• ETRI Journal
• /
• v.38 no.1
• /
• pp.90-99
• /
• 2016

In this work, we investigate differentially encoded blind transceiver design in low signal-to-noise ratio (SNR) regimes for orthogonal frequency-division multiplexing (OFDM) signaling. Owing to the fact that acquisition of channel state information is not viable for short coherence times or in low SNR regimes, we propose a time-spread frequency-encoded method under OFDM modulation. The repetition (spreading) of differentially encoded symbols allows us to achieve a target energy per bit to noise ratio and higher diversity. Based on the channel order, we optimize subcarrier assignment for spreading (along time) to achieve frequency diversity of an OFDM modulated signal. We present the performance of our proposed transceiver design and investigate the impact of Doppler frequency on the performance of the proposed differentially encoded transceiver design. To further improve reliability of the decoded data, we employ capacity-achieving low-density parity-check forward error correction encoding to the information bits.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.2
• /
• pp.281-288
• /
• 2004

In this paper, we consider the diversity combining method for multiple symbol differential detection (MSDD) over the slow fading diversity channel. Though the performance of the optimum maximum-likelihood sequence estimator for MSDD approaches the performance of maximal-ratio combining with differential encoding, the complexity increases exponentially as the size of MSDD block is increased. This new pre-combining method can make use of the efficient MSDD algorithm that has a complexity increasing linearly with the block length or MSDD. Thus, in many wireless scenarios where it is not possible to perform coherent detection. this pre-combined diversity MSDD can be applied to obtain substantial gain compare to conventional differential detection.

• Journal of radiological science and technology
• /
• v.16 no.2
• /
• pp.19-26
• /
• 1993

Magnetic Resonance Image represents three-dimensional diagnostic imaging technique using both nuclear magnetic resonance phenomenon and computer. Compared with computed tomography (CT), MRI have advantages harmless to patient's body, three-dimensional image with high resolution and disadvantages long data acquisition time because of long T1 relaxation time, relatively low signal to noise ratio, high cost of setting, also. As physiologic motion of tissue results in motion ghost in MRI, high 2.0Tesla make improve low signal to noise ratio. This study have aim to improve image quality with controling motion ghost of tissue. Supposing a moving pixel in constant frequency, one pixel make two ghosts which are same size and different anti-phase. So, this study will show adjust parameter on locational control of motion ghost. Author made moving phantom replaced by respiratory movement of human, researched change of motion frequency, FOV by location shift, and them decided optimal FOV (field of view). The results are as follows: 1. The frequency content of the motion determines how far the image always appear in phase-encoding direction, the morphology of the ghost image is characteristic of the direction of the motion and its amplitude. 2. Double FOV of fixed signal object for locational control of motion ghost is recommended. Decreasement of spatial resolution by increasing FOV can compensate on increasing of matrix in spite of scan time increasement.

• Journal of Broadcast Engineering
• /
• v.19 no.2
• /
• pp.250-256
• /
• 2014

Non-reference P frame coding is used to enhance coding efficiency in low-delay encoding configuration of Internet Video Coding (IVC), which is being standardized as a royalty-free video codec in MPEG. The existing method of non-reference P frame coding which was adopted in the reference Test Model of IVC (ITM) 4.0 adaptively applies a non-reference P frame with a fixed coding structure based on the magnitude of motion vectors (MVs), however, which unexpectedly degrades the coding efficiency for some sequences. In this paper, the existing non-reference P frame coding is improved by changing non-reference P frame coding structure and applying a new adaptive method using the ratio of the amount of generated bits of non-reference frames to that of reference frames as well as MVs. Experimental results show that the proposed non-reference P frame coding gives 6.6% BD-rate bit saving in average over ITM 7.0.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.14 no.9
• /
• pp.1957-1964
• /
• 2010

In Video coding, the first frame is encoded in intra mode which generates a larger number of bits. In addition, the first frame is used for the inter mode encoding of the following frames. Thus the intial QP for the first frame of GOP affects the first frame as well as the following frames. Traditionally, the initial QP of a GOP is determined by the initial QP of the previous GOP and the average QP of the inter mode frames. In case of JM, the initial QP of a GOP is adjusted as the initial QP being less than the average QP of inter mode frames by two. However, this method is not suitable for the low bit rate video coding. In this paper, the linear relationship between the optimal QP and the ratio of the PSNR of the first frame and the average PSNR of the inter mode frames is first investigated and the linear model is proposed based on the results of the investigation. The proposed model calculate the optimal initial QP using the encoding results of the previous GOP. It is shown by experimental results that the new algorithm can predict the optimal initial QP more accurately and generate the PSNR performance better than that of the existing JM algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.6A
• /
• pp.575-583
• /
• 2002

JBIG2 is an International Standard fur compression of Bi-level images and documents. JBIG2 supports three encoding modes for high compression according to region features of documents. One of which is generic region coding for bitmap coding. The basic bitmap coder is either MMR or arithmetic coding. Pattern matching coding method is used for text region, and halftone pattern coding is used for halftone region. In this paper, a document is segmented into line-art, halftone and text region for JBIG2 encoding and JBIG2 CODEC is implemented. For efficient region segmentation of documents, region segmentation method using wavelet coefficient is applied with existing boundary extraction technique. In case of facsimile test image(IEEE-167a), there is improvement in compression ratio of about 2% and enhancement of subjective quality. Also, we propose arbitrary shape halftone region coding, which improves subjective quality in talc neighboring text of halftone region.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.11C
• /
• pp.1077-1084
• /
• 2006

This paper proposed a fast algorithm to reduce the amount of calculation for inter prediction which takes a great deal of the operational time in H.264/AVC. This algorithm decides a search range according to the direction of predicted motion vector, and then performs an adaptive spiral search for the candidates with JM(Joint Model) FME(Fast Motion Estimation) which employs the rate-distortion optimization(RDO) method. Simultaneously, it decides a threshold cost value for each of the variable block sizes and performs the motion estimation for the variable search ranges with the threshold. These activities reduce the great amount of the complexity in inter prediction encoding. Experimental results by applying the proposed method .to various video sequences showed that the process time was decreased up to 80% comparing to the previous prediction methods. The degradation of video quality was only from 0.05dB to 0.19dB and the compression ratio decreased as small as 0.58% in average. Therefore, we are sure that the proposed method is an efficient method for the fast inter prediction.

• Journal of Advanced Navigation Technology
• /
• v.15 no.2
• /
• pp.298-306
• /
• 2011

In this paper, the RUNCODE encoder hardware IP was designed and implemented for symbol ID code length encoding, which is one of major modules of JBIG2 encoder for FAX. ImpulseC Codeveloper and Xilinx ISE/EDK program are used for the hardware generation and synthesis of VHDL code. The synthesized hardware was downloaded to Virtex-4 FX60 FPGA on ML410 development board. The synthesized hardware utilizes 13% of total slice of FPGA. Using Active-HDL tool, the hardware was verified showing normal operation. Compared with the software operating using Microblaze cpu on ML410 board, the synthesized hardware was better in operation time. The improvement ratio of operation time between the synthesized hardware and software showed about 40 times faster than software only operation. The synthesized H/W and S/W module cooperated to succeed in compressing the CCITT standard document.

• Investigative Magnetic Resonance Imaging
• /
• v.20 no.4
• /
• pp.215-223
• /
• 2016

Purpose: The management of metal-induced field inhomogeneities is one of the major concerns of distortion-free magnetic resonance images near metallic implants. The recently proposed method called "Slice Encoding for Metal Artifact Correction (SEMAC)" is an effective spin echo pulse sequence of magnetic resonance imaging (MRI) near metallic implants. However, as SEMAC uses the noisy resolved data elements, SEMAC images can have a major problem for improving the signal-to-noise ratio (SNR) without compromising the correction of metal artifacts. To address that issue, this paper presents a novel reconstruction technique for providing an improvement of the SNR in SEMAC images without sacrificing the correction of metal artifacts. Materials and Methods: Low-rank approximation in each coil image is first performed to suppress the noise in the slice direction, because the signal is highly correlated between SEMAC-encoded slices. Secondly, SEMAC images are reconstructed by the best linear unbiased estimator (BLUE), also known as Gauss-Markov or weighted least squares. Noise levels and correlation in the receiver channels are considered for the sake of SNR optimization. To this end, since distorted excitation profiles are sparse, $l_1$ minimization performs well in recovering the sparse distorted excitation profiles and the sparse modeling of our approach offers excellent correction of metal-induced distortions. Results: Three images reconstructed using SEMAC, SEMAC with the conventional two-step noise reduction, and the proposed image denoising for metal MRI exploiting sparsity and low rank approximation algorithm were compared. The proposed algorithm outperformed two methods and produced 119% SNR better than SEMAC and 89% SNR better than SEMAC with the conventional two-step noise reduction. Conclusion: We successfully demonstrated that the proposed, novel algorithm for SEMAC, if compared with conventional de-noising methods, substantially improves SNR and reduces artifacts.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.18 no.3
• /
• pp.679-686
• /
• 2014

Recently, users can get countless images and videos by network. So, the compression technology of image and video is researched more and more. However, the situation which is the interested range of the image is occurred. For instance, since the region of face is more important than background, the image compression technology bases on the region of interest (ROI) is necessary, in the ATM environment. In this research, given the human visual system, which are not sensitive to illumination variations at very dark and light regions of image, we calculate the standard deviation of block and use this value to define the ROI. In encoding process, the relatively high quality can be obtained at the ROI and the relatively low quality can be obtained at the non ROI. In proposed scheme, the feature which is the encoding process according to subjectively image quality can be demonstrated. Finally, this proposed scheme is applied to JPEG standard. The experimental results demonstrate that proposed scheme can achieve better image quality at the high compression ratio.