| 1. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Low-Latency and Secure Computation Offloading Assisted by Hybrid Relay-Reflecting Intelligent Surface
- 2021
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Ingår i: International Conference on Advanced Technologies for Communications. - 2162-1020 .- 2162-1039. ; 2021-October, s. 306-311
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Konferensbidrag (refereegranskat)abstract
- Recently, the hybrid relay-reflecting intelligent surface (HRRIS) has been introduced as a spectral-and energy-efficient architecture to assist wireless communication systems. In the HRRIS, a single or few active relay elements are deployed along with a large number of passive reflecting elements, allowing it to not only reflect but also amplify the incident signals. In this work, we investigate the potential of the HRRIS in aiding the computation offloading in a single-user mobile edge computing system. The objective is to minimize the offloading latency while ensuring the secrecy of user data against a malicious eavesdropper. We develop efficient solutions to this latency minimization problem based on alternating optimization. Through numerical results, we show that the deployment of the HRRIS can result in a considerable reduction in latency. Furthermore, the latency reduction gain offered by the HRRIS is much more significant than that of the conventional reconfigurable intelligent surface (RIS).
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| 2. |
- Duong, Ngoc Son, et al.
(författare)
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Sparse Bayesian Learning with Atom Refinement for mmWave MIMO Channel Estimation
- 2023
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Ingår i: IEEE Workshop on Statistical Signal Processing Proceedings. ; 2023-July, s. 155-159
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Konferensbidrag (refereegranskat)abstract
- In this paper, we introduce a novel estimation method for the downlink millimeter-wave (mmWave) multiple-input multiple-output (MIMO) channel. The proposed method is able to determine the angles, time delays, and gains of the multi-path components by using the spatially sparse nature of mmWave channels. We first use on-grid sparse Bayesian learning (SBL) to coarsely estimate the channel parameters in the beamspace domain. We then develop a refinement method based on Newton-Raphson and Least Square-based atomic tuning to generate a mismatch-free basis. Finally, we finely reconstruct the channel by SBL using the basis found in the previous step. Simulation results show that the proposed channel estimation method outperforms the traditional ones in terms of mean square error and algorithmic complexity.
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| 3. |
- Gur, Gurkan, et al.
(författare)
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Integration of ICN and MEC in 5G and Beyond Networks: Mutual Benefits, Use Cases, Challenges, Standardization, and Future Research
- 2022
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Ingår i: IEEE Open Journal of the Communications Society. - 2644-125X. ; 3, s. 1382-1412
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Tidskriftsartikel (refereegranskat)abstract
- Multi-access Edge Computing (MEC) is a novel edge computing paradigm that moves cloud-based processing and storage capabilities closer to the mobile users by implementing server resources in the access nodes. MEC helps fulfill the stringent requirements of 5G and beyond networks to offer anytime-anywhere connectivity for many devices with ultra-low delay and huge bandwidths. Information-Centric Networking (ICN) is another prominent network technology that builds on a content-centric network architecture to overcome host-centric routing/operation shortcomings and to realize efficient pervasive and ubiquitous networking. It is envisaged to be employed in Future Internet including Beyond 5G (B5G) networks. The consolidation of ICN with MEC technology offers new opportunities to realize that vision and serve advanced use cases. However, various integration challenges are yet to be addressed to enable the wide-scale co-deployment of ICN with MEC in future networks. In this paper, we discuss and elaborate on ICN MEC integration to provide a comprehensive survey with a forward-looking perspective for Beyond 5G networks. In that regard, we deduce lessons learned from related works (for both 5G and Beyond 5G networks). We present ongoing standardization activities to highlight practical implications of such efforts. Moreover, we render key B5G use cases and highlight the role for ICN MEC integration for addressing their requirements. Finally, we layout research challenges and identify potential research directions. For this last contribution, we also provide a mapping of the latter to ICN integration challenges and use cases.
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| 4. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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A Generalized Gaussian Model for Wireless Communications
- 2021
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Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2021-July, s. 3237-3242
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Konferensbidrag (refereegranskat)abstract
- We propose a class of parametric channel models that we call generalized Gaussian model (GGM). In particular, given the input, the output is Gaussian with both mean and covariance depending on the input. More general than the conventionallinear model, the GGM can capture nonlinearities and self-interference present in more and more wireless communication systems. We focus on three key problems. First, we propose a data-driven model identification algorithm that uses training data to fit the underlying channel with a GGM. This is a generalization of the conventional channel estimation procedure. Second, for an identified GGM, we investigate the receiver design problem and propose several detection metrics. Third, we are interested in the capacity bounds of the GGM. Both the mismatched lower bound and duality upper bound are proposed. Finally, we apply the GGM to fit the multiple-input multiple-output phase-noise channel. Numerical results show the near optimality of the model identification and detection algorithms.
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| 5. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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A Riemannian Metric for Noncoherent Constellation Design and Its Application to Multiple Access Channel
- 2021
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Ingår i: WSA 2021 - 25th International ITG Workshop on Smart Antennas. ; , s. 451-456
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Konferensbidrag (refereegranskat)abstract
- We extend the study of the joint constellation design problem for noncoherent multiple-input multiple-output multiple-access channels in Rayleigh block fading. First, we derive the pairwise error probability (PEP) exponent of the noncoherent maximum-likelihood detector to within a multiplicative factor of two. In particular, the lower bound of this exponent is obtained from a Chernoff upper bound of the error probability. Then, we show that the PEP exponent scales linearly with the Riemannian distance between the shifted Gram matrices of the symbols. This gives a geometric interpretation for our proposed metrics: a pair of joint symbols achieves a low PEP if the corresponding shifted Gram matrices are well separated, i.e., joined by a long geodesic, in the manifold of Hermitian positive definite matrices. Finally, we run numerical results to show that our metrics are meaningful for joint constellation design and evaluation, and result in constellations that outperform the constellations optimized with existing metrics and a pilot-based scheme.
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| 6. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Age of Information in Prioritized Random Access
- 2021
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Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. - 9781665458283 ; 2021-October
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Konferensbidrag (refereegranskat)abstract
- Age of information (AoI) is a performance metric that captures the freshness of status updates. While AoI has been studied thoroughly for point-to-point links, the impact of modern random-access protocols on this metric is still unclear. In this paper, we extend the recent results by Munari to prioritized random access where devices are divided into different classes according to different AoI requirements. We consider the irregular repetition slotted ALOHA protocol and analyze the AoI evolution by means of a Markovian analysis following similar lines as in Munari (2021). We aim to design the protocol to satisfy the AoI requirements for each class while minimizing the power consumption. To this end, we optimize the update probability and the degree distributions of each class, such that the probability that their AoI exceeds a given threshold lies below a given target and the average number of transmitted packets is minimized.
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| 7. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Age of Information in Slotted ALOHA With Energy Harvesting
- 2023
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Ingår i: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. ; , s. 3579-3584
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Konferensbidrag (refereegranskat)abstract
- We examine the age of information (AoI) of a status update system that incorporates energy harvesting and uses the slotted ALOHA protocol. We derive analytically the average AoI and the probability that the AoI exceeds a given threshold. Via numerical results, we investigate two strategies to minimize the age of information (AoI): transmitting a new update whenever possible to exploit every chance to reduce the AoI, and transmitting only when sufficient energy is available to increase the chance of successful delivery. The two strategies are beneficial for low and high update generation rates, respectively. However, an optimized approach that balances the two strategies outperforms them significantly in terms of both AoI and throughput.
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| 8. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Irregular Repetition Slotted ALOHA Over the Binary Adder Channel
- 2023
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Ingår i: IEEE International Conference on Communications. - 1550-3607. ; 2023-May, s. 5346-5351
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Konferensbidrag (refereegranskat)abstract
- We propose an irregular repetition slotted ALOHA (IRSA) based random-access protocol for the binary adder channel (BAC). The BAC captures important physical-layer concepts, such as packet generation, per-slot decoding, and information rate, which are neglected in the commonly considered collision channel model. We divide a frame into slots and let users generate a packet, to be transmitted over a slot, from a given codebook. In a state-of-the-art scheme proposed by Paolini et al. (2022), the codebook is constructed as the parity-check matrix of a BCH code. Here, we construct the codebook from independent and identically distributed binary symbols to obtain a random-coding achievability bound. Our per-slot decoder progressively discards incompatible codewords from a list of candidate codewords, and can be improved by shrinking this list across iterations. In a regime of practical interests, our scheme can resolve more colliding users in a slot and thus achieves a higher average sum rate than the scheme in Paolini et al. (2022).
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| 9. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Joint Constellation Design for Noncoherent MIMO Multiple-Access Channels
- 2022
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 68:11, s. 7281-7305
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Tidskriftsartikel (refereegranskat)abstract
- We consider the joint constellation design problem for the noncoherent multiple-input multiple-output multiple-access channel (MAC). By analyzing the noncoherent maximum-likelihood detection error, we propose novel design criteria so as to minimize the error probability. As a baseline approach, we adapt several existing design criteria for the point-to-point channel to the MAC. Furthermore, we propose new design criteria. Our first proposed design metric is the dominating term in nonasymptotic lower and upper bounds on the pairwise error probability exponent. We give a geometric interpretation of the bound using Riemannian distance in the manifold of Hermitian positive definite matrices. From an analysis of this metric at high signal-to-noise ratio, we obtain further simplified metrics. For any given set of constellation sizes, the proposed metrics can be optimized over the set of constellation symbols. Motivated by the simplified metric, we propose a simple constellation construction consisting in partitioning a single-user constellation. We also provide a generalization of our previously proposed construction based on precoding individual constellations of lower dimensions. For a fixed joint constellation, the design metrics can be further optimized over the per-user transmit power, especially when the users transmit at different rates. Considering unitary space-time modulation, we investigate the option of building each individual constellation as a set of truncated unitary matrices scaled by the respective transmit power. Numerical results show that our proposed metrics are meaningful, and can be used as objectives to generate constellations through numerical optimization that perform better, for the same transmission rate and power constraint, than a common pilot-based scheme and the constellations optimized with existing metrics.
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| 10. |
- Ngo, Khac-Hoang, 1992, et al.
(författare)
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Massive Uncoordinated Access with Random User Activity
- 2021
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Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2021-July, s. 3014-3019
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Konferensbidrag (refereegranskat)abstract
- We extend the seminal work by Polyanskiy (2017) on massive uncoordinated access to the case where the number of active users is random and unknown a priori. We define a random-access code accounting for both misdetection (MD) and false-alarm (FA), and derive a random-coding achievability bound for the Gaussian multiple access channel. Our bound captures the fundamental trade-off between MD and FA probabilities. It suggests that lack of knowledge of the number of active users entails a small penalty in power efficiency. For a typical scenario, to achieve both MD and FA probabilities below 0.1, the required energy per bit predicted by our bound is 0.5-0.7 dB higher than that predicted by the bound in Polyanskiy (2017) for a known number of active users. Taking both MD and FA into account, we use our bound to benchmark the energy efficiency of some recently proposed massive random access schemes.
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