About

Costas N. Georghiades is an Interim Vice President for Research and a Professor in the Department of Electrical & Computer Engineering at Texas A&M University. He holds the Delbert A. Whitaker Chair and is an affiliated faculty member in Multidisciplinary Engineering. His educational background includes a D.Sc. and an M.S. in Electrical Engineering from Washington University, obtained in 1985 and 1983 respectively, and a B.E. in Electrical Engineering from the American University of Beirut in 1980. His research interests encompass statistical communication theory, receiver design, mobile radio including multipath and fading channels, synchronization and equalization, distributed source and space-time coding, interference rejection techniques, multicarrier modulation, and optical and magnetic recording channels. He is a Fellow of the Institute of Electrical and Electronics Engineers (IEEE) and has received several honors, including the Brocket Professorship in 2002, the J.W. Runyon, Jr., Professorship in 1997, and the Halliburton Professorship at Texas A&M University in 1995.

Research topics

• Computer Science
• Mathematics
• Algorithm
• Telecommunications
• Artificial Intelligence
• Arithmetic
• Computer network
• Statistics
• Acoustics
• Theoretical computer science
• Physics

Selected publications

• PolarAir: A Compressed Sensing Scheme for Over-the-Air Federated Learning

  arXiv (Cornell University) · 2023-01-24

  preprintOpen accessSenior author

  We explore a scheme that enables the training of a deep neural network in a Federated Learning configuration over an additive white Gaussian noise channel. The goal is to create a low complexity, linear compression strategy, called PolarAir, that reduces the size of the gradient at the user side to lower the number of channel uses needed to transmit it. The suggested approach belongs to the family of compressed sensing techniques, yet it constructs the sensing matrix and the recovery procedure using multiple access techniques. Simulations show that it can reduce the number of channel uses by ~30% when compared to conveying the gradient without compression. The main advantage of the proposed scheme over other schemes in the literature is its low time complexity. We also investigate the behavior of gradient updates and the performance of PolarAir throughout the training process to obtain insight on how best to construct this compression scheme based on compressed sensing.

  PublisherOA PDFDOI

• PolarAir: A Compressed Sensing Scheme for Over-the-Air Federated Learning

  2023-04-23 · 1 citations

  articleSenior author

  We explore a scheme that enables the training of a deep neural network in a Federated Learning configuration over an additive white Gaussian noise channel. The goal is to create a low complexity, linear compression strategy, called PolarAir, that reduces the size of the gradient at the user side to lower the number of channel uses needed to transmit it. The suggested approach belongs to the family of compressed sensing techniques, yet it constructs the sensing matrix and the recovery procedure using multiple access techniques. Simulations show that it can reduce the number of channel uses by ∼30% when compared to conveying the gradient without compression. The main advantage of the proposed scheme over other schemes in the literature is its low time complexity. We also investigate the behavior of gradient updates and the performance of PolarAir throughout the training process to obtain insight on how best to construct this compression scheme based on compressed sensing.

  PublisherDOI

• FASURA: A Scheme for Quasi-Static Fading Unsourced Random Access Channels

  IEEE Transactions on Communications · 2023-07-18 · 29 citations

  articleSenior author

  Unsourced random access emerged as a novel wireless paradigm enabling massive device connectivity on the uplink. We consider quasi-static Rayleigh fading wherein the access point has multiple receive antennas and every mobile device a single transmit antenna. The objective is to construct a coding scheme that minimizes the energy-per-bit subject to a maximum probability of error given a fixed message length and a prescribed number of channel uses. Every message is partitioned into two parts: the first determines pilot values and spreading sequences; the remaining bits are encoded using a polar code. The transmitted signal contains two distinct sections. The first features pilots and the second is composed of spread modulated symbols. The receiver has three modules: an energy detector, tasked with recovering the set of active pilot sequences; a bank of Minimum Mean Square Error (MMSE) estimators acting on measurements at the receiver; and a polar list-decoder, which seeks to retrieve the coded information bits. A successive cancellation step is applied to subtract recovered codewords, before the residual signal is fed back to the decoder. Empirical evidence suggests that an appropriate combination of these ideas can outperform state-of-the-art coding techniques when the number of active users exceeds one hundred.

  PublisherDOI

• Scalable Cell-Free Massive MIMO Unsourced Random Access System

  arXiv (Cornell University) · 2023-04-12 · 1 citations

  preprintOpen access

  Cell-Free Massive MIMO systems aim to expand the coverage area of wireless networks by replacing a single high-performance Access Point (AP) with multiple small, distributed APs connected to a Central Processing Unit (CPU) through a fronthaul. Another novel wireless approach, known as the unsourced random access (URA) paradigm, enables a large number of devices to communicate concurrently on the uplink. We consider a quasi-static Rayleigh fading channel paired to a scalable cell-free system, wherein a small number of receive antennas in the distributed APs serve devices equipped with a single antenna each. The goal of the study is to extend previous URA results to more realistic channels by examining the performance of a scalable cell-free system. To achieve this goal, we construct a coding scheme that adapts the URA paradigm to various cell-free scenarios. Empirical evidence suggests that using a cell-free architecture can improve the performance of a URA system, especially when taking into account large-scale attenuation and fading.

  PublisherOA PDFDOI

• FASURA: A Scheme for Quasi-Static Massive MIMO Unsourced Random Access Channels

  arXiv (Cornell University) · 2022-02-22

  preprintOpen accessSenior author

  This article considers the massive MIMO unsourced random access problem on a quasi-static Rayleigh fading channel. Given a fixed message length and a prescribed number of channel uses, the objective is to construct a coding scheme that minimizes the energy-per-bit subject to a fixed probability of error. The proposed scheme differs from other state-of-the-art schemes in that it blends activity detection, single-user coding, pilot-aided and temporary decisions-aided iterative channel estimation and decoding, minimum-mean squared error (MMSE) estimation, and successive interference cancellation (SIC). We show that an appropriate combination of these ideas can substantially outperform state-of-the-art coding schemes when the number of active users is more than 100, making this the best performing scheme known for this regime.

  PublisherOA PDFDOI

• FASURA: A Scheme for Quasi-Static Massive MIMO Unsourced Random Access Channels

  2022 IEEE 23rd International Workshop on Signal Processing Advances in Wireless Communication (SPAWC) · 2022 · 34 citations

  Senior authorCorresponding
  • Computer Science
  • Computer Science
  • Algorithm

  This article considers the massive MIMO unsourced random access problem on a quasi-static Rayleigh fading channel. Given a fixed message length and a prescribed number of channel uses, the objective is to construct a coding scheme that minimizes the energy-per-bit subject to a fixed probability of error. The proposed scheme differs from other state-of-the-art schemes in that it blends activity detection, single-user coding, pilot-aided and temporary decisions-aided iterative channel estimation and decoding, minimum-mean squared error (MMSE) estimation, and successive interference cancellation (SIC). We show that an appropriate combination of these ideas can substantially outperform state-of-the-art coding schemes when the number of active users is more than 100, making this the best performing scheme known for this regime.

  PublisherDOI

• Approximate Support Recovery using Codes for Unsourced Multiple Access

  2021-07-12

  preprintOpen accessSenior author

  We consider the approximate support recovery (ASR) task of inferring the support of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$K$</tex> -sparse vector <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{x}\in \mathbb{R}^{n}$</tex> from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$m$</tex> noisy measurements. We examine the case where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$n$</tex> is large, which precludes the application of standard compressed sensing solvers, thereby necessitating solutions with lower complexity. We design a scheme for ASR by leveraging techniques developed for unsourced multiple access. We present two decoding algorithms with computational complexities <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathcal{O}(K^{2}\log n+ K\log n\log\log n)$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathcal{O}(K^{3}+K^{2}\log n+K\log n\log \log n)$</tex> per iteration, respectively. When <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$K\ll n$</tex> , this is much lower than the complexity of approximate message passing with a minimum mean squared error denoiser, which requires <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathcal{O}(mn)$</tex> operations per iteration. This gain comes at a slight performance cost. Our findings suggest that notions from multiple access can play an important role in the design of measurement schemes for ASR.

  PublisherOA PDFDOI

• On the Throughput of Interference-Based Wireless Powered Communications With Receive Antenna Selection

  IEEE Transactions on Vehicular Technology · 2020-01-14 · 10 citations

  article

  We propose an interference-based wireless powered communication system in which an energy constrained source harvests energy from a single dominant co-channel interferer and then transmits information to a destination equipped with N receive antennas. Assuming interference dominates noise power at the destination and the receive antenna that maximizes the signal-to-interference ratio is selected, we investigate the average throughput for the delay-limited and delay-tolerant transmission modes. In particular, we derive an analytical expression of the average throughput for the delay-limited transmission mode, and a precise lower bound on the average throughput for the delay-tolerant transmission mode. Furthermore, we derive simplified asymptotic expressions of the average throughput for both transmission modes assuming asymptotically large number of receive antennas (i.e., N → ∞). We use the obtained asymptotic expressions to derive insightful closed-form expressions for the optimal energy harvesting time, which maximizes the average throughput, for both transmission modes. We show that the throughput-optimal energy harvesting time for the delay-limited and the delay-tolerant transmission scale like O(1/√N) and O(1/log(N)), respectively, for asymptotically large N.

  PublisherDOI

• Performance Analysis of Monostatic Multi-Tag Backscatter Systems With General Order Tag Selection

  IEEE Wireless Communications Letters · 2020 · 26 citations

  Senior authorCorresponding
  • Computer Science
  • Computer Science
  • Algorithm

  We investigate the performance of a monostatic multi-tag backscatter communication system with a general order tag selection criterion. In particular, we derive novel exact expressions for the average throughput and effective throughput. We further obtain simplified closed-form asymptotic expressions for the average and effective throughputs assuming a large number of tags. In addition, we obtain a unified exact expression for the average bit error rate, which is applicable to a wide class of binary modulation formats.

  PublisherDOI

• Coding for Visible Light Communication Using Color-Shift Keying Constellations

  IEEE Transactions on Communications · 2019-03-27 · 18 citations

  articleSenior author

  Color-shift keying (CSK) is a modulation scheme used in visible light communication (VLC) to transmit data by varying the intensity of red, green, and blue LEDs. We study the channel coding for VLC using CSK under constraints of no color shift and no illumination flicker during transmission and design codes over newly introduced symmetric symbol constellations over a triangle intensity plane. One class of codes contains the transmitted sequence based on finite-state machines, and the other is based on the concept of trellis-coded modulation for mitigating color shifts during transmission. The codes have a trellis structure which allows optimal soft-decision decoding using the Viterbi algorithm providing asymptotic coding gain improvements of 1.5 to 3.5 dB with respect to the uncoded transmission while complying with the color shift and flicker constraints.

  PublisherDOI

Frequent coauthors

• Krishna R. Narayanan

  23 shared

• Murat Uysal

  17 shared

• A.D. Liveris

  15 shared

• P.D. Papadimitriou

  Nokia (Finland)

  14 shared

• Yazan H. Al-Badarneh

  University of Jordan

  12 shared

• Alex Sprintson

  11 shared

• Qinghua Li

  Chongqing Normal University

  11 shared

• Emina Soljanin

  Rutgers, The State University of New Jersey

  10 shared

Education

• D.Sc., Electrical Engineering

  Washington University in Saint Louis

  1985

• MS, Electrical Engineering

  Washington University in Saint Louis

  1983

• BE, Electrical Engineering

  American University of Beirut

  1980

Awards & honors

• Brocket Professorship (2002)
• J.W. Runyon, Jr., Professorship (1997)
• Halliburton Professor, Texas A&M University (1995)
• Fellow, Institute of Electrical and Electronics Engineers (I…