Joo Young Choi

Bio: Joo Young Choi is an academic researcher from Yonsei University. The author has contributed to research in topics: Communication channel & IEEE 802.11p. The author has an hindex of 1, co-authored 3 publications receiving 9 citations.

Preamble-Based Adaptive Channel Estimation for IEEE 802.11p

Abstract: Recently, research into autonomous driving and traffic safety has been drawing a great deal of attention. To realize autonomous driving and solve traffic safety problems, wireless access in vehicular environments (WAVE) technology has been developed, and IEEE 802.11p defines the physical (PHY) layer and medium access control (MAC) layer in the WAVE standard. However, the IEEE 802.11p frame structure, which has low pilot density, makes it difficult to predict the properties of wireless channels in a vehicular environment with high vehicle speeds; thus, the performance of the system is degraded in realistic vehicular environments. The motivation for this paper is to improve the channel estimation and tracking performance without changing the IEEE 802.11p frame structure. Therefore, we propose a channel estimation technique that can perform well over the entire SNR range of values by changing the method of channel estimation accordingly. The proposed scheme selectively uses two channel estimation schemes, each with outstanding performance for either high-SNR or low-SNR signals. To implement this, an adaptation algorithm based on a preamble is proposed. The preamble is a signal known to the transmitter-receiver, so that the receiver can obtain channel estimates without demapping errors, evaluating performance of the channel estimation schemes. Simulation results comparing the proposed method to other schemes demonstrate that the proposed scheme can selectively switch between the two schemes to improve overall performance.

Symbol-Level Selective Channel Estimation in Packet-Based OFDM Systems.

Abstract: Wireless access in vehicular environments to support wireless communication between vehicles has been developed to provide road safety and infotainment services. In vehicular environments where the channel changes rapidly, channel estimation is very important in improving the reliability of wireless communication. Therefore, numerous channel estimation schemes have been proposed; however, none of the schemes proposed so far can perform well over the entire signal-to-noise ratio (SNR) region. In this paper, we propose a novel channel estimation scheme that selectively uses the better scheme between two channel estimation schemes on a symbol-by-symbol basis. The results show that the proposed scheme performs symbol-by-symbol selection of the better channel estimation scheme within a packet, and thus shows excellent performance over the entire SNR region in vehicular environments in terms of the bit error rate and packet error rate.

Regulatory Binding Partners and Complexes of NHE3

Abstract: NHE3 is the brush-border (BB) Na + /H + exchanger of small intestine, colon, and renal proximal tubule which is involved in large amounts of neutral Na + absorption. NHE3 is a highly regulated transporter, being both stimulated and inhibited by signaling that mimics the postprandial state. It also undergoes downregulation in diarrheal diseases as well as changes in renal disorders. For this regulation, NHE3 exists in large, multiprotein complexes in which it associates with at least nine other proteins. This review deals with short-term regulation of NHE3 and the identity and function of its recognized interacting partners and the multiprotein complexes in which NHE3 functions.

Nanostructured nickel oxide electrodes for non-enzymatic electrochemical glucose sensing

Abstract: Nanostructured nickel (Ni) and nickel oxide (NiO) electrodes were fabricated on Ni foils using the glancing angle deposition (GLAD) technique. Cyclic voltammetry and amperometry showed the electrodes enable non-enzymatic electrochemical determination of glucose in strongly alkaline media. Under optimized conditions of NaOH concentration and working potential (~ 0.50 V vs. Ag/AgCl), the GLAD electrodes performed far better than bare Ni foil electrodes, with the GLAD NiO electrode showing an outstanding sensitivity (4400 μA mM−1 cm−2), superior detection limit (7 nM), and wide dynamic range (0.5 μM–9 mM), with desirable selectivity and reproducibility. Based on their performance at a low concentration, the GLAD NiO electrodes were also used to quantify glucose in artificial urine and sweat samples which have significantly lower glucose levels than blood. The GLAD NiO electrodes showed negligible response to the common interferents in glucose measurement (uric acid, dopamine, serotonin, and ascorbic acid), and they were not poisoned by high amounts of sodium chloride.

CPW-Fed Transparent Antenna for Vehicle Communications

Abstract: In this paper, a fully transparent multiband antenna for vehicle communications is designed, fabricated, and analyzed. The antenna is coplanar waveguide-fed to facilitate its manufacture and increase its transmittance. An indium-tin-oxide film, a type of transparent conducting oxide, is selected as the conductive material for the radiation path and ground plane, with 8 ohms/square sheet resistance. The substrate is glass with a relative permittivity of 5.5, and the overall dimensions of the optimized design are 50 mm × 17 mm × 1.1 mm. The main antenna parameters, namely, sheet resistance, reflection coefficient, and radiation diagram, were measured and compared with simulations. The proposed antenna fulfills the frequency requirements for vehicular communications according to the IEEE 802.11p standard. Additionally, it covers the frequency bands from 1.82 to 2.5 GHz for possible LTE communications applied to vehicular networks.

Adaptive Pilot Pattern for Massive MIMO Systems

Abstract: This work proposes a new adaptive pilot pattern used for pilot arrangement at the mobile station and a new channel estimation at the base station. It addresses the bit error rate (BER) performance optimization of wireless channel estimation in massive multiple-input multiple-output systems. First, we propose a new adaptive pilot pattern (APP) that offers a lower BER than the conventional pilot patterns. Then, we suggest a new channel estimation algorithm based on the APP. It is called the shifted APP-channel estimation (SACE). As a result, APP guarantees an optimal BER performance for the different system configurations, channel models, and carrier frequencies. It offers better BER performance than conventional pilot patterns, such as the long-term evolution (LTE) pilot pattern. Moreover, the shifted APP-based channel estimation algorithm solves the error floor caused by the usage of multiple subcarriers. It also offers a signal-to-noise ratio (SNR) improvement that reaches 17 dB at BER $= 10^{-2}$ compared to the conventional minimum mean square error (MMSE) channel estimation.

A new hybrid approach for reducing the high PAPR in OFDM and F-OFDM systems with low complexity

Abstract: The large (peak to average power ratio (PAPR)) phenomenon is a downside in filtered multiplexing of the orthogonal frequency division (F-OFDM- Beyond 5G candidate) because of the nonlinearity design of the transmitter. Recently, several hybrid approaches have been implemented to minimize the high value of PAPR, at the expense of increasing the level of computational complexity in the system. In this paper, a new hybrid approach has been introduced throughout parallel to combine the approach of selective mapping (SLM) with the approach of partial transmit sequence (PTS) with (CSS) to improve the efficiency of PAPR reduction with lower complexity in numerical methods. The results indicate that the F-OFDM systems with the proposed hybrid method have superior performance compared to existing hybrid methods in terms of PAPR reduction, side-information, and computational complexity. Furthermore, a new hybrid approach suggested preserving the BER and PSD efficiency without deterioration.