Conventional IoT applications rely on seamless data collection from the distributed sensor nodes of Wireless Sensor Networks (WSNs). The energy supplied to the sensor node is limited and it depletes after each cycle of data collection. Therefore, data flow from the network to the base station may cease at any time due to the nodes with a dead battery. A replacement of the battery in WSNs is often challenging and requires additional efforts. To ensure the robust operation of WSNs, many fault recovery routing mechanisms have been proposed. Most of the previous fault recovery routing methods incur considerable delays in recovery and high overhead in either energy consumption or device cost. We propose an energy-efficient fail recovery routing method that is aimed to operate over a data aggregation network topology using a TDMA media access control (MAC). This paper introduces a novel fault recovery routing algorithm for TDMA-based WSNs. It finds an optimal neighbor backup parent (NBP) for each node in a way that reduces the energy consumption. The proposed method allows the NBPs to utilize the time slot of the faulty parent nodes, so it eliminates the overhead of TDMA rescheduling for NBPs. To evaluate the fault recovery performance and energy efficiency of the proposed method, we implemented it in C++ simulation program. Simulation experiments with an extensive set of network examples demonstrate that the proposed method can extend the network lifetime by 21% and reduce the energy consumption by 23% compared with the reference methods.Electronics 2018, 7, 444 2 of 21 collisions, which incur retransmissions of packets causing extra energy loss. A time division multiple access (TDMA) protocol is regarded as an effective alternative to CSMA, since it can ensure fair and collision-free data forwarding from all nodes, therefore reducing the energy loss [4,5]. Our proposed method is thus based on TDMA. Regardless of the choice of protocol, however, any WSN is susceptible to devise failure or battery depletion, and therefore it may lose network connectivity.Recent studies on WSNs have achieved considerable enhancement in network architecture and data forwarding protocols to reduce the energy consumption [2]. The primary goal of many WSNs is to maximize the network lifetime even under the event of node failures [6]. Hence, it needs a fail recovery method that operates the rest of the WSN to maintain the desired lifetime.For low-power WSNs, a tree structure topology is often adopted [7], since it permits simple routing paths from all the nodes towards the sink (root) node, which acts as a gateway collecting all the sensing data. In WSNs of tree structure topology, each child node at a lower level forwards its sensing data to its parent node at a higher level until all data are delivered to the sink node [7]. If any parent node fails, then, all nodes in the subtree under the failed parent lose their routing path towards the sink node. A large portion of the network, therefore, can be isolated, resulting in all their sensing ...
In vehicular networks, efficient multi-hop message dissemination can be used for various purposes, such a informing the driver about the recent emergency event or propagating the local dynamic map of a predefined region. Dissemination of warning information up to a longer distance can reduce the accidents on the road. It provides a driver additional time to react to the situations adequately and assists in finding a safe route towards the destination. The adopted V2X standards, ETSI TS’s C-ITS and IEEE 1609/IEEE 802.11p, specify only primitive multi-hop message dissemination schemes. IEEE 1609.4 standard disseminates the broadcast messages using the method of flooding, which causes high redundancy, severe congestion, and long delay during multi-hop propagation. To address these problems, we propose an effective broadcast message dissemination method. It introduces a notion of source Lateral Crossing Line (LCL) algorithm, which elects a set of relay vehicles for each hop based on the vehicle locations in a way that reduces the redundant retransmission and congestion, consequently minimizing the delays. Our simulation results demonstrated that the proposed method can achieve about 15% reduction in delays and 2 times the enhancement in propagation distance compared with the previous methods.
In this paper, we propose a novel decentralized channel resource allocation algorithm for V2V communication based on deep multi-agent reinforcement learning. Each vehicle behaves as an independent agent and uses its local observation to select the optimal resource blocks (RBs) from pre-configured resource pool (environment). The selected RB is considered optimal if transmission within this RB causes a minimum interference to other ongoing transmissions. We applied an actor-critic reinforcement learning algorithm to let each agent conduct a centralized training and decentralized execution. In centralized training, agents share their actions and local observations through the centralized critic network. While making a decision (choosing the optimal resource blocks), therefore, each agent can estimate the policies of other agents. In decentralized execution, each agent uses its local observation to optimize its local policy independently. Each action taken by an agent in actor network is judged by its private critic network.
IEEE 1609/802.11p standard obligates each vehicle to broadcast a periodic basic safety message (BSM). The BSM message comprises a positional and kinematic information of a transmitting vehicle. It also contains emergency information that is to be delivered to all the target receivers. In broadcast communication, however, existing carrier sense multiple access (CSMA) medium access control (MAC) protocol cannot guarantee a high reliability as it suffers from two chronic problems, namely, access collision and hidden terminal interference. To resolve these problems of CSMA MAC, we propose a novel enhancement algorithm called a neighbor association-based MAC (NA-MAC) protocol. NA-MAC utilizes a time division multiple access (TDMA) to distribute channel resource into short time-intervals called slots. Each slot is further divided into three parts to conduct channel sensing, slot acquisition, and data transmission. To avoid a duplicate slot allocation among multiple vehicles, NA-MAC introduces a three-way handshake process during slot acquisition. Our simulation results revealed that NA-MAC improved packet reception ratio (PRR) by 19% and successful transmission by 30% over the reference protocols. In addition, NA-MAC reduced the packet collisions by a factor of 4. Using the real on-board units (OBUs), we conducted an experiment where our protocol outperformed in terms of PRR and average transmission interval by 82% and 49%, respectively.
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