Ardalan Amiri Sani

Directional antenna diversity for mobile devices: characterizations and solutions

We report a first-of-its-kind realization of directional transmission for smartphone-like mobile devices using multiple passive directional antennas, supported by only one RF chain. The key is a multi-antenna system (MiDAS) and its antenna selection methods that judiciously select the right antenna for transmission. It is grounded by two measurement-driven studies regarding 1) how smartphones rotate during wireless usage in the field and 2) how orientation and rotation impact the performance of directional antennas under various propagation environments. We implement MiDAS and its antenna selection methods using the WARP platform. We evaluate the implementation using a computerized motor to rotate the prototype according to traces collected from smartphone users in the field. Our evaluation shows that MiDAS achieves a median of 3dB increase in link gain. We demonstrate that rate adaptation and power control can be combined with MiDAS to further improve goodput and power saving. Real-time experiments with the prototype show that the link gain translates to 85% goodput improvement for a low SNR scenario. The same gain translates to 51% transmit power reduction for a high SNR scenario. Compared to other methods in realizing directional communication, MiDAS does not require any changes to the network infrastructure, and is therefore suitable for immediate or near-future deployment.

Video: Rio: a system solution for sharing i/o between mobile systems

Mobile systems are equipped with a diverse collection of I/O devices, including cameras, microphones, sensors, and modems. There exist many novel use cases for allowing an application on one mobile system to utilize I/O devices from another. This paper presents Rio, an I/O sharing solution that supports unmodified applications and exposes all the functionality of an I/O device for sharing. Rios design is common to many classes of I/O devices, thus significantly reducing the engineering effort to support new I/O devices. Our implementation of Rio on Android consists of about 7100 total lines of code and supports four I/O classes with fewer than 500 class-specific lines of code. Rio also supports I/O sharing between mobile systems of different form factors, including smartphones and tablets. We show that Rio achieves performance close to that of local I/O for audio devices, sensors, and modem, but suffers noticeable performance degradation for camera due to network throughput limitations between the two systems, which is likely to be alleviated by emerging wireless standards.

I/o paravirtualization at the device file boundary

Paravirtualization is an important I/O virtualization technology since it uniquely provides all of the following benefits: the ability to share the device between multiple VMs, support for legacy devices without virtualization hardware, and high performance. However, existing paravirtualization solutions have one main limitation: they only support one I/O device class, and would require significant engineering effort to support new device classes and features. In this paper, we present Paradice, a solution that vastly simplifies I/O paravirtualization by using a common paravirtualization boundary for various I/O device classes: Unix device files. Using this boundary, the paravirtual drivers simply act as a class-agnostic indirection layer between the application and the actual device driver. We address two fundamental challenges: supporting cross-VM driver memory operations without changes to applications or device drivers and providing fault and device data isolation between guest VMs despite device driver bugs. We implement Paradice for x86, the Xen hypervisor, and the Linux and FreeBSD OSes. Our implementation paravirtualizes various GPUs, input devices, cameras, an audio device, and an Ethernet card for the netmap framework with ~7700 LoC, of which only ~900 are device class-specific. Our measurements show that Paradice achieves performance close to native for different devices and applications including netmap, 3D HD games, and OpenCL applications.

The wireless data drain of users, apps, & platforms

Cellular data consumption is an important issue for users and network operators. However, little is understood about data consumption differences between similar apps, smartphone platforms, and different classes of users. We examine data consumption behavior in the lab, comparing different apps of the same category, comparing the same top apps across different platforms, and comparing network APIs that apps use across different platforms. We also collect data from 387 Android users in India, where users pay for cellular data consumed, with little prevalence of unlimited data plans. Our findings can inform users on how their choice of platform and apps has a drastic impact on their data bill. Our findings can also inform operators on how to use incentives to induce desired data consumption.

SchrodinText: Strong Protection of Sensitive Textual Content of Mobile Applications

Many mobile applications deliver and show sensitive and private textual content to users including messages, social network posts, account information, and verification codes. All such textual content must only be displayed to the user but must be strongly protected from unauthorized access in the device. Unfortunately, this is not the case in mobile devices today: malware that can compromise the operating system, e.g., gain root or kernel privileges, can easily access textual content of other applications. In this paper, we present SchrodinText, a system solution for strongly protecting the confidentiality of applications selected UI textual content from a fully compromised operating system. SchrodinText leverages a novel security monitor based on two hardware features on modern ARM processors: virtualization hardware and TrustZone. Our key contribution is a set of novel techniques that allow the operating system to perform the text rendering without needing access to the text itself, hence minimizing the Trusted Computing Base (TCB). These techniques, collectively called oblivious rendering, enable the operating system to rasterize and lay out all the characters without access to the text; the monitor only resolves the right character glyphs onto the framebuffer observed by the user and protects them from the operating system, e.g., against DMA attacks. We present our prototype using an ARM Juno development board and Android operating system. We show that SchrodinText incurs noticeable overhead but that its performance is usable.

Power-efficient directional wireless communication on small form-factor mobile devices

Wireless access is known to be power-hungry for mobile devices. A key reason is that devices radiate power in all directions and much of this power will not reach the destination. To address this waste, we present BeamSwitch, a multi-antenna system designed to realize directional communication efficiently. Unlike power-hungry and expensive beamforming, BeamSwitch requires only one transceiver. We provide an 802.11-compliant design and prototype of BeamSwitch. Our measurements show that with three passive directional antennas, BeamSwitch reduces the power consumption of a commercial 802.11 adapter by up to 20% and provide better quality under diverse propagation environments and extreme rotation.

Eliminating State Entanglement with Checkpoint-based Virtualization of Mobile OS Services

Mobile operating systems have adopted a service model in which applications access system functionality by interacting with various OS Services in separate processes. These interactions cause application-specific states to be spread across many service processes, a problem we identify as state entanglement. State entanglement presents significant challenges to a wide variety of computing goals: fault isolation, fault tolerance, application migration, live update, and application speculation. We propose CORSA, a novel virtualization solution that uses a lightweight checkpoint/restore mechanism to virtualize OS Services on a per-application basis. This cleanly encapsulates a single applications service-side states into a private virtual service instance, eliminating state entanglement and enabling the above goals. We present empirical evidence that our ongoing implementation of CORSA on Android is feasible with low overhead, even in the worst case of high frequency service interactions.

Ultra-compact multipass laser absorption spectroscopy platform for distributed sensor networks

A prototype three-node wireless sensor network of portable, battery-powered spectroscopic trace-gas sensors equipped with custom 24-pass Herriott cells has been developed. Individual sensor performance and sensor network localization of a gas plume will be reported.

Ditio: Trustworthy Auditing of Sensor Activities in Mobile & IoT Devices

Mobile and Internet-of-Things (IoT) devices, such as smartphones, tablets, wearables, smart home assistants (e.g., Google Home and Amazon Echo), and wall-mounted cameras, come equipped with various sensors, notably camera and microphone. These sensors can capture extremely sensitive and private information. There are several important scenarios where, for privacy reasons, a user might require assurance about the use (or non-use) of these sensors. For example, the owner of a home assistant might require assurance that the microphone on the device is not used during a given time of the day. Similarly, during a confidential meeting, the host needs assurance that attendees do not record any audio or video. Currently, there are no means to attain such assurance in modern mobile and IoT devices. To this end, this paper presents Ditio, a system approach for auditing sensor activities. Ditio records sensor activity logs that can be later inspected by an auditor and checked for compliance with a given policy. It is based on a hybrid security monitor architecture that leverages both ARMs virtualization hardware and TrustZone. Ditio includes an authentication protocol for establishing a logging session with a trusted server and a formally verified companion tool for log analysis. Ditio prototypes on ARM Juno development board and Nexus 5 smartphone show that it introduces negligible performance overhead for both the camera and microphone. However, it incurs up to 17% additional power consumption under heavy use for the Nexus 5 camera.

Sugar: Secure GPU Acceleration in Web Browsers

Modern personal computers have embraced increasingly powerful Graphics Processing Units (GPUs). Recently, GPU-based graphics acceleration in web apps (i.e., applications running inside a web browser) has become popular. WebGL is the main effort to provide OpenGL-like graphics for web apps and it is currently used in 53% of the top-100 websites. Unfortunately, WebGL has posed serious security concerns as several attack vectors have been demonstrated through WebGL. Web browsers» solutions to these attacks have been reactive: discovered vulnerabilities have been patched and new runtime security checks have been added. Unfortunately, this approach leaves the system vulnerable to zero-day vulnerability exploits, especially given the large size of the Trusted Computing Base of the graphics plane. We present Sugar, a novel operating system solution that enhances the security of GPU acceleration for web apps by design. The key idea behind Sugar is using a dedicated virtual graphics plane for a web app by leveraging modern GPU virtualization solutions. A virtual graphics plane consists of a dedicated virtual GPU (or vGPU) as well as all the software graphics stack (including the device driver). Sugar enhances the system security since a virtual graphics plane is fully isolated from the rest of the system. Despite GPU virtualization overhead, we show that Sugar achieves high performance. Moreover, unlike current systems, Sugar is able to use two underlying physical GPUs, when available, to co-render the User Interface (UI): one GPU is used to provide virtual graphics planes for web apps and the other to provide the primary graphics plane for the rest of the system. Such a design not only provides strong security guarantees, it also provides enhanced performance isolation.