• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.2047-2066
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• 2016

In this paper, we investigate joint power allocation and relay selection (PARS) schemes in non-orthogonal cooperative protocol (NOCP) based cognitive relay networks. Generally, NOCP outperforms the orthogonal cooperative protocol (OCP), since it can provide more transmit diversity. However, most existing PARS schemes in cognitive relay networks focus on OCP, which are not suitable for NOCP. In the context of NOCP, we first derive the joint constraints of transmit power limit for secondary user (SU) and interference constraint for primary user (PU). Then we formulate optimization problems under the aforementioned constraints to maximize the capacity of SU in amplify-and-forward (AF) and decode-and-forward (DF) modes, respectively. Correspondingly, we derive the closed form solutions with respect to different parameters. Numerical results are provided to verify the performance improvement of the proposed PARS schemes.

• 한국통신학회논문지
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• 제39A권7호
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• pp.404-412
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• 2014

이동 단말기에 다중 안테나를 장착하는 것은 단말기의 크기와 전력 소모 문제로 현실적인 어려움을 안고 있다. 본 논문에서는 셀룰러 네트워크에서 단일 안테나를 가지는 이동 단말기의 전송 용량 증대를 위해, 다중안테나 통신 (MIMO)을 통해서 얻을 수 있는 선형적인 전송 용량 증대를 달성하는 신호 중계 기반 분산 다중 안테나기법을 제안하고 성능을 분석한다. 분산 다중안테나 시스템을 위한 단말 간 신호 중계에 증폭 후 전달 기법(Amplify-and-Forward)을 사용할 경우에 비해 양자화 후 전달 (Quantize-Map-and-Forward) 기법을 사용하는 경우, 처리율 측면에서 보다 우수한 성능을 달성할 수 있음을 실험을 통해서 보인다. 또한, 선형적 전송 용량 증대폭을 보다 향상시키기 위해 양자화 후 전달 중계 방식을 활용하여 다중접속채널을 구성하는 방법을 제안하고, 이러한 다중접속채널 구성이 가능한 조건을 충족시키기 위한 단말기 선택을 가능하게 하는 후보 이동 단말기 수를 분석하였다. 이러한 분산 다중 안테나 통신 기법은 셀룰러 시스템에서 지역적으로 분리된 클러스터들을 서비스하기 때문에 주파수 재사용을 가능하게 하며, 이로 인해 클러스터의 숫자에 비례하는 전체 셀룰러 용량 증대에 기여한다.

• 한국통신학회논문지
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• 제34권2A호
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• pp.124-131
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• 2009

Cognitive radio has been proposed to mitigate the spectrum scarcity problem by allowing the secondary users to access the under-utilized frequency bands and opportunistically transmit. Spectrum sensing, as a key technology in cognitive radio, is required to reliably detect the presence of primary users to avoid the harmful interference. However, it would be very hard to reliably detect the presence of primary users due to the channel fading, shadowing. In this paper, we proposed a distributed cooperative spectrum sensing scheme based on conventional DF (decode-and-forward) cooperative diversity protocol. We fist consider the cooperation between two secondary users to illustrate that cooperation among secondary users can obviously increase the detection performance. We then compare the performance of DF based scheme with another conventional AF (amplify-and-forward) protocol based scheme. And it is found that the proposed scheme based on DF has a better detection performance than the one based on AF. After that, we extend the number of cooperative secondary users, and demonstrate that increasing the cooperation number can significantly improve the detection performance.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.15-18
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• 2005

Cooperative diversity is a transmission technique, in which multiple terminals pool their resources to form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. In this paper, we propose a new type of cooperative transmission protocol with a full rate and show that its BER performance is improved by 8dB over the existing protocol under the AF (amplify-and-forward) mode of relaying.

• 전자공학회논문지
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• 제49권12호
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• pp.10-19
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• 2012

본 논문에서는 AMC(Adaptive Modulation and Coding) 기법을 적용한 릴레이 프로토콜을 제안한다. AMC 기법은 다양한 변조와 코딩 기법을 통해, 통신 시스템의 전송률과 신뢰도를 향상시킬 수 있다. 본 논문에서는 AMC 기법을 적용한 릴레이 프로토콜의 성능을 분석하고, AMC 기법이 적용된 릴레이 프로토콜이 AMC 기법이 적용되지 않은 기존의 기법과 비교하여 낮은 SNR(Signal to Noise Ratio) 레벨에서 더 좋은 평균 전송률을 제공할 수 있음을 확인하였다. 비적응적 MCS(Modulation and Coding Scheme) 릴레이 프로토콜과 적응적 MCS 릴레이 프로토콜의 성능을 증명하기 위해 LTE-A(Long Term Evolution-Advanced) 파라미터와 함께 몬테카를로 시뮬레이션을 수행하였다. 모의실험 결과, 적응적 MCS가 적용된 시스템에서 AF(Amplify-and-Forward), DF(Decode-and-Forward) 및 DMF(DeModulate-and-Forward) 프로토콜 중 DMF 프로토콜이 낮은 SNR 값에서 가장 좋은 성능을 보이고, 더 좋은 평균 전송률을 제공하는 것을 확인하였다.

• Journal of Communications and Networks
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• 제11권5호
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• pp.433-444
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• 2009

The bi-directional relay channel is the natural extension of a three-terminal relay channel where node a transmits to node b with the help of a relay r to allow for two-way communication between nodes a and b. That is, in a bi-directional relay channel, a and b wish to exchange independent messages over a shared channel with the help of a relay r. The rates at which this communication may reliably take place depend on the assumptions made on the relay processing abilities. We overview information theoretic limits of the bi-directional relay channel under a variety of conditions, before focusing on half-duplex nodes in which communication takes place in a number of temporal phases (resulting in protocols), and nodes may forward messages in four manners. The relay-forwarding considered are: Amplify and forward (AF), decode and forward (DF), compress and forward (CF), and mixed forward. The last scheme is a combination of CF in one direction and DF in the other. We derive inner and outer bounds to the capacity region of the bi-directional relay channel for three temporal protocols under these four relaying schemes. The first protocol is a two phase protocol where a and b simultaneously transmit during the first phase and the relay r alone transmits during the second. The second protocol considers sequential transmissions from a and b followed by a transmission from the relay while the third protocol is a hybrid of the first two protocols and has four phases. We provide a comprehensive treatment of protocols in Gaussian noise, obtaining their respective achievable rate regions, outer bounds, and their relative performance under different SNR and relay geometries.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2019년도 춘계학술대회
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• pp.288-289
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• 2019

This paper studies the secrecy capacity for a wireless cooperative network with perfect channel state information at the relays, and receiver. A similar assumption is also made for the instance where there exist a direct link between the transmitter and receiver. Physical Layer security techniques are employed in wireless networks to mitigate against the activity of eavesdroppers. It offers a viable alternative to computationally intensive encryption. In this paper the design of a protocol utilizing jamming (via jamming nodes) for better security and relaying (via relay nodes) for the amplify-and-forward (AF) operation, is investigated. A a signal-to-noise variant of secrecy known as secrecy gap is explored because of its use of lesser computational power - preferable for practical systems. Thus we maximize this signal-to-noise approach instead of the conventional secrecy capacity maximization method. With this, an iterative algorithm using geometric programming (GP) and semi-definite programming (SDP) is presented with appreciable benefits. The results show here highlight the benefits of using fractional components of the powers of the relays to offer better secrecy capacity.

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

• 한국전자통신학회논문지
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• 제9권7호
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• pp.805-810
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• 2014

중계기를 이용해서 신호를 전송하는 협력통신은 여러 개의 안테나를 사용해야하는 물리적인 시스템의 제약없이 가상 다중입출력 이득을 제공함으로서 전체적인 통신시스템의 성능을 향상시킬 수 있다. 두 개의 대표적인 중계 프로토콜로는 증폭 후 전송방식과 복조 후 전송방식이 있는데, 본 논문에서는 복조 후 전송 중계 프로토콜을 적용하여 부분적으로 차등변조 방식을 사용하는 협력통신기법의 성능에 대해 분석한다. 성능분석은 심볼오류율을 이용하여 이루어지며 중계기의 위치가 통신성은에 미치는 영향을 분석한다. 또한 제안된 부분차등변조 방식과 기존의 차등변조 방식의 성능을 비교한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권5호
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• pp.2009-2028
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• 2018

Considering a dual-hop energy-harvesting (EH) relaying system, this paper advocates novel relaying protocols based on adaptive time power switching-based relaying (AR) architecture for amplify-and-forward (AF) mode. We introduce novel system model relaying network with impacts of co-channel interference (CCI) and derive analytical expressions for the average harvested energy, outage probability, and the optimal throughput of the information transmission link, taking into account the effect of CCI from neighbor cellular users. In particular, we consider such neighbor users procedure CCI both on the relay and destination nodes. Theoretical results show that, in comparison with the conventional solutions, the proposed model can achieve optimal throughput efficiency for sufficiently small threshold SNR with condition of reasonable controlling time switching fractions and power splitting fractions in concerned AR protocol. We also explore impacts of transmission distances in each hop, transmission rate, the other key parameters of AR to throughput performance for different channel models. Simulation results are presented to corroborate the proposed methodology.