Aim of this contribution is to validate our deterministic UWB channel model which integrates the real characteristics of the UWB antennas in the whole effective channel. Our analysis relies on a UWB ray tracing approach since this reflects the dependence on the angle of arrival (AoA) and angle of departure (AoD) of any multipath. In the meanwhile, EM-Simulation tool has been used to compute the transfer functions of the real antennas used. Office environment was considered in both the simulation and measurements with Line of Sight (LoS) and NLoS scenarios. A comprehensive comparison between the deterministic channel model and the real measurements from IMST shows a good agreement between them regarding to the Channel Impulse Response (CIR), Power Delay Profile (PDP) and Delay Spread (DS). This can offer the UWB system designers an efficient and reliable tool to examine their systems performance on a real world simulations.
It is believed that chipless tags, often printable, will play a fundamental role for radio frequency identification technology to replace the currently widely used barcode technology. An application scenario of chipless tags that raises concerns is that the object attached with a chipless tag can be bent and even folded or crumbled. In this case, it is very difficult to identify the tag identity (ID) since some peaks or notches, which reflect the information encoded in the tag ID, in the radar cross section of the tag may disappear. In this paper, we propose to insert some error-correcting bits to the code of tag ID to improve the reliability of identifying chipless tag IDs. An error-detection channel model for dealing with this problem is developed. It is found that the channel model is asymmetric. Several error-correcting codes, namely Golay, BCH, and majority-rule-based multiple interrogations, are proposed to apply to the chipless tag encoding/decoding problem. Some performance indices of these codes, namely successful reading rate and expected successful interrogation times, are analyzed. The asymmetric property of the channel model entails the performance analysis to be conducted in a different way from the literature. Numerical and simulation results are presented to show the effectiveness of the proposed methods.
Linear least squares (LLS) estimation is a suboptimum but low-complexity localization method based on measurements of location-related parameters. It has been proved that selection of the reference anchor influences the LLS localization accuracy. In addition, hybridization of different types of measurements can fix the deficiencies of one type of measurements. In this paper, we proposed a new reference selection criterion for the hybrid TOA/RSS LLS localization technique (called H-LLSRS), which considers both measured ranges and the information about their coarse variances. Moreover, we consider a general scenario that variances of range measurements are different, and derive a weighted LLS (WLLS) estimator for hybrid TOA/RSS localization according to the information about the accurate ranging variances and the correlations among the observations. Simulation results show that if the RSS-based ranging variances are considerably larger than the TOA-based ranging variances, the H-LLS-RS localization technique yields better accuracy than the conventional LLS localization techniques. Furthermore, reference selection has no effect on the accuracy of WLLS localization technique.
As a new process to synthesize materials,mechanical alloying has been widely used in preparation of functional materials during last few decades.In the present paper,the development of mechanical alloying was simply reviewed,the principles and reactive mechanisms of mechanical alloying were introduced,the application of mechanical alloying in supersaturated solid solution,amorphous phase,nanocrystalline phase and intermetallic phase was discussed too respectively.And it is pointed out that the thermodynamics and kinetics of mechanical alloying and the dependence of phase structure or property on ball-milling conditions should be the research emphasises of the near future,the subsequent processing technology should be improved to make sure the change from laboratory to industry application.
In this paper, we present detect-and-forward relaying approaches for a coherent ultra-wideband (UWB) detection (specifically selective-Rake reception) system and for a noncoherent UWB detection (specifically differential transmittedreference, DTR) system in order to achieve greater coverage in multipath fading channels. Multiple-antenna relay system are also proposed to further enhance the overall system performance. The corresponding bit error rate (BER) performance is evaluated theoretically and via simulations. The effect of some design factors on this performance is investigated. Analytical and simulation results verify the performance improvement of the proposed relay systems over the direct transmission systems.
Welding characteristics of duplex stainless steel are analyzed in this paper.The common welding materials,methods and technology are introduced.The research progress of duplex stainless steels welding has been mainly revealed in domestic and abroad.
The mobile position estimation using time-of-arrival (ToA) is considered for the wireless NLoS geolocation exploring a signal strength(SS) based on path loss. As exploited the path attenuation, a hybrid SS-ToA approach indicates a performance improvement compared with the usual ToA method. To realize this prospect, it calls for an estimator to determine the mobile position from the time delay. In this paper, we show that the use of line-of-sight (LoS) time delay provides the same performance as that given by using both the LoS and non-LoS (NLoS) time delays. We then propose least squares (LS), weighted least squares (WLS) and maximum likelihood (ML) to estimate the mobile position. Theoretical performance of the LS and WLS is analyzed. It reveals that for different LoS time delay error variances, the LS error variance is larger than the WLS error variance, which is equal to the Cramer-Rao bound (CRB). Numerical results illustrate that the time delay performance analysis is accurate when the time delay estimate is close to its true value, i.e. for small time delay error variance. For high SNR and large effective bandwidth, the LS cannot provide the performance compared with the CRB, whereas the WLS and ML are statistically efficient.
This paper discusses the idea of merging massive Multiple Input Multiple Output (mMIMO) technology into backscatter radio communication systems. Specifically, we consider a passive - battery-less - Radio Frequency IDentification (RFID) system. The paper provides a mathematical framework for channel modelling of mMIMO-RFID system including the effect of large scale fading on the communication process. Furthermore, a novel beamforming scheme will be proposed which enhances the overall mMIMO-RFID system detection capability in terms of bit error rate over different interrogator ranges. The proposed idea would shift the complexity and cost to the reader side while simplifying the tag. The overall mMIMO-RFID system performance is investigated considering the case of multiple tags; each of them is equipped with a single antenna, in the interrogation zone of mMIMO based reader.
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