For an updated list of publications, I recommend checking my Google Scholar.
Journal Publications
Deep Reinforcement Learning for Latency-Sensitive Communication With Adaptive Redundant Retransmissions
Gustavo Kasper Facenda, Ashish Khisti, Wai-Tian Tan and John Apostolopoulos
IEEE Transactions on Communications, 2023.
This paper studies packet repetition strategies over erasure channels with memory and a long feedback delay. The problem is initially formulated as a communications problem where a source wishes to transmit one message packet to a destination while minimizing both the delay and the number of transmissions. At each time instant, the sender is provided a delayed acknowledgement feedback about past attempts, and must decide whether to attempt a new transmission or not. This problem is then re-formulated as an episodic reinforcement learning problem, where an agent attempts to learn the optimal transmission policy, provided delayed feedback about past transmission attempts. The agent is helped by a channel estimator, which attempts to capture the channel memory and use that to predict probabilities of erasures in a future window. This channel estimator is also data-driven and learns the channel model without any a priori channel knowledge. The paper presents a lower bound on the achievable trade-off between delay and number of transmissions for any channel modeled as a Markov process. Experimental results show that the combination of the proposed channel estimator and the agent can noticeably outperform naive strategies for channels with memory, and achieves results close to the lower bound.
Adaptive relaying for streaming erasure codes in a three node relay network
Gustavo Kasper Facenda, M. Nikhil Krishnan, Elad Domanovitz, Silas L. Fong, Ashish Khisti, Wai-Tian Tan and John Apostolopoulos
IEEE Transactions on Information Theory, 2023.
This paper investigates adaptive streaming codes over a three-node relayed network. In this setting, a source node transmits a sequence of message packets to a destination through a relay. The source-to-relay and relay-to-destination links are unreliable and introduce at most N1 and N2 packet erasures, respectively. The destination node must recover each message packet within a strict delay constraint T. The paper presents achievable streaming codes for all feasible parameters {N1,N2,T} that exploit the fact that the relay naturally observes the erasure pattern occurring in the link from source to relay, thus it can adapt its relaying strategy based on these observations. In a recent work, Fong et al. provide streaming codes featuring channel-state-independent relaying strategies. The codes proposed in this paper achieve rates higher than the ones proposed by Fong et al. whenever N2>N1, and achieve the same rate when N2=N1. The paper also presents an upper bound on the achievable rate that takes into account erasures in both links in order to bound the rate in the second link. The upper bound is shown to be tighter than a trivial bound that considers only the erasures in the second link.
Streaming Erasure Codes over Multi-Access Relayed Networks
Gustavo Kasper Facenda, Elad Domanovitz, Ashish Khisti, Wai-Tian Tan and John Apostolopoulos
Transactions on Information Theory, 2022.
Many emerging multimedia streaming applications involve multiple users communicating under strict latency constraints. In this paper we study streaming codes for a network involving two source nodes, one relay node and a destination node. In our setting, each source node transmits a stream of messages, through the relay, to a destination, who is required to decode the messages under a strict delay constraint. For the case of a single source node, a class of streaming codes has been proposed by Fong et al. [2], using the concept of {\em delay-spectrum}. In the present work we present an in-depth analysis of the properties of delay-spectrum and apply them to develop streaming codes for our proposed setting through a novel framework. Our first scheme involves greedily selecting the rate on the link from relay to destination and using properties of the delay-spectrum to find feasible streaming codes that satisfy the required delay constraints. We provide a closed form expression for the achievable rate region and identify conditions when the proposed scheme is optimal by establishing a natural outer bound. Our second scheme builds upon this approach, but uses a numerical optimization-based approach to improve the achievable rate region over the first scheme. We demonstrate that our proposed schemes achieve significant improvements over baseline schemes based on single-user codes.
Efficient scheduling for the massive random access Gaussian channel
Gustavo Kasper Facenda and Danilo Silva
IEEE Transactions on Wireless Communications, 2020
This article investigates the massive random access Gaussian channel with a focus on small payloads. For this problem, grant-based schemes have been regarded as inefficient due to the necessity of large feedbacks and the use of inefficient scheduling request methods. This articles attempts to answer whether grant-based schemes can be competitive against state-ot-art grantless schemes and worthy of further investigation. In order to compare these schemes fairly, a novel model is proposed, and, under this model, a novel grant-based scheme is proposed. The scheme uses Ordentlich and Polyanskiy's grantless method to transmit small coordination indices in order to perform the scheduling request, which allows both the request from the users to be efficient and the feedback to be small. We also present improvements to the Ordentlich and Polyanskiy's scheme, allowing it to transmit information through the choice of sub-block, as well as to handle collisions of the same message, significantly improving the method for very small messages. Simulation results show that, if a small feedback is allowed, the proposed scheme performs closely to the state-of-art while using simpler coding schemes, suggesting that novel grant-based schemes should not be dismissed as a potential solution to the massive random access problem.
Journal Pre-prints
Conference Papers
English Papers
High Rate Streaming Codes Over the Three-Node Relay Network
Nikhil Krishnan, Gustavo Kasper Facenda, Elad Domanovitz, Ashish Khisti, Wai-Tian Tan and John Apostolopoulos
2021 IEEE Information Theory Workshop (ITW)
In this paper, we investigate streaming codes over a three-node relay network. Source node transmits a sequence of message packets to the destination via a relay. Source-to-relay and relay-to-destination links are unreliable and introduce at most N1 and N2 packet erasures, respectively. Destination needs to recover each message packet with a strict decoding delay constraint of T time slots. We propose streaming codes under this setting for all feasible parameters {N1, N2, T}. Relay naturally observes erasure patterns occurring in the source-to-relay link. In our code construction, we employ a channel-state-dependent relaying strategy, which rely on these observations. In a recent work, Fong et al. provide streaming codes featuring channel-state-independent relaying strategies, for all feasible parameters {N1, N2, T}. Our schemes offer a strict rate improvement over the schemes proposed by Fong et al., whenever N1<N2.
Guaranteed Rate of Streaming Erasure Codes over Multi-Link Multi-hop Network
Elad Domanovitz, Gustavo Kasper Facenda, Ashish Khisti, Wai-Tian Tan and John Apostolopoulos
2021 IEEE Information Theory Workshop (ITW)
We study the problem of transmitting a sequence of messages (streaming messages) through a multi-link, multi-hop packet erasure network. Each message must be reconstructed in-order and under a strict delay constraint. Special cases of our setting with a single link on each hop have been studied recently - the case of a single relay-node, is studied in Fong et al [1]; the case of multiple relays, is studied in Domanovitz et al [2]. As our main result, we propose an achievable rate expression that reduces to previously known results when specialized to their respective settings. Our proposed scheme is based on the idea of concatenating single-link codes from [2] in a judicious manner to achieve the required delay constraints. We propose a systematic approach based on convex optimization to maximize the achievable rate in our framework.
Streaming erasure codes over multi-access relay networks
Gustavo Kasper Facenda, Elad Domanovitz, Ashish Khisti, Wai-Tian Tan and John Apostolopoulos
2021 IEEE International Symposium on Information Theory (ISIT)
Applications where multiple users communicate with a common server and desire low latency are common and increasing. This paper studies a network with two source nodes, one relay node and a destination node, where each source nodes wishes to transmit a sequence of messages, through the relay, to the destination, who is required to decode the messages with a strict delay constraint T . The network with a single source node has been studied in [1]. We start by introducing two important tools: the delay spectrum, which generalizes delay-constrained point-to-point transmission, and concatenation, which, similar to time sharing, allows combinations of different codes in order to achieve a desired regime of operation. Using these tools, we are able to generalize the two schemes previously presented in [1], and propose a novel scheme which allows us to achieve optimal rates under a set of well-defined conditions. Such novel scheme is further improved in order to achieve higher rates in the scenarios where the conditions for optimality are not met.
An Efficient Grant-Based Scheme for the Massive Random Access Gaussian Channel
Gustavo Kasper Facenda and Danilo Silva
XXXVII Brazilian Symposium on Telecommunications and Signal Processing, 2019
Best communications paper award
This paper investigates the Massive Random Access Gaussian Channel with a focus on small payloads. For this problem, grant-based schemes have been regarded as inefficient due to the necessity of large feedbacks and use of inefficient scheduling request methods. In this paper, a novel grant-based scheme, which appears to outperform other methods, is proposed. The scheme uses Ordentlich and Polyanskiy’s grantless method to transmit small coordination indices in order to perform the scheduling request, which allows both the request from the users to be efficient and the feedback to be small. The simulation results show that, if a short feedback is allowed, our method requires lower energy per bit than existing practical grantless methods.
Portuguese Papers
Detecção de Atividade para Canal de Acesso Aleatório Massivo Gaussiano Utilizando Sensoriamento Compressivo
Henrique Pickler da Silva, Gustavo Kasper Facenda e Danilo Silva
XXXVIII Simpósio Brasileiro de Telecomunicações e Processamento de Sinais (SBrT 2020)
Este trabalho investiga métodos eficientes de transmissão para o canal de acesso aleatório gaussiano com um número massivo de usuários. Em um trabalho recente, um método grant-based com resultados promissores comparado a métodos grantless foi proposto. Este artigo é baseado nesse método e foca em aprimorar o estágio de detecção de atividade. O sistema proposto utiliza da interpretação do acesso aleatório como um problema de sensoriamento compressivo para obter uma detecção eficiente. Os resultados de simulação mostram que, para um número suficientemente grande de usuários ativos, o esquema proposto tem um desempenho significativamente superior ao estado-da-arte.
This paper investigates efficient methods for the random access Gaussian channel with a massive number of users. A recent work has proposed a grant-based method that has shown promising results compared to grantless methods. This paper is based on that approach and focuses on improving the activity detection stage. The proposed system takes advantage of the compressive sensing interpretation of the problem, leveraging it to achieve an efficient detection. Simulation results show that the proposed scheme is able to significantly outperform the stateof-art for a large enough number of active users.
Um método para discriminaçao entre PSK e FSK utilizando estatısticas de ordem superior
Gustavo Kasper Facenda e Danilo Silva
XXXV Simpósio Brasileiro de Telecomunicações e Processamento de Sinais (SBrT 2017)
Este artigo apresenta um novo algoritmo para discriminaç ao entre modulaç oes digitais em fase e em frequência. Dado um sinal modulado em PSK (Phase-Shift Keying) ou FSK (Frequency-Shift Keying), com quaisquer números de níveis, o algoritmo é capaz de identificar a qual classe (PSK ou FSK) o sinal pertence. O método proposto consiste no uso de estatısticas de ordem superior da frequência instantânea do sinal recebido em banda base como atributos utilizados por um classificador SVM, apresentando um bom compromisso entre complexidade, conhecimento a priori e desempenho em comparaçao com os métodos existentes.
This paper presentes a new method to discriminate between phase and frequency digital modulations. The algorithm is able to identify the class of an M-PSK or M-FSK modulated signal, for any modulation order M. The proposed method is based on machine learning, using higher-order statistics of the instantaneous frequency of the baseband received signal as features, presenting a good tradeoff between complexity, a priori knowledge and performance, compared to the existing methods.