A Cross-Layer Approach for Minimizing Interference and Latency of Medium Access in Wireless Sensor Networks

In low power wireless sensor networks, MAC protocols usually employ periodic sleep/wake schedule to reduce idle listening time. Even though this mechanism is simple and efficient, it results in high end-to-end latency and low throughput. On the other hand, the previously proposed CSMA/CA-based MAC protocols have tried to reduce inter-node interference at the cost of increased latency and lower network capacity. In this paper we propose IAMAC, a CSMA/CA sleep/wake MAC protocol that minimizes inter-node interference, while also reduces per-hop delay through cross-layer interactions with the network layer. Furthermore, we show that IAMAC can be integrated into the SP architecture to perform its inter-layer interactions. Through simulation, we have extensively evaluated the performance of IAMAC in terms of different performance metrics. Simulation results confirm that IAMAC reduces energy consumption per node and leads to higher network lifetime compared to S-MAC and Adaptive S-MAC, while it also provides lower latency than S-MAC. Throughout our evaluations we have considered IAMAC in conjunction with two error recovery methods, i.e., ARQ and Seda. It is shown that using Seda as the error recovery mechanism of IAMAC results in higher throughput and lifetime compared to ARQ.Comment: 17 pages, 16 figure

CAMA: Efficient Modeling of the Capture Effect for Low Power Wireless Networks

Network simulation is an essential tool for the design and evaluation of wireless network protocols, and realistic channel modeling is essential for meaningful analysis. Recently, several network protocols have demonstrated substantial network performance improvements by exploiting the capture effect, but existing models of the capture effect are still not adequate for protocol simulation and analysis. Physical-level models that calculate the signal-to-interference-plus-noise ratio (SINR) for every incoming bit are too slow to be used for large-scale or long-term networking experiments, and link-level models such as those currently used by the NS2 simulator do not accurately predict protocol performance. In this article, we propose a new technique called the capture modeling algorithm (CAMA) that provides the simulation fidelity of physical-level models while achieving the simulation time of link-level models. We confirm the validity of CAMA through comparison with the empirical traces of the experiments conducted by various numbers of CC1000 and CC2420-based nodes in different scenarios. Our results indicate that CAMA can accurately predict the packet reception, corruption, and collision detection rates of real radios, while existing models currently used by the NS2 simulator produce substantial prediction error

Multipath Routing in Wireless Sensor Networks: Survey and Research Challenges

A wireless sensor network is a large collection of sensor nodes with limited power supply and constrained computational capability. Due to the restricted communication range and high density of sensor nodes, packet forwarding in sensor networks is usually performed through multi-hop data transmission. Therefore, routing in wireless sensor networks has been considered an important field of research over the past decade. Nowadays, multipath routing approach is widely used in wireless sensor networks to improve network performance through efficient utilization of available network resources. Accordingly, the main aim of this survey is to present the concept of the multipath routing approach and its fundamental challenges, as well as the basic motivations for utilizing this technique in wireless sensor networks. In addition, we present a comprehensive taxonomy on the existing multipath routing protocols, which are especially designed for wireless sensor networks. We highlight the primary motivation behind the development of each protocol category and explain the operation of different protocols in detail, with emphasis on their advantages and disadvantages. Furthermore, this paper compares and summarizes the state-of-the-art multipath routing techniques from the network application point of view. Finally, we identify open issues for further research in the development of multipath routing protocols for wireless sensor networks

A detailed hydrothermal investigation of a helical micro double-tube heat exchanger for a wide range of helix pitch length

The present study was numerically inquired the heat transfer performance and fluid flow characteristic of a helical micro double-tube heat exchanger (HMDTHX) using the finite volume method. The tube length was considered to be constantly equal to 30 mm, and 12 different configurations were modeled by changing in turn number and pitch length (P) for Reynolds numbers of 50, 100, 150, and 200. The findings indicated that the heat transfer would enhance by applying any helix angle in the straight tube. However, it had an optimum point which varied by Reynolds number (Re). Rising Re caused overall heat transfer coefficient (OHTC), pressure drop, and pumping power augment for all cases. Increasing P in overall reduced OHTC, pressure drop, and pumping power which had different maximum points between P = 0.5 to 3. Maximum overall heat transfer coefficient (OHTC) enhancement was equal to 45% for Re = 200 and P = 2. Also, maximum effectiveness was 11.5% for P = 2 and Re = 200. Moreover, a 42% maximum increment was achieved for pressure drop, pumping power, and friction factor at Re = 200 and P = 2. Shear stress for Re = 100 to 200 showed that the values are almost the same for P = 0.5 and 1. Then by increasing P, the shear stress decreases. While, for Re = 50, a maximum is seen at P = 2. The temperature distribution was indicated that the maximum temperature of the straight tube and helical tube are the same, but the difference is in the average temperature, which was 3.2 K between straight and helical tubes. Finally, by investigating the velocity contour, it was determined that a secondary flow through the HMDTHX, affected by centrifugal force, was existed, enhancing the fluid flow turbulency and heat transfer rate

Remocao anaerobia de corantes texteis.

The textile industry is predominant in the region of Beira Interior and studies on the processes leading to a reduction of pollution are necessary. In this work, the application of the anaerobic treatment is proposed, in view of its low energy consumption and relatively high efficiency. Preliminary's tests have been performed on the removal of acid, direct and disperse dyes in an Upflow Anaerobic Sludge Blanket Reactor (UASB) and the almost complete removal of the acid and direct dyes has been observed, while the disperse one made the digester to collapse. The more detailed study of an acid dye, Acid Red 73, performed in batch reactors, has enable the assessment of its influence in the degradation of easily metabolized subtracts. A kinetic model has been established for the dye biodegradation, and it was observed that this was much faster then the degradation of the subtract. The influence of the homogenization of these systems on the kinetic of the subtract degradation was also studied. The removal of the same dye, Acid Red 73, was also studied in a "UASB" reactor, inoculated with digested sludge, where the organic load was relatively low (3 kg COD m"-"3 d"-"1) and the hydraulic retention time was about 12 hours. A kinetic model for this mechanism is proposed, based on simple mathematical models and on hydrodynamic behaviour of the reactor...Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

A Medium Access Control Protocol with Adaptive Parent Selection Mechanism for Large-Scale Sensor Networks

Abstract—In the MAC protocols based on the S-MAC scheme, usually the combination of periodic sleep/listen scheduling and four-way handshake mechanism is employed to reduce idle listening and avoid interference. However, this combination greatly degrades network capacity and results in high end-toend latency. In this paper, we propose Adaptive IAMAC to increase channel utilization and improve communication efficiency, specifically in large-scale sensor networks with low duty cycle. Adaptive IAMAC allows multiple nodes to transmit to their common parent during a frame. Moreover, it includes the adaptive parent selection mechanism, which enables the nodes to change their parent according to the currently overheard control packets at the MAC layer. Through these techniques, Adaptive IAMAC enhances network throughput, reduces end-to-end latency, and moderates the overhead of four-way handshake mechanism. Simulation results confirm that Adaptive IAMAC provides significant improvements over S-MAC in terms of throughput, latency, and energy efficiency

DICSA: Distributed and Concurrent Link Scheduling Algorithm for Data Gathering in Wireless Sensor Networks

Although link scheduling has been used to improve the performance of data gathering applications, unfortunately, existing link scheduling algorithms are either centralized or they rely on specific assumptions that are not realistic in wireless sensor networks. In this paper, we propose a distributed and concurrent link scheduling algorithm, called DICSA, that requires no specific assumption regarding the underlying network. The operation of DICSA is managed through two algorithms: (i) Primary State Machine (PSM): Enables each node to perform its own slot reservation; (ii) Secondary State Machine (SSM): Enables each node to concurrently participate in the slot reservation of its neighbors. Through these algorithms and a set of forbidden slots managed by them, DICSA provides concurrent and collision-free slot reservation. Our results show that the execution duration and energy consumption of DICSA are at least 50% and 40% less than that of DRAND, respectively. In terms of slot assignment efficiency, while our results show higher spatial reuse over DRAND, the maximum slot number assigned by DICSA is at least 60% lower than VDEC. In data-gathering applications, our results confirm the higher performance of DICSA in terms of throughput, delivery ratio and packet delay. We show that the network throughput achievable by DICSA is more than 50%, 70%, 90% and 170% higher than that of DRAND, SEEDEX, NCR and FPS, respectively

LINKORD: link ordering-based data gathering protocol for wireless sensor networks

With respect to the multi-hop communication pattern of wireless sensor networks, all the nodes should establish multi-hop paths towards a common data gathering point to provide a data gathering service for the underlying applications. Although data gathering protocols provide a simple service, these protocols suffer from poor performance in practice due to the power constraints of low-power sensor nodes and unreliability of wireless links. Existing data gathering protocols rely on the ETX metric to find high-throughput paths through assuming there is an infinite number of transmission attempts at the link layer for delivering a single packet over every link. However, in practice the link layer provides a bounded number of transmissions per packet over individual links. Therefore, employing existing data gathering protocols in these situations may result in the construction of the paths that require more than maximum number of provided link layer transmissions for delivering a single packet over each link. In this regard, we propose a path cost function which considers the limitation on the number of provided link layer transmissions and relative position of the links along the paths according to their data transmission probability. Furthermore, we introduce a data gathering protocol which uses the proposed path cost function to construct high-throughput paths. Moreover, this protocol employs a newly designed congestion control mechanism during the data transmission process to provide energy-efficient and high-throughput data delivery. The simulation results show that, the proposed protocol improves data delivery ratio by 70 % and network goodput by 80 %, while it reduces the consumed energy for data delivery by 50 % compared to the default data gathering protocol of TinyOS