Browsing by Author "Murphy, Patrick"

Now showing 1 - 19 of 19
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    Architectures for Cognitive Radio Testbeds and Demonstrators – An Overview
    (IEEE, 2010-06-01) Gustafsson, Oscar; Amiri, Kiarash; Andersson, Dennis; Blad, Anton; Bonner, Christian; Cavallaro, Joseph R.; Declerck, Jeroen; Dejonghe, Antoine; Eliardsson, Patrik; Glasse, Miguel; Hayar, Aawatif; Hollevoet, Lieven; Hunter, Chris; Joshi, Madhura; Kaltenberger, Florian; Knopp, Raymond; Le, Khanh; Miljanic, Zoran; Murphy, Patrick; Naessens, Frederik; Nikaein, Navid; Nussbaum, Dominique; Pacalet, Renaud; Raghavan, Praveen; Sabharwal, Ashutosh; Sarode, Onkar; Spasojevic, Predrag; Sun, Yang; Tullberg, Hugo M.; Vander Aa, Tom; Van der Perre, Liesbet; Wetterwald, Michelle; Wu, Michael; Center for Multimedia Communication
    Wireless communication standards are developed at an ever-increasing rate of pace, and significant amounts of effort is put into research for new communication methods and concepts. On the physical layer, such topics include MIMO, cooperative communication, and error control coding, whereas research on the medium access layer includes link control, network topology, and cognitive radio. At the same time, implementations are moving from traditional fixed hardware architectures towards software, allowing more efficient development. Today, field-programmable gate arrays (FPGAs) and regular desktop computers are fast enough to handle complete baseband processing chains, and there are several platforms, both open-source and commercial, providing such solutions. The aims of this paper is to give an overview of five of the available platforms and their characteristics, and compare the features and performance measures of the different systems.
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    Breakdown of Boltzmann-type models for the alignment of self-propelled rods
    (Elsevier, 2024) Murphy, Patrick; Perepelitsa, Misha; Timofeyev, Ilya; Lieber-Kotz, Matan; Islas, Brandon; Igoshin, Oleg A.; Bioengineering; Biosciences; Chemistry; Center for Theoretical Biological Physics
    Studies in the collective motility of organisms use a range of analytical approaches to formulate continuous kinetic models of collective dynamics from rules or equations describing agent interactions. However, the derivation of these kinetic models often relies on Boltzmann’s “molecular chaos” hypothesis, which assumes that correlations between individuals are short-lived. While this assumption is often the simplest way to derive tractable models, it is often not valid in practice due to the high levels of cooperation and self-organization present in biological systems. In this work, we illustrated this point by considering a general Boltzmann-type kinetic model for the alignment of self-propelled rods where rod reorientation occurs upon binary collisions. We examine the accuracy of the kinetic model by comparing numerical solutions of the continuous equations to an agent-based model that implements the underlying rules governing microscopic alignment. Even for the simplest case considered, our comparison demonstrates that the kinetic model fails to replicate the discrete dynamics due to the formation of rod clusters that violate statistical independence. Additionally, we show that introducing noise to limit cluster formation helps improve the agreement between the analytical model and agent simulations but does not restore the agreement completely. These results highlight the need to both develop and disseminate improved moment-closure methods for modeling biological and active matter systems.
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    Cell behaviors underlying Myxococcus xanthus aggregate dispersal
    (American Society for Microbiology, 2023) Murphy, Patrick; Comstock, Jessica; Khan, Trosporsha; Zhang, Jiangguo; Welch, Roy; Igoshin, Oleg A.; Bioengineering; Biosciences; Chemistry; Center for Theoretical Biological Physics
    The soil bacterium Myxococcus xanthus is a model organism with a set of diverse behaviors. These behaviors include the starvation-induced multicellular development program, in which cells move collectively to assemble multicellular aggregates. After initial aggregates have formed, some will disperse, with smaller aggregates having a higher chance of dispersal. Initial aggregation is driven by two changes in cell behavior: cells slow down inside of aggregates and bias their motion by reversing direction less frequently when moving toward aggregates. However, the cell behaviors that drive dispersal are unknown. Here, we use fluorescent microscopy to quantify changes in cell behavior after initial aggregates have formed. We observe that after initial aggregate formation, cells adjust the bias in reversal timings by initiating reversals more rapidly when approaching unstable aggregates. Using agent-based modeling, we then show dispersal is predominantly generated by this change in bias, which is strong enough to overcome slowdown inside aggregates. Notably, the change in reversal bias is correlated with the nearest aggregate size, connecting cellular activity to previously observed correlations between aggregate size and fate. To determine if this connection is consistent across strains, we analyze a second M. xanthus strain with reduced levels of dispersal. We find that far fewer cells near smaller aggregates modified their bias. This implies that aggregate dispersal is under genetic control, providing a foundation for further investigations into the role it plays in the life cycle of M. xanthus.
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    Design of the Transit Access Point Hardware Platform
    (2005-09-01) Murphy, Patrick; Frantz, Patrick; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
    Our objective is to design, analyze, prototype and experimentally study the theoretical underpinnings for a wireless internet that simultaneously achieves deployability, scalability, high performance and a cost-effective economic model. A core building block will be what we call wireless Transit Access Points. A transit access point, or TAP, is a wireless base station with two major features. First, like any standard base station, it provides wireless data services to mobile users. Second, and more importantly, a TAP is capable of high speed wireless links to other TAPs. These connections utilize multiple antennas at each end to dramatically increase the spectral efficiency and throughput of the link. Such TAP-to-TAP links are designed to supplement, or even replace, the wired network infrastructure usually required when deploying wireless data systems. This paper presents the custom hardware platform designed for the TAPs project.
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    Design of WARP: A Wireless Open-Access Research Platform
    (2006-09-01) Murphy, Patrick; Sabharwal, Ashutosh; Aazhang, Behnaam; Center for Multimedia Communications (http://cmc.rice.edu/)
    This paper presents the design of WARP, a custom platform for research in advanced wireless algorithms and applications. The platform consists of both custom hardware and FPGA implementations of key communications blocks. The hardware consists of FPGA-based processing boards coupled to wideband radios and other I/O interfaces; the algorithm implementations already include a flexible OFDM physical layer. Both the hardware specifications and algorithm implementations will be freely available to academic researchers to enable the development of a widely disseminated, highly capable platform for wireless research.
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    A DSP-Based Platform for Wireless Video Compression
    (2002-11-01) Murphy, Patrick; Bharadwaj, Vinay; Welsh, Erik; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    With the exponential growth of wireless voice markets, demand for wireless video services is soon to follow. However, bandwidth limited wireless channels coupled with mobility issues pose a great challenge in the hardware, software and algorithm design of communication systems. Raw video transmission is a high bandwidth application due to its spatial and temporal redundancies. Hence effective video communication over wireless channels calls for intelligent video coding and protection schemes. Also, the real-time nature of video necessitates high performance hardware and efficient software. This paper describes a modular and standards-independent DSP-based testbed (Paladin) designed for real-time video communication over low-bandwidth channels. In particular, we demonstrate the real-time transmission of MPEG-4 video and JPEG2000 still images over the Bluetooth wireless standard. Such a demonstration has many potential applications. We have designed the testbed to explore the possibilities, demands, and challenges of real-time wireless video transmission. We have implemented the MPEG-4 and JPEG2000 source coding on two DSP platforms: a Texas Instruments (TI) TMS320C6211, and a TI TMS3206416.
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    An FPGA Based Rapid Prototyping Platform for MIMO Systems
    (2003-11-20) Murphy, Patrick; Lou, Feifei; Sabharwal, Ashutosh; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    There exists a seemingly limitless demand for wireless communications systems capable of higher datarates with lower power consumption. While the demand for improvement in these systems seems limitless, the spectrum allocated for providing such services is undeniably restricted. There is a great deal of research directed at solving the problem of providing more wireless communications capabilities without any increase in allocated spectrum. One significant result of this research has been the development of algorithms targeted at transmitters and receivers equipped with multiple antennas, often described as multiple-input multiple-output (MIMO) systems. We describe in this paper a FPGA-based platform designed to explore MIMO algorithms and architectures in real hardware. This system utilizes Xilinx?s System Generator for DSP, a Simulink blockset designed to allow both PC-based simulation and FPGA implementation of DSP designs. MIMO algorithms implemented in System Generator are targeted to FPGA systems connected to 2.4 GHz spread spectrum radios. These radios are interconnected via a pair of Spirent RF channel emulators and can realize a variety of transmitter and receiver configurations. The use of FPGAs as baseband processors allows a great deal of flexibility in implementing designs while maintaining the capability to measure the resource utilization and power consumption of real hardware. Such measurements play a crucial role in evaluating the suitability of algorithms for deployment in real-world systems.
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    An FPGA Implementation Of Alamouti's Transmit Diversity Technique
    (2003-10-01) Murphy, Patrick; Frantz, Patrick; Dick, Chris; Center for Multimedia Communications (http://cmc.rice.edu/)
    This paper presents the FPGA implementation of a multiple antenna wireless communications system based on Alamouti's transmit diversity scheme. Alamouti's transmit diversty scheme is a space-time block code with support for two transmit antennas and an arbitrary number of receive antennas. Our implementaiton demonstrates this space-time code in a system with two transmit and just one antenna at the receiver. In addition to implementing the encoding and decoding algorithms described in Alamouti's paper, we have designed and implemented additional subsystems necessary to establish an end-to- end link over real wireless channels. These systems, described in detail below, address the challenges of timing synchronization, carrier offset recovery and channel estimation. When combined with an implementaiton of Alamouti's code, these designs form a complete multiple antenna wireless communications sytem.
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    An FPGA-based Daughtercard for TIs C6000 family of DSKs
    (2005-06-01) Gadhiok, Manik; Hardy, Ricky; Murphy, Patrick; Frantz, Patrick; Choi, Hyeokho; Cavallaro, Joseph R.; Digital Signal Processing (http://dsp.rice.edu/)
    In this paper we present an FPGA-based daughtercard designed for TIs C6000 family of DSP Starter Kits (DSKs). The hardware, initially designed for a course project, provides a platform for studying heterogeneous systems and hardware software co-design. Students will leverage the DSK-FPGA system for rapid prototyping of signal processing algorithms and to study task-partitioning and system integration. These techniques are becoming increasingly important for system designers as we move to system-on-chip (SOC) devices. The daughtercard hardware is fully functional, and a software package is being developed to provide a seamless communication interface between the DSK and FPGA.
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    A FPGA­Based Experimental PHY for 802.11b WLAN
    (2003-10-20) Lou, Feifei; Murphy, Patrick; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    The swift proliferation of wireless data communication systems, and the ever-increasing demand for faster data rates requires that engineers be able to quickly design, implement and test new wireless algorithms for data communications. While simulation is useful, it is often beneficial to verify these algorithms in real hardware. This process of implementation can provide useful feedback to the algorithm designer (e.g. the hardware resources used by an algorithm). This paper provides a description of a rapid prototyping system used to design, implement, and validate an 802.11b PHY as a starting point for developing new wireless data algorithms.
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    A Hardware Testbed for the Implementation and Evaluation of MIMO Algorithms
    (2003-10-20) Murphy, Patrick; Lou, Feifei; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    As the demand for higher performance wireless communications continues to grow, novel algorithms have been developed which provide increased performance and efficiency. One such class of algorithms involves the use of multiple antennas on either end of a wireless link. Many of these multiple input, multiple output (MIMO) algorithms offer impressive performance gains over their single antenna counterparts. The practicality of implementing such algorithms in a real system, however, is a topic in need of further exploration. We present in this paper a testbed designed specifically to test such algorithms. This testbed provides hardware for baseband processing, up and downconversion to RF and emulation of multiple wireless channels. It was designed to provide sufficient exibility to implement a wide range of algorithms while preserving the ability to evaluate an algorithm's resource and power requirements. The testbed hardware and configuration options are presented, along with a basic demonstration of its functionality.
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    Improving Connection Times for Bluetooth Devices in Mobile Environments
    (2002-03-20) Welsh, Erik; Murphy, Patrick; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    Communications devices in a highly mobile environment need to minimize connection setup times in order to maximize useful data transfer. In this paper we investigate - empirically and through simulations - the device discovery process of Bluetoothâ ¢, a technology that has potential in short-range, high-mobility applications. In order to improve Bluetooth's performance in a mobile environment, it is desirable to lessen the amount of time it takes to set up connections between two devices. We suggest three possible changes to the Bluetooth specification: eliminating or decreasing the random backoff delay in INQUIRY SCAN, using a single frequency train instead of two in INQUIRY, and a combination of the two. These simple changes can dramatically decrease connection setup times without having deleterious effects on overall system performance.
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    Mean-field model for nematic alignment of self-propelled rods
    (American Physical Society, 2022) Perepelitsa, Misha; Timofeyev, Ilya; Murphy, Patrick; Igoshin, Oleg A.; Bioengineering; Biosciences; Chemistry; Center for Theoretical Biological Physics
    Self-propelled rods are a facet of the field of active matter relevant to many physical systems ranging in scale from shaken granular media and bacterial alignment to the flocking dynamics of animals. In this paper we develop a model for nematic alignment of self-propelled rods interacting through binary collisions. We avoid phenomenological descriptions of rod interaction in favor of rigorously using a set of microscopic-level rules. Under the assumption that each collision results in a small change to a rod's orientation, we derive the Fokker-Planck equation for the evolution of the kinetic density function. Using analytical and numerical methods, we study the emergence of the nematic order from a homogeneous, uniform steady state of the mean-field equation. We compare the level of orientational noise needed to destabilize this nematic order and compare our results to an existing phenomenological model that does not explicitly account for the physical collisions of rods. We show the presence of an additional geometric factor in our equations reflecting a reduced collision rate between nearly aligned rods that reduces the level of noise at which nematic order is destroyed, suggesting that alignment that depends on purely physical collisions is less robust.
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    A Mobile Testbed for GPS-Based ITS/IVC and Ad Hoc Routing Experimentation
    (2002-10-01) Welsh, Erik; Murphy, Patrick; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    Past investigations into the formation of ad hoc networks and ad hoc routing have focused on computer simulations of mobile traffic. However, the proliferation of mobile electronic devices (mobile phones, PDAs, and laptop computers) combined with the commoditization of GPS chipsets has made realizable the construction of a large-scale testbed for both GPS and non-GPS aware ad hoc network applications. In this paper we present the Rice University Shuttle Bus Project (RUSH) as such a testbed in its first stages of development, in which we have outfitted the shuttle bus system at Rice University with custom wireless and GPS hardware.
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    Prototyping Platforms for Multiple Antenna Wireless Communications
    (2005-04-01) Murphy, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    As the demand for higher performance wireless communications continues to grow, novel algorithms have been developed which provide increased performance and efficiency. One such class of algorithms involves the use of multiple antennas on either end of a wireless link. Many of these multiple input multiple output (MIMO) algorithms offer impressive performance gains over their single antenna counterparts. The practicality of implementing such algorithms in a real system, however, has received far less attention. A primary reason for this is the scarcity of hardware platforms suitable for implementing and evaluating complex wireless communications algorithms. We present in this thesis two such platforms designed specifically to fill this void. The first platform is constructed from commercial off the shelf hardware, including equipment for baseband processing, RF up/downconversion and wireless channel emulation. The second, more ambitious platform, is built from custom hardware designed specifically for flexible MIMO prototyping.
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    Using Bluetooth for Short-Term Ad-Hoc Connections Between Moving Vehicles: A Feasibility Study
    (2002-05-01) Murphy, Patrick; Welsh, Erik; Frantz, Patrick; Center for Multimedia Communications (http://cmc.rice.edu/)
    Bluetoothâ ¢ is a promising wireless technology designed for short-range ad-hoc connections, and it has many potentially useful applications. One such use is the transfer of data between two fast-moving vehicles such as automobiles. In this paper we explore the suitability of Bluetooth to make connections in highly mobile environments. In particular, we have developed a hardware testbed to make an empirical analysis of the time it takes to establish Bluetooth connections and the impact this will have on any potential data transfer. We also propose changes in the Bluetooth standard that may offer faster connection setup times.
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    VALID: Custom ASIC Verification and FPGA Education Platform
    (2003-06-01) Murphy, Patrick; Welsh, Erik; Frantz, Patrick; Hardy, Ricky; Mohsenin, Tinoosh; Cavallaro, Joseph R.; Center for Multimedia Communications (http://cmc.rice.edu/)
    This paper describes VALID, a platform for testing student designed ASICs and for teaching the basics of FPGA design. VALID is designed to maximize ease of use from a student?s perspective while maintaining enough flexibility for its use as an FPGA development and instruction platform. This system was designed entirely by students, has been successfully manufactured and is currently being used in a number of courses at Rice.
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    WARP, a Modular Testbed for Configurable Wireless Network Research at Rice
    (IEEE, 2007-03-01) Amiri, Kiarash; Sun, Yang; Murphy, Patrick; Hunter, Chris; Cavallaro, Joseph R.; Sabharwal, Ashutosh; Center for Multimedia Communication
    Wireless Open-Access Research Platform (WARP), developed at CMC lab, Rice University, provides a scalable and configurable platform for wireless network research. Its programmability and flexibility makes it easy to prototype and implement various physical and network layer protocols and standards. In order to share algorithms and implementations developed at different research centers, an online open-access repository is used so that wireless network researchers can collaborate to initiate multi-disciplinary system designs.
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    WARP, a UnifiedWireless Network Testbed for Education and Research
    (IEEE, 2007-06-01) Amiri, Kiarash; Sun, Yang; Murphy, Patrick; Hunter, Chris; Cavallaro, Joseph R.; Sabharwal, Ashutosh; Center for Multimedia Communication
    In this paper, we introduce the Wireless Open-Access Research Platform (WARP) developed at CMC lab, Rice University. WARP provides a scalable and configurable platform mainly designed to prototype wireless communication algorithms for educational and research oriented applications. Its programmability and flexibility makes it easy to implement various physical and network layer protocols and standards. Moreover, the online open-access WARP repository is used to document and share different wireless architectures and cross-layer designs developed at educational and research centers. This repository is a fast and easy solution for students and researchers with a wide range of backgrounds in hardware implementation and algorithm development to collaborate and initiate multi-disciplinary system designs.