Energy efficiency is one of the critical issues for Wireless Sensor Networks (WSN). IEEE 802.15.4 beacon-enabled MAC protocol achieves low energy consumption by having periodical inactive portions, where nodes run in low power. However, IEEE 802.15.4 beacon-enabled protocol cannot respond to dynamic changes in the number of sensor nodes and data rates in WSN because its duty cycle is fixed and immutable. In this paper, we propose a dynamic superframe duration adaptation scheme based on the Markov chain-based analysis methods for IEEE 802.15.4 beacon-enabled protocol. The proposed methods are flexible enough to accommodate changes in the number of sensor nodes and differences in data rates in WSNs while maintaining low latency and low energy consumption despite slight degradation in packet delivery ratio.

As the nodes of AWSN (Aerial Wireless Sensor Networks) fly around, the network topology changes frequently with high energy consumption and high cluster head mortality, and some sensor nodes may fly away from the original cluster and interrupt network communication. To ensure the normal communication of the network, this paper proposes an improved LEACH-M protocol for aerial wireless sensor networks. The protocol is improved based on the traditional LEACH-M protocol and MCR protocol. A Cluster head selection method based on maximum energy and an efficient solution for outlier nodes is proposed to ensure that cluster heads can be replaced prior to their death and ensure outlier nodes re-home quickly and efficiently. The experiments show that, compared with the LEACH-M protocol and MCR protocol, the improved LEACH-M protocol performance is significantly optimized, increasing network data transmission efficiency, improving energy utilization, and extending network lifetime.

This paper proposes an ultra-low quiescent current low-dropout regulator (LDO) with a flipped voltage follower (FVF)-based load transient enhanced circuit for wireless sensor network (WSN). Some characteristics of an FVF are low output impedance, low voltage operation, and simple circuit configuration [1]. In this paper, we focus on the characteristics of low output impedance and low quiescent current. A load transient enhanced circuit based on an FVF circuit configuration for an LDO was designed in this study. The proposed LDO, including the new circuit, was fabricated in a 0.6 µm CMOS process. The designed LDO achieved an undershoot of 75 mV under experimental conditions of a large load transient of 100 µA to 10 mA and a current slew rate (SR) of 1 µs. The quiescent current consumed by the LDO at no load operation was 204 nA.

This paper is primarily concerned with the performance of Medium Access Control (MAC) layer plans for Wireless Sensor Networks (WSNs) in the context of buffer management solutions. We propose a novel buffer management solution that improves the general performance of MAC layer plans, in particular those crafted for WSNs. An analytical model is introduced in order to evaluate the cost of different buffer management solutions. The proposed buffer management solution, Single Queue Multi Priority (SQMP), is compared with well-known Single Queue Single Priority (SQSP) and Multi Queue Multi Priority (MQMP) buffer management solutions. All buffer management solutions are investigated in terms of throughput performance, utilization of the buffer and prioritization capabilities. Despite the relatively good performance of the different buffer management solutions in uncongested networks, the characteristic features of WSNs cause a degradation in the performance. In bursty conditions, SQMP controls and manages this degradation more effectively in comparison with the other two solutions. Simulations based on Omnet++ and Castalia confirm the performance improvements of our buffer management solution.

Wireless Sensor Networks (WSNs) have been proposed for monitoring vital signs of patients at home. This scenario requires inter-cell mobility; however, WSNs are not designed to support this characteristic. In this paper we propose a cross-layer protocol to manage the handoff, called WSN-HaDaS (Handoff aware of Data Sending), which operates in the transport layer and medium access control (MAC) sub-layer based on an interaction between the layers (transport and MAC). This protocol interacts with a sending data mechanism (like TCP protocol) to notify the beginning or ending of the handoff process; therefore, the mechanism can stop or resume data sending, respectively. Therefore, WSN-HaDaS prevents packet loss during the handoff process. WSN-HaDaS comprises two main processes to manage mobility: Monitoring Handoff Trigger (MHT) and Handoff Execution Process (HEP); they are responsible for generating the handoff warning messages and executing the handoff process, respectively. Therefore, MHT delay and HEP delay are used as the key performance metrics. To evaluate the proposal, we use a physical test-bed in an indoor environment with the intention of obtaining practical results. The results demonstrate that the proposed protocol performs the handoff process with less delay than the selected reference work. They also show that WSN-HaDaS is an appropriate solution to provide inter-cell mobility in WSNs. Furthermore, we demonstrate the possibility of embedding the WSN-HaDaS in devices with limited resources using the IEEE 802.1.5.4 standard.

In this paper, we propose a modeling approach for wireless sensor networks (WSNs) that is based on non-volatile two-dimensional cellular automata (CA) and analyze the space-time dynamics of a WSN based on the proposed model. We introduce the fourth circuit element with memory function — memristor into the cells of CA to model a non-volatile CA and employ the non-volatile CA in modeling a WSN. A state transition method is designed to implement the synchronous updates of the states between the central sensor nodes and its neighbors which might behave asynchronously in sending messages to the central one. Therefore, the energy consumption in sensor nodes can be reduced by lessening the amount of exchanged information. Simulations demonstrate that the energy consumption of a WSN can be reduced greatly based on the proposed model and the lifetime of the whole network can be increased.

The problem of coexistence between IEEE 802.11g based wireless LANs (WLANs) and IEEE 802.15.4 based wireless personal area networks (WPANs) in the 2.4GHz band is an important issue for the operation of a home energy management system (HEMS) for smart grids. This paper proposes a coexistence scheme that is called a Hybrid station aided coexistence (HYSAC) scheme to solve this problem. This scheme employs a hybrid-station (H-STA) that possesses two types of network device functions. The scheme improves the data transmission quality of the WPAN devices which transmit energy management information such as power consumption. The proposed HYSAC scheme employs WLAN control frames, which are used to assign WPAN system traffic resources. Moreover, we propose a coexistence method to achieve excellent WLAN throughput where multiple WPANs coexist with a WLAN. We theoretically derive the performance of the proposed scheme by considering the QoS support in WLAN and show that the results of the simulation and theoretical analysis are in good agreement. The numerical results show that the HYSAC scheme decreases the beacon loss rate of WPAN to less than 1% when the WLAN system consists of 10 STAs under saturated traffic conditions. Furthermore, the WLAN throughput of the proposed synchronization method is shown to be 30.6% higher than that of the HYSAC scheme without synchronization when the WLAN that consists of 10 STAs coexists with four WPANs.

In this paper, a real-time medium access control (MAC) protocol based on a coding-black-burst mechanism with low latency and high energy efficiency is proposed for wireless sensor networks. The Black-Burst (BB) mechanism is used to provide real-time access. However, when the traffic load is heavy, BB will cause a lot of energy loss and latency due to its large length. A binary coding mechanism is applied to BB in our coding-black-burst-based protocol to reduce the energy consumption and latency by at least (L-2(log2 L+1)) for L-length BB. The new mechanism also gives priority to the real-time traffic with longer waiting delays to access the channel. The theoretical analysis and simulation results indicate that our protocol provides low end-to-end delay and high energy efficiency for real-time communication.

In typical end-to-end recovery protocols, an ACK segment is delivered to a source node over a single path. ACK loss requires the source to retransmit the corresponding data packet. However, in underwater wireless sensor networks which prefer flooding-based routing protocols, the source node has redundant chances to receive the ACK segment since multiple copies of the ACK segment can arrive at the source node along multiple paths. Since existing RTO calculation algorithms do not consider inherent features of underlying routing protocols, spurious packet retransmissions are unavoidable. Hence, in this letter, we propose a new ACK loss-aware RTO calculation algorithm, which utilizes statistical ACK arrival times and ACK loss rate, in order to reduce such retransmissions.

In wireless sensor networks, energy depletion of bottleneck nodes which have more data packets to relay than others, dominates the network lifetime referred to as the funnel effect problem. To overcome this problem, multiple sink methods have been proposed where sensor nodes send observed data packets toward several sinks to distribute traffic load of bottleneck nodes. If both of the topology and the traffic pattern are symmetric, bottleneck nodes are located near sinks. However, in a general sensor network with an asymmetric topology and/or an asymmetric traffic pattern, bottleneck nodes may exist any place in the network. In this paper, we propose DCAM (DispersiveCast of packets to Avoid bottleneck nodes for Multiple sink sensor network), which is a load balancing method to improve lifetime of a sensor network with an asymmetric topology and an asymmetric traffic pattern. DCAM first finds bottleneck nodes, and then balances the load on the bottleneck nodes. Selected nodes send data packets to several sinks dispersively according to some criteria. The criteria classify DCAM into three variations: DCAM with probability (DCAM-P), DCAM with moving boarder (DCAM-MB), and DCAM with round-robin (DCAM-RR). This paper gives details of the DCAM methods, and thereafter evaluates them with asymmetric topologies and asymmetric traffic patterns. To deal with these dynamic asymmetry, the topology is modeled by a grid network with virtual holes that are defined as vacant places of nodes in the network. Asymmetry of traffic pattern is modeled by defining a hot area where nodes have heavier data traffic than the others. The evaluations are conducted as changing hot-area traffic patterns as well as fixing hot-area patterns. The results show that DCAM improves network lifetime up to 1.87 times longer than the conventional schemes, (i.e., nearest sink transmissions and optimal dispersive cast of packet). We also discuss DCAM on several aspects such as overhead, energy consumption, and applications.

Optimizing lifetime of a wireless sensor network has received considerable attention in recent years. In this paper, using the feasibility and simplicity of grid-based clustering and routing schemes, we investigate optimizing lifetime of a two-dimensional wireless sensor network. Thus how to determine the optimal grid sizes in order to prolong network lifetime becomes an important problem. At first, we propose a model for lifetime of a grid in equal-grid model. We also consider that nodes can transfer packets to a grid which is two or more grids away in order to investigate the trade-off between traffic and transmission energy consumption. After developing the model for an adjustable-grid scenario, in order to optimize lifetime of the network, we derive the optimal values for dimensions of the grids. The results show that if radio ranges are adjusted appropriately, the network lifetime in adjustable-grid model is prolonged compared with the best case where an equal-grid model is used.

In the sensor networks for surveillance, the requirements of providing energy efficiency and service differentiation, which is to deliver high-priority packets preferentially, while maintaining high goodput, which is to deliver many packets within their deadline are increasing. However, previous works have difficulties in satisfying the requirements simultaneously. Thus, we propose GES-MAC, which satisfies the requirements simultaneously. GES-MAC reduces idle listening energy consumption by using a duty cycle, periodic listen (i.e., turn on radio module) and sleep (i.e. turn off radio module) of sensor nodes. Cluster-based multi-hop scheduling provides high goodput in a duty-cycled environment by scheduling clusters of nodes in the listen period and opportunistically forwarding data packets in the sleep period. Priority-aware schedule switching makes more high-priority packets reach the sink node by letting high-priority packets preempt the schedules of low-priority packets. In experiments with MICA2 based sensor nodes and in simulations, the energy consumption of the radio module is reduced by 70% compared to the approaches without a duty cycle, while providing 80% 100% goodput of the approaches that provide high goodput. Service differentiation is also supported with little overhead.

This paper introduces the basics of energy harvesters and demonstrates two specific vibratory-type energy harvesters developed at the University of Hyogo. The fabrication and evaluation results of the vibratory-type energy harvesters, which employ electrostatic and electromagnetic mechanisms, are described. The aim of developing these devices is to realize a power source for an autonomous human monitoring system. The results of harvesting from actual human activities obtained using a data logger are also described. Moreover, challenges in the power management of electronic circuitry used for energy harvesting are briefly discussed.

This paper proposes a dynamic bandwidth allocation algorithm that improves the network performance and bandwidth sharing efficiency in the upstream channels of a hybrid passive optical network (PON) that combines a fiber-to-the-home (FTTH) access network and wireless sensor networks (WSNs). The algorithm is called the adaptive limited dynamic bandwidth allocation (ALDBA) algorithm. Unlike existing algorithms, the ALDBA algorithm is not limited to controlling just FTTH access networks, it also supports WSNs. For the proposed algorithm, we investigate the difference in the lengths of generated data packets between the FTTH terminals and sensor nodes of WSN to effectively evaluate the end-to-end average packet delay, bandwidth utilization, time jitter, and upstream efficiency. Two variants of the proposed algorithm and a limited service (LS) scheme, which is an existing well-known algorithm, are compared under non-uniform traffic conditions without taking into consideration priority scheduling. We demonstrate the proposed scheme through simulation by generating a realistic network traffic model, called self-similar network traffic. We conducted a detailed simulation using several performance parameters to validate the effectiveness of the proposed scheme. The results of the simulation showed that both ALDBA variants outperformed the existing LS scheme in terms of average packet delay, bandwidth utilization, jitter, and upstream efficiency for both low and high traffic loads.

Sensor deployment to achieve better system performance is one of the critical issues in wireless sensor networks (WSN). This letter proposes an effective sensor deployment scheme for large area sensor networks, where the event occurrence rate varies over the sensor-deployed region. Based on local event occurrence rate, the proposed scheme determines the number of sensors that should be deployed in each local region to maximize the overall detection probability. Simulation results show that the sensor deployment by the proposed scheme improves detection capability by 21% in comparison to the Incidence algorithm.

We propose a novel scheme that aims to determine the optimal number of clusters based on the field conditions and the positions of mobile sink nodes. In addition, we merge algorithms of tree-based index structures to form an energy-efficient cluster structure. A performance evaluation shows that the proposed method produces highly-balanced clusters that are energy efficient and achieves up to 1.4 times higher survival rates than the previous clustering schemes, under various operational conditions.

This paper presents an efficient algorithm, NEAR, that allows sensor nodes to acquire their off-duty eligibility. Any node only needs to calculate the coverage degrees of the intersections on its sensing boundary, and cooperates with its neighbors to know if it is redundant or not. The computing complexity of NEAR is only O(nlogn).

A 1.8 V, 5 GHz low power frequency synthesizer for Wireless Sensor Networks is presented in 0.18 µm CMOS technology. A low power phase-switching prescaler is designed, and the current mode phase rotator is merged into the first divide-by-2 circuit of the prescaler to reduce power and propagation delay. An improved charge pump circuit is proposed to compensate for the dynamic effects with the charge pump. By a divide-by-2 circuit, the frequency synthesizer can provide a 2.324-2.714 GHz quadrature output frequency in 1 MHz steps with a 4 MHz reference frequency. The measured output phase noise is -110 dBc/Hz at 1-MHz offset frequency. The power consumption of the PLL is 11.2 mW at 1.8 V supply voltage.

Routing is still a challenging issue for wireless sensor networks (WSNs), in particular for WSNs with a non-uniform deployment of nodes. This paper introduces a Node Aggregation Degree-aware Random Routing (NADRR) algorithm for non-uniform WSNs with the help of two new concepts, namely the Local Vertical Aggregation Degree (LVAD) and Local Horizontal Aggregation Degree (LHAD). Our basic idea is to first apply the LVAD and LHAD to determine one size-proper forwarding region (rather than a fixed-size one as in uniform node deployment case) for each node participating in routing, then select the next hop node from the size-proper forwarding region in a probabilistic way, considering both the residual energy and distribution of nodes. In this way, a good adaptability to the non-uniform deployment of nodes can be guaranteed by the new routing algorithm. Extensive simulation results show that in comparison with other classical geographic position based routing algorithms, such as GPSR, TPGF and CR, the proposed NADRR algorithm can result in lower node energy consumption, better balance of node energy consumption, higher routing success rate and longer network lifetime.

Duty-cycle MAC protocols have been proposed for wireless sensor networks (WSNs) to reduce the energy consumed by idle listening, but they introduce significant end-to-end delivery latency. Several works have attempted to mitigate this latency, but they still have a problem on handling the packet loss. The quality of the wireless channel in WSNs is quite bad, so packets are frequently lost. In this letter, we present a novel duty-cycle MAC protocol, called REMAC (Retransmission-Enhanced duty-cycle MAC), which exploits both the network layer and the physical layer information. REMAC estimates the quality of the wireless channel and properly reserves the wireless channel to handle the packet loss. It can reduce the end-to-end packet delivery latency caused by the packet loss without sacrificing the energy efficiency. Simulation results show that REMAC outperforms RMAC in terms of the end-to-end packet delivery latency.