| 1. |
- Le, Khanh Duy, et al.
(author)
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HybridMingler: Towards Mixed-Reality Support for Mingling at Hybrid Conferences
- 2023
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In: Conference on Human Factors in Computing Systems - Proceedings.
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Conference paper (peer-reviewed)abstract
- Mingling, the activity of ad-hoc, private, opportunistic conversations ahead of, during, or after breaks, is an important socializing activity for attendees at scheduled events, such as in-person conferences. The Covid-19 pandemic had a dramatic impact on the way conferences are organized, so that most of them now take place in a hybrid mode where people can either attend on-site or remotely. While on-site attendees can resume in-person mingling, hybrid modes make it challenging for remote attendees to mingle with on-site peers. In addressing this problem, we propose a collaborative mixed-reality (MR) concept, including a prototype, called HybridMingler. This is a distributed MR system supporting ambient awareness and allowing both on-site and remote conference attendees to virtually mingle. HybridMingler aims to provide both on-site and remote attendees with a spatial sense of co-location in the very same venue location, thus ultimately improving perceived presence.
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| 2. |
- Nguyen, Khoa D., et al.
(author)
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Defect-engineered metal-organic frameworks (MOF-808) towards the improved adsorptive removal of organic dyes and chromium (vi) species from water
- 2023
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In: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1369-9261 .- 1144-0546. ; 47:13, s. 6433-6447
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Journal article (peer-reviewed)abstract
- In this work, two defective zirconium-based metal-organic frameworks (Zr-MOFs), MOF-808-OH and MOF-808-NH2, were synthesized by partially replacing the 1,3,5-benzenetricarboxylate building block with 5-hydroxyisophthalate and 5-aminoisophthalate, respectively. The structural features of the defective materials were analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen physisorption at 77 K, and thermogravimetric analysis (TGA). Importantly, the number of defect sites determined via proton nuclear magnetic resonance (1H-NMR) analysis of the digested materials was approximately 7 mol% for MOF-808-OH and 3 mol% for MOF-808-NH2. The presence of the defect sites increased the number of acidic centers on Zr-clusters originating from missing-linker nodes which accounted for a remarkable adsorption capacity towards various anionic organic dyes and chromium (vi) species. Compared to standard MOF-808, the defect-engineered ones showed significant increments by 30-60% in trapping capacity for anionic contaminants including sunset yellow, quinoline yellow, methyl orange, and potassium dichromate, while they exhibited modest improvements by 5-15% in the removal of cationic dyes, namely malachite green and methylene blue.
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| 3. |
- Dao, Van-Lan, et al.
(author)
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Defeating Jamming Using Outage Performance Aware Joint Power Allocation and Access Point Placement in Uplink Pairwise NOMA
- 2021
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In: IEEE Open Journal of the Communications Society. - 2644-125X. ; 2, s. 1957-1979
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Journal article (peer-reviewed)abstract
- In this paper, an uplink pairwise Non-Orthogonal Multiple Access (NOMA) scenario using a mobile access point (AP) or an unmanned aerial vehicle in the presence of a jamming attack is considered. To mitigate the influence of the jamming attack, a joint power allocation and AP placement design is proposed. Accordingly, closed-form expressions of the overall outage probability (OOP) and the individual outage probability (TOP) considering imperfect channel state information for each of the source nodes the AP serves, are derived over Nakagami-m fading channels using dynamic decoding order and fixed pairwise power allocation. We conduct an investigation of the effect of different parameters such as power allocation, source node placements, AP placement, target rates, and jammer location on the OOP and the IOP performance. By adapting the power allocation and the AP placement to the jamming attack, the communication reliability can be increased significantly compared to neglecting the presence of the jammer or treating the jammer as noise. Since the malicious jammer and the AP have conflicting interests in terms of communication reliability, we formulate a non-cooperative game for the two players considering their positions and the power allocation of the NOMA nodes as their strategies and the OOP as utility function. We propose using hybrid simulated annealing - greedy algorithms to address the joint power allocation and AP placement problem for the cases of both a fixed and a mobile jammer. Finally, the Nash equilibrium points are obtained and then the UAV goes directly to this position and keeps staying there to save power consumption.
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| 4. |
- Dao, Van-Lan, et al.
(author)
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Outage Performance of Pairwise NOMA Allowing a Dynamic Decoding Order and Optimal Pairs of Power Levels
- 2020
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In: IEEE Open Journal of the Communications Society. - Sweden : IEEE OJCOMS. - 2644-125X. ; 1, s. 1886-1906
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Journal article (peer-reviewed)abstract
- In this article, we evaluate the overall outage probability (OOP) of pairwise Non-orthogonal Multiple Access (NOMA) for both uplink and downlink. We also propose a dynamic decoding order (DDO) together with a fixed pairwise power allocation (FPPA) scheme, in which the optimal decoding order is decided based on the instantaneous channel gains, and thereafter, a pair of power levels is assigned in accordance with the selected decoding order. Exact closed-form expressions of the OOPs for both uplink and downlink pairwise NOMA considering all proposed decoding orders over Nakagami- m fading are derived. Further, we find the optimal fixed power levels for different power allocation strategies so that the OOPs are minimized. Moreover, we investigate the influence of the distances between the source nodes and the access point (AP), the target transfer rates and the path-loss exponents on the OOPs for all cases of decoding orders. In addition, we benchmark our proposed DDO against other decoding orders in terms of the OOP. The results show that assigning optimal fixed power levels which takes the instantaneous decoding order into account not only improves the communication reliability, but also reduces the complexity and computational load at the AP.
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| 5. |
- Dao, Van-Lan, 1987-
(author)
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Tailoring Pairwise Non-Orthogonal Multiple Access to the Requirements of Critical Cyber-Physical Systems
- 2021
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Licentiate thesis (other academic/artistic)abstract
- Within the context of Industry 4.0, many devices have become more intelligent and connected, leading to challenges on how to meet the stringent requirements on latency and reliability in networks of critical cyber-physical systems. In particular, timely channel access and high reliability are of essence to guarantee real-time deadlines. To this end, time-division multiple-access (TDMA) schemes are often used in industrial applications to get contention-free access to the channel. Using pairwise non-orthogonal multiple access (NOMA) on top of such an existing TDMA scheme has recently emerged as a promising solution. With pairwise NOMA, two nodes are served simultaneously using the same time-frequency resources but with different power levels. To separate the signals, successive interference cancellation is used at the receiver. In addition, by adjusting the power allocation, pairwise NOMA can easily switch to TDMA by assigning zero power to one user, if and when needed. Due to this flexibility, pairwise NOMA can be integrated into existing wireless networks and schedulers with improved performance as a result. In particular, if pairwise NOMA could be tailored to the requirements of systems of collaborating cyber-physical systems, it would be possible to enhance performance in terms of latency and reliability, while still providing timely channel access to critical users using TDMA. This is the scope of the thesis work.In order to evaluate the communication reliability for each user in the system as well as for the overall system, the individual outage probability (IOP) and the overall outage probability (OOP) are of essence, but have so far not been available for pairwise NOMA used on top of TDMA. In this thesis work, closed-form expressions for the IOP and the OOP of both uplink and downlink NOMA are derived – also in the presence of a mobile smart jammer. Using these performance metrics, insightful guidelines on the impact of some key parameters on the communication reliability such as power allocation, decoding order, node placements and so on are provided. It should be noted that the conclusions on node placement can be used for smart user pairing, but also for placement of access points (AP) or even mobile APs, using a UAV. Moreover, by formulating a non-cooperative game between a malicious smart mobile jammer and a friendly mobile AP serving two friendly sensor nodes simultaneously, Nash equilibrium points are obtained to reduce power consumption for the AP, while satisfying the communication reliability requirements. Using the derived expressions for OOP and IOP to select proper settings for pairwise NOMA, it is shown that NOMA can be tailored to ensure user fairness, provide timely channel access and high reliability, which is useful for enhancing performance of critical cyber-physical systems even in the presence of jamming.
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| 6. |
- Dao, Van-Lan, 1987-
(author)
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Using Outage Probability to Tailor Communication Protocols Suitable for Cyber-Physical Systems Operating in Confined Areas
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Some types of Cyber-Physical System (CPS) applications found within e.g., quarrying, mining, harbors, and construction sites, operate within confined areas. To guarantee that communications between nodes in such systems operate smoothly, the adopted wireless communication protocols must meet stringent requirements, even in the presence of interference and/or jamming. This thesis work targets finding performance metrics suitable for designing and evaluating wireless networks when used for CPSs in confined areas. Given the shortage of spectrum and the increased risk of cyber-attacks experienced lately, the protocols must also be adjusted to perform well when subject to strong interference and/or adversary jamming. Hence, to be useful in practice, metrics that can be recalculated during runtime are needed, such that they can be used not only to propose, select and tailor the communication protocols to fulfill the stringent CPS requirements but also to optimize their performance during runtime. The literature survey conducted in this thesis shows that a reliability metric in terms of thresholding the so-called outage probability is valuable for all design steps as well as for continuously optimizing the communications. However, since the outage probability is defined as the probability that an individual wireless link will experience outage, it does not address the reliability of the entire network within the confined area. The thesis work shows that it is possible to consider overall outage probabilities and evaluates the probability of outage for each individual packet from a specific source node to a final destination, including all possible links in the network. This way, it is possible to consider the overall outage for all packets within the network in the confined area. Outage probability measures are defined for different system models and closed-form expressions for the outage are derived for the Individual Outage Probability (IOP), the Overall Outage Probability (OOP), the IOP for one packet (IOPP), and the OOP for all packets (OOPP), with and without the presence of attackers and/or strong interference. These reliability metrics can be adopted to analyze the effects of a wide range of parameters such as power allocation, node positions, the use of relay nodes or retransmissions, etc. on the individual link, individual source packet, and overall network reliability. The analysis thereby makes it possible to provide a set of general guidelines for tailoring the protocols and enhance the communication reliability of all legitimate nodes in the CPS. Having the closed-form expressions readily available also enables recalculating and adjusting parameters faster in order to find the best solution to improve the communication reliability during runtime. The thesis work demonstrates how outage probability can be used to enhance system performance in several example scenarios, including a multiple access scheme, pairwise Non-Orthogonal Multiple Access (NOMA), mobile access points and/or relay nodes. The outage analysis can thereby be applied to an existing CPS application to enhance reliability, robustness, and flexibility while maintaining a low delay.
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| 7. |
- Duong, Quang Trung, et al.
(author)
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On the Performance of Two-Way Amplify-and-Forward Relay Networks
- 2009
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In: IEICE transactions on communications. - : IEICE. - 0916-8516 .- 1745-1345. ; E92-B:12, s. 3957-3959
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Journal article (peer-reviewed)abstract
- The performance of two-way amplify-and-forward (AF) relay networks is presented. In particular, we derive exact closed-form expressions for symbol error rate (SER), average sum-rate, and outage probability of two-way AF relay systems in independent but not identically distributed (i.n.i.d.) Rayleigh fading channels. Our analysis is validated by a comparison against the results of Monte-Carlo simulations.
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| 8. |
- Hoang, Le-Nam, 1984-, et al.
(author)
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A Simple Relaying Scheme to Guarantee Timeliness and Reliability in Wireless Networks
- 2015
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Other publication (other academic/artistic)abstract
- Many emerging applications based on wireless networks involves distributed control. This implies high requirements on reliability, but also on maximum delay and sometimes jitter. The total delay depends on the packet error rate and the time until channel access is granted. With e.g., TDMA, channel access is upper-bounded and the jitter zero. To reduce the packet error rate given a certain deadline (a set of TDMA time-slots), we propose a simple relaying scheme, including a full analysis of its resulting error probability and delay. Numerical results show that the proposed relaying strategy significantly improves reliability given a certain message deadline.
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| 9. |
- Hoang, Le-Nam, 1984-, et al.
(author)
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Low Complexity Algorithm for Efficient Relay Assignment in Unicast/Broadcast Wireless Networks
- 2017
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In: 2017 IEEE 85th Vehicular Technology Conference (VTC Spring). - : IEEE. - 9781509059324 - 9781509059331 ; June
-
Conference paper (peer-reviewed)abstract
- Using relayers in wireless networks enables higher throughput, increased reliability or reduced delay. However, when building networks using commercially available hardware, concurrent transmissions by multiple relayers are generally not possible. Instead one specific relayer needs to be assigned for each transmission instant. If the decision regarding which relayer to assign, i.e., which relayer that has the best opportunity to successfully deliver the packet, can be taken online, just before the transmission is to take place, much can be gained. This is particularly the case in mobile networks, as a frequently changing network topology considerably affects the choice of a suitable relayer. To this end, this paper addresses the problem of online relay assignment by developing a low-complexity algorithm highly likely to find the optimal combination of relaying nodes that minimizes the resulting error probability at the targeted receiver(s) using a mix of simulated annealing and ant colony algorithms, such that relay assignments can be made online also in large networks. The algorithm differs from existing works in that it considers both unicast as well as broadcast and assumes that all nodes can overhear each other, as opposed to separating source nodes, relay nodes and destination nodes into three disjoint sets, which is generally not the case in most wireless networks.
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| 10. |
- Hoang, Le-Nam, et al.
(author)
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Relay Grouping to Guarantee Timeliness and Reliability in Wireless Networks
- 2019
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In: IEEE Communications Letters. - Piscataway : Institute of Electrical and Electronics Engineers Inc.. - 1089-7798 .- 1558-2558. ; 23:9, s. 1661-1664
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Journal article (peer-reviewed)abstract
- Relaying can increase reliability, range, or throughput. In many cyber-physical systems (CPS), relaying is used to maximize reliability before a given deadline. Since concurrent transmissions are not supported by most CPS, time-division multiple access (TDMA) is typically used. However, a major drawback of relaying in TDMA is that pre-allocated time-slots are wasted if their respective transmitters do not have any correctly received packet to relay. Therefore, in this letter, we propose a novel relay grouping scheme to overcome this drawback. Numerical results show that the proposed scheme significantly enhances the reliability while guaranteeing the deadline for each message.
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