Seok Woo

LaMSM: localization algorithm with merging segmented maps for underwater sensor networks

Underwater sensor networks (UWSNs) are considered a costeffective solution to ocean applications, such as the acquisition of natural resources in oceans, protection from underwater disasters, etc. These applications basically require location information of nodes to identify the venue of reported events. To locate more accurately the position of nodes, multidimensional scaling (MDS) is widely used because of its good tolerance to errors in measured distances. MDS requires measured distances between every pair of nodes but in practice, only distances between nodes within a communication range can be measured. Hence, the well-known MDS-MAP(P) [6] calculates unmeasured distances for MDS but these calculations result in large errors. In this paper, we proposed a localization algorithm with merging segmented maps (LaMSM) that constructs many reliable segmented maps composed of only nodes within a communication range, and then merges them together based on their common nodes. The segmented maps are built from only the measured distances and as a result, LaMSM provides more accurate node positions than MDS-MAP(P).

Tight Upper Bound for Stability of TCP/RED Systems in AQM Routers

Stability of TCP/RED systems can be achieved by tuning random early detection (RED) parameters. The authors present a tight upper bound of the maximum packet drop probability in the RED to obtain a stable queue performance in TCP/RED systems. Simulation results show that the derived stability condition is exact and match up well to our analysis.

APC-MAC/TA: Adaptive Power Controlled MAC Protocol with Traffic Awareness for Wireless Sensor Networks

In this paper, we propose an adaptive power controlled MAC protocol with a traffic-aware scheme specifically designed to reduce both energy and latency in wireless sensor networks. Typically, existing MAC protocols for sensor networks sacrifice latency performance for node energy efficiency. However, some sensor applications for emergencies require rather fast transmissions of sensed data, where we need to consider both energy and latency together. The proposed MAC protocol includes two novel ideas: one is a transmission power control scheme for improving latency in high traffic loads, and the other is a traffic-aware scheme to save more energy in low traffic loads. The transmission power control scheme increases channel utilization by mitigating interference between nodes, and the traffic-aware scheme allows nodes to sleep to reduce idle energy consumption when there are no traffic loads in a network. Simulation results show that the proposed protocol significantly reduces the latency as well as the energy consumption compared to the S-MAC protocol specifically for a large transmission power of nodes and low network traffic.

Improved Energy Efficiency of DMAC with Periodic Full Sleep Cycle for Wireless Sensor Networks with Heavy Traffics

Although data-gathering MAC in (G. Lu et al., 2004) is an energy efficient and low latency protocol designed for data gathering tree structures, nodes which are located in the vicinity of the sink node, may suffer from packet collision and loss due to many-to-one traffic patterns in tree structures under heavy traffic loads. In addition, this leads to wastes energy for retransmissions of dropped packets. In this paper, we propose an energy-efficient MAC protocol with a periodic full sleep cycle at leaf nodes to mitigate overloads at low depth nodes in heavy traffics. In the protocol, leaf nodes go into a full sleep state for one cycle in heavy traffics, which results in a considerably reduction of packet collisions, drops, and energy consumption at low depth nodes. Simulations show the proposed protocol saves more energy and achieves a better packet delivery ratio compared to the existing protocols.

Packet Delay and Energy Consumption Based on Markov Chain Model of the Frame-Based S-MAC Protocol under Unsaturated Conditions

In this paper, we analyze packet delay and energy consumption of the sensor-medium access control (S-MAC) protocol under unsaturated conditions. Since the S-MAC protocol always behaves with a fixed frame length, the frame-based architecture should be reflected in the S-MAC analysis. In addition, the node contention for transmitting a packet is also considered for more practical analysis on packet delay than that in the original paper suggested by Ye et al. [2]. Hence, we employ a Markov chain model to express the S-MAC behavior for the consideration of back-off delay, including node contention. Numerical results show the average packet delay and energy consumption of the node according to offered load and duty cycle where a practical mote running S-MAC is used.

Duty Cycle Criterion for Target Packet Delay of S-MAC Protocol

Generally, in sensor-medium access control (S-MAC) protocol, lower duty cycle (DC) causes longer packet delay, although it gives more efficient energy consumption. Moreover, under the environments of burst packet generation, the increase of packet delay by node contention will also induce serious performance degradation. Therefore, we find the criterion of the DC value to satisfy a target packet delay of the S-MAC protocol with contention-based access mechanism. For this, the packet delay of the S-MAC protocol in single-hop is first analyzed by reflecting the S-MAC architecture with a constant cycle under saturated condition, and then we provide the DC criterion for the target packet delay. Finally, numerical results show the DC criterion and its corresponding life time of a practical sensor mote running the S-MAC, when the target packet delay is given

Parameter Setting and 2-D Stability Conditions for TCP/RED Networks

This paper provides parameter setting and 2-D local stability conditions for TCP/RED networks. In general, a network cannot avoid congestions due to the limit of network capacity. The RED scheme is one of the representative AQM that was proposed to avoid and alleviate network congestions. However, the issue of network stability with many TCP subscribers needs to be considered when setting the RED parameters, where the classical RED has not considered the problem. In this paper, we set up a linear time-delay system for the TCP dynamic behavior and derive some stability conditions with simple RED network parameters by utilizing the 2-D Laplace-Z transform technique. Simulation results show that the proposed stability conditions can gain the effective stability in regard to the router queue length.

Energy Consumption Analysis of the S-MAC Protocol with Contending Nodes under Unsaturated Conditions

We analyze the energy consumption of the sensor-medium access control (S-MAC) protocol, where contending nodes exist. Because all nodes running the S-MAC within a virtual cluster always behave with a fixed frame length, the behavior should be analyzed based on its frame. Hence, reflecting the frame architecture, we first present an analytic model for the S-MAC behavior with a discrete-time Markov chain, and then we analyze energy consumption under unsaturated conditions.