Brian D. Cordill

KUAR: A Flexible Software-Defined Radio Development Platform

In this paper, we present the details of a portable, powerful, and flexible software-defined radio development platform called the Kansas University Agile Radio (KUAR). The primary purpose of the KUAR is to enable advanced research in the areas of wireless radio networks, dynamic spectrum access, and cognitive radios. The KUAR hardware implementation and software architecture are discussed in detail. Radio configurations and applications are presented. Future research made possible by this flexible platform is also discussed.

COGNITIVE RADIOS FOR DYNAMIC SPECTRUM ACCESS - An Agile Radio for Wireless Innovation

We present the details of a portable, powerful, and flexible software-defined radio development platform called the Kansas University Agile Radio (KUAR). The primary purpose of the KUAR is to enable advanced research in the areas of wireless radio networks, dynamic spectrum access, and cognitive radios. We describe the KUAR hardware implementation and software architecture and present example application of the KUAR to modulation, spectrum measurement, channel estimation, and rapid configuration and adaptation. We outline research directions enabled by the KUAR

The impact of mutual coupling on MIMO radar emissions

The effects of mutual coupling between antenna elements are considered with regard to the impact upon co-located MIMO radar emissions. Because this sensing scheme intentionally couples the spatial and fast-time (waveform) domains, it is shown that MIMO radar is sensitive to any electromagnetic mutual coupling effects that are not adequately characterized in the transmit array manifold. This sensitivity leads to mismatch that will degrade the radars sensitivity on receive.

Electromagnetic interference to radar receivers due to in-band OFDM communications systems

Radar and communication system interoperability is an ongoing problem that is increasing due to acute spectral crowding. This paper will focus on examining the performance degradation to radar system receivers from OFDM communication signals such as WiMAX and LTE. Specifically, a simulated S-Band long range weather radar will be subjected to OFDM interference and the performance degradation measured. Notional radar systems using both incoherent and coherent radar processing techniques will be examined. The effectiveness of first order interference mitigation techniques, such as notch filtering, will be measured and compared. These types of measurements can aid design engineers and system operators as the OFDM interference becomes more prevalent.

Shielding effectiveness of composite and aluminum aircraft, model and measurement comparison

Modern aircraft are subject to a barrage of high intensity radiated fields (HIRF) from a wide variety of man-made sources. Fortunately, the aluminum skin of traditional aircraft provides significant shielding to the sensitive electronics inside the aircraft. However, the drive to create lighter, more fuel efficient aircraft has created a trend in the aerospace industry away from aluminum, to lighter composite materials. These composite materials do not always provide the same level of shielding as their aluminum counterparts and has created an urgent need to characterize and measure the shielding effectiveness of entire airframes in a timely, cost effective manner. This paper presents preliminary results for an airframe analog and a composite Uncrewed Arial Vehicle (UAV) that show the viability of virtual measurements to identify and help correct shielding problems earlier in the design phase of an aircraft than traditional measurements.

Mutual coupling calibration using the Reiterative Superresolution (RISR) algorithm

An integral element of a blind array calibration routine is an estimate of the direction of arriving signals. The work herein integrates the Reiterative Superresolution (RISR) algorithm into a calibration framework suitable for estimating the array mutual coupling. The RISR algorithm is a recursive minimum mean-squared error (RMMSE) Direction of Arrival (DoA) estimator that does not require a Sample Covariance Matrix (SCM) be computed. In addition, the RISR algorithm directly estimates the spatial spectrum, rather than just the angle measurement, making it well suited for assessing the array mutual coupling. Here a calibration method is derived using RISR to estimate mutual coupling. The effectiveness of the approach is via simulation.

Radar system impacts due to spectrum attributes of frequency-steerable phased array antennas

Possible differences between boresight and off-boresight emissions of phased array radar systems can impact a radar systems performance. This could result in a distorted transmitted radar waveform. In order to understand the significance of this distortion on a radar system, a simulation study was completed for a notional 3.5 GHz radar having both a continuous wave pulsed waveform and a linear FM waveform. This simulation study was verified using available measurement data. The radar systems performance was then assessed by using radar ambiguity plots for each of these radar waveforms. It was concluded that some distortion is present even on-boresight in addition to the off-boresight emissions difference. Further understanding of the specific off-boresight distortion could lead to better clutter suppression.

Shielding Effectiveness of Carbon–Fiber Composite Aircraft Using Large Cavity Theory

This paper extends reverberation chamber theory to include chambers constructed out of non-metallic composite materials. This extension allows reverberation chamber theory to predict the shielding effectiveness (SE) of modern aluminum and composite aircraft. Existing theory is based on a power balance approach for aperture-excited cavities, and this paper extends it to include leakage through the cavity walls. Cavity excitation and power dissipation mechanisms are examined in detail, and the cavity SE is related to cavity energy loss in terms of the “quality factor.” SE measurements were made on a partially assembled Uncrewed Aerial System constructed with a carbon-fiber composite skin. The test-analysis agreement shows a high degree of correlation.

On intermittent OFDM transmitter saturation and radar system performance

The effects of spectral crowding are becoming acutely problematic as new wireless systems are being deployed in adjacent bands to legacy systems. Current spectrum management practices seek to control and limit persistent out-of-band emissions, but fall short on addressing intermittent emissions. Such intermittent interference can be caused by the occasional saturation of a transmitting power amplifier, resulting in unintended emissions into adjacent bands. Such transmitter saturations are common for the high peak-to-average power waveforms commonly found in OFDM systems. This work seeks to quantify the performance degradation of a notional radar system in the face of intermittent interference falling in the radars operating bandwidth. The results show a rise in the false alarm rate of the radar system in proportion to the saturation rate of the adjacent band system.

Radar performance degradation with in-band OFDM communications system interference

Summary form only given. New technology and innovations are giving rise to novel and diverse wireless systems. Unfortunately, as these systems come to fruition worldwide, the already crowded spectrum becomes even more congested due to the high-speed data links offered by systems like WiMAX and LTE. Spectral crowding is acutely problematic in S-Band (2000-4000 MHz), where favorable propagation characteristics make spectrum attractive to both long-range radar and communication systems. The widespread deployment of 4G cellular systems (for example LTE) has the potential to cause widespread interference with existing radar systems, such as those used for weather surveillance. Ideally, these two systems would peacefully coexist in adjacent bands, but the non-constant modulus nature of 4G OFDM waveforms and the relatively high peak-to-average power ratios can lead to intermittent transmitter saturation, resulting in both in-band and adjacent-band interference to a radar receiver. Their intermittent nature and wide bandwidth make interfering OFDM waveforms difficult to eliminate at the radar receiver. The first instinct when dealing with an interfering signal is often to apply a notch filter in an attempt to mitigate the interfering signals impact on the system. This talk assesses the effectiveness of this instinctive solution. The impact of OFDM interference on a simulated weather radar system is presented, as well as an assessment of the effectiveness of applying a notch filter to mitigate an interfering OFDM signal. As part of this assessment, radar performance data, probability of detection statistics, and receiver operating characteristic (ROC) curves are presented. This type of assessment will help quantify this first instinct solution and help define the trade space for radar system engineers and spectrum managers when considering interference mitigation techniques. Successful mitigation of both in-band and adjacent-channel OFDM interference should not only improve current radar system performance, but it will also allow mission requirements to be met in a crowded spectrum.