| 1. |
- Xu, Yuxin, et al.
(författare)
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Cross-layer static resource provisioning for dynamic traffic in flexible grid optical networks
- 2021
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Ingår i: Journal of Optical Communications and Networking. - 1943-0620 .- 1943-0639. ; 13:3, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Flexible grid networks need rigorous resource planning to avoid network over-dimensioning and resource over-provisioning. The network must provision the hardware and spectrum resources statically, even for dynamic random bandwidth demands, due to the infrastructure of flexible grid networks, hardware limitations, and reconfiguration speed of the control plane. We propose a flexible online–offline probabilistic (FOOP) algorithm for the static spectrum assignment of random bandwidth demands. The FOOP algorithm considers the probabilistic nature of random bandwidth demands and balances hardware and control plane pressures with spectrum assignment efficiency. The FOOP algorithm uses the probabilistic spectrum Gaussian noise (PSGN) model to estimate the physical-layer impairment (PLI) for random bandwidth traffic. Compared to a benchmark spectrum assignment algorithm and a widely applied PLI estimation model, the proposed FOOP algorithm using the PSGN model saves up to 49% of network resources.
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| 2. |
- Agrell, Erik, 1965, et al.
(författare)
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Glued lattices are better quantizers than K 12
- 2024
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- 40 years ago, Conway and Sloane proposed using the highly symmetrical Coxeter–Todd lattice K 12 for quantization, and estimated its second moment. Since then, all published lists identify K 12 as the best 12-dimensional lattice quantizer. Surprisingly, K 12 is not optimal: we construct two new 12-dimensional lattices with lower normalized second moments. The new lattices are obtained by gluing together products of two 6-dimensional lattices.
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| 3. |
- Agrell, Erik, 1965
(författare)
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Kryptovalutor – energiförbrukning och miljöeffekter
- 2023
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Ingår i: En samhällsvetenskaplig introduktion till bitcoin och kryptovalutor.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Detta kapitel fokuserar på bitcoins elförbrukning och även, i ett bredare perspektiv, annan miljöpåverkan. Efter en kort inledning i avsnitt 4.1 redovisas i avsnitt 4.2 några försök att uppskatta hur stor elförbrukningen egentligen är, och vilka källor till osäkerhet som finns i sådana uppskattningar. Motsvarande uppskattning av klimatskadliga utsläpp redovisas i avsnitt 4.3. Siffrorna sätts i perspektiv med några jämförelser i avsnitt 4.4. Utvecklingen över tid illustreras i avsnitt 4.5 och därmed kopplingen till bitcoinpriset. Miljöfrågan breddas till ett livscykelperspektiv i avsnitt 4.6, där produktion och skrotning av den specialtillverkade elektronik som används i bitcoinfabrikerna diskuteras. I avsnitt 4.7 ställs sedan den naturliga frågan: Vad finns det för alternativ? Kapitlet avslutas med några övergripande reflektioner i avsnitt 4.8.
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| 4. |
- Agrell, Erik, 1965, et al.
(författare)
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On the Best Lattice Quantizers
- 2023
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 69:12, s. 7650-7658
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Tidskriftsartikel (refereegranskat)abstract
- A lattice quantizer approximates an arbitrary real-valued source vector with a vector taken from a specific discrete lattice. The quantization error is the difference between the source vector and the lattice vector. In a classic 1996 paper, Zamir and Feder show that the globally optimal lattice quantizer (which minimizes the mean square error) has white quantization error: for a uniformly distributed source, the covariance of the error is the identity matrix, multiplied by a positive real factor. We generalize the theorem, showing that the same property holds (i) for any lattice whose mean square error cannot be decreased by a small perturbation of the generator matrix, and (ii) for an optimal product of lattices that are themselves locally optimal in the sense of (i). We derive an upper bound on the normalized second moment (NSM) of the optimal lattice in any dimension, by proving that any lower- or upper-triangular modification to the generator matrix of a product lattice reduces the NSM. Using these tools and employing the best currently known lattice quantizers to build product lattices, we construct improved lattice quantizers in dimensions 13 to 15, 17 to 23, and 25 to 48. In some dimensions, these are the first reported lattices with normalized second moments below the best known upper bound.
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| 5. |
- Agrell, Erik, 1965, et al.
(författare)
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Performance Prediction Recipes for Optical Links
- 2021
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 33:18, s. 1034-1037
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Tidskriftsartikel (refereegranskat)abstract
- Although forward error-correction (FEC) coding is an essential part of modern fiber-optic communication systems, it is impractical to implement and evaluate FEC in transmission experiments and simulations. Therefore, it is desirable to accurately predict the end-to-end link performance including FEC from transmission data recorded without FEC. In this tutorial, we provide ready-to-implement “recipes” for such prediction techniques, which apply to arbitrary channels and require no knowledge of information or coding theory. The appropriate choice of recipe depends on properties of the FEC encoder and decoder. The covered metrics include bit error rate, symbol error rate, achievable information rate, and asymptotic information, in all cases computed using a mismatched receiver. Supplementary software implementations are available.
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| 6. |
- Alfredsson, Arni, 1989, et al.
(författare)
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Optimization of Transmitter-Side Signal Rotations in the Presence of Laser Phase Noise
- 2020
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 38:15, s. 3850-3858
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Tidskriftsartikel (refereegranskat)abstract
- The effects of transmitter-side multidimensional signal rotations on the performance of multichannel optical transmission are studied in the presence of laser phase noise. In particular, the laser phase noise is assumed to be uncorrelated between channels. To carry out this study, a simple multichannel laser-phase-noise model that has been experimentally validated for weakly-coupled multicore-fiber transmission is considered. As the considered rotation scheme is intended to work in conjunction with receiver-side carrier phase estimation (CPE), the model is modified to further assume that imperfect CPE has taken place, leaving residual phase noise in the processed signal. Based on this model, two receiver structures are derived and used to numerically optimize transmitter-side signal rotations through Monte Carlo simulations. For reasonable amounts of residual phase noise, rotations based on Hadamard matrices are found to be near-optimal for transmission of four-dimensional signals. Furthermore, Hadamard rotations can be performed for any dimension that is a power of two. By exploiting this property, an increase of up to 0.25 bit per complex symbol in an achievable information rate is observed for transmission of higher-order constellations.
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| 7. |
- Alfredsson, Arni, 1989, et al.
(författare)
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Pilot Distributions for Joint-Channel Carrier-Phase Estimation in Multichannel Optical Communications
- 2020
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 38:17, s. 4656-4663
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Tidskriftsartikel (refereegranskat)abstract
- Joint-channel carrier-phase estimation can improve the performance of multichannel optical communication systems. In the case of pilot-aided estimation, the pilots are distributed over a two-dimensional channel-time symbol block that is transmitted through multiple channels. However, suboptimal pilot distributions reduce the effectiveness of the carrier-phase estimation and thus result in unnecessary pilot overhead, which reduces the overall information rate of the system. It is shown that placing pilots identically in all channels is suboptimal in general. By instead optimizing the pilot distribution, the mean squared error of the phase-noise estimates can be decreased by over 90% in some cases. Moreover, it is shown that the achievable information rate can be increased by up to 0.05, 0.16, and 0.41 bits per complex symbol for dual-polarization 20 GBd transmission of 64-ary, 256-ary, and 1024-ary quadrature amplitude modulation over 20 four-dimensional channels, respectively, assuming a total laser linewidth of 200 kHz.
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| 8. |
- Allen, Bruce, et al.
(författare)
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The Optimal Lattice Quantizer in Nine Dimensions
- 2021
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804 .- 1521-3889. ; 533:12
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Tidskriftsartikel (refereegranskat)abstract
- The optimal lattice quantizer is the lattice that minimizes the (dimensionless) second moment G. In dimensions 1 to 3, it has been proven that the optimal lattice quantizer is one of the classical lattices, and there is good numerical evidence for this in dimensions 4 to 8. In contrast, in 9 dimensions, more than two decades ago, the same numerical studies found the smallest known value of G for a non-classical lattice. The structure and properties of this conjectured optimal lattice quantizer depend upon a real parameter (Formula presented.), whose value was only known approximately. Here, a full description of this one-parameter family of lattices and their Voronoi cells is given, and their (scalar and tensor) second moments are calculated analytically as a function of a. The value of a which minimizes G is an algebraic number, defined by the root of a 9th order polynomial, with (Formula presented.). For this value of a, the covariance matrix (second moment tensor) is proportional to the identity, consistent with a theorem of Zamir and Feder for optimal quantizers. The structure of the Voronoi cell depends upon a, and undergoes phase transitions at (Formula presented.), 1, and 2, where its geometry changes abruptly. At each transition, the analytic formula for the second moment changes in a very simple way. The methods can be used for arbitrary one-parameter families of laminated lattices, and may thus provide a useful tool to identify optimal quantizers in other dimensions as well.
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| 9. |
- Bhar, Chayan, 1988, et al.
(författare)
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Energy-and Bandwidth-Efficient, QoS-Aware Edge Caching in Fog-Enhanced Radio Access Networks
- 2021
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 39:9, s. 2762-2771
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Tidskriftsartikel (refereegranskat)abstract
- The emerging video services are associated with stringent quality-of-service (QoS) requirements and place high bandwidth demands on the core networks. Edge caching can facilitate the stringent QoS demands while easing the bandwidth requirement from core networks. However, such schemes require on-field caching equipment, in which energy consumption is a function of cache utilization. Designing opportunistic caching strategies for energy efficiency is therefore essential in such schemes. This paper studies the possibilities for achieving high energy efficiency, QoS, and low bandwidth consumption from the core network, in an optically fronthauled fog-enhanced radio access network that implements edge caching. An analytical model for such a network has been derived to measure latency, bandwidth consumption, and cache utilization. It is deduced from the results that low latency (high QoS) and bandwidth consumption can be ensured in such schemes while reducing the energy consumption by up to 93%. The derived model allows to design caching strategies for addressing the trade-off between energy efficiency, QoS, and bandwidth efficiency.
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| 10. |
- Bhar, Chayan, et al.
(författare)
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Resource-Efficient QoS-Aware Video Streaming Using UAV-Assisted Networks
- 2024
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Ingår i: IEEE Transactions on Cognitive Communications and Networking. - 2332-7731. ; 10:2, s. 649-659
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Tidskriftsartikel (refereegranskat)abstract
- Emerging video services are associated with stringent quality-of-service (QoS) and high data-rate requirements. Moreover, the presence of data-rate-hungry mobile users in future networks necessitate sophisticated design strategies. The deployment of unmanned aerial vehicle access point (UAP)-assisted networks (UANs) has been proposed to ensure high data-rates to mobile users. Moreover, UAPs can be equipped with energy-efficient caches to facilitate video delivery with stringent QoS. However, the mobility of users and UAPs may cause temporal variations in the QoS experienced by users. This paper conducts an extensive performance evaluation of a UAN, by studying the effect of user behavior, mobility of users and UAPs, and a temporal variation of video popularity on the QoS. The QoS is measured in terms of the delay experienced by the users. To that end, a time-dependent queueing model and its associated fluid approximation models are derived, which are illustrated to be reasonably accurate in an appropriate asymptotic regime. A detailed analysis of these models reveals that low delay, i.e., high QoS, can be ensured in UANs. Finally, a reinforcement-learning (RL) approach based on these models is utilized to minimize the number of deployed UAPs and the playout buffer size while guaranteeing a certain QoS.
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