Kyung Hoon Won

Sampling Frequency Offset Estimation Methods for DVB-T/H Systems

A precise estimation and compensation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system, because sampling frequency mismatch between the transmitter and the receiver dramatically degrades the system performance due to the loss of orthogonality between the subcarriers. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose two SFO estimation methods which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation / compensation are mainly specialized on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has good performance and stable operation through extensive simulation.

Timing synchronization method for device-to-device communication system

In this paper, we propose a timing synchronization method for device-to-device (D2D) system. In the past several years, many synchronization protocols have been investigated for ad-hoc network system. However, it is difficult to apply them to D2D system directly because of some difficulties. In D2D system, these protocols have some structural limitations and might show inefficient performance, because cellular base station can be employed to D2D network to enhance performance and reduce resources. Also, D2D network should be able to support a variable number of devices. Therefore, in this paper, we propose a new timing synchronization method for D2D system. In the proposed method, synchronization can be achieved in different ways according to the existence of available cellular base station. In the proposed method, we first consider cellular-assisted (CA) method based on random access process in cellular uplink procedure. On the other hand, when cellular base station is not available, user equipment performs stand-alone (SA) method. In SA-D2D, three step synchronization process and a new reference clock decision rule are proposed. We verify that the proposed method can achieve high accuracy synchronization in a short period.

A carrier frequency synchronization method for device-to-device communication network

Device-to-device (D2D) communication has received considerable attention in recent years as one of the key technologies for future communication system. Among the typical D2D communication systems, FlashLinQ (FLQ) adopted single-tone orthogonal frequency division multiplexing (OFDM) transmission which enables wide-sense discovery by time domain spreading and very low peak to average power ratio (PAPR). Although synchronization based on a common external source (CES) is basically assumed in FLQ, a means to support devices when they are unable to use a CES is still necessary. In OFDM system, generally, carrier frequency offset (CFO) induces inter-carrier interference (ICI) which degrades overall system performance drastically. Especially in D2D system, ICI can be amplified due to not only different frequency selectivity but also different path losses between links. Accordingly, a precise estimation and compensation of CFO are very important. Therefore, in this paper, we propose a new CFO estimation method for OFDM based D2D system. In the proposed method, the estimation of CFO is obtained by using two correlation results in a symbol. The estimation procedure of the proposed method enables the independent estimation of CFO between links and the estimation range can be adaptively defined depending on the distance between the two windows. By numerical analysis and performance evaluation, we verified that the proposed method achieves precise estimation performance compared to the conventional method.

Technical Characteristics and Trends of Capsule Endoscope

Capsule Endoscope(CE) is a capsule-shaped electronic device which can examine the lesions in digestive tract of human body. Recently the medical procedure using capsule endoscope is receiving great attention to both doctors and patients, since the conventional push-typed endoscope using cables brings great pain and fear to the patients. The technique was firstly available in 2000 and is based on a convergence techniques among BT(Bio Technology), IT(Information Technology), and NT(Nano Technology). The device consists of an optical parts including LEDs(Light Emitting Diodes), an image sensor, a communication module and a power module. Capsule endoscope is the embodiment of the state-of-the art technology and requires key technologies in the various engineering fields. Therefore, in this paper, we introduce the composition of the capsule endoscope system, and compare the communication method between RF(Radio Frequency) communication and HBC(Human Body Communication), which are typically used for data transmission in the capsule endoscope. Futhermore, we analyze the specification of commercialized capsule endoscopes and present the future developments and technical challenges.

A fine timing synchronization method on group communication system enablers for LTE

Recently, 3rd generation partnership project has adopted a new study item for device-to-device (D2D) communication service in long term evolution (LTE) system, called the group communication system enablers for LTE (GCSE_LTE). In GCSE_LTE, synchronization is an important issue; therefore, many synchronization methods of wireless sensor network and ad-hoc network can be considered. In these conventional methods, they only consider synchronizing the transmission time of signal. However, in case of ideal synchronization method, conventional methods cause a link delay spread (LDS) problem. LDS means a time difference between received signals which are caused by the different propagation delays among user equipments (UEs). The problem is that all UE need an extra length of cyclic prefix (CP) to receive multi-path delayed signals, and it can be a substantial resource waste. Therefore, in this paper, we propose a fine timing synchronization method by a master node which can reduce the maximum LDS in D2D group. We verify that the proposed method can reduce the average length of additionally required CP compared to conventional methods.

An efficient iterative ICI cancellation method for cooperative STBC-OFDM system

In this paper, we propose an enhanced iterative ICI (Inter Carrier Interference) cancellation method for cooperative STBC-OFDM (Space Time Block Coded-Orthogonal Frequency Division Multiplexing) system. In cooperative STBC-OFDM system, ICI cancellation is necessary because ICI due to the independent local oscillators always exits. The conventional iterative ICI cancellation method has severe performance degradation due to the initial estimation error. Also the performance degradation increases as CFOs (Carrier Frequency Offsets) and modulation order increases. Therefore, in this paper, we propose an enhanced iterative ICI cancellation method which can reduce the initial estimation error by giving a priority to initial estimation and cancellation process. Through the complexity and performance comparisons, we verify that the proposed method has better performance with approximately same complexity compared with the conventional method.

An enhanced fine timing synchronization method for diagonal pilot OFDM system

In this paper, a new fine timing synchronization method of orthogonal frequency division multiplexing (OFDM) system is presented to solve the performance degradation from the diagonally allocated pilot structure. For systems based on diagonal pilots, by using the conventional timing estimation method which is proposed by Hsieh and Wei, the estimation performance can be degraded due to the relatively large pilot distance in the frequency selective fading channel. Therefore, we propose a new fine timing synchronization method, which is based on symbol accumulation with phase interpolation, and that can reduce the effect of frequency selectivity and frequency offset. By mathematical analysis and simulation, we verified that the proposed method can achieve better performance than conventional method in large frequency selective fading environment.

Group manchester code modulation for medical in-body WBAN systems

In this paper, we propose group Manchester code (GM) modulation scheme for medical in-body wireless body area network (WBAN) systems. In IEEE, the WBAN system is assigned as 802.15. Task Group 6 (TG6), and the related standardization is being progressed. Recently, in this Group, group pulse position modulation (GPPM), which can obtain data rate increase by grouping pulse position modulation (PPM) symbols, is proposed as a new modulation scheme for low-power operation of WBAN system. However, the conventional method suffers from BER performance degradation due to the absence of gray coding and its demodulation characteristics. Therefore, in this paper, we propose a modified GM scheme which groups Manchester code instead of PPM. In the proposed GM scheme, a low-complexity maximum likelihood (ML) demodulation method is employed in order to maximize the BER performances. Also, log likelihood ratio (LLR) decision method is proposed to employ the Turbo code as forward error correction (FEC). Finally, we verified that the proposed method has a good performance and is an appropriate scheme for in-body WBAN system through extensive performance evaluation.

Doppler Frequency and Noise Insensitive Sampling Frequency Offset Estimation Method for DVB-T/H Systems

A precise estimation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose a SFO estimation method which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation /compensation are mainly based on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has a good performance and stable operation through extensive simulation.

A low computational equalization method for capsule endoscope system

In this paper, we propose a low computational equalization method for capsule endoscope (CE) system. In CE system, low power transmission and reception is essential because the devices which are transplanted or patched on human body should be small and durable to allow the patient to move freely. Also, the pace of change in channel between CE and receiver is quite variable due to the bowel movements. Therefore, it is necessary to design a low computational equalizer structure for CE system, because there are difficulties in practical application of the conventional equalization due to its high computational complexity. Therefore, we propose an equalization method that focuses on reducing computational complexity. The proposed method adaptively decides the requirement of filter update with simple operation, and we verified that the proposed method improves the performance versus computational complexity trade-offs efficiently compared to the conventional method.