• Journal of Communications and Networks
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• 제13권3호
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• pp.257-265
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• 2011

In this paper, a cooperative relaying protocol called soft-decision-and-forward (SDF) with multiple antennas in each node is introduced. SDF protocol exploits the soft decision source symbol values from the received signal at the relay node. For orthogonal transmission (OT), orthogonal codes including Alamouti code are used and for non-orthogonal transmission (NT), distributed space-time codes are designed by using a quasi-orthogonal space-time block code. The optimal maximum likelihood (ML) decoders for the proposed protocol with low decoding complexity are proposed. For OT, the ML decoders are derived as symbolwise decoders while for NT, the ML decoders are derived as pairwise decoders. It can be seen through simulations that SDF protocol outperforms AF protocol for both OT and NT.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권9호
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• pp.2081-2100
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• 2013

In this paper, we propose a cooperative hybrid spectrum sharing protocol by jointly considering interweave (opportunistic) and underlay schemes. In the proposed protocol, secondary users can access the licensed spectrum along with the primary system. Our network scenario comprises a single primary transmitter-receiver (PTx-PRx) pair and a group of M secondary transmitter-receiver (STx-SRx) pairs within the transmission range of the primary system. Secondary transmitters are divided into two groups: active and inactive. A secondary transmitter that gets an opportunity to access the secondary spectrum is called "active". One of the idle or inactive secondary transmitters that achieves the primary request target rate $R_{PT}$ will be selected as a best decode-and-forward (DF) relay (Re) to forward the primary information when the data rate of the direct link between PTx and PRx falls below $R_{PT}$. We investigate the ergodic capacity and outage probability of the primary system with cooperative relaying and outage probability of the secondary system. Our theoretical and simulation results show that both the primary and secondary systems are able to achieve performance improvement in terms of outage probability. It is also shown that ergodic capacity and outage probability improve when the active secondary transmitter is located farther away from the PRx.

• Journal of Communications and Networks
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• 제16권5호
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• pp.502-511
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• 2014

In this paper, we evaluate performance of a hybrid decode-amplify-forward relaying protocol in underlay cognitive radio. In the proposed protocol, a secondary relay which is chosen by partial relay selection method helps a transmission between a secondary source and a secondary destination. In particular, if the chosen relay decodes the secondary source's signal successfully, it will forward the decoded signal to the secondary destination. Otherwise, it will amplify the signal received from the secondary source and will forward the amplified signal to the secondary destination. We evaluate the performance of our scheme via theory and simulation. Results show that the proposed protocol outperforms the amplify-and-forward and decode-and-forward protocols in terms of outage probability.

• 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.

• Journal of electromagnetic engineering and science
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• 제9권3호
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• pp.111-117
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• 2009

This paper presents an energy-efficient and bandwidth-efficient 2-1-1 relaying scheme in which a sensor node(SN) assists two others in their data transmission to a clusterhead in WSNs(Wireless Sensor Networks) using LEACH (Low-Energy Adaptive Clustering Hierarchy). We derive the closed-form BER expression of this scheme which is also a general BER one for the decode-and-forward cooperative protocol and prove that the proposed scheme performs the same as the conventional relaying scheme but obtains higher channel utilization efficiency. A variety of numerical results reveal the relaying can save the network energy up to 11 dB over single-hop transmission at BER of $10^{-3}$.

• Journal of Communications and Networks
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• 제13권5호
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• pp.463-471
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• 2011

Cooperative communications using relays in wireless networks have similar effects of multiple-input and multiple-output without the need of multiple antennas at each node. To implement cooperation into a system, efficient protocols are desired. In IEEE 802.11 families such as a/b/g, mobile stations can automatically adjust transmission rates according to channel conditions. However throughput performance degradation is observed by low-rate stations in multi-rate circumstances resulting in so-called performance anomaly. In this paper, we propose active relay-based cooperative medium access control (AR-CMAC) protocol, in which active relays desiring to transmit their own data for cooperation participate in relaying, and it is designed to increase throughput as a solution to performance anomaly. We have analyzed the performance of the simplified AR-CMAC using an embedded Markov chain model to demonstrate the gain of AR-CMAC and to verify it with our simulations. Simulations in an infrastructure network with an IEEE 802.11b/g access point show noticeable improvement than the legacy schemes.

• 한국통신학회논문지
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• 제33권4A호
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• pp.418-425
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• 2008

분산 다중 안테나 기반의 상호협력 통신(cooperative MIMO)을 구현하기 위해 대역 효율성 있는 두 가지 방식의 상호협력 전송 프로토콜을 제안하고 비교 분석한다. 같은 시분할 슬롯에 전송된 모든 심볼들 간에 간섭이 없다고 가정한 경우에 대해 각 전송 프로토콜의 BER 성능을 AF (Amplify-and-Forward)와 DF (Decode-and-Forward) 방식에서 각각 분석한다. 수학적 분석과 모의실험 결과를 통해 제안한 전송 방식이 직접 전송 방식(direct transmission)에 비해 대역폭을 추가로 사용하지 않고 많은 이득이 있음을 보여준다.

• 한국인터넷방송통신학회논문지
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• 제11권5호
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• pp.53-58
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• 2011

본 논문에서는 새로운 협력 전송 프로토콜을 제안한다. 기존의 협력 전송 프로토콜은 송신단과 수신단 사이에 위치하는 다수의 노드들 중에서 가장 높은 SNR을 가지는 노드를 이용하여 수신단으로 신호를 전송한다. 그러나 본 논문에서 제안하는 협력 전송 프로토콜은 노드의 위치정보를 기반으로 하여 송신단으로부터 복호에 성공한 노드들 중 수신단에 가장 가까운 노드를 선택하여 선택된 노드만이 수신단으로 신호를 전송하게 한다. 본 논문에서 제안하는 위치 정보를 기반으로 하는 중계기 선택 기법을 이용하는 협력 전송 프로토콜에 대해 수학적으로 분석하고 모의실험을 통해 이를 증명한다.

• 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.

• 한국통신학회논문지
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• 제35권7A호
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• pp.639-645
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• 2010

In the paper, a selection relaying scheme is proposed and analyzed in which relays retransmit the erroneous packet without checking the correctness of their received packets. The proposal not only achieves the full diversity gain in a limited number of retransmissions but it also gets better performance than other schemes. Additionally, a threshold in the number of retransmissions and the closed form expression for packet error rate (PER) are derived. Simulation results are given to confirm the accuracy of analysis and to significantly prove advantages of the proposal.