Seongjoo Lee

Motion compensated frame interpolation by new block-based motion estimation algorithm

In this paper, a motion compensated frame interpolation (MCI) algorithm adapting new block-based motion estimation (BME), which is overlapped block-based motion estimation (OBME), is proposed for frame rate up-conversion (FRC). Unlike conventional BME algorithms, where a video frame is divided into many non-overlapping square blocks of pixels, the proposed BME is executed using an overlapped matching block in order to get more accurate motion trajectory. To reduce computational complexity caused by the OBME, a sub-sampled pixel block is used for the OBME. The proposed OBME is executed with the various overlapped blocks that have different block sizes and sub-sampling ratios. In this paper, instead of mean absolute difference (MAD) used for general BME, a modified MAD is applied for the OBME. The MAD proposed is weighted using the magnitude of MV that corresponds to the estimating position. From the simulation results, the proposed methods show better performance in estimating true motion and reducing blocking artifacts with less complexity in calculation compared to a conventional method.

HF-BAND WIRELESS POWER TRANSFER SYSTEM: CONCEPT, ISSUES, AND DESIGN

High-frequency (HF) band wireless power transfer systems ofier the promise of cutting the last cord, allowing users to seamlessly recharge mobile devices as easily as wireless communication. Yet there are still many technical issues that need to be overcome. Among them, one of the most di-cult problems is maintaining impedance match over a short range, where the distance between a transmitter and receiver could vary. In this paper, the efiect of impedance mismatch of a HF- band wireless power transfer system is carefully investigated and two compensation methods are suggested to overcome this within a short range, where frequent impedance mismatch can occur. Each method has pros and cons. In order to verify the feasibility of the proposed methods, HF-band wireless power transfer systems, with a pair of rectangular loop resonators, were designed. The e-ciency and input impedance variation were simulated and measured. From these results, proposed methods show enhanced e-ciency performance than a typical wireless power transfer system without any compensation circuits.

Pipelined Intra Prediction Using Shuffled Encoding Order for H.264/AVC

In this paper, we propose a pipelined intra prediction using shuffled encoding order for H.264/AVC. Due to a dependency problem of 4times4 intra prediction mode, a new 4times4 block cannot be predicted before reconstruction of a previous 4times4 block. To minimize this latency, we shuffle the encoding order of 4times4 intra prediction while maintaining the consistency with the standard. To further reduce the processing time, two prediction modes are not used in some blocks. With the proposed method, we can implement the intra prediction block as a pipelined architecture. The processing time can be reduced by maximum 40%, because the latency caused by reconstruction of the previous 4times4 block was hidden. It was implemented into the hardware with some parallel processing architecture. The required cycles were 470 cycles

An Adaptive Threshold Technique for Fast PN Code Acquisition in DS-SS Systems

This paper presents an efficient technique to considerably reduce pseudonoise (PN) code acquisition time by adjusting threshold values, depending on the pre-estimated correlation energy in direct-sequence spread spectrum (DS-SS) systems. The proposed technique utilizing a threshold generation mode (TM) prior to a search mode is employed to a conventional double-dwell serial-search algorithm, and the TM determines the threshold values of both search and verification modes, depending on its correlation energy. We present a mathematical model of the proposed scheme to analyze it with respect to the mean code acquisition time in synchronous code-division multiple-access (CDMA) systems such as Third-Generation Partnership Project 2 (3GPP2) under a Rayleigh-fading channel. Numerical results show that the proposed method can reduce the mean code acquisition time by more than 60% and compensate for the performance degradation in high signal-to-noise ratios (SNRs) with no increase in hardware costs, compared with the conventional algorithm that adopts a soft-decision technique.

A Robust Estimation of Residual Carrier Frequency Offset With I/Q Imbalance in OFDM Systems

In this paper, we focus on improving the accuracy of frequency offset estimation for an orthogonal frequency-division multiplexing (OFDM) system under the conditions of the joint impairments in both carrier frequency offset (CFO) and in-phase/quadrature (I/Q) imbalance. To propose a robust CFO estimation scheme and to benchmark its performance, the performance of the conventional frequency estimation algorithm in the presence of I/Q imbalance is analyzed, and some modifications to the conventional estimation scheme are highlighted. We show via simulations that such a design achieves a remarkable robustness against I/Q imbalance; thereby, the proposed scheme can efficiently estimate the CFO, irrespective of the I/Q mismatch.

Efficient Hybrid Modulation with Phase-Directed Pulse Position Estimation for UWB-IR Systems

This paper proposes an efficient hybrid modulation scheme for a mixed phase-shift keying and pulse-position modulation (PSK/PPM) for heterogeneous networks employing ultra-wideband impulse radio (UWB-IR). The proposed scheme can support both coherent and noncoherent reception and is compatible with the IEEE 802.15.4a standard. Conventional hybrid modulation schemes for heterogeneous networks are generally constructed with a super-orthogonal coding (SOC) technique with which coherent receivers can get an additional performance improvement by encoding the phase bits. However, with the proposed modulation scheme, a coherent receiver can achieve a performance improvement by displaying its best capability on phase detection through a simple waveform mapping scheme. The proposed scheme requires no extra hardware or power consumption for performance improvement in coherent receivers. Simulations show that the BER of the proposed scheme in a coherent receiver is increased by 2.7dB over the hybrid modulation with no combined phase coding and also comparable to the SOC-combined modulation scheme employed in the IEEEE 802.15.4a. The error performance of the proposed scheme is analyzed, and the numerical results are presented in this paper.

Improved frequency offset estimation scheme for UWB systems with cyclic delay diversity

This paper proposes an improved pilot-based algorithm for joint estimation of carrier frequency offset (CFO) and sampling frequency offset (SFO) in ultrawideband orthogonal frequency division multiplexing (UWB-OFDM) systems with cyclic delay diversity. By proper selection of cyclic delay time and a frequency band with maximum channel power, a joint estimation of CFO and SFO is derived. Via computer simulation and analysis, the proposed frequency estimator is shown to benefit from the properly selected delay parameter and frequency band.

Low complexity demodulation scheme for IEEE 802.15.4 LR-WPAN systems

In this paper, a low complexity demodulation scheme is proposed for IEEE 802.15.4 LR-WPAN systems. In the proposed scheme, multiple active correlators for demodulation are replaced with a matched filter-based cross-correlator shared with a synchronization unit, which requires only a few additional control units. Consequently, with the proposed demodulation scheme, the total hardware complexity for the LR-WPAN baseband modem is 54% less than that of the existing architecture to have the separated demodulation and synchronization units.

An Image Sequence Transmission Method in Wireless Video Surveillance Systems

Under unpredictable wireless communication environments such as a battlefield, uncompressed video data is easy to restore and more effective to decipher than compressed video data when there are lots of errors in the received data. This paper proposes a wireless uncompressed video transmission system to ensure image quality even under a low signal to noise ratio (SNR). It utilizes a method of transmitting data asymmetrically on the basis of the image information in the wireless communication system using multiple antennas. The proposed algorithm is applied to the IEEE 802.11ac system and can improve about 5dB in terms of the peak signal to noise ratio under the SNR environment of 10xa0dB or less compared to an existing algorithm. From the simulation results, the proposed method is very suitable for wireless video surveillance systems that should provide video streams with a certain level of quality even under severe conditions.

Cost-Effective Frame-Layer H.264 Rate Control for Low Bit Rate Video

The rate control is important to allocate bits efficiently for getting better performance, such as high quality, low fluctuation of quality and low mismatch between a target bit rate and an encoded bit rate. In this paper, we present an improved frame-layer H.264/AVC rate control scheme using enhanced complexity measure, scene-change detection, and quantization parameter adjustment for low bit rate video. Especially, our complexity measure contains not only the residual information but also the motion information. We use the motion vector difference encoded previously as motion information for low computation-load encoder. Experimental results show that Y-PSNR and bit-rate mismatch are remarkably improved and the fluctuation of Y-PSNR is similar as compared with the conventional H.264/AVC rate control scheme (JVT-G012)