Improved Code Timing Estimator for DS-CDMA Systems Using Correlated Antennas in Time-Varying Fading Channels

김상준,정봉식,Kim Sang-Choon,Jeong Bong-Sik The Korea Institute of Information and Commucation 2006 한국정보통신학회논문지 Vol.10 No.5

본 논문에서는 평탄 페이딩과 근거리/원거리 현상이 존재할 때 안테나 어레이를 사용하는 DS-CDMA 신호의 코드 타이밍을 추정하는 문제를 다루고자 한다. 페이딩 과정의 시변 페이딩 특성을 보다 잘 활용할 수 있도록 DS-CDMA 시스템에 대한 희망하는 사용자의 코드 타이밍을 추정하는 최대가능성 알고리즘을 유도한다. 코드 타이밍 추정기의 개발에 있어서 주어진 관찰 비트들을 포함하는 윈도우를 각각의 부-윈도우가 충분히 큰 길이를 갖도록 나눈다. 제안된 방법은 채널 페이딩의 일관성 시간과 연관된 똑같은 크기를 가지는 부-윈도우들을 이용한다. 또한 페이딩 속도를 추정하지 않고 충분히 긴 관찰 비트들을 두 개의 연속적 인 부-윈도우로 나누는 방법을 대안으로 제시한다. 알고리즘의 유도과정은 공간적으로 상관성이 있는 다중안테나를 바탕으로 한다. 공간적인 페이딩 상관성이 제안된 알고리즘의 동기 획득 및 평균 동기 획득 성능에 미치는 영향을 분석한다. We consider the problem of estimating a code-timing of DS-CDMA signal in antenna array systems in the presence of flat fading channels and near-far environments. We derive an approximate maximum likelihood algorithm of estimating the code-timing of a desired user for DS-CDMA systems to better utilize the time-varying characteristics of the fading process. In the development of code timing estimator, the given observation bits are divided into many sets of sub-windows with each sufficiently large. The proposed method uses sub-windows with equal size associated with the coherence time of channel fading. The alternative approach is that without the estimation of the fading rate, the sufficiently given observation bits are simply separated into two consecutive sets of sub-windows. The derivation of the proposed algorithms is based on multiple antennas partially correlated in space. The impacts of spatial fading correlation on acquisition and men acquisition time performance of the proposed algorithms are also examined.

Frame Synchronization Algorithm for LDPC Coded Burst Systems

Xin Man,Haitao Zhai,Eryang Zhang 한국전자통신연구원 2015 ETRI Journal Vol.37 No.5

We present a frame synchronization algorithm for low-density parity-check (LDPC) coded burst transmissions, which combines a conventional pilots-assisted frame synchronization algorithm and a code-aided algorithm based on the mean magnitude of the soft outputs from the LDPC decoder. With moderate computational complexity, the proposed algorithm is more efficient in bandwidth than conventional pilots-assisted algorithms. When compared with other code-aided algorithms, the proposed algorithm offers a better trade-off between complexity and performance. Simulation results in the case of an 8-PSK system with (1944, 972) LDPC code show that the proposed algorithm can achieve a performance equivalent to that of the perfect frame synchronization, with a bandwidth efficiency loss of 0.06 dB due to the use of pilot symbols.

On closing codes

Somayyeh Jangjooye Shaldehi 대한수학회 2018 대한수학회보 Vol.55 No.2

We extend Jung's result about the relations among bi-closing, open and constant-to-one codes between general shift spaces to closing codes. We also show that any closing factor code $ \varphi:X\rightarrow Y $ has a degree $ d $, and it is proved that $ d $ is the minimal number of preimages of points in $ Y $. Some other properties of closing codes are provided. Then, we show that any closing factor code is hyperbolic. This enables us to determine some shift spaces which preserved by closing codes.

ON CLOSING CODES

Shaldehi, Somayyeh Jangjooye Korean Mathematical Society 2018 대한수학회보 Vol.55 No.2

We extend Jung's result about the relations among bi-closing, open and constant-to-one codes between general shift spaces to closing codes. We also show that any closing factor code ${\varphi}:X{\rightarrow}Y$ has a degree d, and it is proved that d is the minimal number of preimages of points in Y. Some other properties of closing codes are provided. Then, we show that any closing factor code is hyperbolic. This enables us to determine some shift spaces which preserved by closing codes.

Efficient Media Synchronization Mechanism for SVC Video Transport over IP Networks

서광덕,Soon-Heung Jung,Jin-Soo Kim 한국전자통신연구원 2008 ETRI Journal Vol.30 No.3

The scalable extension of H.264, known as scalable video coding (SVC) has been the main focus of the Joint Video Team’s work and was finalized at the end of 2007. Synchronization between media is an important aspect in the design of a scalable video streaming system. This paper proposes an efficient media synchronization mechanism for SVC video transport over IP networks. To support synchronization between video and audio bitstreams transported over IP networks, a real-time transport protocol/RTP control protocol (RTP/RTCP) suite is usually employed. To provide an efficient mechanism for media synchronization between SVC video and audio, we suggest an efficient RTP packetization mode for inter-layer synchronization within SVC video and propose a computationally efficient RTCP packet processing method for inter-media synchronization. By adopting the computationally simple RTCP packet processing, we do not need to process every RTCP sender report packet for inter-media synchronization. We demonstrate the effectiveness of the proposed mechanism by comparing its performance with that of the conventional method.

부 대역을 이용한 수중 음향 통신 송수신 구조 및 실험 결과 분석

정현우(Hyun-Woo Jeong),신지은(Ji-Eun Shin),정지원(Ji-Won Jung) 한국정보전자통신기술학회 2020 한국정보전자통신기술학회논문지 Vol.13 No.6

본 논문에서는 부 대역 처리를 이용하는 수중 통신에서 은밀성과 성능 향상 관점에서 효율적인 송수신 구조를 제시하였다. 은밀성적인 측면에서는 암호화된 부호화 비트를 블록으로 나누어 각 비트의 정보를 이용하여 중심 주파수와 부 대역을 결정하므로 은밀성을 유지하는 측면에서 효과적이다. 수중 통신에서 성능적인 측면에서는 다중 경로 특성, 도플러 확산, 프레임 동기 등이 성능에 영향을 미치는 결정적인 요소이다. 따라서 본 논문에서는 이러한 요소들을 극복하기 위해, 비동기 에너지 검출 방식과 터보 등화 기법, 그리고 최적의 프레임 동기 방식을 제안하여 수신부에 적용하였다. 호수 실험에서 최적의 프레임 동기 방식을 수신부에 적용한 결과 다섯 개의 프레임 중에서 네 개의 프레임에서 오류를 모두 정정함을 확인하였다. This paper presented efficient transceiver structure using sub-band processing for underwater communication in terms of covertness and performance improvement. In aspect of covertness, encrypted coded-bits are divided into groups, and center frequency and sub band are determined by coded-bits of each group. Therefore, as center frequencies are changed randomly, it maintain the covertness effectively. In aspect of performance improvement, the performance of underwater communication mainly depends on multi-path propagation characteristics, Doppler-spread, and frame synchronization. Accordingly, in order to overcome these effects, non-coherent energy detector and turbo equalization method are employed in receiver side. Furthermore, optimal frame synchronization was proposed. Through the simulation and lake experiment, performance analysis was conducted. Especially in the lake experiment, as a result of applying optimal frame synchronization method to receiver structure, errors are corrected in most frames.

Application of Correlation-Aided DSA(CDSA) Technique to Fast Cell Search in IMT-2000 W-CDMA Systems.

Kim, Byoung-Hoon,Jeong, Byeong-Kook,Lee, Byeong-Gi The Korean Institute of Communications and Informa 2000 Journal of communications and networks Vol.2 No.1

In this paper we introduce the correlation-aided distributed sample acquisition (CDSA) scheme for fast cell search in IMT-2000 W-CDMA cellular system. The proposed scheme incorporates the state symbol correlation process into the comparison-correction based synchronization process of the original DSA scheme to enable fast acquisition even under very poor channel environment. for its realization, each mobile station (MS) has to store in its memory a set of state sample sequences. which are determined by the long-period scrambling sequences used in the system and the sampling interval of the state samples. CDSA based cell search is carried out in two stages : First, the MS first acquires the slot timing by using the primary synch code (PSC) and then identifies the igniter code which conveys the state samples of the current cell . Secondly. the MS identifies the scrambling code and frame timing by taking the comparison-correction based synchronization approach and, if the identification is not done satisfactorily within preset time. it initiates the state symbol correlation process which correlates the received symbol sequence with the pre-stored state sample sequences for a successful identification. As the state symbol SNR is relatively high. the state symbol correlation process enables reliable synchronization even in very low chip-SNR environment. Simulation results show that the proposed CDSA scheme outperforms the 3GPP 3-step approach, requiring the signal power of about 7 dB less for achieving the same acquisition time performance in low-SNR environments. Furthermore, it turns out very robust in the typical synchronization environment where large frequency offset exists.

A Synchronization Scheme Based on Moving Average for Robust Audio Watermarking

Jinquan Zhang,Bin Han 한국정보처리학회 2019 Journal of information processing systems Vol.15 No.2

The synchronization scheme based on moving average is robust and suitable for the same rule to be adopted inembedding watermark and synchronization code, but the imperceptibility and search efficiency is seldomreported. The study aims to improve the original scheme for robust audio watermarking. Firstly, the survival ofthe algorithm from desynchronization attacks is improved. Secondly, the scheme is improved in inaudibility. Objective difference grade (ODG) of the marked audio is significantly changed. Thirdly, the imperceptibility ofthe scheme is analyzed and the derived result is close to experimental result. Fourthly, the selection of parametersis optimized based on experimental data. Fifthly, the search efficiency of the scheme is compared with those ofother synchronization code schemes. The experimental results show that the proposed watermarking schemeallows the high audio quality and is robust to common attacks such as additive white Gaussian noise,requantization, resampling, low-pass filtering, random cropping, MP3 compression, jitter attack, and time scalemodification. Moreover, the algorithm has the high search efficiency and low false alarm rate.

A Synchronization Scheme Based on Moving Average for Robust Audio Watermarking

Zhang, Jinquan,Han, Bin Korea Information Processing Society 2019 Journal of information processing systems Vol.15 No.2

The synchronization scheme based on moving average is robust and suitable for the same rule to be adopted in embedding watermark and synchronization code, but the imperceptibility and search efficiency is seldom reported. The study aims to improve the original scheme for robust audio watermarking. Firstly, the survival of the algorithm from desynchronization attacks is improved. Secondly, the scheme is improved in inaudibility. Objective difference grade (ODG) of the marked audio is significantly changed. Thirdly, the imperceptibility of the scheme is analyzed and the derived result is close to experimental result. Fourthly, the selection of parameters is optimized based on experimental data. Fifthly, the search efficiency of the scheme is compared with those of other synchronization code schemes. The experimental results show that the proposed watermarking scheme allows the high audio quality and is robust to common attacks such as additive white Gaussian noise, requantization, resampling, low-pass filtering, random cropping, MP3 compression, jitter attack, and time scale modification. Moreover, the algorithm has the high search efficiency and low false alarm rate.

180°Rotationally Invariant Repeat-Accumulate Codes

OH, Wangrok,CHEUN, Kyungwhoon The Institute of Electronics, Information and Comm 2009 IEICE TRANSACTIONS ON COMMUNICATIONS - Vol.92 No.5

<P>In digital communication systems employing binary phase-shift keying and non-data-aided carrier phase recovery, a 180°carrier phase ambiguity is inevitable. Here, we propose a simple modification to the standard regular repeat-accumulate (RA) code structure by exploiting the differential encoding inherent to the inner encoder of RA codes resulting in codes that are 180°rotationally invariant. The proposed code structure exhibit performance virtually identical to that of standard regular RA codes with zero carrier phase offset under both zero and 180°carrier phase offsets with negligible additional hardware complexity.</P>