Namkoo Ha

A partition prediction algorithm for group mobility in ad-hoc networks

One of important issues associated with group mobility in ad-hoc networks is predicting the partition time. The existing algorithms predict the partition time assuming that the partitioned groups move to opposite direction with the same speed and the same coverage. So, these algorithms could not accurately predict partition time in practical situation. In this paper, we propose a partition prediction algorithm considering network partition in any direction, at any speed, and with different coverage of group. To validate the proposed algorithm, we carried out a simulation study. We observe a sound agreement between numerical results obtained by our algorithm and computer simulation. Our algorithm can predict the partition time more accurately in real situations.

A limited flooding scheme for query delivery in wireless sensor networks

In query-driven sensor networks, query is generally disseminated to the whole sensor. When the query needs information on a specific area, it is unnecessary for the query to be flooded over the entire network. In this paper, we propose a query delivery scheme which does not flood the query over the entire area but only to a restricted area. Also, our scheme also offers fault tolerance capability in order to prolong the network lifetime and to provide reliability for query transmissions. A performance evaluation shows that the total energy consumption can be significantly reduced and the sensor network lifetime can be prolonged by our scheme.

Load Balancing for Efficient Routing in Wireless Sensor Networks

Congestion is generated by buffer overflow and generally is considered in transport layer. However, there is almost no considered one about existing routing protocols of sensor network because it is difficult to apply congestion control in transport layer of WSNs (wireless sensor networks) that have limited resources such as energy, buffer, and bandwidth of sensor nodes. Therefore, routing protocol of sensor networks must deliberate how to control congestion. In order to overcome this problem, we propose the routing protocol avoidable congestion to improve throughput, packet drop rate, lifetime, and so on. Consequently, each node can evenly distribute loads. We demonstrate how to achieve congestion-free load balancing when there are multiple routing paths towards sink.

Positioning method for outdoor systems in wireless sensor networks

In recent years, many researchers have actively studied communi- cation protocols for wireless sensor networks. Most works are based on the assumption that each sensor node knows its own geographical position by GPS (Global Positioning System). For this, however, we have to pay an extra cost for implementing GPS modules in sensor nodes, and thus the size of sensor node should become large. In this paper, we propose a method by which all the nodes in the sensing field can recognize their own positions without equipping GPS modules in every node. In our scheme, only some nodes are equipped with the GPS modules when the sensing field is deployed, and the others can find out their positions through communications to GPS nodes. To validate our method, we carried out a computer simulation, and observed that all nodes could successfully recognize their own positions in 3 rounds.

Routing protocols based on super cluster header in wireless sensor network

In a variety of applications, wireless sensor networks have received more attention in recent years. Sensor nodes, however, have many limitations including limited battery power and communication range. In this network, data gathering and data fusion help to reduce energy consumption and redundant data. LEACH (Low Energy Adoptive Clustering Hierarchy) is the most representative protocol using data gathering and data fusion, but it has several problems including inefficient energy consumption by many cluster headers to the distant sink and a single-hop routing path. In this paper, we propose two routing protocols called Routing Protocol based on Super-Cluster Header (RPS) and Multi-hop Routing Protocol based on Super-Cluster Header (MRPS) in order to resolve the problems of LEACH. The key idea of our protocols is that only one node sends the combined data to the sink and every node uses multi-hop routing in order to gather data in the cluster. We evaluate performance of our protocols through simulations. Simulation results show that our protocols offer a much better performance than the legacy protocols in terms of energy cost, the network lifetime, and fairness of the energy consumption.

A server selection algorithm for group mobility

One of the most important issues associated with group mobility predicts the partition time. The existing algorithms predict partition time assuming that the partitioned groups move in opposite direction with the same speed and coverage. Thus, QoS is not guaranteed, since these algorithms could not accurately predict partition time in practical situations. We propose a partition prediction algorithm and server selection algorithm considering network partition in any direction, at any speed and with different coverage of groups. The analytical and simulation results show that our algorithm can predict partition time and select a child server more accurately in real situations.

Robust Routing Scheme for Wireless Sensor Networks

In wireless sensor networks, energy consumption is one of the most important issues since each node has a limited power capacity. Particularly, in routing, energy is unnecessarily consumed because the information of energy level to find the next hop is exchanged frequently. In this paper, we propose a robust routing scheme which does not require the exchange of control messages to reduce unnecessary transmissions and overhead. The next hop is optimally selected based on the residual energy and distance between each node and the sink. Our scheme additionally offers a capability to alleviate the loop and detour problems. Simulation results showed that our scheme can enhance performance in terms of energy conservation, network lifetime, and path optimization.

A locating method for ubiquitous robots based on wireless sensor networks

Applications of Ubiquitous Robot (UR) based on wireless sensor networks usually require the location information of all sensor nodes deployed on the sensor field. For this, every sensor node should be aware of its own geographical location, which forces us to pay an expensive cost and make the size of sensor node larger. In this paper, we propose a cheap solution for positioning all sensor nodes without necessitating all sensor nodes in the field equipped with GPS modules. In our method, only some sensor nodes equipped with GPS modules are initially deployed, and the other nodes without GPS modules will find out their locations through communications to GPS nodes. To show effectiveness of our method, we carried out a computer simulation, and observed that all nodes could successfully recognize their locations, which can considerably save the price for implementing wireless sensor networks.

An adaptive transmission power control protocol for mobile ad hoc networks

In this paper, we propose the possibility of bringing the concepts of power control and route relay functions together in the MAC design in mobile multi-channel ad hoc networks. Our protocol makes use of multi-channel route relay function with power control capability to cope with inter-channel interference and path breakage caused by mobility in multi-channel mobile ad hoc networks. We provide simulation results showing a good performance for re-establishing a path.