Showing papers by "Daniel D. Stancil published in 2005"

GrooveSim: a topography-accurate simulator for geographic routing in vehicular networks

Abstract: Vehicles equipped with wireless communication devices are poised to deliver vital services in the form of safety alerts, traffic congestion probing and on-road commercial applications. Tools to evaluate the performance of vehicular networks are a fundamental necessity. While several traffic simulators have been developed under the Intelligent Transport System initiative, their primary focus has been on modeling and forecasting vehicle traffic flow and congestion from a queuing perspective. In order to analyze the performance and scalability of inter-vehicular communication protocols, it is important to use realistic traffic density, speed, trip, and communication models. Studies on multi-hop mobile wireless routing protocols have shown the performance varies greatly depending on the simulation models employed. We introduce GrooveSim, a simulator for geographic routing in vehicular networks to address the need for a robust, easy-to-use realistic network and traffic simulator. GrooveSim accurately models inter-vehicular communication within a real street map-based topography. It operates in five modes capable of actual on-road inter-vehicle communication, simulation of traffic networks with thousands of vehicles, visual playback of driving logs, hybrid simulation composed of real and simulated vehicles and easy test-scenario generation. Our performance results, supported by field tests, establish geographic broadcast routing as an effective means to deliver time-bounded messages over multiple-hops.

A Multi-hop Mobile Networking Test-bed for Telematics

Abstract: An onboard vehicle-to-vehicle multi-hop wireless networking system has been developed to test the realworld performance of telematics applications. The system targets emergency and safety messaging, traffic updates, audio/video streaming and commercial announcements. The test-bed includes a Differential GPS receiver, an IEEE 802.11a radio card modified to emulate the DSRC standard, a 1xRTT cellular-data connection, an onboard computer and audio-visual equipment. Vehicles exchange data directly or via intermediate vehicles using a multi-hop routing protocol. The focus of the test-bed is to (a) evaluate the feasibility of high-speed inter-vehicular networking, (b) characterize 5.8GHz signal propagation within a dynamic mobile ad hoc environment, and (c) develop routing protocols for highly mobile networks. The test-bed has been deployed across five vehicles and tested over 400 miles on the road.

Apparatus for excitation, enhancement, and confinement of surface electromagnetic waves for confined optical power delivery

Abstract: An apparatus for producing an optical spot on the order of 25 nm in a recording media. The apparatus includes an optical transducer comprising a waveguide which defines an aperture adjacent to an air bearing surface of the transducer adjacent a recording media. The transducer includes a protrusion extending beyond the plane of the air bearing surface extending toward the recording media.

Single antenna time reversal adaptive interference cancellation

Abstract: This paper presents the time reversal adaptive interferer canceller (TRAIC), a novel algorithm that uses time reversal techniques to cancel the presence of interferers. TRAIC is developed for broadband signals and a single emitting antenna. Experimental tests in the electromagnetic domain show the viability and the power of TRAIC.

"chip-size" antennas for implantable sensors and smart dust

Abstract: In this paper, we present the analysis, design and experimental results of /spl lambda//4-patch antennas operating at /spl sim/10 GHz. The ground plane has been adjusted to the patch area in order to drastically reduce the antenna size. Several geometries are presented, with HFSS simulation results. Impedance matching calculations for maximum power transfer between the antenna and the rectifying circuit is also presented. For a 4/spl times/5/spl times/1.6 mm/sup 3/ rectangular antenna fabricated on an RT/Duroid 5880 PCB, the measured maximum gain is 0.75 dB/sub i/ at 10.3 GHz.

On the capacity limits of HVAC duct channel for high-speed Internet access

Abstract: In this paper, we report theoretical and experimental channel-capacity estimates of heating, ventilation, and air conditioning (HVAC) ducts based on multicarrier transmission that uses M-ary quadrature amplitude modulation and measured channel responses at the 2.4-GHz industrial, scientific, and medical band. It is shown theoretically that data rates in excess of 1 Gb/s are possible over distances up to 500 m in straight ducts in which reflections have been suppressed. Our experimental results also show that even in the case of more complex HVAC duct networks (i.e., HVAC duct networks that include bends, tees, etc.) data rates over 2 Gb/s are possible. Our estimations in this case are valid for distances of up to 22 m, which was the maximum distance of our experimental setup. These experimental results, measured with a large-scale testbed set up at Carnegie Mellon University, Pittsburgh, PA, albeit limited in terms of transmitter-receiver separation distance, provide further evidence on the potential of HVAC systems as an attractive solution for providing communications in indoor wireless networks.

Single antenna microwave nulling using time-reversal techniques

Abstract: In this paper, we describe a single antenna microwave nulling technique that makes use of time-reversal concepts. The time-domain experiments have shown that by using single antenna and time-reversal technique, we can have focusing as well as nulling at any point in space. We have done experiments at 2.45 GHz in a cylindrical cavity environment. The degree of nulling (or focusing) depends on the multipath components in the channel as well as the bandwidth of the signal. The cavity provides a multipath rich-environment where we can show focusing and nulling by using a relatively small bandwidth compared to free space.

A novel time reversal method for target detection in cluttered media

Abstract: A cluttered environment with highly scattering objects significantly enhances the difficulty for detecting targets using electromagnetic waves. Time reversal methods have been developed in acoustic wave propagation. It has been shown that the super resolution focusing effect in acoustic wave propagation can also be achieved electromagnetic wave propagation. We present a novel time reversal method that nullifies the scattering objects to allow automatic focusing of the propagated electromagnetic wave on a target that is to be detected. Numerical simulations using the FDTD method have been carried out. The results show that the method significantly enhances the dynamic range of target detection in a highly scattering environment and could substantially increase target detectability.

Experimental results on target detection in cluttered medium using electromagnetic time-reversal techniques

Abstract: We describe an experimental technique that can be used to improve the detection performance of a radar system in cluttered environments. The detection algorithm depends on time-reversal techniques. By using time-reversal, the response from cluttered medium is first nulled. When the target enters into the medium, the electromagnetic energy focuses around the target so that a stronger echo is obtained. The initial experimental results show that using time-reversal techniques, we can improve the signal-to-noise ratio of the return-echo due to the target compared to conventional change-detection radar.

Microwave signal nulling using multiple antennas and time-reversal method

Abstract: In this paper, we describe a multiple antenna microwave nulling technique that makes use of time-reversal concepts. The time-domain simulations and frequency domain experiments have shown that by using multiple antennas and time-reversal technique, we can maximize (focusing) as well as minimize (nulling) RF energy at active or passive target points in the medium. We have done experiments between 4 to 6 GHz in a laboratory environment. The degree of nulling as well as focusing depends on the multipath components in the channel and the bandwidth of the waveform. Using a 2-GHz bandwidth waveform, we have experimentally shown high-resolution microwave nulling results in a 2-D plane.

Waveform Shaping for Time Reversal Interference Cancellation: A Time Domain Approach

Abstract: In this paper, we present a time domain interference cancellation scheme using time reversal, in time reversal, a signal, for example, transmitted by a weak source through a dispersive medium, is received by an array, time reversed, power normalized, and retransmitted through the same medium. If the channel is reciprocal, and the clutter is sufficiently rich, the retransmitted waveform refocuses on the original source. This focusing effect implies that a significant portion of the received signal energy concentrates in a very small time/space, support compared with the rest of the signal components. In this paper, we consider the opposite problem: rather than refocusing, we reshape the retransmitted waveform to reduce the returned echo, i.e., to mitigate the clutter returns. Proof of concept is provided using experimental electromagnetic data and wave propagation simulations

Characterizing dispersion in the enclosed-space radio channel using a composite mode model

Abstract: Wireless communications inside enclosed space environments (e.g. aircraft wings and fuselage, auto-mobile engine compartments, etc.) provides a unique opportunity for sensor networks and instrumentation systems native to these spaces to operate with improved reliability, flexibility and capabilities. Since these enclosed environments are typically surrounded by reflective boundaries (i.e. metallic walls), the enclosed-space radio channel is very dispersive and presents a significant challenge to radio communications. In this work, empirical dispersion measurements in representative enclosed space environments are made and a simple model which considers only the enclosure volume, surface area, conductivity and frequency of operation, is found to predict dispersion parameters in the enclosed space channel with good results.

Wireless sensors in reverberant enclosures: characterizing a new radio channel

Abstract: Wireless sensor networks operating inside aircraft wings, unmanned air vehicles (UAV's), small submarines and/or automobile engine compartments experience a radio channel that can be highly reverberant and is not yet thoroughly characterized. To obtain a better understanding of these spaces as radio communications environments, measurements in the enclosed space radio channel are performed and models are presented that describe the channel dispersion properties. Communications performance is evaluated using a signal excitation/analysis method using a variety of signaling techniques and in several different frequency bands.

Antenna radiation resistance in waveguide and in free-space

Abstract: In this paper, we discuss the connection between radiation resistance formulas for antenna in free-space and in rectangular waveguide. We demonstrate with the example of monopole antenna that a transformation between the angular direction in free-space and mode indices in waveguide makes the formulas for antenna radiation resistance in free-space and in rectangular waveguide equivalent to each other.

Dispersion in the enclosed-space radio channel: measurements and model

Abstract: Sensor and instrumentation networks operating inside aircraft wings, unmanned air vehicle (UAV) fuselage, small submarine craft and/or automobile engine compartments could be significantly enhanced or enabled by implementing radio communications within these spaces However, these enclosures are highly reverberant, and radio channel dispersion has been shown to be considerable in an empty-enclosure configuration In this work, further dispersion measurements incorporating environmentally realistic objects are presented Results are introduced that allow the channel dispersion parameters to be represented by a single measured channel parameter, making an important advance towards complete enclosed space channel dispersion predictions

Improved wireless performance from mode scattering in ventilation ducts

Abstract: Ventilation ducts are a convenient infrastructure for distributing wireless signals indoors. Conventional and historical use of single conductor metal waveguides for transmission of communications signals has focused on careful excitation and control of mode content in the waveguide - something that is possibly infeasible or financially undesirable in a ventilation duct setting. With this in mind, we investigate the mode scattering effects present in a ventilation duct T-junction and note with some surprise that improvement in the performance of an IEEE 802.11g communication can result from this scattering.

Mechanism for domain expansion in MAMMOS

Abstract: A magnetic amplifying magnetooptical system (MAMMOS) model was created which calculates the size of the expanded domains in the readout layer by computing the forces on the domain wall. Using the model, the ratio of nucleation coercivity to domain wall motion coercivity, H/sub c,n//H/sub c,m/, was found to be an important factor governing the final expanded domain size in MAMMOS. Simulation results indicated that H/sub c,n//H/sub c,m/>5 is needed for a good readout signal. Experiments measuring the nucleation coercivity in localized areas on a MAMMOS readout layer agree with the modeling results. In the experiments, a wafer was patterned with islands of magnetic material and the switching behavior was measured. For a MAMMOS film, the ratio of H/sub c,n//H/sub c,m/ was measured to be 13 on average in a 400 /spl mu/m/sup 2/ area.

Scalar network analysis of wireless channels using IEEE 802.11g transmissions

Abstract: In this work we demonstrate the feasibility of scalar network analysis of wireless channels using an IEEE 802.11g waveform with a separate receiver. We explore the concept using a laboratory grade Orthogonal Frequency Division Multiplexing (OFDM) signal generator and spectrum analyzer. We also demonstrate the technique with field test equipment. All results are confirmed using a network analyzer. We find that utilizing field test equipment allows us to obtain valid channel responses and statistics. Keywords—channel characterization; scalar network analysis; IEEE 802.11g; OFDM.