Gihwan Cho

A Selective Flooding Method for Propagating Emergency Messages in Vehicle Safety Communications

An intelligent vehicle safety system can be constructed by exchanging emergency-related information between any unrelated vehicles, such as urgency stop, traffic accident, and obstacles. In the most of vehicle safety communication applications, an emergency message is propagated in the form of broadcasting. However, it causes a lot of problems in terms of efficiency due to the multi-hop propagation and radio collision problems. This paper presents a selective message forwarding method by assigning a defer time based on the number of the common neighbors. With benefit of this method, only selected vehicles perform a re-broadcasting the received emergency event among the vehicles included in the same wireless coverage. Moreover, the proposed scheme improves the efficiency of message transmission with the selective assignment of priority for forwarding message. To analyze its performance, it has been evaluated by network simulator.

An Energy Efficient Cluster Formation and Maintenance Scheme for Wireless Sensor Networks

Nowadays, wireless sensor networks (WSNs) comprise a tremendously growing infrastructure for monitoring the physical or environmental conditions of objects. WSNs pose challenges to mitigating energy dissipation by constructing a reliable and energy saving network. In this paper, we propose a novel network construction and routing method by defining three different duties for sensor nodes, that is, node gateways, cluster heads, and cluster members, and then by applying a hierarchical structure from the sink to the normal sensing nodes. This method provides an efficient rationale to support the maximum coverage, to recover missing data with node mobility, and to reduce overall energy dissipation. All this should lengthen the lifetime of the network significantly.

Improving prediction level of prefetching for location-aware mobile information service

An essential quality for future information services is their ability to evolve and adapt to deliver the information corresponding into the current situation of user and/or device in the face of constantly changing environment. This paper deals with the prefetching schemes to improve prediction level of for location-aware mobile information service. The prefetching aims to reduce the latency to get refreshed information appropriated to the current location. Thus, in order to effectively limit the prefetched information into the most likely future location context, the rectangle-shaped Prefetching Zone (PZ) is firstly defined with a users moving speed and direction. Then, a method is given to make use of the mobility reference count that shows how often the user has been visited to a given area, to further predict the prefetching candidates.

An effective message flooding method for vehicle safety communication

An intelligent vehicle safety system can be constructed by exchanging emergency-related information between any unrelated vehicles, such as urgency stop, traffic accident, and obstacles. In the most of vehicle safety communication applications, an emergency message is propagated in the form of broadcasting. However, it causes a lot of problems in terms of efficiency due to the multi-hop propagation and radio collision problems. This paper presents a selective message forwarding method by proposing the stem and branch structure. With benefit of the structure, only one vehicle performs forwarding a received emergency event among the vehicles that are included in the same wireless coverage. Moreover, the proposed scheme improves the efficiency of message transmission with the selective assignment of priority for forwarding message. To analyze its performance, it has been evaluated by network simulator.

Lightweight Key Renewals for Clustered Sensor Networks

In sensor networks, sensors are likely to be c aptured by attackers because they are usually deployed in an unprotected or even a hostile environment . If an adversarial compromises a sensor, he/she uses the keys from the compromised sensor to uncover the keys of others sensors. Therefore, it is very important to renew the keys of sensors in a proactive or reactive manner. Even though many group key renewal schemes have been proposed, they have some security flaws. First, they employ a single group key in a cluster so that the compromise of one sensor discloses the group key . Second, they evict the compromised nodes by updating the compromised keys with non-compromised keys. This eviction scheme is useless when the non-compromised keys are exhausted due to the increase of compromised nodes. In this paper, we propose a lightweight key renewal scheme , which evicts the compromised nodes clearly by reforming clusters excluding compromised nodes. Besides, in a cluster, each member employs a pairwise key for communication with its CH (Cluster Head) so that our scheme is tolerable against sensor compromise. Our simulation results prove that the proposed scheme is more tolerable against the compromise of sensors and it is more energy-saving than the group key renewal schemes.

Secure Cluster Head Sensor Elections Using Signal Strength Estimation and Ordered Transmissions

In clustered sensor networks, electing CHs (Cluster Heads) in a secure manner is very important because they collect data from sensors and send the aggregated data to the sink. If a compromised node is elected as a CH, it can illegally acquire data from all the members and even send forged data to the sink. Nevertheless, most of the existing CH election schemes have not treated the problem of the secure CH election. Recently, random value based protocols have been proposed to resolve the secure CH election problem. However, these schemes cannot prevent an attacker from suppressing its contribution for the change of CH election result and from selectively forwarding its contribution for the disagreement of CH election result. In this paper, we propose a modified random value scheme to prevent these disturbances. Our scheme dynamically adjusts the forwarding order of contributions and discards a received contribution when its signal strength is lower than the specified level to prevent these malicious actions. The simulation results have shown that our scheme effectively prevents attackers from changing and splitting an agreement of CH election result. Also, they have shown that our scheme is relatively energy-efficient than other schemes.

Enhancing of the prefetching prediction for context-aware mobile information services

This paper deals with a prefetching method to enhance its prediction for context-aware services in mobile information system. This method aims to reduce the latency time to get the refreshed information appropriated to the current location of mobile users. To achieve this, our approach is to effectively limit the prefetched information into the most next location context. It makes use of the prefetching zone that reflects the user’s mobility speed and direction, and the mobile reference count that stands for the user’s visiting frequency to a given area. Then it considers the residence time, in order to further predict the prefetching candidates.

A Pair-Wise Key Agreement Scheme in Ad Hoc Networks

Mobile Ad-hoc networks are exposed to various security threats because all traffics are carried in air and there is no central management authority. For the sake of secure communication in an Ad-hoc network, a scheme is inevitable to securely distribute security keys in the network. Based on the cluster structure and the verifiable secret sharing scheme[1], this paper proposes a pairwise key agreement scheme which is secure and induces a lower overhead. The proposed scheme is safe against a man-in-the-middle attack while not all private keys within the destination’s cluster are exposed. In addition, our simulation result shows that the proposed scheme is more efficient and scalable than CABM(Clusterhead Authentication Based Method)[2].

Reputation-based cluster head elections in wireless sensor networks

In clustered sensor networks, because CHs (cluster heads) collect data from sensors and transmit the aggregated data to the sink, it is very important to elect the CHs in a secure manner. In order to protect CH elections from attackers, unpredictability, non-manipulability, and agreement property should be guaranteed in CH elections. However, existing schemes for secure CH election cannot prevent intelligent attackers from violating the properties via cooperation. In this paper, we propose a scheme that securely elects CHs by detecting intelligent attackers and excluding them. For every CH election round, each CH candidate provides reputation values to other CH candidates according to their behavior and extracts real reputation values. Then, each node evaluates the real reputation values of members in its cluster and excludes some disreputable nodes from CH candidates. The scheme greatly enhances the non-manipulability and agreement property of CH election results compared to other rival schemes. Furthermore, the scheme presents higher non-manipulability and higher agreement property than other schemes, even in an environment where message losses can occur.

An adaptive UDT congestion control method with reflecting of the network status

Nowadays, most of networks support several tens of Gb/s with advance of the optical technologies. However, TCP protocol is known to be less suitable for fast transmission due to its AIMD characteristic. As an alternative, UDT protocol has been invented to efficiently utilize network bandwidth; it periodically controls the sending rate for the fixed sync-interval, 0.01 sec. Here, if the network status varies quickly, the available bandwidth is not able to be properly utilized in-between the sync-intervals. In this paper, we propose an adaptive congestion control method in order to reflect the network status. The network status is estimated based on RTT variances. It is divided into four classes, and then properly utilized to differentiate the sending rate. The simulation results show that the proposed method improves the message delivery throughput as well as stability than that of the UDT protocol.