Mirror Kirchhoff approximation (MKA) is a technology to quantify the shadowing effect in the 5^th generation mobile communication systems. However, the conventional MKA using equal interval segmentation is inefficient in computation time since it does not consider the change in the slope of the shadowing object. In this letter, the unequal interval mirror Kirchhoff approximation (UMKA) is proposed to reduce computation time. In the proposal, the unequal internal is designed concerning the change in the slope of the object. The proposed method is validated for circular and elliptical conductor cylinders, which are considered to model the cross-section of the human body. The results show that UMKA achieves less computation time than the conventional MKA in the acceptable error range.

This letter reports the nonlinearity tolerance properties of hierarchical distribution matching (HiDM), which is a distribution matcher of reasonable complexity for probabilistic amplitude shaping (PAS) in nonlinear fiber-optic transmission. Recent studies have demonstrated that PAS exhibits unique nonlinearity tolerance, which varies depending on channel conditions. This tolerance is influenced by the choice of distribution matcher, as analyzed using statistical moments. In this work, we explore the nonlinearity tolerance of HiDM through moment-based analysis and numerical simulations. The results show that the dependence on blocklength in nonlinearity tolerance of HiDM is significantly smaller than in one of enumerative sphere shaping, a common DM. In addition, the property in HiDM is almost independent on the number of layers.

This paper proposes to use single-sideband modified duobinary (SSB-MDB) signaling in order to improve cascaded filtering tolerance in metro optical networks. The SSB-MDB signal is detected by using Kramers-Kronig (KK) reception scheme, and maximum likelihood sequence estimation (MLSE) is employed to improve the transmission performance. We show that the SSB-MDB has superior filtering tolerance compared with the 16-ary quadrature amplitude modulation (16QAM) with the same bit rate when the CW tone for KK reception is multiplexed at the receiver side.

This letter addresses the performance of the unmanned aerial vehicle (UAV)-aided multi-user terahertz (THz) systems using non-orthogonal multiple access (NOMA) and hybrid automatic repeat request (HARQ) protocols. Specifically, the total achievable throughput performance is analyzed over the THz channels, incorporating path-loss, small-scale fading characterized by the α-µ model, and fog attenuation. Notably, the imperfect channel-state information (CSI) is also considered. Simulation results demonstrate that the HARQ-aided NOMA-THz-based UAV systems can achieve a significant throughput performance enhancement compared to the state-of-the-art solutions. Moreover, proper parameter selection for HARQ-aided NOMA-THz-based UAV systems is also provided.

Non-orthogonal multiple access (NOMA), which multiplexes users in the power domain, degrades performance when the channel gain difference between users is small. To mitigate the performance degradation specific to NOMA, a hybrid multiple access scheme that simultaneously utilizes NOMA and orthogonal multiple access (OMA) is effective. So far, we have proposed a resource allocation method that allows for flexible settings of the NOMA power allocation ratios and OMA bandwidths and selects the optimal resource pattern based on the users’ channel conditions and desired traffic volumes. In this study, we propose a resource pattern reduction method to reduce the cost of resource allocation in the conventional method by focusing on the applicability of NOMA and OMA, which depend on the number of transmit antennas. Furthermore, to clarify the effectiveness of the proposed method, we compared it with a conventional method that performs high-granularity resource allocation for different power ratios and bandwidths in terms of the system throughput.

In this article, we propose a pre-equalization method in a wired-wireless multiple-input and multiple-output (MIMO) transmission over an analog radio-on-fiber (A-RoF) network. The MIMO transmission based on A-RoF suffers from un-flat and unbalanced response in the wired part, resulting in decreased channel capacity. A partial pre-equalization technique for wired part is compared to the one for the joint channels of wired-and-wireless by using 2×2 transmission of orthogonal frequency division multiplexing (OFDM) in a 5-GHz band testbed.

This letter proposes the application of the precise point positioning (PPP) technique used in the GNSS for detecting the dust and sandstorm (DSS) in the atmosphere. Many of the papers have reported that the GNSS-derived zenith total delay (ZTD) is affected to aerosols and sandstorms, however, directivity for arrival angles of sandstorms is not considered. Since the suspended particulate matter (SPM) including the yellow sand and PM2.5 usually comes from the west side from Japan, azimuthal angle filtering is introduced in the process of estimation of the ZTD. The enhancement in the cross-correlation between the proposed SPM-induced delay and measured time series of the ground SPM has shown.

We design a center-feed post-wall waveguide slot subarray of 25 radiating elements that suppresses E-plane sidelobes below -18 dB for the 76.5 GHz band (76.0 GHz to 77.0 GHz). First, by adjusting the dimension of the feeding aperture, the feeding part is designed to suppress reflection. Then, the slot lengths and post positions are adjusted, and the radiating elements are designed so that the excitation distribution calculated from the Taylor distribution is obtained. The overall structure is analyzed by combining the radiating part, in which the radiating elements are arranged so that their excitation phase distribution is uniform, and the feeding part. A prototype is fabricated and measured based on the design. The reflection is below -10 dB in a range of 74.1 GHz to 76.4 GHz for the calculated value and 74.5 GHz to 76.5 GHz for the experimental value. The sidelobe levels are sufficiently suppressed below -18 dB from 76.0 GHz to 76.6 GHz in both analysis and experiment.

This letter addresses the error-control design for unmanned aerial vehicles (UAV)-aided Terahertz (THz) systems. Particularly, we propose the design of a non-orthogonal chase combining hybrid automatic repeat request (N-CC-HARQ) scheme, where the retransmission request is served together with the new frame through a nonorthogonal signal superposition within the same time slot. The performance of the proposed N-CC-HARQ is evaluated over the THz channels incorporating path loss, fading, and pointing misalignment. Different performance metrics, including frame error rate (FER), Goodput, and energy efficiency, are analytically obtained based on the Markov model. Numerical results confirm the effectiveness of the proposed N-CC-HARQ schemes over the state-of-the-art.

We design a 3×2-slot subarray antenna for millimeter-wave car radars in the 76GHz band. A cavity is introduced and designed to reduce phase differences among the slots. We change the slot length, width, and spacing to improve the gain. The antenna is designed for a wide bandwidth to have double resonance by two reflection-suppressing walls in the feeding part. The measured antenna has a reflection below -10dB across 76.4GHz-82.0GHz. The gain is 15.5dBi and the sidelobe level is -15.5dB at 78.5GHz in the measurement.

This paper addresses issues in realizing a whole-body tactile display system. Individual wiring for each actuator requires many wires and presents a dilemma of durability and flexibility. Wireless transmission can eliminate these wires; however, practical wireless power supply to drive actuators is not currently available. Two-dimensional (2-D) communications on conductive textiles enable DC supply and data transfer while suppressing interference with other radio communications. Previously, a concept of multi-carrier frequency modulation (FM)-based vibrotactile waveform transmission on conductive textiles has been presented. However, practical implementations, in particular how to implement realtime multi-carrier FM, have not been clarified. In this paper, we propose a software-defined radio (SDR)-based multi-carrier FM transmitter capable of transmitting non-preprogrammed arbitrary waveforms of vibrotactile sensation.

Predicting wireless link quality (LQ) is a promising approach to enhancing Quality of Experience (QoE). This paper examines the impact of physical space on LQ; it uses machine learning to predict RSSI and throughput from physical space information. Experiments show that the position/orientation of user equipment (UE) are crucial, with orientation affecting RSSI, and velocity significantly impacting throughput. It is revealed that these LQ parameters have different spatial factor dependencies. An experiment is conducted in a static indoor environment with clear line of sight to simplify the problem. We focus on deriving LQ from current physical space information rather than forecasting future quality.