We present techniques for synchronizing nodes that periodically broadcast content and presence updates to colocated nodes over an ad hoc network, where nodes may exhibit Byzantine malicious behavior. Instead of aligning duty cycles, our algorithms synchronize the periodic transmissions of nodes. This allows nodes to save battery power by switching off their network cards without missing updates from their neighbors. We propose several novel attack classes and show that they are able to disrupt synchronization even when launched by a single attacker. Finally, we devise a rating based algorithm (RBA) that rates neighbors based on the consistency of their behavior. By favoring well-behaved nodes in the synchronization process, we show that RBA quickly stabilizes the synchronization process and reduces the number of lost updates by 85 percent. Our evaluation also shows that all our algorithms are computationally efficient and, for the setup considered, extend the device lifetime by 30 percent over an always-on Wi-Fi scenario.

In this paper, we present techniques for synchronizing nodes that periodically broadcast content and presence updates to co-located nodes over an ad-hoc network, where nodes may exhibit Byzantine malicious behavior. We first propose an algorithm for synchronizing the periodic transmissions of all the nodes in an attacker-free multi-hop network. This allows nodes to save battery power by switching off their network cards without missing updates from their neighbors. We then introduce a suite of spoofing attacks and show that they are able to disrupt synchronization and destabilize the network even when launched by a single attacker in large, multi-hop networks. Finally, we devise a rating based algorithm that rates neighbors based on the consistency of their behaviors. By favoring well-behaved nodes in the synchronization process, we show that we can address the issue of Byzantine malicious behavior very effectively. Our evaluation shows that the algorithms are computationally efficient and, for the setup considered, extend the device lifetime by 30% over an always-on Wi-Fi scenario. Moreover, in the presence of attacks, our rating based algorithm quickly stabilizes the synchronization process and reduces the number of lost updates by 85%.

Previous work on routing in MANETs has resulted in numerous routing protocols that aim at satisfying constraints such as minimum hop or low energy. Existing routing protocols often fail to discover stable routes between source and sink when route availability is transient, i.e., due to mobile devices switching their network cards into low-power sleep modes whenever no communication is taking place. In this paper, we introduce a stability aware dynamic source routing protocol (SA-DSR) that is capable of predicting the stability (i.e., expiration time) of multiple routes. SA-DSR then selects the route that minimizes hop count while staying available for the expected duration of packet transmission. Comparisons of SA-DSR to the original DSR (Dynamic Source Routing) protocol indicate a significant (up to 60%) increase in route discovery success rate with comparable route establishment and maintenance overheads.

In this paper, we present the design and implementation of a cross-layer framework for evaluating power and performance tradeoffs for video streaming to mobile handheld systems. We utilize a distributed middleware layer to perform joint adaptations at all levels of system hierarchy - applications, middleware, OS, network and hardware for optimized performance and energy benefits. Our framework utilizes an intermediate server in close proximity of the mobile device to perform end-to-end adaptations such as admission control, intelligent network transmission and dynamic video transcoding. The knowledge of these adaptations are then used to drive "on-device" adaptations, which include CPU voltage scaling through OS based soft realtime scheduling, LCD backlight intensity adaptation and network card power management. We first present and evaluate each of these adaptations individually and subsequently report the performance of the joint adaptations. We have implemented our cross-layer framework (called DYNAMO) and evaluated it on Compaq iPaq running Linux using streaming video applications. Our experimental results show that such joint adaptations can result in energy savings as high as 54% over the case where no optimization are used while substantially enhancing the user experience on hand-held systems.

For a typical portable handheld device, the backlight accounts for a significant percentage of the total energy consumption (e.g., around 30% for a Compaq iPAQ 3650). Substantial energy savings can be achieved by dynamically adapting backlight intensity levels on such low- power portable devices. In this paper, we analyze the characteristics of video streaming services and propose an adaptive scheme called Quality Adapted Backlight Scaling (QABS), to achieve backlight energy savings for video playback applications on handheld devices. Specifically, we present a fast algorithm to optimize backlight dimming while keeping the degradation in image quality to a minimum so that the overall service quality is close to a specified threshold. Additionally, we propose two effective techniques to prevent frequent backlight switching, which negatively affects user perception of video. Our initial experimental results indicate that the energy used for backlight is significantly reduced, while the desired quality is satisfied. The proposed algorithms can be realized in real time. I. INTRODUCTION With the widespread availability of 3G cellular networks, mobile hand-held devices are increasingly being designed to support stream- ing video content. These devices have stringent power constraints because they use batteries with finite lifetime. On the other hand, multimedia services are known to be very resource intensive and tend to exhaust battery resources quickly. Therefore, conserving power to prolong battery life is an important research problem that needs to be addressed, specifically for video streaming applications on mobile handheld devices. Most hand-held devices are equipped with a TFT (Thin-Film Transistor) LCD (Liquid Crystal Display). For these devices, the display unit is driven by the illumination of backlight. The backlight consumes a considerable percentage of the total energy usage of the handheld device; it consumes 20%-40% of the total system power (for Compaq iPAQ) (?). Dynamically dimming the backlight is considered an effective method to save energy (?), (?), (?) with scaling up of the pixel luminance to compensate for the reduced fidelity. The luminance scaling, however, tends to saturate the bright part of the picture, thereby affecting the fidelity of the video quality. In (?), a dynamic backlight luminance scaling (DLS) scheme is proposed. Based on different scenarios, three compensation strategies are discussed, i.e., brightness compensation, image enhancement, and context processing. However, their calculation of the distortion does not consider the fact that the clipped pixel values do not contribute equally to the quality distortion. In (?), a similar method, named concurrent brightness and contrast scaling (CBCS), is proposed. CBCS aims at conserving power by reducing the backlight illumi- nation while retaining the image fidelity through preservation of the image contrast. Their distortion definition and proposed compensation technique may be good for static image based applications, such as the graphic user interface (GUI) and maps, but might not be suitable for streaming video scenarios, because their contrast compensation further compromises the fidelity of the images. In addition, neither (?) nor (?) solves the problem associated with frequent backlight switching which can be quite distracting to the end user. In this paper, we explicitly incorporate video quality into the backlight switching strategy and propose a quality adaptive back- light scaling (QABS) scheme. The backlight dimming affects the brightness of the video. Therefore, we only consider the luminance compensation such that the lost brightness can be restored. The lumi- nance compensation, however, inevitably results in quality distortion. For the video streaming application, the quality is normally defined as the resemblance between the original and processed video. Hence, for the sake of simplicity and without loss of generality, we define the quality distortion function as the mean square error (MSE)(see Equation (1)) and the quality function as the peak signal to noise ratio (PSNR)(see Equation (2)), both of which are well accepted objective video quality measurements.

In this paper, we present various challenges that arise in the delivery and exchange of multimedia information to mobile devices. Specifically, we focus on techniques for maintaining QoS to end-user multimedia applications (e.g. video streaming, multimedia conferencing) while maximizing device lifetimes. In order to cope with the resource intensive nature of multimedia applications (in terms of computation, bandwidth and consequently power) and dynamic congestion levels in wireless networks, an end-to-end approach to QoS-aware power optimization is required. We discuss the trend towards such an integrated approach that couples the architectural, OS, middleware and application layers to achieve both user experience and device energy gains. We conclude with a discussion of tools for integrated system design and testing that will aid in rapid deployment of wireless multimedia.

In distributed environments, generic middleware services (e.g. caching, location management etc.) are widely used to satisfy application needs in a cost-effective manner. Such middleware services consume system resources such as storage, computation and communication and can be sources of significant power overheads when executed on low-power devices. We present a distributed middleware framework (PARM), that is inherently power-aware and reconfigures itself to adapt to diminishing power levels of low-power devices. In this paper, we i) determine whether a reconfigurable component-based middleware framework can be utilized to achieve energy gains in low-power devices, while preserving the semantics of the middleware services, ii) present and evaluate a graph theoretic approach for dynamically determining middleware component reconfigurations and ascertaining the optimal frequency at which the restructuring should occur, for maximal energy gains at the device. We use extensive profiling to chart the energy usage patterns of middleware components and applications, and use the profiled data to drive our reconfiguration decisions. Our simulation results demonstrate that our framework is able to save 5% to 35% of energy depending on the nature and class of applications and middleware components used.

Optimizing user experience for streaming video applications on handheld devices is a significant research challenge. In this paper, we propose an integrated power management approach that unifies low level architectural optimizations (CPU, memory, register), OS power-saving mechanisms (Dynamic Voltage Scaling) and adaptive middleware techniques (admission control, optimal transcoding, network traffic regulation). Specifically, we identify interaction parameters between the different levels and optimize them to significantly reduce power consumption. With knowledge of device configurations, dynamic device parameters and changing system conditions, the middleware layer selects an appropriate video quality and fine tunes the architecture for optimized delivery of video. Our performance results indicate that architectural optimizations that are cognizant of user level parameters(e.g. transcoded video quality) can provide energy gains as high as 57.5% for the CPU and memory. Middleware adaptations to changing network noise levels can save as much as 70% of energy consumed by the wireless network interface. Furthermore, we demonstrate how such an integrated framework, that supports tight coupling of inter-level parameters can enhance user experience on a handheld substantially.

With the evolution of the global information infrastructure, service providers will need to provide effective and adaptive resource management mechanisms that can serve more concurrent clients and deal with applications that exhibit quality-of-service (QoS) requirements. Flexible, scalable and customizable middleware can be used as an enabling technology for next-generation systems that adhere to the QoS requirements of applications that execute in highly dynamic distributed environments. To enable application-aware resource management, we are developing a customizable and composable middleware framework called CompOSE|Q (Composable Open Software Environment with QoS), based on a reflective meta-model. In this paper, we describe the architecture and runtime environment for CompOSE|Q and briefly assess the performance overhead of the additional flexibility. We also illustrate how flexible communication mechanisms can be supported efficiently in the CompOSE|Q framework.