Browsing by Author "Mostafa, Raqibul"

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    Design and Implementation of a DSP-Based MIMO System Prototype for Real-Time Demonstration and Indoor Channel Measurements
    Mostafa, Raqibul; Gozali, Ran; Palat, Ramesh Chembil; Robert, Max; Newhall, William G.; Woerner, Brian D.; Reed, Jeffrey H. (2005-09-21)
    The design and implementation of the Virginia Tech Space-Time Advanced Radio (VT-STAR), a multiple antenna element space-time (ST) processing prototype testbed, is presented. The testbed is a research tool for comparing practical and theoretical performance metrics (e.g., throughput, link reliability) in different wireless channel conditions. The prototype builds around software-defined radio (SDR) concepts on a DSP platform and provides the flexibility to implement various forms of ST techniques. Different components of the system are described in detail, including the software implementation, I/O schemes with custom hardware, and data transfer mechanisms between the DSP and the host PC. Two different example realizations are presented, a real-time demonstration and an offline measurement tool. Finally, some representative measurement results obtained in indoor environments are presented. These results show VT-STAR to be a promising tool for performing MIMO experiments and generating channel measurements that can complement simulation studies in this area.
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    Feasibility of Smart Antennas for the Small Wireless Terminals
    Mostafa, Raqibul (Virginia Tech, 2003-04-25)
    Smart antenna is a potential performance enhancement tool in a communications link that can be used at either end (transmitter or receiver) of the link in the form of beamforming or diversity operation. While receive smart antenna techniques and operations have matured over the years, transmit smart antenna is relatively a new concept that has seen its growth over the past few years. Both these smart antenna operations have been traditionally designed for base station applications. But with the advent of high-speed processors, transmit smart antenna can also be feasible at a small wireless terminal (SWT). This dissertation studied the feasibility of using smart antenna at a SWT. Both smart transmit and receive antennas are studied, including multiple input and multiple output (MIMO) systems, however the emphasis is placed on transmit smart antennas. The study includes algorithm developments and performance evaluations in both flat fading and frequency selective channels. Practical issues, i.e., latency and amount of feedback, related to transmit smart antenna operation are discussed. Various channel measurements are presented to assess the performance of a transmit smart antenna in a real propagation environment. These include vector channel measurements for narrowband and wideband signals, channel reciprocity, and effect of antenna element spacing on diversity performance. Real-time demonstrations of transmit smart antenna have been performed and presented, and, the applicability of the proposed techniques in the Third Generation standards and wireless local area networks (WLAN) is discussed. Receive beamforming with a small number of antenna elements (which is usually the case for a SWT) is analyzed in an interference-limited environment.
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    Wideband electromagnetic characterization of Portland cement concrete
    Mostafa, Raqibul (Virginia Tech, 1995)
    Wideband electromagnetic characterization of Portland cement concrete (PCC) has been investigated in this study. This is necessary to correlate the material properties of PCC with its physical condition and hence aid in nondestructive evaluation of practical PCC structures. A test fixture has been designed to characterize PCC test specimens in the frequency range of 100-1000 MHz. Measurements have been performed in both time domain and frequency domain. The focus of this research has been to investigate time domain techniques for the characterization of PCC specimens under different test conditions. A simplified TDR measurement technique using one-port calibration scheme has been proposed for the research. Measurements have been carried on reference materials (e.g. Teflon) to verify the accuracy of the proposed technique. Extensive calibration and de-embedding have been studied to minimize the systematic errors involved in the measurement process. A computer simulation based verification process has been studied to validate the proposed calibration and de-embedding scheme. Sensitivity analysis and study of repeatability of the measurement process has been done as well.