• 한국통신학회논문지
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• 제35권4A호
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• pp.322-331
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• 2010

본 논문에서는 폐루프 다중입출력 무선통신 환경을 위한 새로운 공간 다중화 기법을 소개한다. 기존에 제안되 었던 직교 공간 다중화 (OSM; orthogonalized spatial multiplexing) 방식을 확장하여, 우리는 임의의 수의 데이터 스트림을 동시에 전송하기 위한 새로운 방식을 제안한다. 이를 위하여 우리는 데이터 스트림을 두 개 이상의 그룹으로 나누고 수신기에서 블록 대각화 과정을 수행한다. 제안하는 기법은 적은 피드백 정보량을 가지며 심볼 단위의 ML (maximum likelihood) 검출을 통해 복잡도를 최소화한다. 실험 결과를 통해 제안하는 기법은 기존의 설계 기법들에 비하여 비트에러율 관점에서 큰 성능 이득을 제공함을 확인한다. 또한 추가적인 피드백을 통해 수신 그룹의 선택을 최적화함으로써 성능을 더욱 향상시킬 수 있음을 관찰한다.

• 한국통신학회논문지
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• 제32권5A호
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• pp.467-474
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• 2007

MB-OFDM UWB 시스템은 고속의 전송률을 달성하기위해 16-QAM형태의 dual carrier modulation(DCM)방식을 이용한다. DCM의 기본 아이디어는 4개의 입력비트를 서로 다른 형태의 2개의 16-QAM을 이용해 변조하고 2개의 변조결과를 최대한 멀리 떨어져 있는 2개의 OFDM 부반송파에 나눠서 중복 전송함으로써 하나의 부반송파가 복구할 수 없는 페이딩을 겪게 되더라도 다른 하나의 부반송파에 실려온 정보를 이용하여 전송한 4비트를 복조할 수 있다는 것이다. 두 개의 부반송파가 모두 열악한 페이딩을 겪게 될 확률은 매우 작으므로 DCM을 이용함으로써 성능향상을 기대할 수 있다. 기본적인 ML검출방식을 이용하여 신호를 복호할 경우 채널정보를 이용하지 않기 때문에 DCM의 본래 목적이라고 할 수 있는 다이버시티의 손실(loss in diversity)을 줄이자는 생각과 부합되지 않는다. 본 논문에서는 채널 상태 정보라는 여분의 신뢰할 만한 정보를 이용함으로써 더 좋은 성능을 얻을 수 있는 향상된 연판정 복조기법을 제안한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 학술대회 논문집 정보 및 제어부문
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• pp.113-114
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• 2008

In this paper, binary pulse-position modulation (2PPM) time-hoping (TH) ultra-wideband (UWB) system is applied to multiple input multiple output (MIMO) system using vertical bell lab layered space-time (V-BLAST) structure to achieve high-data-rate communications. This UWB-MIMO system and its receivers are analyzed, and its BER performances are evaluated. In the receiver, various MIMO detection algorithms such as zero-forcing (ZF), ZF-ordered successive interference cancellation (OSIC), minimum-mean-square-error (MMSE), MMSE-OSIC and maximum likelihood (ML) are comparatively studied.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.217-218
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• 2008

A new diversity technique is proposed for multi-user single-input single-output (SISO) orthogonal frequency division multiplexing (OFDM) uplink system. Each user transmit a symbol using frequency band of all users that are active in the uplink. In addition, a receiver detect each signal using maximum likelihood (ML) method. Simulation results show that the proposed technique improves a diversity order without an additional bandwidth and a loss of data rate.

• International journal of advanced smart convergence
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• 제9권1호
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• pp.98-108
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• 2020

We consider transmit antenna selection combined with power allocation for quadrature spatial modulation (QSM) systems to improve the error rate performance. The Euclidean distance-based joint optimization criterion is presented for transmit antenna selection and power allocation in QSM. It requires an exhaustive search and thus high computational complexity. Thus its reduced-complexity algorithm is proposed with a strategy of decoupling, which is employed to successively find transmit antennas and power allocation factors. First, transmit antennas are selected without considering power allocation. After selecting transmit antennas, power allocation factors are determined. Simulation results demonstrate considerable performance gains with lower complexity for transmit antenna selected QSM systems with power allocation, which can be achieved with limited rate feedback.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.525-530
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• 2008

There are a few core technologies to enable high-performance $4^{th}$ generation (4G) broadband wireless communication system. A multiple input multiple output (MIMO) provides high-rate transmission through expended channels by multiple array antennas in both sender and receiver side. Also orthogonal frequency division multiplexing (OFDM) is well-known as the most appropriate technique for high data rate transmission such as Mobile WiMAX and WLAN. Efficient decrease of inter-carrier interference (ISI) and inter-carrier interference (ICI) are the reasons for why OFDM is suitable for high-performance transmission, 4G mobile communication. In this paper, we mainly focus on two of objects, combination between MIMO and OFDM, and OFDM channel simulator using Ray-tracing algorithm. The results of this paper can be used implementation of a Wireless Software Platform for 4G Mobile Communication Systems.

• Journal of information and communication convergence engineering
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• 제9권4호
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• pp.385-390
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• 2011

In this paper, various ultra-wideband (UWB) spatial multiplxing (SM) multiple input multiple output (MIMO) receivers based on a prerake diversity combining scheme are discussed and their performance is analyzed. Several UWB MIMO detection approaches such as zero forcing (ZF), minimum mean square error (MMSE), ordered successive interference cancellation (OSIC), sorted QR decomposition (SQRD), and maximum likelihood (ML) are considered in order to cope with inter-channel interference. The UWB SM systems based on transmitter-side multipath preprocessing and receiver-side MIMO detection can either boost the transmission data rate or offer significant diversity gain and improved BER performance. The error performance and complexity of linear and nonlinear detection algorithms are comparatively studied on a lognormal multipath fading channel.

• Journal of Information Processing Systems
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• 제10권2호
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• pp.215-222
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• 2014

In this paper, we discuss optical encryption and decryption considering wireless communication channels. In wireless communication systems, the wireless channel causes noise and fading effects of the transmitted information. Optical encryption technique such as double-random-phase encryption (DRPE) is used for encrypting transmitted data. When the encrypted data is transmitted, the information may be lost or distorted because there are a lot of factors such as channel noise, propagation fading, etc. Thus, using digital modulation and maximum likelihood (ML) detection, the noise and fading effects are mitigated, and the encrypted data is estimated well at the receiver. To the best of our knowledge, this is the first report that considers the wireless channel characteristics of the optical encryption technique.

• ETRI Journal
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• 제42권1호
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• pp.17-25
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• 2020

Multiple-input multiple-output systems can achieve a full sum rate (SR) via full duplex (FD). However, its performance is degraded by self-interference (SI) that occurs between the transmitter and receiver at the same node and thus is constrained by error floors. Conversely, half duplex (HD) can avoid the SI albeit at lower spectral efficiency, and the slope of its error curve is determined by the diversity order. In this study, a link selection scheme based on switching between FD and HD is examined as a simple method to improve the bit error rate (BER) performance of FD systems. In the proposed link selection algorithm, either FD or HD is selected based on the received minimum distance and signal-to-interference plus noise ratio. Simulation results indicate that the proposed hybrid FD/HD switching system offers significant BER performance improvement when compared with that of the conventional FD and FD based on only the received minimum distance under the same fixed SR. Under relatively sufficient SI cancellation, it is demonstrated to outperform the HD with a diversity advantage in low and medium signal-to-noise ratio region.

• 한국산학기술학회논문지
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• 제15권11호
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• pp.6838-6844
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• 2014

LTE-A 시스템은 고속 데이터 전송을 위해 다중안테나를 장착하고 있다. 일반적으로 공간다중화 다중안테나 시스템의 수신기 복잡도는 후보벡터의 개수에 따라 증가한다. 후보벡터의 개수가 증가함에 따라 연판정 값의 신뢰도가 향상된다. 많은 수의 후보벡터를 생성하는 최우도 신호검출방식을 사용하면 우수한 성능을 달성할 수 있다. 반면 적은 개수의 후보벡터를 생성하는 저복잡도 수신기는 신뢰도가 낮은 연판정 값을 생성한다. 본 논문에서는 적은 수의 후보벡터를 사용해서 얻게되는 연판정 값의 신뢰도를 향상시키는 새로운 기술을 제안하고 모의실험을 통해 개선된 성능을 확인한다.