Lulu Liang

A Novel Reliable Transmission Protocol for Urgent Information in Wireless Sensor Networks

In monitoring wireless sensor networks (WSNs), the occurrence of an emergency will generate a large amount of data in a very short time. Among them, some urgent information is more critical and needs to be transmitted out reliably as soon as possible. In this scenario, congestion is inevitable due to the limited resources, especially near the sink. To address this problem, we propose a novel reliable transmission protocol for urgent information (RETP-UI) in WSNs. In RETP-UI, not only the current queue length but also the ratio of queue lengths fluctuation is adopted as indication of congestion. Each sensor node evaluates its congestion level locally and determines its congestion state with a state machine. Furthermore, we use a multistage rate adjustment mechanism to adjust each nodes sending rate cooperatively according to different congestion states. Finally, with extensive simulation results we illustrate that the performance of RETP-UI is significantly improved over traditional protocols.

Queue-based congestion detection and multistage rate control in event-driven wireless sensor networks

Protocols for sensor networks have traditionally been designed using the best effort delivery model. However, there are many specific applications that need reliable transmissions. In event-driven wireless sensor networks, the occurrence of an event may generate a large amount of data in a very short time. Among them, some critical urgent information needs to be transmitted reliably in a timely manner. In this scenario, congestion is inevitable because of the constraints in available resources. How to control the congestion is very important for the reliable transmission of urgent information. To address this problem, we propose a queue-based congestion detection and a multistage rate control mechanism. In our proposed mechanism, not only the current queue length but also the queue fluctuation are adopted as indications of congestion. Each sensor node evaluates its congestion level locally and determines its congestion state with a state machine. We design a multistage rate adjustment mechanism for nodes to adjust their rates depending on their congestion states. We also distinguish high-priority critical traffic from low-priority non-critical traffic. Extensive simulation results confirm the superior performance of our proposed protocol with respect to throughput, loss probability, and delay.Copyright

An adaptive congestion-aware MAC protocol for wireless sensor networks

In monitoring wireless sensor networks (WSNs) with event-driven applications, the generated traffic usually has bursty characteristics when an event occurs. Transient congestion in the networks would increase delay and packet loss rate severely, reducing the network performance greatly. Through the analysis on delay and packet loss rate in congestion, this paper proposes a congestion-aware mac protocol (C-MAC) for wireless sensor networks. In C-MAC, backoff delay of the nodes around contention area is adopted as a congestion indication. In normal state, the CSMA/CA is working well at sensor nodes. And when the congestion occurs, localized TDMA replaces the CSMA/CA in the congestion nodes. With the above mechanism, the congestion nodes only deliver their data during its assigned slots to control the contention overhead. Finally, we implement the C-MAC in our sensor network testbed. The experiment results show that the proposed MAC protocol could effectively operate on the congestion caused by burst information, and reduce both the delay and packet loss rate significantly.

Gradient-based micro sensor routing protocol in wireless sensor networks

In most of existing routing protocols of wireless sensor networks (WSNs), a route is set up through broadcasting the route request (RREQ) messages throughout the entire network, which often brings broadcast storm. In this paper, we propose a new gradient-based micro sensor routing protocol (GMSRP) to alleviate the broadcast storm. With the GMSRP, during the network initialization, the sink node broadcasts a GRAI (GRAdient Information) message to the entire network and with the message each sensor node can learn its gradient information, which is the minimal number of hops away from the sink node. Later, when a sensor node launches the route discovery procedure with the GMSRP, the RREQ messages will be forwarded with limited broadcasting scheme by each middle sensor node. Finally, we develop the GSMRP routing module in NS-2 and conduct detail experiments. The experiment results show that the GMSRP improves the routing performance significantly comparing with the classical routing protocol AODV.

An efficient event detecting protocol in event-driven wireless sensor networks

The most important goal in event-driven wireless sensor networks is to transmit the event information to users as soon as possible. One of the most important factors that would make it possible to reach this goal is the design of efficient detecting protocols. In this paper, we present an efficient event detecting protocol (EEDP) specified for event monitoring applications. In the event occuring area, each node broadcasts its primary detection result to make a decision corporately. And then the decision-made node will choose the next hop using the underlying routing protocol to forward a single alarm packet. To improve the reliable transmission of the single alarm packet, we use a dynamic multicopy scheme similar as conventional multipath routing for continuous flow. The simulation results validate that EEDP is a practical and efficient protocol for event detection applications where the constraints of end-to-end delay and reliability are stringent.

A smart notification scheme for wireless sensor networks

The reliable transmission problem in Wireless Sensor Networks (WSNs) is quite different from that in traditional networks. Especially in event-driven wireless sensor networks, the most critical goal is to transmit the event alarm to users reliably and timely. For most current protocols, the raw event packets are periodically sent to the destination. However, the occurrence of the emergency event is hardly reported timely, which has been a stringent requirement for event monitoring applications. In this paper, the raw event packets are processed around the event area and only a few packets need to be transmitted to the destination quickly. To improve the reliability, a smart notification scheme proposed. Once a critical packet is facing the risk of path failure, it will clone itself and forward it to another next hop appropriately for reducing the loss probability. The parameter which indicates the clone capability is assigned depending on the wireless channel condition. Simulation results have shown that our scheme can enhance the performance in latency and energy consumption perspective.

Rate control in wireless multi-hop networks based on receiver capacity model

The state of the art rate control algorithms for wireless multi-hop networks respond to feedback regarding available capacity in the bandwidth constrained networks. However, the accurate estimation of link capacity is challenging in wireless channel since the interference reduces the link capacity obviously. In [4], a receiver capacity model is proposed, which associates capacities with nodes instead of links. This paper analyses the node constraints and time constraints in multi-hop wireless networks based on the receiver capacity model, and proposes a hop-by-hop rate control algorithm using an optimization-based framework. The results show that the proposed rate control algorithm could allocate the rate fairly and improve the network performance effectively.