Kultida Rojviboonchai

V-DESYNC: Desynchronization for Beacon Broadcasting on Vehicular Networks

Several prospective applications on vehicular networks have been defined. Most applications rely on beaconing mechanisms to broadcast the presence and updated information of a vehicle to surrounding neighbors. However, due to the broadcasting nature, no acknowledgement mechanism is provided. Therefore, vehicles do not perceive beacon collision if two or more vehicles simultaneously broadcast the beacons. Consequently, vehicles miss updated information from their neighbors. In this paper, we propose V-DESYNC, an algorithm that distributively desynchronizes vehicles to broadcast beacons at different times based on only timing information. V-DESYNC is designed to avoid the beacon collision and tolerate the highly dynamic behavior of vehicular networks. Our evaluation results indicate that V-DESYNC can significantly reduce the number of beacon collisions without decreasing the beaconing rate on vehicular networks.

Message dropping policy in congested social Delay Tolerant Networks

Congestion in DTNs happens when the forwarding path to destination does not exist and a node runs out of buffer space. Several works have shown that the situation is hard to mitigate. Consequently, to choose the right message to drop is a crucial task. Moreover, there has not been much attention to the buffer management policy in the Social-DTNs contexts. Therefore, an efficient buffer management policy for Social-DTNs is needed to achieve a better performance for communication in challenging disruptive scenarios. In this paper, we propose a novel message dropping policy for Social-DTNs. Our proposed policy utilizes social relation of nodes to avoid dropping meaningful messages in congested social-DTNs. We have implemented and evaluated our policy on the ONE simulator, and used real contact traces obtained during a conference. Our evaluation results show that our proposed policy can significantly reduce the number of overhead and can outperform the traditional policy under investigated scenarios.

Comparison of reliable broadcasting protocols for vehicular ad-hoc networks

Reliable broadcasting in vehicular ad hoc networks is one of the keys to success for services and applications on intelligent transportation system. Many reliable broadcasting protocols have been proposed but none of them has been evaluated in realistic scenario. In this paper, we discuss and evaluate these reliable broadcasting protocols on VANET. First, we separate mechanisms of the protocols into three main modules, which are preferred node selection algorithm, waiting timeout calculation and beaconing mechanism. These modules are employed on the reliable broadcasting protocols. Then, we evaluate performance of the protocols by simulation. To be more realistic, in our simulation, multiple broadcast messages are concurrently generated on highway and urban scenarios. None of the previous works we found in the literature uses more than one broadcast message on their simulation. From simulation result, we found a problem on the preferred node selection algorithm, the waiting timeout calculation and the beaconing mechanism of some protocols, which can lead to broadcast storm problem and inefficient operation.

DecaFriend: Serverless indoor localization system on mobile phone platform

Mobile phone is now becoming a necessary gadget in our daily life. Mobile applications have been proposed to advance the function of mobile phone. Location service application is a kind of mobile application that provides location information such as current location of the mobile phone. GPS is the popular technology for location service on mobile phone because many models of mobile phone are embedded with GPS sensor. Although GPS can provide high accuracy over outdoor scenario, GPS cannot provide good accuracy in indoor environment because the GPS signal from GPS satellites is blocked by the structure of building. The indoor localization systems have been proposed to address the above-mentioned problem. Many indoor localization systems require costly back-end server to process location. Moreover, the devices need to connect to the back-end servers to request the service. In this paper, we propose a serverless indoor localization system for mobile phone platform. The proposed system does not need any support from back-end server. The localization is processed on mobile phone. The system is developed as an Android application, utilizing Wi-Fi signal to determine the current location of mobile phone and uses mobile ad hoc network to disseminate the current location to other users in the system. The proposed system achieves accuracy up to 83.43% when the system is deployed in the two-floors building, which is the experimental site.

Non-GPS Data Dissemination for VANET

Fast, reliable, and efficient data dissemination in VANET is a key of success for intelligent transportation system. This requires a broadcasting protocol which has efficient forwarder nodes and an efficient broadcasting mechanism. In this paper, we propose a self-decision algorithm that allows a node to know that it belongs to a member of connected dominating set or not. The algorithm is a combination of density based algorithm and topology based algorithm, called “DTA.” The algorithm does not require any geographical knowledge. Therefore, it can avoid violating a privacy issue. Moreover, the algorithm can resist inaccurate data than position-base algorithms that need high frequent beaconing for accurate data. The simulation results show that our algorithm provides the highest coverage results compared to existing solutions. We also propose a new broadcasting protocol, called “NoG.” NoG consists of a broadcasting mechanism, a waiting timeout mechanism, and a beaconing mechanism. The proposed protocol operates without any geographical knowledge and provides reliable and efficient data dissemination. The performance is evaluated with a realistic network simulator (NS-3). Simulation results show that NoG with DTA outperforms other existing protocols in terms of reliability and data dissemination speed.

DNH-SaW: The Different Neighbor-History Spray and wait routing scheme for Delay Tolerant Networks

In Delay Tolerant Networks (DTNs), network partitioning is likely to happen due to sparse and mobile nodes with limited transmission ranges. The network partitioning leads to the unavailability of fully connected paths from sources to destinations. To deal with this problem, many routing schemes are proposed such as Epidemic routing and Spray and Wait routing. These schemes obtain high delivery rate but incur high overhead. In this paper, we propose a Different Neighbor-History Spray and Wait (DNH-SaW) routing scheme. DNH-SaW calculates the number of data copies to forward based on the neighbor-history of each receiver. Our simulation result shows that DNH-SaW can reduce overhead up to 27% and increases delivery utility up to 21.68% while achieving comparable delivery probability with previous works.

Improving reliable broadcast over asymmetric VANETs based on a RSSI-voting algorithm

An asymmetric link problem is a considerable effect in vehicular network, but usually overlooked by many researchers. Most of researches concerning this problem are extensions on unicasting routing protocols which have a primary route of data transmission. However, reliable broadcasting protocols such as Density-Aware Reliable Broadcasting protocol (DECA) have no exact route for sending data but do data dissemination. Therefore, in this paper, we focus on making a solution for broadcasting protocols. Specifically, we design a method to select the most efficient preferred node with broadly transmission range and vastly neighbor coverage. In this paper, we propose a RSSI-Voting algorithm as a new node selection algorithm. Each node votes a neighbor who has the highest Received Signal Strength Indicator (RSSI). When a sender wants to broadcast a message, it will select a preferred forwarder node who gains a majority vote. The simulation results show that our mechanism can improve protocol performance up to 17% and decrease its retransmission overhead up to 28%.

2PMP: A push-pull with buffer-map prediction algorithm for peer to peer live streaming

Push-pull approaches for peer-to-peer live streaming systems have gained tremendous popularity due to their high scalability and low latency. However, such approaches rely on buffer-map information of all neighbors to determine which piece to push and which peer to pull. Therefore, those approaches incur significant overhead in order to maintain the up-to-date buffer-maps of all neighbors. In this paper, we propose an algorithm to predict the buffer-map of a neighbor. Peers in our approach no longer need to frequently exchange their buffer-maps. We have implemented and evaluated our algorithm on ns-2. Under investigated scenarios, our approach can reduce up to 97% of overhead as well as simultaneously decrease duplicates of the previous system.

A hybrid communication approach for disaster recovery system

In this paper, we proposed a hybrid communication approach for disaster recovery system. Playing an important role in rescuing victims, the communication system in the disaster area is usually destroyed. The mobile ad-hoc network (MANET) can replace the original system. MANET can be deployed in the form of peer-to-peer (P2P) approach or infrastructure-based (IB) approach. However, both approaches still have limited flexibility and reliability. Our hybrid approach overcomes the limitations by combining advantages of P2P approach and those of IB approach. The hybrid approach allows victims to directly communicate to rescuers in the disaster area. Since victims need immediate helps from rescuers, appropriate destinations must be selected. Our design of hybrid approach allows victims to quickly send messages to the nearest rescuers without compromising the traffic to a base station. The experiment shows that our hybrid approach provides more than 98% of packet delivery ratio to rescuers.

FloorLoc-SL: floor localization system with fingerprint self-learning mechanism

Nowadays, a mobile phone plays an important role in daily life. There are many applications developed for mobile phones. Location service application is one kind of mobile application that serves location information. GPS receiver is embedded on a mobile phone for localization. However, GPS cannot provide localization service over indoor scenario efficiently. This is because obstacles and structures of building block GPS signal from the satellites. Many indoor localization systems have been proposed but most of them are developed over single-floor scenario only. The dimension of altitudes in localization results will be missed. In this paper, we propose floor localization system. The proposed system does not need any site survey and any support from back-end server. It has a self-learning algorithm for creating fingerprint in each floor. The self-learning algorithm utilizes sensors on the mobile phone for detecting trace of mobile phone user. This algorithm is low computation complexity, which can be operated on any mobile phones. Moreover, the mobile phone can exchange fingerprints with others via virtual ad hoc network instead of learning all floor fingerprints by themselves only. Our proposed floor localization system achieves 87% of accuracy.