Violeta Felea

OBMAC: An Overhearing Based MAC Protocol for Wireless Sensor Networks

In this paper, we propose OBMAC, an enhancement for medium access control (MAC) protocol based on the overhearing technique in wireless sensor networks (WSNs). In this type of networks, sensors are spatially correlated and they often sense and send the same information to the sink. Therefore, sensors waste energy in transmitting redundant data. Here, we want to find a method to reduce these redundant transmissions. Although in WSN, overhearing is often considered a cause of energy waste. In this paper, we want to show that overhearing is not always an energy waste. Moreover, it can be an efficient method to reduce redundant transmissions in sensor networks, thus diminishing energy consumption and transmission delay. Hence, the network lifetime can last longer and the sink receives events within shorter delays. We propose to apply our technique in IEEE 802.15.4, a recent standard for WSN. By simulation and experimentation, we prove that OBMAC overpasses IEEE 80215.4 in terms of energy consumption and transmission delay.

Wireless Sensor Network Infrastructure: Construction and Evaluation

Large area wireless sensor deployments rely on multi-hop communication. Efficient packet transmission and virtual topologies, which structure sensor networks, are two main features for efficient energy management in wireless sensor networks. This paper aims to present a distributed and low-cost topology construction algorithm for wireless sensor networks, addressing the following issues: large-scale, random network deployment, energy efficiency and small overhead. We propose structuring nodes in zones, meant to reduce the global view of the network to a local one. This zone-based architecture is the infrastructure used by our hierarchical routing protocol. The experimental results show that the proposed algorithm has low overhead and is scalable.

Wireless sensor network system helping navigation of the visually impaired

Navigation aids for the pedestrians are considered new research challenges. The visually impaired are particularly concerned, because of their need to detect and avoid obstacles, as well as to orient themselves in unknown environments. In this paper, we discuss some existing projects in this domain and we propose a novel aid system formed of wireless sensors, meant to help navigation of the visually impaired, which addresses both orientation and obstacle negotiation. The proposed system is GPS-free and does not need external assistance in navigation.

Energy-efficient WSN infrastructure

Energy conserving communication is one of the main challenges of wireless sensor networks. A number of studies and research are focused on saving energy and on extending the lifetime of these networks. Architectural approaches, like hierarchical structures, tend to organize network nodes in order to save energy. Most of these protocols need background information on the network in order to be efficient. In this paper, we describe a new approach for organizing large sensor networks into zones, based on the number of hops. This network architecture enables a hierarchical network view, with the purpose of offering efficient routing protocols based on zone partitioning. Simulations undertaken demonstrate that our approach is energy-efficient; this is highlighted by the reduction of traffic overhead.

A low latency MAC scheme for event-driven wireless sensor networks

In this paper, we present a low latency media access control scheme which we call LLMAC (Low Latency MAC) for event-driven wireless sensor networks (WSN). In this kind of WSN, sensors do not regularly send data to the sink. They send a burst data only when there is an event in the monitoring area. It takes time for this burst data to arrive to the sink. Normally, these events are critical and we hope to obtain the information on the event in the shortest delay. Hence, the latency is considered to be a crucial requirement in event-driven WSN contrary to the traditional wireless networks where the fairness is the most important requirement. Our proposal LLMAC makes a trade-off between fairness and latency in order to offer a shorter latency transmission when certain events happen. The performance evaluation shows that our proposal reduces the latency in comparison to existing MAC protocols.

Latency optimization through routing-aware time scheduling protocols for wireless sensor networks

The main contribution concerns designing TDMA schedules based on routing information in order to optimize communication latency.The Optimal TDMA Scheduling algorithm provides the schedule with the minimal latency but its execution time grows exponentially because of its complexity.We propose two classes of heuristics, the routing tree oriented TDMA schedules class and the graph and routing tree oriented TDMA schedules class.The simulations results show better performance of the different heuristics than the state of the art and close performance to the optimal scheduling. Display Omitted Communications in wireless sensor networks are mainly controlled by the temporal decisions of the data link layer and the spatial decisions of the network layer. When taken independently, these decisions may not be correlated which affects the latency metric. To tackle this problem, we propose cross-layer algorithms to define TDMA (Time Division Multiple Access) schedules based on routing information. Two main strategies are applied, based on routing tree traversals or on adapted ones using information from the networks graph. We also present the Optimal scheduling algorithm which finds the scheduling with the minimal latency; the latter is used to compute the efficiency of our heuristics. Extensive simulations have been performed and show improvement in latency up to 29% compared with existing works. The effect of the heuristics on the duty-cycle is studied in the perspective of energy consumption. The duty-cycle is improved up to 11.54%.

MAC-aware routing in wireless sensor networks

Generally, the traditional layered protocol architecture is used to design protocols for wireless sensor networks in which MAC and Routing protocols act independently and this may cause counteraction between them. Cross-layer protocols are known to be more efficient. In this paper, we present MAR-WSN, a MAC-aware Routing protocol for Wireless Sensor Networks, in which the next hop decisions are made based on the TDMA scheduling and the two-hop neighbourhood knowledge. Coherent decisions in space, taken by the routing protocol, with those taken by the MAC protocol, in time, prove to be efficient against several metrics: delay, energy consumption and hop number. The simulation results show good performance of our strategy in medium and high density networks compared to the state of the art.

MAC-Aware Routing in Multi-Sink WSN with Dynamic Back-Off Time and Buffer Constraint

Multi-hop Wireless Sensor Networks (WSNs) are subject to network latency, that is highly affected by the transmission delay. Real-time applications, such as healthcare monitoring systems, based on this network technology need to meet time-quality requirements. In this paper, we address the issue of communication latency using Multi-sink WSN (MS-WSN) deployment and cross-layer protocols. MAC-aware routing protocols are proposed, for soft real-time applications, with packets being preventively routed through the lowest latency paths in unicast schemes. Moreover, with the network size growth, buffer occupancy is impacted generating, incrementally, high network latency. We propose buffer control mechanisms to manage this. Obtained simulation results show better average delay, improved of 58%, and better average maximum buffer occupancy, decreased of 89%.

Routing-Aware Time Slot Allocation Heuristics in Contention-Free Sensor Networks

Traditionally, in Wireless Sensor Networks, protocols are designed independently in the layered protocol stack, and metrics involved in several layers can be affected. Communication latency is one metric example, impacted by both the routing protocol in the network layer and the MAC protocol in the data link layer. Better performances can be obtained using cross-layer approaches.

Routing and TDMA Joint Cross-Layer Design for Wireless Sensor Networks

This paper presents a new cross-layer approach in which the network layer and the data link layer are combined in one new layer in order to correlate decisions on forwarding nodes involved in multi-hop communications in wireless sensor networks. More particularly, we propose a Routing and MAC joint protocol that takes the network as an input parameter and provides a routing tree and a collision-free (TDMA) schedule as output parameters while minimizing the latency of communications.