Massive MIMO is expected to realize a large capacity for wireless communication technology. To reduce the number of devices of the massive MIMO, utilizing a two-dimensional Butler matrix for the feed circuit has been investigated, but complexing its design. We have proposed a Massive MIMO configuration using a stacked Butler matrix and a staircase array antenna to reduce the circuit design cost. This letter proposes a V-shape staircase array antenna with a stacked Butler matrix to reduce antenna profile. Computer simulation clarifies the beam steering range for the proposed antenna.

Asynchronous Pulse Code Multiple Access (APCMA) is a pulse-based communication system for massive IoT. It enables high-density communication because it can decode messages with a high probability even if they collide. We evaluate the performance of APCMA with Chirp Spread Spectrum-modulated pulses (CSS-APCMA) by comparing it with On-Off Keying APCMA (OOK-APCMA) and LoRa. Our first experiment shows that APCMA has a lower packet error rate (PER) than LoRa in a congested environment. Our second experiment shows that CSS-APCMA has a smaller PER than OOK-APCMA in a noisy environment. Our results confirm that CSS-APCMA is suitable for massive IoT.

Maintenance of social infrastructure, such as utility poles and bridges, is a major challenge in the era of declining labor force. While remote maintenance with drones is expected to solve this problem, it requires high-quality images for error-free decisions by a remote maintainer and low-latency to prevent many retries of remote operations since they directly affect maintenance efficiency. For that purpose, low-compression video with low encoding delay and small distortion is a leading candidate. However, we found that such traffic with high-burstiness causes a microburst, which is a short-time congestion experienced at the aggregation point even though the network capacity seems to be sufficient. We also propose a congestion avoidance method by designating appropriate timing to the encoders without losing image quality and report latency reduction in 5G-NR simulations.

This letter investigates the impact of the antenna element directivity on compressed sensing (CS)-based direction of arrival (DOA) estimation employing the uniform circular array (UCA) antenna. In the CS-based approach, the reconstruction accuracy of sparse signals is determined by a sensing matrix, which depends on the array antenna configuration in the DOA estimation. In our study, we analyze the cross-correlation between column vectors of the sensing matrix and clarify the estimation accuracy for various antenna element radiation patterns.

Geometrically shaped multi-dimensional modulation formats are designed by a bit-wise autoencoder (AE), which is one of the deep learning applications. The optimized four-dimensional (4-D) modulation constellation diagrams in two-dimensional (2-D) projection have highly unique symmetrical constellations with clever labeling. In addition, the numerically evaluated BER performances show that the receiver sensitivities of the optimally shaped multi-dimensional modulation format are equivalent to or better than those of the conventional 4-D and 2-D formats with the same transmission capacity.

Many fatal traffic accidents caused by professional drivers are attributed not only to fatigue and stress, but also heart and cardiovascular disease. Heartbeat interval (HBI) is one of the primary vital signs that indicates a sudden change in a person’s physical condition. In addition, blood pressure, particularly continuous blood pressure (BP), is highly correlated with cardiovascular disease. However, to our knowledge, there are no studies on monitoring a driver’s HBI and continuous BP simultaneously. In this paper, we present a 60 GHz millimeter-wave vital signs sensor to monitor the driver’s HBI and continuous BP in a non-contact manner. The driver’s HBI and continuous BP were measured while driving and each measured vital sign was evaluated using correlation and Bland-Altman analysis.

This paper investigates the performance of the hybrid automatic repeat request (HARQ) protocol, considering the bubble blockage and Generalized Gamma fading channel in underwater optical wireless communication (UOWC) systems. The system performance in terms of bit-error rate and throughput is analytically analyzed. Computer simulations using the Monte Carlo method are also presented to validate the correctness of our analysis. From the obtained results, we discuss the effects of the bubble blockage and the effectiveness of the HARQ in different system settings.

Unmanned Aerial Vehicles (UAVs) routing methods have been studied using protocols for ad hoc networks composed of smart meter wireless devices. By using weighting, both safety and time could be judged comprehensively, and a “safe and shortest time route” could be constructed. The requirement of route construction corresponds to the service. We proposed a method in which multiple different routes can be listed as candidates, for the key requirement to deliver the object to the destination within the time limit by each service. The total number of messages received by the destination node could explode. Therefore, we propose a Route Request (RREQ) message discard method to suppress unnecessary RREQ messages. Simulation evaluation experiments were conducted using real maps. We were able to increase the number of RREQ messages that were safely routed. This confirmed the effectiveness of the proposed method.

ARIB-TTML is a subtitle and caption standard for broadcasting systems in Japan. TTML profiles for Internet media subtitles and captions (IMSC) is a W3C recommendation. ARIB-TTML and IMSC are widely used in UHD satellite broadcasting in Japan and OTT operators; however, they have incompatible features and different description methods. These differences impede program exchange between broadband and broadcast. In this study, we propose a method for the interconversion of subtitles and captions described in ARIB-TTML and IMSC. We organized the features of each standard and proposed a conversion algorithm. The interconverted caption files were confirmed using a JavaScript-based caption renderer.

This letter considers a diamond network with two untrusted relays with low-security clearance level. Lossy decoder-and-forward is utilized at both the untrusted relays to enhance the reliability of transmission and to keep the source information confidential to the untrusted relays. The reliable-and-secure probability (RSP), which is the probability that the original messages can be retrieved at the destination while keeping confidential to the relays, is derived. It is found that with the help of cooperative jamming signal, superior reliability and security performance in terms of RSP can be achieved.