117 research outputs found
SINR profile for spectral efficiency optimization of SIC receivers in the many-user regime
© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In dense wireless scenarios, and particularly under
high traffic loads, the design of efficient random access protocols
is necessary. Some candidate solutions are based on Direct-
Sequence Spread Spectrum (DS-SS) combined with a Successive
Interference Cancellation (SIC) demodulator, but the perfor-
mance of these techniques is highly related to the distribution
of the users received power. In that context, this paper presents
a theoretical analysis to calculate the optimum user SINR profile
at the decoder maximizing the spectral efficiency in bps/Hz for
a specific modulation and practical Forward Error Correction
(FEC) code. This solution is achieved by means of Variational
Calculus operating in the asymptotic large-user case. Although
a constant SINR function has been typically assumed in the
literature (the one maximizing capacity), the theoretical results
evidence that the optimum SINR profile must be an increasing
function of the users received power. Its performance is compared
with that of the uniform profile for two representative scenarios
with different channel codes in a slightly overloaded system.
The numerical results show that the optimum solution regulates
the network load preventing the aggregate throughput from
collapsing when the system is overloaded. In scenarios with a
large number of transmitters, this optimum solution can be
implemented in an uncoordinated manner with the knowledge
of a few public system parameters.Peer ReviewedPostprint (published version
Optimal power control law for equal-rate DS-CDMA networks governed by a successive soft interference cancellation scheme
©2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper studies the throughput maximization of a dense multiple access network of low-rate subscribers that share the same practical Forward Error Correction (FEC) code and modulation scheme, and transmit to a central node that implements a Successive Soft Interference Cancellation (soft SIC) strategy in order to mitigate Multiple Access Interference (MAI). In the user-asymptotic case, we make use of Variational Calculus (VC) tools to derive, in terms of the Packet Error Rate (PER) of the shared encoder and the Residual Energy (RE) from imperfect cancellation, the optimum energy profile that maximizes the network spectral efficiency, when a sum power constraint at the SIC input is enforced. Comparative performance analyses using a representative encoder are carried out. Simulation results show the benefit of the adopted soft SIC scheme in front of other SIC strategies, obtaining relevant throughput gains under high traffic loads.Peer ReviewedPostprint (author's final draft
Joint energy and rate allocation for successive interference cancellation in the finite blocklength regime
© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This work addresses the optimization of the network spectral efficiency (SE) under successive interference cancellation (SIC) at a given blocklength n. We adopt a proof-of-concept satellite scenario where network users can vary their transmission power and select their transmission rate from a set of encoders, for which decoding is characterized by a known packet error rate (PER) function. In the large-system limit, we apply variational calculus (VC) to obtain the user-energy distribution, the assigned per-user rate and the SIC decoding order maximizing the network SE under a sum-power constraint at the SIC input. We analyze two encoder sets: (i) an infinite set of encoders achieving information-theoretic finite blocklength PER results over a continuum of code rates, where the large-n second order expansion of the maximal channel coding rate is used; (ii) a feasible finite set of encoders. Simulations quantify the
performance gap between the two schemes.Peer ReviewedPostprint (author's final draft
Decentralized random energy allocation for massive non-orthogonal code-division multiple access
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This work studies the spectral efficiency achievable when a very large number of terminals are connected simultaneously to a central node (uplink) through independent and identically-distributed flat-fading channels. Assuming that terminals only have statistical channel state information (CSI), the optimum random transmitted-energy allocation is formulated considering a non-orthogonal direct-sequence code-division multiple access (DS-CDMA) where all users transmit using the same modulation and error correcting code and the receiver implements successive interference cancellation (SIC). Focusing on low-power terminals, optimization is carried out by imposing constraints on both the average and peak peruser transmitted energy. Simulations have revealed that a limited number of random energy levels, whose number is determined by the channel power gain variance, is sufficient to achieve approximately the maximum spectral efficiency that would be obtained under direct optimization of the received energy profile.Peer ReviewedPostprint (author's final draft
Channel-aware energy allocation for throughput maximization in massive low-rate multiple access
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.A multiple access (MA) optimization technique for massive low-rate direct-sequence spread spectrum communications is analyzed in this work. A dense network of users transmitting at the same rate to a common central node under channelaware energy allocation is evaluated. At reception, successive interference cancellation (SIC) aided by channel decoding is adopted. Our contribution focuses on wireless scenarios involving a vast number of users for which the provided user-asymptotic model holds. Variational calculus (VC) is employed to derive the energy allocation function that, via user-power imbalance, maximizes the network spectral efficiency (SE) when perfect channel state information at transmission (CSIT) is available and both average and maximum per-user energy constraints are set.
Monte Carlo simulations at chip-level of a SIC receiver using a real decoder assess the proposed optimization method.Peer ReviewedPostprint (published version
Energy and rate allocation for massive multiple access with interference cancelation
This article addresses the problem of energy and code allocation to many users accessing, under spreading-based nonorthogonal multiple access, a wireless node set up with a successive interference cancellation architecture aided by redundancy-check error control. As an application, we consider the asynchronous access of a delay-tolerant satellite system, where users employ finite-length channel codes and are subject to a known power unbalance induced by the known distribution of the channelâs attenuation. The article develops, as a mathematically tractable approximation to massively populated systems, a unified framework to compute the best energy and code allocation rules that maximize the spectral efficiency of a network that handles asymptotically many users. Concretely, the presented approach circumvents the exponential complexity in the number of users when modeling the propagation of packet decoding failures through the receiverâs decoding scheme. It also enables a deterministic analysis of the more complex features affecting the receiver, making the related performance optimization problem amenable to systematic tools from differential and variational calculus. The derived expressions evidence the most favorable three-way unbalance between energy, rate, and reliability for receiver performance. Low-level system simulations are carried out for validation.This work was supported in part by the Spanish Ministry of Science and Innovation through project RODIN (PID2019-105717RB-C22/AEI/10.13039/501100011033) and in part by Grant 2017 SGR 578.Peer ReviewedPostprint (published version
ADC Quantization Requirements
In this document, we analyze the impact of the quantization at the input of the demultiplexer. The required number of bits of the Analog-to-Digital-Converter (ADC) is obtained, along with the corresponding quantization losses.Preprin
Indexed left atrial size predicts all-cause and cardiovascular mortality in patients undergoing aortic valve surgery
[Abstract] OBJECTIVES: The enlargement of the left atrium has been identified as a marker of chronically increased left ventricular filling pressure and left ventricular diastolic dysfunction. This study aims to evaluate the association of indexed left atrial diameter with stroke, cardiovascular mortality, the combined event, and all-cause mortality in patients who underwent aortic valve surgery.
METHODS: Indexed left atrial diameter was measured in 2011 adult patients (mean age, 70.9 ± 10.8 years; 58.7% were men) who underwent aortic valve surgery between January 2008 and March 2016.
RESULTS: On the basis of the criteria of the American Society of Echocardiography, indexed left atrial diameter was normal in 64% of patients, mildly enlarged in 12.4% of patients, moderately enlarged in 9.2% of patients, and severely enlarged in 14.3% of patients. Over a mean follow-up period of 3.2 ± 2.1 years, there were 334 deaths and 97 strokes. Cardiovascular mortality survival at 5 years among patients with normal, mild, moderate, and severe left atrial enlargement was 91.6%, 86.8%, 77.9%, and 77.4%, respectively (P < .001). After covariable adjustment, Cox regression analysis showed indexed left atrial diameter as an independent predictor of all-cause mortality (hazard ratio per 1-cm/m2 increment, 1.545; 95% confidence interval, 1.252-1.906, P < .001), cardiovascular death (hazard ratio per 1-cm/m2 increment, 1.971; 95% confidence interval, 1.541-2.520; P < .001), and the combined event (hazard ratio per 1-cm/m2 increment, 1.673; 95% confidence interval, 1.321-2.119; P < .001).
CONCLUSIONS: Indexed left atrial diameter is a strong predictor of long-term outcomes in patients with aortic valve diseases who undergo surgery
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