SwePub - sökning: WFRF:(Durisi Giuseppe 1977)

Numrering	Referens	Omslagsbild	Hitta
51.	Hu, Anzhong, et al. (författare) EVM Analysis of Distributed Massive MIMO with 1-Bit Radio-Over-Fiber Fronthaul 2024 Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; In Press Tidskriftsartikel (refereegranskat)abstract We analyze the uplink performance of a distributed massive multiple-input multiple-output (MIMO) architecture in which the remotely located access points (APs) are connected to a central processing unit via a fiber-optical fronthaul carrying a dithered and 1-bit quantized version of the received radio-frequency (RF) signal. The innovative feature of the proposed architecture is that no down-conversion is performed at the APs. This eliminates the need to equip the APs with local oscillators, which may be difficult to synchronize. Under the assumption that a constraint is imposed on the amount of data that can be exchanged across the fiber-optical fronthaul, we investigate the tradeoff between spatial oversampling, defined in terms of the total number of APs, and temporal oversampling, defined in terms of the oversampling factor selected at the central processing unit, to facilitate the recovery of the transmitted signal from 1-bit samples of the RF received signal. Using the so-called error-vector magnitude (EVM) as performance metric, we shed light on the optimal design of the dither signal, and quantify, for a given number of APs, the minimum fronthaul rate required for our proposed distributed massive MIMO architecture to outperform a standard co-located massive MIMO architecture in terms of EVM.
52.	Hussain, Ahmed, 1985, et al. (författare) Modeling system throughput of single and multi-port wireless LTE devices 2012 Ingår i: IEEE Antennas and Propagation Society, AP-S International Symposium (Digest). - 1522-3965. - 9781467304627 Konferensbidrag (refereegranskat)abstract We have recently introduced a simple theoretical model for estimating the relative throughput of LTE devices. We validated the model through measurements performed in reverberation chamber for 1×2 SIMO with 90ns channel delay spread. In the present paper, we extend our previous study to compare the frequency diversity offered by different channel delay spreads emulated in reverberation chamber for SISO and 1×2 SIMO configurations
53.	Jacobsson, Sven, 1990, et al. (författare) All-digital massive MIMO with a fronthaul constraint 2018 Ingår i: IEEE Workshop Stat. Signal Process. (SSP). Konferensbidrag (refereegranskat)
54.	Jacobsson, Sven, 1990, et al. (författare) Linear Precoding With Low-Resolution DACs for Massive MU-MIMO-OFDM Downlink 2019 Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 18:3, s. 1595-1609 Tidskriftsartikel (refereegranskat)abstract We consider the downlink of a massive multiuser (MU) multiple-input multiple-output (MIMO) system in which the base station (BS) is equipped with low-resolution digital-to-analog converters (DACs). In contrast to most existing results, we assume that the system operates over a frequency-selective wideband channel and uses orthogonal frequency division multiplexing (OFDM) to simplify equalization at the user equipments (UEs). Furthermore, we consider the practically relevant case of oversampling DACs. We theoretically analyze the uncoded bit error rate (BER) performance with linear precoders (e.g., zero forcing) and quadrature phase-shift keying using Bussgang's theorem. We also develop a lower bound on the information-theoretic sum-rate throughput achievable with Gaussian inputs, which can be evaluated in closed form for the case of 1-bit DACs. For the case of multi-bit DACs, we derive approximate, yet accurate, expressions for the distortion caused by low-precision DACs, which can be used to establish the lower bounds on the corresponding sum-rate throughput. Our results demonstrate that, for a massive MU-MIMO-OFDM system with a 128-antenna BS serving 16 UEs, only 3-4 DAC bits are required to achieve an uncoded BER of 10(-4) with a negligible performance loss compared to the infinite-resolution case at the cost of additional out-of-band emissions. Furthermore, our results highlight the importance of considering the inherent spatial and temporal correlations caused by low-precision DACs.
55.	Jacobsson, Sven, 1990, et al. (författare) Massive MU-MIMO-OFDM Downlink with One-Bit DACs and Linear Precoding 2018 Ingår i: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. ; 2018-January, s. 1-6 Konferensbidrag (refereegranskat)abstract Massive multiuser (MU) multiple-input multiple- output (MIMO) is foreseen to be a key technology in future wireless communication systems. In this paper, we analyze the downlink performance of an orthogonal frequency division multiplexing (OFDM)-based massive MU-MIMO system in which the base station (BS) is equipped with 1-bit digital-to-analog converters (DACs). Using Bussgang’s theorem, we characterize the performance achievable with linear precoders (such as maximal-ratio transmission and zero forcing) in terms of bit error rate (BER). Our analysis accounts for the possibility of oversampling the time-domain transmit signal before the DACs. We further develop a lower bound on the information-theoretic sum-rate throughput achievable with Gaussian inputs.Our results suggest that the performance achievable with 1-bit DACs in a massive MU-MIMO-OFDM downlink are satisfactory provided that the number of BS antennas is sufficiently large.
56.	Jacobsson, Sven, 1990, et al. (författare) Massive MU-MIMO-OFDM uplink with direct RF-sampling and 1-Bit ADCs 2019 Ingår i: 2019 IEEE Globecom Workshops, GC Wkshps 2019 - Proceedings. Konferensbidrag (refereegranskat)abstract Advances in analog-to-digital converter (ADC) technology have opened up the possibility to directly digitize wideband radio frequency (RF) signals, avoiding the need for analog down- conversion. In this work, we consider an orthogonal frequency- division multiplexing (OFDM)-based massive multi-user (MU) multiple-input multiple-output (MIMO) uplink system that relies on direct RF-sampling at the base station and digitizes the received RF signals with 1-bit ADCs. Using Bussgang's theorem, we provide an analytical expression for the error-vector magnitude (EVM) achieved by digital down-conversion and zero-forcing combining. Our results demonstrate that direct RF-sampling 1-bit ADCs enables low EVM and supports high-order constellations in the massive MU-MIMO- OFDM uplink.
57.	Jacobsson, Sven, 1990, et al. (författare) Massive MU-MIMO-OFDM Uplink with Hardware Impairments: Modeling and Analysis 2018 Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2018-October, s. 1829-1835 Konferensbidrag (refereegranskat)abstract © 2018 IEEE. We study the impact of hardware impairments at the base station (BS) of an orthogonal frequency-division multiplexing (OFDM)-based massive multiuser (MU) multiple-input multiple-output (MIMO) uplink system. We leverage Bussgang's theorem to develop accurate models for the distortions caused by nonlinear low-noise amplifiers, local oscillators with phase noise, and oversampling finite-resolution analog-to-digital converters. By combining the individual effects of these hardware models, we obtain a composite model for the BS-side distortion caused by nonideal hardware that takes into account its inherent correlation in time, frequency, and across antennas. We use this composite model to analyze the impact of BS-side hardware impairments on the performance of realistic massive MU-MIMO-OFDM uplink systems.
58.	Jacobsson, Sven, 1990, et al. (författare) Massive multiuser MIMO downlink with low- resolution converters 2018 Ingår i: International Zurich Seminar on Information and Communication (IZS 2018) Proceedings. Konferensbidrag (refereegranskat)abstract In this review paper, we analyze the downlink of a massive multiuser multiple-input multiple-output system in which the base station is equipped with low-resolution digital-to-analog converters (DACs). Using Bussgang’s theorem, we characterize the sum-rate achievable with a Gaussian codebook and scaled nearestneighbor decoding at the user equipments (UE). For the case of 1-bit DACs, we show how to evaluate the sum-rate using Van Vleck’s arcsine law. For the case of multi-bit DACs, for which the sum-rate cannot be expressed in closed-form, we present two approximations. The first one, which is obtained by ignoring the overload (or clipping) distortion caused by the DACs, turns out to be accurate provided that one can adapt the dynamic range of the quantizer to the received-signal strength so as to avoid clipping. The second approximation, which is obtained by modeling the distortion noise as a white process, both in time and space, is accurate whenever the resolution of the DACs is sufficiently high and when the oversampling ratio is small. We conclude the paper by discussing extensions to orthogonal frequency-division multiplexing systems; we also touch upon the problem of out-of-band emissions in lowprecision-DAC architectures.
59.	Jacobsson, Sven, 1990, et al. (författare) MSE-Optimal 1-Bit Precoding for Multiuser MIMO Via Branch and Bound 2018 Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. ; 2018-April, s. 3589-3593 Konferensbidrag (refereegranskat)abstract In this paper, we solve the sum mean-squared error (MSE)-optimal 1-bit quantized precoding problem exactly for small-to-moderate sized multiuser multiple-input multiple-output (MU-MIMO) systems via branch and bound. To this end, we reformulate the original NP-hard precoding problem as a tree search and deploy a number of strategies that improve the pruning efficiency without sacrificing optimality. We evaluate the error-rate performance and the complexity of the resulting 1-bit branch-and-bound (BB-1) precoder, and compare its efficacy to that of existing, suboptimal algorithms for 1-bit precoding in MU-MIMO systems.
60.	Jacobsson, Sven, 1990, et al. (författare) Nonlinear 1-bit precoding for massive MU-MIMO with higher-order modulation 2017 Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; , s. 763-767 Konferensbidrag (refereegranskat)abstract Massive multi-user (MU) multiple-input multiple-output (MIMO) is widely believed to be a core technology for the upcoming fifth-generation (5G) wireless communication standards. The use of low-precision digital-to-analog converters (DACs) in MU-MIMO base stations is of interest because it reduces the power consumption, system costs, and raw baseband data rates. In this paper, we develop novel algorithms for downlink precoding in massive MU-MIMO systems with 1-bit DACs that support higher-order modulation schemes such as 8-PSK or 16-QAM. Specifically, we present low-complexity nonlinear precoding algorithms that achieve low error rates when combined with blind or training-based channel-estimation algorithms at the user equipment. These results are in stark contrast to linear-quantized precoding algorithms, which suffer from a high error floor if used with high-order modulation schemes and 1-bit DACs
61.	Jacobsson, Sven, 1990, et al. (författare) Nonlinear Precoding for Phase-Quantized Constant-Envelope Massive MU-MIMO-OFDM 2018 Ingår i: 2018 25TH INTERNATIONAL CONFERENCE ON TELECOMMUNICATIONS (ICT). - 9781538623213 ; , s. 367-372 Konferensbidrag (refereegranskat)abstract We propose a nonlinear phase-quantized constant-envelope precoding algorithm for the massive multi-user (MU) multiple-input multiple-output (MIMO) downlink. Specifically, we adapt the squared-infinity norm Douglas-Rachford splitting (SQUID) precoder to systems that use oversampling digital-to-analog converters (DACs) at the base station (BS) and orthogonal frequency-division multiplexing (OFDM) to communicate over frequency-selective channels. We demonstrate that the proposed SQUID-OFDM precoder is able to generate transmit signals that are constrained to constant envelope, which enables the use of power-efficient analog radio-frequency circuitry at the BS. By quantizing the phase of the resulting constant-envelope signal, we obtain a finite-cardinality transmit signal that can be synthesized by low-resolution (e.g., 1-bit) DACs. We use error-rate simulations to demonstrate the superiority of SQUID-OFDM over linear-quantized precoders for massive MU-MIMO-OFDM systems.
62.	Jacobsson, Sven, 1990, et al. (författare) On Out-of-Band Emissions of Quantized Precoding in Massive MU-MIMO-OFDM 2017 Ingår i: Conference Record of the Asilomar Conference on Signals Systems and Computers. - 1058-6393. - 9781538618233 ; 2017-October, s. 21-26 Konferensbidrag (refereegranskat)abstract We analyze out-of-band (OOB) emissions in the massive multi-user (MU) multiple-input multiple-output (MIMO) downlink. We focus on systems in which the base station (BS) is equipped with low-resolution digital-to-analog converters (DACs) and orthogonal frequency-division multiplexing (OFDM) is used to communicate to the user equipments (UEs) over frequency- selective channels. We demonstrate that analog filtering in combination with simple frequency-domain digital predistortion (DPD) at the BS enables a significant reduction of OOB emissions, but degrades the signal-to-interference-noise-and-distortion ratio (SINDR) at the UEs and increases the peak-to-average power ratio (PAR) at the BS. We use Bussgang’s theorem to characterize the tradeoffs between OOB emissions, SINDR, and PAR, and to study the impact of analog filters and DPD on the error-rate perfor- mance of the massive MU-MIMO-OFDM downlink. Our results show that by carefully tuning the parameters of the analog filters, one can achieve a significant reduction in OOB emissions with only a moderate degradation of error-rate performance and PAR.
63.	Jacobsson, Sven, 1990, et al. (författare) One-Bit Massive MIMO: Channel Estimation and High-Order Modulations 2015 Ingår i: 2015 IEEE International Conference on Communication Workshop, ICCW 2015. - 9781467363051 ; , s. 1304-1309 Konferensbidrag (refereegranskat)abstract We investigate the information-theoretic throughout achievable on a fading communication link when the receiver is equipped with one-bit analog-to-digital converters (ADCs). The analysis is conducted for the setting where neither the transmitter nor the receiver have a priori information on the realization of the fading channels. This means that channel-state information needs to be acquired at the receiver on the basis of the one-bit quantized channel outputs. We show that least-squares (LS) channel estimation combined with joint pilot and data processing is capacity achieving in the single-user, single-receive-antenna case. We also investigate the achievable uplink throughput in a massive multiple-input multiple-output system where each element of the antenna array at the receiver base-station feeds a one-bit ADC. We show that LS channel estimation and maximum-ratio combining are sufficient to support both multiuser operation and the use of high-order constellations. This holds in spite of the severe nonlinearity introduced by the one-bit ADCs.
64.	Jacobsson, Sven, 1990, et al. (författare) Quantized Precoding for Massive MU-MIMO 2017 Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 65:11, s. 4670-4684 Tidskriftsartikel (refereegranskat)abstract Massive multiuser (MU) multiple-input multiple-output (MIMO) is foreseen to be one of the key technologies in fifth-generation wireless communication systems. In this paper, we investigate the problem of downlink precoding for a narrowband massive MU-MIMO system with low-resolution digital-to-analog converters (DACs) at the base station (BS). We analyze the performance of linear precoders, such as maximal-ratio transmission and zero-forcing, subject to coarse quantization. Using Bussgang's theorem, we derive a closed-form approximation on the rate achievable under such coarse quantization. Our results reveal that the performance attainable with infinite-resolution DACs can be approached using DACs having only 3-4 bits of resolution, depending on the number of BS antennas and the number of user equipments (UEs). For the case of 1-bit DACs, we also propose novel nonlinear precoding algorithms that significantly outperform linear precoders at the cost of an increased computational complexity. Specifically, we show that nonlinear precoding incurs only a 3 dB penalty compared with the infinite-resolution case for an uncoded bit-error rate of 10-3, in a system with 128 BS antennas that uses 1-bit DACs and serves 16 single-antenna UEs. In contrast, the penalty for linear precoders is about 8dB.
65.	Jacobsson, Sven, 1990, et al. (författare) Throughput Analysis of Massive MIMO Uplink With Low-Resolution ADCs 2017 Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 16:6, s. 4038-4051 Tidskriftsartikel (refereegranskat)abstract We investigate the uplink throughput achievable by a multiple-user (MU) massive multiple-input multiple-output (MIMO) system, in which the base station is equipped with a large number of low-resolution analog-to-digital converters (ADCs). Our focus is on the case where neither the transmitter nor the receiver have any a priori channel state information. This implies that the fading realizations have to be learned through pilot transmission followed by channel estimation at the receiver, based on coarsely quantized observations. We propose a novel channel estimator, based on Bussgang's decomposition, and a novel approximation to the rate achievable with finite-resolution ADCs, both for the case of finite-cardinality constellations and of Gaussian inputs, that is accurate for a broad range of system parameters. Through numerical results, we illustrate that, for the 1-bit quantized case, pilot-based channel estimation together with maximal-ratio combing, or zero-forcing detection enables reliable multi-user communication with high-order constellations, in spite of the severe nonlinearity introduced by the ADCs. Furthermore, we show that the rate achievable in the infinite-resolution (no quantization) case can be approached using ADCs with only a few bits of resolution. We finally investigate the robustness of low-ADC-resolution MU-MIMO uplink against receive power imbalances between the different users, caused for example by imperfect power control.
66.	Jacobsson, Sven, 1990, et al. (författare) Timing and Frequency Synchronization for 1-bit Massive MU-MIMO-OFDM Downlink 2019 Ingår i: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC. - 9781538665282 ; 2019-July Konferensbidrag (refereegranskat)abstract We consider timing and frequency synchronization for the massive multiuser (MU) multiple-input multiple-output (MIMO) downlink where 1-bit digital-to-analog converters (DACs) are used at the base station (BS). We focus on the practically relevant scenario in which orthogonal-frequency division multiplexing (OFDM) is used to communicate over frequency-selective channels. Our contributions are twofold. First, we use Bussgang's theorem to analyze the impact on performance caused by timing and frequency offsets in the presence of 1-bit DACs at the BS. Second, we demonstrate the efficacy of the widely used Schmidl-Cox synchronization algorithm. Our results demonstrate that the 1-bit massive MU-MIMO-OFDM downlink is resilient against timing and frequency offsets.
67.	Jose, Sharu Theresa, et al. (författare) Transfer Meta-Learning: Information-Theoretic Bounds and Information Meta-Risk Minimization 2022 Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 68:1, s. 474-501 Tidskriftsartikel (refereegranskat)abstract Meta-learning automatically infers an inductive bias by observing data from a number of related tasks. The inductive bias is encoded by hyperparameters that determine aspects of the model class or training algorithm, such as initialization or learning rate. Meta-learning assumes that the learning tasks belong to a task environment, and that tasks are drawn from the same task environment both during meta-training and meta-testing. This, however, may not hold true in practice. In this paper, we introduce the problem of transfer meta-learning, in which tasks are drawn from a target task environment during meta-testing that may differ from the source task environment observed during meta-training. Novel information-theoretic upper bounds are obtained on the transfer meta-generalization gap, which measures the difference between the meta-training loss, available at the meta-learner, and the average loss on meta-test data from a new, randomly selected, task in the target task environment. The first bound, on the average transfer meta-generalization gap, captures the meta-environment shift between source and target task environments via the KL divergence between source and target data distributions. The second, PAC-Bayesian bound, and the third, single-draw bound, account for this shift via the log-likelihood ratio between source and target task distributions. Furthermore, two transfer meta-learning solutions are introduced. For the first, termed Empirical Meta-Risk Minimization (EMRM), we derive bounds on the average optimality gap. The second, referred to as Information Meta-Risk Minimization (IMRM), is obtained by minimizing the PAC-Bayesian bound. IMRM is shown via experiments to potentially outperform EMRM.
68.	Keykhosravi, Kamran, 1990, et al. (författare) A Tighter Upper Bound on the Capacity of the Nondispersive Optical Fiber Channel 2017 Ingår i: European Conference on Optical Communication, ECOC. ; 2017-September Konferensbidrag (refereegranskat)abstract An upper bound on the capacity of the nondispersive optical fiber channel is presented. This bound, which is valid for arbitrary launch powers, confines the capacity within a much narrower range compared to what the previously known upper bound provided.
69.	Keykhosravi, Kamran, 1990, et al. (författare) Accuracy Assessment of Nondispersive Optical Perturbative Models through Capacity Analysis 2019 Ingår i: Entropy. - : MDPI AG. - 1099-4300. ; 21:8 Tidskriftsartikel (refereegranskat)abstract A number of simplified models, based on perturbation theory, have been proposed for the fiber-optical channel and have been extensively used in the literature. Although these models are mainly developed for the low-power regime, they are used at moderate or high powers as well. It remains unclear to what extent the capacity of these models is affected by the simplifying assumptions under which they are derived. In this paper, we consider single-channel data transmission based on three continuous-time optical models: (i) a regular perturbative channel, (ii) a logarithmic perturbative channel, and (iii) the stochastic nonlinear Schrödinger (NLS) channel. To obtain analytically tractable discrete-time models, we consider zero-dispersion fibers and a sampling receiver. We investigate the per-sample capacity of these models. Specifically, (i) we establish tight bounds on the capacity of the regular perturbative channel; (ii) we obtain the capacity of the logarithmic perturbative channel; and (iii) we present a novel upper bound on the capacity of the zero-dispersion NLS channel. Our results illustrate that the capacity of these models departs from each other at high powers because these models yield different capacity pre-logs. Since all three models are based on the same physical channel, our results highlight that care must be exercised in using simplified channel models in the high-power regime.
70.	Keykhosravi, Kamran, 1990, et al. (författare) Demodulation and Detection Schemes for a Memoryless Optical WDM Channel 2018 Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 66:7, s. 2994-3005 Tidskriftsartikel (refereegranskat)abstract It is well known that matched filtering and sampling (MFS) demodulation together with minimum Euclidean distance (MD) detection constitute the optimal receiver for the additive white Gaussian noise channel. However, for a general nonlinear transmission medium, MFS does not provide sufficient statistics, and therefore is suboptimal. Nonetheless, this receiver is widely used in optical systems, where the Kerr nonlinearity is the dominant impairment at high powers. In this paper, we consider a suite of receivers for a two-user channel subject to a type of nonlinear interference that occurs in wavelength-division-multiplexed channels. The asymptotes of the symbol error rate (SER) of the considered receivers at high powers are derived or bounded analytically. Moreover, Monte-Carlo simulations are conducted to evaluate the SER for all the receivers. Our results show that receivers that are based on MFS cannot achieve arbitrary low SERs, whereas the SER goes to zero as the power grows for the optimal receiver. Furthermore, we devise a heuristic demodulator, which together with the MD detector yields a receiver that is simpler than the optimal one and can achieve arbitrary low SERs. The SER performance of the proposed receivers is also evaluated for some single-span fiber-optical channels via split-step Fourier simulations.
71.	Keykhosravi, Kamran, 1990, et al. (författare) How to Increase the Achievable Information Rate by Per-Channel Dispersion Compensation 2019 Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 37:10, s. 2443-2451 Tidskriftsartikel (refereegranskat)abstract Deploying periodic inline chromatic dispersion compensation enables reducing the complexity of the digital back propagation (DBP) algorithm. However, compared with nondispersion-managed (NDM) links, dispersion-managed (DM) ones suffer a stronger cross-phase modulation (XPM). Utilizing per-channel dispersion-managed (CDM) links (e.g., using fiber Bragg grating) allows for a complexity reduction of DBP, while abating XPM compared to DM links. In this paper, we show for the first time that CDM links enable also a more effective XPM compensation compared to NDM ones, allowing a higher achievable information rate (AIR). This is explained by resorting to the frequency-resolved logarithmic perturbation model and showing that per-channel dispersion compensation increases the frequency correlation of the distortions induced by XPM over the channel bandwidth, making them more similar to a conventional phase noise. We compare the performance (in terms of the AIR) of a DM, an NDM, and a CDM link, considering two types of mismatched receivers: one neglects the XPM phase distortion and the other compensates for it. With the former, the CDM link is inferior to the NDM one due to an increased in-band signal--noise interaction. However, with the latter, a higher AIR is obtained with the CDM link than with the NDM one owing to a higher XPM frequency correlation. The DM link has the lowest AIR for both receivers because of a stronger XPM.
72.	Khanzadi, M Reza, 1983, et al. (författare) Capacity of SIMO and MISO Phase-Noise Channels with Common/Separate Oscillators 2015 Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 63:9, s. 3218-3231 Tidskriftsartikel (refereegranskat)abstract In multiple antenna systems, phase noise due to instabilities of the radio-frequency (RF) oscillators, acts differently depending on whether the RF circuitries connected to each antenna are driven by separate (independent) local oscillators (SLO) or by a common local oscillator (CLO). In this paper, we investigate the high-SNR capacity of single-input multiple-output (SIMO) and multiple-output single-input (MISO) phase-noise channels for both the CLO and the SLO configurations.Our results show that the first-order term in the high-SNR capacity expansion is the same for all scenarios (SIMO/MISO and SLO/CLO), and equal to 0.5ln(SNR), where SNR stands for the signal-to-noise ratio. On the contrary, the second-order term, which we refer to as phase-noise number, turns out to be scenario-dependent. For the SIMO case, the SLO configuration provides a diversity gain, resulting in a larger phase-noise number than for the CLO configuration. For the case of Wiener phase noise, a diversity gain of at least 0.5ln(M) can be achieved, where M is the number of receive antennas. For the MISO, the CLO configuration yields a higher phase-noise number than the SLO configuration. This is because with the CLO configuration one can obtain a coherent-combining gain through maximum ratio transmission (a.k.a. conjugate beamforming). This gain is unattainable with the SLO configuration.
73.	Khanzadi, M Reza, 1983, et al. (författare) High-SNR Capacity of Multiple-Antenna Phase-Noise Channels with Common/Separate RF Oscillators 2015 Ingår i: IEEE International Conference on Communications. - 1550-3607. - 9781467364324 ; 2015-September, s. 4012-4017 Konferensbidrag (refereegranskat)abstract In multiple antenna systems, phase noise due to instabilities of the radio-frequency (RF) oscillators, acts differently depending on whether the RF circuitries connected to each antenna are driven by separate (independent) local oscillators (SLO) or by a common local oscillator (CLO). In this paper, we investigate the high-SNR capacity of single-input multiple-output (SIMO) and multiple-output single-input (MISO) phase-noise channels for both the CLO and the SLO configurations.Our results show that the first-order term in the high-SNR capacity expansion is the same for all scenarios (SIMO/MISO and SLO/CLO), and equal to 0.5ln(SNR), where SNR stands for the signal-to-noise ratio. On the contrary, the second-order term, which we refer to as phase-noise number, turns out to be scenario-dependent. For the SIMO case, the SLO configuration provides a diversity gain, resulting in a larger phase-noise number than for the CLO configuration. For the case of Wiener phase noise, a diversity gain of at least 0.5ln(M) can be achieved, where M is the number of receive antennas. For the MISO, the CLO configuration yields a higher phase-noise number than the SLO configuration. This is because with the CLO configuration one can obtain a coherent-combining gain through maximum ratio transmission (a.k.a. conjugate beamforming). This gain is unattainable with the SLO configuration.
74.	Kildal, Per-Simon, 1951, et al. (författare) LTE MIMO multiplexing performance measured in reverberation chamber and accurate simple theory 2012 Ingår i: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012. Prague, 26-30 March 2012. - 9781457709180 ; , s. 2299-2302 Konferensbidrag (refereegranskat)abstract We present measurement results of the data-rate throughput inside a reverberation chamber of a commercial USB dongle operating in 2×2 MIMO spatial multiplexing configuration. A simple and accurate theory is provided by which the measured throughput can be accurately explained. The theory is based on a recently published digital threshold receiver model.
75.	Kislal, Ahmet Oguz, 1993, et al. (författare) Efficient evaluation of the error probability for pilot-assisted finite-blocklength transmission 2022 Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2022-October, s. 1038-1044 Konferensbidrag (refereegranskat)abstract We propose a numerically efficient method for evaluating the random-coding union bound with parameter s on the error probability achievable in the finite-blocklength regime by a pilot-assisted transmission scheme employing Gaussian code-books and operating over a memoryless block-fading channel. Our method relies on the saddlepoint approximation, which, differently from previous results reported for similar scenarios, is performed with respect to the number of fading blocks (a.k.a. diversity branches) spanned by each codeword, instead of the number of channel uses per block. This different approach avoids a costly numerical averaging of the error probability over the realizations of the fading process and of its pilot-based estimate at the receiver and yields a significant reduction of the number of channel realizations required to estimate the error probability via Monte-Carlo simulation. For example, in a single-input single-output scenario, when four or more diversity branches are available, an error probability of 10-4can be estimated accurately using our method by using less than 3000 samples. In contrast, the conventional saddlepoint approach requires around 106samples.
76.	Kislal, Ahmet Oguz, 1993, et al. (författare) Efficient evaluation of the error probability for pilot-assisted URLLC with Massive MIMO 2023 Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 41:7, s. 1969-1981 Tidskriftsartikel (refereegranskat)abstract We propose a numerically efficient method for evaluating the random-coding union bound with parameter s on the error probability achievable in the finite-blocklength regime by a pilot-assisted transmission scheme employing Gaussian code-books and operating over a memoryless block-fading channel. Our method relies on the saddlepoint approximation, which, differently from previous results reported for similar scenarios, is performed with respect to the number of fading blocks (a.k.a. diversity branches) spanned by each codeword, instead of the number of channel uses per block. This different approach avoids a costly numerical averaging of the error probability over the realizations of the fading process and of its pilot-based estimate at the receiver and results in a significant reduction of the number of channel realizations required to estimate the error probability accurately. Our numerical experiments for both single-antenna communication links and massive multiple-input multiple-output (MIMO) networks show that, when two or more diversity branches are available, the error probability can be estimated accurately with the saddlepoint approximation with respect to the number of fading blocks using a numerical method that requires about two orders of magnitude fewer Monte-Carlo samples than with the saddlepoint approximation with respect to the number of channel uses per block.
77.	Koliander, Günther, et al. (författare) A Lower Bound on the Noncoherent Capacity Pre-log for the MIMO Channel with temporally correlated fading 2012 Ingår i: 50th Annual Allerton Conference on Communication, Control, and Computing, 2012. - 9781467345378 ; , s. 1198 - 1205 Konferensbidrag (refereegranskat)abstract We derive a lower bound on the capacity pre-log of a temporally correlated Rayleigh block-fading multiple-input multiple-output (MIMO) channel with T transmit antennas and R receive antennas in the noncoherent setting (no a priori channel knowledge at the transmitter and the receiver). In this model, the fading process changes independently across blocks of length L and is temporally correlated within each block for each transmit-receive antenna pair, with a given rank Q of the corresponding correlation matrix. Our result implies that for almost all choices of the coloring matrix that models the temporal correlation, the pre-log can be lower-bounded by T(1 - 1/L) for T ≤ (L - 1)/Q provided that R is sufficiently large. The widely used constant block-fading model is equivalent to the temporally correlated block-fading model with Q = 1 for the special case when the temporal correlation for each transmit-receive antenna pair is the same, which is unlikely to be observed in practice. For the constant block-fading model, the capacity pre-log is given by T(1 - T/L), which is smaller than our lower bound for the case Q = 1. Thus, our result suggests that the assumptions underlying the constant blockfading model lead to a pessimistic result for the capacity pre-log.
78.	Koliander, Günther, et al. (författare) Degrees of Freedom of Generic Block-Fading MIMO Channels Without a Priori Channel State Information 2014 Ingår i: IEEE Transactions on Information Theory. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9448 .- 1557-9654. ; 60:12, s. 7760-7781 Tidskriftsartikel (refereegranskat)abstract We study the high-signal-to-noise-ratio capacity of generic multiple-input multiple-output (MIMO) Rayleigh block-fading channels in the noncoherent setting where neither transmitter nor receiver has a priori channel state information but both are aware of the channel statistics. In contrast to the well-established constant block-fading model, we allow the fading to vary within each block with a temporal correlation that is generic (in the sense used in the interference-alignment literature). We show that the number of degrees of freedom of a generic MIMO Rayleigh block-fading channel with T transmit antennas and block length N is given by T(1 - 1/N) provided that T
79.	Koliander, Günther, et al. (författare) Generic correlation increases noncoherent MIMO capacity 2013 Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. - 9781479904464 ; , s. 2084-2088 Konferensbidrag (refereegranskat)abstract We study the high-SNR capacity of MIMO Rayleigh block-fading channels in the noncoherent setting where neither transmitter nor receiver has a priori channel state information. We show that when the number of receive antennas is sufficiently large and the temporal correlation within each block is “generic” (in the sense used in the interference-alignment literature), the capacity pre-log is given by T(1 − 1/N) for T
80.	Kuppinger, Patrick, et al. (författare) Uncertainty Relations and Sparse Signal Recovery for Pairs of General Signal Sets 2012 Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 58:1, s. 263 - 277 Tidskriftsartikel (refereegranskat)abstract We present an uncertainty relation for the representation of signals in two different general (possibly redundant or incomplete) signal sets. Specifically, our results improve on the well-known (1+1/d)/2-threshold for dictionaries with coherence d by up to a factor of two. Furthermore, the new uncertainty relation is shown to lead to improved sparsity thresholds for recovery of signals that are sparse in general dictionaries. Furthermore, we provide probabilistic recovery guarantees for pairs of general dictionaries that also allow us to understand which parts of a general dictionary one needs to randomize over to ``weed out'' the sparsity patterns that prohibit breaking the square-root bottleneck.This uncertainty relation is relevant for the analysis of signals containing two distinct features each of which can be described sparsely in a suitable general signal set.
81.	Lancho, Alejandro, et al. (författare) A High-SNR Normal Approximation for Single-Antenna Rayleigh Block-Fading Channels 2017 Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; , s. 1773-1777 Konferensbidrag (refereegranskat)abstract This paper concerns the maximal achievable rate at which data can be transmitted over a non-coherent, single- antenna, Rayleigh block-fading channel using an error-correcting code of a given blocklength with a block-error probability not exceeding a given value. In particular, a high-SNR normal approximation of the maximal achievable rate is presented that becomes accurate as the signal-to-noise ratio (SNR) and the number of coherence intervals L over which we code tend to infinity. Numerical analyses suggest that the approximation is accurate already at SNR values of 15 dB.
82.	Lancho, Alejandro, et al. (författare) Normal Approximations for Fading Channels 2018 Ingår i: 2018 52ND ANNUAL CONFERENCE ON INFORMATION SCIENCES AND SYSTEMS (CISS). - 9781538605790 - 9781538605790 Konferensbidrag (refereegranskat)abstract Capacity and outage capacity characterize the maximum coding rate at which reliable communication is feasible when there are no constraints on the packet length. Evaluated for fading channels, they are important performance benchmarks for wireless communication systems. However, the latency of a communication system is proportional to the length of the packets it exchanges, so assuming that there are no constraints on the packet length may be overly optimistic for communication systems with stringent latency constraints. Recently, there has been great interest within the information theory community in characterizing the maximum coding rate for short packet lengths. Research on this topic is often concerned with asymptotic expansions of the coding rate with respect to the packet length, which then give rise to normal approximations. In this paper, we review existing normal approximations for single-antenna Rayleigh block-fading channels and compare them with the highSNR normal approximation we presented at the 2017 IEEE International Symposium on Information Theory (Lancho, Koch, and Durisi, 2017). We further discuss how these normal approximations may help to assess the performance of communication protocols.
83.	Lancho Serrano, Alejandro, 1991, et al. (författare) A Finite-Blocklength Analysis for URLLC with Massive MIMO 2021 Ingår i: IEEE International Conference on Communications. - 1550-3607. ; June 2021 Konferensbidrag (refereegranskat)abstract This paper presents a rigorous finite-blocklength framework for the characterization and the numerical evaluation of the packet error probability achievable in the uplink and downlink of Massive MIMO for ultra-reliable low-latency communications (URLLC). The framework encompasses imperfect channel-state information, pilot contamination, spatially correlated channels, and arbitrary linear signal processing. For a practical URLLC network setup involving base stations with M = 100 antennas, we show by means of numerical results that a target error probability of 10-5 can be achieved with MMSE channel estimation and multicell MMSE signal processing, uniformly over each cell, only if orthogonal pilot sequences are assigned to all the users in the network. For the same setting, an alternative solution with lower computational complexity, based on least-squares channel estimation and regularized zero-forcing signal processing, does not suffice unless M is increased significantly.
84.	Lancho Serrano, Alejandro, 1991, et al. (författare) Cell-Free Massive MIMO for URLLC: A Finite-Blocklength Analysis 2023 Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 22:12, s. 8723-8735 Tidskriftsartikel (refereegranskat)abstract We present a general framework for the characterization of the packet error probability achievable in cell-free Massive multiple-input multiple output (MIMO) architectures deployed to support ultra-reliable low-latency (URLLC) traffic. The framework is general and encompasses both centralized and distributed cell-free architectures, arbitrary fading channels and channel estimation algorithms at both network and user-equipment (UE) sides, as well as arbitrary combing and precoding schemes. The framework is used to perform numerical experiments on specific scenarios, which illustrate the superiority of cell-free architectures compared to cellular architectures in supporting URLLC traffic in uplink and downlink. Also, these numerical experiments provide the following insights into the design of cell-free architectures for URLLC: i) minimum mean square error (MMSE) spatial processing must be used to achieve the URLLC targets; ii) for a given total number of antennas per coverage area, centralized cell-free solutions involving single-antenna access points (APs) offer the best performance in the uplink, thereby highlighting the importance of reducing the average distance between APs and UEs in the URLLC regime; iii) this observation applies also to the downlink, provided that the APs transmit precoded pilots to allow the UEs to estimate accurately the precoded channel.
85.	Lancho Serrano, Alejandro, 1991, et al. (författare) Cell-free Massive MIMO with Short Packets 2021 Ingår i: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC. ; 2021-September, s. 416-420 Konferensbidrag (refereegranskat)abstract In this paper, we adapt to cell-free Massive MIMO (multiple-input multiple-output) the finite-blocklength framework introduced by Ostman et al. (2020) for the charac- ¨ terization of the packet error probability achievable with Massive MIMO, in the ultra-reliable low-latency communications (URLLC) regime. The framework considered in this paper encompasses a cell-free architecture with imperfect channelstate information, and arbitrary linear signal processing performed at a central-processing unit connected to the access points via fronthaul links. By means of numerical simulations, we show that, to achieve the high reliability requirements in URLLC, MMSE signal processing must be used. Comparisons are also made with both small-cell and Massive MIMO cellular networks. Both require a much larger number of antennas to achieve comparable performance to cell-free Massive MIMO.
86.	Lancho Serrano, Alejandro, 1991, et al. (författare) On Joint Detection and Decoding in Short-Packet Communications 2021 Ingår i: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. Konferensbidrag (refereegranskat)abstract We consider a communication problem in which the receiver must first detect the presence of an information packet and, if detected, decode the message carried within it. We present general nonasymptotic upper and lower bounds on the maximum coding rate that depend on the blocklength, the probability of false alarm, the probability of misdetection, and the packet error probability. The bounds, which are expressed in terms of binary-hypothesis-testing performance metrics, generalize finiteblocklength bounds derived previously for the scenario when a genie informs the receiver whether a packet is present. The bounds apply to detection performed either jointly with decoding on the entire data packet, or separately on a dedicated preamble. The results presented in this paper can be used to determine the blocklength values at which the performance of a communication system is limited by its ability to perform packet detection satisfactorily, and to assess the difference inperformance between preamblebased detection, and joint detection and decoding. Numerical results pertaining to the binary-input AWGN channel are provided.
87.	Lancho Serrano, Alejandro, 1991, et al. (författare) On single-antenna Rayleigh block-fading channels at finite blocklength 2020 Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 66:1, s. 496-519 Tidskriftsartikel (refereegranskat)abstract This article concerns the maximum coding rate at which data can be transmitted over a noncoherent, single-antenna, Rayleigh block-fading channel using an error-correcting code of a given blocklength with a block-error probability not exceeding a given value. A high-SNR normal approximation of the maximum coding rate is presented that becomes accurate as the signal-to-noise ratio (SNR) and the number of coherence intervals $L$ over which we code tend to infinity. Numerical analyses suggest that the approximation is accurate at SNR values above 15dB and when the number of coherence intervals is 10 or more.
88.	Lancho Serrano, Alejandro, 1991, et al. (författare) Saddlepoint Approximations for Noncoherent Single-Antenna Rayleigh Block-Fading Channels 2019 Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2019-July, s. 612-616 Konferensbidrag (refereegranskat)abstract This paper presents saddlepoint approximations of state-of-the-art converse and achievability bounds for noncoherent, single-antenna, Rayleigh block-fading channels. These approximations can be calculated efficiently and are shown to be accurate for SNR values as small as 0 dB, blocklengths of 168 channel uses or more, and when the channel's coherence interval is not smaller than two. It is demonstrated that the derived approximations recover both the normal approximation and the reliability function of the channel.
89.	Lancho Serrano, Alejandro, 1991, et al. (författare) Saddlepoint Approximations for Short-Packet Wireless Communications 2020 Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 19:7, s. 4831-4846 Tidskriftsartikel (refereegranskat)abstract In recent years, the derivation of nonasymptotic converse and achievability bounds on the maximum coding rate as a function of the error probability and blocklength has gained attention in the information theory literature. While these bounds are accurate for many scenarios of interest, they need to be evaluated numerically for most wireless channels of practical interest, and their evaluation is computationally demanding. This paper presents saddlepoint approximations of state-of-the-art converse and achievability bounds for noncoherent, single-antenna, Rayleigh block-fading channels. These approximations can be calculated efficiently and are shown to be accurate for SNR values as small as 0 dB and blocklengths of 168 channel uses or more.
90.	Liva, Gianluigi, et al. (författare) Short Codes with Mismatched Channel State Information: A Case Study 2017 Ingår i: Proc. IEEE Int. Workshop Signal Process. Advances Wireless Commun. (SPAWC). ; 2017-July Konferensbidrag (refereegranskat)abstract The rising interest in applications requiring the transmission of small amounts of data has recently lead to the development of accurate performance bounds and of powerful channel codes for the transmission of short-data packets over the AWGN channel. Much less is known about the interaction between error control coding and channel estimation at short blocks when transmitting over channels with states (e.g., fading channels, phase-noise channels, etc. . . ) for the setup where no a priori channel state information (CSI) is available at the trans- mitter and the receiver. In this paper, we use the mismatched- decoding framework to characterize the fundamental tradeoff occurring in the transmission of short data packet over an AWGN channel with unknown gain that stays constant over the packet. Our analysis for this simplified setup aims at showing the potential of mismatched decoding as a tool to design and analyze transmission strategies for short blocks. We focus on a pragmatic approach where the transmission frame contains a codeword as well as a preamble that is used to estimate the channel (the codeword symbols are not used for channel estimation). Achievability and converse bounds on the block error probability achievable by this approach are provided and compared with simulation results for schemes employing short low-density parity-check codes. Our bounds turn out to predict accurately the optimal trade-off between the preamble length and the redundancy introduced by the channel code.
91.	Marti, Gian, et al. (författare) Hybrid Jammer Mitigation for All-Digital mmWave Massive MU-MIMO 2021 Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. - 9781665458283 ; 2021-October Konferensbidrag (refereegranskat)abstract Low-resolution analog-to-digital converters (ADCs) simplify the design of millimeter-wave (mmWave) massive multi-user multiple-input multiple-output (MU-MIMO) base-stations, but increase vulnerability to jamming attacks. As a remedy, we propose HERMIT (short for Hybrid jammER MITigation), a method that combines a hardware-friendly adaptive analog transform with a corresponding digital equalizer: The analog transform removes most of the jammer’s energy prior to data conversion; the digital equalizer suppresses jammer residues while detecting the legitimate transmit data. We provide theoretical results that establish the optimal analog transform as a function of the user equipments' and the jammer’s channels. Using simulations with mmWave channel models, we demonstrate the superiority of HERMIT compared both to purely digital jammer mitigation as well as to a recent hybrid method that mitigates jammer interference with a nonadaptive analog transform.
92.	Morgenshtern, Veniamin I., et al. (författare) Capacity Pre-Log of Noncoherent SIMO Channels via Hironaka’s Theorem 2013 Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 59:7, s. 4213-4229 Tidskriftsartikel (refereegranskat)abstract We find the capacity pre-log of a temporally correlatedRayleigh block-fading single-input multiple-output (SIMO)channel in the noncoherent setting. It is well known that for blocklength $L$ and rank of the channel covariance matrix equal to $Q$, the capacity pre-log in the single-input single-output (SISO) case is given by $1-Q/L$. Here, $Q/L$ can be interpreted as the pre-log penalty incurred by channel uncertainty. Our main result reveals that, by adding only one receive antenna, this penalty can be reduced to $1/L$ and can, hence, be made to vanish for the blocklength$L\to\infty$, even if $Q/L$ remains constant as $L\to\infty$. Intuitively, even though the SISO channels between the transmit antenna and the two receive antennas are statistically independent, the transmit signal induces enough statistical dependence between the corresponding receive signals for the second receive antenna to be able to resolve the uncertainty associated with the first receive antenna’s channel and thereby make the overall system appear coherent. The proof of our main theorem is based on a deep result from algebraic geometry known as Hironaka’s Theorem on the Resolution of Singularities.
93.	Movahed, A., et al. (författare) A robust {RFPI}-based 1-bit compressive sensing reconstruction algorithm 2012 Ingår i: IEEE Information Theory Workshop (ITW), Lausanne, 3-7 September 2012. - 9781467302234 ; , s. 567-571 Konferensbidrag (refereegranskat)abstract n this paper, we introduce a 1-bit compressive sensing reconstruction algorithm that is not only robust against bit flips in the binary measurement vector, but also does not require a priori knowledge of the sparsity level of the signal to be reconstructed. Through numerical experiments, we show that our algorithm outperforms state-of-the-art reconstruction algorithms for the 1-bit compressive sensing problem in the presence of random bit flips and when the sparsity level of the signal deviates from its estimated value.
94.	Munari, Andrea, et al. (författare) An Age of Information Characterization of Frameless ALOHA 2021 Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2021-October, s. 1488-1495 Konferensbidrag (refereegranskat)abstract We provide a characterization of the peak age of information (AoI) achievable in a random-access system operating according to the frameless ALOHA protocol. Differently from previous studies, our analysis accounts for the fact that the number of terminals contending the channel may vary over time, as a function of the duration of the previous contention period. The exact characterization of the AoI provided in this paper, which is based on a Markovian analysis, reveals the impact of some key protocol parameters such as the maximum length of the contention period, on the average peak AoI. Specifically, we show that setting this parameter so as to maximize the throughput may result in an AoI degradation.
95.	Munari, Andrea, et al. (författare) The Dynamic Behavior of Frameless ALOHA: Drift Analysis, Throughput, and Age of Information 2023 Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 71:12, s. 6914-6927 Tidskriftsartikel (refereegranskat)abstract We study the dynamic behavior of frameless ALOHA, both in terms of throughput and age of information (AoI). In particular, differently from previous studies, our analysis accounts for the fact that the number of terminals contending the channel may vary over time, as a function of the duration of the previous contention period. The stability of the protocol is analyzed via a drift analysis, which allows us to determine the presence of stable and unstable equilibrium points. We also provide an exact characterization of the AoI performance, through which we determine the impact of some key protocol parameters, such as the maximum length of the contention period, on the average AoI. Specifically, we show that configurations of parameters that maximize the throughput may result in a degradation of the AoI performance.
96.	Ngo, Khac-Hoang, 1992, et al. (författare) Age of Information in Prioritized Random Access 2021 Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. - 9781665458283 ; 2021-October Konferensbidrag (refereegranskat)abstract Age of information (AoI) is a performance metric that captures the freshness of status updates. While AoI has been studied thoroughly for point-to-point links, the impact of modern random-access protocols on this metric is still unclear. In this paper, we extend the recent results by Munari to prioritized random access where devices are divided into different classes according to different AoI requirements. We consider the irregular repetition slotted ALOHA protocol and analyze the AoI evolution by means of a Markovian analysis following similar lines as in Munari (2021). We aim to design the protocol to satisfy the AoI requirements for each class while minimizing the power consumption. To this end, we optimize the update probability and the degree distributions of each class, such that the probability that their AoI exceeds a given threshold lies below a given target and the average number of transmitted packets is minimized.
97.	Ngo, Khac-Hoang, 1992, et al. (författare) Age of Information in Slotted ALOHA With Energy Harvesting 2023 Ingår i: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. ; , s. 3579-3584 Konferensbidrag (refereegranskat)abstract We examine the age of information (AoI) of a status update system that incorporates energy harvesting and uses the slotted ALOHA protocol. We derive analytically the average AoI and the probability that the AoI exceeds a given threshold. Via numerical results, we investigate two strategies to minimize the age of information (AoI): transmitting a new update whenever possible to exploit every chance to reduce the AoI, and transmitting only when sufficient energy is available to increase the chance of successful delivery. The two strategies are beneficial for low and high update generation rates, respectively. However, an optimized approach that balances the two strategies outperforms them significantly in terms of both AoI and throughput.
98.	Ngo, Khac-Hoang, 1992, et al. (författare) Irregular Repetition Slotted ALOHA Over the Binary Adder Channel 2023 Ingår i: IEEE International Conference on Communications. - 1550-3607. ; 2023-May, s. 5346-5351 Konferensbidrag (refereegranskat)abstract We propose an irregular repetition slotted ALOHA (IRSA) based random-access protocol for the binary adder channel (BAC). The BAC captures important physical-layer concepts, such as packet generation, per-slot decoding, and information rate, which are neglected in the commonly considered collision channel model. We divide a frame into slots and let users generate a packet, to be transmitted over a slot, from a given codebook. In a state-of-the-art scheme proposed by Paolini et al. (2022), the codebook is constructed as the parity-check matrix of a BCH code. Here, we construct the codebook from independent and identically distributed binary symbols to obtain a random-coding achievability bound. Our per-slot decoder progressively discards incompatible codewords from a list of candidate codewords, and can be improved by shrinking this list across iterations. In a regime of practical interests, our scheme can resolve more colliding users in a slot and thus achieves a higher average sum rate than the scheme in Paolini et al. (2022).
99.	Ngo, Khac-Hoang, 1992, et al. (författare) Massive Uncoordinated Access with Random User Activity 2021 Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 2021-July, s. 3014-3019 Konferensbidrag (refereegranskat)abstract We extend the seminal work by Polyanskiy (2017) on massive uncoordinated access to the case where the number of active users is random and unknown a priori. We define a random-access code accounting for both misdetection (MD) and false-alarm (FA), and derive a random-coding achievability bound for the Gaussian multiple access channel. Our bound captures the fundamental trade-off between MD and FA probabilities. It suggests that lack of knowledge of the number of active users entails a small penalty in power efficiency. For a typical scenario, to achieve both MD and FA probabilities below 0.1, the required energy per bit predicted by our bound is 0.5-0.7 dB higher than that predicted by the bound in Polyanskiy (2017) for a known number of active users. Taking both MD and FA into account, we use our bound to benchmark the energy efficiency of some recently proposed massive random access schemes.
100.	Ngo, Khac-Hoang, 1992, et al. (författare) Unsourced Multiple Access for Heterogeneous Traffic Requirements 2022 Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2022-October, s. 687-691 Konferensbidrag (refereegranskat)abstract We investigate the coexistence of critical and massive Internet of Things (IoT) services in the context of the unsourced multiple access (UMA) framework, introduced by Polyanskiy (2017). We consider the standard UMA setup in which all users employ a common codebook and the receiver returns an unordered list of codewords. To model the critical IoT service, we assume that the users can also communicate a common alarm message. We further assume that the number of active users in each transmission attempt is random and unknown. We derive a random-coding bound for the Gaussian multiple access channel and demonstrate that orthogonal network slicing enables the two traffic types to coexist with high energy efficiency.

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