Peter Ruckebusch

Efficient Calculation of Sensor Utility and Sensor Removal in Wireless Sensor Networks for Adaptive Signal Estimation and Beamforming

Wireless sensor networks are often deployed over a large area of interest and therefore the quality of the sensor signals may vary significantly across the different sensors. In this case, it is useful to have a measure for the importance or the so-called “utility” of each sensor, e.g., for sensor subset selection, resource allocation or topology selection. In this paper, we consider the efficient calculation of sensor utility measures for four different signal estimation or beamforming algorithms in an adaptive context. We use the definition of sensor utility as the increase in cost (e.g., mean-squared error) when the sensor is removed from the estimation procedure. Since each possible sensor removal corresponds to a new estimation problem (involving less sensors), calculating the sensor utilities would require a continuous updating of K different signal estimators (where K is the number of sensors), increasing computational complexity and memory usage by a factor K. However, we derive formulas to efficiently calculate all sensor utilities with hardly any increase in memory usage and computational complexity compared to the signal estimation algorithm already in place. When applied in adaptive signal estimation algorithms, this allows for on-line tracking of all the sensor utilities at almost no additional cost. Furthermore, we derive efficient formulas for sensor removal, i.e., for updating the signal estimator coefficients when a sensor is removed, e.g., due to a failure in the wireless link or when its utility is too low. We provide a complexity evaluation of the derived formulas, and demonstrate the significant reduction in computational complexity compared to straightforward implementations.

GITAR: generic extension for internet-of-things architectures enabling dynamic updates of network and application modules

Abstract The Internet-of-Things (IoT) represents the third wave of computing innovation and relies on small, cheap and/or energy efficient devices, densely deployed in various spaces. Automatically managing, updating and upgrading the software on these devices, particularly the network stacks, with new, improved functionality is currently a major challenge. In this paper we propose GITAR, a generic extension for Internet-of-Things architectures, that enables dynamic application and network level upgrades in an efficient way. GITAR consists of four design concepts which can be applied to any operating system running on IoT/M2M devices. The proof of concept implementation in this paper uses the Contiki OS and the evaluation, based on analytical and experimental methods, shows that GITAR i) is up to 14% more efficient in terms of memory usage and ii) has less or similar run-time CPU overhead as state of the art solutions while offering upgrade functionality down to the network level and iii) can reuse existing Contiki network protocols for dynamic updates without requiring modifications to the code.

TAISC: A cross-platform MAC protocol compiler and execution engine

Abstract MAC protocols significantly impact wireless performance metrics such as throughput, energy consumption and reliability. Although the choice of the optimal MAC protocol depends on time-varying criteria such as the current application requirements and the current environmental conditions, MAC protocols cannot be upgraded after deployment since their implementations are typically written in low level, hardware specific code which is hard to reuse on other hardware platforms. To remedy this shortcoming, this paper introduces TAISC, Time Annotated Instruction Set Computer, a framework for hardware independent MAC protocol development and management. The solution presented in this paper allows describing MAC protocols in a platform independent language, followed by a straightforward compilation step, yielding dedicated binary code, optimized for specific radio chips. The compiled code is as efficient in terms of memory footprint as custom-written protocols for specific devices. To enable time-critical operation, the TAISC compiler adds exact time annotations to every instruction of the optimized binary code. As a result, the TAISC approach can be used for energy-efficient cross-platform MAC protocol design, while achieving up to 97% of the theoretical throughput at an overhead of only 20 µs per instruction.

Greedy distributed node selection for node-specific signal estimation in wireless sensor networks

A wireless sensor network is envisaged that performs signal estimation by means of the distributed adaptive node-specific signal estimation (DANSE) algorithm. This wireless sensor network has constraints such that only a subset of the nodes are used for the estimation of a signal. While an optimal node selection strategy is NP-hard due to its combinatorial nature, we propose a greedy procedure that can add or remove nodes in an iterative fashion until the constraints are satisfied based on their utility. With the proposed definition of utility, a centralized algorithm can efficiently compute each nodess utility at hardly any additional computational cost. Unfortunately, in a distributed scenario this approach becomes intractable. However, by using the convergence and optimality properties of the DANSE algorithm, it is shown that for node removal, each node can efficiently compute a utility upper bound such that the MMSE increase after removal will never exceed this value. In the case of node addition, each node can determine a utility lower bound such that the MMSE decrease will always exceed this value once added. The greedy node selection procedure can then use these upper and lower bounds to facilitate distributed node selection.

Intra-, Inter-, and Extra-Container Path Loss for Shipping Container Monitoring Systems

This letter presents empirical path loss models for an environment of stacked shipping containers. Specifically, a system for wireless monitoring of containers is considered for which three different types of wireless links are identified, namely intra-, inter-, and extra-container links. Furthermore, the inter-container link is investigated for the two most common types of container stacking: row and block stacking. Intra- and inter-container path loss are investigated at IEEE 802.15.4 frequencies of 433, 868, and 2400 MHz. Extra-container path loss is examined at GSM/UMTS frequencies of 900, 1850, and 2100 MHz. Distance-dependent path loss models are proposed for the inter- and extra-container links (high-correlation coefficients between 0.76 and 0.86). The resulting path loss models can be used in link budget calculations for container monitoring systems.

Supporting Protocol-Independent Adaptive QoS in Wireless Sensor Networks

Next-generation wireless sensor networks will be used for many diverse applications in time-varying network/environment conditions and on heterogeneous sensor nodes. Although Quality of Service (QoS) has been ignored for a long time in the research on wireless sensor networks, it becomes inevitably important when we want to deliver an adequate service with minimal efforts under challenging network conditions. Until now, there exist no general-purpose QoS architectures for wireless sensor networks and the main QoS efforts were done in terms of individual protocol optimizations. In this paper we present a novel layerless QoS architecture that supports protocol-independent QoS and that can adapt itself to time-varying application, network and node conditions. We have implemented this QoS architecture in TinyOS on TmoteSky sensor nodes and we have shown that the system is able to support protocol-independent QoS in a real life office environment.

An Evaluation of Link Estimation Algorithms for RPL in Dynamic Wireless Sensor Networks

Link estimators are extremely important in dynamic wireless sensor networks for obtaining a good network performance because they drive the decisions made by the routing protocol. Many estimators exist but the quality of their estimation depends on the scenario at hand. In this paper, the impact of the estimator on the network performance is investigated in different networking scenarios. Also the influence of the underlying MAC protocol was evaluated. The evaluation was performed both in simulation and on a real-life testbed.

WiSHFUL: Enabling Coordination Solutions for Managing Heterogeneous Wireless Networks

The paradigm shift toward the Internet of Things results in an increasing number of wireless applications being deployed. Since many of these applications contend for the same physical medium (i.e., the unlicensed ISM bands), there is a clear need for beyond-state-of-the-art solutions that coordinate medium access across heterogeneous wireless networks. Such solutions demand fine-grained control of each device and technology, which currently requires a substantial amount of effort given that the control APIs are different on each hardware platform, technology, and operating system. In this article an open architecture is proposed that overcomes this hurdle by providing unified programming interfaces (UPIs) for monitoring and controlling heterogeneous devices and wireless networks. The UPIs enable creation and testing of advanced coordination solutions while minimizing the complexity and implementation overhead. The availability of such interfaces is also crucial for the realization of emerging software-defined networking approaches for heterogeneous wireless networks. To illustrate the use of UPIs, a showcase is presented that simultaneously changes the MAC behavior of multiple wireless technologies in order to mitigate cross-technology interference taking advantage of the enhanced monitoring and control functionality. An open source implementation of the UPIs is available for wireless researchers and developers. It currently supports multiple widely used technologies (IEEE 802.11, IEEE 802.15.4, LTE), operating systems (Linux, Windows, Contiki), and radio platforms (Atheros, Broadcom, CC2520, Xylink Zynq, ), as well as advanced reconfigurable radio systems (IRIS, GNURadio, WMP, TAISC).

A unified radio control architecture for prototyping adaptive wireless protocols

Experimental optimization of wireless protocols and validation of novel solutions is often problematic, due to limited configuration space present in commercial wireless interfaces as well as complexity of monolithic driver implementation on SDR-based experimentation platforms. To overcome these limitations a novel software architecture is proposed, called WiSHFUL, devised to allow: i) maximal exploitation of radio functionalities available in current radio chips, and ii) clean separation between the logic for optimizing the radio protocols (i.e. radio control) and the definition of these protocols.

Network-wide synchronization in Wireless Sensor Networks

The implementation of network-wide synchronization in Wireless Sensor Networks has generally been perceived by the research community to incur a considerable overhead. In this paper it is argued however that the expense for network-wide synchronization can be rather low, and that such synchronization can moreover provide opportunities for energy-efficient communication protocols. A network-wide synchronization mechanism is proposed and evaluated through both simulation and testbed experiments.