• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권10호
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• pp.2455-2472
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• 2012

Although underlay spectrum sharing has been shown as a promising technique to promote the spectrum utilization in cognitive radio networks (CRNs), it may suffer bad secondary performance due to the strict power constraints imposed at secondary systems and the interference from primary systems. In this paper, we propose a two-phase based cooperative transmission protocol with the interference cancellation (IC) and best-relay selection to improve the secondary performance in underlay models under stringent power constraints while ensuring the primary quality-of-service (QoS). In the proposed protocol, IC is employed at both the secondary relays and the secondary destination, where the IC-based best-relay selection and cooperative relaying schemes are well developed to reduce the interference from primary systems. The closed-form expression of secondary outage probability is derived for the proposed protocol over Rayleigh fading channels. Simulation results show that, with a guaranteed primary outage probability, the proposed protocol can achieve not only lower secondary outage probability but also higher secondary diversity order than the traditional underlay case.

• 한국멀티미디어학회논문지
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• 제15권3호
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• pp.345-355
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• 2012

본 논문에서는 UWB 기술 기반 WiMedia Distributed Medium Access Control (D-MAC) 무선 USB 표준 프로토콜에 적용할 수 있는 Satisfaction of QoS (SoQ) 기반 협력 통신 프로토콜을 제안한다. 이를 위해 UWB 링크 전송 속도와 QoS 척도에 따른 릴레이 노드 선정 알고리즘을 제안한다. 본 논문에서 제안하는 SoQ 기반 협력 통신 프로토콜은 분산적인 D-MAC 무선 USB 표준 기술과 호환성을 갖고, 각 디바이스에서 독립적으로 실행되는 SoQ 기반 Relay Node Selection (RNS) 기준에 따라 실행된다.

• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권7호
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• pp.3447-3469
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• 2019

It is well-known that the cooperative communication and error control technology can improve the network performance, but most existing cooperative MAC protocols have not focused on how to cope with the contention process caused by cooperation and how to reduce the bad influence of channel packet error rate on the system performance. Inspired by this, this paper first modifies and improves the basic rules of the IEEE 802.11 Medium Access Control (MAC) protocol to optimize the contention among the multi-relay in a cooperative ARQ scheme. Secondly, a hybrid ARQ protocol with soft combining is adopted to make full use of the effective information in the error data packet and hence improve the ability of the receiver to decode the data packet correctly. The closed expressions of network performance including throughput and average packet transmission delay in a saturated network are then analyzed and derived by establishing a dedicated two-dimensional Markov model and solving its steady-state distribution. Finally, the performance evaluation and superiority of the proposed protocol are validated in different representative study cases through MATLAB simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권11호
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• pp.5322-5342
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• 2016

In vehicle-to-vehicle (V2V) networks, where selfishness degrades node activity, countermeasures for collaboration enforcement must be provided to enable application of a sage and efficient network environment. Because vehicular networks feature both high mobility and various topologies, selfish behavior judgment and establishment of a stable routing protocol become intensely challenging. In this paper, a two-phase-based generous cooperative routing protocol (called GEC) is presented for V2V networks to provide resistance to selfishness. To detect selfish behaving vehicles, a packet forwarding watchdog and an average connection rate based on the multipath weight method are used, where evidence is gathered from different watchdogs. Then, multihop relay decisions are made using a generous cooperative algorithm based on game theory. Finally, through buffering of the multiple end-to-end paths and judicious choice of optimal cooperative routes, route maintenance phase is capable of dealing with congestion and rapidly exchanging traffic. Specifically, it is proved that the GEC is theoretically subgame perfect. Simulation results show that for V2V networks with inherently selfish nodes, the proposed method isolates uncooperative vehicles and is capable of accommodating both the mobility and congestion circumstances by facilitating information dissemination and reducing end-to-end delay.

• 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.

• 한국정보통신학회논문지
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• 제17권8호
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• pp.1811-1819
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• 2013

본 논문에서는 무선통신에서의 시스템 성능을 향상시키기 위해 협력통신에서 매우 중요한 도움노드를 선정하는 방법에 대하여 연구를 수행하였다. 본 논문에서 제안한 BT-COMAC (busy tone cooperative MAC) 프로토콜은 사후(reactive) 도움노드 선정기법을 채용하였으며, 기존 기법의 장점을 극대화하면서 단점을 보완한 새로운 협력통신용 MAC 프로토콜이다. 컴퓨터 모의실험을 통해 성능평가를 수행하였으며, 시스템 처리량과 채널 액세스 지연시간을 성능평가 척도로 사용하였다. 모든 통신노드들이 통신영역 내에서 독자적으로 움직이는 이동성 모델을 사용하였으며, 슬로우 페이딩 채널 환경에서 수신 전력을 기반으로 전송속도를 결정하는 방법을 사용하였다. 성능평가 결과 본 논문에서 제안한 기법이 기존 방식에 비해 시스템 처리량 측면에서 최대 15% 정도 성능개선을 달성한 것을 확인할 수 있었다.

• 한국통신학회논문지
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• 제33권4A호
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• pp.361-370
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• 2008

Cooperative relaying permits one or more relay to transmit a signal from the source to the destination, thereby increasing network coverage and spectral efficiency. The performance of cooperative relaying is often measured as outage probability. However, appropriate measure for the channel quality is outage capacity. Although the outage probability for cooperative relaying protocol has been analyzed before, very little research has been addressed for the outage capacity. This paper is the first of its kind to derive a closed-form analytical solution of outage capacity using fixed decode and forward relaying and amplify and forward relaying in dissimilar Rayleigh fading channels, considering channel coefficients known to the receiver side. The analytical results show a tradeoff between the SNR and the number of relays for specific outage capacity. A comparison between decode and forward relaying and amplify and forward relaying shows that decode and forward relaying outperforms amplify and forward relaying for a large number of relays.

• ETRI Journal
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• 제33권5호
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• pp.759-769
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• 2011

Cooperative hybrid-automatic repeat request (HARQ) protocols, which can exploit the spatial and temporal diversities, have been widely studied. The efficiency of cooperative HARQ protocols is higher than that of cooperative protocols because retransmissions are only performed when necessary. We classify cooperative HARQ protocols as three decode-and-forward-based HARQ (DF-HARQ) protocols and two amplified-and-forward-based HARQ (AF-HARQ) protocols. To compare these protocols and obtain the optimum parameters, two unified frameworks are developed for protocol analysis. Using the frameworks, we can evaluate and compare the maximum throughput and outage probabilities according to the SNR, the relay location, and the delay constraint. From the analysis we can see that the maximum achievable throughput of the DF-HARQ protocols can be much greater than that of the AF-HARQ protocols due to the incremental redundancy transmission at the relay.

• Journal of Communications and Networks
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• 제12권4호
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• pp.358-365
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• 2010

We develop a low complexity cooperative diversity protocol for low energy adaptive clustering hierarchy (LEACH) based wireless sensor networks. A cross layer approach is used to obtain spatial diversity in the physical layer. In this paper, a simple modification in clustering algorithm of the LEACH protocol is proposed to exploit virtual multiple-input multiple-output (MIMO) based user cooperation. In lieu of selecting a single cluster-head at network layer, we proposed M cluster-heads in each cluster to obtain a diversity order of M in long distance communication. Due to the broadcast nature of wireless transmission, cluster-heads are able to receive data from sensor nodes at the same time. This fact ensures the synchronization required to implement a virtual MIMO based space time block code (STBC) in cluster-head to sink node transmission. An analytical method to evaluate the energy consumption based on BER curve is presented. Analysis and simulation results show that proposed cooperative LEACH protocol can save a huge amount of energy over LEACH protocol with same data rate, bit error rate, delay and bandwidth requirements. Moreover, this proposal can achieve higher order diversity with improved spectral efficiency compared to other virtual MIMO based protocols.