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IEEE 802.15.4 standard has been proposed for low power wireless personal area networks. It can be used as an important component in machine to machine (M2M) networks for data collection, monitoring and controlling functions. With an increasing number of machine devices enabled by M2M technology and equipped with 802.15.4 radios, it is likely that multiple 802.15.4 networks may be deployed closely, for example, to collect data for smart metering at residential or enterprise areas. In such scenarios, supporting reliable communications for monitoring and controlling applications is a big challenge. The problem becomes more severe due to the potential hidden terminals when the operations of multiple 802.15.4 networks are uncoordinated. In this paper, we investigate this problem from three typical scenarios and propose an analytic model to reveal how performance of coexisting 802.15.4 networks may be affected by uncoordinated operations under these scenarios. Simulations will be used to validate the analytic model. It is observed that uncoordinated operations may lead to a significant degradation of system performance in M2M applications. With the proposed analytic model, we also investigate the performance limits of the 802.15.4 networks, and the conditions under which coordinated operations may be required to support M2M applications. [ABSTRACT FROM AUTHOR]

Wireless communications play an important role in improving transportation environment safety and providing Internet access for vehicles. This paper proposes a QoS-aware two-level uplink dynamic bandwidth allocation (DBA) algorithm for IEEE 802.16j-based vehicular networks. IEEE 802.16j is an extension of standard IEEE 802.16 to support relay mode operation where traffics from/to subscriber stations (SS) are relayed to/from a base station (BS) via a relay station (RS). In such a vehicular network, the IEEE 802.16j BSs are installed along a highway, RSs are installed in large vehicles such as coaches, and the 802.16j interface is equipped on SSs such as individual passengers' mobile devices within a moving coach. In the proposed DBA algorithm, a utility function, which considers characteristics of different types of services, is designed. The objective of the proposed two-level DBA algorithm is to allocate bandwidth to different types of services from BS to RSs and then from a RS to SSs with given quality of service (QoS) requirements. It aims at maximizing the utility of the overall network and minimizing the average queuing delay of the overall network. The simulation results show the effectiveness and efficiency of the proposed DBA algorithm. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Orthogonal user pairing (OUP) was proposed for virtual multiple-input multiple-output (V-MIMO) in uplink 3G LTE system. However, its complexity is too high for practical implementation, especially when user population is large. To improve on this, semi-orthogonal user pairing (SUP) was suggested as an alternative. In this paper, two novel SUP algorithms, namely correlative angle-based SUP (CA-SUP) and Frobenius norm-based SUP (FN-SUP) algorithms are proposed. In view of the fact that ideal power control is difficult to implement, fixed power allocation (FPA) and adaptive power allocation (APA) constraints for the user pairing algorithms are introduced. Ergodic capacities for CA-SUP and FN-SUP algorithms with APA and FPA constraints, in terms of the numbers of users and antennas at Node-B, are evaluated and their capacity upper bounds are derived. Analysis and simulation results show that FN-SUP and CA-SUP algorithms requiring only limited channel state information (CSI) perform well and suit in particular for virtual V-MIMO systems. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented in which the editor discusses a research on the latest advances in mobile computing, networking, and wireless communications.

In this paper, we study the performance of IEEE 802.11a/b in a large-scale mobile railway networks and introduce our developed passive measurement approach. To provide a comprehensive evaluation, we built an outdoor multi-hop multi-interface railroad testbed (UNL-FRA Testbed), which consists of eight access points deployed along 3.5 mile of railroad track. We propose a novel large-scale passive measurement approach that synchronizes the system clocks of our monitoring systems, merges packet traces collected from multiple wireless channels across a multi-hop network, and enables a global performance view for the entire monitored network and across multiple layers. Based on the testing data collected from 15 field experiments carried out using BNSF locomotives and HyRail vehicles over a period of 18 months we conclude that in typical outdoor 802.11 railway environments the wireless link quality, the channel assignment scheme, and the handoff latency have much more significant impacts on the performance than the velocity. Furthermore, we discuss the implications of our conclusions on guaranteeing the quality of mobile services. We believe this is the first analysis on such a scale for 802.11-family railway networks. [ABSTRACT FROM AUTHOR]

As an indispensable part of intelligent transportation system (ITS), inter-vehicle communication (IVC) emerges as an important research topic. The inter-vehicle communication works based on vehicular ad hoc networking (VANET), and provides communications among different vehicles. The wide applications of VANET helps to improve driving safety with the help of traffic information updates. To ensure that messages can be delivered effectively, the security in VANET becomes a critical issue. Conventional security systems rely heavily on centralized infrastructure to perform security operations such as key assignment and management, which may not suit well for VANET due to its high mobility and ad hoc links. Some works suggested that vehicles should be connected to fixed devices such as road side units (RSUs), but this requires deployment of a large number of costly RSUs in a specific area. This paper is focused on the issues on decentralized IVC without fixed infrastructure and proposes a method for Dynamic Establishment of Secure Communications in VANET (DESCV), which works in particular well for VANET communication key management when centralistic infrastructure or RSU is not available. We will demonstrate through synergy analysis and simulations that DESCV performs well in providing secure communications among vehicles traveling at a relative velocity as high as 240 km/h. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors discuss various reports within the issue on topics including dynamic spectrum access in cognitive radio systems, a new video-on-demand (VoD) architecture based on mesh-based peer-to-peer (P2P) overlay networks, and sensor scheduling issues in target tracking systems with the use of ultrasonic sensors.

An introduction is presented in which the authors discuss various reports within the issue on topics including spectrum allocation in cellular cognitive radio networks, multiple-input multiple-output (MIMO) wireless sensor networks and multi-hop networks.

An introduction to the journal is presented in which the editor discusses wireless networking, computer systems, and ad hoc networks.

An introduction is presented in which the editor discusses various reports within the issue on topics including wireless local area networks, critical aspects of cognitive orthogonal frequency division mutiplexing (OFDM) systems, and ways to improve Attribute-Based Encryption's (ABE) efficiency.