scholarly journals Optimum Elements Selection in IRS-Assisted UAV Communications with Phase Errors

2021 ◽  
Author(s):  
sobia Jangsher ◽  
Arafat Al-Dweik ◽  
MOHAMMAD AHMAD Al-Jarrah ◽  
Emad Alsusa ◽  
Mohamed-Slim Alouini
Keyword(s):  
Selection Process ◽  
Least Square ◽  
High Signal ◽  
Phase Errors ◽  
Optimum Selection ◽  
Np Hard Problem ◽  
Aerial Vehicle ◽  
Lower Complexity ◽  
Von Mises ◽  
Reflecting Surfaces

<div>This letter considers minimizing the bit error rate (BER) of unmanned aerial vehicle (UAV) communications assisted by intelligent reflecting surfaces (IRSs). By noting that increasing the number of IRS elements in the presence of phase errors does not necessarily improve the BER, it is crucial to use only the elements that contribute to reducing the BER. Consequently, we propose an efficient algorithm to activate only the elements that improve the BER. The proposed algorithm has lower complexity and comparable BER to the optimum selection process, which is an NP-hard problem. The accuracy of the estimated phase is evaluated by deriving the probability distribution function (PDF) of the least-square (LS) channel estimator, and showing that the PDF can be closely approximated by the von Mises distribution at high signal-to-noise ratios (SNRs). The obtained analytical and simulation results show that using all the available reflectors can significantly deteriorate the BER, and thus, elements’ selection is necessary. In particular scenarios, using about 26% of the reflectors provides more than 10 fold BER reduction.</div>

scholarly journals Optimum Elements Selection in IRS-Assisted UAV Communications with Phase Errors

2021 ◽  
Author(s):  
sobia Jangsher ◽  
Arafat Al-Dweik ◽  
MOHAMMAD AHMAD Al-Jarrah ◽  
Emad Alsusa ◽  
Mohamed-Slim Alouini
Keyword(s):  
Selection Process ◽  
Least Square ◽  
High Signal ◽  
Phase Errors ◽  
Optimum Selection ◽  
Np Hard Problem ◽  
Aerial Vehicle ◽  
Lower Complexity ◽  
Von Mises ◽  
Reflecting Surfaces

<div>This letter considers minimizing the bit error rate (BER) of unmanned aerial vehicle (UAV) communications assisted by intelligent reflecting surfaces (IRSs). By noting that increasing the number of IRS elements in the presence of phase errors does not necessarily improve the BER, it is crucial to use only the elements that contribute to reducing the BER. Consequently, we propose an efficient algorithm to activate only the elements that improve the BER. The proposed algorithm has lower complexity and comparable BER to the optimum selection process, which is an NP-hard problem. The accuracy of the estimated phase is evaluated by deriving the probability distribution function (PDF) of the least-square (LS) channel estimator, and showing that the PDF can be closely approximated by the von Mises distribution at high signal-to-noise ratios (SNRs). The obtained analytical and simulation results show that using all the available reflectors can significantly deteriorate the BER, and thus, elements’ selection is necessary. In particular scenarios, using about 26% of the reflectors provides more than 10 fold BER reduction.</div>

scholarly journals Capacity Analysis of IRS-Based UAV Communications with Imperfect Phase Compensation

2021 ◽  
Author(s):  
MOHAMMAD AHMAD Al-Jarrah ◽  
Emad Alsusa ◽  
Arafat Al-Dweik ◽  
Daniel K. C. So
Keyword(s):  
Signal To Noise Ratio ◽  
Phase Error ◽  
Random Variable ◽  
System Capacity ◽  
High Signal ◽  
Capacity Analysis ◽  
Capacity Loss ◽  
Von Mises ◽  
Reflecting Surfaces ◽  
Incident Waves

<div>This paper presents the capacity analysis of unmanned aerial vehicles (UAVs) communications supported by flying intelligent reflecting surfaces (IRSs). In the considered system, some of the UAVs are equipped with an IRS panel that applies certain phase-shifts to the incident waves before being reflected to the receiving UAV. In contrast to existing work, this letter considers the effect of imperfect phase knowledge on the system capacity, where the phase error is modeled as a von Mises random variable with parameter k. Analytical results, corroborated by Monte Carlo simulations, show that the achievable capacity is dependent on the phase error, however, the capacity loss becomes negligible at high signal-to-noise ratio (SNR) and when k>6.</div>

scholarly journals Capacity Analysis of IRS-Based UAV Communications with Imperfect Phase Compensation

2021 ◽  
Author(s):  
MOHAMMAD AHMAD Al-Jarrah ◽  
Emad Alsusa ◽  
Arafat Al-Dweik ◽  
Daniel K. C. So
Keyword(s):  
Signal To Noise Ratio ◽  
Phase Error ◽  
Random Variable ◽  
System Capacity ◽  
High Signal ◽  
Capacity Analysis ◽  
Capacity Loss ◽  
Von Mises ◽  
Reflecting Surfaces ◽  
Incident Waves

<div>This paper presents the capacity analysis of unmanned aerial vehicles (UAVs) communications supported by flying intelligent reflecting surfaces (IRSs). In the considered system, some of the UAVs are equipped with an IRS panel that applies certain phase-shifts to the incident waves before being reflected to the receiving UAV. In contrast to existing work, this letter considers the effect of imperfect phase knowledge on the system capacity, where the phase error is modeled as a von Mises random variable with parameter k. Analytical results, corroborated by Monte Carlo simulations, show that the achievable capacity is dependent on the phase error, however, the capacity loss becomes negligible at high signal-to-noise ratio (SNR) and when k>6.</div>

scholarly journals THE INFLUENCE OF RECRUITMENT AND SELECTION PROCESS ON TECHNICAL EMPLOYEE PERFORMANCE IN PT. TELKOM AKSES NORTH SURABAYA

2020 ◽  
Vol 4 (1) ◽  
pp. 84-93
Author(s):  
Agustiawan Djoko Baruno ◽  
Leny Novita Permatasari
Keyword(s):  
Selection Process ◽  
Employee Performance ◽  
Selection Effect ◽  
Analytical Techniques ◽  
Partial Least Square ◽  
Least Square ◽  
Primary Data ◽  
P Values ◽  
Recruitment And Selection ◽  
Selection Of

This research  aims to  analyze the influence of the process of recruitment and  selection simultaneously as well as partially against employee performance support. In this study using a type of associative methods and quantitative data primary data sources by using the instrument of the questionnaire. The population in this research is the employee technician  PT. Telkom Akses Surabaya Utara as many as 56 respondents.Sampling technique used was saturated samples or often called as well with a sample of the total. Analytical techniques used in this research is the Partial Least Square (PLS) includes test convergen validity, discriminan validity, composite realibility, cronch alpha, R- square, simulan test (test F) and partial test (test T). The results of the analysis explains that the process of recruitment and selection effect simultaneously against the performance of the employee, this is indicated by the value of the count of 40.991 F is greater than F table 4.02 and significance value (S ig) 0.000 smaller than 0.05 and the process of recruitment of influential partially against the performance of the employee, this is shown by the value T calculate of 3.024 is greater than 1.96 table T and value its significance (P values) 0.003 smaller than 0.05. As well as a selection of influential partially against the performance of the employee, this is shown by the value T calculate of 2.856 is greater than 1.96 table T and value its significance (P values) 0.004 smaller than 0.05

scholarly journals New Lindley Half Cauchy Distribution: Theory and Applications

2020 ◽  
Vol 9 (4) ◽  
pp. 1-7
Keyword(s):  
Maximum Likelihood ◽  
Real Data ◽  
Cauchy Distribution ◽  
Least Square ◽  
Cumulative Distribution ◽  
Likelihood Method ◽  
Estimation Methods ◽  
Model Parameters ◽  
Data Set ◽  
Von Mises

In this paper, we have defined a new two-parameter new Lindley half Cauchy (NLHC) distribution using Lindley-G family of distribution which accommodates increasing, decreasing and a variety of monotone failure rates. The statistical properties of the proposed distribution such as probability density function, cumulative distribution function, quantile, the measure of skewness and kurtosis are presented. We have briefly described the three well-known estimation methods namely maximum likelihood estimators (MLE), least-square (LSE) and Cramer-Von-Mises (CVM) methods. All the computations are performed in R software. By using the maximum likelihood method, we have constructed the asymptotic confidence interval for the model parameters. We verify empirically the potentiality of the new distribution in modeling a real data set.

Firm-level agreements, employment strategies and temporary workers

2020 ◽  
Vol 42 (1) ◽  
pp. 194-212
Author(s):  
Saverio Minardi
Keyword(s):  
Fixed Effects ◽  
Selection Process ◽  
Temporary Employment ◽  
Least Square ◽  
Temporary Workers ◽  
Firm Level ◽  
Data Set ◽  
Content Type ◽  
Collective Agreements ◽  
The Impact

Purpose The purpose of this paper is to investigate the impact of two-tier firm-level collective agreements on firms’ propensity to use temporary employment, accounting for the process of self-selection of firms into different bargaining levels in the Italian context. It further examines which firm-level characteristics drive this process of selection. Design/methodology/approach The empirical analysis uses a panel data set of Italian firms for the years 2005, 2007, 2010 and 2015. Estimations are produced and compared through ordinary least square regression, random-effects and fixed-effects models. Findings Results show that enterprises adopting two-tier firm-level agreements (TTFA) are associated with lower levels of temporary workers. However, a longitudinal analysis suggests that introducing a TTFA does not impact firms’ propensity to employ temporary workers. This novel finding highlights the presence of a selection process based on firm-level time-constant characteristics. The paper argues that these characteristics refer to management orientation toward high-road rather than low-road employment strategies. Further evidence is brought in support of this claim, showing that firms’ propensity toward the provision of training for their labor force partially explain the process of selection. Originality/value The study is the first to analyze the impact of secondary-level collective agreements on firms’ reliance on temporary employment, offering new evidence on the causes of the expansion of temporary employment. It further highlights the relevance of employers’ strategies in shaping the impact of the bargaining structure.

scholarly journals Optimization of Unmanned Aerial Vehicle Augmented Ultra-Dense Networks

2020 ◽  
Author(s):  
Alireza Zamani ◽  
Robert Kämmer ◽  
Yulin Hu ◽  
Anke Schmeink
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Optimization Problem ◽  
Original Problem ◽  
Heuristic Method ◽  
Linear Structure ◽  
Small Cells ◽  
Simulation Studies ◽  
Dense Networks ◽  
Aerial Vehicle ◽  
Lower Complexity

Abstract In this paper, we study the integration of unmanned aerial vehicle small cells (UAV-SC) for the purpose of augmenting or temporarily restoring service to an ultra-dense cellular network. The aim is to minimize the overall power consumption of the network by jointly optimizing the number of UAV-SCs, their placement, associations and the power allocation, subject to user QoS, transmit power and fronthaul capacity constraints. As the resulting optimization problem is non-convex and computationally inefficient to solve, we investigate lower complexity alternatives. By reformulating the original problem, a linear structure can be obtained that is efficiently solved by off-the-shelf solvers. Furthermore, we also propose a meta-heuristic method that is based on particle swarm optimization. The performance of the proposed methods is evaluated via simulation studies and compared to state-of-the-art techniques. The results illustrate that the proposed methods consistently outperform conventional techniques by deploying fewer UAV-SCs and also lowering the transmit powers. Furthermore, considerable power savings were observed particularly for low QoS demands and dense scenarios.

scholarly journals HALF LOGISTIC MODIFIED EXPONENTIAL DISTRIBUTION: PROPERTIES AND APPLICATIONS

2020 ◽  
pp. 276-287
Author(s):  
Arun Kumar Chaudhary ◽  
Vijay Kumar
Keyword(s):  
Exponential Distribution ◽  
Likelihood Estimation ◽  
Real Data ◽  
Least Square ◽  
Estimation Methods ◽  
Logistic Distribution ◽  
Model Parameters ◽  
Type I ◽  
Data Set ◽  
Von Mises

In this study, we have introduced a three-parameter probabilistic model established from type I half logistic-Generating family called half logistic modified exponential distribution. The mathematical and statistical properties of this distribution are also explored. The behavior of probability density, hazard rate, and quantile functions are investigated. The model parameters are estimated using the three well known estimation methods namely maximum likelihood estimation (MLE), least-square estimation (LSE) and Cramer-Von-Mises estimation (CVME) methods. Further, we have taken a real data set and verified that the presented model is quite useful and more flexible for dealing with a real data set. KEYWORDS— Half-logistic distribution, Estimation, CVME ,LSE, , MLE

scholarly journals An Optimal Receive Antenna Selection Algorithm using GA in MIMO Communication System

2020 ◽  
Vol 9 (5) ◽  
pp. 630-633
Keyword(s):  
Wireless Communication ◽  
Communication Systems ◽  
Data Transfer ◽  
Selection Process ◽  
Antenna Selection ◽  
Wireless Communication Systems ◽  
Optimum Selection ◽  
Receiving Antenna ◽  
Mimo Technology ◽  
Selection Of

MIMO technology offers large improvements in data transfer and connection range no bandwidth extra or processing potential in wireless communication,. Multiple transmitters and receivers are used to simultaneously transfer enormous amounts of data. Using many antennas transmitting and receiving, efficiency can be enhanced for wireless communication systems operating in fading environments. But the key downside in the new MIMO scheme, due to multiple Radio Frequency chains, is increased complexity and high cost. A daunting incentive is the development of techniques to reduce hardware and computing costs of the systems with a huge amount of antennas. The optimum selection of the receiver antenna subset is a very effective approach to achieving this goal. Genetic algorithm is used in this paper to choose the receivers from the available set of antennas that would then be compared with an existing receiving antenna selection process.

scholarly journals Performance Evaluation of UAV-Based NOMA Networks with Hardware Impairment

Electronics ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 94
Author(s):  
Chung Ho Duc ◽  
Sang Quang Nguyen ◽  
Chi-Bao Le ◽  
Ngo Tan Vu Khanh
Keyword(s):  
System Performance ◽  
Performance Metrics ◽  
Signal To Noise Ratio ◽  
Ergodic Capacity ◽  
High Signal ◽  
Performance Loss ◽  
Hardware Impairments ◽  
Asymptotic Expressions ◽  
Aerial Vehicle ◽  
Hardware Impairment

In this paper, we evaluate the outage performance of a non-orthogonal multiple access (NOMA)-enabled unmanned aerial vehicle (UAV) where two users on the ground are simultaneously served by a UAV for a spectral efficiency purpose. In practice, hardware impairments at the transceiver cause distortion noise, which results in the performance loss of wireless systems. As a consequence, hardware impairment is an unavoidable factor in the system design process. Hence, we take into account the effects of hardware impairment (HI) on the performance of the proposed system. In this setting, to evaluate the system performance, the closed-form expressions of the outage probability of two NOMA users and the ergodic capacity are derived as well as their asymptotic expressions for a high signal-to-noise ratio (SNR). Finally, based on Monte-Carlo simulations, we verify the analytical expressions and investigate the effects on the main system parameters, i.e., the transmit SNR and level of HI, on the system performance metrics. The results show that the performance for the near NOMA user is better than of that for the far NOMA user in the case of perfect hardware; however, in the case of hardware impairment, an inversion happens at a high transmit power of the UAV in terms of the ergodic capacity.

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