BYU Mobile Computing Lab

With the proliferation of mobile applications and the abundance of wireless devices, it is increasingly common for devices to support multiple radios. When two devices are communicating they should choose the best available radio based on user preference and application requirements. This type of “radio switching” should happen automatically, so that the system optimizes performance dynamically. To achieve this objective, we design an Autonomous and Intelligent Radio Switching (AIRS) system to leverage the radio heterogeneity common in today’s wireless devices. The AIRS system consists of three key components. First, we design a radio preference evaluation module to dynamically select the best radio according to users’ preference, application’s QoS requirements, and the device battery usage. Second, we propose a link quality measurement and prediction module to predict the radio quality under a variety of mobility and interference conditions. Third, we present a radio switching decision making module to switch to the preferred available radio intelligently, based on the preference and link quality evaluations. The AIRS system maintains connectivity, as well as improves link quality, via dynamic and intelligent radio switching, regardless of interference or collisions from the interfaces of other devices. The radio preference evaluation module is able to generate and adjust a preference list dynamically. Multiple users’ requirements are satisfied in a mutually beneficial manner and the selected radio is Pareto optimal. The link prediction module is able to achieve an accuracy above 90% under a variety of mobility and interference conditions. The module can dynamically increase the link measurement interval and significantly reduce its power consumption, without sacrificing accuracy. The decision algorithm uses several parameters to avoid switching radios too frequently, and is able to provide dynamic, but stable radio switching, while balancing the competing objectives of high throughput and low power consumption. Overall, the AIRS system is able to achieve high goodput (application level throughput) and long battery life as applied to handoff management in a frequently changing mobile environment.

As wireless devices continue to become more prevalent, heterogeneous wireless networks - in which communicating devices have at their disposal multiple types of radios - will become the norm. Communication between nodes in these networks ought to be as simple as possible; they should be able to seamlessly switch between different radios and network stacks on the fly in order to better serve the user. To make this a possibility, we consider the challenging problems of when two communicating devices should decide to switch to a different radio, and which radio they should choose. We design an autonomous and intelligent radio switch (AIRS) decision algorithm that uses predicted radio availability and user profiles to choose the best available radio for two adjacent devices. The decision algorithm uses several parameters to avoid switching radios too frequently. We use a simulation study to evaluate the best settings for several parameters, then show that the AIRS system performs better than several alternative algorithms. AIRS is able to provide dynamic, but stable radio switching, while balancing the competing objectives of high throughput and low power consumption.

Communication between wireless devices ought to be as simple as possible; they should be able to seamlessly switch between different radios and network stacks on the fly in order to better serve the user. To make this a possibility, we consider the challenging problem of predicting link quality in a changing mobile environment. In this paper we present an algorithm that uses Weighted Least Squares Regression to predict whether a given link can meet application requirements in terms of throughput, delay, and jitter. We use a simulation study to demonstrate that our algorithm is able to predict link quality accurately and stably in a frequently changing mobile environment. The prediction algorithm is more accurate than several alternative algorithms, and the overhead caused by the link measurements is negligible in terms of throughput and power consumption.

Devices with multiple wireless interfaces are becoming increasingly popular. We envision that these devices will become the building block for future mesh networks, providing seamless connectivity across a range of heterogeneous devices. Although these devices typically implement frequency sharing, using either direct sequence spread spectrum (DSSS) or frequency hopping spread spectrum (FHSS), they may still interfere with one another. In this paper we provide a novel radio interference avoidance (RIA) algorithm that solves the problem of interference between IEEE 802.11 and Bluetooth. We then extend this algorithm to other types of DSSS and FHSS combinations. Though the algorithm is limited to devices with both of these interfaces, this is a very common case. We analytically derive the expected value of the response time for RIA and run simulations to demonstrate its effectiveness. Our results indicate that RIA is able to eliminate interference with a very short response time. RIA also outperforms adaptive frequency hopping, a solution proposed by the IEEE 802.15 co-existence working group.

Multi-transport devices are becoming more common, but sophisticated software is needed to fully realize the advantages of these devices. In this paper, we examine the performance of dynamic transport switching, which selects the best available transport for communication between two devices. We simulate transport switching within the Quality of Transport (QoT) architecture and show that it can effectively mitigate the effects of congestion and interference for connections between two multi-transport devices. We then evaluate dynamic transport switching overhead to characterize its effect on application throughput. Based on these insights, we identify several limitations of the QoT architecture and present solutions to improve performance.

Wireless communication is increasingly ubiquitous. However, mobility depends intrinsically on battery life. Power can be conserved at the Media Access Control (MAC) layer by intelligently adjusting transmission power level and data rate encoding. WirelessUSB is a low-latency wireless technology developed by Cypress Semiconductor Corporations for human interface devices such as keyboards and mice. WirelessUSB devices conserve power by employing power-efficient hardware, dynamic power level adjustment and dynamic data rate adjustment. We characterize the effects on power consumption of dynamically adjusting mode power using two dynamic power negotiation techniques. We also characterize the effects of dynamically adjusting data rate using three rate adjustment techniques. We further characterize the effects of collaboratively adjusting both power and data rate we validate our techniques through simulation and find that such collaboration yields the greatest energy conservation for a wide variety of conditions and usage models.

Computing devices are commonly equipped with multiple transport technologies such as IrDA, Bluetooth and WiFi. Transport switching technologies, such as Quality of Transport (QoT), take advantage of this heterogeneity to keep network sessions active as users move in and out of range of various transports or as the networking environment changes. Autonomous transport switching technologies rely on information regarding current network status and the ambient wireless environment in order to make intelligent decisions. This thesis proposes Brand X, a cross-layer architecture designed for a QoT environment to provide timely and accurate environment information in order to facilitate autonomous transport switching. This thesis also presents a performance analysis of network protocol stack latency in a QoT environment considering the various cross-layer mechanisms utilized in Brand X and other architectures.

Transport selection mechanisms are designed to facilitate seamless connectivity in heterogeneous multi-transport environments, allowing access to the "best" available transport according to user requirements. Evaluating transport configurations dynamically according to the user's preferences and quality of service (QoS) requirements is a challenging task. This paper describes a quantitative approach that applies the Utility Theorem and Nash's Bargaining solution to heterogeneous wireless environments. The mathematical model presented generates and adjusts the transport preference list dynamically depending on the degree to which a transport satisfies user preferences and the application's QoS requirements. We incorporate a negotiation engine using the axiomatic multi-transport bargaining algorithm to integrate local and remote users' requirements in a mutually beneficial manner as devices are connected via a peer-to-peer link. The transport selection model discussed in this paper is computationally light with modest communication overhead, making it suitable for mobile devices

My thesis will demonstrate that Rate Adaptive Runlength Limited encoding (RA-RLL) achieves high data rates with acceptable error rate over a wide range of signal distortion/attenuation, and background noise. RA-RLL has performance superior to other infrared modulation schemes in terms of bandwidth e±ciency, duty cycle control, and synchronization frequency. Rate adaptive techniques allow for quick convergence of RA-RLL parameters to acceptable values. RA-RLL may be feasibly implemented on systems with non-ideal timing and digital synchronization.

A model for determining the performance of 11Mbps 802.11b in the presence of Bluetooth signals is presented. A summary of the different factors that can impact performance is presented. Analysis and experimentation are performed to determine which of these factors are relevant and should be included in the mode. Based on these factors, a model that operates in the ISMulator simulation environment is presented. Simulation results are compared with actual measurements to verify the model.

Mobile wireless PANs demonstrate the importance of matching the right usage model to the most appropriate technology.

We examine several architectures for extending the nascent technology of automated trust negotiation to bring nonidentity-based authentication and authorization to mobile devices. We examine how the location of trust agents and secure repositories affects such a system. We also present an implementation of one of these models. This protocol leverages software proxies, autonomous trust agents, and secure repositories to allow portable devices from different security domains (i.e., with no pre-existing relationship) to establish trust and perform secure transactions. This proposed system is called surrogate trust negotiation as the sensitive and resource-intense tasks of authentication are performed vicariously for the mobile device by a surrogate trust agent.

Computing devices are commonly equipped with multiple transport technologies such as IrDA, Bluetooth and WiFi. Transport switching technologies, such as Quality of Transport (QoT), take advantage of this heterogeneity to keep network sessions active as users move in and out of range of various transports or as the networking environment changes. During an active session, the goal is to keep the device connected over the best transport currently available. To accomplish that, this thesis introduces a two-phase decision making protocol. In phase one, intra-device prioritization, users indicate the relative importance of criteria such as speed, power, service charge, or signal range through a comprehensive user interface. QoT-enabled devices process this information with the prioritized soft constraint satisfaction (PSCS) scoring function to ascertain the transport that best meets the user's needs. The second phase, interdevice negotiation, facilitates two QoT-enabled devices in agreeing to a united selection of the best transport. This phase uses a modifed version of the PSCS scoring function based on the preferences of both users. Additionally, devices may utilize multiple transports simultaneously to more accurately meet user demands. The PSCS scoring function considers pairs of transports and calculates the ratio that will yield the desired performance. Another set of functions, also presented in this thesis, is then used to accomplish the desired performance level despite the potential introduction of additional overhead.

Standards from the Infrared Data Association today permit tens of millions of users to easily beam items between handheld devices. Professionals beam business cards from PDA to cell phone. School children wirelessly exchange games at recess. Shoppers make purchases at grocery stores by pointing a handheld device at point of sale terminal. The "point and shoot" ease of IrDA technology has made the small dark plastic window an ubiquitous feature on devices of all kinds, including laptops, cell phones, PDAs, printers, wristwatches and digital cameras. IrDA Principles and Protocols is the first definitive book on the standards of the Infrared Data Association, providing an accessible overview of the technology for novices, while delivering the most relevant technical details for experts.

This paper presents prioritized soft constraint satisfaction (PSCS), a novel approach to selecting the ''best" transport in dynamic wireless transport switching systems. PSCS maintains a satisfying connection to another end point by choosing transports based on a user-established range of preferences and priority for criteria such as speed, power, range and cost. Additionally, feedback is provided regarding tradeoffs among the criteria, thus enabling the user to adjust inputs according to the capabilities of the system. We also recommend guidelines for setting preferences and priorities.

In this paper, we introduce quality of transport (QoT), an architecture for synergistically and autonomously managing session-layer protocol access to multiple transports in heterogeneous wireless environments. We present an overview of the QoT architecture including: 1) transport discovery, 2) service discovery, 3) object exchange, 4) transport switching, and 5) intelligent transport selection. Preliminary successes with our design and implementation of QoT suggest that dynamic intelligent autonomous transport switching can help to optimize user experience and session layer performance in multi-transport environments.

This paper demonstrates that careful tuning of the OBEX and IrLAP negotiated parameters allows OBEX to scale well for use with large data objects and high transmission rates. Due to the substantial time overhead inherent in link turnarounds, minimizing turnarounds during the transmission of a large object helps to maximize link efficiency. The IrLAP window size and OBEX packet size significantly impact the number of required turnarounds during the transmission of a large object. When these parameters are properly tuned, maximum throughput can be achieved, and OBEX performs efficiently at high data rates.

The expanding availability of health information in an electronic format is strategic for industry-wide efforts to improve the quality and reduce the cost of health care. The implementation of electronic medical record systems has been hindered by inadequate security provisions. This paper describes the use of trust negotiation as a framework for providing authentication and access control services in healthcare information systems. Trust negotiation enables two parties with no preexisting relationship to establish the trust necessary to perform sensitive transactions via the mutual disclosure of attributes contained within digital credentials. An extension of this system, surrogate trust negotiation is introduced as a way to meet the security requirements of healthcare delivery systems based on mobile computing devices and wireless communication technologies. These innovative technologies have enormous potential to improve the current state of security in healthcare information systems.

Despite recent improvements in the gathering and sharing of patient medical information among healthcare providers, there remains a gap in the electronic medical record infrastructure. Patient data is not available in some situations, either because the infrastructure is inaccessible (as in a natural disaster) or because there is no way to link the patient to the infrastructure (e.g., the patient cannot supply necessary identification information). This thesis introduces a system that allows an individual to carry personal electronic medical information on a wireless handheld debvice such as a smart card, cell phone, or PDA. Medical workers can obtain this information wirelessly using handheld devices, desktop computers, network access points, etc. In this way, patients may become a more integral part of the medical information infrastructure, facilitating better delivery of medical care.

Despite recent improvements in the gathering and sharing of patient medical information among healthcare providers, there remains a gap in the electronic medical record infrastructure. Patient data is not available in some situations, either because the infrastructure is inaccessible (as in a natural disaster) or because there is no way to link the patient to the infrastructure (e.g., the patient cannot supply necessary identification information). We describe the Poket Doktor System, an architecture that allows an individual to carry personal electronic medical information on a wireless handheld device such as a smart card, cell phone, or PDA. Medical workers can obtain this information wirelessly using handheld devices, desktop computers, network access points, etc. In this way, patients play an active role in the medical information infrastructure, resulting in a better healthcare delivery system.

The Poket Doktor is a wireless personal healthcare system that can obtain accurate patient medical information in situations where it may not otherwise be available. The system is designed to provide a flexible, scalable method of storing and communicating critical electronic medical record information using personal handheld electronic devices. The first phase of development has succeeded in: designing the architecture for a wireless, power-efficient smart card to store and communicate medical information incorporating Bluetooth wireless technology with radiofrequency identification wakeup on the smart card to enable a fast wireless connection to a healthcare provider's device; and selecting a platform and creating application software for a handheld computing device used by healthcare providers. The Poket Doktor system assists medical personnel in obtaining accurate patient medical information in situations where it may not otherwise be available. In this manner, Poket Doktor technology will improve the quality of care delivered in emergency situations.

Significant efforts are being made to improve methods for gathering and sharing patient medical information among healthcare providers. Key to the success of these efforts is the active participation of the patient in the Electronic Medical Information Infrastructure (EMII). By equipping patients with personal electronic devices containing electronic medical records, medical workers can obtain information wirelessly using handheld devices, desktop computers, network access points, etc. The proliferation of mobile computing devices along with the increasingly widespread use of wireless data communications technologies make it possible to achieve this vision of a “patient-centric” EMII. This thesis discusses the architecture and design of a wireless power-efficient smart card that operates with an EMII. This device incorporates a power savings module to extend battery life of resource limited mobile electronic devices. Detail of the implementation and analysis of the power savings module are included in this thesis. Also included are the requirements for and implementation details of healthcare provider software which enables communication with the smart card. Finally, the roles and requirements of the patient and healthcare provider devices are discusses as they relate to the broader EMII.

In order to utilize multiple transports, devices must discover common mechanisms for communication, a procedure we call multi-transport discovery. The multi-transport discovery algorithm presented in this paper is a four-phase procedure (transport probing, transport querying, address-to-device mapping, and transport accessibility) that can discover common transports within a multi-transport environment. Transport probing uses a transport-dependent device discovery mechanism to discover an initial link. Transport querying communicates over the probed link to query additional transports. Address-to-device mapping correctly correlates each transport to a remote device. Finally, transport accessibility periodically ascertains link availability during an application session.

This paper describes a mechanism for utilizing inverse multiplexing to significantly increase the bandwidth available to short-range wireless devices. Previous work with inverse multiplexing has focused on wired networks; its implementation with short-range wireless transports introduces heterogeneity in the links, which must be taken into account. A mathematical model for an inverse multiplexing system is derived for several scheduling algorithms. Both process limited and transport limited systems are examined. The validity of this model is shown by our implementation of an inverse multiplexing layer that uses IrDa and Bluetooth transports. Concepts related to inverse multiplexing such as usage models, negotiation, quality of service, and the simultaneous use of multiple Bluetooth transports are discussed.

Many wireless transports are available in mobile devices today including 802.11b, Bluetooth, IrDA, cellular data, and a host of others, with more wireless transports emerging every year. Although many handheld devices support multiple communication transports, there is little if any interoperability between them, leaving transports isolated from each other even when residing in the same device. This normal forces a user to actively decide which transport to use for each connection. If conditions change, the user may be required to disconnect the transport and start a new connection over a different transport. This thesis presents Quality of Transport (QoT), a network abstraction layer that allows transparent and dynamic transport switching in wireless personal area networks (WPANs).

The rapid proliferation of short-range wireless technologies such as 802.11b and Bluetooth in industrial, scientific, and medical radio frequency bands suggests an impending digital traffic jam. Wireless communication technologies utlize various signal encoding schemes (such as direct sequence spread spectrum and frequency hopping spread spectrum) and involve heterogeneous transport topologies. In addition, noise-emitting devices (such as microwave ovens) create interference in these bands. IN order to effectively model heterogeneous interference in industrial, scientific, and medical bands, we present the design and architecture of ISMulator, a frequency band simulation framework to model, analyze, and quantify the traffic and interference in industrial, scientific, and medical radio frequency bands.

In order for existing applications to use multiple transports for data communication, devices must (1) discover common mechanisms for communication and (2) handle application set up procedures that incorporate transport-specific service discovery protocols. The Multi-Transport Discovery algorithm presented in this thesis is a four-phase procedure (Transport Probing, Transport Querying, Address-to-Device Mapping, and Transport Accessibility) that can discover common transports within a multi-transport environment. Service discovery tunneling is conjunction with the Quality of Transport (QoT) architecture provides a solution for untethering service to operate over arbitrary transports, enabling initial application setup procedures to be transport independent.

In resource-limited mobile computing devices, Bluetooth wireless technology imposes a weighty burden due to inefficient power utilization and a sluggish device discovery process. Buttressing Bluetooth with radiofrequency identification (RFID) technology by performing an operation we call "Rendez-Blue" alleviates these limitations. In the Rendez-Blue process, an RFID signal is used as a cue to "wake-up" a sleeping Bluetooth radio. This ensures that the Bluetooth radio is active only when needed, significantly reducing power consumption. In addition, RFID is used to communicate Bluetooth device information, allowing the user to bypass the traditional 10.24-second discovery process.

Bluetooth is a recently developed technology that uses radio frequency transceivers to provide point-to-multipoint wireless connectivity within a personal space. Bluetooth was designed for both voice and data communication at low per-unit costs while consuming little power. This paper describes how Bluetooth is helping to usher in a new era of short-range wireless connectivity. As transceiver costs decline and handheld computing devices proliferate, Bluetooth is well positioned to bring significant value to a wide variety of users.

This paper discusses an alternate approach for the Transport Querying phase wihin the Multi-Transport Discovery Algorithm. The prurpose of the algorithm is to assist dynamic transport switching architectures in ascertaining mutual transport support between communication devices. The Multi-Transport Discovery algorithm is a four-phase procedure (Transport Probing, Trasport, Querying, Address-to-Device Mapping, and Transport Accessibility) that can discover common transports within a multi-transport environment. Transport Probing uses a transport-dependent device discovery mechanism to discover an initial link. Transport Querying communicates over the probed link to query for additional transports. Address-to-Device Mapping correctly correlates each transport to a remote device. Finally Transport Accessibiity pericodially ascertains link availability dring an application session.

As infrared (IR) bandwidth increases, the physical limitations of optical components and receiving circuitry require the use of modulation codes with lower bandwidth efficiency. The hardware-imposed constraints on modulation codes may be expressed as Runlength Limited (RLL) encoding parameters. A method for determining the Shannon capacity for RLL encoding given various constraints is introduced. This method is used to evaluate the efficiency of the HHH(1,13) modulation code used in Very Fast Infrared (VFIR). It is also used to explore optimal density ratios. This work has application in evaluating future modulation codes for high bandwidth IR channels.

Bluetooth device discovery is a time-intensive phase of the Bluetooth connection-establishment procedure. In this paper we propose a technique that integrates existing IrDA technology with Bluetooth technology to improve the ad hoc connection establishment time of Bluetooth devices. We accomplish this improvement by first establishing an IrDA connection between two devices equipped with both Bluetooth and IrDA capabilities and then exchanging Bluetooth device discovery information via the established IrDA connection. As a result of this cooperative exchange, the devices are able to bypass the time-intensive Bluetooth device discovery procedure. Our research shows that IrDA-assisted Bluetooth connection establishment is up to four times faster than the normal ad hoc Bluetooth connection establishment procedure. In addition, it provides other time-savings in subsequent device selection procedures.

The Infrared Data Association's (IrDA) infrared data transmission protocol is a widely used mechanism for short-range wireless data communications. In order to provide flexibility for connections between devices of potentially disparate capabilities, IrDA devices negotiate the values of several transmission parameters based on the capabilities of the devices establishing the connection. This paper describes the design and implementation of a software tool, Irdaperf, to model IrDA performance based on negotiated transmission parameters. Using Irdaperf, we demonstrate that for fast data rates, maximizing the window size and data size are key factors for overcoming the negative effects of a relatively long link turnaround time. At slower speeds (especially 115.2 Mbps and below), these factors have a less pronounced effect

IrDA infrared communication is an inexpensive and widely adopted short-range wireless technology that allows devices to "speak" easily to each other. Key protocol features make operation simple even for inexperienced users or devices with very little user interface. Digital cameras, phones, pagers, data collectors, set-top boxes, modems, kiosks, instruments, machinery, ID badges, watches, and computer peripherals are some of the natural users of this technology. This paper introduces IrDA infrared data communications and explores both mandatory and optional IrDA protocol layers and strategies.