Browsing by Author "Murphy, Patrick O."

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    Design of prototyping platforms for multiple antenna wireless communications
    (2005) Murphy, Patrick O.; Aazhang, Behnaam
    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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    Design, Implementation and Characterization of a Cooperative Communications System
    (2011) Murphy, Patrick O.; Sabharwal, Ashutosh
    Cooperative communications is a class of techniques which seek to improve reliability and throughput in wireless systems by pooling the resources of distributed nodes. While cooperation can occur at different network layers and time scales, physical layer cooperation at symbol time scales offers the largest benefit. However, symbol level cooperation poses significant implementation challenges, especially in the context of a network of distributed nodes. We first present the design and implementation of a complete cooperative physical layer transceiver, built from scratch on the Wireless Open-Access Research Platform (WARP). In our implementation fully distributed nodes employ physical layer cooperation at symbol time scales without requiring a central synchronization source. Our design supports per-packet selection of non-cooperative or cooperative communication, with cooperative links utilizing either amplify-and-forward or decode-and-forward relaying. A single design implements transmission, reception and relaying, allowing each node to assume the role of source, destination or relay per packet. We also present experimental methodologies for evaluating our design and extensive experimental results of our transceiver's performance under a variety of topologies and propagation conditions. Our methods are designed to test both overall performance and to isolate and understand the underlying causes of performance limitations. Our results clearly demonstrate significant performance gains (more than 50× improvement in PER in some topologies) provided by physical layer cooperation even when subject to the constraints of a real-time implementation. As with all our work on WARP, our transceiver design and experimental framework are available via the open-source WARP repository for use by other wireless researchers.