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Sökning: WFRF:(Durisi Giuseppe 1977)

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1.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • Short-packet transmission
  • 2021
  • Ingår i: Information Theoretic Perspectives on 5G Systems and Beyond. - 9781108416474
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • 5G, a new generation of cellular technology under deployment worldwide, can provide about 100 times faster communications than current 4G technology. But a higher speed is not the sole differentiating factor: 5G is also more reliable, secure, and capable of ubiquitously connecting a massively large number of devices. Ultra-reliable, low-delay, omni-present 5G networks hold the promise of enabling a range of new applications, including self-driving cars, highly automatized industrial tasks, virtual reality gaming, as well as of providing the connectivity platform for the Internet of Things (IoT). Since its introduction in 1948, information theory has underpinned the mathematical foundations of communication systems, including 5G networks, and it will impact the design of cellular systems beyond 5G. The theoretical insights obtained by information theory point to the optimal system performance under a given model, offering strong guidelines and benchmarks for the design and validation of modern communication technologies. Information Theoretic Perspectives on 5G Systems and Beyond provides a comprehensive overview of the state-of-art information-theoretic approaches that led to realization of 5G. Three main areas are discussed, namely network architecture, coding and modulation, and network protocols. Examples of covered topics include cloud/fog radio access networks (a central component in future 6G (beyond 5G) cell-less structure), device-to-device communications, caching, energy harvesting, polar coding, Massive MIMO, short-packet transmission, NOMA,  5G protocols, interference management, content delivery, and cooperative and confidential communications. Information Theoretic Perspectives on 5G Systems and Beyond is the result of a grand effort by more than 40 experts in the field of information theory. It includes 19 chapters, offering a detailed introduction to advanced topics in information theory, and it took several years in making. We are extremely excited that the book is now available. We hope that it can serve as a tool for researchers and graduate students in the fields of information theory and wireless communications, as well as for practitioners in the telecommunications industry.
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2.
  • Dörpinghaus, Meik, 1977, et al. (författare)
  • Oversampling increases the pre-log of noncoherent Rayleigh fading channels
  • 2014
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 60:9, s. 5673-5681
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyze the capacity of a continuous-time, time- selective, Rayleigh block-fading channel in the high signal-to-noise ratio regime. The fading process is assumed stationary within each block and to change independently from block to block; further- more, its realizations are not known a priori to the transmitter and the receiver (noncoherent setting). A common approach to analyzing the capacity of this channel is to assume that the receiver performs matched filtering followed by sampling at symbol rate (symbol matched filtering). This yields a discrete-time channel in which each transmitted symbol corresponds to one output sample. Liang & Veeravalli (2004) showed that the capacity of this discrete- time channel grows logarithmically with the signal-to noise ratio (SNR), with a capacity pre-log equal to 1 − Q/N . Here, N is the number of symbols transmitted within one fading block, and Q is the rank of the covariance matrix of the discrete-time channel gains within each fading block. In this paper, we show that sym- bol matched filtering is not a capacity-achieving strategy for the underlying continuous-time channel. Specifically, we analyze the capacity pre-log of the discrete-time channel obtained by oversam- pling the continuous-time channel output, i.e., by sampling it faster than at symbol rate. We prove that by oversampling by a factor two one gets a capacity pre-log that is at least as large as 1 − 1/N . Since the capacity pre-log corresponding to symbol-rate sampling is 1−Q/N , our result implies indeed that symbol matched filtering is not capacity achieving at high SNR.
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3.
  • Rezazadeh, Arezou, 1987, et al. (författare)
  • Conditional Mutual Information-Based Generalization Bound for Meta Learning
  • 2021
  • Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2021-July, s. 1176-1181
  • Konferensbidrag (refereegranskat)abstract
    • Meta-learning optimizes an inductive bias—typically in the form of the hyperparameters of a base-learning algorithm—by observing data from a finite number of related tasks. This paper presents an information-theoretic bound on the generalization performance of any given meta-learner, which builds on the conditional mutual information (CMI) framework of Steinke and Zakynthinou (2020). In the proposed extension to meta-learning, the CMI bound involves a training meta-supersample obtained by first sampling 2N independent tasks from the task environment, and then drawing 2M independent training samples for each sampled task. The meta-training data fed to the meta-learner is modelled as being obtained by randomly selecting N tasks from the available 2N tasks and M training samples per task from the available 2M training samples per task. The resulting bound is explicit in two CMI terms, which measure the information that the meta-learner output and the base-learner output provide about which training data are selected, given the entire meta-supersample. Finally, we present a numerical example that illustrates the merits of the proposed bound in comparison to prior information-theoretic bounds for meta-learning
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4.
  • Yang, Wei, 1987, et al. (författare)
  • Finite-Blocklength Channel Coding Rate Under a Long-Term Power Constraint
  • 2014
  • Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. - 9781479951864 ; , s. 2067-2071
  • Konferensbidrag (refereegranskat)abstract
    • This paper investigates the maximal channel coding rate achievable at a given blocklength $n$ and error probability $\epsilon$, when the codewords are subject to a long-term (i.e., averaged-over-all-codeword) power constraint. The second-order term in the large-n expansion of the maximal channel coding rate is characterized both for AWGN channels and for quasi-static fading channels with perfect channel state information at the transmitter and the receiver. It is shown that in both cases the second-order term is proportional to $\sqrt{(\log n)/n}$.
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5.
  • Yang, Wei, 1987, et al. (författare)
  • Optimum Power Control at Finite Blocklength
  • 2015
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 61:9, s. 4598-4615
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper investigates the maximal channel coding rate achievable at a given blocklength $n$ and error probability $\epsilon$, when the codewords are subject to a long-term (i.e., averaged-over-all-codeword) power constraint. The second-order term in the large-$n$ expansion of the maximal channel coding rate is characterized both for additive white Gaussian noise (AWGN) channels and for quasi-static fading channels with perfect channel state information available at both the transmitter and the receiver. It is shown that in both cases the second-order term is proportional to $\sqrt{n^{-1}\ln n}$. For the quasi-static fading case, this second-order term is achieved by \emph{truncated channel inversion}, namely, by concatenating a dispersion-optimal code for an AWGN channel subject to a short-term power constraint, with a power controller that inverts the channel whenever the fading gain is above a certain threshold. Easy-to-evaluate approximations of the maximal channel coding rate are developed for both the AWGN and the quasi-static fading case.
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6.
  • Zetterberg, P., et al. (författare)
  • Initial multi-node and antenna transmitter and receiver architectures and schemes; Deliverable D5.1
  • 2016
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • This deliverable provides the initial concepts and solutions from the technical work related to multi-antenna and multi-node transceiver schemes in millimetre wave (denoted as 6-100GHz) spectrum. It also briefly presents the use cases on which the work will be based and categorises the solutions in terms of their applicability to access, backhaul and relay deployments. Another important contribution from this report is the modelling of the hardware impairments in millimetre wave transceivers and the analysis of their impact on system performance.
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7.
  • Aabel, Lise, et al. (författare)
  • A TDD Distributed MIMO Testbed Using a 1-bit Radio-Over-Fiber Fronthaul Architecture
  • 2024
  • Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; In Press
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the uplink and downlink of a time-division duplex distributed multiple-input multiple-output (D-MIMO) testbed, based on a 1-bit radio-over-fiber architecture, which is low cost and scalable. The proposed architecture involves a central unit (CU) that is equipped with 1-bit digital-to-analog and analog-to-digital converters, operating at 10 GS/s. The CU is connected to multiple single-antenna remote radio heads (RRHs) via optical fibers, over which a binary radio frequency (RF) waveform is transmitted. In the uplink, a binary RF waveform is generated at the RRHs by a comparator, whose inputs are the received RF signal and a suitably designed dither signal. In the downlink, a binary RF waveform is generated at the CU via bandpass sigma-delta modulation. Our measurement results show that low error-vector magnitude (EVM) can be achieved in both the uplink and the downlink, despite 1-bit sampling at the CU. Specifically, for point-to-point over-cable transmission between a single user equipment (UE) and a CU equipped with a single RRH, we report, for a 10-MBd signal using single-carrier (SC) 16 quadratic-amplitude modulation (QAM) modulation, an EVM of 3.3% in the downlink, and of 4.5% in the uplink. We then consider a CU connected to three RRHs serving over the air two UEs, and show that, after over-the-air reciprocity calibration, a downlink zero-forcing precoder designed on the basis of uplink channel estimates at the CU achieves an EVM of 6.4% and 10.9% at UE 1 and UE 2, respectively. Finally, we investigate the ability of the proposed architecture to support orthogonal frequency-division multiplexing (OFDM) waveforms, and its robustness against both in-band and out-of-band interference.
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8.
  • Aabel, Lise, 1992, et al. (författare)
  • Distributed Massive MIMO via all-Digital Radio Over Fiber
  • 2020
  • Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2020-November, s. 319-323
  • Konferensbidrag (refereegranskat)abstract
    • A crucial challenge in the implementation of distributed massive multiple-input multiple-output (MIMO) architectures is to provide phase coherence while, at the same time, limit the complexity of the remote-radio heads (RRHs), which is important for cost-efficient scalability. To address this challenge, we present in this paper a phase-coherent distributed MIMO architecture, based on off-the-shelf, low-cost components. In the proposed architecture, up- and down-conversion are carried out at the central unit (CU). The RRHs are connected to the CU by means of optical fibers carrying oversampled radio-frequency (RF) 1-bit signals. In the downlink, the 1-bit signal is generated via sigma-delta modulation. At the RRH, the RF signal is recovered from the 1-bit signal through a bandpass filter and a power amplifier, and then fed to an antenna. In the uplink, the 1-bit signal is generated by a comparator whose inputs are the low-noise-amplified received RF signal and a suitably designed dither signal. The performance of the proposed architecture is evaluated with satisfactory results both via simulation and measurements from a testbed.
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9.
  • Agrell, Erik, 1965, et al. (författare)
  • Capacity of a nonlinear optical channel with finite memory
  • 2014
  • Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 32:16, s. 2862-2876
  • Tidskriftsartikel (refereegranskat)abstract
    • The channel capacity of a nonlinear, dispersive fiber-optic link is revisited. To this end, the popular Gaussian noise (GN) model is extended with a parameter to account for the finite memory of realistic fiber channels. This finite-memory model is harder to analyze mathematically but, in contrast to previous models, it is valid also for nonstationary or heavy-tailed input signals. For uncoded transmission and standard modulation formats, the new model gives the same results as the regular GN model when the memory of the channel is about ten symbols or more. These results confirm previous results that the GN model is accurate for uncoded transmission. However, when coding is considered, the results obtained using the finite-memory model are very different from those obtained by previous models, even when the channel memory is large. In particular, the peaky behavior of the channel capacity, which has been reported for numerous nonlinear channel models, appears to be an artifact of applying models derived for independent input in a coded (i.e., dependent) scenario. © 1983-2012 IEEE.
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10.
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11.
  • Athley, F., et al. (författare)
  • Analysis of Massive MIMO with hardware impairments and different channel models
  • 2015
  • Ingår i: 9th European Conference on Antennas and Propagation, EuCAP 2015, Lisbon, Portugal, 13-17 May 2015. - 9788890701856
  • Konferensbidrag (refereegranskat)abstract
    • Massive Multiple-Input Multiple-Output (MIMO) is foreseen to be one of the main technology components in next generation cellular communications (5G). In this paper, fundamental limits on the performance of downlink massive MIMO systems are investigated by means of simulations and analytical analysis. Signal-to-noise-and-interference ratio (SINR) and sum rate for a single-cell scenario multi-user MIMO are analyzed for different array sizes, channel models, and precoding schemes. The impact of hardware impairments on performance is also investigated. Simple approximations are derived that show explicitly how the number of antennas, number of served users, transmit power, and magnitude of hardware impairments affect performance.
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12.
  • Atzeni, Italo, et al. (författare)
  • Low-Resolution Massive MIMO Under Hardware Power Consumption Constraints
  • 2021
  • Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. - 9781665458283
  • Konferensbidrag (refereegranskat)abstract
    • We consider a fully digital massive multipleinput multiple-output architecture with low-resolution analogto-digital/digital-to-analog converters (ADCs/DACs) at the base station (BS) and analyze the performance trade-off between the number of BS antennas, the resolution of the ADCs/DACs, and the bandwidth. Assuming a hardware power consumption constraint, we determine the relationship between these design parameters by using a realistic model for the power consumption of the ADCs/DACs and the radio frequency chains. Considering uplink pilot-aided channel estimation, we build on the Bussgang decomposition to derive tractable expressions for uplink and downlink ergodic achievable sum rates. Numerical results show that the ergodic performance is boosted when many BS antennas with very low resolution (i.e., 2 to 3 bits) are adopted in both the uplink and the downlink.
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13.
  • Balatsoukas-Stimming, Alexios, et al. (författare)
  • Neural-Network Optimized 1-bit Precoding for Massive MU-MIMO
  • 2019
  • Ingår i: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC. ; 2019-July
  • Konferensbidrag (refereegranskat)abstract
    • Base station (BS) architectures for massive multiuser (MU) multiple-input multiple-output (MIMO) wireless systems are equipped with hundreds of antennas to serve tens of users on the same time-frequency channel. The immense number of BS antennas incurs high system costs, power, and interconnect bandwidth. To circumvent these obstacles, sophisticated MU precoding algorithms that enable the use of 1-bit DACs have been proposed. Many of these precoders feature parameters that are, traditionally, tuned manually to optimize their performance. We propose to use deep-learning tools to automatically tune such 1-bit precoders. Specifically, we optimize the biConvex 1-bit PrecOding (C2PO) algorithm using neural networks. Compared to the original C2PO algorithm, our neural-network optimized (NNO-)C2PO achieves the same error-rate performance at 2× lower complexity. Moreover, by training NNO-C2PO for different channel models, we show that 1-bit precoding can be made robust to vastly changing propagation conditions.
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14.
  • Castaneda, Oscar, et al. (författare)
  • 1-bit Massive MU-MIMO Precoding in VLSI
  • 2017
  • Ingår i: IEEE Journal on Emerging and Selected Topics in Circuits and Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3365 .- 2156-3357. ; 7:4, s. 508-522
  • Tidskriftsartikel (refereegranskat)abstract
    • Massive multi-user (MU) multiple-input multiple-output (MIMO) will be a core technology in fifth-generation (5G) wireless systems as it offers significant improvements in spectral efficiency compared to existing multi-antenna technologies. The presence of hundreds of antenna elements at the base station (BS), however, results in excessively high hardware costs and power consumption, and requires high interconnect throughput between the baseband-processing unit and the radio unit. Massive MU-MIMO that uses low-resolution analog-to-digital and digital-toanalog converters (DACs) has the potential to address all these issues. In this paper, we focus on downlink precoding for massive MU-MIMO systems with 1-bit DACs at the BS. The objective is to design precoders that simultaneously mitigate MU interference and quantization artifacts. We propose two nonlinear 1-bit precoding algorithms and corresponding very large-scale integration (VLSI) designs. Our algorithms rely on biconvex relaxation, which enables the design of efficient 1-bit precoding algorithms that achieve superior error-rate performance compared with that of linear precoding algorithms followed by quantization. To showcase the efficacy of our algorithms, we design VLSI architectures that enable efficient 1-bit precoding for massive MU-MIMO systems, in which hundreds of antennas serve tens of user equipments. We present corresponding field-programmable gate array (FPGA) reference implementations to demonstrate that 1-bit precoding enables reliable and high-rate downlink data transmission in practical systems.
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15.
  • Castaneda, Oscar, et al. (författare)
  • Finite-alphabet MMSE equalization for all-digital massive MU-MIMO mmWave communications
  • 2020
  • Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 38:9, s. 2128 -2141
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose finite-alphabet equalization, a new paradigm that restricts the entries of the spatial equalization matrix to low-resolution numbers, enabling high-throughput, low-power, and low-cost hardware equalizers. To minimize the performance loss of this paradigm, we introduce FAME, short for finite-alphabet minimum mean-square error (MMSE) equalization, which is able to significantly outperform a naïve quantization of the linear MMSE matrix. We develop efficient algorithms to approximately solve the NP-hard FAME problem and showcase that near-optimal performance can be achieved with equalization coefficients quantized to only 1-3 bits for massive multi-user multiple-input multiple-output (MU-MIMO) millimeter-wave (mmWave) systems. We provide very-large scale integration (VLSI) results that demonstrate a reduction in equalization power and area by at least a factor of 3.9× and 5.8×, respectively.
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16.
  • Castaneda, Oscar, et al. (författare)
  • Finite-Alphabet Wiener Filter Precoding for mmWave Massive MU-MIMO Systems
  • 2019
  • Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; , s. 178-183
  • Konferensbidrag (refereegranskat)abstract
    • Power consumption of multi-user (MU) precoding is a major concern in all-digital massive MU multiple-input multiple-output (MIMO) base-stations with hundreds of antenna elements operating at millimeter-wave (mmWave) frequencies. We propose to replace part of the linear Wiener filter (WF) precoding matrix by a finite-alphabet WF precoding (FAWP) matrix, which enables the use of low-precision hardware that consumes low power and area. To minimize the performance loss of our approach, we present methods that efficiently compute FAWP matrices that best mimic the WF precoder. Our results show that FAWP matrices approach infinite-precision error-rate and error-vector magnitude performance with only 3-bit precoding weights, even when operating in realistic mmWave channels. Hence, FAWP is a promising approach to substantially reduce power consumption and silicon area in all-digital mmWave massive MU-MIMO systems.
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17.
  • Castañeda, Oscar, et al. (författare)
  • Hardware-Friendly Two-Stage Spatial Equalization for All-Digital mmWave Massive MU-MIMO
  • 2020
  • Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2020-November, s. 388-392
  • Konferensbidrag (refereegranskat)abstract
    • Next generation wireless communication systems are expected to combine millimeter-wave communication with massive multi-user multiple-input multiple-output technology. All-digital base-station implementations for such systems need to process high-dimensional data at extremely high rates, which results in excessively high power consumption. In this paper, we propose two-stage spatial equalizers that first reduce the problem dimension by means of a hardware-friendly, low-resolution linear transform followed by spatial equalization on a lower-dimensional signal. We consider adaptive and non-adaptive dimensionality reduction strategies and demonstrate that the proposed two-stage spatial equalizers are able to approach the performance of conventional linear spatial equalizers that directly operate on high-dimensional data, while offering the potential to reduce the power consumption of spatial equalization.
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18.
  • Castañeda, Oscar, et al. (författare)
  • High-Bandwidth Spatial Equalization for mmWave Massive MU-MIMO with Processing-in-Memory
  • 2020
  • Ingår i: IEEE Transactions on Circuits and Systems II: Express Briefs. - 1549-7747 .- 1558-3791. ; 67:5, s. 891-895
  • Tidskriftsartikel (refereegranskat)abstract
    • All-digital basestation (BS) architectures enable superior spectral efficiency compared to hybrid solutions in massive multi-user MIMO systems. However, supporting large bandwidths with all-digital architectures at mmWave frequencies is challenging as traditional baseband processing would result in excessively high power consumption and large silicon area. The recently-proposed concept of finite-alphabet equalization is able to address both of these issues by using equalization matrices that contain low-resolution entries to lower the power and complexity of high-throughput matrix-vector products in hardware. In this brief, we explore two different finite-alphabet equalization hardware implementations that tightly integrate the memory and processing elements: (i) a parallel array of multiply-accumulate (MAC) units and (ii) a bit-serial processing-in-memory (PIM) architecture. Our all-digital VLSI implementation results in 28nm CMOS show that the bit-serial PIM architecture reduces the area and power consumption up to a factor of 2× and 3×, respectively, when compared to a parallel MAC array that operates at the same throughput.
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19.
  • Castañeda, Oscar, et al. (författare)
  • Resolution-Adaptive All-Digital Spatial Equalization for mmWave Massive MU-MIMO
  • 2021
  • Ingår i: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC. ; , s. 386-390
  • Konferensbidrag (refereegranskat)abstract
    • All-digital basestation (BS) architectures for millimeter-wave (mmWave) massive multi-user multiple-input multiple-output (MU-MIMO), which equip each radio-frequency chain with dedicated data converters, have advantages in spectral efficiency, flexibility, and baseband-processing simplicity over hybrid analog-digital solutions. For all-digital architectures to be competitive with hybrid solutions in terms of power consumption, novel signal-processing methods and baseband architectures are necessary. In this paper, we demonstrate that adapting the resolution of the analog-to-digital converters (ADCs) and spatial equalizer of an all-digital system to the communication scenario (e.g., the number of users, modulation scheme, and propagation conditions) enables orders-of-magnitude power savings for realistic mmWave channels. For example, for a 256-BS-antenna 16-user system supporting 1 GHz bandwidth, a traditional baseline architecture designed for a 64-user worst-case scenario would consume 23 W in 28 nm CMOS for the ADC array and the spatial equalizer, whereas a resolution-adaptive architecture is able to reduce the power consumption by 6.7×.
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20.
  • Castañeda, Oscar, et al. (författare)
  • Soft-Output Finite Alphabet Equalization for mmWave Massive MIMO
  • 2020
  • Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. ; 2020-May, s. 1764-1767
  • Konferensbidrag (refereegranskat)abstract
    • Nxt-generation wireless systems are expected to combine millimeter-wave (mmWave) and massive multi-user multiple-input multiple-output (MU-MIMO) technologies to deliver high data-rates. These technologies require the basestations (BSs) to process high-dimensional data at extreme rates, which results in high power dissipation and system costs. Finite-alphabet equalization has been proposed recently to reduce the power consumption and silicon area of uplink spatial equalization circuitry at the BS by coarsely quantizing the equalization matrix. In this work, we improve upon finite-alphabet equalization by performing unbiased estimation and soft-output computation for coded systems. By simulating a massive MU-MIMO system that uses orthogonal frequency-division multiplexing and per-user convolutional coding, we show that soft-output finite-alphabet equalization delivers competitive error-rate performance using only 1 to 3 bits per entry of the equalization matrix, even for challenging mmWave channels.
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21.
  • Castaneda, Oscar, et al. (författare)
  • VLSI Design of a 3-bit Constant-Modulus Precoder for Massive MU-MIMO
  • 2018
  • Ingår i: Proceedings - IEEE International Symposium on Circuits and Systems. - 0271-4310.
  • Konferensbidrag (refereegranskat)abstract
    • Fifth-generation (5G) cellular systems will build on massive multi-user (MU) multiple-input multiple-output (MIMO) technology to attain high spectral efficiency. However, having hundreds of antennas and radio-frequency (RF) chains at the base station (BS) entails prohibitively high hardware costs and power consumption. This paper proposes a novel nonlinear precoding algorithm for the massive MU-MIMO downlink in which each RF chain contains an 8-phase (3-bit) constantmodulus transmitter, enabling the use of low-cost and powerefficient analog hardware. We present a high-throughput VLSI architecture and show implementation results on a Xilinx Virtex-7 FPGA. Compared to a recently-reported nonlinear precoder for BS designs that use two 1 -bit digital-to-analog converters per RF chain, our design enables up to 3:75 dB transmit power reduction at no more than a 2.7x increase in FPGA resources.
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22.
  • Coskun, Mustafa C., et al. (författare)
  • Efficient error-correcting codes in the short blocklength regime
  • 2019
  • Ingår i: Physical Communication. - : Elsevier BV. - 1874-4907. ; 34, s. 66-79
  • Tidskriftsartikel (refereegranskat)abstract
    • The design of block codes for short information blocks (e.g., a thousand or less information bits) is an open research problem that is gaining relevance thanks to emerging applications in wireless communication networks. In this paper, we review some of the most promising code constructions targeting the short block regime, and we compare them with both finite-length performance bounds and classical error-correction coding schemes. The work addresses the use of both binary and high-order modulations over the additive white Gaussian noise channel. We will illustrate how to effectively approach the theoretical bounds with various performance versus decoding complexity tradeoffs.
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23.
  • Coskun, Mustafa Cemil, et al. (författare)
  • Low-Complexity Joint Channel Estimation and List Decoding of Short Codes
  • 2019
  • Ingår i: SCC 2019 - 12th International ITG Conference on Systems, Communications and Coding. - 9783800748624
  • Konferensbidrag (refereegranskat)abstract
    • A pilot-assisted transmission (PAT) scheme is proposed for short blocklengths, where the pilots are used only to derive an initial channel estimate for the list construction step. The final decision of the message is obtained by applying a non-coherent decoding metric to the codewords composing the list. This allows one to use very few pilots, thus reducing the channel estimation overhead. The method is applied to anordered statistics decoder for communication over a Rayleigh block-fading channel. Gains of up to 1.2 dB as compared to traditional PAT schemes are demonstrated for short codes with QPSK signaling. The approach can be generalized to other list decoders, e.g., to list decoding of polar codes.
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24.
  • Devassy, Rahul, 1985, et al. (författare)
  • Delay and Peak-Age Violation Probability in Short-Packet Transmissions
  • 2018
  • Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2018-June, s. 2471-2475
  • Konferensbidrag (refereegranskat)abstract
    • This paper investigates the distribution of delay and peak age of information in a communication system where packets, generated according to an independent and identically distributed Bernoulli process, are placed in a single-server queue with first-come first-served discipline and transmitted over an additive white Gaussian noise (AWGN) channel. When a packet is correctly decoded, the sender receives an instantaneous error-free positive acknowledgment, upon which it removes the packet from the buffer. In the case of negative acknowledgment, the packet is retransmitted. By leveraging finite-blocklength results for the AWGN channel, we characterize the delay violation and the peak-age violation probability without resorting to approximations based on large deviation theory as in previous literature. Our analysis reveals that there exists an optimum blocklength that minimizes the delay violation and the peak-age violation probabilities. We also show that one can find two blocklength values that result in very similar average delay but significantly different delay violation probabilities. This highlights the importance of focusing on violation probabilities rather than on averages.
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25.
  • Devassy, Rahul, 1985, et al. (författare)
  • Finite-blocklength analysis of the ARQ-protocol throughput over the Gaussian collision channel
  • 2014
  • Ingår i: 6th International Symposium on Communications, Control and Signal Processing 2014. - 9781479928903 ; , s. 173-177
  • Konferensbidrag (refereegranskat)abstract
    • We present a finite-blocklength analysis of the throughput and the average delay achievable in a wireless system where i) several uncoordinated users transmit short coded packets, ii) interference is treated as noise, and iii) 1-bit feedback from the intended receivers enables the use of a simple automatic repeat request (ARQ) protocol. Our analysis exploits the recent results on the characterization of the maximum coding rate at finite blocklength and finite block-error probability by Polyanskiy, Poor, and Verdu ́ (2010), and by Yang et al. (2013). For a given number of information bits, we determine the coded-packet size that maximize the per-user throughput and minimize the average delay. Our numerical results indicate that, when optimal codes are used, very short coded packets (of length between 50 to 100 channel uses) yield significantly lower average delay at an almost negligible throughput loss, compared to longer coded packets.
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26.
  • Devassy, Rahul, 1985, et al. (författare)
  • Finite-SNR Bounds on the Sum-Rate Capacity of Rayleigh Block-Fading Multiple-Access Channels with no a Priori CSI
  • 2015
  • Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 63:10, s. 3621-3632
  • Tidskriftsartikel (refereegranskat)abstract
    • We provide nonasymptotic upper and lower bounds on the sum-rate capacity of Rayleigh block-fading multiple-access channels for the set up where a priori channel state information is not available. The upper bound relies on a dual formula for chan- nel capacity and on the assumption that the users can cooperate perfectly. The lower bound is derived assuming a noncooperative scenario where each user employs unitary space-time modulation (independently from the other users). Numerical results show that the gap between the upper and the lower bound is small already at moderate SNR values. This suggests that the sum-rate capac- ity gains obtainable through user cooperation are minimal for the scenarios considered in the paper.
  •  
27.
  • Devassy, Rahul, 1985, et al. (författare)
  • Nonasymptotic coding-rate bounds for binary erasure channels with feedback
  • 2016
  • Ingår i: IEEE Information Theory Workshop (ITW), Cambridge, ENGLAND, SEP 11-14, 2016. - 9781509010912 ; , s. 86-90
  • Konferensbidrag (refereegranskat)abstract
    • We present nonasymptotic achievability and converse bounds on the maximum coding rate (for a fixed average error probability and a fixed average blocklength) of variable-length full-feedback (VLF) and variable-length stop-feedback (VLSF) codes operating over a binary erasure channel (BEC). For the VLF setup, the achievability bound relies on a scheme that maps each message onto a variable-length Huffman codeword and then repeats each bit of the codeword until it is received correctly. The converse bound is inspired by the meta-converse framework by Polyanskiy, Poor, and Verdú (2010) and relies on binary sequential hypothesis testing. For the case of zero error probability, our achievability and converse bounds match. For the VLSF case, we provide achievability bounds that exploit the following feature of BEC: the decoder can assess the correctness of its estimate by verifying whether the chosen codeword is the only one that is compatible with the erasure pattern. One of these bounds is obtained by analyzing the performance of a variable-length extension of random linear fountain codes. The gap between the VLSF achievability and the VLF converse bound, when number of messages is small, is significant: 23% for 8 messages on a BEC with erasure probability 0.5. The absence of a tight VLSF converse bound does not allow us to assess whether this gap is fundamental.
  •  
28.
  • Devassy, Rahul, 1985, et al. (författare)
  • Reliable Transmission of Short Packets Through Queues and Noisy Channels Under Latency and Peak-Age Violation Guarantees
  • 2019
  • Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 37:4, s. 721-734
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper investigates the probability that the delay and the peak-age of information exceed a desired threshold in a point-to-point communication system with short information packets. The packets are generated according to a stationary memoryless Bernoulli process, placed in a single-server queue and then transmitted over a wireless channel. A variable-length stop-feedback coding scheme - a general strategy that encompasses simple automatic repetition request (ARQ) and more sophisticated hybrid ARQ techniques as special cases - is used by the transmitter to convey the information packets to the receiver. By leveraging finite-blocklength results, the delay violation and the peak-age violation probabilities are characterized without resorting to approximations based on larg-deviation theory as in previous literature. Numerical results illuminate the dependence of delay and peak-age violation probability on system parameters such as the frame size and the undetected error probability, and on the chosen packet-management policy. The guidelines provided by our analysis are particularly useful for the design of low-latency ultra-reliable communication systems.
  •  
29.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • Capacity bounds for MIMO microwave backhaul links affected by phase noise
  • 2014
  • Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 62:3, s. 920-929
  • Tidskriftsartikel (refereegranskat)abstract
    • We present bounds and a closed-form high-SNR expression for the capacity ofmultiple-antenna systems affected by Wiener phase noise. Our results aredeveloped for the scenario where a single oscillator drives all theradio-frequency circuitries at each transceiver (common oscillator setup), theinput signal is subject to a peak-power constraint, and the channel matrix isdeterministic. This scenario is relevant for line-of-sight multiple-antennamicrowave backhaul links with sufficiently small antenna spacing at thetransceivers. For the 2 by 2 multiple-antenna case, for a Wiener phase-noiseprocess with standard deviation equal to 6 degrees, and at the medium/high SNRvalues at which microwave backhaul links operate, the upper bound reported inthe paper exhibits a 3 dB gap from a lower bound obtained using 64-QAM.Furthermore, in this SNR regime the closed-form high-SNR expression is shown tobe accurate.
  •  
30.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • High-SNR Capacity of Wireless Communication Channels in the Noncoherent Setting: A Primer
  • 2011
  • Ingår i: AEU - International Journal of Electronics and Communications. - : Elsevier BV. - 1434-8411. ; 65:8, s. 707-712
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper, mostly tutorial in nature, deals with the problem of characterizing the capacity of fading channels in the high signal-to-noise ratio (SNR) regime.We focus on the practically relevant noncoherent setting, where neither transmitter nor receiver know the channel realizations, but both are aware of the channel law.We present, in an intuitive and accessible form, two tools, first proposed by Lapidoth & Moser (2003), of fundamental importance to high-SNR capacity analysis:the duality approach and the escape-to-infinity property of capacity-achieving distributions.Furthermore, we apply these tools to refine some of the results that appeared previously in the literature and to simplify the corresponding proofs.
  •  
31.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • Information Theory of underspread WSSUS channels
  • 2011
  • Ingår i: Wireless Communications over Rapidly Time-Varying Channels. - 9780123744838 ; , s. 65--115-
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • The chapter focuses on the ultimate limit on the rate of reliable communication through Rayleigh-fading channels that satisfy the wide-sense stationary (WSS) and uncorrelated scattering (US) assumptions and are underspread. Therefore, the natural setting is an information-theoretic one, and the performance metric is channel capacity. The family of Rayleigh-fading underspread WSSUS channels constitutes a good model for real-world wireless channels: their stochastic properties, like amplitude and phase distributions match channel measurement results. The Rayleigh-fading and the WSSUS assumptions imply that the stochastic properties of the channel are fully described by a two-dimensional power spectral density (PSD) function, often referred to as scattering function. The underspread assumption implies that the scattering function is highly concentrated in the delay-Doppler plane. Two important aspects need to be accounted for by a model that aims at being realistic: neither the transmitter nor the receiver knows the realization of the channel; and the peak power of the transmit signal is limited. Based on these two aspects the chapter provides an information-theoretic analysis of Rayleigh-fading underspread WSSUS channels in the noncoherent setting, under the additional assumption that the transmit signal is peak-constrained.
  •  
32.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • On the capacity of MIMO Wiener phase-noise channels
  • 2013
  • Ingår i: 2013 Information Theory and Applications Workshop, ITA 2013 - Conference Proceedings. ; 2013, s. 69-75
  • Konferensbidrag (refereegranskat)abstract
    • The capacity of multiple-antenna systems affected by Wiener phase noise is investigated. We present a non-asymptotic capacity upper bound that is shown to be tight in the large-SNR regime. The capacity upper bound is compared with a lower bound obtained by evaluating numerically the information rates achiev- able with QAM constellations. For a Wiener phase-noise process with standard deviation of the phase increments equal to 6◦, our results suggest that QAM constellations incur a penalty of more than 3 dB for medium/high SNR values.
  •  
33.
  • Durisi, Giuseppe, 1977 (författare)
  • On the capacity of the block-memoryless phase-noise channel
  • 2012
  • Ingår i: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 16:8, s. 1157-1160
  • Tidskriftsartikel (refereegranskat)abstract
    • Bounds are presented on the capacity of the block-memoryless phase-noise channel.The bounds capture the first two terms in the asymptotic expansion of capacity for SNR going to infinity and turn out to be tight for a large range of SNR values of practical interest.Through these bounds, the capacity dependency on the coherence time of the phase-noise process is determined.
  •  
34.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • On the multiplexing gain of MIMO Microwave backhaul links affected by Phase Noise
  • 2013
  • Ingår i: IEEE International Conference on Communications. - 1550-3607. - 9781467331227 ; , s. 3209-3214
  • Konferensbidrag (refereegranskat)abstract
    • We consider a multiple-input multiple-output (MIMO) AWGN channel affected by phase noise. Focusing on the 2 × 2 case, we show that no MIMO multiplexing gain is to be expected when the phase-noise processes at each antenna are independent, memoryless in time, and with uniform marginal distribution over [0,2π] (strong phase noise), and when the transmit signal is isotropically distributed on the real plane. The scenario of independent phase-noise processes across antennas is relevant for microwave backhaul links operating in the 20–40 GHz range.
  •  
35.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • On the Sensitivity of Continuous-Time Noncoherent Fading Channel Capacity
  • 2012
  • Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 58:10, s. 6372-6391
  • Tidskriftsartikel (refereegranskat)abstract
    • he noncoherent capacity of stationary discrete-time fading channels is known to be very sensitive to the fine details of the channel model. More specifically, the measure of the support of the fading-process power spectral density (PSD) determines if noncoherent capacity grows logarithmically in SNR or slower than logarithmically. Such a result is unsatisfactory from an engineer- ing point of view, as the support of the PSD cannot be determined through measurements. The aim of this paper is to assess whether, for general continuous-time Rayleigh-fading channels, this sensi- tivity has a noticeable impact on capacity at SNR values of prac- tical interest.To this end, we consider the general class of band-limited continuous-time Rayleigh-fading channels that satisfy the wide- sense stationary uncorrelated-scattering (WSSUS) assumption and are, in addition, underspread. We show that, for all SNR values of practical interest, the noncoherent capacity of every channel in this class is close to the capacity of an AWGN channel with the same SNR and bandwidth, independently of the measure of the support of the scattering function (the two-dimensional channel PSD). Our result is based on a lower bound on noncoherent capacity, which is built on a discretization of the channel input-output relation induced by projecting onto Weyl-Heisenberg (WH) sets. This approach is interesting in its own right as it yields a mathematically tractable way of dealing with the mutual information between certain continuous-time random signals.
  •  
36.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • Short-Packet Communications over Multiple-Antenna Rayleigh-Fading Channels
  • 2016
  • Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 64:2, s. 618-629
  • Tidskriftsartikel (refereegranskat)abstract
    • Motivated by the current interest in ultra-reliable, low-latency, machine-type communication systems, we investigate the tradeoff between reliability, throughput, and latency in the transmission of information over multiple-antenna Rayleigh block-fading channels. Specifically, we obtain finite-blocklength, finite-SNR upper and lower bounds on the maximum coding rate achievable over such channels for a given constraint on the packet error probability. Numerical evidence suggests that our bounds delimit tightly the maximum coding rate already for short blocklengths (packets of about 100 symbols). Furthermore, our bounds reveal the existence of a tradeoff between the rate gain obtainable by spreading each codeword over all available time-frequency-spatial degrees of freedom, and the rate loss caused by the need of estimating the fading coefficients over these degrees of freedom. In particular, our bounds allow us to determine the optimal number of transmit antennas and the optimal number of time-frequency diversity branches that maximize the rate. Finally, we show that infinite-blocklength performance metrics such as the ergodic capacity and the outage capacity yield inaccurate throughput estimates.
  •  
37.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • Toward Massive, Ultrareliable, and Low-Latency Wireless Communication With Short Packets
  • 2016
  • Ingår i: Proceedings of the IEEE. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2256 .- 0018-9219. ; 104:9, s. 1711-1726
  • Tidskriftsartikel (refereegranskat)abstract
    • Most of the recent advances in the design of highspeed wireless systems are based on information-theoretic principles that demonstrate how to efficiently transmit long data packets. However, the upcoming wireless systems, notably the fifth-generation (5G) system, will need to support novel traffic types that use short packets. For example, short packets represent the most common form of traffic generated by sensors and other devices involved in machine-to-machine (M2M) communications. Furthermore, there are emerging applications in which small packets are expected to carry critical information that should be received with low latency and ultra-high reliability. Current wireless systems are not designed to support short-packet transmissions. For example, the design of current systems relies on the assumption that the metadata (control information) is of negligible size compared to the actual information payload. Hence, transmitting metadata using heuristic methods does not affect the overall system performance. However, when the packets are short, metadata may be of the same size as the payload, and the conventional methods to transmit it may be highly suboptimal. In this paper, we review recent advances in information theory, which provide the theoretical principles that govern the transmission of short packets. We then apply these principles to three exemplary scenarios (the two-way channel, the downlink broadcast channel, and the uplink random access channel), thereby illustrating how the transmission of control information can be optimized when the packets are short. The insights brought by these examples suggest that new principles are needed for the design of wireless protocols supporting short packets. These principles will have a direct impact on the system design.
  •  
38.
  • Durisi, Giuseppe, 1977, et al. (författare)
  • Towards Massive, Ultra-Reliable, and Low-Latency Wireless Communication with Short Packets
  • 2016
  • Ingår i: Proceedings of the IEEE. - 1558-2256 .- 0018-9219.
  • Tidskriftsartikel (refereegranskat)abstract
    • Most of the recent advances in the design of high-speed wireless systems are based on information-theoretic principles that demonstrate how to efficiently transmit long data packets. However, the upcoming wireless systems, notably the 5G system, will need to support novel traffic types that use short packets. For example, short packets represent the most common form of traffic generated by sensors and other devices involved in Machine-to-Machine (M2M) communications. Furthermore, there are emerging applications in which small packets are expected to carry critical information that should be received with low latency and ultra-high reliability. Current wireless systems are not designed to support short-packet transmissions. For example, the design of current systems relies on the assumption that the metadata (control information) is of negligible size compared to the actual information payload. Hence, transmitting metadata using heuristic methods does not affect the overall system performance. However, when the packets are short, metadata may be of the same size as the payload, and the conventional methods to transmit it may be highly suboptimal. In this article, we review recent advances in information theory, which provide the theoretical principles that govern the transmission of short packets. We then apply these principles to three exemplary scenarios (the two-way channel, the downlink broadcast channel, and the uplink random access channel), thereby illustrating how the transmission of control information can be optimized when the packets are short. The insights brought by these examples suggest that new principles are needed for the design of wireless protocols supporting short packets. These principles will have a direct impact on the system design.
  •  
39.
  • Erkip, Elza, et al. (författare)
  • Editorial Issue on 'Information Theoretic Foundations of Future Communication Systems'
  • 2022
  • Ingår i: IEEE Journal on Selected Areas in Information Theory. - 2641-8770. ; 3:1, s. 2-4
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Information theory, starting with Shannon’s groundbreaking work, has fundamentally shaped the way communication systems are designed and operated. Information theoretic principles form the underpinnings of modern communication networks. This issue explores how new advances in information theory can impact future communication systems. Several papers address issues at the heart of next generation wireless and wired networks: Multiple access, including access by a massive number of devices, multi-hop, large antenna arrays, communication security, and timeliness of information. Others consider new applications such as joint communication and sensing, communication for learning and inference, wireless imaging, and new storage mediums such as DNA, thereby providing the information theoretic foundations of modalities beyond human-to-human communications.
  •  
40.
  • Ettefagh, Yasaman, 1989, et al. (författare)
  • All-Digital Massive MIMO Uplink and Downlink Rates under a Fronthaul Constraint
  • 2019
  • Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. - 9781728143002 ; 2019-November, s. 416-420
  • Konferensbidrag (refereegranskat)abstract
    • We characterize the rate achievable in a bidirectional quasi-static link where several user equipments communicate with a massive multiple-input multiple-output base station (BS). In the considered setup, the BS operates in full-digital mode, the physical size of the antenna array is limited, and there exists a rate constraint on the fronthaul interface connecting the (possibly remote) radio head to the digital baseband processing unit. Our analysis enables us to determine the optimal resolution of the analog-todigital and digital-to-analog converters as well as the optimal number of active antenna elements to be used in order to maximize the transmission rate on the bidirectional link, for a given constraint on the outage probability and on the fronthaul rate. We investigate both the case in which perfect channel-state information is available, and the case in which channel-state information is acquired through pilot transmission, and is, hence, imperfect. For the second case, we present a novel rate expression that relies on the generalized mutual-information framework.
  •  
41.
  • Ettefagh, Yasaman, 1989, et al. (författare)
  • Performance of Quantized Massive MIMO with Fronthaul Rate Constraint over Quasi-Static Channels
  • 2023
  • Ingår i: IEEE Access. - 2169-3536 .- 2169-3536. ; 11, s. 56935-56950
  • Tidskriftsartikel (refereegranskat)abstract
    • We provide a rigorous framework for characterizing and numerically evaluating the error probability achievable in the uplink and downlink of a fully digital quantized multiuser multiple-input multiple-output (MIMO) system. We assume that the system operates over a quasi-static channel that does not change across the finite-length transmitted codewords, and only imperfect channel state information (CSI) is available at the base station (BS) and at the user equipments. The need for the novel framework developed in this paper stems from the fact that, for the quasi-static scenario, commonly used signal-to-interference-and-distortion-ratio expressions that depend on the variance of the channel estimation error are not relatable to any rigorous information-theoretic achievable-rate bound. We use our framework to investigate how the performance of a fully digital massive MIMO system subject to a fronthaul rate constraint, which imposes a limit on the number of samples per second produced by the analog-to-digital and digital-to-analog converters (ADCs and DACs), depends on the number of BS antennas and on the precision of the ADCs and DACs. In particular, we characterize, for a given fronthaul constraint, the trade-off between the number of antennas and the resolution of the data converters, and discuss how this trade-off is influenced by the accuracy of the available CSI. Our framework captures explicitly the cost, in terms of spectral efficiency, of pilot transmission—an overhead that the outage capacity, the classic asymptotic metric used in this scenario, cannot capture. We present extensive numerical results that validate the accuracy of the proposed framework and allow us to characterize, for a given fronthaul constraint, the optimal number of antennas and the optimal resolution of the converters as a function of the transmitted power and of the available CSI.
  •  
42.
  • Ferrante, Guido, 1987, et al. (författare)
  • Pilot-Assisted Short Packet Transmission over Memoryless Block-Fading Channels
  • 2018
  • Ingår i: Annual Conference on Information Sciences and Systems (CISS). - 9781538605806 ; , s. 389-394
  • Konferensbidrag (refereegranskat)abstract
    • Leveraging recent results in finite-blocklength information theory, we investigate the problem of designing a control channel in a 5G system. The setup involves the transmission, under stringent latency and reliability constraints, of a short data packet containing a small information payload, over a propagation channel that offers limited frequency diversity and no time diversity. We present an achievability bound, built upon the random-coding union bound with parameter s (Martinez & Guillen i Fabregas, 2011), which relies on quadrature phase-shift keying modulation, pilot-assisted transmission to estimate the fading channel, and scaled nearest-neighbor decoding at the receiver. Using our achievability bound, we determine how many pilot symbols should be transmitted to optimally trade between channel-estimation errors and rate loss due to pilot overhead. Our analysis also reveals the importance of using multiple antennas at the transmitter and/or the receiver to provide the spatial diversity needed to meet the stringent reliability constraint.
  •  
43.
  • Ferrante, Guido, 1987, et al. (författare)
  • Pilot-Assisted Short-Packet Transmission over Multiantenna Fading Channels: A 5G Case Study
  • 2018
  • Ingår i: 2018 52nd Annual Conference on Information Sciences and Systems, CISS 2018. - 9781538605790 ; 21 May 2018, s. 1-6
  • Konferensbidrag (refereegranskat)abstract
    • Leveraging recent results in finite-blocklength information theory, we investigate the problem of designing a control channel in a 5G system. The setup involves the transmission, under stringent latency and reliability constraints, of a short data packet containing a small information payload, over a propagation channel that offers limited frequency diversity and no time diversity. We present an achievability bound, built upon the random-coding union bound with parameter s (Martinez & Guillén i Fàbregas, 2011), which relies on quadrature phase-shift keying modulation, pilot-assisted transmission to estimate the fading channel, and scaled nearest-neighbor decoding at the receiver. Using our achievability bound, we determine how many pilot symbols should be transmitted to optimally trade between channel-estimation errors and rate loss due to pilot overhead. Our analysis also reveals the importance of using multiple antennas at the transmitter and/or the receiver to provide the spatial diversity needed to meet the stringent reliability constraint.
  •  
44.
  • Fountoulakis, Emmanouil, 1991- (författare)
  • Performance Analysis and Optimization for Time Critical Networking
  • 2019
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Future communication systems will be characterized by heterogeneous traffic and requirements. Time critical applications like cyberphysical systems, augmented and virtual reality, raise the need for a low-latency based network. At the same time, conventional devices requiring for high throughput will co-exist with time critical applications. Besides the new technologies, new scheduling and optimization techniques are needed to face these challenges. In this thesis, we investigate the issues arising from the deployment of these technologies. In Paper I, we explore the benefits of dynamic Transmission Time Interval (TTI) selection in a heterogeneous network environment. We consider packets with deadlines and we optimize jointly the TTI length and the channel allocation. After proving the NP-hardness of the problem, we propose a greedy algorithm taking decisions in polynomial time. The first work opens new questions regarding the deadline-constrained traffic such as how the minimum average drop rate can be achieved. In Paper II, we consider power-limited devices with deadline-constrained traffic. Lyapunov optimization methods are explored to solve the problem with time average objective and constraints. We develop a dynamic, polynomial time, algorithm that finds an approximation of the dropping rate minimization problem under average power constraints. Besides the new techniques, future communication systems will require the development of new technologies for a more exible and elastic network. Multi-access Edge Computing (MEC) and Virtual Network Function (VNF) technologies are considered two of the key technologies for next generation networks. In Paper III, we analyze the performance of a network that hosts VNF and consists of MEC servers and servers at the core. As a first step, we consider a simple end-to-end communication system and provide analytical expressions for the end-to-end delay and system throughput by applying tools from queueing theory. Based on the first step, we provide the methodology for analyzing scaled-up systems with arbitrary number of servers. Simulation results show that our analytical model performs well. Furthermore, this work provides insights for the design and performance optimization of such systems such as optimal ow control and resource allocation.
  •  
45.
  • Gustavsson, Ulf, 1975, et al. (författare)
  • On the Impact of Hardware Impairments on Massive MIMO
  • 2014
  • Ingår i: IEEE Globecom 2014 Workshop - Massive MIMO: From Theory to Practice, 2014-12-08, Austin, Texas, USA. - 9781479974702 ; , s. 294-300
  • Konferensbidrag (refereegranskat)abstract
    • Massive multi-user (MU) multiple-input multiple-output (MIMO) systems are one possible key technology for next generation wireless communication systems. Claims have been made that massive MU-MIMO will increase both the radiated energy efficiency as well as the sum-rate capacity by orders of magnitude, because of the high transmit directivity. However, due to the very large number of transceivers needed at each base-station (BS), a successful implementation of massive MU-MIMO will be contingent on of the availability of very cheap, compact and power-efficient radio and digital-processing hardware. This may in turn impair the quality of the modulated radio frequency (RF) signal due to an increased amount of power-amplifier distortion, phase-noise, and quantization noise. In this paper, we examine the effects of hardware impairments on a massive MU-MIMO single-cell system by means of theory and simulation. The simulations are performed using simplified, well-established statistical hardware impairment models as well as more sophisticated and realistic models based upon measurements and electromagnetic antenna array simulations.
  •  
46.
  • Hellström, Fredrik, 1993, et al. (författare)
  • Evaluated CMI Bounds for Meta Learning: Tightness and Expressiveness
  • 2022
  • Ingår i: Advances in Neural Information Processing Systems. - 1049-5258. - 9781713871088 ; 35
  • Konferensbidrag (refereegranskat)abstract
    • Recent work has established that the conditional mutual information (CMI) framework of Steinke and Zakynthinou (2020) is expressive enough to capture generalization guarantees in terms of algorithmic stability, VC dimension, and related complexity measures for conventional learning (Harutyunyan et al., 2021, Haghifam et al., 2021). Hence, it provides a unified method for establishing generalization bounds. In meta learning, there has so far been a divide between information-theoretic results and results from classical learning theory. In this work, we take a first step toward bridging this divide. Specifically, we present novel generalization bounds for meta learning in terms of the evaluated CMI (e-CMI). To demonstrate the expressiveness of the e-CMI framework, we apply our bounds to a representation learning setting, with $n$ samples from $\hat n$ tasks parameterized by functions of the form $f_i \circ h$. Here, each $f_i \in \mathcal F$ is a task-specific function, and $h \in \mathcal H$ is the shared representation. For this setup, we show that the e-CMI framework yields a bound that scales as $\sqrt{ \mathcal C(\mathcal H)/(n\hat n) + \mathcal C(\mathcal F)/n} $, where $\mathcal C(\cdot)$ denotes a complexity measure of the hypothesis class. This scaling behavior coincides with the one reported in Tripuraneni et al. (2020) using Gaussian complexity.
  •  
47.
  • Hellström, Fredrik, 1993, et al. (författare)
  • Fast-Rate Loss Bounds via Conditional Information Measures with Applications to Neural Networks
  • 2021
  • Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2021-July, s. 952-957
  • Konferensbidrag (refereegranskat)abstract
    • We present a framework to derive bounds on the test loss of randomized learning algorithms for the case of bounded loss functions. Drawing from Steinke Zakynthinou (2020), this framework leads to bounds that depend on the conditional information density between the output hypothesis and the choice of the training set, given a larger set of data samples from which the training set is formed. Furthermore, the bounds pertain to the average test loss as well as to its tail probability, both for the PAC-Bayesian and the single-draw settings. If the conditional information density is bounded uniformly in the size n of the training set, our bounds decay as 1/n, This is in contrast with the tail bounds involving conditional information measures available in the literature, which have a less benign 1/√n dependence. We demonstrate the usefulness of our tail bounds by showing that they lead to nonvacuous estimates of the test loss achievable with some neural network architectures trained on MNIST and Fashion-MNIST.
  •  
48.
  • Hellström, Fredrik, 1993, et al. (författare)
  • Generalization Bounds via Information Density and Conditional Information Density
  • 2020
  • Ingår i: IEEE Journal on Selected Areas in Information Theory. - 2641-8770. ; 1:3, s. 824-839
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a general approach, based on an exponential inequality, to derive bounds on the generalization error of randomized learning algorithms. Using this approach, we provide bounds on the average generalization error as well as bounds on its tail probability, for both the PAC-Bayesian and single-draw scenarios. Specifically, for the case of sub-Gaussian loss functions, we obtain novel bounds that depend on the information density between the training data and the output hypothesis. When suitably weakened, these bounds recover many of the information-theoretic bounds available in the literature. We also extend the proposed exponential-inequality approach to the setting recently introduced by Steinke and Zakynthinou (2020), where the learning algorithm depends on a randomly selected subset of the available training data. For this setup, we present bounds for bounded loss functions in terms of the conditional information density between the output hypothesis and the random variable determining the subset choice, given all training data. Through our approach, we recover the average generalization bound presented by Steinke and Zakynthinou (2020) and extend it to the PAC-Bayesian and singledraw scenarios. For the single-draw scenario, we also obtain novel bounds in terms of the conditional α-mutual information and the conditional maximal leakage.
  •  
49.
  • Hellström, Fredrik, 1993, et al. (författare)
  • Generalization Error Bounds via mth Central Moments of the Information Density
  • 2020
  • Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2020-June, s. 2741-2746
  • Konferensbidrag (refereegranskat)abstract
    • We present a general approach to deriving bounds on the generalization error of randomized learning algorithms. Our approach can be used to obtain bounds on the average generalization error as well as bounds on its tail probabilities, both for the case in which a new hypothesis is randomly generated every time the algorithm is used - as often assumed in the probably approximately correct (PAC)-Bayesian literature - and in the single-draw case, where the hypothesis is extracted only once.For this last scenario, we present a novel bound that is explicit in the central moments of the information density. The bound reveals that the higher the order of the information density moment that can be controlled, the milder the dependence of the generalization bound on the desired confidence level.Furthermore, we use tools from binary hypothesis testing to derive a second bound, which is explicit in the tail of the information density. This bound confirms that a fast decay of the tail of the information density yields a more favorable dependence of the generalization bound on the confidence level.
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50.
  • Hellström, Fredrik, 1993, et al. (författare)
  • New Family of Generalization Bounds Using Samplewise Evaluated CMI
  • 2022
  • Ingår i: Advances in Neural Information Processing Systems. - 1049-5258. ; 35
  • Konferensbidrag (refereegranskat)abstract
    • We present a new family of information-theoretic generalization bounds, in which the training loss and the population loss are compared through a jointly convex function. This function is upper-bounded in terms of the disintegrated, samplewise, evaluated conditional mutual information (CMI), an information measure that depends on the losses incurred by the selected hypothesis, rather than on the hypothesis itself, as is common in probably approximately correct (PAC)-Bayesian results. We demonstrate the generality of this framework by recovering and extending previously known information-theoretic bounds. Furthermore, using the evaluated CMI, we derive a samplewise, average version of Seeger's PAC-Bayesian bound, where the convex function is the binary KL divergence. In some scenarios, this novel bound results in a tighter characterization of the population loss of deep neural networks than previous bounds. Finally, we derive high-probability versions of some of these average bounds. We demonstrate the unifying nature of the evaluated CMI bounds by using them to recover average and high-probability generalization bounds for multiclass classification with finite Natarajan dimension.
  •  
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