This paper investigates the problem of detection and classification of unmanned aerial vehicles (UAVs) in the presence of wireless interference signals using a passive radio frequency (RF) ...surveillance system. The system uses a multistage detector to distinguish signals transmitted by a UAV controller from the background noise and interference signals. First, RF signals from any source are detected using a Markov models-based naïve Bayes decision mechanism. When the receiver operates at a signal-to-noise ratio (SNR) of 10 dB, and the threshold, which defines the states of the models, is set at a level 3.5 times the standard deviation of the preprocessed noise data, a detection accuracy of 99.8% with a false alarm rate of 2.8% is achieved. Second, signals from Wi-Fi and Bluetooth emitters, if present, are detected based on the bandwidth and modulation features of the detected RF signal. Once the input signal is identified as a UAV controller signal, it is classified using machine learning (ML) techniques. Fifteen statistical features extracted from the energy transients of the UAV controller signals are fed to neighborhood component analysis (NCA), and the three most significant features are selected. The performance of the NCA and five different ML classifiers are studied for 15 different types of UAV controllers. A classification accuracy of 98.13% is achieved by k-nearest neighbor classifier at 25 dB SNR. Classification performance is also investigated at different SNR levels and for a set of 17 UAV controllers which includes two pairs from the same UAV controller models.
This study investigates the effect of COVID-19-induced uncertainty on the overall stock market and the stock performance of the tourism and hospitality industry and its subsectors utilizing a novel ...time-varying robust Granger causality test. The results show that the COVID-19 pandemic–induced uncertainty has an adverse impact on the overall economy, tourism and hospitality industry, and subsectors of tourism and hospitality. However, the impact of COVID-19 pandemic–induced uncertainty is more significant in the tourism and hospitality industry and its subsectors. In particular, hotels sector has experienced the largest impact from the COVID-19 pandemic, followed by restaurants and airline sectors, respectively. Research and practical implications are discussed.
JEL Classification: C1, C5, F2, G11, G17, G41
The future 5G networks are expected to use millimeter wave (mmWave) frequency bands to take advantage of the large unused spectrum. However, due to the high path loss at mmWave frequencies, coverage ...of mmWave signals can get severely reduced, especially for non-line-of-sight (NLOS) scenarios as mmWave signals are severely attenuated when going through obstructions. In this work, we study the use of passive metallic reflectors of different shapes/sizes to improve 28 GHz mmWave signal coverage for both indoor and outdoor NLOS scenarios. We quantify the gains that can be achieved in the link quality with metallic reflectors using measurements, analytical expressions, and ray tracing simulations. In particular, we provide an analytical model for the end-to-end received power in an NLOS scenario using reflectors of different shapes and sizes. For a given size of the flat metallic sheet reflector approaching to the size of the incident beam, we show that the reflected received power for the NLOS link is the same as line-of-sight (LOS) free space received power of the same link distance. Extensive results are provided to study the impact of environmental features and reflector characteristics on NLOS link quality.
Purpose
This study aims to examine the link between corporate social responsibility (CSR) and idiosyncratic risk in the restaurant industry. The study also explores whether brand diversification ...magnifies the risk reduction effect of CSR in the restaurant industry.
Design/methodology/approach
The study uses an unbalanced panel of 274 firm-year observations for 43 restaurant firms over the period 1995–2015. Models are estimated via fixed effect regression with robust standard errors.
Findings
The study finds that CSR involvement reduces idiosyncratic risk and this risk reduction is intensified when restaurant firms operate a portfolio of brands.
Research limitations/implications
The study’s findings are limited to restaurant industry, therefore, generalization of the findings to other industries requires delicate care. Brand diversification is a simple brand count due to a lack of brand sales data.
Practical implications
CSR activities are not cost burden for restaurant firms. Indeed, CSR could be a viable strategy to reduce the volatility in future expected cash flows, hence the idiosyncratic risk. This risk reduction could help owners/managers access to capital with lower cost. Moreover, the study suggests that CSR practices should not be implemented in isolation from firm marketing strategy such as portfolio of brands.
Originality/value
Although prior hospitality research puts forth some evidence using systematic risk as the measure of firm risk, this measure may not best suit the purpose in CSR context given that CSR is a direct, firm-specific strategy. Hence, the current study provides both new evidence with firm-specific, idiosyncratic risk and introduces an important contingency situation when the risk reduction effect of CSR would become more profound for restaurant firms.
This study examines the effect of board diversity on risk-taking for tourism firms and analyzes the moderating effect of board independence, CEO duality, and free cash flows in this proposed ...relationship. Using a composite index of board diversity and a sample of tourism firms from the US hotel, restaurant, and airline industries, we find that greater board diversity leads to lower risk-taking, measured in standard deviation of return on assets. Moreover, we report that the risk-reduction effect of board diversity is more profound when tourism firms have less board independence and less free cash flows for investments. When board diversity is decomposed into relation-oriented and task-oriented diversity attributes, we find that only the task-oriented diversity is influential in reducing firm risk-taking for tourism firms. Akin to main analysis, the board independence and free cash flows are significant moderators of the relationship between task-oriented diversity and firm risk-taking.
Phase noise (PHN) and in-phase/quadrature (I/Q) imbalance are two major radio-frequency (RF) impairments in direct-conversion wireless transceivers. Beamforming and orthogonal frequency-division ...multiplexing (OFDM) schemes have been adopted in broadband wireless standards due to their significant performance gains. In this paper, we analyze the impact of joint I/Q imbalance and PHN on beamforming OFDM direct-conversion transceivers. We derive an exact normalized-mean-square-error expression (NMSE) and examine several special and asymptotic cases to gain insights. One such insight is that, asymptotically, for both large signal-to-noise ratio (SNR) and the beamforming array size, the PHN and I/Q imbalance effects become decoupled.
•This study examines the relationship between board diversity and firm performance in the U.S. tourism sector.•The moderating effect of institutional ownership is explored as a contingency that might ...affect the proposed relationship.•Models are estimated via two-way fixed-effects regression analysis using a panel data set of 279 firm-year observations.•A positive association is found between board diversity and firm performance as proxied by Tobin’s Q.•The positive effect of board diversity on tourism firms’ performance is stronger when institutional ownership is weak.
This study examines the relationship between board diversity and firm performance in the U.S. tourism sector by using institutional ownership as a contingency that moderates this relationship. The study's sample includes publicly-traded companies from the U.S. restaurant, hotel and airline industries. The hypotheses are tested via two-way fixed-effects regression, and the findings of the study indicate that board diversity is positively associated with financial performance (Tobin's Q), and the effect of board diversity on performance is contingent on the degree of institutional ownership. More precisely, the study finds that board diversity has a larger effect on financial performance when institutional ownership is low on a tourism firm's ownership structure. Overall, the findings suggest that boards' internal control and monitoring on management is important to derive higher financial performance, and even yet it is more important when external monitoring by institutional owners, proxied by percentage of institutional ownership, is weak.
In this study, we examine the effect of corporate social responsibility (CSR) performance on mergers and acquisitions (M&A) deal premiums. More precisely, we explore the value enhancing role of ...target’s pre-acquisition CSR performance at an M&A transaction by focusing on the deal premiums. We also examine whether firms in the service industries experience a higher deal premium due to their CSR performance compared to firms in other industries. We use several data sources (i.e. MSCI ESG KLD STATS, FactSet, Compustat and CRSP) to compile the final sample of the study, 277 completed acquisitions over the period 1996–2018. We use ordinary least square regression to estimate empirical models and find that target’s pre-acquisition CSR performance is positively related to deal premium. Moreover, the moderation analysis indicates that the positive effect of targets’ CSR performance on deal premium is more profound for firms operating in the service industries than those in non-service industries. The findings of the study is robust to different operationalizations of deal premium. Additionally, examining the positive and negative CSR attributes separately, we reveal consistent evidence with the prediction that positive CSR involvement of target firms increases the deal premium.
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