Vikas Kukshya

Spatial and temporal characteristics of 60-GHz indoor channels

This article presents measurement results and models for 60-GHz channels. Multipath components were resolved in time by using a sliding correlator with 10-ns resolution and in space by sweeping a directional antenna with 7/spl deg/ half power beamwidth in the azimuthal direction. Power delay profiles (PDPs) and power angle profiles (PAPs) were measured in various indoor and short-range outdoor environments. Detailed multipath structure was retrieved from PDPs and PAPs and was related to site-specific environments. Results show an excellent correlation between the propagation environments and the multipath channel structures. The measurement results confirm that the majority of the multipath components can be determined from image based ray tracing techniques for line-of-sight (LOS) applications. For non-LOS (NLOS) propagation through walls, the metallic structure of composite walls must be considered. From the recorded PDPs and PAPs, received signal power and statistical parameters of angle-of-arrival and time-of-arrival were also calculated. These parameters accurately describe the spatial and temporal properties of millimeter-wave channels and can be used as empirical values for broadband wireless system design for 60-GHz short-range channels.

Spatial and temporal characterization of 60 GHz indoor channels

This paper presents measurement results and models for 60 GHz channels. Multipath components were resolved in time by using a sliding correlator with 10 ns resolution, and in space by sweeping a directional antenna with 70 half power azimuthal beamwidth around the azimuth. Power delay profiles (PDPs) and power angle profiles (PAPs) were measured in various indoor and short-range outdoor environments. Detailed multipath structure was retrieved from PDPs and PAPs, and compared with site-specific environments. Results show an excellent correlation between the propagation environments and the multipath channel structures. The measurement results confirm that the majority of the multipath components can be determined from image based ray tracing techniques for LOS applications. For NLOS propagation through walls, the metallic structure of composite walls must be considered for propagation predictions. From the recorded PDPs and PAPs, received signal power and statistical parameters of angle-of-arrival (AOA) and time-of-arrival (TOA) were also calculated.

Wideband measurements of angle and delay dispersion for outdoor and indoor peer-to-peer radio channels at 1920 MHz

The paper presents spatio-temporal measurements for the peer-to-peer radio channel at a center frequency of 1920 MHz with 140 MHz of radio-frequency bandwidth. The measurements were taken using a spread-spectrum channel sounder and an automated spatial probing system that uses precise computer-controlled positioning and orientation of omnidirectional and directional (30/spl deg/ beamwidth) antennas to measure both the angles-of-arrival and time-delays of multipath components. We use a unitless definition of angular spread which we proposed previously (see Durgin, G.D. and Rappaport, T.S., IEE Electron. Lett., vol.34, no.25, p.2431-2, 1998). Transmitter-receiver configurations include six outdoor-to-outdoor cross-campus locations at Virginia Polytechnic Institute and State University (17-219 ns rms delay spread, 0.36-0.91 angular spread), three outdoor-to-indoor locations (27-34 ns rms delay spread, 0.78-0.98 angular spread), and three indoor-to-indoor locations (29-45 ns rms delay spread, 0.73-0.90 angular spread). The paper also quantitatively describes a trend that shows how angular spread increases with increasing delay spread.

High-availability free space optical and RF hybrid wireless networks

We introduce hybrid free-space optical and RF wireless links as potential technology for designing next-generation broadband wireless networks. We present various design challenges and potential solutions for real-time link performance characterization and adaptation for enhanced performance during adverse weather conditions. First, we introduce the hybrid wireless architecture and emphasize its significant role in achieving ubiquitous carrier-grade wireless connectivity. Second, we propose a link monitoring scheme that accurately reflects the performance of optical wireless links under various weather conditions. In addition, we examine the role of known link performance restoration schemes - power and data rate control. Third, we propose two novel link restoration schemes that efficiently utilize the hybrid architecture: dynamic load switching and multihop routing. Finally, the article describes an elaborate field testbed based on the hybrid architecture and various link restoration techniques. The dynamic load switching scheme is shown to have a profound impact on the overall hybrid link availability. The results, recorded from the experiments during extreme weather conditions, validate the impact of the hybrid architecture concept and conclusively prove the availability and reliability of the architecture in achieving sustained highspeed wireless connectivity.

Design of a system solution for relative positioning of vehicles using vehicle-to-vehicle radio communications during GPS outages

Active safety applications for vehicles have been at the forefront of the automotive safety community for a number of years. Cooperative collision warning based on vehicle-to-vehicle radio communications and GPS systems is one such promising active safety application that has evoked considerable interest among automobile manufacturers and research communities worldwide. In this paper, we address one of the key functional components of the cooperative collision warning application, which is, accurate estimation of relative positions of all the neighboring vehicles based on real-time exchange of their individual GPS position coordinates, and then propose a novel system solution for achieving the same (relative positioning functionality) during persistent GPS outages. Based on survey results, we also qualitatively assess various radio based ranging and relative positioning techniques, experimentally evaluate the received signal strength based ranging technique, and comment on their suitability for our proposed solution.

Experimental Measurements and Modeling for Vehicle-to-Vehicle Dedicated Short Range Communication (DSRC) Wireless Channels

The dedicated short range communication (DSRC) standard (also known as IEEE 802.11p) can be used to enable a number of vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) wireless radio communication based active safety and telematics applications. In this paper, we briefly document various experimental measurement scenarios and characterize performance of the DSRC standard based radio modules in ldr Additive White Gaussian Noise (AWGN) wireless channel ldr Line-of-sight, no-vehicle-traffic, street road environment ldr Line-of-sight, parking lot environment with moderate-to- dense (surrounding) vehicle density ldr Line-of-sight, freeway environment with low-to-moderate (surrounding) vehicle density The wireless channel models, derived from performance statistics for above mentioned experimental measurement environments, have been incorporated into a DSRC wireless network simulator, and are being used to quantitatively characterize the large-scale network performances (and functional feasibilities) of several V2V, DSRC wireless communication standard based active safety and telematics applications.

Performance Evaluation of a System for Estimating Relative Positions of Vehicles During GPS Outages

Active safety applications for vehicles have been at the forefront of the automotive safety community for a number of years. Cooperative collision warning based on vehicle-to-vehicle radio communications and GPS systems is one such promising active safety application that has evoked considerable interest among automobile manufacturers and research communities worldwide. In this paper, we address one of the key functional components of the cooperative collision warning application, which is, accurate estimation of relative positions of all the neighboring vehicles based on real-time exchange of their individual GPS position coordinates, and then we propose a novel system solution for achieving the same (relative positioning functionality) during persistent GPS outages. Our proposed system solution essentially involves integration of the most suitable set of vehicle clustering, radio based ranging, and relative position coordinate establishment techniques, and based on the results of a comprehensive literature survey, we reason that the two-way reciprocal time of arrival based ranging, and the distributed beacon-less relative positioning techniques may constitute the most viable set for our proposed system solution. Having developed a system simulator to accurately model the functionality of our proposed system solution, we then quantify the impact of various levels of ranging error on the overall performance of the system and thereby assess the functional viability of our proposed system solution. The simulation results look quite promising and support the fact that our proposed system solution can enable relative positioning of vehicles without any GPS information within acceptable levels of positioning accuracy, as required for the 360-degrees cooperative collision warning application

Characterizing performance of tire pressure monitoring systems using experimental measurements and system simulations

In this paper, we focus on the design and development of a system simulator that can assess the performance of a direct measurement TPMS in various operational scenarios. Our end goal is to use this TPMS simulator as a virtual test environment for a number of different experimental scenarios and possibly reduce the number of actual physical tests that may be required otherwise.

Impact of Inter-Vehicular Interference on the Performance of Tire Pressure Monitoring Systems

In this paper, we present a system simulator that can evaluate the performance of direct measurement Tire Pressure Monitoring Systems (TPMS) in various operational scenarios. We also discuss the following capabilities of the simulator: (1) modeling the wireless channel characteristics experienced by the signal between various transmitters and the receiver of a given vehicle, (2) modeling collisions among wireless signals of a given vehicle and those of the nearby vehicles, and (3) quantifying the impact of wireless channel characteristics and collisions among wireless signals on the performance of the TPMS. Using results for hypothetical simulation scenarios, we demonstrate the impact of wireless channel characteristics, receiver sensitivity level, and inter-vehicular interference on the performance of the TPMS.

A Time-Encoding Machine Based High-Speed Analog-to-Digital Converter

A time-encoding machine (TEM) based new analog-to-digital converter (ADC) architecture is presented in this paper. The main advantage of this architecture is that it relies on asynchronous process and removes an important performance limiting factor in conventional ADCs: the clock jitter. Therefore, this architecture is suitable for very high speed ADCs. To expand the bandwidth coverage, the compressive sensing techniques is employed to reconstruct sparse signals with very high frequency. The system can run under two different modes: the normal mode where the signal is sampled at above Nyquist rate and the compressive sensing mode. Nonidealities in circuits and system parameter setting tradeoffs are analyzed to determine the best parameters for the system to reach optimal performance.