A bottleneck in multiple-input multiple-output communications systems is the complexity of detection at the receiver. The complexity of optimum maximum-likelihood detection is often prohibitive, ...especially for large numbers of antennas and large alphabets. A suboptimal tree-search-based detector known as the K-best detector is an effective scheme that provides a flexible performance-complexity tradeoff. In this paper, we identify scalar list detection as a key building block of the K-best detector, and we propose an efficient low-complexity implementation of the scalar list detector for M-ary QAM using a slicing operation. Embedding the slicing list detector into the K-best framework leads to our proposed slicing K-best detector. Simulation results show that the proposed detector offers comparable performance to the conventional K-best detector, but with significantly reduced complexity when K is less than the QAM alphabet size M. Since the slicing list detection is performed at each visited node in the detection tree, the complexity reduction is especially significant when the number of antennas and the alphabet size are large, making the proposed detector a competitive option for high spectral-efficiency wireless systems.
In this paper, we propose a non-orthogonal multiple access-based multiuser beamforming (NOMA-BF) system designed to enhance the sum capacity. In the proposed NOMA-BF system, a single BF vector is ...shared by two users, so that the number of supportable users can be increased. However, sharing a BF vector leads to interference from other beams as well as from the other user sharing the BF vector. Therefore, to reduce interference and improve the sum capacity, we additionally propose a clustering and power allocation algorithm. This clustering algorithm, which selects two users with high correlation and a large gain-difference between their channels, can reduce the interference from other beams and from the other user as well. Furthermore, power allocation ensures that each user's transmit power is allocated so as to maximize the sum capacity. Numerical results verify that the proposed NOMA-BF system improves the sum capacity, compared to the conventional multiuser BF system.
Excavators are typical machinery in the construction industry, and have advantages when applied in various tasks. Among various tasks of excavators, loading a dump truck is a very important task that ...could be automated. However, most of the previous studies are focused on the excavation/digging operation, and the studies on the loading efficiency are limited. Therefore, the spatial factors affecting loading operation were identified and investigated with regard to the different types of the movements of the machine in this study. To observe changes in the loading time according to the affecting factors, two main hypotheses were examined as follows: 1) loading time changes according to the height difference and distance between the excavator and dump truck; and 2) loading time changes by the rotation angle. In order to verify the hypotheses, the movements of three excavators were studied under the different conditions of the spatial factors. We believe that the automation of loading operation for excavators can benefit from the results of hypothesis validation, and from the analysis of the detailed loading operation in relation to the categorized movement and the patterns of loading operation.
•The spatial factors affecting the loading operation of excavation work were identified.•The loading operation was broken down into several movements to collect data.•The relationship between loading efficiency and spatial factors of excavators was analyzed.•Two hypotheses on the loading efficiency were examined based on the truck loading cycle time.
In this paper, we propose a uplink (UL) non-orthogonal multiple access (NOMA) systems equipped with multiple antennas to enhance the sum capacity of UL. In the proposed UL NOMA system, a base station ...(BS) with N antennas can support 2N users by sharing the space resource. However, sharing the space resource leads to interference between users. Therefore, to mitigate the interference and improve the sum capacity, we additionally propose a set selection algorithm and power control scheme. The set selection algorithm, which selects 2N users based on orthogonality and gain-difference between their channels, reduces the interference between users. Furthermore, the power control scheme can maximize the sum capacity with ensuring minimum target rate. Numerical results show that the proposed system improves the sum capacity over that of the conventional orthogonal multiple access (OMA) system.
Construction accidents result from a combination of factors, including both the actions of workers and the safety conditions on site. Despite advancements in enhancing construction site safety, there ...remains a gap in comprehending the cognitive processes underlying workers' unsafe behavior. This paper investigates and validates a qualitative model that delves into the potential causes of workers' unsafe actions by examining their cognitive processes, employing a system dynamics approach. By analyzing the interplay of various loops within this model, it offers both short- and long-term safety strategies for managers intent on minimizing unsafe behavior among workers. Specifically, safety managers should prioritize increasing workers' awareness of hazards through education and fostering a positive safety mindset. Moreover, they should task frontline supervisors with directly addressing and rectifying instances of unsafe behavior by workers. Lastly, construction safety managers ought to formulate safety strategies that take into account the cognitive states of workers to mitigate any adverse consequences of biased safety management. The outcomes of this research contribute to our comprehension of methods to enhance hazard perception among workers, curtail unsafe actions, and ultimately reduce construction accidents from a cognitive standpoint.
The modulation and demodulation blocks in an orthogonal frequency-division multiplexing (OFDM) system are typically implemented digitally using a fast Fourier transform circuit. We propose an analog ...implementation of an OFDM demodulator as a means for reducing power consumption. The proposed receiver implements the discrete Fourier transform (DFT) as a vector-matrix multiplier using floating-gate transistors on a field-programmable analog array (FPAA). The DFT coefficients can be tuned to counteract an inherent device mismatch by adjusting the amount of electrical charge stored in the floating-gate transistors. When compared to a digital field-programmable gate array implementation, the analog FPAA implementation of the DFT reduces power consumption at the cost of a slight performance degradation. Considering the errors in the DFT coefficients as intersymbol interference, the performance degradation can be further mitigated by employing a least mean-square or minimum mean-square-error equalizer.
With the overwhelming adoption of Orthogonal Frequency Division Multiplexing (OFDM) technique in many recent wireless communications standards, there have been extensive approaches to tackle the high ...Peak-to-Average Power Ratio (PAPR) problem that yields low efficiency in RF power amplifiers, which is the major drawback of OFDM systems. One of the approaches is to replace power amplifiers with the Linear Amplification using Nonlinear Components (LINC) block. However, this produces additional nonlinear distortions caused by amplitude or phase mismatch between two power amplifiers inside the LINC block. In this paper, we introduce a noble LINC calibration technique that utilizes the channel estimator block that is initiated by the Media Access Control (MAC) layer during the Distributed Interframe Space (DIFS) or Short Interframe Space (SIFS). For DIFS or SIFS, pilot symbols are allocated in a payload field and then the outputs of the transmitter are internally forwarded to the receiver to characterize the LINC channel with a pilot-aided Least Square Error (LSE) channel estimator. By applying a reverse distortion onto information symbols after the LINC channel distortion is obtained by channel estimation, we can significantly improve the Symbol Error Rate (SER) and Error Vector Magnitude (EVM) of the OFDM system with the LINC transmitter.
In order to devise a rebar usage optimization algorithm, it is necessary to calculate the exact rebar length and revise the arrangement of rebars into special lengths. However, the process of ...rearranging numerous rebars and manually calculating their quantities is time-consuming and requires significant human resources. To address this challenge, it is necessary to develop an algorithm that can automatically estimate the length of rebars and calculate their quantities. This study aims to create an automatic estimation algorithm that improves work efficiency while ensuring accurate and reliable calculations of rebar quantities. The algorithm considers various factors such as concrete cover, hook length, development length, and lapping length, mandated by the building codes, to calculate the quantity of rebars for wall structures. The effectiveness of the proposed method is validated by comparing the rebar quantities generated by the algorithm with manually calculated quantities, resulting in a difference rate of 1.14% for the hook case and 1.37% for the U-bar case. The implementation of this method enables fast and precise estimation of rebar quantities, adhering to relevant regulatory codes.
The purpose of this research is to present a low-power wireless communication receiver with an enhanced performance by relieving the system complexity and performance degradation imposed by a ...quantization process. With an overwhelming demand for more reliable communication systems, the complexity required for modern communication systems has been increased accordingly. A byproduct of this increase in complexity is a commensurate increase in power consumption of the systems. Since the Shannon's era, the main stream of the methodologies for promising the high reliability of communication systems has been based on the principle that the information signals flowing through the system are represented in digits. Consequently, the system itself has been heavily driven to be implemented with digital circuits, which is generally beneficial over analog implementations when digitally stored information is locally accessible, such as in memory systems. However, in communication systems, a receiver does not have a direct access to the originally transmitted information. Since the received signals from a noisy channel are already continuous values with continuous probability distributions, we suggest a mixed-signal system in which the received continuous signals are directly fed into the analog demodulator and the subsequent soft-decision Viterbi decoder without any quantization involved. In this way, we claim that redundant system complexity caused by the quantization process is eliminated, thus gives better power efficiency in wireless communication systems, especially for battery-powered mobile devices. This is also beneficial from a performance perspective, as it takes full advantage of the soft information flowing through the system.
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