esa-sceva/satcom-chunk-collection huggingface dataset:
# A Wideband Digital Pre-Distortion Algorithm Based on Edge Signal Correction
## 2 Wideband DPD Model Based on Edge Signal Correction
### Wideband DPD Architecture Based on Edge Signal Correction  
Figure 1 illustrates the wideband DPD architecture based on edge signal correction designed in this study. The model design is inspired by the direct learning method [14], which learns and corrects non-linear distortions directly from the differences between the input and output signals, thereby effectively reducing or eliminating distortions caused by the power amplifier.  
The source signal \(v(n)\) passes through a bandpass filter to generate a band-limited input signal \(x(n)\). The signal \(x(n)\) is then processed by a band-limited pre-distorter to produce the pre-distorted signal \(u(n)\). The band-limited pre-distorter applies non-linear compensation to the input signal, thereby linearizing the in-band output of the power amplifier. The signal \(u(n)\) is converted into an analog pre-distortion signal via a Digitalto-Analog Converter (DAC). Before being sent to the power amplifier, it undergoes up-conversion to align with the amplifier's center frequency. After passing through the power amplifier, the signal's bandwidth becomes five times wider than that of the source signal [15]. Directly processing this wideband signal would significantly increase data rates and computational complexity. Therefore, a bandpass filter is employed to selectively capture feedback signals in the vicinity of the center frequency. The feedback signal is first down-converted and then digitized through an Analog-to-Digital Converter (ADC) to obtain an estimated input signal \(y(n)\). The difference between the estimated input signal \(y(n)\) and the band-limited input signal \(x(n)\) is calculated. This difference is then processed through parameter calculations to determine the parameters of the pre-distortion model. To enhance the accuracy of the pre-distortion model, edge frequency signals \(x^{\prime}(n)\) are collected and fed into a parameter calibrator to compute the model's cross-term parameters, thereby finalizing the calibration of the pre-distortion model. From the acquisition of the pre-distortion model parameters, through parameter calibration, a wideband digital pre-distortion model is ultimately generated, marking the completion of one iteration. Through multiple iterative updates, the inverse model of the power amplifier's non-linear effects is progressively approximated, which compensates for non-linear distortions and thereby improves the quality and stability of communication transmission.
## 5 Conclusions  
Based on data from MODIS and Landsat, this study constructs evaluation indicators to characterize improvements in cropland productivity, disaster resistance ability and homogenous yield degree. Henan Province, a major grain-producing province in China, is taken as the research area. By combining the general survey and sampling survey in typical grain planting project regions, the effectiveness of HSF projects is evaluated. The results show that there are 109 project regions with continuous grain planting within the 630 HSF construction project regions in Henan Province. The cropland productivity in all 109 project regions of the general survey has improved. Among the eight sampling regions, seven regions show that the level of cropland productivity stability is higher than that of the non-project region in the case of severe drought. All regions show that the homogenous yield degree of cropland productivity is also effectively improved.  
These results suggest that in order to achieve the goal of the HSF plan in China, in addition to the effectiveness of improving cropland productivity, it is necessary to pay close attention to the spatial layout and structural adjustment of agricultural planting in order to recover cropland, store grain and effectively ensure lasting food security.  
H.Y.: Conceptualization, Methodology, Writing--Review and Editing, Funding acquisition. W.D.: Writing--Review and Editing, Visualization. Y.Z.: Writing--Review and Editing, Funding acquisition. L.L.: Writing--Original Draft, Visualization. Z.N.: Methodology. All authors have read and agreed to the published version of the manuscript.  
This work was financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA28060300), National Natural Science Foundation of China (42130508), and Establishment of National Ecological Environmental Accounting System (Project No: 2110105).  
Not applicable.  
The authors sincerely thank anonymous reviewers and members of the editorial team for their comments.  
The authors declare no conflict of interest.
###### Abstract  
Solar-induced chlorophyll fluorescence (SIF), when used as a proxy for plant photosynthesis, can provide an indication of the photosynthesis rate and has the potential to improve our understanding of carbon exchange mechanisms within an ecosystem. However, the relationships between SIF and vegetation indices (VIs) operating within different ecological contexts and the effect of other environmental factors on SIF remain unclear. This study focused on three ecosystems (cropland, forest, and grassland), with different ecological characteristics, located in Northeast China. These areas provide case studies where numerous relationships can be explored, including the correlations between the Orbiting Carbon Observatory-2 (OCO-2) SIF and MODIS products, meteorological factors, and the differences in the relationships between the three different ecosystems. Some interesting results and conclusions were obtained. First, in different ecosystems, the relationships between SIF and MODIS products show different correlations, whereby the enhanced vegetation index (EVI) has a close relationship with SIF in all the three ecosystems of forest, cropland, and grassland. Second, forest-type ecosystems appear to be sensitive to changes in daily temperature, whereas cropland and grassland areas respond more closely to changes in previous 16-day daily minimum temperature. Compared with forest and cropland areas, grasslands were more sensitive to precipitation (although the R\({}^{2}\) value was small). Third, different ecosystems have different mechanisms of photosynthesis. Hence, we suggest that it is better to use SIF in areas exhibiting different ecological characteristics, and different models should be employed while simulating SIF.  
solar-induced chlorophyll fluorescence (SIF); OCO-2; ecosystem; cropland; forest; grassland +
Footnote †: journal: remote sensing  
0000-0002-0001-9999-22001
# Wireless Covert Communication with Polarization Dirty Constellation
## 6 Conclusions  
In this paper, we have proposed a novel scheme for wireless covert communication based on polar codes. By extending the polarization theory to wireless covert communication, we have demonstrated that a portion of covert information can be transmitted with Shannon capacity, provided that the length of the code block is sufficiently long. Specifically, we have polarized the dirty constellation in wireless covert communication and decoded the covert information using SC decoder and SCL decoder. Our simulation and analysis have revealed that we can achieve improved reliability and undetectability with the polarization of the dirty constellation.  
Through experiments, we have shown that the WCC-PDC covert channel can achieve high reliability under low signal-to-noise ratio and better detection resistance compared to traditional WCC-DC covert channels when the bit error rate is not higher than 0.01. However, the WCC-PDC covert channel also has limitations, particularly its strong dependence on the code block length. Incomplete polarization of the code block may occur if the length of the concealed code block is insufficient, which may negatively affect both the reliability and concealment of the channel. In future research, we plan to explore the combination of MIMO channel optimization schemes to further enhance the performance of wireless covert communication.  
Conceptualization, M.H. and S.Q.; methodology, M.H. and S.Q.; software, M.H.; validation, S.Q. and X.J.; writing--original draft preparation, M.H. and S.Q.; writing--review and editing, X.J.; visualization, S.Q.; supervision, X.J.; funding acquisition, X.J. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China grant number U1836104, 61801073, 61931004, 62072250, National Key Research and Development Program of China grant number 2021 QY0700, and The Startup Foundation for Introducing Talent of NUIST grant number 2021r039.  
Not applicable.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} IoT & Internet of Things \\ AWGN & Additive White Gaussian Noise \\ WCC-DC & Wireless Covert Communication with Dirty Constellation \\ OFDM & Linear dichroism \\ BPSK & Binary Phase Shift Keying \\ QPSK & Quadrature Phase Shift Keying \\ BLER & Block Error Rate \\ BLER & Block Error Rate \\ SNR & Signal Noise Ratio \\ B-DMC & Binary Discrete Memoryless Channel \\ ML & Maximum-Likehood \\ LLR & Log-Likehood Ratio \\ SC & Successive Cancellation \\ SCL & Successive Cancellation List \\ \end{tabular}
## 4 Experimental Studies
### Location Determination in 3D by iaABC
#### 4.2.1 Scenario  
To determine the locations of target nodes (TNs), a single anchor node (AN) positioned at the top can be utilized. This method organizes all nodes in three distinct layers: a single AN in the top layer, and 50 randomly distributed TNs in the middle and bottom layers (total 100). Virtual anchors (VAs) are situated in the upper layer, while the TNs are randomly positioned in the lower layers. The beacon signal generated by the AN plays a crucial role in the random placement of the TNs. When a TN falls within the AN's range, it obtains the Received Signal Strength Indicator (RSSI) information from the anchor, which allows it to calculate the distance between the AN and the TN using the Euclidean formula. In this study, the degree of irregularity (DOI) value was set to 0.01.  
After determining this distance, the umbrella projection approach is employed for positioning the TNs, as illustrated in Figure 5. In this approach, six VAs are projected in a circular formation, each spaced 60 degrees apart.  
In a 3D environment, as illustrated in Figure 6, four anchors are needed to position the TNs: one anchor to identify the center point and three virtual anchors (VAs). Using the information from the calculated center point, the iaABC method is then applied for optimal positioning.  
Figure 5: Umbrella projection used in the proposed method [11].  
Figure 6: Anchor, VAs, and TN in a 3D environment [11].
## 2 Materials
### Model Validation  
Figure 2 depicts the information related to the 1D modeling results compared to experimental data. In Figure 2, the plot's title gives the information on the engine speed in rpm, load condition--Full Load (FL)/Partial Load (PL)--and the last digit 1 or 2 is the exhaust configuration, which is either config-1 or config-2, respectively. The results plotted in Figure 2A-D are the instantaneous pressure traces in the exhaust manifold, while Figure 2E-H depict pressure traces inside the cylinder during the scavenging process. The results only illustrate the information while the exhaust ports are open because the gas exchange occurs during this process and defines the trapped mass in the cylinder for the next engine cycle.  
Firstly, from Figure 2E-H, it can be observed that the exhaust port opening occurs at 130 CAD. The results depicted before the exhaust port opening is the expansion process, where it can be observed that the modeling results follow experimental results closely. Also, it can be observed that the port closing occurs approximately at 255 CAD and the process after this CAD is the compression stroke. During this process, it can be seen that the 1D model accurately predicts the compression stroke's pressure compared to experimental results. The process between CAD 130 and 255 is the scavenging process, where the modeling pressure traces follow the experimental measurements with an absolute  
Figure 2: Comparison between experimental and 1D modeling results: CAD vs. (**A–D**) Exhaust pressure; (**E–H**) In-cylinder pressure.  
maximum deviation of less than 2%. Observing the results, it can be justified that modeling strategies employed in developing this novel engine provide accurate results during the expansion, scavenging, and compression strokes in the combustion chamber.  
Secondly, as mentioned earlier, during the experimental campaign, different exhaust manifolds were employed and tested at both full load and partial load conditions; this has also been accounted for during the modeling stage. To achieve coherence between experimental results and the 1D model predictions, heat transfer and friction multipliers in the exhaust manifold were calibrated. Once a peak deviation of less than 2% was accomplished, these multipliers were held constant, and simulations were analyzed with different engine speeds and load conditions. Figure 2A-D shows that the model is calibrated to predict experimental peaks and trends accurately. Figure 2 justifies that the model provides fluid dynamically stable results to a satisfactory level and can be used for further perspective analysis, and that the results can be used as initial and boundary conditions for CFD.
# A Review on Recent Advancements in FOREX Currency Prediction
###### Abstract  
In recent years, the foreign exchange (FOREX) market has attracted quite a lot of scrutiny from researchers all over the world. Due to its vulnerable characteristics, different types of research have been conducted to accomplish the task of predicting future FOREX currency prices accurately. In this research, we present a comprehensive review of the recent advancements of FOREX currency prediction approaches. Besides, we provide some information about the FOREX market and cryptocurrency market. We wanted to analyze the most recent works in this field and therefore considered only those papers which were published from 2017 to 2019. We used a keyword-based searching technique to filter out popular and relevant research. Moreover, we have applied a selection algorithm to determine which papers to include in this review. Based on our selection criteria, we have reviewed 39 research articles that were published on \"Elsevier\", \"Springer\", and \"IEEE Xplore\" that predicted future FOREX prices within the stipulated time. Our research shows that in recent years, researchers have been interested mostly in neural networks models, pattern-based approaches, and optimization techniques. Our review also shows that many deep learning algorithms, such as gated recurrent unit (GRU) and long short term memory (LSTM), have been fully explored and show huge potential in time series prediction.  
foreign exchange (FOREX) market; time series prediction; currency prediction; machine learning +
Footnote †: journal: _arxiv:1409.1130801_
# Influence of Medium Frequency Light/Dark Cycles on the Cultivation of _Auxenochlorella pyrenoidosa_
###### Abstract  
Light (wavelength, intensity, and light/dark cycle) have been considered as one of the most important parameters for microalgae cultivation. In this paper, the effect of medium frequency intermittent light on _Auxenochlorella pyrenoidosa_ (formerly _Chlorella pyrenoidosa_) cultivation was investigated. Three parameters of intermittent light, light intensity, light/dark ratio, and light/dark cycle were employed and the influence of these parameters on the productivity of _Auxenochlorella pyrenoidosa_ was studied. The biomass yield and growth rates were mainly affected by the light fraction and cycle time. Light with 220 uE m\({}^{-2}\) s\({}^{-1}\) light intensity was determined as the optimal light intensity for biomass production. At the light intensity of 420 uE m\({}^{-2}\) s\({}^{-1}\), the results indicated that the intermittent light improved the biomass production with larger light/dark ratio compared with the continuous light. At a lower mean light intensity over time, the intermittent light should be more suitable for biomass growth and the decrease in the light/dark ratio (L/D) will lead to a higher biomass productivity. The light/dark cycle time has little influence on the biomass yield.  
light-emitting diode (LED); _Auxenochlorella pyrenoidosa_; medium frequency; light/dark cycle +
Footnote †: journal: Applied Sciences
# A Secure CDM-Based Data Analysis Platform (SCAP) in Multi-Centered Distributed Setting
## 3 Methods
### Communication between User and CS  
It is assumed that the user accessing the CS has passed the authentication of the AS. Figure 3 shows how a user receives a digital signature for the AC to analyze the CDM data. Before accessing the CS, the user creates an AC to analyze the CDM data of hospitals through the SCAP. An AC can be written in a variety of ways. Because the SCAP is implemented based on the OMOF-CDM, users can use software [15; 36] provided by OHDSI. The AC is generally written in R language and contains all information for analyzing the CDM data, such as cohort definitions and SQL queries. Because the AC is used to analyze medical data, it should not be tampered with until it is delivered to each hospital over the network. A digital signature is used to guarantee data integrity and non-repudiation during transmission. To satisfy this requirement, the user requests the CS to create a digital signature for the AC. To this end, the user delivers a message \(M_{C-CS}\) and its signature \(sig_{M_{C-CS}}\) (flow 1 in Figure 3). The message \(M_{C-CS}\) includes the AC and the token issued from the AS in the previous section. The CS creates a signature \(sig^{AC}\) for the AC using its private key and wraps it in message \(M_{CS-C}\). The CS then delivers \(M_{CS-C}\) and its signature \(sig_{M_{CS-C}}\) in response to the user (flow 2 in Figure 3). Because this signature was created with the private key of the CS, no one except the CS can create the same signature. However, anyone can verify the digital signature to obtain the public key of the CS. If the user modifies a part of the AC or writes a completely new AC, the user requests a new signature to use the CS.  
Figure 2: Sequence diagram for communication between the user and AS.
# Secure and Efficient Authentication Scheme in IoT Environments
## 6 Conclusions  
In this study, we examined current authentication schemes reported to be secure, lightweight architecture in IoT environments. The analysis of the study indicates that the current schemes do not achieve the target of lightweight computing with resilience to all forms of known attack. This would also reduce the performance of embedded devices, which results in the consumption of additional resources (e.g., electricity power, memory). Therefore, this can be a significant loss while satisfying users' needs in a vast organizational scenario. To address this issue, we proposed a novel lightweight-computation authentication scheme. We verified the security strength of the proposed scheme using mathematical formulation (i.e., informal security analysis for 16 security attacks). Then, we verified the mathematical proof using widely accepted standard AVISPA and ProVerif tools. The result confirms that the proposed scheme is preventive against all kinds of active and passive attacks. Moreover, we verified the performance of the proposed scheme by implementing the widely accepted standard PBC library on the embedded devices. The outcome shows that the proposed scheme is lightweight (i.e., lowest computation  
Figure 11: Summary of performance analysis.  
(0.933 ms), communication (1408 bit), and storage (384 bit)) compared with other recent authentication protocols, rendering the proposed scheme reasonable and realistic for massive implementation scenarios based on industrial IoT environments. In the future, we would like to build an interoperable architecture to allow devices to use the same kind of lightweight authentication mechanism when accessing different types of cloud network services. The interesting fundamental question that arises from our research analysis is whether the lack of sufficient security and a lightweight goal can explain many of the possible repeated errors in past authentication protocols and the importance of building a more efficient, robust, lightweight authentication scheme in future work.  
Formal analysis, A.T.; funding acquisition, Y.-G.K.; investigation, A.T.; validation, Y.-G.K.; writing--original draft, A.T.; writing--review and editing, Y.-G.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by an Institute of Information and Communications Technology Planning and Evaluation (IITP) grant funded by the Korea government (MSIT; No.2019- 0-00231, development of artificial intelligence-based video security technology and systems for public infrastructure safety).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.
# Bi-Stability in Flexure Beams: Introducing a Setup for Experimental Characterization
## 1 Introduction
A more sophisticated example uses steel fixtures designed to be bolted to the base of the machine and metal clamps that uses rods, springs, and ball bearings to allow the beam to slide back and forth horizontally [28]. Although this setup is robust, the fabrication of steel parts requires more sophisticated equipment and is expensive. This manuscript presents an alternative to improve the consistency and quickness of experimental approaches for studying the bi-stability of flexure beams. This work has two objectives. First, the proposal of a versatile experimental setup that is easy to assemble and that allows the evaluation of beams of different lengths, thicknesses, initial angles, materials, and fabrication methods. It consists of a base with perforations in various places that allow modifying the testing area's dimension. Parts can be fabricated with standard equipment and commercial materials. Second, it uses the setup to perform an experimental study of the behavior of bi-stable mechanisms (critical force, snapping distances, and deformation) made of different thicknesses of commercial styrene stripes. The first part of this paper presents the design and construction of the bi-stable mechanism (Section 2.1), followed by a detailed description of the design and fabrication of the experimental setup in Section 2.2. Section 2.3 explains the implementation of the two experiments: one to evaluate the beams on cyclic loading and another to identify the maximum required force for the mechanism to snap-through (critical force). Section 3 presents and analyses the results of the experiments, including findings about the critical force (Section 3.2), the distances each mechanism travels to snap-through (Section 3.3) and the deformation of the buckling beams (Section 3.4). Finally, in Section 4, conclusions are drawn.