Typical Multipath Environment Research Articles

Localization of Passive UHF RFID Tags Using the AoAct Transmitter Beamforming Technique

The localization of passive ultra-high frequ- ency (UHF) radio frequency identification (RFID) tags is an emerging technology that has reached a high level of interest in industry and research. Most solutions use classical techniques, such as the angle-of-arrival or the received-signal-strength methods. As an alternative, we present a new approach for estimating the position of a passive UHF RFID tag by using a transmitter beamforming technique that we call angle-of-activation (AoAct). It is based on manipulating the shape of the radiation pattern of the interrogator’s transmitter antenna array. By pivoting the main lobe of the pattern in the azimuth plane of the array and by utilizing the very sensitive response threshold of passive UHF RFID tags, we are able to estimate the tag direction. We use three-channel digital beamforming, where the phases and amplitudes of the antenna array’s feeding radio frequency signals are controlled by the baseband $I$ and $Q$ components of the interrogator’s transmitter signal. Our self-developed hardware pivots the main lobe of a three-element antenna array in a range of ±52° with a resolution of 0.02°. It senses the AoAct with a mean measured accuracy of 1.2° in the anechoic chamber, 1.9° in a basic multipath environment, and 2.5° in a real-world multipath environment. After estimating the AoAct of a tag from different locations, the tag position is triangulated. Experiments show that our AoAct system delivers a localization accuracy of 7 cm in a typical multipath environment.

Multipath Insensitive Delay Lock Loop in GNSS Receivers

The code measurement suffers from multiple error sources and especially multipath. The latter is unpredictable and changes in space and over time. Many interesting multipath mitigation techniques have been proposed. Most of them are not sufficiently effective for precise positioning using the code measurement. This paper presents a multipath insensitive delay lock loop that aims to improve the pseudorange measurement precision in the presence of multipath. This code loop is simple and does not require postprocessing of observables. Simulation and real implementation results showed that the proposed code loop dramatically improves the tracking error due to multipaths. Tracking error is limited to 1 m on pseudorange in typical multipath environments. This loop is more sensitive than the standard delay lock loop to thermal noise and applies predominantly to strong GNSS signals.

LOCALIZATION OF OMNI-DIRECTIONAL MOBILE DEVICE IN MULTIPATH ENVIRONMENTS

This paper presents a comprehensive Non Line of Sight (NLOS) localization scheme in a multipath environment where the scatterers with smooth surfaces are aligned parallel or perpendicular to each other. It leverages on the estimation of Angle of Arrival (AOA) and Time of Arrival (TOA) of the omni-directional mobile device's signal received at the reference devices. Unlike the conventional Line of Sight (LOS) localization schemes that rely on the various mitigation techniques to mitigate the multipaths that are mistaken as the LOS signal, our proposed two step localization scheme not only utilizes the LOS path but also any one bound scattering NLOS multipath arriving at the reference devices for localization. Channel experiment coupled with simulation results in a typical multipath environment has demonstrated that our proposed localization scheme outperforms the conventional localization schemes that are coupled with their own mitigation techniques. Robustness in performance of our proposed localization scheme towards different scatterers' orientation where they are not aligned parallel or perpendicular to each other are also investigated.

A Novel Antenna Concept for Double-Directional Channel Measurements

In this paper, a novel concept for the characterization of the double-directional mobile radio channel is presented. It is based on a broad-band real-time channel-sounding device together with appropriate antenna arrays, thus forming a multiple-input-multiple-output system. For the propagation measurements within the 5.2-GHz wireless local area network band presented here, a uniform linear antenna array at the receiver site and a switched multibeam antenna at the transmitter site have been employed. By application of the multibeam antenna, the entire azimuthal range of 360/spl deg/ is covered without ambiguities. The measurement data obtained with this platform in a simple synthetic scenario, as well as in a typical multipath environment, is then analyzed in terms of the propagation path properties. Using the three-dimensional estimation of signal parameters via rotational invariance techniques algorithm together with a proper Fourier transform, the channel parameters of all relevant multipaths such as delay, direction of arrival, direction of departure, and path loss are extracted from the measurement data. For both scenarios, the obtained estimated paths are verified to the underlying physical propagation environment by means of geometrical considerations. This geometrical matching accounts for multipath components due to single-bounce as well as multiple-bounce reflections and demonstrates the high suitability and good performance of the proposed concept.

Dual-mode equalization for digital mobile radio

The performance of digital mobile radio systems when transmitting at over several tens of kbit/s severely degrades with the onset of fast fading multipath propagation. This paper proposes a dual-mode equalization (DME) method to overcome the degradation and experimentally verifies the effectiveness of the method. The new method uses decision feedback equalizers (DFEs) in two modes simultaneously, a normal mode, and a time-reversal mode, and selects the best equalization result. The time-reversal equalization mode improves the characteristics of equalization and adaptation in the non-minimum phase condition. It converts the nonminimum phase to the minimum phase condition by the time-reversal operation. Principles of dual-mode equalization, an algorithm for mode output selection, and timing problems are discussed in detail. Experiments demonstrate average BER performance in two-path and typical multipath environments. The proposed dual-mode equalization technique improves average BER performance by 2 dB Eb/N0.

Diversity reception for v.h.f. mobile radio

Multipart fading on y.h.f. mobile radio links is investigated, and aerial diversity reception considered for improved reception at the mobile terminal. A 3-channel adaptive array has been built using a conventional v.h.f.-a.m. receiver modified to measure signal amplitudes and relative phases. Experimental results show the effects of typical multipath environments, and the improvement obtained with an adaptive array.

Space-diversity reception for v.h.f. mobile radio

Work on aerial diversity reception to combat multipath fading is described. A 3-channel adaptive array has been built around a conventional v.h.f.–a.m. receiver, and been modified to measure signal amplitudes and relative phases. Experimental results show the effects of typical multipath environments, and the improvement obtained with an adaptive array.