QoS Differentiation for IEEE 802.16 WiMAX Mesh Networking

Recently IEEE 802.16 WiMAX has attracted a lot of attention in wireless networking research and applications. To enable a flexible and cost-effective deployment, mesh networking mode is defined in WiMAX standard. In this paper, we introduce a system model of WiMAX mesh networking with the focus on entry process, frame structure, centralized and distributed scheduling. The state-of-the-art WiMAX mesh networking research is reviewed. In addition, we propose an effective QoS differentiation scheme for the IEEE 802.16 WiMAX mesh networks. Both collocated scenario and general topology are theoretically analyzed and compared. Illustrative numerical examples are presented to demonstrate the effectiveness of the proposed strategy. The impact of key parameters on the performance is discussed for differentiating multiple classes of services. Several open issues are summarized as a guideline for future topics in WiMAX mesh networking research.     

An Improved Deterministic SoS Channel Simulator for Multiple Uncorrelated Rayleigh Fading Channels

The generation of multiple uncorrelated Rayleigh fading waveforms is often demanded for simulating wideband fading channels, multiple-input multiple-output (MIMO) channels, and diversity-combined fading channels. In this letter, an improved deterministic sum-of-sinusoids (SoS) channel simulator with a new parameter computation method is proposed to simulate a large number of uncorrelated Rayleigh fading processes. Compared with the existing SoS channel simulators, the proposed deterministic SoS model yields a much better simulation efficiency while still preserving satisfactory approximations to the desired statistical properties of the reference model.     

Security in wireless mobile ad hoc and sensor networks [Guest Editorial]

The goal of this feature topic is to report recent advances in and significant contributions to all aspects of security in resource-constrained mobile ad hoc and sensor networks. Specific areas of interest include key management, secure communications, secure location discovery, secure clock synchronization, and intrusion detection.     

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.     

Multiuser Pairing-up Schemes under Power Constraints for Uplink Virtual MIMO Networks

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.     

Optimal Utilization and Effects of Inaccurate Estimation in Mobile Database Failure Restoration

Mobility databases such as home location register and visitor location register are adopted to support mobility management in personal communications services networks. If a visitor location register fails or crashes, the subscribers' services will be seriously degraded due to the loss or corruption of location information. In this paper, we optimize utilization of demand re-registration messages for an adaptive p-persistent backoff database failure restoration scheme. An analytical model is developed and validated with simulations to obtain the optimal utilization using appropriate parameters so that the failed visitor location register is restored with the fastest speed. Some interesting aspects on the performance are studied and their deep insights are observed, such as effects of message sizes on choices of system parameters, effects of the inaccurate estimated number of stations, etc. One observation is that optimizations of utilization and successful transmission probability are two different goals, and a value to achieve the optimal successful transmission probability does not necessarily ensure optimal utilization. Furthermore, we also propose a scheme how to handle the problem with inaccurate (estimated) number of stations.     

DESCV—A Secure Wireless Communication Scheme for Vehicle ad hoc Networking

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.     

Topology control for service-oriented wireless mesh networks - [Service-oriented broadband wireless network architecture]

Topology control is one of the most critical design issues in multihop wireless networks. Topology control has been investigated extensively in the literature. Nevertheless, it is noted that most existing studies do not consider the requirements on upper layer applications or services. In this article we address the topology control issues on service-oriented wireless mesh networks. In particular, we provide a comprehensive survey of existing works on topology control from a service- oriented perspective. We then propose a general framework for topology control in service- oriented WMNs. To demonstrate the effectiveness of the framework, we conduct a case study in which the main objective is to maximize the overall throughput in a network with random unicast traffic. The performance of this topology control scheme is evaluated by numerical results. In addition, it is illustrated that the generated topology can support advanced technologies, including network coding and physical-layer network coding, which can significantly improve the throughput capacity of a network.     

On capacity of cognitive radio networks with average interference power constraints

Cognitive radio (CR) has been considered as a promising technology to improve the spectrum utilization. In this paper we analyze the capacity of a CR network with average received interference power constraints. Under the assumptions of uniform node placements and a simple power control scheme, the maximum transmit power of a target CR transmitter is characterized by its cumulative distribution function (CDF). We study two CR scenarios for future applications. The first scenario is called the CR based central access network, which aims at providing broadband access to CR devices. In the second scenario, the so-called CR assisted virtual multiple-input multiple-output (MIMO) network, CR is used to improve the access capability of a cellular system. The uplink ergodic channel capacities of both scenarios are derived and analyzed with an emphasis on understanding the impact of numbers of primary users and CR users on the capacity. Numerical and simulation results suggest that the CR based central access network is more suitable for less-populated rural areas where a relatively low density of primary receivers is expected; while the CR assisted virtual MIMO network performs better in urban environments with a dense population of mobile CR users.