Jae-Hyun Ro

Adaptive Femtocell Design Scheme in Mobile Communication Systems

Mobile communication technologies have been evolving very rapidly and providing many advantages with mobile users. However, the amount of data traffic has increased significantly due to rapid expansion of mobile market. Recently, femtocell which is known as indoor base station is considered as the key solution to combat the data traffic. Femtocell provides mobile users with better quality of service. However, deployment of femtocell is not so easy due to inter-cell-interference (ICI) with existing macrocell. Signals from base stations are transmitted by a form of electronic magnetic waves. So, these waves undergo interference each other. Thus, this paper proposes the design scheme for femtocell which can reduce the influence of ICI. And also, proposed femtocell operates adaptively in accordance with reliability of system. With this proposed scheme, free and easy deployment of femtocell is expected.

Immersive Signage Transmission with Low-Complexity Detection Scheme

This paper proposes low-complexity detection scheme for immersive transmission in digital signage system based on multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM). For immersive signage transmission, a receiver of digital signage requires signal detection scheme with high reliability and low complexity. In this paper, low-complexity QR decomposition-M algorithm (QRD-M) is proposed. The proposed QRD-M calculates a threshold and eliminates unnecessary survival paths which have larger accumulated squared Euclidean distance (ASED) than a threshold. The simulation results show that the proposed QRD-M has the same error performance as conventional QRD-M. Also, the complexity of the QRD-M is very lower than the conventional QRD-M and it is decreased according to increased signal-to-noise ratio (SNR). An algorithm of the proposed QRD-M is used well in a receiver of small digital signage which requires high reliability and low complexity.

Adaptive Deactivation of Subcarriers for OFDM based Cognitive Radio

In this paper, an adaptive deactivation method for secondary user (SU) subcarriers is proposed. The deactivation method is applied to reverse link since the receiver uses same cognitive radio (CR) parameters for receiving signals in the reverse link. The proposed method protects the primary user (PU) bands from out of bound (OOB) interference of subcarriers allocated to SUs in the reverse link. The method can be used to prevent the continuous degradation of communication performance by notifying need for reconfiguration to the receiver. In the simulation results, comparison of total interference with a fixed deactivation method is shown.

Wireless Transmission System for the Improved Reliability in the Flying Ad-hoc Network

Unmanned aerial vehicle (UAV) has unlimited availability not only in war but in various fields such as reconnaissance, observation, exploration. The wireless communication system between UAVs is very important and is known as flying ad-hoc network (FANET). The reason is that the FANET for UAV transfers data such as the information on mission accomplishment, collision prevention, etc. Therefore, the FANETs require the robust and spectral efficient communication scheme in the fading channel. Due to the high-mobility of the UAVs, these channels are very dynamic and time varying channel. In a dynamic channel environment, the adaptive modulation and coding (AMC) scheme is necessary to provide a reliable communication. This paper provides the improved wireless communication scheme applied with the AMC scheme. The proposed scheme uses the modulation and coding according to the channel state information (CSI) in the FANETs. The receiver obtains the CSI by using the channel estimation and transmits the feedback information to the transmitter. And then, the transmitter confirms the channel conditions via the CSI and adaptively uses the modulation scheme and code rate according to the channel conditions. Because the proposed scheme provides the reliable wireless communication, it does not require unnecessary re-transmission.

Channel Estimation Scheme for the Enhanced Reliability in the Flying Ad-hoc Network

This paper proposes the improved channel estimation for flying ad-hoc network (FANET). The FANET means the wireless communication network between the unmanned aerial vehicle (UAV). UAVs have unlimited availability not only in war but in various fields such as reconnaissance, observation, exploration. Due to the high-mobility of the UAVs, these channels of the FANET environment are very dynamic and time varying channel. Because the FANET for UAV transfers data such as the information on mission accomplishment, collision prevention, etc., the FANET requires the robust and spectral efficient communication scheme in the fading channel. IEEE 802.11p is considered as a communication method between UAVs. However, IEEE 802.11p suffers from the challenge of robust channel estimation due to rapid time-varying nature of the channel. In the IEEE 802.11p, the long training symbols are used for fine synchronization and channel estimation. This channel estimation scheme isn’t suitable in the time varying channel. This paper proposes the scheme that uses the pilot symbols and recovered symbols to estimate channel. The proposed scheme can provide the reliable wireless communication for the FANET.

Adaptive encoding scheme providing optimal performance for Internet of Things industry in the backscatter system

In the wireless communication market, Internet of Things is one of the major issues. Internet of Things is a technology which connects all objects to the Internet and enables to share the information of the objects with each other. Also, energy harvesting for batteryless devices is also one of the new issues in order to realize Internet of Things. Through the realization of Internet of Things, all objects can connect to the Internet and share own information with each other. Since the sensor communication with the low-power battery or without the battery is possible by the backscatter technique, a backscatter technique is highly useful for the realization of Internet of Things. This article proposes a scheme that a sensor is connected to the Internet and the optimal performance is obtained. For reliable backscatter technique for mobile user, this article proposes the two encoding schemes which are FM0 and Miller-n. Also, to minimize the loss of the data rate, these two encoding schemes are adaptively used according to mobility. The mobility is decided by signal-to-noise ratio and channel state. For mobile user, the proposed backscatter technique has high error performance due to proposed adaptive encoding scheme.