Myung Kyun Kim

Characteristics of ETX Link Quality Estimator Under High Traffic Load in Wireless Networks

Effective link quality estimation is a vital issue for reliable routing in wireless networks. This paper studies the performance of ETX (Expected Transmission Count) under different traffic loads. Although ETX shows the good performance under light load, its performance gets significantly worse as traffic load is increased. Broadcast route request packet storm due to new route discoveries affects severely the calculation of link ETX values under high traffic load, which makes it difficult to find a good path. This paper presents the design and implementation of a variation of ETX called HETX(High load -Expected Transmission Count), which reduces the impact of route request packets to the link ETX values under high load. We conduct the evaluation of the performance of three metrics - HETX, ETX and minimum hop-count. The simulation results showed that HETX improves the average route throughput by up to 25% over ETX under high traffic. Minimum hop-count has the poor performance compared with both HETX and ETX at all different traffic loads. Under light load, HETX and ETX show the same performance.

Real-Time Communications on an Integrated Fieldbus Network Based on a Switched Ethernet in Industrial Environment

In recent years, fieldbuses have been more widely used in real-time distributed control systems. There are many international fieldbus protocol standards, but they are not interoperable among themselves. This paper proposes an integrated fieldbus network architecture based on a switched Ethernet which provides real-time communication features to the nodes in different fieldbuses. This paper also analyzes the schedulability conditions for real-time periodic messages on the switched Ethernet and an EDF (Earliest Deadline First)-based scheduling algorithm to support the real-time communication requirements of the periodic messages without any change in the principles of the switch.

A reliable and energy efficient routing protocol in industrial wireless sensor networks

This paper proposes a reliable an energy efficient routing protocol for transmitting periodic packets on industrial wireless sensor networks. For reliable transmission of periodic packets, the proposed protocol chooses the path has highest end-to-end packet reception rate (e2e_PRR) to transmit data packets. Also, a mechanism is used to reduce the number of control packets. The simulation result has shown that the proposed protocol has a better performance in terms of reliability and control packet overhead than the previous routing protocols.

RP-MAC: A cross-layer duty cycle MAC protocol with a Reduced Pipelined-forwarding feature for Wireless Sensor Networks

Recently, duty-cycle MAC protocols with pipelined-forwarding and routing-integrated features such as P-MAC and PRI-MAC were proposed for efficient communication in terms of power consumption and end-to-end delay in Wireless Sensor Networks (WSNs). However, they remain unnecessary idle listening time at each cycle and their handshake mechanism introduces unnecessary delay at each hop. In this paper, we propose a new cross-layer duty-cycle MAC protocol, called RP-MAC (Reduced Pipelined-forwarding) protocol, which improves performance by reducing idle listening time and control overhead. In RP-MAC, the RTS/CTS handshake procedure in the pipeline is shortened by taking advantage of ACK mechanism. A relaying node overhears the ACK message from its potential senders instead of listening to RTS. Right after receiving the data successfully, the relaying node just needs to listen to the CTS without sending the RTS. The simulation results using Qualnet show that RP-MAC achieves significant improvement in comparison with PRI-MAC in terms of energy consumption and end-to-end delivery latency.

Link quality estimation in static wireless networks with high traffic load

Effective link quality estimation is a vital issue for reliable routing in wireless networks. This paper studies the performance of expected transmission count (ETX) under different traffic loads. Although ETX shows good performance under light load, its performance gets significantly worse when the traffic load is high. A broadcast packet storm due to new route discoveries severely affects the link ETX values under high traffic load, which makes it difficult to find a good path. This paper presents the design and implementation of a variation of ETX called high load - ETX (HETX), which reduces the impact of route request broadcast packets to link metric values under high load. We also propose a reliable routing protocol using link quality metrics, which is called link quality distance vector (LQDV). We conducted the evaluation of the performance of three metrics - HETX, ETX and minimum hop-count. The simulation results show that HETX improves the average route throughput by up to 25% over ETX under high traffic load. Minimum hop-count has poor performance compared with both HETX and ETX at all of the different traffic loads. Under light load, HETX and ETX show the same performance.

Schedule optimization of static messages with precedence relations in FlexRay

In this paper, we study the problem of scheduling static messages in FlexRay. We assume that static messages have precedence relations. This implies that each message must be sent after the transmission of all its predecessors. Our problem model supports slot multiplexing as defined in the FlexRay v3.0 protocol specification. Our objective is to provide a schedule that satisfies FlexRay specifications and precedence relations between messages and minimizes the bandwidth usage. To solve the problem, a scheme for transformation of the message scheduling problem to Strip Packing Problem (SPP) is proposed. We solve the optimization problem using a Linear Integer Programming formulation. We study our approach based on some advanced automotive control applications.

Discovering High-Quality Paths with Load Balancing in Wireless Sensor Networks

This paper proposes a reliable routing protocol called LBR for wireless sensor networks, which find high-quality paths with considering load balance among nodes. The LBR protocol transmits messages through a reliable path to reduce the packet loss rate. To the problem of increasing data transmission reliability, our routing protocol uses ETX as a metric for estimating link quality. By using ETX, the LBR protocol can choose good links in the network. In addition to the above, the problem of load balance is also considered in our protocol. By taking this into account, the LBR protocol avoid routing through the congested nodes and balance load among nodes better. This results in increasing the lifetime of the network. The simulation results using the Qualnet simulator showed that the proposed protocol outperforms other protocols in terms of packet delivery ratio, end-to-end delay and the efficiency of load balance.

Message scheduling on static segment of FlexRay networks

FlexRay is a hybrid in-vehicle communication protocol whichcarries out the transmission of time-triggered data in the static segment as well as event-triggered data in the dynamic segment. In this paper, we study the problem of scheduling static messages with precedence relations in FlexRay protocol. Our objective is to obtain the minimum number of used slots. To this end, a scheme for transformation of the precedence constrained message scheduling problem to a Strip Packing Problem is proposed. In thisproblem a set of rectangles must be placed within a strip. The goal is to place the rectanglesso that they do not overlap and so that the height ofthe area covered by rectangles is minimized. However, since Strip Packing Problem cannot solely deal with flexray specifications and precedence relations between items we introduce new constraints called FlexRay Constraints. We elaborate on a Linear Integer Programming that obtains the optimal solution. We study our approach based on a case study involving someadvanced automotive control applications.

A real-time communication protocol considering load balancing in Ad hoc network

This paper proposes a real-time routing protocol considering balancing the load traffic in Ad hoc wireless network. Recently, the authors have proposed a multipath-based reliable routing protocol on MANETs called MRFR, which is an appealing protocol for real-time reliable data transmission in ad hoc networks. However, MRFR did not concern the problem of balancing load, which results in increasing congestion and consuming high energy at some network nodes. As a result, that affects negatively performance of the protocol when a node is congested. Taking account of load balancing as route selection criteria can avoid routing through these nodes and find better routes. In this paper, we extend MRFR by considering balancing load in routing process of real-time reliable communication in MANETs. Experiments on Qualnet simulator show that the proposed protocol outperforms MRLR and AODV in term of end-to-end delay, packet delivery radio, average jitter, and load balancing in network.

Reducing idle listening time in pipeline-forwarding MAC protocols of wireless sensor networks

In order to reduce the end-to-end delay in duty-cycle MAC protocols of Wireless Sensor Networks (WSNs), the pipeline-forwarding technique has been proposed. According to this technique, sensor nodes along the forwarding path are scheduled with sequential wakeup time slots. Even though the previous pipeline-forwarding protocols such as P-MAC and PRI-MAC showed a good result in term of reducing end-to-end delay, a significant per-hop delay is remained due to the unnecessary idle listening of sensor nodes in each cycle. In this paper, we propose a new pipeline-forwarding technique which tries to resolve this problem. In the proposed protocol, the RTS/CTS handshaking procedure is shortened by taking advantage of ACK mechanism. By waking up right before the upstream node sends ACK frame and overhearing it, a sensor node can be aware of the possibility of receiving data without waiting for and listening RTS frame. Therefore, the unnecessary idle listening can be reduced. When comparing with the existing solution PRI-MAC using QualNet simulator, our protocol shows the significant improvement in term of end-to-end delay and energy consumption.