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The intensity of the reflected measuring beam is greatly reduced for laser-Doppler vibrometer (LDV) measurements on rough surfaces since a considerable part of the light is scattered and cannot reach the photodetector (laser speckle effect). The low intensity of the reflected laser beam leads to a so-called signal dropout, which manifests as noise peaks in the demodulated velocity signal. In such cases, no light reaches the detector at a specific time and, therefore, no signal can be detected. Consequently, the overall quality of the signal decreases significantly. In the literature, first attempts and a practical implementation to reduce this effect by signal diversity can be found. In this article, a practical implementation with four measuring heads of a Multipoint Vibrometer (MPV) and an evaluation and optimization of an algorithm from the literature is presented. The limitations of the algorithm, which combines velocity signals, are shown by evaluating our measurements. We present a modified algorithm, which generates a combined detector signal from the raw signals of the individual channels, reducing the mean noise level in our measurement by more than 10 dB. By comparing the results of our new algorithm with the algorithms of the state-of-the-art, we can show an improvement of the noise reduction with our approach.

This paper analyzes the secrecy outage probability of amplify and forward (AF) relaying with triple selection over real valued Nakagami fading channels. This paper derives the new upper bound cumulative distribution function expressions of the proposed system for the received signal to noise ratio in which maximal ratio combining and selection combining receivers are considered. Further, this paper derives the lower bound and asymptotic expressions for the secrecy outage probability. An interesting numerical result is that the secrecy performance of the AF relaying with selection combining is superior to the AF relaying with maximal ratio combining over arbitrary Nakagami fading channels. This paper analyzes the secrecy outage probability of amplify and forward relaying with triple selection over real valued Nakagami fading channels. This paper derives the lower bound and asymptotic expressions of the proposed scheme for the secrecy outage probability.

A simplc formulation Io compute thc envelope correlation of an antenna divemiry system is dcrired. 11 is shown how to compute the envelope correlation hom the S-parameter descnplian of the antenna system. This approach has the advantage that i t does not require the computation nor the measurement of the radiation panem of the antenna system. It also offers the advantage of providing a clca understanding ofthe effects ofmutual coupling and input match on the diversity performance of the antcnnii system.

A compact planar ultra-wideband (UWB) multiple-input–multiple-output antenna array with two radiating elements is proposed in this work. Elements separation is kept at 5.5 mm and the isolation is achieved with a floating parasitic decoupling structure not known for UWB diversity antennas previously. The antenna system performs very well over the entire UWB frequency range of 3.1–10.6 GHz. The mutual coupling between the radiating elements is below −20 dB in most of the band. The decoupling structure is investigated in detail and the diversity analysis of the antenna in Rayleigh fading environment for indoor and outdoor propagations is also presented by computing envelope correlation coefficients. The proposed antenna array measures 33 × 45.5 mm2 only and it is suitable for handheld devices, personal digital assistant (PDA)s, next generation home entertainment systems and robots.

Digital audio watermarking is a promising technology for copyright protection, yet its low embedding capacity remains a challenge for widespread applications. In this paper, the spread-spectrum watermarking algorithm is viewed as a communication channel, and the embedding capacity is analyzed and modeled with information theory. Following this embedding capacity model, we propose the extended-codebook spread-spectrum (ECSS) watermarking algorithm to heighten the embedding capacity. In addition, the diversity reception (DR) mechanism is adopted to optimize the proposed algorithm to obtain both high embedding capacity and strong robustness while the imperceptibility is guaranteed. We experimentally verify the effectiveness of the ECSS algorithm and the DR mechanism, evaluate the performance of the proposed algorithm against common signal processing attacks, and compare the performance with existing high-capacity algorithms. The experiments demonstrate that the proposed algorithm achieves a high embedding capacity with applicable imperceptibility and robustness.

The flexible job shop scheduling problem (FJSP) is an extension of the classical job shop scheduling problem and one of the more well-known NP-hard problems. To get better global optima of the FJSP, a novel hybrid whale optimization algorithm (HWOA) is proposed for solving FJSP, in which minimizing the makespan is considered as the objective. Firstly, the uniformity and extensiveness of the initial population distribution are increased with a good point set (GPS). Secondly, a new nonlinear convergence factor (NCF) is proposed for coordinating the weight of global and local search. Then, a new multi-neighborhood structure (MNS) is proposed, within which a total of three new neighborhoods are used to search for the optimal solution from different directions. Finally, a population diversity reception mechanism (DRM), which ensures to some extent that the population diversity is preserved with iteration, is presented. Seven international benchmark functions are used to test the performance of HWOA, and the results show that HWOA is more efficient. Finally, the HWOA is applied to 73 FJSP and four Ra international instances of different scales and flexibility, and the results further verify the effectiveness and superiority of the HWOA.

In this paper, we have investigated and reported the performance of free-space optical (FSO) links operating in adverse atmospheric conditions. Since FSO links share operational similarity with fiber communication; hence, we believe that a cost-effective FSO framework can play a significant role in the transparent integration of high-speed network access backbones with the end-users. Different modulation formats, complemented with spatial diversity techniques, are discussed in this paper to strategize performance optimization of FSO links. Using bit error rate (BER) and signal-to-noise ratio (SNR) as performance metrics, it was found that binary phase-shift keying (BPSK) qualifies as the best technique modulation technique delivering SNR gain of 10 dB over on–off keying (OOK) operating link under similar channel conditions. Further performance optimization was achieved using space diversity reception wherein SNR witnessed a gain of 3 dB gain over the single-channel FSO link. In terms of application, the proposed model can help in developing a citizen-centric smart city ecosystem that can support seamless communication between heterogeneous smart devices.

Orthogonal frequency division multiplexing (OFDM) technology is presented for use in free-space optical (FSO) communications accompanied by the spatial diversity reception. Using quadrature phase shift keying (QPSK) modulation formats, the OFDM signals show robustness to support high spectral efficiency and compatibility with the spatial diversity reception to improve receiver sensitivity. Compared with the single-carrier QPSK signal, the OFDM-QPSK signal with 64 sub-carriers can reduce the BER from 2.87 × 10−3 to 2.98 × 10−4 at the SNR of 6 dB. Using a two-aperture spatial diversity reception with OFDM, the BER can be reduced from 2.45 × 10−3 of a single receiver to 6.10 × 10−4 under moderate turbulence conditions. Under strong turbulence, the BER of the single receiver is 2.14 × 10−2. It can be improved to 1.16 × 10−3 by using four-aperture receivers, and even 6.87 × 10−4 by using six-aperture receivers. The optimized aperture number should be selected according to channel conditions.

Compared with point-to-point underwater wireless optical communication (UWOC) systems with a single direction, the underwater multi-faceted optical base station (OBS) offers independent fields of view and directions for each receiving detector, supporting multiple user access and mobile communication. This study aims at the issue of link interruptions and a limited communication area caused by restricted OBS receiver fields of view when underwater devices move. A field-of-view model and spatial angle diversity reception framework for the multi-faceted OBS in underwater channels have been developed, visualizing the effective reception field of the OBS. This model helps analyze the impact of multi-faceted OBS detector layouts on link performance in underwater environments. Furthermore, under constraints on the number of detectors, configuration adjustments are made to the field-of-view angles and deflection angles of detectors. Simulation results show that, under the same typical underwater environmental conditions, the optimized configuration reduces the blind area compared to the typical configuration, enhancing the effective spatial field of view of the OBS receiver by over 10%. The OBS’s effective communication coverage for mobile devices on different planes is also improved. This research provides a theoretical model and parameter configuration guidelines for the design of the underwater multi-faceted OBS.

A new compact, uniplanar, polarisation-diversity, monopole-like slot antenna for ultra-wideband (UWB) systems is presented. The proposed design effectively integrates orthogonally fed slot antennas, utilising the uniplanar nature of coplanar waveguide without degrading the time-domain characteristics and diversity performance. To achieve high isolation between the ports, a strip is integrated diagonally in the ground plane. Furthermore, by loading arc shaped slot resonators on the feeding structures, the proposed antenna successfully rejects the undesired subband, assigned for IEEE 802.11a and HIPERLAN/2. The measured results demonstrate that the antenna provides a 2:1 voltage standing wave ratio (VSWR) band from 2.76 to 10.75 GHz whereas showing rejection in the frequency band 4.75–6.12 GHz, along with an inter-port isolation better than 15 dB. The proposed radiator displays a nearly omnidirectional radiation pattern, along with a moderate gain and efficiency. The envelope correlation coefficient discloses a good diversity performance across the UWB spectrum. Furthermore, the time-domain analysis shows minimum dispersion to the radiated pulse. In addition, the experimental analysis indicates that the proposed design is less disposed to the housing effects when mounted in metallic casing. All these features make the proposed antenna a viable candidate for UWB dual-polarised multiple-input–multiple-output applications.