• Title, Summary, Keyword: cooperative communications

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Increasing Secrecy Capacity via Joint Design of Cooperative Beamforming and Jamming

  • Guan, Xinrong;Cai, Yueming;Yang, Weiwei;Cheng, Yunpeng;Hu, Junquan
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.6 no.4
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    • pp.1041-1062
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    • 2012
  • In this paper, we propose a hybrid cooperative scheme to improve the secrecy rate for a cooperative network in presence of multiple relays. Each relay node transmits the mixed signal consisting of weighted source signal and intentional noise. The problem of power allocation, the joint design of beamforming and jamming weights are investigated, and an iterative scheme is proposed. It is demonstrated by the numerical results that the proposed hybrid scheme further improves secrecy rate, as compared to traditional cooperative schemes.

Error Probability Evaluation of a Novel Cooperative Communications Signaling Strategy in CDMA Systems

  • Khuong Ho-Van;Kong Hyung-Yun
    • Journal of Communications and Networks
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    • v.8 no.3
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    • pp.257-266
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    • 2006
  • The powerful benefits of multi-antenna systems can be obtained by cooperative communications among users in multiple access environments without the need for physical arrays. This paper studies a novel cooperative signaling strategy that achieves high performance and low implementation complexity for synchronous code division multiple access (CDMA) wireless mobile networks. The validity of the proposed strategy under slow flat Rayleigh fading channel plus additive white Gaussian noise (AWGN) is verified through closed-form error probability expressions and MonteCarlo simulations. A variety of analytical results reveal that the new cooperative strategy significantly outperforms direct transmission subject to the same spectral efficiency and transmit power constraint.

A Novel Cooperative Spectrum Sensing Algorithm in Cognitive Radio Systems

  • Zheng, Xueqiang;Wang, Jinlong;Wu, Qihui;Shen, Liang
    • Journal of Communications and Networks
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    • v.11 no.2
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    • pp.115-121
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    • 2009
  • In cognitive radio (CR) systems, cognitive users can use the frequency bands when the primary users are not present. Hence, reliable detection of available spectrum is foundation of cognitive radio technology. To ensure unimpaired operation of primary users, cooperative spectrum sensing is needed. To reduce the network overhead of cooperative spectrum sensing, a novel cooperative spectrum sensing algorithm based on credibility is proposed. In particular, the close-form expressions for probability of detection and false-alarm are derived for the novel algorithm, and expression for the average overhead used for cooperation is given. The thresholds design method for the algorithm is also discussed. The conclusion is proved by computer simulations.

A Study on Cooperative Communication using Space-Time Codes

  • Pham, Van-Su;Mai, Linh;Lee, Jae-Young;Yoon, Gi-Wan
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • pp.87-90
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    • 2007
  • In cooperative communication systems, the source terminal transmits signal to the destination terminal with the aid of partner terminals. Therefore, the source terminal obtains extra spatial diversity gain. As a result, its performance is enhanced in term of higher achievable transmission rate, the larger coverage range, and the lower bit-error-rate (BER). Space-time codes (STCs) have been applied to cooperative communication systems in distributed fashion, in which the signal is spatially time exploited to obtain gains analogous to those provided by STCs. In this work, we consider the application of orthogonal Space-time Block Codes (OSTBCs) to the cooperative communication systems to further achieve higher diversity gain. The advances of the proposed approach are verified via computer simulations.

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Combined Relay Selection and Cooperative Beamforming for Physical Layer Security

  • Kim, Jun-Su;Ikhlef, Aissa;Schober, Robert
    • Journal of Communications and Networks
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    • v.14 no.4
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    • pp.364-373
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    • 2012
  • In this paper, we propose combined relay selection and cooperative beamforming schemes for physical layer security. Generally, high operational complexity is required for cooperative beamforming withmultiple relays because of the required information exchange and synchronization among the relays. On the other hand, while it is desirable to reduce the number of relays participating in cooperative beamforming because of the associated complexity problem, doing so may degrade the coding gain of cooperative beamforming. Hence, we propose combined relay selection and cooperative beamforming schemes, where only two of the available relays are selected for beamforming and data transmission. The proposed schemes introduce a selection gain which partially compensates for the decrease in coding gain due to limiting the number of participating relays to two. Both the cases where full and only partial channel state information are available for relay selection and cooperative beamforming are considered. Analytical and simulation results for the proposed schemes show improved secrecy capacities compared to existing physical layer security schemes employing cooperative relays.

Selection Based Cooperative Beamforming and Power Allocation for Relay Networks

  • Liu, Yi;Nie, Weiqing
    • Journal of Communications and Networks
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    • v.13 no.4
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    • pp.377-384
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    • 2011
  • Cooperative beamforming has previously been proven to be an efficient way to improve the cooperative diversity. This method generally requires all relay nodes to participate in beamforming, which can be seen as "all participate" cooperative beamforming. However, not all relay nodes have constructive impacts on the end-to-end bit error rate (BER) performance. Based on this observation, we propose a new cooperative scheme which only selects those "appropriate" relay nodes to perform cooperative beamforming. Such relay nodes can be simply determined with mean channel gains. Therefore, the selection complexity is significantly reduced as global instantaneous channel state information is not required. This scheme guarantees that energy is only allocated to the "appropriate" relay nodes, and hence provides superior diversity. We also prove that power allocation among source and selected relay nodes is a convex problem, and can be resolved with lower computational complexity. Simulation results demonstrate that our scheme achieves an essential improvement in terms of BER performance for both optimal and limited feedback scenarios, as well as high energy-efficiency for the energy-constrained networks.

Minimum Energy Cooperative Path Routing in All-Wireless Networks: NP-Completeness and Heuristic Algorithms

  • Li, Fulu;Wu, Kui;Lippman, Andrew
    • Journal of Communications and Networks
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    • v.10 no.2
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    • pp.204-212
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    • 2008
  • We study the routing problem in all-wireless networks based on cooperative transmissions. We model the minimum-energy cooperative path (MECP) problem and prove that this problem is NP-complete. We hence design an approximation algorithm called cooperative shortest path (CSP) algorithm that uses Dijkstra's algorithm as the basic building block and utilizes cooperative transmissions in the relaxation procedure. Compared with traditional non-cooperative shortest path algorithms, the CSP algorithm can achieve a higher energy saving and better balanced energy consumption among network nodes, especially when the network is in large scale. The nice features lead to a unique, scalable routing scheme that changes the high network density from the curse of congestion to the blessing of cooperative transmissions.

Throughput and Delay Performance with a Cooperative Retransmission Scheme Using Distributed Beamforming

  • Kim, Hae-Soo
    • Journal of Communications and Networks
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    • v.13 no.4
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    • pp.306-312
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    • 2011
  • In this paper, an efficient retransmission scheme using cooperation from neighboring nodes is investigated. In the cooperative retransmission scheme, an erroneous packet is retransmitted to the destination by cooperative nodes where distributed beamforming is used to accommodate multiple cooperating nodes. A Markov model is used to analyze throughput efficiency and average delay of the proposed retransmission scheme. It is shown that the analytical results are well matched with the simulated results and improved throughput and delay performance can be achieved as compared to the traditional retransmission scheme. The performance of the proposed cooperative retransmission is investigated in the multi-hop configuration via computer simulation. The transmit power for retransmission packet is also investigated and it can be significantly reduced by using a small feedback channel.

Power Allocation for OFDM-Based Cooperative Relay Systems

  • Wu, Victor K. Y.;Li, Ye (Geoffrey);Wylie-Green, Marilynn P.;Reid, Tony;Wang, Peter S. S.
    • Journal of Communications and Networks
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    • v.10 no.2
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    • pp.156-162
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    • 2008
  • Cooperative relays can provide spatial diversity and improve performance of wireless communications. In this paper, we study subcarrier power allocation at the relays for orthogonal frequency division multiplexing (OFDM)-based wireless systems. For cooperative relay with amplify-and-forward (AF) and decode-and-forward (DF) algorithms, we investigate the impact of power allocation to the mutual information between the source and destination. From our simulation results on word~error-rate (WER) performance, we find that the DF algorithm with power allocation provides better performance than that of AF algorithm in a single path relay network because the former is able to eliminate channel noise at each relay. For the multiple path relay network, however, the network structure is already resistant to noise and channel distortion, and AF approach is a more attractive choice due to its lower complexity.

Cooperative MAC Protocol Using Active Relays for Multi-Rate WLANs

  • Oh, Chang-Yeong;Lee, Tae-Jin
    • Journal of Communications and Networks
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    • v.13 no.5
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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.