The use of microprocessors and software to build real-time applications is expanding from traditional domains such as digital control, data acquisition, robotics, and digital switching, to include emerging domains like multimedia, virtual reality, optical navigation, and audio processing. These emerging real-time application domains require much more bandwidth and processing capability than the traditional real-time systems applications. Furthermore, at the same time, the potential performance and complexity of microprocessor and I/O architectures is also rapidly evolving to meet these new application demands (e.g. a super-scalar, pipelined architecture with multilevel cache with burst transmission I/O bus). Finally, the complexity of typical realtime system algorithms is increasing extant to include functions such as image processing, rulebased fault protection, and intelligent sensor processing. The foundation of real-time systems theory is the recognition that bandwidth and processing resources will always be constrained (a more demanding application always exists that can make use of increased resources as they become available). Given this reality, the question is how does an engineer formally ensure, given resource constraints, that the system will not only function correctly, but also meet timing deadlines. Since the introduction of Liu and Layland's rate-monotonic analysis and the development of the formal theory of hard real-time systems, significant progress has been made on extending this theory and developing an engineering process for it. The problem is that the current hard real-time theory and process assumes full reliability and constrains systems more than necessary by requiring either deterministic use of resources or worst-case models of such usage. R...

With the proliferation of wireless local area network (WLAN) technologies, wireless Internet access via public hotspots will become a necessity in the near future. In outdoor areas where the installation of a large number of wired access points is practically or economically infeasible, mobile users located at the edge of the network communicate with the access point at a very low rate and in turn waste network resources. In this work, we promote the use of tetherless relay points (TRPs) to improve the throughput of a WLAN in such environments. We first provide a high level description on how to integrate TRPs in a multi-rate WLAN architecture. We then propose an integer-programming optimization formulation and an iterative approach to compute the best placement of a fixed number of TRPs. Finally, we show in numerical analysis, through a case study based on relay-enabled rate adaptation and IEEE 802.11-like multi-rate physical model with Rayleigh fading, that for a wide range of system parameters, significant performance gain can be achieved when TRPs are strategically installed in the network.

We propose a novel data delivery strategy, called Whirlpool, for efficient SHM using Wireless Sensor Networks. Whirlpool implements a rotating interrogation of a monitoring structure and provides collision-aware scheduling of the monitoring queries. The Whirlpool strategy can be tuned for the required Quality of Data (QoD). We apply Whirlpool to examine the unique properties of output signals of the structure under critical integrity conditions and to perform instability detection using redundancy-based estimation of Kolmogorov-Sinai entropy. 1.

Abstract — Wireless sensor networks represent a key technology enabler for enhanced health care and assisted living systems. Recent standardization efforts to ensure compatibility among sensor network systems sold by different vendors have produced the IEEE 802.15.4 standard, which specifies the MAC and physical layer behavior. This standard has certain drawbacks: it supports only single-hop communication; it does not mitigate the hidden terminal problem; and it does not coordinate node sleeping patterns. The IEEE 802.15.4 standard design philosophy assumes that higher layer mechanisms will take care of any added functionality. Building on IEEE 802.15.4, this paper proposes TImezone COordinated Sleep Scheduling (TICOSS), a mechanism inspired by MERLIN [2] that provides multi-hop support over 802.15.4 through the division of the network into timezones. TICOSS is cross-layer in nature, as it closely coordinates MAC and routing layer behavior. The main contributions of TICOSS are threefold: (1) it allows nodes to alternate periods of activity and periods of inactivity to save energy; (2) it mitigates packet collisions due to hidden terminals belonging to nearby star networks; (3) it provides shortest path routing for packets from a node to the closest gateway. Simulation experiments confirm that augmenting IEEE 802.15.4 networks with TICOSS doubles the operational lifetime for high traffic scenarios. TICOSS has also been implemented on the Phillips AquisGrain modules for testing and eventual deployment in assisted living systems. I.

Fixed Broadband Wireless Access (FBWA) technology is designed to serve as a wireless DSL replacement to provide broadband Internet access in underserved areas where no other access technology exists. Due to the enormousness of the target service area, relay equipment play an important role in such networks, and the installation and maintenance cost of the network is directly proportional to the cost of the relay equipment. To minimize the network operational cost, an optimization framework which computes the minimum number of relay stations and their corresponding placements and channel assignments in the network is desired. Because the problem is NP-hard, we propose an efficient optimization algorithm based on a modified version of Bender’s decomposition to iteratively compute converging bounds to the problem solution. Our numerical results show that by using a few relay stations in a rural community, broadband Internet access can be established in a cost effective manner. Key words: Fixed broadband wireless access, relay stations, placement and channel assignment, Bender’s decomposition, mathematical programming/optimization.

Abstract—Sensor network monitoring and control are currently addressed separately through specialized tools. However, the high degree of coupling of network state to the physical environment in which the network is deployed demands that users can monitor the network and respond to network state changes continuously. This paper presents the open-source Octopus visualization and control tool. Octopus is a protocol-independent tool that provides live information about the network topology and sensor data in order to enable live debugging of deployed sensor networks. It enables operators to reconfigure the network behavior, such as switching between time-driven, event-driven, and query-driven modes or between awake and sleep modes of one, many, or all nodes through its graphical interface. Octopus also supports changing duty cycles of nodes, data reporting period, or sensing thresholds in event-driven networks. Reconfiguration of nodes is achieved through short request messages that support typical reconfiguration options without the overhead of epidemically sending new program images over the air. Our empirical tests showcase Octopus’s capacity to debug application behavior and to characterize heterogeneous network performance under multiple settings, as a step towards establishing a rules database that relates data delivery to network-level parameters, and towards enabling autonomous network reconfiguration. I.

While deployment of new network technologies has not been steady over the years, it is useful to take a long-term view of how major new telecommunications infrastructures evolve. Since the beginning of this decade, we have witnessed the emergence of new generations of three major communication networks. This article addresses the market conditions, technology innovations, and services driving the need for intelligent alloptical, 3G wireless, and QoS-based packet networks. Market forces such as traffic and subscriber growth, equipment cost reduction, and new technology penetration have a deep impact on network buildouts. Technology innovations abound, especially in the optical domain. For example, Raman amplification, pure optical switches, and tunable lasers have had a major impact on the architecture of optical networks. Many key services, such as streaming audio and high-quality image transfer, were not possible using wireless access because of its limited bandwidth and performance. With 3G wireless technology, a true mobile Internet will become a reality. Businesses have shied away from the use of the public Internet because of service quality. Thanks to advances in MPLS and service intelligence, this is expected to change. For each type of network, we will survey the key factors shaping its evolution and implications on network architectures.

Some wireless sensor network applications forward data to a central aggregation point (AP) that is responsible for processing, aggregating, and relaying information to the base station. For example one node in a body sensor network is responsible for aggregating data and then forwarding only useful information to an external ambient network. This procedure leads to asymmetry in the AP node energy consumption due to (1) higher forwarding activity for nodes in the vicinity of the AP and (2) higher AP activity relative to nodes. Existing approaches of load and energy consumption balancing employ either suboptimal periodical route changes or random AP rotations. In contrast, we propose a novel technique 1 to enable a dynamic reassignment of the sensor AP according to a novel cost function that is based on relevant node energy metrics. We show that the technique lead to a network lifetime extension up to 50 % for applications, such as medical, that require power-intensive tasks at the AP and for high traffic applications.