Yao Hua Ho

Performance Study of Live Video Streaming Over Highway Vehicular Ad Hoc Networks

Live video streaming over vehicular ad hoc networks (VANET) is an attractive feature to many applications, such as emergency live video transmission, road-side video advertisement broadcasting and inter-vehicle video conversation. Though vehicles have ample bandwidth, computation and storage capacity to support data intensive communication, the high mobility may cause persistent network partition. The performance of video streaming suffers from the delay and packet loss incurred by the long time disconnection. Although many solutions have been proposed to handle the high mobility problem, few of them addressed the problem in the context of video transmission. In this paper, we focus on video streaming between vehicles in highway, where the traffic density is adequate to mitigate frequent link disconnections and persistent network partitions. We study the performance of video streaming under different data forwarding and buffer management schemes. Real video data and the dedicated short range communications (DSRC) are used in the simulation study to better match the reality. The result of this paper gives insight for the design of the future inter-vehicle video streaming system.

Routing protocols for inter-vehicular networks: A comparative study in high-mobility and large obstacles environments

An ad hoc network is composed of mobile nodes without the presence of a fixed infrastructure. Communications among nodes are accomplished by forwarding data packets for each other, on a hop-by-hop basis along the current connection to the destination node. In particular, vehicle-to-vehicle communications have been studied, in recent years, to improve driver safety. As more of such applications of high-mobility ad hoc networks emerge, it is critical that the routing protocol employed is capable of efficiently coping with the high-frequency of broken links (i.e., robust with respect to high-mobility). This paper presents a comprehensive comparative study in a city environment of eight representative routing protocols for wireless mobile ad hoc networks and inter-vehicular networks developed in recent years. In a city environment, communication protocols need adapt fast moving nodes (e.g., vehicles on streets) and large obstacles (e.g., office buildings). In this paper, we elaborate upon extensive simulation results based on various network scenarios, and discuss the strengths and weaknesses of these techniques with regard to their support for highly mobile nodes.

A connectionless approach to mobile ad hoc networks in street environments

In this paper we adapt an earlier work called connectionless approach to mobile ad hoc network (CLA) to vehicular ad hoc networks in a city environment with fast moving nodes (e.g., vehicles on streets) and large obstacles (e.g., office buildings). Fast moving nodes result in frequent topology changes. Large buildings surrounded by relative narrow streets allow only a short window of communication among nodes (meaning established hop-by-hop routes do not last long). Large buildings also obstruct straight line paths between nodes (meaning selection of closest nodes or nodes on straight line geographical path would not work). We propose a protocol that can relay data around obstacles, can quickly adapt to topology change, can utilize short communication windows, and can provide multiple communicating paths to the destination.

Semi-Split TCP: Maintaining End-to-End Semantics for Split TCP

It has long been acknowledged that TCP performance suffers in hybrid networks. A Split TCP approach has been proposed to address this problem. In this approach, a proxy is employed at the boundary of wired networks (e.g. the Internet) and wireless networks (e.g. cellular networks, WLan or mobile ad hoc networks). This strategy significantly improves TCP performance. However, it does not maintain the end-to-end semantics of TCP. The loss of end-to-end semantics may cause problems to applications that rely on such a guarantee provided by TCP. In this paper, we introduce a novel technique called Semi-Split TCP to address the problem without sacrificing the benefits of Split TCP. We present the architecture and algorithms of the proposed technique; and give implementation, simulation, and analytical results to illustrate the feasibility of this method. Our simulation results demonstrate that Semi-Split TCP can achieve similar performance as Split-TCP without sacrificing the end-to-end semantics.

Cooperation Enforcement in Vehicular Networks

Operations of vehicular ad hoc networks rely on the collaboration of participating nodes to route data for each other. This standard approach using a fixed set of nodes for each communication link cannot cope with high mobility due to a high frequency of link breaks. A recent approach based on virtual routers has been proposed to address this problem. In this new environment, virtual routers are used for forwarding data. The functionality of each virtual router is provided by the mobile devices currently within its spatial proximity. Since these routers do not move, the communication links are much more robust compared to those of the conventional techniques. In this paper, we investigate techniques to enforce collaboration among mobile devices in supporting the virtual router functionality. Simulation results based on various system configurations are given. They indicate that the proposed technique is effective.

PLASH: a platform for location aware services with human computation

The PLASH platform is designed to help location- aware service providers deploy their applications easily so that users can contribute their efforts and location-related data by using the services, which is the main difference from traditional location-aware services. The collective efforts and data that may be generated by humans or sensors (or both) can be used to help solve difficult location awareness problems, such as realtime surface traffic estimation, city panoramas, and social networking analysis. The PLASH platform comprises three layers: communication, data, and service. An LAS application developed on PLASH can exploit the functions provided in each layer by using an application specification language provided by PLASH. In addition, application builders can contribute their mature applications as a service accommodated in the service layer for other application builders to expand and create more sophisticated applications.

An Efficient Broadcast Technique for Vehicular Networks

Vehicular networks are a promising application of mobile ad hoc networks. In this paper, we introduce an efficient broadcast technique, called CB-S (Cell Broadcast for Streets), for vehicular networks with occlusions such as skyscrapers. In this environment, the road network is fragmented into cells such that nodes in a cell can communicate with any node within a two cell distance. Each mobile node is equipped with a GPS (Global Positioning System) unit and a map of the cells. The cell map has information about the cells including their identifier and the coordinates of the upper-right and lower-left corner of each cell. CB-S has the following desirable property. Broadcast of a message is performed by rebroadcasting the message from every other cell in the terrain. This characteristic allows CB-S to achieve an efficient performance. Our simulation results indicate that messages always reach all nodes in the wireless network. This perfect coverage is achieved with minimal overhead. That is, CB-S uses a low number of nodes to disseminate the data packets as quickly as probabilistically possible. This efficiency gives it the advantage of low delay. To show these benefits, we give simulations results to compare CB-S with four other broadcast techniques. In practice, CB-S can be used for information dissemination, or to reduce the high cost of destination discovery in routing protocols. By also specify the radius of affected zone, CB-S is also more efficient when broadcast to a subset of the nodes is desirable.

ADF: An Anomaly Detection Framework for Large-Scale PM2.5 Sensing Systems

As the population density continues to grow in the urban settings, air quality is degrading and becoming a serious issue. Air pollution, especially fine particulate matter (PM2.5), has raised a series of concerns for public health. As a result, a number of large-scale, low cost PM2.5 monitoring systems have been deployed in several international smart city projects. One of the major challenges for such environmental sensing systems is ensuring the data quality. In this paper, we propose an anomaly detection framework (ADF) for large-scale, real-world environmental sensing systems. The framework is composed of four modules: 1) time-sliced anomaly detection (TSAD), which detects spatial, temporal, and spatio-temporal anomalies in the real-time sensor measurement data stream; 2) real-time emission detection, which detects potential regional emission sources; 3) device ranking, which provides a ranking for each sensing device; and 4) malfunction detection, which identifies malfunctioning devices. Using real world measurement data from the AirBox project, we demonstrate that the proposed framework can effectively identify outliers in the raw measurement data as well as infer anomalous events that are perceivable by the general public and government authorities. Because of its simple design, ADF is highly extensible to other advanced applications, and it can be exploited to support various large-scale environmental sensing systems.

An Open Framework for Participatory PM2.5 Monitoring in Smart Cities

As the population in cities continues to increase rapidly, air pollution becomes a serious issue from public health to social economy. Among all pollutants, fine particulate matters (PM2.5) directly related to various serious health concerns, e.g., lung cancer, premature death, asthma, and cardiovascular and respiratory diseases. To enhance the quality of urban living, sensors are deployed to create smart cities. In this paper, we present a participatory urban sensing framework for PM2.5 monitoring with more than 2500 devices deployed in Taiwan and 29 other countries. It is one of the largest deployment project for PM2.5 monitor in the world as we know until May 2017. The key feature of the framework is its open system architecture, which is based on the principles of open hardware, open source software, and open data. To facilitate the deployment of the framework, we investigate the accuracy issue of low-cost particle sensors with a comprehensive set of comparison evaluations to identify the most reliable sensor. By working closely with government authorities, industry partners, and maker communities, we can construct an effective eco-system for participatory urban sensing of PM2.5 particles. Based on our deployment achievements to date, we provide a number of data services to improve environmental awareness, trigger on-demand responses, and assist future government policymaking. The proposed framework is highly scalable and sustainable with the potential to facilitate the Internet of Things, smart cities, and citizen science in the future.

Missing data handling for meter data management system

We study the meter data management systems (MDMS) with a focus on missing data handling, and propose two approaches, called Lookback-N and Sandwich-N, based on the historical data. Using a realistic dataset, we demonstrate that Lookback-N is effective for online processing, and Sandwich-N outperforms the conventional offline approach, in terms of estimation accuracy, in all test cases. The proposed approaches are simple, effective, and show promise in handling missing data for emerging smart meter data management systems.