• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권1호
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• pp.260-279
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• 2015

In this paper, we investigate physical layer security for multiple decode-and-forward (DF) relaying underlay cognitive radio networks (CRNs) with fixed transmit power at the secondary network against passive eavesdropping attacks. We propose a simple relay selection scheme to improve wireless transmission security based on the instantaneous channel information of all legitimate users and the statistical information about the eavesdropper channels. The closed-form expressions of the probability of non-zero secrecy capacity and the secrecy outage probability (SOP) are derived over independent and non-identically distributed Rayleigh fading environments. Furthermore, we conduct the asymptotic analysis to evaluate the secrecy diversity order performance and prove that full diversity is achieved by using the proposed relay selection. Finally, numerical results are presented to verify the theoretical analysis and depict that primary interference constrain has a significant impact on the secure performance and a proper transmit power for the second transmitters is preferred to be energy-efficient and improve the secure performance.

• 한국통신학회논문지
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• 제32권7A호
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• pp.694-699
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• 2007

본 논문에서는 레일리 페이딩 채널환경에서 폐루프 송신 안테나 다이버시티 시스템을 위한 최적의 안테나 가중치 방식을 연구한다. 평균전력 및 첨두 전력의 제한이 있는 경우에 폐루프 송신 안테나 다이버시티의 평균 비트 오류율을 최소화하는 최적의 송신 안테나 가중치를 닫힌 형식의 수학식으로 유도한다. 본 논문의 결과로부터 첨두 전력의 제한으로 인한 평균 비트 오류율 성능의 열화는 사용가능 한 평균전력이 커질수록 그리고/또는 송신 안테나 개수가 증가할수록 그 성능 열화의 정도가 더욱 커짐을 알 수 있다.

• Journal of Communications and Networks
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• 제17권3호
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• pp.231-240
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• 2015

To facilitate the base station planning in high speed railway communication systems, it is necessary to consider the functional relationships between the base station transmit power and space parameters such as train velocity and cell radius. Since these functions are able to present some inherent system properties determined by its spatial topology, they will be referred to as the power-space functions in this paper. In light of the fact that the line-of-sight path persists the most power of the received signal of each passing train, this paper considers the average transmission rate and bounds on power-space functions based on the additive white Gaussian noise channel (AWGN) model. As shown by Monte Carlo simulations, using AWGN channel instead of Rician channel introduces very small approximation errors, but a tractable mathematical framework and insightful results. Particularly, lower bounds and upper bounds on the average transmission rate, as well as transmit power as functions of train velocity and cell radius are presented in this paper. It is also proved that to maintain a fixed amount of service or a fixed average transmission rate, the transmit power of a base station needs to be increased exponentially, if the train velocity or cell radius is increased, respectively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권6호
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• pp.2204-2224
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• 2021

This paper studies secure wireless transmission from a multi-antenna transmitter to a single-antenna intended receiver overheard by multiple eavesdroppers with considering the imperfect channel state information (CSI) of wiretap channel. To enhance security of communication link, the artificial noise (AN) is generated at transmitter. We first design the robust joint optimal beamforming of secret signal and AN to minimize transmit power with constraints of security quality of service (QoS), i.e., minimum allowable signal-to-interference-and-noise ratio (SINR) at receiver and maximum tolerable SINR at eavesdroppers. The formulated design problem is shown to be nonconvex and we transfer it into linear matrix inequalities (LMIs). The semidefinite relaxation (SDR) technique is used and the approximated method is proved to solve the original problem exactly. To verify the robustness and tightness of proposed beamforming, we also provide a method to calculate the worst-case SINR at eavesdroppers for a designed transmit scheme using semidefinite programming (SDP). Additionally, the secrecy rate maximization is explored for fixed total transmit power. To tackle the nonconvexity of original formulation, we develop an iterative approach employing sequential parametric convex approximation (SPCA). The simulation results illustrate that the proposed robust transmit schemes can effectively improve the transmit performance.

• 한국인터넷방송통신학회논문지
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• 제12권2호
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• pp.215-220
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• 2012

무선 Ad-Hoc 네트워크는 전력제한을 갖기 때문에 네트워크의 소모 전력을 최소화 하는 것이 최근의 연구 주제 중 하나이다. 본 논문은 최근에 제안된 수신가지 수가 제한된 이중기회전송 릴레이 시스템의 전력 소모를 줄이고, 시스템의 성능을 개선하기 위하여 각 송신 노드의 최적 전력 분배방식을 제안하고 시스템의 성능을 유도하였다. 분석결과 각 송신 노드가 동일한 전력으로 송신할 경우보다 각 송신노드에 최적의 전력을 할당한 경우가 오수신율이 항상 우수함을 보였고, 또한 평균 채널전력 이득이 작을 경우 평균 송신 릴레이 수를 증가시켜 다이버시티 이득을 크게 함으로써 오수신율을 최소화 하는 것을 알 수 있었다.

• 한국통신학회논문지
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• 제33권12A호
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• pp.1138-1146
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• 2008

This paper considers 2-hop wireless cooperative communications networks with fixed decode-and-forward relays. Specifically, we first derive the closed-form BER expression for theoretically evaluating the end-to-end performance of these networks. Then, based on this expression and long-tenn fading statistics, we propose a power allocation method for source and relay. Such a method brings about multiple advantages in tenn of spectral efficiency and implementation complexity over other power allocation methods based on instantaneous fading statistics. A variety of numerical results reveal that the cooperative communications scheme with the proposed power allocation significantly outperforms that with the equal power allocation and the direct transmission scheme for any position of the relay subject to the same total transmit power constraint.

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

• 한국통신학회논문지
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• 제33권7A호
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• pp.727-732
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• 2008

The transmit diversity as well as beamforming can increase the performance of wireless communication systems. It is well known that the requirement for the spacing between the neighboring antennas in transmit diversity and beamforming is contradictive to each other. Therefore it is necessary to find the optimum configuration of multiple antennas for getting the maximum performance under the condition that the total number of antennas at transmitter site and the total power of transmitter are fixed. In this paper, the procedure for finding the optimum configuration of multiple antennas was derived through searching the maximum capacity and BER in the combined system with the transmit diversity (Tx diversity) and beamforming.

• Journal of Communications and Networks
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• 제9권2호
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• pp.136-140
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• 2007

In this paper, an adaptive minimum transmit power modulation scheme under constant data rate and fixed bit error rate (BER) for the multiple-input multiple-output (MIMO) system is proposed. It adjusts the modulation order and allocates the transmit power to each spatial sub-channel when meeting the user's requirements at the cost of minimum transmission power. Compared to the other algorithm, it can obtain good performance with lower computational complexity and can be applied to the wireless communication system. Computer simulation results present the efficiency of the proposed scheme. And its performance under different channel condition has been compared with the other algorithm.

• 한국정보통신학회논문지
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• 제18권8호
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• pp.1877-1884
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• 2014

원격 무선 네트워크 환경에서의 무인 센서 신호처리기의 임무 수행을 위해서는 한정된 전력 자원으로 인해 무인 원격 센서 무선운용 상황에 적합한 신뢰성 있는 저전력 매체 접속 제어 기법이 요구된다. 저전력 무선 네트워크에서 효과적인 신호 전송을 위해서는 CSMA/CA, X-MAC을 일반적으로 고려한다. 본 논문에서는 고정 노드로 구성되는 무선 네트워크에서 노드 제어를 위한 이동 노드의 망 참여/탈퇴가 유동적인 망 형태에서의 신속한 데이터 전달 및 소모 전력 최소화 달성이 가능한 저전력 성능이 향상된 LP-MAC 동작 기법을 제안한다. 고정노드는 망 자율구성을 수행하여 망에 수시로 참여/탈퇴하는 이동 노드로의 빠른 정보 전달을 위해 비동기 방식으로 동작한다. 이동 노드가 망에서 탈퇴할 경우, 망 전체 운용모드가 소모 전력의 최소화를 위한 동기모드로 천이됨으로써 최소 전력 운용이 가능한 매체접속 제어 기법이다.