A quantization error caused by digital amplitude adjusters and phase shifters on array antennas leads to deterioration of directional patterns. Especially, it affects null depth and null angle. In this paper, reduction method of quantization error using auxiliary antenna on array antenna is proposed. One element in the array antenna is operated as auxiliary antenna to reduce the quantization error of other array elements. The null accuracy is improved by the effect of the auxiliary antenna, therefore, the deeper null is formed in correct angle. The validity of the proposed method is shown through numerical simulation.

For years, researchers have been studying the relation between earthquakes and geomagnetic field signals using observation results. Following our continuous geomagnetic observation, this report describes geomagnetic signal changes generated by earthquakes and tsunami waves. Results show that detection of their occurrence using geomagnetic field measurement is effective for providing an early alarm system for disaster mitigation. Robust detection requires the robust estimation of a geomagnetic field using multiple observation results. This study introduced a deep neural network (DNN) to estimate geomagnetic fields. Results clarified that the proposed DNN model using data of multiple axes at multiple observation points as input data provides efficient solutions for geomagnetic estimation.

A cooperative precoding scheme is proposed for cognitive wireless energy transfer networks, where a multiple-input multiple-output multiple-antenna eavesdropper (MIMOME) primary link coexists with a multi-antenna wireless energy transfer secondary link. Unlike the traditional wireless networks, the co-channel interference here is a useful rather than harmful resource. Our design objective is to maximize the secrecy rate of the primary link by optimizing the transmit covariance matrices, subject to the energy harvesting requirement at the energy receiver. The block coordinate descent (BCD)-based iterative algorithm is proposed to deal with the formulated non-convex optimization problem. Simulation results show that the proposed cooperative precoding design outperforms the non-cooperative scheme in terms of both secrecy rate and energy harvesting.

In recent years, MIMO technology which uses multiple antennas has been introduced in mobile terminal to increase communication capacity. However, if MIMO antennas are put closely, a strong mutual coupling occurred. Then it causes decreasing radiation efficiency and channel capacity. Therefore, reducing the mutual coupling is required. In previous study, connecting MIMO antennas by inductor L or added branch elements to antennas instead of L. In this paper, we propose a novel decoupling method by using a short stub and confirm that proposed model performed decoupling, increased radiation efficiency.

Wireless communications channel is multipath propagation channel and its main drawback is fading that degrades system performance. Multipath fading effects can be mitigated by using diversity combing scheme at the receiver. Many diversity combining schemes were considered in the literature to study their performance in different multipath fading environments. Recently, N. C. Beaulieu considered generalized framework for performance analysis of selection combining diversity in Rayleigh fading channel by deriving expressions for average error rate. However, experimental measures shown that the Nakagami fading channel model is a good fit to different multi-path fading environments. Hence the performance analysis of selection diversity combining scheme in Nakagami fading channels with Laplace cochannel interference is presented in this paper by deriving the average error rate of binary phase shift keying signals.

Crash Warning Application (CWA) for vehicle safety is expected one of the most important applications in smart city. CWA exchanges status information between all nodes by broadcast frames in V2X (Vehicle-to-Everything) communications. Since CWA has some QoS requirements, the number of nodes such as vehicles and pedestrians must be less than a certain value to avoid congestion. In order to accommodate more communication nodes in CWA, a novel cluster-based communication method is proposed. In this method, a cluster head estimates its members’ status and transmit them on behalf of the members instead of collecting members’ information with using additional spectrums. Members transmit correction frames if they hear unacceptable error in the estimation. Depending on the error value, congestion level is to decrease in frames simultaneously sent by cluster head but to increase in additional frames for the error correction. The proposed method is evaluated to show its effectiveness for the number of cluster members and error values (error probabilities).

We demonstrate the relationship between inter-core crosstalk and Q-factor in a multicore transmission line including a multicore fiber and a multicore amplifier by using an in-service inter-core crosstalk monitoring method we propose. The method estimates inter-core crosstalk by using tones with different wavelengths for each core. We measured Q-factors at the center wavelength of the WDM channel. The measured crosstalk was −20.2 dB and the Q-factor was 5.8 dB after 411.2-km transmission. The Q-factor estimated from the monitored crosstalk was found to closely match the measured value.

The power amplifier non-linearity and In-Phase/Quadrature (I/Q) imbalance of a transmitter is important RF communication impairment. This paper proves that the distortion of power amplifier output signal in the transmitter includes the non-negligible PM-AM and PM-PM distortion exists in transmitter impairment. Moreover, this paper presents a novel low-complexity dual-band Cartesian Memory Polynomial for modeling and compensating for a concurrent dual-band transmitter. The experimental results verify the high performance of the proposed model in suppressing the adjacent channel error power with low complexity.