• ETRI Journal
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• v.42 no.3
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• pp.341-350
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• 2020

In a wireless sensor network (WSN), the data transmission technique based on the cooperative multiple-input multiple-output (CMIMO) scheme reduces the energy consumption of sensor nodes quite effectively by utilizing the space-time block coding scheme. However, in networks with high node density, the scheme is ineffective due to the high degree of correlated data. Therefore, to enhance the energy efficiency in high node density WSNs, we implemented the distributed source coding (DSC) with the virtual multiple-input multiple-output (MIMO) data transmission technique in the WSNs. The DSC-MIMO first compresses redundant source data using the DSC and then sends it to a virtual MIMO link. The results reveal that, in the DSC-MIMO scheme, energy consumption is lower than that in the CMIMO technique; it is also lower in the DSC single-input single-output (SISO) scheme, compared to that in the SISO technique at various code rates, compression rates, and training overhead factors. The results also indicate that the energy consumption per bit is directly proportional to the velocity and training overhead factor in all the energy saving schemes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.1
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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.

• Journal of Communications and Networks
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• v.16 no.5
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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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.5
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• pp.1957-1975
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• 2016

The outage probability (OP) performance of multiple-relay-based incremental hybrid decode-amplify-forward (IHDAF) relaying mobile-to-mobile (M2M) networks with transmit antenna selection (TAS) over N-Nakagami fading channels is investigated in this paper. The closed-form expressions for approximate OP of the optimal and suboptimal TAS schemes are derived. The power allocation problem is formulated for performance optimization. Then the OP performance under different conditions is evaluated through numerical simulations to verify the analysis. The simulation results showed that optimal TAS scheme has a better OP performance than suboptimal TAS scheme; the power-allocation parameter has an important influence on the OP performance.

• Journal of Communications and Networks
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• v.11 no.5
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• pp.480-488
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• 2009

Cooperative transmission is an effective solution to improve the performance of wireless communications over fading channels without the need for physical co-located antenna arrays. In this paper, selection combining is used at the destination instead of maximal ratio combing to optimize the structure of destination and to reduce power consumption in selective decode-and-forward relaying networks. For an arbitrary number of relays, an exact and closed-form expression of the bit error rate (BER) is derived for M-PAM, M-QAM, and M-PSK, respectively, in both independent identically distributed and independent but not identically distributed Rayleigh fading channels. A variety of simulations are performed and show that they match exactly with analytic ones. In addition, our results show that the optimum number of relays depend not only on channel conditions (operating SNRs) but also on modulation schemes which to be used.

• ETRI Journal
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• v.34 no.2
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• pp.159-167
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• 2012

In this paper, a new distributed resource allocation algorithm is proposed to alleviate the cross-tier interference for orthogonal frequency division multiplexing access macrocell and femtocell overlay. Specifically, the resource allocation problem is modeled as a non-cooperative game. Based on game theory, we propose an iterative algorithm between subchannel and power allocation called distributed resource allocation which requires no coordination among the two-hierarchy networks. Finally, a macrocell link quality protection process is proposed to guarantee the macrocell UE's quality of service to avoid severe cross-tier interference from femtocells. Simulation results show that the proposed algorithm can achieve remarkable performance gains as compared to the pure waterfilling algorithm.

• Journal of Communications and Networks
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• v.18 no.1
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• pp.19-26
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• 2016

In this paper, the performance of dual-hop multi-relay maximum ratio transmission (MRT) over Rayleigh flat fading channels is studied with both conventional (all relays participate the transmission) and opportunistic (best relay is selected to maximize the received signal-to-noise ratio (SNR)) relaying. Performance analysis starts with the derivation of the probability density function, cumulative distribution function and moment generating function of the SNR. Then, both approximate and asymptotic expressions of symbol error rate (SER) and outage probability are derived for arbitrary numbers of antennas and relays. With the help of asymptotic SER and outage probability, diversity and array gains are obtained. In addition, impact of imperfect channel estimations is investigated and optimum power allocation factors for source and relay are calculated. Our analytical findings are validated by numerical examples which indicate that multi-relay MRT can be a low complexity and reliable option in cooperative networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6A
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• pp.538-546
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• 2010

This paper presents an overview of position-based routing algorithms. We analyze performances of routing algorithms such as Hybrid Opportunistic Forwarding (HOF), Opportunistic multi-hop routing (ExOR), Location based Geocasting and Forwarding (LGF), and Greedy Forwarding in nearest with forward Progress (GFP) routing algorithms to find the best one in terms of packet error rate and throughput efficiency over effects of fading and noise variance in wireless networks. The analyses in closed form expressions are confirmed by the simulation results, which fully agree to analysis results. Additionally, the simulation results indicate significant differences among algorithms when varying the average SNR or the number of relays.

• International Journal of Computer Science & Network Security
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• v.22 no.4
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• pp.329-339
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• 2022

Small cells, particularly femtocells, are regarded a promising solution for limited resources required to handle the increasing data demand. They usually boost wireless network capacity. While widespread usage of femtocells increases network gain, it also raises several challenges. Interference is one of such concerns. Interference management is also seen as a main obstacle in the adoption of two-tier networks. For example, placing femtocells in a traditional macrocell's geographic area. Interference comes in two forms: cross-tier and co-tier. There have been previous studies conducted on the topic of interference management. This study investigates the principle of categorization of interference management systems. Many methods exist in the literature to reduce or eliminate the impacts of co-tier, cross-tier, or a combination of the two forms of interference. Following are some of the ways provided to manage interference: FFR, Cognitive Femtocell and Cooperative Resource Scheduling, Beamforming Strategy, Transmission Power Control, and Clustering/Graph-Based. Approaches, which were proposed to solve the interference problem, had been presented for each category in this work.

• International Journal of Computer Science & Network Security
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• v.22 no.10
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• pp.137-144
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• 2022

Wireless community networks (WCNs) are considered another form of ownership of internet protocol (IP) networks, where community members manage and own every piece of equipment in a decentralized way, and routing for traffic is done in a cooperative manner. However, the current routing protocols for WCNs suffer from stability and scalability issues. In this paper, an enhanced routing protocol is proposed based on the optimized link state routing (OLSR) protocol to meet the standards of efficiency in terms of stability and scalability. The proposed routing protocol is enhanced through two phases: multicasting expansion and multipoint relay (MPR) selection based on an analytical hierarchical process (AHP). The experimental results demonstrate that the proposed routing protocol outperforms the OLSR protocol in terms of network control overhead and packet delivery ratio by 18% and 1% respectively.