• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제6권4호
• /
• pp.989-1005
• /
• 2012

In this paper, throughput of IEEE 802.11 carrier-sense multiple access (CSMA) with collision-avoidance (CA) protocols in non-saturated traffic conditions is presented taking into account the impact of imperfect channel sensing. The imperfect channel sensing includes both missed-detection and false alarm and their impact on the utilization of IEEE 802.11 analyzed and expressed as a closed form. To include the imperfect channel sensing at the physical layer, we modified the state transition probabilities of well-known two state Markov process model. Simulation results closely match the theoretical expressions confirming the effectiveness of the proposed model. Based on both theoretical and simulated results, the choice of the best probability detection while maintaining probability of false alarm is less than 0.5 is a key factor for maximizing utilization of IEEE 802.11.

• Journal of electromagnetic engineering and science
• /
• 제11권2호
• /
• pp.128-132
• /
• 2011

In interference tolerance based spectrum sharing systems, primary receivers (PRs) are protected by a predefined peak or average interference power constraint. To implement such systems, cognitive radio (CR) transmitters are required to adjust their transmit power so that the interference power received at the PR receivers is kept below the threshold value. Hence, a CR-transmitter requires knowledge of its channel and the primary receiver in order to allocate the transmit power. In practice, it is impossible or very difficult for a CR transmitter to have perfect knowledge of this channel state information (CSI). In this paper, we investigate the impact of imperfect knowledge of this CSI on the performances of both a primary and cognitive radio network. For fixed transmit power, average interference power (AIP) constraint can be maintained through knowledge of the channel distribution information. To maintain the peak interference power (PIP) constraint, on the other hand, the CR-transmitter requires the instantaneous CSI of its channel with the primary receiver. First, we show that, compared to the PIP constraint with perfect CSI, the AIP constraint is advantageous for primary users but not for CR users. Then, we consider a PIP constraint with imperfect CSI at the CR-transmitter. We show that inaccuracy in CSI reduces the interference at the PR-receivers that is caused by the CR-transmitter. Consequently the proposed schemes improve the capacity of the primary links. Contrarily, the capacities of the CR links significantly degrade due to the inaccuracy in CSI.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제11권1호
• /
• pp.253-271
• /
• 2017

In this paper, considering that perfect channel state information (CSI) is hard to achieve in practice, the downlink capacity of distributed antenna systems (DAS) with imperfect CSI and multiple receive antennas is investigated over composite Rayleigh fading channel. According to the performance analysis, using the numerical calculation, the probability density function (PDF) of the effective output SNR is derived. With this PDF, accurate closed-form expressions of ergodic capacity and outage probability of DAS with imperfect CSI are, respectively, obtained, and they include the ones under perfect CSI as special cases. Besides, the outage capacity of DAS in the presence of imperfect CSI is also derived, and a Newton's method based practical iterative algorithm is proposed to find the accurate outage capacity. By utilizing the Gaussian distribution approximation, another approximate closed-form expression of outage capacity is also derived, and it may simplify the calculation of accurate outage capacity. These theoretical expressions can provide good performance evaluation for downlink DAS for both perfect and imperfect CSI. Simulation results verify the effectiveness of the theoretical analysis, and the system capacity can be improved by increasing the receive antennas, and decreasing the estimation error or path loss. Moreover, the system can tolerate the estimation error variance up to about 0.01 with a slight degradation in the capacity.

• 인터넷정보학회논문지
• /
• 제13권1호
• /
• pp.7-14
• /
• 2012

본 논문은 불완전한 채널 감지를 고려한 포화 상태에서의 IEEE 802.11 carrier-sense multiple access with collision-avoidance(CSMA/CA)의 성능을 분석한다. 불완전한 채널 감지는 missed-detection과 false alarm을 포함하는데, 이러한 불완전한 채널 감지가 IEEE 802.11의 성능에 미치는 영향을 분석하고 이를 수식적으로 표현한다. 물리 계층의 불완전한 채널 감지를 표현하기 위해, 본 논문에서는 기존의 2차원 마코프 프로세스 모델을 수정했다. 모의실험 결과와 제안된 모델의 이론적인 결과가 일치하는 것을 보였다. 이러한 실험 결과를 바탕으로, 감지 확률이 IEEE 802.11의 성능에 있어 가장 중요한 요소임을 확인하였다.

• 대한전자공학회논문지TC
• /
• 제45권12호
• /
• pp.26-33
• /
• 2008

신호의 검파는 무선통신시스템에서 매우 중요한 문제이며 최근에는 다중입력다중출력(MIMO) 통신을 위한 검파 알고리즘에 대한 연구가 많이 진행되었다. 그러나 이러한 연구의 많은 부분이 주파수 비선택적 채널을 가정하였거나 주파수 선택적 채널을 가정하더라도 수신단에서의 채널상태정보는 완전하다는 가정 하에 연구가 수행되었다. 따라서, 본 연구에서는 주파수 선택적 채널에서 불완전한 채널정보를 사용할 때 몇 가지 MIMO 검파 알고리즘에 대해 얻을 수 있는 오류율 성능을 비교해 보고자 한다.

• Journal of information and communication convergence engineering
• /
• 제9권2호
• /
• pp.193-196
• /
• 2011

Transmit antenna selection techniques are prominent since they exploit the spatial selectivity at the transmitter side. In the literature, antenna selection techniques assume full knowledge of the channel state information (CSI). In this paper, we consider that the CSI is not perfectly known at the transmitter; however, a quantized version of the channel coefficients is fed back by the users. We employ the non-uniform Lloyd-Max quantization algorithm which takes into consideration the distribution of the channel coefficients. Simulation results show that the degradation in the BER of the system with imperfect CSI at the transmitter is tolerable, especially when the transmit diversity order is high.

• 전자공학회논문지
• /
• 제53권4호
• /
• pp.79-86
• /
• 2016

물리계층보안은 신호의 물리적 특성을 이용하여 정보를 보호하는 보안 기법이다. 현재 이에 대한 연구가 활발히 진행 중이지만 해결해야할 다음과 같은 문제점들이 존재한다. 도청자는 자신의 존재를 숨기기 위해서 자신의 채널상태정보를 다른 합법적인 노드와 공유하지는 않는다. 그리고 노드가 신호를 전송할 때 하드웨어 왜곡이 발생하지만 많은 연구들은 노드 모델들이 이상적인 것으로 가정을 하고, 하드웨어 왜곡문제를 고려하지 않고 있다. 이와 같은 문제점들을 해결하기 위한 본 논문의 주요한 특징 및 기여도는 다음과 같다. 첫째, 도청자의 채널상태정보를 얻기 위해서 조력자노드를 합법적인 노드주변에 설치하고, 조력자노드의 채널상태정보를 이용하여 노드모델에서 하드웨어 왜곡을 고려한다. 둘째, 제안된 시스템 모델의 인터셉트 확률에 대한 Closed-Form Expression을 제시한다. 제안된 시스템의 성능평가를 위해서 다양한 시뮬레이션를 통하여 제안된 시스템 모델의 물리계층보안에 미치는 영향을 알아본 결과, 불완전한 채널상태정보는 인터셉트 확률에는 영향을 미치지 못한 반면에, 불완전한 노드모델의 경우, 인터셉트 확률, 에르고딕 시크리스 용량과 보안채널용량에 영향을 준다는 것을 보여준다.

• ETRI Journal
• /
• 제45권6호
• /
• pp.929-938
• /
• 2023

The detection of all the symbols transmitted simultaneously in multiuser systems using limited wireless resources is challenging. Traditional model-based methods show high performance with perfect channel state information (CSI); however, severe performance degradation will occur if perfect CSI cannot be acquired. In contrast, data-driven methods perform slightly worse than model-based methods in terms of symbol error ratio performance in perfect CSI states; however, they are also able to overcome extreme performance degradation in imperfect CSI states. This study proposes a novel deep learning-based method by improving a state-of-the-art data-driven technique called deep soft interference cancellation (DSIC). The enhanced DSIC (EDSIC) method detects multiuser symbols in a fully sequential manner and uses an efficient neural network structure to ensure high performance. Additionally, error-propagation mitigation techniques are used to ensure robustness against channel uncertainty. The EDSIC guarantees a performance that is very close to the optimal performance of the existing model-based methods in perfect CSI environments and the best performance in imperfect CSI environments.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제10권9호
• /
• pp.4223-4239
• /
• 2016

In this paper, we consider an amplify-and-forward (AF) full-duplex relay network (FDRN) using simultaneous wireless information and power transfer, where a battery-free relay node harvests energy from the received radio frequency (RF) signals from a source node and uses the harvested energy to forward the source information to destination node. The time-switching relaying (TSR) protocol is studied, with the assumption that the channel state information (CSI) at the relay node is imperfect. We deliver a rigorous analysis of the outage probability of the proposed system. Based on the outage probability expressions, the optimal time switching factor are obtained via the numerical search method. The simulation and numerical results provide practical insights into the effect of various system parameters, such as the time switching factor, the noise power, the energy harvesting efficiency, and the channel estimation error on the performance of this network. It is also observed that for the imperfect CSI case, the proposed scheme still can provide acceptable outage performance given that the channel estimation error is bounded in a permissible interval.

• Journal of Communications and Networks
• /
• 제16권1호
• /
• pp.45-55
• /
• 2014

The paper investigates the problem of designing the multiple-antenna relay in a two-way relay network by taking into account the imperfect channel state information (CSI). The objective is to design the multiple-antenna relay based upon the CSI estimates, where the estimation errors are included to attain the robust design under the worst-case philosophy. In particular, the worst-case transmit power at the multiple-antenna relay is minimized while guaranteeing the worst-case quality of service requirements that the received signal-to-noise ratio (SNR) at both sources are above a prescribed threshold value. Since the worst-case received SNR expression is too complex for subsequent derivation and processing, its lower bound is explored instead by minimizing the numerator and maximizing the denominator of the worst-case SNR. The aforementioned problem is mathematically formulated and shown to be nonconvex. This motivates the pursuit of semidefinite relaxation coupled with a randomization technique to obtain computationally efficient high-quality approximate solutions. This paper has shown that the original optimization problem can be reformulated and then relaxed to a convex problem that can be solved by utilizing suitable randomization loop. Numerical results compare the proposed multiple-antenna relay with the existing nonrobust method, and therefore validate its robustness against the channel uncertainty. Finally, the feasibility of the proposed design and the associated influencing factors are discussed by means of extensive Monte Carlo simulations.