The recent approval granted by the Federal Communications Commission (FCC) for the use of ultra-wideband signals for vehicular radar applications has provided a gateway for the introduction of these sensors in the commercial arena as early as 2004. However, the rules governing the allowable spectral occupancy create significant constraints on the sensors' operation. This is further complicated by the variety of applications that these sensors are being required to fulfill. A review of the motivation for the development of these sensors is followed by a discussion of the consequent implications for waveform design and limitations on system architecture. Other practical considerations such as available semiconductor technology, packaging, and assembly techniques are reviewed, and results are presented for conventional surface-mount plastic packages illustrating their usefulness in the greater than 20-GHz frequency range. Suitable antenna technology for wide-band transmission is presented that is compliant with the specific restrictions stipulated in the FCC ruling. Finally, all of these considerations are combined with the presentation of a compatible integrated-circuit-based transceiver architecture. Measured results are presented for several critical circuit components including a +12-dBm driver amplifier for the transmitter, an RF pulse generator that can produce sub-1-ns pulses at a carrier frequency of 24 GHz, and a single-chip homodyne in-phase/quadrature down-conversion receiver that has a cascaded noise figure of less than 7 dB. All circuit components are fabricated in SiGe.

Ultra-wideband radar sensors for short-range vehicular applications

Ultra-wideband radar holds great promise for a variety of medical applications. We have demonstrated the feasibility of using ultra-wideband sensors for detection of internal injuries, monitoring of respiratory and cardiac functions, and continuous non-contact imaging of the human body. Sensors are low-power, portable, and do not require physical contact with the patient. They are ideal for use by emergency responders to make rapid diagnosis and triage decisions. In the hospital, vital signs monitoring and imaging application could improve patient outcomes. In this paper we present an overview of ultra-wideband radar technology, discuss key design tradeoffs, and give examples of ongoing research in applying ultra-wideband technology to the medical field.

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Ultra-wideband radar methods and techniques of medical sensing and imaging

New emission limit requirements are needed to protect digital communication systems from radiated interference. Traditionally, standard emission requirements have focused on protecting analog amplitude modulated radio services. However, developments in digital technology require emission limit requirements adapted to protect digital radio communication services. The amplitude probability distribution (APD) of the envelope or the quadrature components of an interfering signal has been shown to be related to the bit error probability of some digital radio receivers. However, a general description of the APD of an interfering signal and its impact on digital coherent radio receivers has not been presented. The aim of this paper is to clarify this relationship for a larger group of digital radio receivers. A method of incorporating the APD in conventional error expressions developed for digital coherent radio receivers in additive white Gaussian noise is presented. Furthermore, the relation between the maximum error probability for different digital modulation schemes and the APD is described, which allows definition of emission requirements on the APD

Relation between the amplitude probability distribution of an interfering signal and its impact on digital radio receivers

In this paper a multi-user communication system based on ultra-wide band (UWB) technology is studied. UWB uses very short pulses, so that the spectrum of the emitted signals may spread over several GHz. In order to implement multi-user communication, the emitted signal must be modulated. One modulation scheme for UWB communications is to use analog waveforms to modulate the data.

In this study, orthogonal waveforms called modified Gegenbauer functions are introduced as basis functions for the pulse shape and compared to the previously proposed modified Hermite functions. It is shown that Gegenbauer functions offer better performance for multi-user UWB communications.

Multi-User Ultra-Wide Band Communication System Based on Modified Gegenbauer and Hermite Functions

Global positioning system (GPS) receivers find growing applications in indoor and outdoor communication environments, including urban and rural areas. Interference and noise sources for GPS receivers may assume Gaussian or non-Gaussian distributions. The GPS receiver performance under Gaussian additive noise has been studied. Non-Gaussian noise may equally contaminate the GPS satellite signals and disturb the receiver delay lock loops (DLL), producing significant tracking errors. These sources include impulsive noise, ultra-wideband (UWB) signals, and impulse and noise radar signals for target tracking and indoor imaging applications. This paper considers non-Gaussian noise of finite variance and examines its effect on the discriminator outputs for the commercial GPS receiver that uses the coarse acquisition (C/A) code. The correlator noise output components are produced from the correlation between the noise sequence and the early, late, and punctual reference C/A code. Due to the long time averaging, which is characteristic of the GPS correlation loops, these components assume Gaussian distributions. The discriminator tracking error variance is derived, incorporating the effect of noise, the front-end precorrelation filter, and the sampling rate.

Performance Analysis of GPS Receivers in Non-Gaussian Noise Incorporating Precorrelation Filter and Sampling Rate

This addendum to NTIA Report 01-384 describes laboratory measurements on two additional Global Positioning System receivers to quantify the effects of ultrawideband interference on those receivers. The laboratory measurements were performed by inserting increased levels of UWB interference until an operating GPS receiver lost lock. At each interference level leading up to loss of lock, reacquisition time was determined. When possible, fundamental GPS measurements (e.g., pseudorange and carrier phase), status flags (e.g., potential cycle slips), and signal-to-noise ratio were also sampled.

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J. Randy Hoffman

Papers

Addendum to NTIA Report 01-384: Measurements to Determine Potential Interference to GPS Receivers from Ultrawideband Transmission Systems