SmartSiren: virus detection and alert for smartphones
Smartphones have recently become increasingly popular because they provide "all-in-one" convenience by integrating traditional mobile phones with handheld computing devices. However, the flexibility of running third-party softwares also leaves the smartphones open to malicious viruses. In fact, hundreds of smartphone viruses have emerged in the past two years, which can quickly spread through various means such as SMS/MMS, Bluetooth and traditional IP-based applications. Our own implementations of two proof-of-concept viruses on Windows Mobile have confirmed the vulnerability of this popular smartphone platform.
 In this paper, we present SmartSiren, a collaborative virusdetection and alert system for smartphones. In order to detect viruses, SmartSiren collects the communication activity information from the smartphones, and performs joint analysis to detect both single-device and system-wide abnormal behaviors. We use a proxy-based architecture to offload the processing burden from resource-constrained smartphones and simplify the collaboration among smartphones. When a potential virus is detected, the proxy quarantines the out-break by sending targeted alerts to those immediately threatened smartphones. We have demonstrated the feasibility of SmartSiren through implementations on a Dopod 577w smartphone, and evaluated its effectiveness using simulations driven by 3-week SMS traces from a national cellular carrier. Our results show that SmartSiren can effectively prevent wide-area virus outbreaks with affordable overhead.

title: An architectural infrastructure and topological optimization for end system multicast
abstract: Although IP-multicast has been proposed and investigated for the some time, there are major problems inherent in the IP-multicasting technique, for example, scalability problems, difficulty to allocate a globally unique multicast address, complexity to support higher level features such as reliable data transfer congestion/flow control and security, and more importantly, deployment problem due to architectural changes to core routers. Recently, end-system multicast (ESM) has been proposed as an alternative solution so that multicasting services can be quickly deployed. In this paper we consider the "architectural" and "optimization " issues on designing an ESM-tree. Specifically, we present a distributed algorithm on how to create and maintain an ESM-tree. We also propose a distributed algorithm to perform a tree optimization (TO) so that an ESM-tree can dynamically adapt to the changing network condition (e.g., drop in transfer bandwidth) so that nodes can receive the multicast data more efficiently. The propose distributed algorithm has the theoretical properties that at all times, a tree-topology can be maintained and that any node joining, leaving, as well as any tree optimization operation will not "partition" an ESM-tree. Therefore, our work can be used to provide an efficient architectural infrastructure for ESM services. We have implemented a prototype ESM system and carried out experiments to illustrate the effectiveness and performance of our ESM optimization protocol.

title: Analysis of the Reliability of a Nationwide Short Message Service
abstract: SMS has been arguably the most popular wireless data service for cellular networks. Due to its ubiquitous availability and universal support by mobile handsets and cellular carriers, it is also being considered for emergency notification and other mission-critical applications. Despite its increased popularity, the reliability of SMS service in real-world operational networks has received little study so far. In this work, we investigate the reliability of SMS by analyzing traces collected from a nationwide cellular network over a period of three weeks. Although the SMS service incorporates a number of reliability mechanisms such as delivery acknowledgement and multiple retries, our study shows that its reliability is not as good as we expected. For example the message delivery failure ratio is as high as 5.1% during normal operation conditions. We also analyze the performance of the service under stressful conditions, and in particular during a "flash-crowd" event that occurred in New Year's Eve of 2005. Two important factors that adversely affect reliability of SMS are also examined: bulk message delivery that may induce network-wide congestion, and the topological structure of the social network formed by SMS users, which may facilitate quick propagation of viruses or other malware.

title: A study of the short message service of a nationwide cellular network
abstract: In recent years, cellular networks have experienced an astronomical increase in the use of Short Message Service (SMS), making it a popular communication means for inter-personal as well as content provider-to-person usage. Yet little is known about the traffic and message user behavior in real SMS systems. In this paper, we present a measurement study of SMS based on traces collected from a nationwide cellular carrier during a three-week period. We characterize message traffic at both the message level and the conversation thread level. We also examine the "store-and-forward" mechanism of SMS and present initial measurements on how messages are actually delivered.

title: Characterizing flows in large wireless data networks
abstract: Several studies have recently been performed on wireless university campus networks, corporate and public networks. Yet little is known about the flow-level characterization in such networks. In this paper, we statistically characterize both static flows and roaming flows in a large campus wireless network using a recently-collected trace. For static flows, we take a two-tier approach to characterizing the flow arrivals, which results a Weibull regression model. We further discover that the static flow arrivals in spatial proximity show strong similarity. As for roaming flows, they can also be well characterized statistically.We explain the results by user behaviors and application demands, and further cross-validate the modeling results by three other traces. Finally, we use two examples to illustrate how to apply our models for performance evaluation in the wireless context.

title: End system multicast: an architectural infrastructure and topological optimization
abstract: Although IP multicast has been proposed and investigated for years, there are major problems inherent in the IP multicasting technique, e.g. difficulty to scale up the system, difficulty in allocating a globally unique multicast address, complexity in supporting higher level features such as reliable data transfer and congestion/flow control, more importantly, difficulty to deploy on the current Internet infrastructure due to necessity to change many core routers. Recently, end-system multicast (ESM) has been proposed as an alternative solution so that multicasting services can be quickly deployed. In this paper, we consider the'architectural' and 'optimization' issues on designing an ESM-tree. Specifically, we present a distributed algorithm on how to create and maintain an ESM-tree. We propose a distributed algorithm to perform tree optimization (TO) so that an ESM-tree can dynamically adapt to the changing network condition (e.g. drop in transfer bandwidth) so that the nodes within an ESM-tree can receive data more efficiently. The distributed algorithm has the important theoretical properties that at all times, a tree topology can be maintained and any node joining, leaving, as well as any TO operation will not 'partition' the underlying ESM-tree. Therefore, our work can be used to provide an efficient architectural infrastructure for ESM services. We have implemented a prototype ESM system and carried out experiments to illustrate the effectiveness and the performance gains of our ESM optimization protocol.

title: A Distributed Approach to Musical Composition
abstract: Current techniques for automated composition use a single algorithm, focusing on one aspect of musical generation. In our system we make use of several algorithms, distributed using an agent oriented middleware, with each specialising on a separate aspect of composition. This paper describes the architecture and algorithms behind this system, with a focus on the agent framework used for implementation. We show early results which encourage a future application of this framework in automated music composition and analysis.

title: 76-Space analysis of grey matter diffusivity: Methods and applications
abstract: Diffusion Weighted Imaging (DWI) and Diffusion Tensor Imaging (DTI) are widely used in the study and diagnosis of neurological diseases involving the White Matter (WM). However, many neurological and neurodegenerative diseases (e.g., Alzheimer's disease and Creutzfeldt-Jakob disease) are generally considered to involve the Grey Matter (GM). Investigation of GM diffusivity of normal aging and pathological brains has both scientific significance and clinical applications. Most of previous research reports on quantification of GM diffusivity were based on the manually labeled Region of Interests (ROI) analysis of specific neuroanatomic regions. The well-known drawbacks of ROI analysis include inter-rater variations, irreproducible results, tediousness, and requirement of a priori definition of interested regions. In this paper, we present a new framework of automated 76-space analysis of GM diffusivity using DWI/DTI. The framework will be evaluated using clinical data, and applied for study of normal brain, Creutzfeldt-Jakob disease and Schizophrenia.

title: Design patterns for lazy evaluation
abstract: We propose an object-oriented (OO) formulation and implementation of lazy/delayed evaluation by reusing and extending an existing linear recursive structure (LRS) framework with the help of the strategy, decorator and factory design patters. The result is a robust, flexible framework that can handle both infinite and finite lists and to which existing algorithms for finite lists can be applied without modification. The OO techniques used to develop this model are effective tools for teaching abstraction and design of data structures.

title: Spurious modulation on current-mode controlled DC/DC converters: an explanation for intermittent chaotic operation
abstract: We explain the mechanism that causes "intermittent" instability and chaos in a current-mode controlled switching converter. The circuit model used to study the phenomenon incorporates a coupling process through which a spurious signal is coupled to the current sensing and ramp compensation circuitry, resulting in a modulation of the compensation slope which causes the system to become unstable intermittently. We describe a way to find the parameter boundaries where intermittent chaotic operation emerges.

title: Object Assisted Video Coding for Video Conferencing System
abstract: An object-based video coding for video conferencing system is proposed. There are two main processes: segmentation process and face detection process. The segmentation process is used to segment each frame of a video sequence into two non-overlapping regions, namely foreground and background. A novel face detection technique based on chrominance and the contour of the segmented region is applied to the foreground region. Smaller quantization step is used for the facial region to improve viewer's perception while a larger quantization step is used for the background to compensate the coding efficiency. The remaining regions are kept in normal coding quality to prevent degradation of important information other than the facial regio.