• ETRI Journal
• /
• 제40권3호
• /
• pp.309-317
• /
• 2018

Single carrier-frequency-division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth-generation cellular networks to facilitate power efficiency transmission in mobile stations. Because multiuser multiple-input multiple-output (MU-MIMO) is a promising technology employed to fully exploit the channel capacity in mobile radio networks, this study investigates the uplink transmission of MU-MIMO SC-FDMA systems with orthogonal space-frequency block codes (SFBCs). It is preferable to minimize the length of the cyclic prefix (CP). In this study, the chained turbo equalization technique with chained turbo estimation is employed in the designed receiver. Chained turbo estimation employs a short training sequence to improve the spectrum efficiency without compromising the estimation accuracy. In this paper, we propose a novel and spectrally efficient iterative joint-channel estimation, multiuser detection, and turbo equalization for an MU-MIMO SC-FDMA system without CP-insertion and with short TR. Some simulation examples are presented for the uplink scenario to demonstrate the effectiveness of the proposed scheme.

• International Journal of Fuzzy Logic and Intelligent Systems
• /
• 제15권1호
• /
• pp.53-59
• /
• 2015

This paper proposes a novel method for acoustically and wirelessly transmitting data underwater with a high transmission rate. The method uses the most promising physical layer and multiple access technique (i.e., the code division multiple channel access technique) to divide the channel into subchannels. Data is transmitted through these subchannels. The codes are pseudo-random noise (PN) sequences. In the spread-spectrum technique, a signal such as electrical, electromagnetic, acoustic signal generated in a particular bandwidth is deliberately spread in the frequency domain, which results in a signal with a wider bandwidth. This paper reviews the possibility of application of the direct-sequence code division multiple access (DS-CDMA) technique in an underwater system using MATLAB. As the result of our review, we recognize that the DS-CDMA technique can be applied to underwater environments.

• 전자공학회논문지
• /
• 제51권10호
• /
• pp.11-20
• /
• 2014

본 논문에서는 안테나 간 상관성이 존재하는 다중 안테나 환경에서도 스펙트럼 효율을 향상시킬 수 있으며 복잡도가 간단한 공간 변조기법의 전송량을 향상시키는 기법을 제안한다. 기존 공간 변조기법은 여러 개의 송신 안테나 중에서 일부 안테나만을 이용하여 신호 성상을 전송하고, 이 때 사용된 송신 안테나 조합을 통하여 추가 데이터를 전송한다. 그러므로 모든 송신안테나를 항상 사용하는 기존 다중안테나(MIMO, multi-input multi-output) 전송기법에 비해서는 채널 용량 증대가 크지 않은 단점이 있다. 본 논문에서는 공간 변조기법의 채널 용량을 증대시키기 위하여 타이트 프레임 행렬을 이용한 프리코더를 적용한 새로운 공간 변조기법을 제안한다. 그리고 컴퓨터 모의실험을 통하여 제안한 공간 변조기법의 채널 용량 향상을 보인다.

• 한국인터넷방송통신학회논문지
• /
• 제14권3호
• /
• pp.99-104
• /
• 2014

본 논문은 유무선융합망에서 스마트스크린 서비스를 효과적으로 제공하기 위하여 이기종 네트워크 환경의 멀티전송기법을 제시하였다. 유무선 융합 이종망 환경에서 다수 협업 장치간에 스마트 스크린 핸드오버 알고리즘과, AV 스트리밍과 파일의 스마트 스크린 서비스를 제공하는 NAS 장치와 서비스 관리 및 운영 시스템을 연구함으로써 이종망간 심리스 스마트 스크린 협업 서비스 호처리 엔진 및 이동성 관리, 멀티 사용자/멀티 스트림 지원하는 AV 스트리밍전송 서비스, 스마트 스크린 협업 서비스 등의 타당성을 제안하였다.

• 한국통신학회논문지
• /
• 제30권5C호
• /
• pp.391-397
• /
• 2005

전송 다이버시티 기법인 시공간 블록코드 (STBC) 부호화 방법이 소개된 이후, 전송 데이터 속도를 향상시키기 위하여 기지국에서 전송다이버시티를 사용하는 MIMO 기술 연구가 활발히 진행되어 왔다. Multiplexed STBC OFDM 시스템은 두 개의 송신 안테나를 하나의 그룹으로 하여 여러 개의 그룹이 동시에 전송하는 방식이며, 수신기에서는 원하는 STBC OFDM 그룹 신호이외의 다른 그룹들의 간섭신호를 억제하여 데이터를 검출하는 방식이다. 본 논문에서는 multiplexed STBC OFDM 시스템에 적용 가능한 복호 및 최대수신결합을 반복적으로 이용하는 새로운 알고리즘을 제안하고, 모의 실험을 통하여 그 성능이 기존의 방법보다 우수함을 확인하였다.

• Journal of Communications and Networks
• /
• 제18권2호
• /
• pp.173-181
• /
• 2016

In this paper, we address a new robust optimization problem in a multiuser multiple-input single-output broadcasting system with simultaneous wireless information and power transmission, where a multi-antenna base station (BS) sends energy and information simultaneously to multiple users equipped with a single antenna. Assuming that perfect channel-state information (CSI) for all channels is not available at the BS, the uncertainty of the CSI is modeled by an Euclidean ball-shaped uncertainty set. To optimally design transmit beamforming weights and receive power splitting, an average total transmit power minimization problem is investigated subject to the individual harvested power constraint and the received signal-to-interference-plus-noise ratio constraint at each user. Due to the channel uncertainty, the original problem becomes a homogeneous quadratically constrained quadratic problem, which is NP-hard. The original design problem is reformulated to a relaxed semidefinite program, and then two different approaches based on convex programming are proposed, which can be solved efficiently by the interior point algorithm. Numerical results are provided to validate the robustness of the proposed algorithms.

• 한국통신학회논문지
• /
• 제33권1C호
• /
• pp.68-78
• /
• 2008

The transmission of multimedia information over error-prone channels such as wireless networks has become an important area of research. In this paper, we propose two Error Concealment(EC) schemes for wireless transmission of JPEG2000 image. The Multiple Representation(MR) is employed as the preprocessing in our schemes, whereas the main error concealing operation is applied in wavelet domain at receiver side. The compressed code-stream of several subsampled versions of original image is transmitted over a single channel with random bit errors. In the decoder side, the correctly reconstructed wavelet coefficients are utilized to recover the corrupted coefficients in other sub-images. The recovery is carried out by proposed basic(MREC-BS) or enhanced(MREC-ES) methods, both of which can be simply implemented. Moreover, there is no iterative processing during error concealing, which results a big time saving. Also, the simulation results confirm the effectiveness and efficiency of our proposed schemes.

• ETRI Journal
• /
• 제41권1호
• /
• pp.117-123
• /
• 2019

This paper presents a tri-wideband bandpass filter (TWB-BPF) with compact size, high band-to-band isolation, and multiple transmission zeros (TZs). The proposed TWB-BPF is based on a multiple-mode resonator (MMR), which is interpreted by the method of the even- and odd-mode analysis technique. The MMR can excite 11 resonant modes, where the first two modes comprise the first passband, the next four modes form the second passband, and the last five modes are used to generate the third passband. In addition, 10 TZs are yielded to obtain high band-to-band isolation and wide stopband suppression characteristics up to $14.95f_{c1}$ ($f_{c1}$ is the center frequency of the first passband). To verify the proposed filter, a TWB-BPF with 3-dB fractional bandwidths (FBWs) of 37.4%, 43.5%, and 40.4% is designed, fabricated, and measured.

• 한국음향학회지
• /
• 제32권1호
• /
• pp.86-94
• /
• 2013

본 논문에서는 높은 비트 오류율을 가지는 수중 환경에 적용 가능한 네트워크 코딩 기법을 제안한다. 제안하는 네트워크 코딩 기법의 매체 접속 방식으로 코드 분할 다중 접속 방식을 사용한다. 또한 제안하는 기법은 다수의 소스 노드와 중계 노드, 하나의 싱크 노드로 이루어진 구조에 적용된다. 성능 분석 파라미터로서 소스 노드가 전송한 전체 패킷의 수에 대한 싱크 노드에 성공적으로 도달한 패킷의 수의 비율인 패킷 전달률을 사용하였고 모의실험 결과 50%에 가까운 패킷 오류율 환경에서도 95% 이상의 패킷 전달률을 나타내었다.

• Journal of Communications and Networks
• /
• 제17권4호
• /
• pp.419-427
• /
• 2015

There have been increases in the elderly population worldwide, and this has been accompanied by rapid growth in the health-care market, as there is an ongoing need to monitor the health of individuals. Wireless body area networks (WBANs) consist of wireless sensors attached on or inside the human body to monitor vital health-related problems, e.g., electrocardiograms (ECGs), electroencephalograms (EEGs), and electronystagmograms (ENGs). With WBANs, patients' vital signs are recorded by each sensor and sent to a coordinator. However, because of obstructions by the human body, sensors cannot always send the data to the coordinator, requiring them to transmit at higher power. Therefore, we need to consider the lifetime of the sensors given their required transmit power. In the IEEE 802.15.6 standard, the transmission topology functions as a one-hop star plus one topology. In order to obtain a high throughput, we reduce the transmit power of the sensors and maintain equity for all sensors. We propose the multiple-hop transmission for WBANs based on the IEEE 802.15.6 carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol. We calculate the throughput and variance of the transmit power by performing simulations, and we discuss the results obtained using the proposed theorems.