Robert N. Mayo

Energy consumption in mobile devices: why future systems need requirements–aware energy scale-down

The current proliferation of mobile devices has resulted in a large diversity of designs, each optimized for a specific application, form-factor, battery life, and functionality (e.g., cell phone, pager, MP3 player, PDA, laptop). Recent trends, motivated by user preferences towards carrying less, have focused on integrating these different applications in a single general-purpose device, often resulting in much higher energy consumption and consequently much reduced battery life. This paper argues that in order to achieve longer battery life, such systems should be designed to include requirements-aware energy scale-down techniques. Such techniques would allow a general-purpose device to use hardware mechanisms and software policies to adapt energy use to the users requirements for the task at hand, potentially approaching the low energy use of a special-purpose device. We make two main contributions. We first provide a model for energy scale-down. We argue that one approach to design scale-down is to use special-purpose devices as examples of power-efficient design points, and structure adaptivity using insights from these design points. To understand the magnitude of the potential benefits, we present an energy comparison of a wide spectrum of mobile devices (to the best of our knowledge, the first study to do so). A comparison of these devices with general-purpose systems helps us identify scale-down opportunities. Based on these insights, we propose and evaluate three specific requirements-aware energy scale-down optimizations, in the context of the display, wireless, and CPU components of the system. Our optimizations reduce the energy consumption of their targeted subsystems by factors of 2 to 10 demonstrating the importance of energy scale-down in future designs.

Controlling who tracks me

Many Ubiquitous Computing applications require tags and sensors that track the daily activates of people and things. For example, tags might be placed on objects to allow a system to remind people of the object’s location. In another application, caretakers of the elderly may wish to monitor the daily activities of those under their care, in order to track decline in functioning and offer appropriate medical care. These forms of tracking, however, raise privacy concerns. A person does not want to be tracked by everybody, but rather only by those that are trusted and only during certain times. We present a method of building tags and tracking devices that ensure a person is tracked only by those that have been granted that right, and only during the times specified.

Controlling who tracks me (transcript of discussion)

Our group is looking for applications in everyday life that involve information processing. Not Internet connected things, not things that are on the network, but things that are in everyday life. For instance, you may forget to buy milk; that’s an information processing problem. If your car gets a flat tyre, that’s probably not an information processing problem, but there may be information processing that can assist you. One basic idea is to track your daily activities for your personal benefit. For instance, you may use devices that give you location awareness, or detect categories in your daily routine. If every Tuesday you throw your laundry in the car and go to the dry cleaners, then a device could conceivably detect this, and if on Tuesday morning it finds you in your car and you don’t have your laundry with you, it lets you know, beep, and tells you that something’s different; and you can either choose to ignore it or run back and get your laundry.

Updating Encrypted XML Documents on Untrusted Machines

With XML and other data types becoming increasingly used in distributed systems, we have a need to update this data in a way that preserves privacy and integrity. Prior work has developed ways of encrypting XML documents for privacy, and adding integrity codes to ensure that the data is not tampered with. In this paper we present an algorithm that allows XML documents, or other tree-structured data, to be updated without decrypting them. In our model of a distributed system, several trusted machines have access to the decrypted form of a document and may request changes to it. These change requests are encrypted and sent to an untrusted update machine for processing. The update machine is able to take the original encrypted document, apply the encrypted changes, and produce an updated encrypted document. In addition, an integrity code is produced that proves the untrusted machine performed the update correctly. In practice, our algorithm allows trusted machines in a distributed system to send incremental updates to a storage server, even if that server is not allowed access to the clear text.