multiple-Antenna Technique for Interleaved-FDD Cellular Communication Systems

This paper investigates the application of Zipper orthogonal frequency-division multiplexing (OFDM), which is a frequency-domain duplexing technique based on interleaving subcarriers, to multiple-antenna cellular communications. By studying the Cramer-Rao lower bound as well as the performance of a minimum-mean-square-error-based interpolator, we show that the interleaved subcarriers make it possible for the base station to obtain accurate instantaneous downlink channel state information (CSI) from uplink channel measurements. However, the interleaved uplink and downlink subcarriers could introduce interference leakage when the intersubcarrier orthogonality is destroyed in multiple-cell environments. We address this issue by analyzing the uplink-to-downlink power leakage and show that with proper system configuration, such interference only has a marginal effect in typical land mobile radio environments. Finally, by considering maximum ratio transmission as an example, we demonstrate the benefit of knowing instantaneous downlink CSI in multiple-antenna Zipper OFDM systems.

Low-Complexity Call-Management Scheme for Cellular Networks

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In wireless mobile environments, where resources are scarce, the basis for quality-of-service (QoS) provisioning is the admission control (AC) of new and handoff subscriber services to avoid future detrimental perturbations of established connections. Most research efforts considered only the bandwidth of the wireless link to control the admission of new services. In addition, proposals for degrading and enhancing services only account for mobility. In this paper, we propose a novel approach for service admission and adaptation that considers, in addition to the station mobility, both bandwidth and error-rate requirements as well as the possibility of multiple services per mobile station, while minimizing interference to neighbor cells as well as signaling overhead. When compared with other proposals in a simulated third-generation (3G) cellular system, our AC approach outperformed by more than 10% the equal priority and guard capacity policies in terms of the total number of accepted services in the cell, particularly at high handoff and new-call rates. Moreover, our adaptation scheme succeeded in improving the admission probability by a further 13% in indoor and outdoor environments. </para>

High-performance sharing of consistent data in ad hoc networks

In mobile wireless environments, Personal Digital Assistants (PDAs) may cache data to work, even when the mobile client is far from the structured network. However, the same cached data may be shared by two or more users and this can be done in an ad hoc wireless network. In this case, it is necessary to always have the most updated data. To solve this problem, we developed software that shares data between the server and mobile devices using a timestamp protocol to always have the most updated data. The experimental environment has one server in a structured network and two mobile clients getting and sending data between the client and the server (when it is covered by the structured wireless network) and between the mobile clients (when a structured wireless network is absent) using an ad hoc network. In this paper, we describe the experimental environment and detail what and how we have done this software.

Mobile agents and mobile devices: friendship or difficult relationship?

Mobile agent technology has traditionally been recognized as a very useful approach to build applications for mobile computing and wireless environments. However, only a few studies report practical experiences with mobile agents in a mobile medium. This leads us to the following question: can current mobile agent platforms be used effectively in environments with mobile devices? In this paper, we study existing mobile agent platforms by analyzing if they are suitable or not in a mobile environment. We identify some key missing features in the platforms and highlight the requirements and challenges that lie ahead. With this work, we expose existing problems and hope to motivate further research in the area.

Discrete Simulation Framework for Wireless Cellular Networks

The aim of the discrete simulation framework is to deal with issues of the next generation of wireless cellular networks (e.g., multimedia traffic, radio resource management and mobility... etc) and to provide a platform for current and future investigations involving wireless cellular networks. The simulator is built from the scratch to enable customization requirements of any research and to provide the freedom to understand, configure protocol modules, draw desired topologies and specifies the movement paths of the mobile users and to plot the necessary performance graphs. In order to evaluate and validate the performance of the designed simulator, a simulation model for the wireless cellular network and mobile environment deployed. The performance of the developed simulator compared with the performance characteristics of existing algorithms. Simulation results verify the developed simulator is able to recapture the results of both the numerical result and simulation results of the comparative system utilizing an idealistic platform. In addition the simulator incorporates detail algorithms for the correlated components between the entities of the cellular networks and the development of the discrete simulator.

Mobile IPv6 환경에서 동적 분기 라우터를 이용한 효율적인 자원 예약 방법

RSVP(Resource reSerVation Protocol)는 송신노드와 수신노드 사이에 네트워크 자원을 예약하여 QoS(Quality of Service) 요구사항을 지원하는 인터넷 표준 프로토콜이다. 무선 이동환경에 RSVP를 적용하기 위해 공유경로 식별 문제와 자원 선-예약 문제가 해결되어야 한다. 본 논문은 후보 라우터와 분기 라우터를 이용하여 공유경로 식별 문제와 자원 선-예약 문제를 해결하는 DBRA(Dynamic Branch Router Approach) 기법을 제안한다. DBRA는 송신노드와 분기 라우터 사이에는 일대일의 RSVP 자원예약 관계를 갖으며, 분기 라우터와 후보 라우터들 사이에는 일대다의 RSVP 자원예약 관계를 갖도록 하여 많은 네트워크 자원 소모를 줄인다. 제안하는 DBRA 기법의 효율성을 분석하기 위해서 시뮬레이션을 이용하여 평균 패킷 전송율과 대역폭 이용률, RSVP 자원 예약 실패율 관점에서 RSVP와 MRSVP(Mobile RSVP), HMRSVP (Hierarchical MRSVP)를 비교대상으로 비교 분석하였다. RSVP (Resource reSerVation Protocol) is the Internet standard protocol for supporting QoS (Quality of Service) requirements by reserving network resources between the sender and the receiver. Several problems, such as common path identification and resource pre-reservation, should be solved to apply RSVP in wireless mobile environments. To resolve these problems, this paper proposes DBRA (Dynamic Branch Router Approach) based on two designated entities, candidate access routers and a branch router. While several RSVP sessions between a branch router and candidate routers are managed, DBRA makes use of only one RSVP session between the sender and a branch router. Based on a network simulation, the proposed scheme has been compared with MRSVP (Mobile RSVP) and HMRSVP (Hierarchical MRSVP) in terms of the average packet transmission rate, bandwidth utilization and RSVP session failure rate.

Maximum likelihood delay estimation in a navigation receiver for aeronautical applications

The potential of the SAGE (Space Alternating Generalized Expectation Maximization) algorithm for navigation systems in order to distinguish the line-of-sight signal (LOSS) is to be considered. The SAGE algorithm is a low-complexity generalization of the EM (Expectation-Maximization) algorithm, which iteratively approximates the maximum likelihood estimator (MLE) and has been successfully applied for parameter estimation (relative delay, incident azimuth, incident elevation, Doppler frequency, and complex amplitude of impinging waves) in mobile radio environments. This study discusses receivers using a single antenna or an antenna array. Whereas we estimate the complex amplitudes, relative delays, and Doppler frequencies of the impinging waves, in the latter additionally the spatial signature of the impinging waves (incident azimuth and elevation) is estimated. The results of the performed computer simulations and discussion indicate that the SAGE algorithm has the potential to be a very powerful high resolution method to successfully estimate parameters of impinging waves for navigation systems. SAGE has proven to be a promising method to combat multipath for aircraft navigation applications due to its good performance, fast convergence, and low complexity.

Effective protocols for kNN search on broadcast multi-dimensional index trees

In a wireless mobile environment, data broadcasting provides an efficient way to disseminate data. Via data broadcasting, a server can provide location-based services to a large client population in a wireless environment. Among different location-based services, the k nearest neighbors ( kNN) search is important and is used to find the k closest objects to a given point. However, the kNN search in a broadcast environment is particularly challenging due to the sequential access to the data on a broadcast channel. We propose efficient protocols for the kNN search on a broadcast R-tree, which is a popular multi-dimensional index tree, in a wireless broadcast environment in terms of latency and tuning time as well as memory usage. We investigate how a server schedules the broadcast and provide the corresponding kNN search algorithms at the mobile clients. One of our kNN search protocols further allows a kNN search to start at an arbitrary time instance and it can skip the waiting time for the beginning of a broadcast cycle, thereby reducing the latency. The experimental results validate that our mechanisms achieve the objectives.

Data Consistency for Cooperative Caching in Mobile Environments

The trend toward wireless communications and advances in mobile technologies are increasing consumer demand for ubiquitous access to Internet-based information and services. A 3D framework provides a basis for designing, analyzing, and evaluating strategies to address data consistency issues in mobile wireless environments. A proposed relay-peer-based cache consistency protocol offers a generic and flexible method for carrying out cache invalidation

Performance of Cooperative Time-Reversal Communication in a Mobile Wireless Environment

In this paper, we study the performance of a technique called time reversal for cooperative communication in a mobile wireless environment. To put the work in context, a brief introduction to time-reversal communication (TRC) in general and cooperative TRC in particular is presented. Performance of a proposed cooperative TRC scheme is evaluated numerically via a simulated indoor environment containing multiple wireless communication nodes. We characterize the behavior of the peak power received at a target node as a function of the number of cooperating transmitting nodes and as a function of the distance of the target from its predicted location within the simulated environment. The results demonstrate that the performance of cooperative TRC is less sensitive to uncertainty in the target position than might be expected from standard assumptions regarding the relationship between signal wavelength and spatial channel correlation in a complex multipath environment.

Disseminating dependent data in wireless broadcast environments

In wireless mobile environments, data broadcasting is an effective approach to disseminate information to mobile clients. In some applications, the access pattern of all the data can be represented by a weighted DAG. In this paper, we explore how to efficiently generate the broadcast schedule in a wireless environment for the data set having a weighted DAG access pattern. Such a broadcast schedule not only minimizes the access latency but also is a topological ordering of the DAG. Minimized access latency ensures the quality of service (QoS). We prove that it is NP-hard to find an optimal broadcast schedule and provide some heuristics. After giving an analysis for these heuristics on the latency and complexity, we implement all the proposed heuristics to compare their performance.

Performance evaluation of Atomic Commit Protocols for mobile transactions

The commitment of a distributed transaction is ensured with the use of an Atomic Commit Protocol (ACP). Due to their great importance for transaction systems, the recent advances in mobile computing development have renewed the interest in the ACPs for mobile transactions. We compare assets of mobile ACPs that have been simulated on the NS-DBsim platform integrating two simulation environments; the NS2 simulator and DBsim a distributed database simulator. NS-DBsim takes into account the various and fluctuant parameters of wireless and mobile systems. The comparison highlights performance indices and orientations to the design of ACPs in mobile wireless environments.

On the fundamental performance limits of peer-to-peer data replication in wireless ad hoc networks

Wireless ad hoc networks are drawing increasing attention from the research community because of their potential applications. However, the fundamental capacity limits of these networks pose various technological challenges to designers of network protocols. In this paper, we attempt to capture the inherent constraints on information dissemination in a mobile wireless environment, with the emphasis on peer-to-peer (P2P) communications. More specifically, we introduce the notion of replication-induced gain to quantify the impact of data replication under the paradigm of P2P query-response mechanisms. Our major contribution lies in presenting several preliminary results with respect to the complexities and trade-offs involved in enhancing data availability. To the best of our knowledge, the data replication problems that arise because of scarce system resources in wireless ad hoc networks have not been investigated from this perspective. We believe that our results could provide additional insights and practical implications for P2P system designers.