Many different types of promising spectrum sensing algorithms for Cognitive Radio (CR) have already been developed. However, many of these algorithms lack robustness with respect to signal statistical parameters uncertainties, such as the noise variance or the shape of its distribution (often assumed to be simply Gaussian). In conjunction with the low Signal-to-Noise Ratio (SNR) requirements, this lack of robustness can often render interesting sensing algorithms impractical for real-life applications. In this thesis, we primarily focus on the impact of heavy-tail noise distributions on different CR detectors and the use of signal limiters (mostly the spatial sign function) to improve their robustness to such noise distributions. Introducing a non-linear transformation of the received signal prior to its processing by the detector fundamentally changes the signal distribution which in turn modifies the distribution of the detector statistic. In order to parametrize the detector and study its performance, it is then necessary to know the shape of the modified distribution.Three types of detectors are investigated: a generic second-order cyclic-feature detectors, a Scaled-Largest Eigenvalue (SLE) detector studied in the context of stationary time-series and a new Sequential Likelihood Ratio Test (SLRT) detector. The analysis conducted for each detector revolves around the influence of its parameters, the distribution of the detector statistic and several comparisons with similar detectors for various detection scenarios. Our results indicate that at the cost of a moderate performance loss in a Gaussian noise environment, all the detectors fitted with a signal limiter become robust to impulsive noise and noise parameters uncertainties. We provide analytical approximations for the detectors statistical distribution that allow us to use the detectors in such configurations as well as to study their performance for different signal limiters and noise distributions. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Impulsive differential equations are often used in mathematical modelling to simplify complicated hybrid models. We propose an inverse framework inspired by impulsive differential equations, called impulse extension equations, which can be used as a tool to determine when these impulsive models are accurate. The linear theory is the primary focus, for which theorems analoguous to ordinary and impulsive differential equations are derived. Results explicitly connecting the stability of impulsive differential equations to related impulse extension equations are proven in what we call time scale consistency theorems. Opportunities for future research in this direction are discussed. Following the work of Smith? and Hove-Musekwa on malaria vector control by impulsive insecticide spraying, we propose a novel autonomous vector control scheme based on human disease incidence. Existence and stability of periodic orbits is established. We compare the implementation cost of the incidence-based control to a fixed-time spraying schedule. Hybrid control strategies are discussed.

Impulsive differential equations are useful for modelling certain biological events. We present three biological applications showing the use of impulsive differential equations in real-world problems. We also look at the effects of stability on a reduced two-dimensional impulsive HIV system. The first application is a system describing HIV induction-maintenance therapy, which shows how the solution to an impulsive system is used in order to find biological results (adherence, etc). A second application is an HIV system describing the interaction between T-cells, virus and drugs. Stability of the system is determined for a fixed drug level in three specific regions: low, intermediate and high drug levels. Numerical simulations show the effects of varying drug levels on the stability of a system by including an impulse. We reduce these two models to a two-dimensional impulsive model. We show analytically the existence and uniqueness of T-periodic solutions, and show how stability changes when varying the immune response rate, the impulses and a certain nonlinear infection term. The third application shows how seasonal changes can be incorporated into an impulsive differential system of Rift Valley Fever, and looks at how stability may differ when impulses are included. The analysis of impulsive differential systems is crucial in developing more realistic mathematical models for infectious diseases.

The emergence of drug resistance is a serious threat to the long-term virologic success and durability of HIV-1 therapy. Adherence has been shown to be a major determinant of drug resistance; however, each pharmacologic class of antiretroviral drugs has a unique adherence–resistance relationship. We develop an immunological model of the HIV-1 infected human immune system that integrates the unique mechanisms of action of reverse transcriptase and protease inhibiting drugs. A system of impulsive differential equations is used to examine the drug kinetics within CD4⁺ T cells. Stability analysis was preformed to determine the long-term dynamics of the model. Using the endpoints of an impulsive periodic orbit in the drug levels, the maximal length of a drug holiday while avoiding drug resistance is theoretically determined; the minimum number of doses that must be subsequently taken to return to pre-interruption drug levels is also established. Heterogeneity in inter-individual differences on drug-holiday length is explored using sensitivity analysis based on Latin Hypercube Sampling and Partial Rank Correlation Coefficient analysis. Extremely short drug holidays are acceptable, as long as they are followed by a period of strict adherence. Numerical simulations demonstrate that if the drug holiday exceeds these recommendations, the cost in virologic rebound is unacceptably high. These theoretical predictions are in line with clinical results and may also help form the basis of future clinical trials.

Background: The expansion of e-commerce and online orders have led to companies creating new marketing strategies, where impulsive purchases are important in order to boost sales. However, this also has negative aspects concerning overconsumption and the environmental impact. Consumers are more likely to have negative post-purchase emotions when making an impulsive purchase, and thus are more prone to return products. This research aims at creating a deeper understanding about consumers’ post-purchase emotions after making an impulsive purchase and how a product return affects the post-purchase emotions.    Problem discussion: Impulsive buying is critical for online stores and retailers are actively trying to increase these purchases for all customers, but at the same time, there is a growing number of product returns. This makes it important for firms to understand how consumers think and react to an impulsive purchase, since this supposedly has an impact on product returns. By providing a deeper understanding regarding the consumer’s post-purchase emotions one can specify such reactions on shoppers and help future marketing activities preventing consumers’ negative emotions in the purpose of increasing organizational profitability and decreasing the environmental impact.    Purpose: The purpose of this research is to build a theory that will provide organizations with knowledge about the chosen segment of Swedish women in the age 18-35 post-purchase emotions after impulsive buying. The findings of this study can contribute with additional insights to previous theoretical knowledge about post-purchase emotions after impulsive shopping.   Method: This qualitative research has been conducted by using 14 semi-structured interviews with the chosen segment of Swedish females in the age 18-35 who had previously shopped impulsively online and returned products. For the data analysis, an interpretative phenomenological analysis was used, providing the research with reflections regarding the perspective of the participants’ experiences of impulsive shopping and their post-purchase emotions.  Results: This research indicates that the participants generally held a negative view of impulsive buying, where they reduced/strengthened their post-purchase emotions through three rationalizations which were named by the authors “Social Proof”, “Use-Principle” and “Limited Funds”. When making a product return, the participants either had strengthened emotions or the negative emotions were turned into positive emotions. This was connected to three themes found by the authors which were called “Income”, “Return Policy”, and “Social and Environment”. The analyzed findings were presented in a developed framework.

Influencer marketing är en effektiv marknadsföringsmetod för att öka köpbeteendet hos konsumenter. Uppsatsens fokus är att undersöka Millenials och Generation Z:s klädkonsumtion av Fast Fashion och hur de påverkas av Influencer marketing samt förhållningssätt till miljöfrågor vid klädköp. En växande klädkonsumtion och klädtillverkning går inte ihop med behovet av att konsumera mindre och engagera sig kring miljöfrågor. En studie har genomförts i form av intervjuer med strategiskt utvalda respondenter inom generationskategorierna Millennials och Generation Z. Resultatet visar att generationerna inte reflekterar över den miljöpåverkan klädindustrin har, samt att kvinnor och yngre personer i större utsträckning än män och äldre personer påverkas av Influencer marketing. Resultatet visar även att Influencer marketing är ett mycket effektivt marknadsföringsverktyg för att öka köpbeteendet hos konsumenter.

Date: 02.06.2021 Level: Bachelor thesis in Business Administration, 15 cr Institution: School of Business, Society and Engineering, Mälardalen University Authors: Avesta Aspitman (94/05/24) , Beata Valeria Karacsonyi (95/08/01), Dalia Uthman (97/01/07)                      Title: Changes in online shopping activities of Generation Z students - A qualitative study on online purchase intent and impulsivity during Covid-19 Tutor: Leanne Johnstone Keywords: Online purchase intent, Covid-19, Generation Z, Students, Impulsive shopping Research question:  How has Covid-19 impacted the online purchase intent of students at Mälardalen region of Sweden? Purpose: To examine how the impact of Covid-19 has affected the online      purchase intent of students of Mälardalen region in Sweden. Method: This study has an inductive approach with a qualitative data collection. Semi-structured interviews were held with nine students within the Mälardalen region and were conducted online through the communication tool ZOOM. A thematic analysis was conducted to analyze the collected primary data and with assistance of the literature review, four dimensions of the topic could be identified: financial, performance, time and psychological. Conclusion: Online purchasing during Covid-19 has increased and thus, affected the online purchasing intent of students in the same way. This is mainly due to restrictions and due to the pandemic and the consumer’s perception of the online retailers’ adaptation to it. Increased impulsivity due to Covid-19 cannot be concluded in this study and thus contradicts existing and recent literature that suggests impulsive shopping increases in crises. Instead, Generation Z students are more inclined to save their money and make strategic choices to purchase online.

The study of impulsive purchase is a facet of consumer behavior that has intrigued the interest of academics for decades. The research primarily focuses on the variables that influence this behavior, indicating the impact of various antecedents. Recent research has shown that age has an impact on customer behavior when it comes to impulse purchases. Furthermore, the results are still few and provide contradictory conclusions. The goal of this study is to close this gap by examining the antecedent elements that affect each person's unique traits, such as extrinsic and extrinsic determinants of impulsiveness, and then comparing post-purchase happiness across generations X and Y. To study the elements that underlie their impulsive buying behavior and the consequences on satisfaction after the purchase, the researchers used largely a qualitative technique, including a questionnaire, interviews, and observation of the phenomena. The findings show that generation X is less prone to impulse purchases than generation Y. In both generations, females were shown to be more prone than males to buy on impulse. The purpose of this study is to contribute to future research because it is critical to further identify the fundamental elements of impulsive purchase and their impact on generations X and Y in order to develop more successful strategies.

<p>  </p> <p>Harshly affected by recent economic recessions, young Millennials had been having a hard time finding a job that meets their expectations or an affordable house. Although it seems like Millennials are suffering financial hardship, media often depict them as impulsive shoppers. Taking inspiration from this contradictory aspect of Millennials, this research explores the relationship between Millennials’ subjective evaluation of their financial status and their spending behaviors. In order to achieve this goal, this study first applies a new psychometric scale, called perceived financial insecurity, to measure Millennials’ feelings and thoughts toward their financial status. Second, it examines the psychological antecedents to perceived financial insecurity. Last, the relationship between financial insecurity and spending behaviors in several consumption areas is examined using the framework of compensatory behavior from social psychology.</p> <p>For the first stage of this research, a perceived financial insecurity scale was developed by conducting literature reviews, in-depth interviews with Millennial consumers, and two online surveys. Consequently, five statements were selected from the initial pool of questionnaire items and used in later stages of this research. Next, another online survey was conducted to empirically test for the impact of six antecedents, namely, perfectionism, self-efficacy, perceived economic mobility, resource scarcity, materialism, and social comparison orientation on perceived financial insecurity. Findings revealed that among the six variables, four (i.e., perfectionism, self-efficacy, perceived economic mobility, and resource scarcity) were found to be the antecedents to financial insecurity. In the final stage, the proposed financial insecurity–compensatory spending model was tested using PLS-SEM. Data used in this stage were self-reported online survey data collected via Prolific. The results showed that financial insecurity directly lessens the amount of dining-out expenditures. However, in four areas of consumption (i.e., fine dining visit frequency, performance visit frequency, short-travel frequency, and long-travel frequency), the indirect path through the increase in dichotomous thinking and impulsivity partially accounted for the relationship between financial insecurity and spending behaviors. Moreover, the relationship between financial insecurity and expenditure amount in the fine dining, short-trip and long-trip areas were fully mediated by dichotomous thinking and impulsivity.</p> <p>In summary, current research shows that a rational thought process prevails in Millennial decision-making for hospitality and tourism consumption, but an irrational thought process through dichotomous thinking and impulsivity accounts for their decision-making for some consumption behaviors. The findings of this research enhance the understanding on Millennials’ subjective evaluation of their financial status by developing a perceived financial insecurity scale and investigating the antecedents to this variable. Moreover, this dissertation offers practical insights to industry professionals by showing the decision-making mechanism behind Millennials’ spending behaviors in several consumption areas. Industry professionals could formulate more detailed marketing strategies using the findings of this dissertation. </p>

The ever-growing demand for higher quality and faster multimedia content delivery over short distances in home environments drives the quest for higher data rates in wireless personal area networks (WPANs). One of the candidate IEEE 802.15.3a WPAN proposals support data rates up to 480 Mbps by using punctured convolutional codes with quadrature phase shift keying (QPSK) modulation for a multi-band orthogonal frequency-division multiplexing (MB-OFDM) system over ultra wideband (UWB) channels. In the first part of this dissertation, we combine more powerful near-Shannon-limit turbo codes with bandwidth efficient trellis coded modulation, i.e., turbo trellis coded modulation (TTCM), to further improve the data rates up to 1.2 Gbps. A modified iterative decoder for this TTCM coded MB-OFDM system is proposed and its bit error rate performance under various impulsive noises over both Gaussian and UWB channel is extensively investigated, especially in mismatched scenarios. A robust decoder which is immune to noise mismatch is provided based on comparison of impulsive noises in time domain and frequency domain. The accurate estimation of the dynamic noise model could be very difficult or impossible at the receiver, thus a significant performance degradation may occur due to noise mismatch. In the second part of this dissertation, we prove that the minimax decoder in \cite, which instead of minimizing the average bit error probability aims at minimizing the worst bit error probability, is optimal and robust to certain noise model with unknown prior probabilities in two and higher dimensions. Besides turbo codes, another kind of error correcting codes which approach the Shannon capacity is low-density parity-check (LDPC) codes. In the last part of this dissertation, we extend the density evolution method for sum-product decoding using mismatched noises. We will prove that as long as the true noise type and the estimated noise type used in the decoder are both binary-input memoryless output symmetric channels, the output from mismatched log-likelihood ratio (LLR) computation is also symmetric. We will show the Shannon capacity can be evaluated for mismatched LLR computation and it can be reduced if the mismatched LLR computation is not an one-to-one mapping function. We will derive the Shannon capacity, threshold and stable condition of LDPC codes for mismatched BIAWGN and BIL noise types. The results show that the noise variance estimation errors will not affect the Shannon capacity and stable condition, but the errors do reduce the threshold. The mismatch in noise type will only reduce Shannon capacity when LLR computation is based on BIL.