| 1. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Huang, Yongming, et al.
(författare)
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Distributed Multicell Beamforming Design Approaching Pareto Boundary with Max-Min Fairness
- 2012
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276 .- 1558-2248. ; 11:8, s. 2921-2933
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses coordinated downlink beamforming optimization in multicell time division duplex (TDD) systems where a small number of parameters are exchanged between cells but with no data sharing. With the goal to reach the point on the Pareto boundary with max-min rate fairness, we first develop a two-step centralized optimization algorithm to design the joint beamforming vectors. This algorithm can achieve a further sum-rate improvement over the max-min optimal performance, and is shown to guarantee max-min Pareto optimality for scenarios with two base stations (BSs) each serving a single user. To realize a distributed solution with limited intercell communication, we then propose an iterative algorithm by exploiting an approximate uplink-downlink duality, in which only a small number of positive scalars are shared between cells in each iteration. Simulation results show that the proposed distributed solution achieves a fairness rate performance close to the centralized algorithm while it has a better sum-rate performance, and demonstrates a better tradeoff between sum-rate and fairness than the Nash Bargaining solution especially at high signal-to-noise ratio.
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| 3. |
- Huang, Yongming, et al.
(författare)
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Distributed Multicell Beamforming With Limited Intercell Coordination
- 2011
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 59:2, s. 728-738
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies distributed optimization schemes for multicell joint beamforming and power allocation in time-division-duplex (TDD) multicell downlink systems where only limited-capacity intercell information exchange is permitted. With an aim to maximize the worst-user signal-to-interference-and-noise ratio (SINR), we devise a hierarchical iterative algorithm to optimize downlink beamforming and intercell power allocation jointly in a distributed manner. The proposed scheme is proved to converge to the global optimum. For fast convergence and to reduce the burden of intercell parameter exchange, we further propose to exploit previous iterations adaptively. Results illustrate that the proposed scheme can achieve near-optimal performance even with a few iterations, hence providing a good tradeoff between performance and backhaul consumption. The performance under quantized parameter exchange is also examined.
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| 4. |
- Kapetanovic, Dzevdan, et al.
(författare)
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Detection of pilot contamination attack using random training and massive MIMO
- 2013
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Ingår i: Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on. ; , s. 13-18
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Konferensbidrag (refereegranskat)abstract
- Channel estimation attacks can degrade the performance of the legitimate system and facilitate eavesdropping. It is known that pilot contamination can alter the legitimate transmit precoder design and strengthen the quality of the received signal at the eavesdropper, without being detected. In this paper, we devise a technique which employs random pilots chosen from a known set of phase-shift keying (PSK) symbols to detect pilot contamination. The scheme only requires two training periods without any prior channel knowledge. Our analysis demonstrates that using the proposed technique in a massive MIMO system, the detection probability of pilot contamination attacks can be made arbitrarily close to 1. Simulation results reveal that the proposed technique can significantly increase the detection probability and is robust to noise power as well as the eavesdropper's power.
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| 5. |
- Liu, Shicong, et al.
(författare)
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LEO Satellite Constellations for 5G and Beyond : How Will They Reshape Vertical Domains?
- 2021
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Ingår i: IEEE Communications Magazine. - : Institute of Electrical and Electronics Engineers (IEEE). - 0163-6804 .- 1558-1896. ; 59:7, s. 30-36
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Tidskriftsartikel (refereegranskat)abstract
- The rapid development of communication technologies in the past decades has provided immense vertical opportunities for individuals and enterprises. However, conventional terrestrial cellular networks have unfortunately neglected the huge geographical digital divide, since high-bandwidth wireless coverage is concentrated in urban areas. To meet the goal of 'connecting the unconnected,' integrating low Earth orbit (LEO) satellites with the terrestrial cellular networks has been widely considered as a promising solution. In this article, we first introduce the development roadmap of LEO satellite constellations (SatCons), including early attempts in LEO satellites with the emerging LEO constellations. Further, we discuss the unique opportunities of employing LEO SatCons for the delivery of integrating 5G networks. Specifically, we present their key performance indicators, which offer important guidelines for the design of associated enabling techniques, and then discuss the potential impact of integrating LEO SatCons with typical 5G use cases, where we engrave our vision of various vertical domains reshaped by LEO SatCons. Technical challenges are finally provided to specify future research directions.
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| 6. |
- Liu, Yijia, et al.
(författare)
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Metasurface-Based Modulation With Enhanced Interference Resilience
- 2023
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 27:5, s. 1447-1451
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Tidskriftsartikel (refereegranskat)abstract
- Reconfigurable Intelligent Surfaces (RISs) have great potential for Internet of Things (IoT) applications due to their cost-effectiveness and energy-efficiency. However, under the application of RIS, current RIS systems cannot actively predict and avoid interference, as evolving interference signals can dynamically change their frequency bands. To address this issue, we develop a learning-based dynamic RIS spectrum access scheme to avoid interference and enhance wireless transmission reliability. An intelligent metasurface-based modulation (MM) is designed for generating and reflecting anti-interference radio-frequency signals. Specifically, a Dyna-Q algorithm is employed at the RIS controller to learn the frequency of interference signals, which is used to determine the frequency of the carrier signals. Experiments are conducted on the proposed RIS demo system to evaluate its anti-interference capability, and the results show that our scheme leads to an increase of at least 50% in the system throughput. These numerical results demonstrate the effectiveness of proposed scheme.
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| 7. |
- Wang, Kewei, et al.
(författare)
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Reconfigurable Intelligent Surfaces Aided Energy Efficiency Maximization in Cell-Free Networks
- 2024
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Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 13:6, s. 1596-1600
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Tidskriftsartikel (refereegranskat)abstract
- As we move towards next-generation wireless networks, the need for sustainability through energy efficiency (EE) concepts becomes more important than ever. Meanwhile, technology enablers, such as beamforming and reconfigurable intelligent surfaces (RISs), if appropriately used in a synergetic manner, can deliver profound excellence in terms of EE. Motivated by this, in this letter, we introduce an EE maximization policy that accounts for the rate demands of the end-users in RIS-assisted cell-free networks. The policy aims at performing joint optimization of the transmit beamforming vectors and the RIS phase-shift matrices in order to maximize the EE. In this direction, we first formulate the corresponding optimization problem, which is non-convex. To solve it, we rely on advanced optimization methods such as quadratic and Lagrangian dual transforms. Numerical results highlight the superiority of the presented policy in comparison to baseline approaches and reveal the most impactful network parameters.
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| 8. |
- Wang, Kewei, et al.
(författare)
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Transmit/Passive Beamforming Design for Multi-IRS Assisted Cell-Free MIMO Networks
- 2023
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Ingår i: IEEE Systems Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-8184 .- 1937-9234. ; 17:4, s. 6282-6291
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Tidskriftsartikel (refereegranskat)abstract
- For beyond fifth-generation and sixth-generation communication, intelligent reflecting surface (IRS)/reconfigurable intelligent surface, and cell-free networks have been proposed as revolutionary technologies, which could significantly improve the connection quality and coverage to meet future communication demands for extremely massive connectivity and high reliability. In this article, a transmit/passive beamforming strategy for multi-IRS assisted cell-free multi-input-multi-output network is proposed to maximize the weighted sum-rate (WSR). Specifically, for passive beamforming of IRS, an elementwise block coordinate descent framework is applied to efficiently solve the unit-modulus constraints and reduce computation complexity greatly. Note that, every variable in our proposed algorithm can be updated with closed-form solutions and our algorithm can be applied with distributed implementation. Both analytical and simulation results demonstrate that, while guaranteeing superiority in WSR performance and information interaction cost, the proposed scheme outperforms the benchmark algorithms with closed-form solutions significantly in terms of complexity cost.
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| 9. |
- Wang, Lifeng, et al.
(författare)
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Massive MIMO in Spectrum Sharing Networks: Achievable Rate and Power Efficiency
- 2017
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Ingår i: IEEE Systems Journal. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1932-8184 .- 1937-9234. ; 11:1, s. 20-31
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Tidskriftsartikel (refereegranskat)abstract
- Massive multiple input multiple output (MIMO) is one of the key technologies for fifth generation and can substantially improve energy and spectrum efficiencies. This paper explores the potential benefits of massive MIMO in spectrum sharing networks. We consider a multiuser MIMO primary network, with N-P-antenna primary base station (PBS) andK singleantenna primary users (PUs), and a multiple-input-single-output secondary network, with N-S-antenna secondary base station and a single-antenna secondary user. Using the proposed model, we derive a tight closed-form expression for the lower bound on the average achievable rate, which is applicable to arbitrary system parameters. By performing large-system analysis, we examine the impact of large number of PBS antennas and large number of PUs on the secondary network. It is shown that, when N-P and K grow large, N-S must be proportional to lnK or larger, to enable successful secondary transmission. In addition, we examine the impact of imperfect channel state information on the secondary network. It is shown that the detrimental effect of channel estimation errors is significantly mitigated as N-S grows large.
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| 10. |
- Zheng, Gan, et al.
(författare)
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Collaborative-Relay Beamforming with Perfect CSI : Optimum and Distributed Implementation
- 2009
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Ingår i: IEEE Signal Processing Letters. - : IEEE. - 1070-9908 .- 1558-2361. ; 16:4, s. 257-260
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Tidskriftsartikel (refereegranskat)abstract
- This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI) in a flat-fading channel. In particular, we optimize the relay weights jointly to maximize the received signal-to-noise ratio (SNR) at the destination terminal with both individual and total power constraints at the relays. We show that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system. Another main contribution of this letter is a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis.
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