Considering the non-convexity of hybrid precoding and the hardware constraints of practical systems, a hybrid precoding architecture, which combines limited-resolution overlapped phase shifter networks with lens array, is investigated. The analogy part is a beam selection network composed of overlapped low-resolution phase shifter networks. In particular, in the proposed hybrid precoding algorithm, the analog precoding improves array gain by utilizing the quantization beam alignment method, whereas the digital precoding schemes multiplexing gain by adopting a Wiener Filter precoding scheme with a minimum mean square error criterion. Finally, in the sparse scattering millimeter-wave channel for the uniform linear array, the proposed method is compared with the existing scheme by computer simulation by using the ideal channel state information and the non-ideal channel state information. It is concluded that the proposed scheme performs better in low signal-to-noise regions and can achieve a good compromise between system performance and hardware complexity.

Methods that embed data into printed images and retrieve data from printed images captured using the camera of a mobile device have been proposed. Evaluating these methods requires printing and capturing actual embedded images, which is burdensome. In this paper, we propose a method for reducing the workload for evaluating the performance of data embedding algorithms by simulating the degradation caused by printing and capturing images using generative adversarial networks. The proposed method can represent various captured conditions. Experimental results demonstrate that the proposed method achieves the same accuracy as detecting embedded data under actual conditions.

Long-range radars (LRRs) for higher level autonomous driving (AD) will require more antennas than simple driving assistance. The point at issue here is 50-60% of the LRR module area is used for antennas. To miniaturize LRR modules, we use horn and lens antenna with highly efficient gain. In this paper, we propose two high-density implementation techniques for radio-frequency (RF) front-end using horn and lens antennas. In the first technique, the gap between antennas was eliminated by taking advantage of the high isolation performance of horn and lens antennas. In the second technique, the RF front-end including micro-strip-lines, monolithic microwave integrated circuits, and peripheral parts is placed in the valley area of each horn. We fabricated a prototype LRR operating at 77 GHz with only one printed circuit board (PCB). To detect vehicles horizontally and vertically, this LRR has a minimum antenna configuration of one Tx antenna and four Rx antennas placed in 2×2 array, and 30 mm thickness. Evaluation results revealed that vehicles could be detected up to 320 m away and that the horizontal and vertical angle error was less than +/- 0.2 degrees, which is equivalent to the vehicle width over 280 m. Thus, horn and lens antennas implemented using the proposed techniques are very suitable for higher level AD LRRs.

This paper presents an efficient method for solving PnP, PnPf, and PnPfr problems, which are the problems of determining camera parameters from 2D-3D point correspondences. The proposed method is derived based on a simple usage of linear algebra, similarly to the classical DLT methods. Therefore, the new method is easier to understand, easier to implement, and several times faster than the state-of-the-art methods using Gröbner basis. Contrary to the existing Gröbner basis methods, the proposed method consists of three algorithms depending on the number of the points and the 3D point configuration. Experimental results show that the proposed method is as accurate as the state-of-the-art methods even in near-planar scenes while achieving up to three times faster.

In this paper, we propose an accurate calibration method for glassless stereoscopic systems. The method uses a lenticular lens on a general display. Glassless stereoscopic displays are currently used in many fields; however, accurately adjusting their physical display position is difficult because an accuracy of several microns or one hundredth of a degree is required, particularly given their larger display area. The proposed method enables a dynamic adjustment of the positions of images on the display to match various physical conditions in three-dimensional (3D) displays. In particular, compared with existing approaches, this avoids degradation of the image quality due to the image location on the screen while improving the image quality by local mapping. Moreover, it is shown to decrease the calibration time by performing simultaneous processing for each local area. As a result of the calibration, the offset jitter representing the crosstalk reduces from 14.946 to 8.645 mm. It is shown that high-quality 3D videos can be generated. Finally, we construct a stereoscopic viewing system using a high-resolution display and lenticular lens and produce high-quality 3D images with automatic calibration.

Smaller antenna structures for long-range radar transmitters and receivers operating in the 77-GHz band for automotive application have been achieved by using antennas with a horn, lens, and microstrip antenna. The transmitter (Tx) antenna height was reduced while keeping the antenna gain high and the antenna substrate small by developing an antenna structure composed of two differential horn and lens antennas in which the diameter and focus distance of the lenses were half those in the previous design. The microstrip antennas are directly connected to the differential outputs of a monolithic microwave integrated circuit. A Tx antenna fabricated using commercially available materials was 14mm high and had an output-aperture of 18×44mm. It achieved an antenna gain of 23.5dBi. The antenna substrate must be at least 96mm2. The antenna had a flat beam with half-power elevation and azimuth beamwidths of 4.5° and 21°, respectively. A receiver (Rx) antenna array composed of four sets of horn and lens antennas with an output-aperture of 9×22mm and a two-by-two array configuration was fabricated for application in a newly proposed small front-end module with azimuth direction of arrival (DOA) estimation. The Rx antenna array had an antenna coupling of less than -31dB in the 77-GHz band, which is small enough for DOA estimation by frequency-modulated continuous wave radar receivers even though the four antennas are arranged without any separation between their output-apertures.

This paper presents results of outdoor experiments conducted in the 39-GHz band. In particular, assuming mobile communications such as the fifth generation mobile communications (5G) and beyond, we focus on achieving 1Gbit/s or greater throughput at transmission distances exceeding 1km in the experiments. In order to enhance the data rate and capacity, the use of higher frequency bands above 6GHz for mobile communications is a new and important technical challenge for 5G and beyond. To extend further the benefits of higher frequency bands to various scenarios, it is important to enable higher frequency bands to basically match the coverage levels of existing low frequency bands. Moreover, mobility is important in mobile communications. Therefore, we assume the 39-GHz band as a candidate frequency for 5G and beyond and prepare experimental equipment that utilizes lens antenna and beam tracking technologies. In the experiments, we achieve the throughput values of 2.14Gbit/s at the transmission distance of 1850m and 1.58Gbit/s at 20-km/h mobility. Furthermore, we show the possibility of achieving high throughput even under non-line-of-sight conditions. These experimental results contribute to clarifying the potential for the 39-GHz band to support gigabit-per-second class data rates while still providing coverage and supporting mobility over a coverage area with distance greater than 1km.

This work presents the lowest power consumption sub-mm2 supply-modulated OOK transmitter for self-powering a continuous glucose monitoring (CGM) contact lens. By combining the transmitter with a glucose fuel cell that functions as both the power source and a sensing transducer, a self-powered CGM contact lens was developed. The 385×385μm2 test chip implemented in 65-nm standard CMOS technology operates at 270pW with a supply voltage of 0.165V. Self-powered operation of the transmitter using a 2×2mm2 solid-state glucose fuel cell was thus demonstrated.

In this paper, the topology optimization method is first applied to obtain high gain characteristics of dielectric flat lens. The topology optimization method used in this study is based on the gradient method with adjoint variable method. The FDTD method is used as the analysis method of electromagnetic fields. Results are compared with those obtained by using metaheuristic methods GA and PSO. As a result, it is shown that the proposed method can efficiently design a high gain dielectric flat lens in a wide frequency band.

This paper explores the potential of orbital angular momentum (OAM) multiplexing as a means to enable high-speed wireless transmission. OAM is a physical property of electro-magnetic waves that are characterized by a helical phase front in the propagation direction. Since the characteristic can be used to create multiple orthogonal channels, wireless transmission using OAM can enhance the wireless transmission rate. Comparisons with other wireless transmission technologies clarify that OAM multiplexing is particularly promising for point-to-point wireless transmission. We also clarify three major issues in OAM multiplexing: beam divergence, mode-dependent performance degradation, and reception (Rx) signal-to-noise-ratio (SNR) reduction. To mitigate mode-dependent performance degradation we first present a simple but practical Rx antenna design method. Exploiting the fact that there are specific location sets with phase differences of 90 or 180 degrees, the method allows each OAM mode to be received at its high SNR region. We also introduce two methods to address the Rx SNR reduction issue by exploiting the property of a Gaussian beam generated by multiple uniform circular arrays and by using a dielectric lens antenna. We confirm the feasibility of OAM multiplexing in a proof of concept experiment at 5.2 GHz. The effectiveness of the proposed Rx antenna design method is validated by computer simulations that use experimentally measured values. The two new Rx SNR enhancement methods are validated by computer simulations using wireless transmission at 60 GHz.

In this paper, we propose an improved method of embedding and detecting data in a printed image using a camera of a mobile device. The proposed method is based on the data diffusion method. We discuss several problems in the conventional lens distortion correction method. In addition, the possibility of using multiple captured images by employing a motion-image-capturing technique is also examined. A method of selecting captured images that are expected to obtain a high detection rate is also proposed. From the experimental results, it is shown that the proposed method is effective for improving data detection.

A 50-Gb/s optical transmitter, consisting of a 25-Gb/s-class lens-integrated DFB-LD (with -3-dB bandwidth of 20GHz) and a LD-driver chip based on 0.18-µm SiGe BiCMOS technology for inter and intra-rack transmissions, was developed and tested. The DFB-LD and LD driver chip are flip-chip mounted on an alumina ceramic package. To suppress inter-symbol interference due to a shortage of the DFB-LD bandwidth and signal reflection between the DFB-LD and the package, the LD driver includes a two-tap pre-emphasis circuit and a high-speed termination circuit. Operating at a data rate of 50Gb/s, the optical transmitter enhances LD bandwidth and demonstrated an eye opening with jitter margin of 0.23UI. Power efficiency of the optical transmitter at a data rate of 50Gb/s is 16.2mW/Gb/s.

We realize homogenous luminance of the directional backlight for the time-division multiplexing autostereoscopic display using a convex lens array with the elemental lenses whose phase of placement in each row differs from one another. The validity of the proposed optical design is confirmed by a prototype system.

A two-dimensional negative refractive index material is proposed. The material has a bulky structure composed of dielectric prism cells with metal patterns. The material is expressed by an equivalent circuit. The propagation regions of two left-handed modes calculated from the equivalent circuit exist near the propagation regions obtained by electromagnetic simulation. It is confirmed by simulation that the incident plane wave goes into the material with low reflection by using the second left-handed mode and attaching metal conversion strips around the material. A negative refractive index slab lens with 15×9 cells is made to measure the field distribution of wave out of the lens. It is shown that the resolution of the slab lens exceeds the diffraction-limit.

We have designed and fabricated a compact 4-array integrated SOA module using a novel parallel optical coupling scheme and polarization-insensitive built-in array isolators. We achieved ultra-high On/Off extinction ratio of more than 60 dB and low cross talk of better than -60 dB as well as high-isolation of over 47 dB in wide wavelength ranges. We also developed a wavelength-insensitive parallel optical coupling scheme and an efficient thermal dissipating structure for a 4-array SOA module. We applied these technologies into 4-array SOA module fabrication and demonstrated a uniform optical coupling with the loss variance of 1 dB over the 140-nm wavelength ranges. We also demonstrated simultaneous operation of 300 mA 4 channels with low thermal degradation of the module gain less than 1 dB.

We describe 25-Gb/s error-free transmission over multi-mode fiber (MMF) by using a transmitter based on a 1.3-µm lens-integrated surface-emitting laser (LISEL) and a CMOS laser-diode driver (LDD). It demonstrates 25-Gb/s error-free transmission over 30-m MMF under the overfilled-launch condition and over 150-m MMF with a power penalty less than 1.0 dB under the underfilled-launch condition.

A can swells due to gas produced from an inner food caused by poor hermetic sealing of the can. This paper presents a measurement for the bottom shape to detect a swelled can by using the millimeter-wave imaging. For get higher spatial resolution and an adjustable focal distance, two collimated beam lenses were applied to the measurement system. First, a configuration of the system was studied with the electrical field intensity and focal distance by using full wave electromagnetic simulation. Next, the bottom shapes of cans with different pressure were evaluated quantitatively using the system. A shape change of 0.5 mm was detected with pressure difference of 50 kPa, and it is reasonable considering actual dimension of the can shape. A potential of the proposed detection method was presented.

This paper presents a compact metal plate lens antenna for evaluating a wave absorber placed on ceiling of the ETC gate. The focal distance of the lens was derived to be 129 cm by the geometrical optics procedure. By arranging the lens in front of a horn antenna, the gain and beamwidth characteristics were improved from 18 dBi to 26 dBi and from 22 degrees to 7 degrees, respectively. Then the antenna characteristics were evaluated when the distance between the antenna and the lens was changed in order to miniaturize the lens antenna. As the result, the changes in beamwidth were held to within 1 dB when the lens came close to the horn antenna. Scattering, phase and electric field intensity of electromagnetic wave were evaluated to clarify the foundation of the given characteristics. It was found that the field intensity for the miniaturized lens antenna is stronger than that for GO designed one though the phase uniformity is worse. The distance between the horn antenna and lens can be reduced to 80 cm. The absorption characteristics for the arranged absorbers which have different absorptions were measured, and it was shown that the proposed method was suitable for specifying the deteriorated absorber in the ETC system.

The left-handed (LH) operation of a three-dimensional (3-D) LH material composed of wired metallic spheres is experimentally confirmed. A 15153-cell periodic structure designed to have an isotropic LH characteristics is fabricated by a 3-D printer with post plating technology, and near-field measurements of refracted waves by the negative refractive index slab lens are carried out. The dispersion characteristics measured from the near-field distributions on the surface of the LH material clearly show that the structure supports the backward waves at 12 GHz band. It is also shown experimentally that the resolution of the slab lens exceeds the diffraction limit by near field measurements with a single source and adjacent two sources. In addition, near-field measurements from the LH material near the Γ-point frequency at 12.90 GHz are carried out. A highly directive plane wave with a single point source is observed and the near-zero-index operation has been confirmed.

This letter proposes a monopole multi-sector antenna with dielectric cylinder, and shows some results of simulations that examined the antenna characteristics. The dependency of radiation characteristics on relative permittivity εr shows the lens effect with increase of εr. Furthermore, the characteristics of the proposed antenna are improved by optimizing the termination conditions at the quiescent antennas. The backlobe level is lower than -10 dB. Also, the vertical HPBW and the conical HPBW are around 70.5° and 63.4°, respectively. The optimization improved the actual gain by 2 dB. It is found that the diameter of the proposed antenna is 1/3rd that of the conventional one.