Assessing accuracy predictors in megatrend qualitative forecasting in the hospitality and tourism industry

Plenty of literature on megatrends escapes the logic of validation. Most publications on forecasting apply quantitative methods and the use of qualitative forecasting is scarce especially in the Hospitality and Tourism (H&T) industry, which is so sensitive to macro level factors. Alongside this, it is surprising that studies that explore the accuracy of such predictions are scarce which hampers the capacity to improve forecasting techniques. With this in consideration, the main goal of this study was to uncover the potential predictors of accuracy in qualitative forecasting sources in H&T. In order to do so, we identified and selected a set of documents that used qualitative forecasting methods to predict trends in H&T for the 1998-2008 period, and devised an empirical study that puts to test the expected trends against the test of time. With a panel of 14 experts in H&T that indicated what occurred in the aforementioned period, we computed a weighted score of accuracy for each document and classified it according to four potential causal variables (Explicit methods, Number of cites, Multisource, and Multimethod, thought of as indicators of forecasting quality). The model was tested with a fuzzy set qualitative comparative analysis (fs/QCA) which indicated that clarifying the qualitative forecasting methods (Explicit) and having multiple sources (Multisource) are the main predictors of the qualitative forecasting sources’ accuracy in H&T.A maioria das publicações sobre previsão usam métodos quantitativos e a previsão de base qualitativa é escassa especialmente no sector da Hospitalidade e Turismo (H&T) que é tão sensível a fatores de nível macro. Em acréscimo, é surpreendente que os estudos que exploram a precisão de tais previsões sejam escassos, o que reduz a capacidade de melhorar as técnicas de previsão. Considerando isto, o principal objetivo deste estudo foi o de descobrir os potenciais preditores de precisão nas fontes de previsão qualitativa em H&T. Para o concretizar, identificámos e selecionámos um conjunto de documentos que usam métodos qualitativos de previsão para as tendências de H&T para o período de 1998-2008 e desenvolvemos um estudo empírico que põe à prova as tendências esperadas em relação ao teste do tempo. Com um painel de 14 peritos em H&T que indicaram o ocorrido no período mencionado calculámos um score ponderado de precisão para cada documento e classificámo-lo de acordo com quatro potenciais variáveis causais (métodos explícitos, número de citações, multi-fonte e multi-método, tidos como indicadores da qualidade da previsão). O modelo foi testado por via da análise comparada qualitativa de conjunto difuso (fs/QCA) que indicou que clarificar os métodos de previsão usados (explícito) e contar com várias fontes de informação (multi-fonte) são os principais preditores da precisão dos documentos que oferecem previsões qualitativas em H&T

Analytical performance evaluation of massive MIMO techniques for SC-FDE modulations

SAICT-45-2017-02 UIDB/EEA/50008/2020In the Fifth Generation of telecommunications networks (5G), it is possible to use massive Multiple Input Multiple Output (MIMO) systems, which require efficient receivers capable of reaching good performance values. MIMO systems can also be extended to massive MIMO (mMIMO) systems, while maintaining their, sometimes exceptional, performance. However, we must be aware that this implies an increase in the receiver complexity. Therefore, the use of mMIMO in 5G and future generations of mobile receivers will only be feasible if they use very efficient algorithms, so as to maintain their excellent performance, while coping with increasing and critical user demands. Having this in mind, this paper presents and compares three types of receivers used in MIMO systems, for further use with mMIMO systems, which use Single-Carrier with Frequency-Domain Equalization (SC-FDE), Iterative Block Decision Feedback Equalization (IB-DFE) and Maximum Ratio Combining (MRC) techniques. This paper presents and compares the theoretical and simulated performance values for these receivers in terms of their Bit Error Rate (BER) and correlation factor. While one of the receivers studied in this paper achieves a BER performance nearly matching the Matched Filter Bound (MFB), the other receivers (IB-DFE and MRC) are more than 1 dB away from MFB. The results obtained in this paper can help the development of ongoing research involving hybrid analog/digital receivers for 5G and future generations of mobile communications.publishersversionpublishe

Uplink of base station cooperation systems with SC-FDE modulations and IB-DFE receivers

This paper considers the uplink transmission in BS (Base Station) cooperation schemes where users in adjacent cells share the same physical channel and the signals received by each BS are sent to a CPU (Central Processing Unit) that combines the different received signals associated to a given user and/or performs the user separation. The signals are modulated through SC (Single-Carrier) schemes combined with FDE (Frequency- Domain Equalization) techniques and with iterative frequency-domain receivers based on the IB-DFE concept (Iterative Block Decision Feedback Equalization). Our performance results show performance results close to the MFB (Matched Filter Bound), where the proposed receivers allow enhancement in macro-diversity gains as well as an efficient user separation, making these techniques an excellent choice for the uplink transmission in future broadband wireless systems employing BS cooperation schemes

Usage of link-level performance indicators for HSDPA network-level simulations in E-UMTS

The paper describes integration of HSDPA (high-speed downlink packet access) link-level simulation results into network-level simulations for enhanced UMTS. The link-level simulations model all physical layer features depicted in the 3GPP standards. These include: generation of transport blocks; turbo coding; rate matching; spreading; scrambling; modulation. At the receiver side, all complementary blocks are designed, with soft-decision demodulation, and a turbo decoder using the MAP (maximum a posteriori) algorithm with 8 iterations. An analytical formula is defined that fits the CQI (channel quality indicator) dependent BLER (block error rate) versus E/sub b//N/sub 0/ results in an AWGN channel. This formula models the physical layer in the network-level simulator. A further extension for frequency selective fading channels has been defined. The network-level simulator includes propagation models that provide SNR values. Based on these SNR values and the simplified physical layer model, an algorithm selects the CQI, and determines the actual BLER at time of reception. The rounding down and delaying of the CQI reporting, which corresponds to the W-CDMA standard, has a significant impact on throughput and transfer delay of the HS-DSCH. Some compensation can be found in a modified transmission. The integration of the link-level and network-level simulators gives accurate and realistic results that can be used in more studies that focus on network layer aspects of packet based services over HSDP

Error rate analysis of M-PSK with magnitude modulation envelope control

Magnitude modulation (MM) envelope control is an efficient way of reducing the peak-to-average power ratio (PAPR) of single-carrier (SC) signals and improves an SC system's overall power efficiency. However, MM techniques reduce the PAPR at the cost of introducing distortion, highlighting a need to characterise the symbol error rate (SER) performance loss due to MM. This reported work focuses on the M-PSK case. An exact probability density function (PDF) based on the generalised extreme value distribution is proposed to model the statistical distribution of MM factors generated by MM techniques applied to SC constant amplitude constellations. By considering MM distortion as a form of fading, it is shown that this PDF may be used to derive an accurate union bound of the SER of M-PSK transmission on the additive white Gaussian channel channel when using MM envelope control

Estimating the performance of mimo sc-fde systems using siso measurements

project 023304 UIDB/50008/2020The demand for ubiquitous telecommunications services forces operators to have a special concern about signal quality and the coverage area they offer to their customers. This was usually checked by using suitable propagation models for Single Input Single Output (SISO) systems, which are no longer the case for new and future mobile generations, such as 5G and beyond. To guarantee good signal quality coverage, operators started to replace these models with Multiple Input Multiple Output (MIMO) ones. To achieve the best results, these models are usually calibrated with Drive Test (DT) measures; however, the DTs available for MIMO propagation models are sparse, in contrast to SISO ones. The main contribution presented in this paper is a methodology to extend the propagation models of SISO systems so they can be applied in MIMO sytems with Single-Carrier and Frequency-Domain Equalization (SC-FDE), while still using DTs acquired for SISO systems. This paper presents the impact on Bit Error Rate (BER) performance and its coverage area resulting from the application of our proposed method. We consider a MIMO SC-FDE system with an Iterative Block Decision Feedback Equalization (IB-DFE) receiver and we present the improvement expressions for the BER that we illustrate with some simulations.publishersversionpublishe

Reduced complexity detection in MIMO systems with SC-FDE modulations and iterative DFE receivers

This paper considers a Multiple-Input Multiple-Output (MIMO) system with P transmitting and R receiving antennas and different overall noise characteristics on the different receiver antennas (e.g., due to nonlinear effects at the receiver side). Each communication link employs a Single-Carrier with Frequency-Domain Equalization (SC-FDE) modulation scheme, and the receiver is based on robust iterative frequency-domain multi-user detectors based on the Iterative Block Decision Feedback Equalization (IB-DFE) concept. We present low complexity efficient receivers that can employ low resolution Analog-to-Digital Converters (ADCs) and require the inversion of matrices with reduced dimension when the number of receive antennas is larger than the number of independent data streams. The advantages of the proposed techniques are particularly high for highly unbalanced MIMO systems, such as in the uplink of Base Station (BS) cooperation systems that aim for Single-Frequency Network (SFN) operation or massive MIMO systems with much more antennas at the receiver side.publishe

Increasing Reliability on UAV Fading Scenarios

Funding Information: This work was supported by the European Union's Horizon 2020 Research and Innovation Programme through the Marie Sklodowska-Curie Project under Grant 813391. Publisher Copyright: © 2013 IEEE.Unmanned aerial vehicles (UAVs) are the next technology to be incorporated into a telecommunications network to improve command and control on a large scale in both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. However, there is still room for improvement in terms of reliability. This paper investigates Constant Packet Combining (CPC) and Adaptive Packet Combining (APC) techniques applied to Unmanned Aerial Vehicle (UAV) communication in the presence of large-scale fading, where the channels are subject to sudden degradation for long periods due to obstructions. We use Single Carrier (SC) Frequency Domain Equalization (FDE) combined with the Iterative Block Decision-Feedback Equalizer (IB-DFE) to handle command and control messages mapped for UAV use cases. We present closed-form equations for the equalization design as well as the performance parameters such as Bit Error Rate (BER), the Packet Error Rate (PER), the throughput, the retransmissions amount, the goodput (the transmission rate without the retransmissions quantity), and the outage probability. Then, we analyze the system performance using correlated, independent, and equal channels. There is a trade-off between the overall available power, throughput, and reliability. For instance, more retransmissions result in higher reliability, power consumption and lower goodputs (effective data rates). CPC validates the transmission system and confirms the improvement of BER and PER parameters without energy efficiency optimization. APC is appealing because it can reduce the number of retransmissions for all channels used with the advantage of meeting energy efficiency requirements by adapting the overall power to the scenario experienced by the UAV.publishersversionpublishe

Turbo TCH Codes for application in CS-CDMA Schemes

In this paper the performance of turbo TCH codes is analyzed in a (Code Spreading) CS-CDMA scheme, for spread spectrum applications in a multiuser and fast fading channel environment, with and without multipath. Several rates are considered, bearing in mind different types of services. In order to get an estimate of performance gains over an existing (Direct Sequence) DS-CDMA system, UMTS coding results are used for comparison against punctured turbo TCH codes, in order to compare equal coding rates. A simulator with the main code structure for both schemes was built, alongside the channel model and Rake receiver, in order to correctly compare both coding schemes. Specific test conditions are defined, and the overall codes of both schemes are compared

Cloud-Based Implementation of an Automatic Coverage Estimation Methodology for Self-Organising Network

UIDB/EEA/50008/2020One of the main concerns of telecommunications operators is related to network coverage. A weak coverage can lead to a performance decrease, not only in the user experience, when using the operators' services, such as multimedia streaming, but also in the overall Quality of Service. This paper presents a novel cloud-based framework of a semi-empirical propagation model that estimates the coverage in a precise way. The novelty of this model is that it is automatically calibrated by using drive test measurements, terrain morphology, buildings in the area, configurations of the network itself and key performance indicators, automatically extracted from the operator's network. Requirements and use cases are presented as motivations for this methodology. The results achieve an accuracy of about 5 dB, allowing operators to obtain accurate neighbour lists, optimise network planning and automate certain actions on the network by enabling the Self-Organising Network concept. The cloud implementation enables a fast and easy integration with other network management and monitoring tools, such as the Metric platform, optimising operators' resource usage recurring to elastic resources on-demand when needed. This implementation was integrated into the Metric platform, which is currently available to be used by several operators.publishersversionpublishe