Min-Te Sun

GPS-based message broadcast for adaptive inter-vehicle communications

The intelligent transportation systems (ITS) use advanced communications and control technologies to improve current transportation systems. To achieve many ITS applications, the ability to exchange messages between vehicles is necessary. This is generally required as inter vehicle communication (IVC). IVC can be considered as a special case of ad hoc networks, where nodes only move along predefined road paths. We propose new broadcast protocols that make use of global positioning system (GPS) information to enhance the performance of broadcast service in IVC. The ability to efficiently broadcast messages is necessary for any communications in IVC (e.g, updating routing tables, etc). We propose two algorithms that effectively reduce the number of re-broadcast messages without affecting the number of hosts (vehicles) that receive the broadcast. The simulation results show up to several hundred percentage of bandwidth utilization improvement can be achieved by our proposed broadcast protocols.

GPS-based message broadcasting for inter-vehicle communication

Intelligent Transportation Systems (ITS) have become a focus for many countries. To achieve ITS, Inter Vehicle Communication (IVC) is required for the exchange and distribution of data such as congestion or emergency information. If this communication can be done without fixed infrastructure, the systems can be deployed quickly and on a larger scale. Ad hoc networking technologies are one such technology to achieve IVC. However, if generic ad hoc network solutions are applied directly to IVC, performance can degrade quickly as the system scales particularly for broadcast type messages. In this paper we propose two new broadcast protocols that reduce bandwidth required for broadcast communication by taking advantage of a vehicles highly directional movement and Global Positioning Information. To show the performance of our new protocols, we compare our approach with generic ad hoc broadcasting techniques. Our results show that it is possible to achieve several hundred percent improvement of bandwidth utilization with very slight sacrifice of reachability.

Reliable MAC layer multicast in IEEE 802.11 wireless networks

Multicast/broadcast is an important service primitive in networks. It is supported by all IEEE 802.x standards, including 802.11. The IEEE 802.11 multicast/broadcast protocol is based on the basic access procedure of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). This protocol does not provide any media access control (MAC) layer recovery on multicast/broadcast frames. As a result, the reliability of the multicast/broadcast service is reduced owing to the increased probability of lost frames resulting from interference or collisions. Recently, a few MAC protocols have been proposed to enhance the reliability and the efficiency of the 802.11 multicast/broadcast protocol. In this paper, we observe that these protocols are still unreliable or inefficient. To redress the problems of reliability and efficiency, we propose a reliable Batch Mode Multicast MAC protocol (BMMM), which in most cases reduces the number of contention phases from n to 1, where n is the number of intended receivers in the multicast/broadcast. This considerably reduces the time required for a multicast/broadcast. We then propose a Location Aware Multicast MAC protocol (LAMM), which uses station location information to further improve upon BMMM. Extensive analysis and simulation results validate the reliability and efficiency of our multicast MAC protocols. Copyright

Leveraging spatio-temporal redundancy for RFID data cleansing

Radio Frequency Identification (RFID) technologies are used in many applications for data collection. However, raw RFID readings are usually of low quality and may contain many anomalies. An ideal solution for RFID data cleansing should address the following issues. First, in many applications, duplicate readings (by multiple readers simultaneously or by a single reader over a period of time) of the same object are very common. The solution should take advantage of the resulting data redundancy for data cleaning. Second, prior knowledge about the readers and the environment (e.g., prior data distribution, false negative rates of readers) may help improve data quality and remove data anomalies, and a desired solution must be able to quantify the degree of uncertainty based on such knowledge. Third, the solution should take advantage of given constraints in target applications (e.g., the number of objects in a same location cannot exceed a given value) to elevate the accuracy of data cleansing. There are a number of existing RFID data cleansing techniques. However, none of them support all the aforementioned features. In this paper we propose a Bayesian inference based approach for cleaning RFID raw data. Our approach takes full advantage of data redundancy. To capture the likelihood, we design an n-state detection model and formally prove that the 3-state model can maximize the system performance. Moreover, in order to sample from the posterior, we devise a Metropolis-Hastings sampler with Constraints (MH-C), which incorporates constraint management to clean RFID raw data with high efficiency and accuracy. We validate our solution with a common RFID application and demonstrate the advantages of our approach through extensive simulations.

A self-routing topology for Bluetooth scatternets

The emerging Bluetooth standard is considered to be the most promising technology to construct ad-hoc networks. It contains specifications of how to build a piconet but left out details of how to automatically construct a scatternet from the piconets. Existing solutions only discussed the scatternet formation issue without considering the ease of routing in such a scatternet. We present algorithms to embed b-trees into a scatternet which enables such a network to become self-routing. It requires only a fixed-size message header and no routing table at each node regardless of the size of the scatternet. These properties make our solution scalable to deal with networks of large sizes. Our solutions are of distributed control and asynchronous. We prove that our algorithm preserves the b-tree property when devices join or leave the scatternet and when one scatternet is merged with another.

The multi-rule partial sequenced route query

Trip planning search (TPS) represents an important class of queries in Geographic Information Systems (GIS). In many real-world applications, TPS requests are issued with a number of constraints. Unfortunately, most of these constrained TPS cannot be directly answered by any of the existing algorithms. By formulating each restriction into rules, we propose a novel form of route query, namely the multi-rule partial sequenced route (MRPSR) query. Our work provides a unified framework that also subsumes the well-known trip planning query (TPQ) and the optimal sequenced route (OSR) query. In this paper, we first prove that MRPSR is NP-hard and then present three heuristic algorithms to search for near-optimal solutions for the MRPSR query. Our extensive simulations show that all of the proposed algorithms can answer the MRPSR query effectively and efficiently. Using both real and synthetic datasets, we investigate the performance of our algorithms with the metrics of the route distance and the response time in terms of the percentage of the constrained points of interest (POI) categories. Compared to the LORD-based brute-force solution, the response times of our algorithms are remarkably reduced while the resulting route length is only slightly longer than the shortest route.

An Efficient Path Pruning Algorithm for Geographical Routing in Wireless Networks

Geographical routing is powerful for its ability to discover a path to the destination without the help of global states. However, stateless geographical routing usually involves a large number of hops when detouring around voids of the network. In this paper, we propose an efficient path pruning (PP) strategy to reduce the excessive number of hops caused by the detouring mode of geographical routing protocols. The PP algorithm finds routing shortcuts by exploiting the channel listening capability of wireless nodes and is able to reduce a large number of hops with the help of a little state information passively maintained by a subset of nodes on the route. We also discuss algorithm properties and implementation considerations and provide simulation results demonstrating the effectiveness of the proposed algorithm in shortening the routing path and improving delivery rate when it is applied to existing geographical routing protocols.

The partial sequenced route query with traveling rules in road networks

In modern geographic information systems, route search represents an important class of queries. In route search related applications, users may want to define a number of traveling rules (traveling preferences) when they plan their trips. However, these traveling rules are not considered in most existing techniques. In this paper, we propose a novel spatial query type, the multi-rule partial sequenced route (MRPSR) query, which enables efficient trip planning with user defined traveling rules. The MRPSR query provides a unified framework that subsumes the well-known trip planning query (TPQ) and the optimal sequenced route (OSR) query. The difficulty in answering MRPSR queries lies in how to integrate multiple choices of points-of-interest (POI) with traveling rules when searching for satisfying routes. We prove that MRPSR query is NP-hard and then provide three algorithms by mapping traveling rules to an activity on vertex network. Afterwards, we extend all the proposed algorithms to road networks. By utilizing both real and synthetic POI datasets, we investigate the performance of our algorithms. The results of extensive simulations show that our algorithms are able to answer MRPSR queries effectively and efficiently with underlying road networks. Compared to the Light Optimal Route Discoverer (LORD) based brute-force solution, the response time of our algorithms is significantly reduced while the distances of the computed routes are only slightly longer than the shortest route.

Timer-Based CDS Construction in Wireless Ad Hoc Networks

The connected dominating set (CDS) has been extensively used for routing and broadcast in wireless ad hoc networks. While existing CDS protocols are successful in constructing CDS of small size, they either require localized information beyond immediate neighbors, lack the mechanism to properly handle nodal mobility, or involve lengthy recovery procedure when CDS becomes corrupted. In this paper, we introduce the timer-based CDS protocols, which first elect a number of initiators distributively and then utilize timers to construct a CDS from initiators with the minimum localized information. We demonstrate that our CDS protocols are capable of maintaining CDS in the presence of changes of network topology. Depending on the number of initiators, there are two versions of our timer-based CDS protocols. The Single-Initiator (SI) generates the smallest CDS among protocols with mobility handling capability. Built on top of SI, the Multi-Initiator (MI) version removes the single point of failure at single-initiator and possesses most advantages of SI. We evaluate our protocols by both the ns-2 simulation and an analytical model. Compared with the other known CDS protocols, the simulation results demonstrate that both SI and MI produce and maintain CDS of very competitive size. The analytical model shows the expected convergence time and the number of messages required by SI and MI in the construction of CDS, which match closely to our simulation results. This helps to establish the validity of our simulation.

Maintaining CDS in Mobile Ad Hoc Networks

The connected dominating set (CDS) has been generally used for routing and broadcasting in mobile ad hoc networks (MANETs). To reduce the cost of routing table maintenance, it is preferred that the size of CDS to be as small as possible. A number of protocols have been proposed to construct CDS with competitive size, however only few are capable of maintaining CDS under topology changes. In this research, we propose a novel extended mobility handling algorithm which will not only shorten the recovery time of CDS mobility handling but also keep a competitive size of CDS. Our simulation results validate that the algorithm successfully achieves its design goals. In addition, we will introduce an analytical model for the convergence time and the number of messages required by the CDS construction.