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This paper investigates a maximum likelihood (ML) approach for direction of arrival (DOA) estimation based on the algorithm suggested by the 3GPP for scalar channels in UTRA-TDD mode. The performance of the algorithm is assessed b...
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This paper investigates a maximum likelihood (ML) approach for direction of arrival (DOA) estimation based on the algorithm suggested by the 3GPP for scalar channels in UTRA-TDD mode. The performance of the algorithm is assessed by resorting to simulations in typical UMTS scenarios. The results indicate that the proposed scheme overcomes the limitation of the angular resolution inherent to classical techniques like subspace or beam-forming methods. In particular, it is shown that waves exhibiting an arbitrarily small difference in azimuth and temporal spacing higher than one chip time interval can be easily separated. A threshold operation is included to select only the most significant paths, in terms of energy, of the estimated channel. The results show that a good performance can be achieved from low to high values of E/sub b//N/sub 0/.
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A close look at the ETSI (European Telecommunications Standards Institute). GSM standard shows that most of the security features were designed from an operator perspective with a view to preventing fraud and network misuse; the r...
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A close look at the ETSI (European Telecommunications Standards Institute). GSM standard shows that most of the security features were designed from an operator perspective with a view to preventing fraud and network misuse; the responsibility for implementing features related to user's privacy was delegated to the operators. This approach failed in providing a trusted environment where mobile users felt confident enough to place commercial transactions and exchange sensitive information. As technology matures and mobile data services appear, users are more than ever questioning the security of mobile communications and are becoming more aware of the associated risks. This is particularly true in the area of m-banking, where bank establishments have been reluctant to introduce sophisticated services and users uncomfortable to use their mobile telephones to transmit sensitive information about their accounts. Aware of the need to boost public confidence in mobile data services, the 3GPP (Third Generation Partnership Project) committee in charge of developing the standards for the Universal Mobile Telephony System (UMTS), took a different approach and incorporated more security requirements into the specification. This article looks at the security aspects associated with mobile communications and the way risks are addressed both in GSM and UMTS.
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We propose an energy-efficient framework, called SAF, for approximate querying and clustering of nodes in a sensor network. SAF uses simple time series forecasting models to predict sensor readings. The idea is to build these loca...
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We propose an energy-efficient framework, called SAF, for approximate querying and clustering of nodes in a sensor network. SAF uses simple time series forecasting models to predict sensor readings. The idea is to build these local models at each node, transmit them to the root of the network (the "sink"), and use them to approximately answer user queries. Our approach dramatically reduces communication relative to previous approaches for querying sensor networks by exploiting properties of these local models, since each sensor communicates with the sink only when its local model varies due to changes in the underlying data distribution. In our experimental results performed on a trace of real data, we observed on average about 150 message transmissions from each sensor over a week (including the learning phase) to correctly predict temperatures to within +/- 0.5°C.SAF also provides a mechanism to detect data similarities between nodes and organize nodes into clusters at the sink at no additional communication cost. This is again achieved by exploiting properties of our local time series models, and by means of a novel definition of data similarity between nodes that is based not on raw data but on the prediction values. Our clustering algorithm is both very efficient and provably optimal in the number of clusters. Our clusters have several interesting features: first, they can capture similarity between far away nodes that are not geographically adjacent; second, cluster membership to variations in sensors' local models; third, nodes within a cluster are not required to track the membership of other nodes in the cluster. We present a number of simulation-based experimental results that demonstrate these properties of SAF.
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As part of the roll out of Universal Mobile Telecommunication Systems (UMTS), a satellite component has been identified, aiming at providing a seamless communication. Since an all IP architecture has been defined by the Third Gene...
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As part of the roll out of Universal Mobile Telecommunication Systems (UMTS), a satellite component has been identified, aiming at providing a seamless communication. Since an all IP architecture has been defined by the Third Generation Partnership Project (3GPP) for the terrestrial component in Release 5 and beyond, an integration of satellite in the IP network is needed. Thus this paper aims to present a possible architecture for a seamless integration of an IP-based terrestrial/satellite network. We describe how sessions based on session initiation protocol (SIP) can be established between the mobile terminal (UE) under the coverage of Satellite-UMTS with other end users. The impact of random access delay and SIP message lengths on the session setup delay are analysed and demonstrated via performance evaluation in OPNET.
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3D-MIMO, using two dimensional antenna array at base station, demonstrates promising throughput gain over conventional antenna system during recent academic and industry studies. To realize the performance gain, accurate channel s...
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3D-MIMO, using two dimensional antenna array at base station, demonstrates promising throughput gain over conventional antenna system during recent academic and industry studies. To realize the performance gain, accurate channel state information (CSI) feedback is one essential aspect. One effective way to obtain this CSI is taking advantage of channel reciprocity between uplink and downlink in TDD system. This paper analyzes the uplink pilot contamination problem in practical TDD LTE system using a novel pilot contamination model, besides, pilot contamination elimination methods in terms of increasing pilot power and reducing pilot collision probability are evaluated. The simulation results show that system performance degradation is less than 21% considering the practical pilot contamination, which still outperform the traditional 2D-MIMO system. Moreover, about 15% performance gain could be benefit from pilot contamination reduction approaches.
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We investigate the energy efficiency in the downlink of a two-tier heterogeneous cellular network with quality of service consideration. By modeling the distributions of the macrocell and small cell base stations follow two indepe...
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We investigate the energy efficiency in the downlink of a two-tier heterogeneous cellular network with quality of service consideration. By modeling the distributions of the macrocell and small cell base stations follow two independent homogeneous Poisson point processes, we derive the analytical expressions of the mean achievable rate and the energy efficiency with the assumption that a mobile user connects to the closest BS. In addition, we evaluate the energy efficiency subject to a constraint of the blocking probability. Considering the dynamic variation of the traffic load, we use the numerical results to show that the optimum value of energy efficiency can be reached at determined deployment densities of the macrocells and the small cells, and the blocking probability has a dramatic impact on the optimal base station deployment.
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This paper addresses the problem of recovering variable-like entities when analyzing executables in the absence of debugging information. We show that variable-like entities can be recovered by iterating Value-Set Analysis (VSA), ...
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This paper addresses the problem of recovering variable-like entities when analyzing executables in the absence of debugging information. We show that variable-like entities can be recovered by iterating Value-Set Analysis (VSA), a combined numeric-analysis and pointer-analysis algorithm, and Aggregate Structure Identification, an algorithm to identify the structure of aggregates. Our initial experiments show that the technique is successful in correctly identifying 88% of the local variables and 89% of the fields of heap-allocated objects. Previous techniques recovered 83% of the local variables, but 0% of the fields of heap-allocated objects. Moreover, the values computed by VSA using the variables recovered by our algorithm would allow any subsequent analysis to do a better job of interpreting instructions that use indirect addressing to access arrays and heap-allocated data objects: indirect operands can be resolved better at 4% to 39% of the sites of writes and up to 8% of the sites of reads. (These are the memory-access operations for which it is the most difficult for an analyzer to obtain useful results).
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This paper addresses the problem of recovering variable-like entities when analyzing executables in the absence of debugging information. We show that variable-like entities can be recovered by iterating Value-Set Analysis (VSA), ...
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This paper addresses the problem of recovering variable-like entities when analyzing executables in the absence of debugging information. We show that variable-like entities can be recovered by iterating Value-Set Analysis (VSA), a combined numeric-analysis and pointer-analysis algorithm, and Aggregate Structure Identification, an algorithm to identify the structure of aggregates. Our initial experiments show that the technique is successful in correctly identifying 88% of the local variables and 89% of the fields of heap-allocated objects. Previous techniques recovered 83% of the local variables, but 0% of the fields of heap-allocated objects. Moreover, the values computed by VSA using the variables recovered by our algorithm would allow any subsequent analysis to do a better job of interpreting instructions that use indirect addressing to access arrays and heap-allocated data objects: indirect operands can be resolved better at 4% to 39% of the sites of writes and up to 8% of the sites of reads. (These are the memory-access operations for which it is the most difficult for an analyzer to obtain useful results.)
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The paper presents the results of the investigation of the implementation of mobile technologies in an under researched area: the police. Five key themes of investigation with relation to mobile information and communications tech...
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The paper presents the results of the investigation of the implementation of mobile technologies in an under researched area: the police. Five key themes of investigation with relation to mobile information and communications technologies were identified in the research: changes in work procedures, changes in the organisational capability, changes in relationships, effectiveness of equipment and effectiveness of infrastructure. These themes provide a framework for analysis of the police context, and one which could perhaps be extended to other contexts in the public safety / service arena.
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The paper presents the results of the investigation of the implementation of mobile technologies in an under researched area: the police. Five key themes of investigation with relation to mobile information and communications tech...
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The paper presents the results of the investigation of the implementation of mobile technologies in an under researched area: the police. Five key themes of investigation with relation to mobile information and communications technologies were identified in the research: changes in work procedures, changes in the organisational capability, changes in relationships, effectiveness of equipment and effectiveness of infrastructure. These themes provide a framework for analysis of the police context, and one which could perhaps be extended to other contexts in the public safety / service arena.
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