The 5-th generation mobile communication system (5G), which is the next generation communication system, is being developed. In 5G, it is assumed that multiple cells with different frequency bands will be used. The attenuation of signal power due to propagation loss in free space and the reflection of radio waves from buildings, etc., differs depending on the frequency. In this paper, a radio propagation measurement is performed for micro and milli-meter waves (5 and 19 GHz bands), which will be used in 5G. The outdoor propagation characteristics of each frequency band based on the measured channel state information are evaluated in terms of the signal to noise ratio and channel capacity.

Many high-frequency antennas have significantly smaller dimensions than the operating wavelength, causing a narrow bandwidths. This paper examines characteristic modes (CMs) of platform-mounted antennas to increase the overall bandwidth of the system. We use the theory of CMs to identify the appropriate platform modes and determine the practical feeding circuits. We fabricate a prototype platform antenna using a scaled model at 860 MHz to verify the simulation results.

An asymmetric biconical antenna is proposed to be used for a borehole radar system to inspect the corrosion of reinforcing bar inside a concrete structure. First, the antenna is designed by considering the hole needed for the borehole diameter. Then, the antenna is fabricated using a three-dimensional printer with polylactic acid plastic and coated with copper tape. Finally, the antenna is tested in free space and concrete environment. The diameter of the antenna is 20 mm and a length of 34 mm, with the usable frequency in free space is 2.4 GHz (2.1 GHz in concrete) to 8 GHz.

We propose a Wiener filter (WF) and a combined zero forcing (ZF)/WF precodings with ant colony optimization (ACO) algorithms as the digital precoder for millimeter wave multiple-input multiple-output (MIMO) systems. In the proposed schemes, beams are selected based on maximal magnitude (MM) criteria and the selection is optimized using ACO algorithm to achieve near optimal solution with highly reduced complexity. According to the simulation results, while ACO-WF scheme achieves higher sum rate in high inter-user interference (IUI) environments compared with conventional precoders, we confirm ACO-ZF/WF scheme can obtain a maximal sum rate in both low and high IUI environments.

Achieving high-precision and high-resolution imaging with millimeter-wave radar requires a large number of antennas and data volumes. In this study, we applied the Khatri-Rao (KR) product extended array processing to synthetic aperture radar (SAR) data to increase the number of antenna elements substantially and extend the synthetic aperture length. The target of interest in this study is relative short range target, which is several meters away from the radar, such as indoor human with a small object on his/her body. When the target is close to the radar, target imaging by SAR using the far-field approximation will often increase the error. In this case target-imaging by using range-migration is required. However, this processing often computationally inefficient. In this study, we evaluate image-quality of short-range 2-dimensional imaging with far-field and near-field mode vector with/without range migration. The image-quality is examined by peak power gain. Numerical results show that the near-filed mode vector works properly for out study without range migration. In addition, SAR imaging using KR product extended arrays shows that image quality can be improved compared to conventional uniform SAR.

With the advent of IoT (Internet of Things) services in recent years, various industries are now working towards operating wireless networks and this in turn gives rise to the need for radio propagation simulations. However, in order to obtain reliable simulation results, an accurate model of the environment is often needed. This paper proposes a method for generating a plane model automatically, for use in ray tracing simulations from 3D point cloud data in order to ease the burden of creating models manually. Ray tracing simulation results using the generated model are compared with measurements and the comparison shows that the trend of normalized received power is similar.

5th generation mobile communication (5G) is being actively researched and developed. We focus on “Ultra-Reliable and Low-Latency Communication” and consider the application of truck platooning as a use case. The latest research on the Doppler spectrum of the vehicle-to-vehicle (V2V) direct communication of platooning vehicles has revealed that the direct wave is not Doppler-shifted and that a component with twice the maximum Doppler frequency was observed.

This paper focuses on road surface reflections and scattered waves, and shows that there is no Doppler shift near the regular reflection point and that the Doppler shift near the transmission/receiving point.

The circularly polarized axial and conical beams from a two-arm spiral antenna are investigated and the radiation phase distributions around the antenna axis are clarified. A tilted beam is created by superimposing the conical beam onto the axial beam. The tilted beam is steered in the azimuth plane when the two arms are excited by different amplitudes and phases. The beam direction of the tilted beam estimated using formulated phase distributions agrees with that obtained from a numerical analysis. The estimation with the formulated phase is simple and has the superiority over the determination of the complex and time-consuming numerical analysis.

This paper presents an extended beamforming method by two-dimensional (2-D) Sparse Arrays. The authors have proposed optimum 2-D sparse arrays and evaluated them in the sense of direction of arrival (DOA) estimation accuracy. We develop a way of beamforming by the difference co-array of 2-D sparse arrays, and evaluate their beamforming performance as well as bit error rate (BER) characteristics through computer simulation.

As a physical layer security technique, directional modulation (DM) using an array antenna was proposed. By the method, modulated signal can be correctly reconstructed in only the pre-specified direction from the array. On the other hand, Space Selective Modulation (SSM) was proposed. SSM shares the similar principle to DM. Using the technique, modulated signal is correctly reconstructed in only the specified space, not the specified direction by utilizing fading characteristics. The originally proposed SSM uses three or four transmitting antennas. However, the transmissible probability is not 100%. Because a modulated signal is formed by summing up phase-controlled channel coefficients in SSM, symbols of the all constellation points may not be formed depending on the channel conditions. It brings about a decrease in the secrecy capacity of the secure information transmission. In this paper, we consider solving the problem by increasing the number of antennas. We quantitatively evaluated the secrecy capacity by computer simulations. The results confirm the improvement of the total performance in the secrecy capacity of SSM.

In this paper, the authors propose a small printed monopole antenna corresponding to the frequency band of UWB (Ultra-wideband) system that use a frequency of 3.1 GHz to 10.6 GHz. This antenna has a structure in which a bell-shaped UWB monopole antenna formed on a dielectric substrate (FR-4) has a half shape and a short stub is attached to the antenna. The size of the antenna is 30 × 12 × 1.6 mm³. The antenna is designed to be smaller than the conventional one proposed by the author, and can operate in the frequency band of the UWB system. From the simulation result, it is shown that good characteristics can be obtained to UWB application for high speed wireless communication.

The near field leaky-wave focusing antenna using the inhomogeneous rectangular waveguide is proposed and a design method is presented. The height of broad-wall of waveguide is inhomogeneous to obtain focusing effect at a desired position. In the antenna design, a relation between the phase constant of traveling wave and the height of broad-wall of the waveguide is derived. Simulation results and measured results at Ka-band are presented to validate the proposed design method.

Compressed sensing (CS) based direction-of-arrival (DOA) estimation has the advantage of high resolution and no need for wave number estimation. Although it is applicable for 2 dimensional estimation, the computation complexity is severe problem due to its increased number of array elements and search domain. This letter proposes a separation approach and pair-matching to resolve the above drawback. Since the CS can extract the original signal source, the pair-matching can be simply attained by cross correlation between source estimates of vertical and horizontal arrays. Computer simulation verifies the fundamental effectiveness of the proposed method.

In a two-tier heterogeneous network, cross-tier interference mitigation between macro-cell (MC) and small-cell (SC) is an important issue, where MC and SC share the same time/frequency resources. In this article, we propose a method to mitigate downlink cross-tier interference between MC and SC, where macro-cell base-station (MBS) and small-cell base-stations have multiple antenna arrays and their precoding weights are optimized to mitigate mutual cross-tier interference under a given pilot overhead. Simulation results show that the proposed scheme improves the downlink sum-rate compared with conventional scheme that coordinates cross-tier interference from MBS to small-cell users under the same pilot overhead condition.

This letter proposes a filter-and-forward relay scheme with multiple relay nodes using wireless energy harvesting. A relay node processes the received signal by using a time-domain filter to suppress inter-symbol interference and forwards its outputs using the energy harvested from the received signals that arrive from the source node and from all the relay nodes. We consider the filter design method based on the signal-to-interference-plus-noise power ratio maximization problem under multiple constraints for relay transmit power. Simulation results show the effectiveness of the proposed scheme owing to the cooperation of multiple relay nodes.

Monitoring applications using sensors are being led by the government to address the problem of aging infrastructure in Japan. There are various methods for sensing but the durability of general infrastructures and buildings have already exceeded 30 years which makes it difficult to address the issue. As one of the solutions we focused on the technology of “Chipless sensor” that applies “Chipless RFID” technology composed only of metal patterns without using electronic components such as IC chips. This report describes a sensor that can detect moisture with just metal patterns by supplying power from the reader.