• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.10 no.7
• /
• pp.2992-3009
• /
• 2016

The performance of D-MIMO systems is not only affected by multipath fading but also from shadowing fading, as well as path loss. In this paper, we investigate the ergodic capacity of D-MIMO systems operating in non-correlated K fading (Rayleigh/Gamma) channels. With the aid of majorization and Minkowski theory, we derive analytical closed-form expressions of the upper and lower bounds on the ergodic capacity for D-MIMO systems over non-correlated K fading channels, which are quite general and applicable for arbitrary signal-to-noise ratio (SNR) and the number of transceiver antennas. To intuitively reveal the impacts of system and fading parameters on the ergodic capacity, we deduce asymptotic approximations in the high and low SNR regimes. Finally, we pursue the massive MIMO systems analysis for the lower bound and derive closed-form expressions when the number of antennas at BS grows large, and when the number of antennas at transceivers becomes large with a fixed and finite ratio. It is demonstrated that the proposed expressions on the ergodic capacity accurately match with the theoretical analysis.

• Proceedings of the IEEK Conference
• /
• 2003.07a
• /
• pp.481-484
• /
• 2003

OFDM(Orthogonall Frequency Division Multiplexing) is an efficient transmission techniques for the frequency selective fading wireless channel where conventional modulations suffer from severe performance degradation. Recently, more efficient techniques for the OFDM are paid much attention such as adaptive modulation for each subcarrier, since more bit rate has been required for the wireless data network [1-3]. The proposed system employs the adaptive modulation between transmitter and receiver in each subcarrier, where the bit and power is properly allocated. Also multiple antenna system called MIMO is considered, which result in robustness in channel delay, improved power efficiency and improved bit SNR for the given BER.

• Proceedings of the KSR Conference
• /
• 2010.06a
• /
• pp.1680-1684
• /
• 2010

CBTC(Communication-Based Train Control) system which is based on wireless communication can provide high density operation of the train using location tracking between ground and onboard train. It can also reduces maintenance expense because it does not require the ground equipment for tracking circuit and signal flag and so on. Recently, research and interest have been done on CBTC system. The high-speed trains up to 300km/h experience multi-path fading channel which bring about the performance degradation of wireless CBTC system. In this paper, we consider MIMO (Multi-Input Multi-Output) antenna-based CBTC system for trains with Alamoutip-type space-time diversity transmission for reliable communication. Also we model a channel considering practical environment and evaluate performance improvement of proposed CBTC system.

• Proceedings of the IEEK Conference
• /
• 2001.06a
• /
• pp.121-124
• /
• 2001

In this paper, we propose a robust trellis coded OFDM(orthogonal frequency division multiplexing) system for wireless communications over frequency selective fading channels. Computer simulations show that the proposed system achieves the better frame error rate(FER) performance as compared with the conventional Space time coded OFDM system in the correlated channel with multiple transmitter antennas.

• Journal of Internet Computing and Services
• /
• v.21 no.2
• /
• pp.19-26
• /
• 2020

This paper analyses the feasibility of using implantable antennas to detect and monitor tumors. We analyze this setting according to the wireless propagation loss and signal fading produced by human bodies and their environment in an indoor scenario. The study is based on the ITU-R propagation recommendations and prediction models for the planning of indoor radio communication systems and radio local area networks in the frequency range of 300 MHz to 100 GHz. We conduct primary estimations on 915 MHz and 2.4 GHz operating frequencies. The path loss presented in most short-range wireless implant devices does not take into account the human body as a channel itself, which causes additional losses to wireless designs. In this paper, we examine the propagation through the human body, including losses taken from bones, muscles, fat, and clothes, which results in a more accurate characterization and estimation of the channel. The results obtained from our simulation indicates a variation of the return loss of the spiral antenna when a tumor is located near the implant. This knowledge can be applied in medical detection, and monitoring of early tumors, by analyzing the electromagnetic field behavior of the implant. The tumor was modeled under CST Microwave Studio, using Wisconsin Diagnosis Breast Cancer Dataset. Features like the radius, texture, perimeter, area, and smoothness of the tumor are included along with their label data to determine whether the external shape has malignant or benign physiognomies. An explanation of the feasibility of the system deployment and technical recommendations to avoid interference is also described.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.3A
• /
• pp.290-296
• /
• 2007

We propose new routing scheme, Cooperative Diversity-based Routing (CDR) which utilizes the cooperative space diversity for power saving and performance enhancement of wireless ad-hoc networks. The improved performance is compared with Multi-hop Relay Routing (NRR) by analytical methods. When the required outage probability is $1\times10^{-3}$ at the destination node in ad-hoc networks with 7 nodes, we noticed that each node can save power consumption by 15.5 dB in average, by using our proposed CDR compared to MRR.

• The KIPS Transactions:PartC
• /
• v.12C no.7 s.103
• /
• pp.1025-1030
• /
• 2005

Cooperative communications among users in multiple access wireless environments is an efficient way to obtain the powerful benefits of multi-antenna systems without the demand for physical arrays. This paper proposes a solution to optimize the weights of partnering users' signals for the minimum error probability at the output of maximum likelihood (ML) detector under the transmit power constraints by taking advantage of channel state information (CSI) feedback from the receiver to the transmitter. Simulation programs are also established to evaluate the performance of the system under flat Rayleigh fading channel plus AWGN (Additive White Gaussian Noise).

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.50 no.8
• /
• pp.400-405
• /
• 2001

Quadrature Amplitude Modulation(QAM) is well known a bandwidth efficient modulation scheme. However, its use for mobile communications has been limited due to noise and signal distortion. Recently, the QAM scheme is emerging as a new modulation scheme for a band-limited wireless system. In this paper, we propose an iterative decoding algorithm assuming QAM signal for a narrow-band mobile channel. The Algorithm is based on the EM(Expectation Maximization) Algorithm, and the performances of the proposed decoder are assessed using computer simulation. The simulation results show that the proposed decoder perform better compared to that of other schemes.

• Journal of electromagnetic engineering and science
• /
• v.6 no.1
• /
• pp.10-17
• /
• 2006

For the sake of the potential ability of overcoming interference in TD-SCDMA(time division-synchronous code division multiple access) systems, pilot signal is adopted, but the presented TD-SCDMA protocol has not considered the Rake technique for their mobile terminals. This paper developed a RAKE receiver algorithm and an implementation circuit, which make use of the pilot signal in the burst structure of the TD-SCDMA base station to estimate main channel parameter(channel delays) in the downlink of TD-SCDMA wireless network. The algorithm can reduce multipath interference for the mobile units in multiusers' case. Theoretic performance analysis presented in the paper and computer simulations show that there is a range of BER for Rake receiver and confirm that the proposed RAKE receiver algorithm achieved a better performance under multipath fading propagation and multiusers conditions.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2011.11a
• /
• pp.121-122
• /
• 2011

본 논문에서는 무선 협력 네트워크(wireless cooperative network)의 전송 신뢰성과 공정성 향상을 위한 비례공정 중계(proportional-fair relaying) 기법을 제안한다. 다중 단말과 단일 기지국이 있는 다원 접속(multiple access) 환경에서 저속 페이딩(slow fading)에 의한 성능 열화를 저감하면서 단말간 자원 사용 공정성 보장하기 위해 비례공정 전송 기법과 중계 기법 결합한다. 이를 통해 기존 기회적(opportunistic) 전송 기법의 비대칭 채널(asymmetric channel)에서의 자원 사용 불공정성을 해결하면서 깊은 페이딩(deep fading)에 의한 데이터 무선 전송 손실을 최소화 한다. 컴퓨터 모의실험 결과를 통해 제안된 기법이 공정성 제한(fairness constraint)이 있는 다원 접속 환경에서 불능 확률(outage probability) 성능을 제고함을 보인다.