Cheeha Kim

A Channel Rendezvous Scheme for Cognitive Radio Networks

Cognitive radio networks need to utilize available spectrum in a dynamic and opportunistic fashion without causing interference to co-located primary nodes. Before data transmission begins, secondary nodes must establish a link on a channel which is not occupied by primary nodes. Unfortunately, in cognitive radio networks, the set of available channels can be different for each node, since it is determined by the relative locations of nodes to primary nodes. We are the first to present a distributed channel rendezvous scheme which finds a commonly available channel between any two nodes in a bounded time without synchronization. Our scheme determines the order, in which two nodes visit channels to find a common channel, if any, within a bounded time.

Fast route recovery scheme for Mobile Ad Hoc Networks

A Mobile Ad Hoc Network (MANET) is a self-configuring network of mobile devices connected by a wireless link. In MANETs, the data packet may fail to be delivered for various reasons including nodes movement, packet collision and bad channel condition. Because re-route recovery of traditional on-demand routing protocols has high latency, several ideas have been proposed to solve this problems. AODV-BR and AODV-ABR schemes improve the AODV routing protocol by supplying multiple backup routes, but may be inefficient in a dense environment. In this paper, we propose a novel fast route recovery scheme which employs local recovery of routes for reliability and reduces the number of control messages for efficiency of the network. Our scheme considers a backup nodes mobility and conducts a route recovery process implicitly. Simulation results show that our scheme improves the routing protocols.

S-RO: simple route optimization scheme with NEMO transparency

Network mobility (NEMO) basic support protocol maintains the connectivity when mobile router (MR) changes its point of attachment to the Internet by establishing a bidirectional tunnel between MR and Home Agent (HA). However, it results in pin-ball routing and multiple encapsulations especially in the nested NEMO. In order to solve these problems, we propose a simple route optimization scheme for NEMO and nested NEMO. In the proposed scheme, a correspondent node (CN) maintains network prefix binding information of intermediate MRs to obtain optimal path to the mobile network node (MNN). For a CN to receive network prefix bindings, each intermediate MR updates its network prefix binding to the inner source of the encapsulated packet, when it receives an encapsulated packet from its HA. The proposed scheme uses the routing header type 0 (RH0) and the routing header type 2 extension (RH2 extension) to deliver packets to the MNN through the optimal path and to remove multiple encapsulations. In addition, we extend the Router Alert Option (RAO) so that the MR knows the original source address of the packet, when ingress filtering is applied.

Dynamic timeout for data aggregation in wireless sensor networks

In-network data aggregation is a cross-layer routing technique which is essential for wireless sensor networks with a large number of nodes. Although the technique enhances energy efficiency by reducing packet transmissions, it may require routing-layer waiting time which introduces additional delays in packet delivery. This implies that there exists an energy-delay tradeoff which can be controlled depending on the delay level an application can tolerate. In this work, we first perform an in-depth analysis of the data aggregation process and validate the strong relationship between the amount of currently accumulated data in a node and the data aggregation timeout to achieve energy efficiency with little delay overhead. Then, we propose a novel timeout control scheme which dynamically changes timeout according to the amount of currently accumulated data in a node. Our scheme is based on local information without involving control messages so that it is not only robust but also light-weight. Evaluation results based on an implementation of the wireless sensor network show that our scheme facilitates efficient tradeoff between energy and delay. Thus, high energy efficiency can be achieved with little overhead in delay, and vice versa.

Localization of Sensor Nodes in Underwater Acoustic Sensor Networks Using Two Reference Points

Underwater acoustic sensor networks (UWASN) is being actively researched for its broad spectrum of potential applications. Submarine or whale tracking can also be greatly leveraged by UWASN. These applications require localization of sensor nodes. We propose a novel scheme that minimizes the influence of node mobility inherent to underwater environment. We evaluate our method analytically, and show that it performs robustly in various network settings and environment.

Optimal transmission range for topology management in wireless sensor networks

Topology management protocols aim to minimize the number of nodes in densely distributed sensor networks that constitute the topology Most protocols construct the topology with a fixed transmission range (i.e maximum transmission power) With respect to the power consumed by data transmission, it is more efficient to communicate with shorter transmission range, even with the number of nodes in the topology increased In the sense of minimizing the total power consumed by the topology management as well as data transmissions, it is necessary to find an optimal transmission range Moreover, data rate is also an important factor to determine the total transmission energy In this paper, we obtain the optimal transmission range for a given data rate and maximum transmission power to minimize the total power consumption.

mMOM: efficient mobile multicast support based on the mobility of mobile hosts

The IETF Mobile IP is the dominant standard for IP mobility support and defines two multicast options for providing multicast to mobile hosts (MHs): remote subscription (RS) and bi-directional tunneling (BT). Since the two options have complementary advantages, improved multicast support can be achieved by combining the two options.In this paper, in order to synthesize the strong points of the two options, we propose a new approach, mMOM, which selectively uses two IETF multicast options based on the mobility pattern of MHs. In mMOM, the RS option is used only when MH is looked upon as being relatively immobile. Otherwise, the BT option is used. Therefore, an optimal routing path is provided for as a long time as possible, so the multicast tree management overhead can be greatly reduced.For performance analysis, we use a new analytical model based on queuing theory. Based on analytical results, the multicast tree management overhead and the expected number of tunneling paths are taken as metrics for performance comparison. This analytical model and results can help multicast service providers to analyze cost effectiveness and to design new protocols for supporting mobile multicast.

New caching-based location management scheme in personal communication systems

We propose a new location management strategy that is based on a centralized database architecture with the home location register/visitor location register (HLR/VLR) concept. Our basic idea is to reduce the cost of call delivery using location information cached at the MSC/VLR. Other proposed caching-based schemes may have cached invalid location information as the MT moves into a new registration area. However, our scheme cannot cache invalid location information as announcing the location of the MT to MSC/VLR or invalidating the location information by the MSC/VLR. That is, with cached location information, a miss cannot occur. Therefore, the call setup delay for our proposed scheme is always shorter than, or equal to that of the current method. Our scheme minimizes the total signaling cost of location management by reducing the cost of call delivery more than the increased cost of the location update. The analysis of the proposed scheme, using simulation, shows that the new scheme outperforms or equals the current methods in cost and has a much better performance at high CMR (call to mobility ratio).

Traffic-Aware MAC Protocol Using Adaptive Duty Cycle for Wireless Sensor Networks

Most of sensor MAC protocols have a fixed duty cycle, which performs poorly under the dynamic traffic condition observed in event-driven sensor applications such as surveillance, fire detection, and object-tracking system. This paper proposes a traffic-aware MAC protocol which dynamically adjusts the duty cycle adapting to the traffic load. Our adaptive scheme operates on a tree topology, and nodes wake up only for the time measured for the successful transmissions. By adjusting the duty cycle, it can prevent packet drops and save energy. The simulation results show that our scheme outperforms a fixed duty cycle scheme [5] and B-MAC [9], hence, it can achieve high packet fidelity and save energy.

Group-Based Location Management Scheme in Personal Communication Networks

Signaling overhead incurred in location management becomes significant in PCS (Personal Communication Systems), especially with many users of high mobility. In such cases, an efficient location management scheme plays an important role in signaling. In this paper, we propose a new location management strategy which is based on the centralized database architecture with HLR/VLR concept. Our main idea is to reduce the number of location registrations by grouping MTs (Mobile Terminals) with a similar velocity and the same moving direction. Our scheme can reduce the total signaling cost of location management by reducing the cost of location registration more than the increased cost of call delivery. Simulation results show that our scheme outperforms current methods in location registration cost as long as CMR (call to mobility ratio) is not high and has a superior performance in the total signaling cost with low CMR and high population.