The wireless sensor networks community, has now an increased understanding of the need for realistic link layer models. Recent experimental studies have shown that real deployments have a "transitional region" with highly unreliable links, and that therefore the idealized perfect-reception-within-range models used in common network simulation tools can be very misleading. In this paper, we use mathematical techniques from communication theory to model and analyze the low power wireless links. The primary contribution of this work is the identification of the causes of the transitional region, and a quantification of their influence. Specifically, we derive expressions for the packet reception rate as a function of distance, and for the width of the transitional region. These expressions incorporate important channel and radio parameters such as the path loss exponent and shadowing variance of the channel; and the modulation and encoding of the radio. A key finding is that for radios using narrow-band modulation, the transitional region is not an artifact of the radio non-ideality, as it would exist even with perfect-threshold receivers because of multi-path fading. However, we hypothesize that radios with mechanisms to combat multi-path effects, such as spread-spectrum and diversity techniques, can reduce the transitional region.

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Analyzing the transitional region in low power wireless links

Radio link quality estimation in Wireless Sensor Networks (WSNs) has a fundamental impact on the network performance and also affects the design of higher-layer protocols. Therefore, for about a decade, it has been attracting a vast array of research works. Reported works on link quality estimation are typically based on different assumptions, consider different scenarios, and provide radically different (and sometimes contradictory) results. This article provides a comprehensive survey on related literature, covering the characteristics of low-power links, the fundamental concepts of link quality estimation in WSNs, a taxonomy of existing link quality estimators, and their performance analysis. To the best of our knowledge, this is the first survey tackling in detail link quality estimation in WSNs. We believe our efforts will serve as a reference to orient researchers and system designers in this area.

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Radio link quality estimation in wireless sensor networks: A survey

A battery management system (BMS) includes at least one sub-BMS and a main BMS. The at least one sub-BMS measures information about a battery, and generates an activation signal according to operating state. The main BMS receives the activation signal and determines the operating state of the at least two sub-BMSs. If the at least two sub-BMSs normally operate, the main BMS generates a synchronization signal and transfers the same to the sub-BMSs. The at least one sub-BMS measures the information about the battery according to the synchronization signal.

Battery management system and driving method thereof

Extensive empirical studies presented in this paper confirm that the quality of radio communication between low power sensor devices varies significantly with time and environment. This phenomenon indicates that the previous topology control solutions, which use static transmission power, transmission range, and link quality, might not be effective in the physical world. To address this issue, online transmission power control that adapts to external changes is necessary. This paper presents ATPC, a lightweight algorithm of Adaptive Transmission Power Control for wireless sensor networks. In ATPC, each node builds a model for each of its neighbors, describing the correlation between transmission power and link quality. With this model, we employ a feedback-based transmission power control algorithm to dynamically maintain individual link quality over time. The intellectual contribution of this work lies in a novel pairwise transmission power control, which is significantly different from existing node-level or network-level power control methods. Also different from most existing simulation work, the ATPC design is guided by extensive field experiments of link quality dynamics at various locations and over a long period of time. The results from the real-world experiments demonstrate that 1) with pairwise adjustment, ATPC achieves more energy savings with a finer tuning capability and 2) with online control, ATPC is robust even with environmental changes over time.

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ATPC: adaptive transmission power control for wireless sensor networks

We present empirical measurements of the packet delivery performance of the latest sensor platforms: Micaz and Telos motes. In this article, we present observations that have implications to a set of common assumptions protocol designers make while designing sensornet protocols—specifically—the MAC and network layer protocols. We first distill these common assumptions in to a conceptual model and show how our observations support or dispute these assumptions. We also present case studies of protocols that do not make these assumptions. Understanding the implications of these observations to the conceptual model can improve future protocol designs.

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An empirical study of low-power wireless

A wireless network is described including a cluster network (Fig. 1) and a sensor/actuator network arranged in a hierarchical manner with the cluster head network. The cluster head network includes at least one cluster head and the sensor/actuator network includes a plurality of sensor/actuator nodes arranged in a plurality of node levels.

Self-organizing hierarchical wireless network for surveillance and control

In wireless sensor networks, a good cost metric encapsulating wireless link quality is essential to an energy-efficient routing topology. For many wireless network scenarios, rapid variation in the channel precludes an efficient mechanism for knowing instantaneous link quality at the time of transmission, thus making it difficult to estimate the instantaneous value of the cost metric. This paper explores what a good cost metric may be and how it can be measured in an energy-efficient way. We present an experimental study of wireless link quality variation over a period of several days in a sensor network placed in two different indoor office environments. The nodes are equipped with low power transceivers operating in the 900 MHz band. Results are documented for several different link configurations, i.e., relative placement of the transmitter and receiver. Based on detailed observations of link quality variation, we form quantitative measures of link quality, and propose a cost metric. We find that reasonably few channel measurements are sufficient to obtain a good estimate of the cost metric, hence even during the initialization phase one can obtain sufficient information about links in order to design an efficient topology. The estimate can be improved further as more measurements are taken during the normal operation of the network.

Measurement and characterization of link quality metrics in energy constrained wireless sensor networks

For energy-constrained stationary wireless networks of sensors, selection of links with high quality rate helps to ensure reliable long-term operation. During the implementation of a protocol targeting industrial applications of such systems, it was found that it is advantageous to acquire accurate information about the availability and quality of the RF communication links prior to the network topology formation. "Link assessment" as part of the initialization process, accomplishes this task by assessing a sufficient number of packets exchanged between neighboring nodes. This paper introduces and analyzes two different approaches to link assessment: The first approach is a random nondeterministic scheme that allows for a probabilistic guarantee of collision-free packet exchange. An alternative method is described which employs 'constant-weight codes' and provides a deterministic guarantee of success. In particular, a special class of constant-weight codes, known as optical orthogonal codes, are considered. Since, these codes are cyclically permutable, they make the link assessment process simpler, and therefore they are preferred over other codes. We evaluate the performance of these methods based on their energy consumption, time duration, and implementation complexity

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Energy-efficient link assessment in wireless sensor networks

A method to wirelessly network a sensor/actuator node is described. The sensor/actuator node is installed in a sensor/actuator node network and arranged in a hierarchical manner with a plurality of node levels and a cluster head network. A unique node identifier is assigned to the sensor node and the sensor node network is initialized. The sensor node is woken-up to perform a task and then set to an active low power mode.

Protocol for reliable, self-organizing, low-power wireless network for security and building automation systems

A method for initializing a wireless network is provided which includes discovering at least one node of the wireless network that is within hearing range of a base station of the wireless network, authenticating the at least one discovered node, assigning a node identifier to the at least one discovered node, and selecting a network frequency, at least one backup frequency, and a locally unique network identifier.

System and method for a communication protocol for wireless sensor systems including systems with high priority asynchronous message and low priority synchronous message

Arati Manjeshwar

Papers

Self-organizing hierarchical wireless network for surveillance and control

Measurement and characterization of link quality metrics in energy constrained wireless sensor networks

Energy-efficient link assessment in wireless sensor networks

Protocol for reliable, self-organizing, low-power wireless network for security and building automation systems

System and method for a communication protocol for wireless sensor systems including systems with high priority asynchronous message and low priority synchronous message