Hong Min

SensorMaker: A Wireless Sensor Network Simulator for Scalable and Fine-Grained Instrumentation

Nowadays, wireless sensor networks have drawn great attention as a new and important research area. These sensor networks typically consist of hundreds or even thousands of sensor nodes deployed in a geographical region to sense events. Therefore, using actual sensor networks in case of developing a new scheme or experimenting functionalities may consume too much time and cost. In this paper, we present a SensorMaker, which is a simulator for wireless sensor networks. It supports scalable and fine-grained instrumentation of the entire sensor networks. We also present the actual simulation results of the various existing routing and clustering algorithms, and network management schemes.

An efficient dynamic memory allocator for sensor operating systems

Dynamic memory allocation mechanism is important aspect of operating system, because an efficient dynamic memory allocator improves the performance of operating systems. In wireless sensor networks, sensor nodes have miniature computing device, small memory space and very limited battery power. Therefore, sensor operating systems should be able to operate efficiently in terms of energy consumption and resource management. And the role of dynamic memory allocator in sensor operating system is more important than one of general operating system. In this pager, we propose new dynamic memory allocation scheme that solves problems of existing dynamic memory allocators. We implement our scheme on Nano-Qplus which is a sensor operating system base on multi-threading. Our experimental results show our scheme performs efficiently in both time and space compared with existing memory allocation mechanism.

Enhancing the Reliability of Head Nodes in Underwater Sensor Networks

Underwater environments are quite different from terrestrial environments in terms of the communication media and operating conditions associated with those environments. In underwater sensor networks, the probability of node failure is high because sensor nodes are deployed in harsher environments than ground-based networks. The sensor nodes are surrounded by salt water and moved around by waves and currents. Many studies have focused on underwater communication environments in an effort to improve the data transmission throughput. In this paper, we present a checkpointing scheme for the head nodes to quickly recover from a head node failure. Experimental results show that the proposed scheme enhances the reliability of the networks and makes them more efficient in terms of energy consumption and the recovery latency compared to the previous scheme without checkpointing.

Molecule: An adaptive dynamic reconfiguration scheme for sensor operating systems

In wireless sensor networks, sensor nodes are located on remote-site and thus it is very difficult to re-gather them. To update or add a program at run-time of the sensor nodes, sensor operating system must support a dynamic reconfiguration. Many kinds of different mechanisms for reconfiguring sensor nodes have been developed ranging from full image replacement to virtual machines. In previous schemes, dynamic linker supports only indirect linking between modules, and the linking is performed on the sensor nodes. Those may increase overhead of the execution time and energy consumption. In this paper, we present an adaptive and dynamic reconfiguration scheme called Molecule for sensor nodes. In Molecule, applications, kernel features, and device drivers are managed as a form of module. By using the cost analysis of the expected execution time of each module, Molecule selects an appropriate method between direct and indirect linking to link modules. It also supports remote linker to exclude the linking overhead from the sensor nodes. Our experimental results show that Molecule performs efficiently in terms of the energy consumption and execution time compared with the existing dynamic reconfiguration schemes.

SESAME: space-efficient stack allocation mechanism for multi-threaded sensor operating systems

This paper proposes a SESAME, which is a Space-Efficient Stack Allocation MEchanism for multi-threaded sensor operating systems. It adaptively adjusts the stack size by allocating or releasing additional stack frame based on the amount of each functions stack usage information. Our experimental results show that the SESAME significantly minimizes spatial overhead of threads stacks with tolerable time overhead compared with fixed stack allocation mechanism of the multi-threaded sensor operating systems.

Adaptive load balancing mechanism for server cluster

Server cluster provides high availability, scalability, and reliability by gathering server nodes into a group. Client requests need to be distributed to each server node fairly to maximize the performance of server cluster. In this paper, we propose an adaptive and efficient load balancing algorithm for the server cluster. The proposed algorithm computes the load of server nodes with the usages of computer resources and their weights. These weights are determined dynamically based on the statistics of the usages. The experimental result shows that the proposed algorithm can prevent the bottleneck of server cluster efficiently compared with existing algorithms. This guarantees its adaptability even though there are changes to the characteristic of service.

A Smart Checkpointing Scheme for Improving the Reliability of Clustering Routing Protocols

In wireless sensor networks, system architectures and applications are designed to consider both resource constraints and scalability, because such networks are composed of numerous sensor nodes with various sensors and actuators, small memories, low-power microprocessors, radio modules, and batteries. Clustering routing protocols based on data aggregation schemes aimed at minimizing packet numbers have been proposed to meet these requirements. In clustering routing protocols, the cluster head plays an important role. The cluster head collects data from its member nodes and aggregates the collected data. To improve reliability and reduce recovery latency, we propose a checkpointing scheme for the cluster head. In the proposed scheme, backup nodes monitor and checkpoint the current state of the cluster head periodically. We also derive the checkpointing interval that maximizes reliability while using the same amount of energy consumed by clustering routing protocols that operate without checkpointing. Experimental comparisons with existing non-checkpointing schemes show that our scheme reduces both energy consumption and recovery latency.

Dynamic Memory Allocator for Sensor Operating System Design and Analysis

Dynamic memory allocation is an important mechanism used in operating systems. An efficient dynamic memory allocator can improve the performance of operating systems. In wireless sensor networks, sensor nodes have miniature computing device, small memory space and very limited battery power. Therefore, it is important that sensor operating systems operate efficiently in terms of energy consumption and resource management. And the role of dynamic memory allocator in sensor operating system is more important than one of general operating system. In this paper, we propose a new dynamic memory allocation scheme that resolves the existing problems in dynamic memory allocators. We implemented our scheme on Nano-Qplus which is a sensor operating system based on multi-threading. Our experimental results and static analysis result show our scheme performs efficiently in terms of the execution time and the memory space compared with existing memory allocation mechanisms.

Energy-Efficient Data Aggregation Protocol for Location-Aware Wireless Sensor Networks

The energy is the most critical resource in wireless sensor networks. Many energy efficient techniques have been studied especially in communication protocol. Among these protocols, PEGASIS proposed by Lindsey is the most superior interms of energy efficiency. In PEGASIS, all sensor nodes aggregate and transmit data along the single chain. However, this single chain causes some problems such as delay, unexpected long transmission and non-directional transmission to the sink. To resolve delay problem, PEGASIS cuts the chain into several chains. In this way, the delay can be decreased but there is new problem, wireless interference. In this paper, we propose a new chain construction algorithm to resolve above problems. The proposed algorithm minimizes the delay without the wireless interferences and maximizes the energy efficiency by removing the non-directional transmission when transmitting packets to the sink node on wireless sensor networks. Our simulation results show that our proposed algorithm can minimize the delay without expense of energy consumption.

Performance analysis of task schedulers in operating systems for wireless sensor networks

In wireless sensor networks, power is a critical resource in battery powered sensor nodes. In this respect, as it is important to efficiently utilize the limited battery power, it would be desirable to make such nodes as energy efficient as possible. Many researchers who develop operating systems of wireless sensor networks have been trying to find a way to enhance energy efficiency of sensor nodes. In this paper, we present an overview of sensor node operating systems and some of its functionalities, and then present a performance analysis of task schedulers and task-related kernel routines of existing sensor node operating systems. The results of performance analysis show some advantages and disadvantages of the existing operating systems, and based on these information, we present some possible improvements for increasing the efficiency of sensor node operating systems.