| 1. |
- Duong, Trung Quang, et al.
(author)
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Cognitive Cooperative Networks in Dual-Hop Asymmetric Fading Channels
- 2013
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In: 2013 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM). - 2334-0983 .- 2576-6813. - 9781479913534 ; , s. 955-961
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Conference paper (peer-reviewed)abstract
- Previous works on cognitive relay networks (CRNs) considered only symmetric fading channels. However, in practical wireless propagation scenarios, it is likely that the channels of the secondary user (SU) and primary user (PU) may undergo different fading characteristics. In this paper, we assume that the channels of the secondary network (SU-source -> SU-relay -> SU-destination) are subject to Rician fading, whereas the channels of the link from the SU to the PU experience Rayleigh fading. Based on this framework, the end-to-end outage probability (OP) of CRNs is investigated for two different relaying schemes: i) in the absence of the direct link with decode-and-forward (DF) protocol and ii) in the presence of the direct link with incremental DF protocol. In particular, we derive both exact and asymptotic OP expressions for the considered CRNs. Our analysis reveals important insights into the impact of fading parameters on the CRN performance under distinct fading distributions.
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| 2. |
- Trung, Hieu Tran, et al.
(author)
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Anti-inflammatory and Antiphytopathogenic Fungal Activity of 2,3-seco-Tirucallane Triterpenoids Meliadubins A and B from Melia dubia Cav. Barks with ChemGPS-NP and In Silico Prediction
- 2023
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 8:40, s. 37116-37127
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Journal article (peer-reviewed)abstract
- Two new rearranged 2,3-seco-tirucallane triterpenoids, meliadubins A (1) and B (2), along with four known compounds, 3-6, were isolated from the barks of Melia dubia Cav. Compound 2 exhibited a significant inflammatory inhibition effect toward superoxide anion generation in human neutrophils (EC50 at 5.54 +/- 0.36 mu M). It bound to active sites of a human inducible nitric oxide synthase (3E7G) through interactions with the residues of GLU377 and PRO350, which may benefit in reducing the neutrophilic inflammation effect. The ChemGPS-NP interpretation combined with bioactivity assay and in silico prediction results suggested 2 to be an agent for targeting iNOS with different mechanisms as compared to a selected set of current approved drugs. Moreover, compounds 1 and 2 showed remarkable inhibition against the rice pathogenic fungus Magnaporthe oryzae in a dose-dependent manner with IC50 values of 137.20 +/- 9.55 and 182.50 +/- 18.27 mu M, respectively. Both 1 and 2 displayed interactions with the residue of TYR223, a key active site of trihydroxynaphthalene reductase (1YBV). The interpretation of 1 and 2 in the ChemGPS-NP physical-chemical property space indicated that both compounds are quite different compared to all members of a selected set of reference compounds. In light of demonstrated biological activity and in silico prediction experiments, both compounds possibly exhibited activity against phytopathogenic fungi via a novel mode of action.
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| 3. |
- Duong, Quang Trung, et al.
(author)
-
Distributed Space-Time Block Codes with Amicable Orthogonal Designs
- 2008
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Conference paper (peer-reviewed)abstract
- In this paper, we generalize the construction of distributed space–time block codes (DSTBCs) using amicable orthogonal designs which are originally applied to co-located multiple-antenna systems. We also derive the closed-form expression of average symbol error probability (SEP). The result is obtained in the form of single finite-range integral whose integrand contains only the trigonometric functions. Using the asymptotic (high signal-to-noise ratio) SEP formulas we show that the orthogonal DSTBCs achieve full diversity order. We also perform Monte-Carlo simulation to validate the analysis.
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| 4. |
- Duong, Quang Trung, et al.
(author)
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Effect of primary network on performance of spectrum sharing AF relaying
- 2012
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In: Electronics Letters. - : IET. - 0013-5194 .- 1350-911X. ; 48:1, s. 25-U95
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Journal article (peer-reviewed)abstract
- Most of the research in spectrum sharing has neglected the effect of interference from primary users. In this reported work, the performance of spectrum sharing amplify-and-forward relay networks under interference-limited environment, where the interference induced by the transmission of primary networks is taken into account, is investigated. In particular, a closed-form expression tight lower bound of outage probability is derived. To reveal additional insights into the effect of primary networks on the diversity and array gains, an asymptotic expression is also obtained.
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| 5. |
- Duong, Quang Trung, et al.
(author)
-
Ergodic Capacity of Cooperative Networks Using Adaptive Transmission and Selection Combining
- 2009
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Conference paper (peer-reviewed)abstract
- Closed-form expressions for channel capacity of repetition-based cooperative networks under adaptive transmission with selection combining are presented under the assumption of independent Rayleigh fading. Specifically, three different adaptive techniques are investigated: optimal simultaneous power and rate adaptation (OPRA), constant power with optimal rate adaptation (OPA) and channel inversion with fixed rate (TIFR). Among them, for an arbitrary number of relays, TIFR gives the worst channel capacity; OPRA gives the best channel capacity and ORA has a channel capacity quality in between the others. The analysis results, based on the upper and lower bound of the end-to-end SNR, agree very well with the simulated results and definitely show the impact of selection combining on the calculated channel capacity per unit bandwidth
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| 6. |
- Duong, Quang Trung, et al.
(author)
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On The Symbol Error Probability of Distributed-Alamouti Scheme
- 2009
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In: Journal of Communications. - : Academy Publisher. - 1796-2021 .- 2374-4367. ; 4:7, s. 437-444
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Journal article (peer-reviewed)abstract
- Taking into account the relay’s location, we analyze the maximum likelihood (ML) decoding performance ofdualhop relay network, in which two amplify-and-forward (AF) relays employ the Alamouti code in a distributed fashion. In particular, using the well-known moment generating function (MGF) approach we derive the closed-form expressions of the average symbol error probability (SEP) for M-ary phase-shift keying (M-PSK) when the relays are located nearby either the source or destination. The analytical result is obtained as a single integral with finite limits and the integrand composed solely of trigonometric functions. Assessing the asymptotic characteristic of SEP formulas in the high signal-to-noise ratio regime, we show that the distributed-Alamouti protocol achieves a full diversity order. We also perform the Monte-Carlo simulations to validate our analysis. In addition, based on the upper bound of SEP we propose an optimal power allocation between the first-hop (the source-to-relay link) and second-hop (the relay-to-destination link) transmission. We further show that as the two relays are located nearby the destination most of the total power should be allocated to the broadcasting phase (the first-hop transmission). When the two relays are placed close to the source, we propose an optimal transmission scheme which is a non-realtime processing, hence, can be applied for practical applications. It is shown that the optimal power allocation scheme outperforms the equal power scheme with a SEP performance improvement by 2-3 dB.
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| 7. |
- Duong, Quang Trung, et al.
(author)
-
Symbol Error Probability of Distributed-Alamouti Scheme in Wireless Relay Networks
- 2008
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Conference paper (peer-reviewed)abstract
- In this paper, we analyze the maximum likelihood decoding performance of non-regenerative cooperation employing Alamouti scheme. Specifically, we derive two closed-form expressions for average symbol error probability (SEP) when the relays are located near by the source or destination. The analytical results are obtained as a single integral with finite limits and an integrand composed solely of trigonometric functions. Assessing the asymptotic (high signal-to-noise ratio) behavior of SEP formulas, we show that the distributed-Alamouti codes achieves a full diversity order. We also perform Monte-Carlo simulations to validate the analysis.
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| 8. |
- Kim, Kyeong Jin, et al.
(author)
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Performance Analysis of Cognitive Spectrum-Sharing Single-Carrier Systems With Relay Selection
- 2012
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In: IEEE Transactions on Signal Processing. - : IEEE. - 1053-587X .- 1941-0476. ; 60:12, s. 6435-6449
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Journal article (peer-reviewed)abstract
- In this paper, we analyze the performance of cooperative spectrum sharing single-carrier (SC) relay systems. Taking into account the peak interference power at the primary user (PU) and the maximum transmit power at the secondary user (SU) network, two separate power allocation constraints are formed. For a two-hop decode-and-forward (DF) relaying protocol and two power allocation constraints, two relay selection schemes, namely, a full-channel state information (CSI)-based best relay selection (BRS) and a partial CSI-based best relay selection (PBRS), are proposed. The distributions of the end-to-end signal-to-noise ratios (e2e-SNRs) for the four cases are derived first, and then their outage probabilities and asymptotic outage probabilities are derived in closed-form. The derived asymptotic outage probabilities are utilized to see different diversity gains. Monte Carlo simulations have verified the derived diversity gains for the four different cases. We also present upper bounds on the ergodic capacities for two particular cases.
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| 9. |
- Luo, Yifei, et al.
(author)
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Technology Roadmap for Flexible Sensors
- 2023
-
In: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 17:6, s. 5211-5295
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Research review (peer-reviewed)abstract
- Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.
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| 10. |
- Phan, Hoc, et al.
(author)
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Cognitive amplify-and-forward relay networks with beamforming under primary user power constraint over Nakagami-m fading channels
- 2015
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In: Wireless Communications & Mobile Computing. - : Wiley. - 1530-8669 .- 1530-8677. ; 15:1, s. 56-70
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Journal article (peer-reviewed)abstract
- In this paper, we analyze the performance of cognitive amplify-and-forward (AF) relay networks with beamforming under the peak interference power constraint of the primary user (PU). We focus on the scenario that beamforming is applied at the multi-antenna secondary transmitter and receiver. Also, the secondary relay network operates in channel state information assisted AF mode, and the signals undergo independent Nakagami-m fading. In particular, closed-form expressions for the outage probability and symbol error rate (SER) of the considered network over Nakagami-m fading are presented. More importantly, asymptotic closed-form expressions for the outage probability and SER are derived. These tractable closed-form expressions for the network performance readily enable us to evaluate and examine the impact of network parameters on the system performance. Specifically, the impact of the number of antennas, the fading severity parameters, the channel mean powers, and the peak interference power is addressed. The asymptotic analysis manifests that the peak interference power constraint imposed on the secondary relay network has no effect on the diversity gain. However, the coding gain is affected by the fading parameters of the links from the primary receiver to the secondary relay network.
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| 11. |
- Tran, Hung, et al.
(author)
-
Average Waiting Time of Packets with Different Priorities in Cognitive Radio Networks
- 2010
-
Conference paper (peer-reviewed)abstract
- In this paper, we investigate the average waiting time of packets with different priorities in cognitive radio networks (CRN) using a preemptive priority queuing system. Specifically, we consider two scenarios for CRN, the first with the secondary user (SU) sensing at the beginning of each time slot and the other with the SU having continues sensing ability. Our analysis shows that the average waiting time of packets for the SU does not only depend on the size of packets and arrival rate of the SU traffic but also depends on the arrival rate and size of packets from primary users (PU). Moreover, the results show that an SU with continuous sensing ability can utilize spectrum better than sensing at the beginning of each time slot.
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| 12. |
- Tran, Hung, et al.
(author)
-
Delay performance of cognitive radio networks for point-to-point and point-to-multipoint communications
- 2012
-
In: EURASIP Journal on Wireless Communications and Networking. - : Springer. - 1687-1472 .- 1687-1499. ; :9
-
Journal article (peer-reviewed)abstract
- In this article, we analyze the packet transmission time in spectrum sharing systems where a secondary user (SU) simultaneously accesses the spectrum licensed to primary users (PUs). In particular, under the assumption of an independent identical distributed Rayleigh block fading channel, we investigate the effect of the peak interference power constraint imposed by multiple PUs on the packet transmission time of the SU. Utilizing the concept of timeout, exact closed-form expressions of outage probability and average packet transmission time of the SU are derived. In addition, employing the characteristics of the M/G/1 queuing model, the impact of the number of PUs and their peak interference power constraint on the stable transmission condition and the average waiting time of packets at the SU are examined. Moreover, we then extend the analysis for point-to-point to point-to-multipoint communications allowing for multiple SUs and derive the related closed-form expressions for outage probability and successful transmission probability for the best channel condition. Numerical results are provided to corroborate our theoretical results and to illustrate applications of the derived closed-form expressions for performance evaluation of cognitive radio networks.
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| 13. |
- Tran, Hung, et al.
(author)
-
On the Performance of Spectrum Sharing Systems Over Alpha-Mu Fading Channel for Non-identical Mu Parameter
- 2011
-
Conference paper (peer-reviewed)abstract
- Spectrum sharing is a promising approach in cognitive radio networks to improve the spectrum utilization of wireless communication systems. In this paper, we analyze the performance of spectrum sharing systems under the peak interference constraint for a general fading model, namely the Alpha-Mu fading channel. In particular, we derive expressions for statistical characteristics such as probability density function and cumulative distribution function of the end-to-end signal-tonoise ratio for dissimilar parameter Mu. Using these statistics, we obtain the closed-form expressions for outage probability, amount of fading and approximate ergodic capacity for the considered spectrum sharing system. Finally, Monte Carlo simulations are presented to verify the analytical results.
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| 14. |
- Tran, Hung, et al.
(author)
-
Performance Analysis of Cognitive Relay Networks Under Power Constraint of Multiple Primary Users
- 2011
-
Conference paper (peer-reviewed)abstract
- Cognitive relaying is a promising technique to improve spectrum utilization in mobile networks. In this paper, we consider a scenario in which a secondary transmitter communicates with a secondary receiver by the help of a secondary relay. The secondary user should adjust its transmission power in order to not cause any harmful interference to the multiple primary users operating in the licensed spectrum. In this context, we investigate the end-to-end performance of cognitive relay networks in terms of outage probability and ergodic capacity over Nakagami-m fading channels. A closed-form expression for outage probability and an approximation for ergodic capacity are derived. Furthermore, the presented numerical examples illustrate the impact of the number of primary users on the performance of cognitive relay networks.
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| 15. |
- Tran, Hung, et al.
(author)
-
Performance of a Spectrum Sharing System over Nakagami-m Fading Channels
- 2010
-
Conference paper (peer-reviewed)abstract
- In this paper, we derive the probability density function and cumulative distribution function of packet transmission time in a spectrum sharing system. In combination with the time-out characteristics of packets, we further study the outage probability and average transmission time under peak power interference constraint over Nakagami-m fading channel. Especially, we employ the M/G/1 queuing model to calculate the average waiting time of packets and average number of packets waiting in the queue of a secondary user. The numerical results show the importance of the peak interference power constraint on the delay of packets at the secondary user.
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| 16. |
- Tran, Hung, et al.
(author)
-
Queuing Analysis For Cognitive Radio Networks Under Peak Interference Power Constraint
- 2011
-
Conference paper (peer-reviewed)abstract
- In this paper, we study the effect of peak interference power constraint on outage probability and transmission time of packets for secondary user (SU) in a spectrum sharing environment. In the considered cognitive radio network scenario, a secondary user transmitter sends its packets over a Rayleigh fading channel. In combination with the analysis of time out characteristics, queuing models are deployed to evaluate average transmission time of packets, average waiting time of packets, and average number of packets waiting in the queue of the cognitive user.
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| 17. |
- Tran, Nguyen Nam, et al.
(author)
-
Training Design upon Mutual Information for Spatially Correlated MIMO-OFDM
- 2010
-
Conference paper (peer-reviewed)abstract
- Our goal in this paper is to address channel estimations for spatially correlated multiple-input multiple-output with orthogonal frequency-division multiplexing (MIMO-OFDM) system upon the conditional mutual information (CMI). The design of superimposed training signal by maximizing the channel CMI is fully investigated. First, the interior-point-method is employed to obtain the optimal superimposed training signals for the general case of channel correlations. In addition, two efficient approximate designs are also proposed by invoking Karush-Kuhn-Tucker condition for optimality of convex programming. The first approximate design is obtained by proposing a iterativebisection-procedure (IBP), while the second one is in “waterfilling” closed-form. Numerical results demonstrate the excellent performance of the proposed designs and give the connection between channel estimation error and mutual information.
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| 18. |
- Tran, Thien Thanh, et al.
(author)
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Performance analysis and optimal relay position of cognitive spectrum-sharing dual-hop decode-and-forward networks
- 2013
-
Conference paper (peer-reviewed)abstract
- The performance of cognitive networks (CNs) has been significantly improved by deploying a third-party, namely relay, to assist the direct communication. However, under a limited transmit power governed by the maximum tolerable interference at the primary network, the cognitive relay network still suffers a performance loss compared to its non-cognitive counterpart. To alleviate this shortcoming, this paper has pro-posed a technique to optimally deploy the relay in CNs. In particular, by assuming the decode-and-forward (DF) relay, we first derive an exact expression for the outage probability (OP) of CNs with spectrum-sharing environment over Nakagami-m channels. Then, using the exact formula, we obtain the asymptotic OP expression which further reveals the impact of networks' parameters on the performance. In addition, the optimal relay placement, i.e., minimizing the system OP, is also investigated by utilizing the asymptotic OP result. We have shown through some representative scenarios that given a fixed coordinate of a primary receiver, the optimal relay deployment significantly outperforms the two conventional approaches, i.e., uniform and random topologies.
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| 19. |
- Yiu, KFC, et al.
(author)
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A fast algorithm for the optimal design of high accuracy windows in signal processing
- 2013
-
In: Optimization Methods and Software. - : Taylor & Francis. - 1055-6788 .- 1029-4937. ; 28:4, s. 900-916
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Journal article (peer-reviewed)abstract
- This paper presents a new optimal window design method with a general window design specification for the passband and stopband. The design problem is formulated as a semi-infinite linear programming problem. With suitable discretizations, an exchange algorithm is employed. The convergence of the proposed algorithm is established. In the formulation, since the stopband is minimized, the method can be employed for the design of very highly optimized windows.
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