Heung-Gyoon Ryu

This paper introduces a novel method for radio frequency (RF) self-interference (SI) cancellation in in-band full-duplex (IBFD) communication systems using a generalized analog least mean square (GALMS) loop. Conventional research in this area has predominantly focused on employing the tapped delay line (DL) structure to process the RF transmitted signal. The proposed GALMS loop utilizes a filter bank applied on the baseband transmitted signal to avoid the limitation of the conventional tapped DL adaptive filters, which require tapped spacing to satisfy the Nyquist principle. We utilize frequency domain representation and steady-state analysis to derive the modeling error and residual SI power of the proposed structure. Notably, the GALMS loop incorporating an allpass filter bank can achieve the same level of SI cancellation as the conventional DL structure with a significantly reduced number of taps. Simulations are conducted to validate the efficiency of the proposed GALMS loop and prove the theoretical findings.

Next-generation wireless technology which will use Sub-THz frequency band will support several new services and applications. However, there is a very high propagation loss of communication signals in Sub-THz frequency band. Furthermore, the power efficiency will be greatly decreased because of the high peak-to-average power ratio (PAPR) in the multi-carrier communication signal. As a result, PAPR reduction is the most important in 6G wireless communication system than 4G long-term evolution (LTE), 5G new radio (NR) schemes because it will use the Sub-THz frequency band of very high propagation loss. Therefore, spread spectrum technology termed as orthogonal chirp division multiplexing (OCDM) takes into account for the orthogonality of cyclically shifted quadratic chirp signals in order to increase the spectral efficiency and reduce the propagation loss. In this paper, we suggest a new discrete Fourier transform (DFT)-Spread OCDM (DFT-Spread OCDM) system for designing waveform and suitably acceptable PAPR reduction. Comparing the proposed scheme to the conventional OFDM and OCDM systems, simulation findings show that this technique greatly reduces PAPR by about 2 dB. Additionally, we examine the bit error ratio (BER) performance in AWGN channel. This DFT-Spread OCDM scheme performs almost similar results as compared to the previous OFDM and OCDM systems.

We present a model of a sub-THz frequency spectrum analyzer based on the antiferromagnet/non–magnetic metal heterostructure. The considered structure operates in the active self–oscillation regime with the high Q–factor (closed to $10^{6}$ ) and is phase–locked to the analyzed signal, while the frequency of the oscillator is linearly tuned by the spin–polarized current flowing through the non–magnetic metal. We find an analytical expression for the duration of the phase–locking interval by analyzing the generalized Kuramoto model with inertia. We show that the speed of the described spectrum analyzer is comparable to and exceeds the speed of modern commercial spectrum analyzers. The presented results can be helpful for practically realizing the room–temperature, tunable, sensitive, and high–speed sub-THz frequency spectrum analyzers.

Orthogonal chirp division multiplexing (OCDM) system has been considered as one candidate for the nextgeneration 6G cellular system that will support many new services and applications but will suffer from the sub-THz frequency band. It is anticipated that this will significantly harm the waveform orthogonality of conventional systems and lead to obnoxious intercarrier interference (ICI) and a very high propagation loss on information signals by introducing peak-to-average power ratio (PAPR). As a result, PAPR reduction is the most important aspect of 6G wireless communication system than 4G long-term evolution (LTE), 5G new radio (NR) schemes because it will use the Sub-THz frequency band which has a very high tendency toward propagation loss component. Therefore, spread spectrum technology termed as orthogonal chirp division multiplexing (OCDM) takes into account for the orthogonality of cyclically shifted quadratic chirp signals in order to increase spectral efficiency and reducing PAPR. The OCDM system, however, emits considerable out-of-band (OOB) power. To solve this problem, we suggest a new discrete Fourier transform (DFT)Spread Windowing and Restructuring (WR)-OCDM (DFT-Spread WR-OCDM) method for a suitably acceptable PAPR and OOB power emission reduction. In the system, the OOB power emissions are successfully reduced at the transmitter using time-domain windowing, and relatively shorter in window length is sufficient to satisfy the standard spectral mask. Comparing the proposed scheme to previous OFDM and OCDM systems, simulation findings show that this technique greatly reduces PAPR by about 2 dB and OOB power emission approximately by 64 dB and 70 dB. Additionally, we examine the bit error ratio (BER) performance using AWGN channel. This DFT-Spread WROCDM scheme performs almost similar results as compared to the conventional OFDM, OCDM, and WR-OCDM systems.

When there is any particular interference or jamming signal against the OFDM (orthogonal frequency division multiplexing) wireless communication system, it is badly serious problem for the communication performance even though the OFDM system is inherently robust to interference than the single carrier communication system. Therefore, it is very important to design the counter-measure to this kind of interference. So, in this paper, window processing using the weighting function is introduced to recover the information data in parallel with the spreading and error correcting method. This paper describes the wireless OFDM communication system in the strong SCI (spectral concentrated interference) channel. To make the windowing processing of OFDM Signal in the SCI channel, several weighting functions are used and analyzed in the time and frequency domain. So, window processing using the weight function in combination with nonlinear compensation method allows to increase robust against SCI and system improvement. Several window functions are proposed and compared to evaluated for the communication performances. Computer simulations show the differences in BER (bit error rate) performance in various conditions with various window functions. It can be concluded that the proposed method is pretty efficient in the SCI channel.

Summary: In this paper, in order to improve the received signal strength (RSS) and signal quality, three arrays of electronically steerable parasitic array radiator (ESPAR) antennas are suggested for the ultra‐high frequency (UHF) radio frequency identification (RFID) communication and sensing system applications. Instead of the single antenna, the array antennas have recently been widely used in many communication systems because of their peak gains, better radiation patterns, and higher radiation efficiency. Also, there are some important issues to use the antenna array like high data rates in wireless communication systems and to better understand the many targets or sensors. In this article, a wireless sensor network (WSN) is being investigated to overcome multipath fading and interference by antenna nulling technology that can be achieved through beam control ESPAR array antennas. The proposed ESPAR array antennas exhibit higher gains like 9.63, 10.2, and 12 dBi and proper radiation patterns from one array to another. Moreover, we investigate the mutual coupling effect on the performance of array antennas with different spacing (0.5λ, 0.75λ, λ) and configurations. It is found that the worst mutual coupling reduced by −28 to −34 dB for 2 × 2 array, −3 to −43 dB for 2 × 3 array, and finally −42 dB to −51 dB due to the antenna spacing from 0.5λ to λ. Thus, these suggested antennas could effectively be applied in the WSN communication systems, internet of things (IoT) networks, and massive wireless and backscatter communication systems.

It is very important to have reliable information signal at the receiver of the UHF (ultra-high frequency) RFID (radio frequency identification) communication system. For this goal, an exact location of the RFID tag must be traced, and the definite direction from the RFID reader to the RFID tag must be stated at the particular boundaries to be communicated properly. In this paper, an advanced direction finding method based on the beam scanning (BS) is studied to receive the stronger information signal from a particular direction. Unlike the traditional systems i.e. peak searching (PS) and symmetrical constant (SC), the beam scanning method (BSM) in the ESPAR (electronically steerable parasitic array radiation) antenna provides efficient advantages to find out the direction, location of tags, and to receive the signals. Likewise, a selective beam switching (SBS) system by designing ESPAR antenna is proposed to minimize the interference. To be noted, the beam scanning method (BSM) is the prerequisite process of the selective beam switching (SBS) since there is an appropriate system configuration about the tag’s location, direction finding, and the optimum SNR (signal to noise ratio) by suppressing noise and interference. The work can be applied into the wireless ECG monitoring system by providing better advantages such as higher accuracy, longer range and the longer battery life span. The antenna nulling is very good to enhance SIR (Signal to Interference Ratio) performance of the system. Thus, it can be concluded that the proposed design is a reliable, robust, relatively long distance, and low power WSN (wireless senor network) communication system and IoT communication networks.

Wireless sensor networks (WSNs) systems based on Internet of Things (IoT) have developed rapidly in recent years. However, interference is a major obstacle to relatively long-distance communications in such networks. It is also very complicated and challenging to fix the exact location of tags in the IoT sensor networks. To overcome these problems, in this paper, an electronic steering parasitic array radiator (ESPAR) antenna used as a beamformer to handle the interference and extend the communication range from the sensors or tags is suggested. In addition, an efficient method, namely beam scanning (BS), is proposed to find the directions of tags. The beam scanning method (BSM) can be used for the selective beam switching (SBS) system by designing an ESPAR or array of ESPAR antennas with the help of CST studio. The antennas exhibit higher gain (8.17 dBi, 11.40 dBi) and proper radiation pattern at a particular direction. In addition, the MATLAB simulation findings indicate that the proposed BSM algorithm provides longer communication range, i.e., 25 m. In order to maximize range while avoiding interference, it is necessary to determine the direction and precise orientation of the tag in the WSN communication systems. Consequently, this work could be applied to an IoT sensor network such as an electrocardiogram system by providing better advantages such as higher localization accuracy and longer operating range.