Mireille SARKISS - Academia.edu (original) (raw)

Papers by Mireille SARKISS

2022 IEEE Information Theory Workshop (ITW)

The main contribution of this paper is a strong converse result for K-hop distributed hypothesis ... more The main contribution of this paper is a strong converse result for K-hop distributed hypothesis testing against independence with multiple (intermediate) decision centers under a Markov condition. Our result shows that the set of type-II error exponents that can simultaneously be achieved at all the terminals does not depend on the maximum permissible type-I error probabilities. Our strong converse proof is based on a change of measure argument and on the asymptotic proof of specific Markov chains. This proof method can also be used for other converse proofs, and is appealing because it does not require resorting to variational characterizations or blowing-up methods as in previous related proofs. Index Terms-Strong converse, change of measure, hypothesis testing, K hops.

Cornell University - arXiv, Nov 7, 2022

Cornell University - arXiv, Aug 30, 2022

We consider a multi-hop distributed hypothesis testing problem with multiple decision centers (DC... more We consider a multi-hop distributed hypothesis testing problem with multiple decision centers (DCs) for testing against independence and where the observations obey some Markov chain. For this system, we characterize the fundamental type-II error exponents region, i.e., the type-II error exponents that the various DCs can achieve simultaneously, under expected rate-constraints. Our results show that this fundamental exponents region is boosted compared to the region under maximum-rate constraints, and that it depends on the permissible type-I error probabilities. When all DCs have equal permissible type-I error probabilities, the exponents region is rectangular and all DCs can simultaneously achieve their optimal type-II error exponents. When the DCs have different permissible type-I error probabilities, a tradeoff between the type-II error exponents at the different DCs arises. New achievability and converse proofs are presented. For the achievability, a new multiplexing and rate-sharing strategy is proposed. The converse proof is based on applying different change of measure arguments in parallel and on proving asymptotic Markov chains. For the special cases K = 2 and K = 3, we provide simplified expressions for the exponents region; a similar simplification is conjectured for arbitrary K ≥ 2. Index Terms Multi-hop, distributed hypothesis testing, error exponents, expected-rate constraints, variable-length coding.

2020 IEEE Information Theory Workshop (ITW)

We investigate the testing-against-independence problem over a cooperative MAC with two sensors a... more We investigate the testing-against-independence problem over a cooperative MAC with two sensors and a single detector under an average rate constraint on the sensors-detector links. For this setup, we design a variable-length coding scheme that maximizes the achievable type-II error exponent when the type-I error probability is limited to. Similarly to the single-link result, we show here that the optimal error exponent depends on and that variable-length coding allows to increase the rates over the optimal fixed-length coding scheme by the factor (1 −) −1 .

2019 IEEE Information Theory Workshop (ITW), 2019

The paper considers a coded caching setup with two libraries and where only one of them needs to ... more The paper considers a coded caching setup with two libraries and where only one of them needs to be kept secret from an external eavesdropper. We provide upper and lower bounds on the secrecy rate-memory tradeoff for systems with K = 2 or K = 3 receivers. Our bounds are tight in some regimes and show that the standard (non-secure) coded caching upper bound can be approached for a wide range of parameters. In some cases, the proposed upper bound on the secrecy rate-memory tradeoff is even lower than the lower bound for standard coded caching. The reason is that in our setup the ratio of receivers requesting secure files over those requesting nonsecure files is fixed and known to everyone in advance. The transmitter can thus adjust the contents stored in the cache memories to this ratio.

2020 IEEE 91st Vehicular Technology Conference (VTC2020-Spring), 2020

This paper proposes a joint packet scheduling and computation offloading policy for an Energy Har... more This paper proposes a joint packet scheduling and computation offloading policy for an Energy Harvesting (EH) mobile terminal wirelessly connected to a Base Station (BS) when the channel between the mobile and the BS is unavailable at the mobile side. The mobile terminal has to decide if its packet related to one application is computed either locally or remotely by the BS within a strict delay imposed by this application without knowing the channel in advance. Our objective is to guarantee reliable communication by minimizing the packet loss. This packet loss is due to buffer overflow, strict delay violation and channel mismatch. We formulate the problem using a Markov Decision Process (MDP) and we propose and implement the optimal deterministic offline policy to solve it. This optimal policy decides: (i) the execution location (locally or remotely), (ii) the number of packets to be executed and (iii) the corresponding transmission power. This policy offers a dramatic increase in the number of executed packets and a significant energy saving.

2021 IEEE Global Communications Conference (GLOBECOM), 2021

The paper studies distributed binary hypothesis testing over a two-hop relay network where both t... more The paper studies distributed binary hypothesis testing over a two-hop relay network where both the relay and the receiver decide on the hypothesis. Both communication links are subject to expected rate constraints, which differs from the classical assumption of maximum rate constraints. We exactly characterize the set of type-II error exponent pairs at the relay and the receiver when both type-I error probabilities are constrained by the same value > 0. No tradeoff is observed between the two exponents, i.e., one can simultaneously attain maximum type-II error exponents both at the relay and at the receiver. For 1 = 2, we present an achievable exponents region, which we obtain with a scheme that applies different versions of a basic two-hop scheme that is optimal under maximum rate constraints. We use the basic two-hop scheme with two choices of parameters and rates, depending on the transmitter's observed sequence. For 1 = 2, a single choice is shown to be sufficient. Numerical simulations indicate that extending to three or more parameter choices is never beneficial. Index Terms-Multi-hop, distributed hypothesis testing, error exponents, expected rate constraints, variable-length coding,

2018 IEEE Middle East and North Africa Communications Conference (MENACOMM), 2018

We derive upper bounds on the rate-memory tradeoff of cache-aided erasure broadcast channels with... more We derive upper bounds on the rate-memory tradeoff of cache-aided erasure broadcast channels with Kw weak receivers and Ks strong receivers. We follow a decentralized placement scenario, where coordination is not needed prior to the delivery phase. We study two setups: a standard scenario without eavesdropper and a wiretap scenario with an external eavesdropper. For both scenarios, we propose joint cache-channel coding schemes that efficiently exploit the cache contents and take into consideration the users' channel characteristics at the same time. We show that the decentralized placement strategy causes only a small increase in delivery rate compared to centralized strategy. Similarly, when cache sizes are moderate, the rate is increased only slightly by securing the communication against external eavesdroppers. This is not the case when cache memories are small and large. Index Terms-Coded caching, receiver caching, joint cachechannel coding, erasure broadcast channels, weak secrecy.

2018 25th International Conference on Telecommunications (ICT), 2018

This paper studies the joint optimization of resource scheduling and computation offloading for m... more This paper studies the joint optimization of resource scheduling and computation offloading for mobile networks where energy harvesting (EH)-enabled devices are wirelessly connected to nearby base stations (BSs), which can be endowed with some computational capabilities. We consider that a mobile device may run its applications either locally or remotely at its serving base station. We also consider that its applications are strict delay constraints. Our objective is to minimize the packets' loss due to buffer overflow or delay violation of the queued packets at the mobile device. We formulate this problem as a Markov Decision Process (MDP) and exhibit an optimal deterministic offline scheduling-offloading policy. This policy makes decision on the processing location (either local or offloading) and on the number of processed packets by relying on the knowledge on the current channel, the past data and energy arrivals as well as the harvested energy available in the battery. We show through numerical results that the proposed policy can significantly improve the successfully received packets' rate and the energy consumption compared to other policies, such as immediate scheduling or only local processing or only offloading policies.

2017 IEEE Information Theory Workshop (ITW), 2017

The paper studies the wiretap erasure broadcast channel (BC) with an external eavesdropper when t... more The paper studies the wiretap erasure broadcast channel (BC) with an external eavesdropper when the legitimate receivers have cache memories. Various secure coding schemes are proposed for a scenario where Kw weak receivers have same erasure probabilities and Ks strong receivers have same erasure probabilities. The coding schemes achieve the cache-aided secrecy capacity when only weak receivers have cache memories and this cache memory is either small or large. They also allow to conclude the following: 1) Under a total cache budget it is often beneficial to assign the cache memories unequally between strong and weak receivers. 2.) Joint cache-channel coding is necessary to attain the optimal performance. 3.) The secrecy capacity can be positive even when the eavesdropper is stronger than the legitimate receivers.

2017 IEEE Wireless Communications and Networking Conference (WCNC), 2017

We derive upper and lower bounds on the secure capacity-memory tradeoff of the two-user wiretap e... more We derive upper and lower bounds on the secure capacity-memory tradeoff of the two-user wiretap erasure BC with cache memory at the weaker receiver. The bounds coincide when the cache memory exceeds a given threshold. The lower bound also exhibits that cache memories provide larger gains under a secrecy constraint than without such a constraint. Moreover, for a large set of parameters the capacity-memory tradeoff is larger if only the weaker receiver has cache memory than when this cache memory is split equally among the receivers. The lower bound is based on a joint cache-channel coding scheme that simultaneously exploits the cache contents and the channel statistics. Such a joint design yields significant gains over a separation-based design.

2018 IEEE Global Communications Conference (GLOBECOM), 2018

We consider a K-receiver wiretap broadcast channel where Kw receivers are weak and have cache mem... more We consider a K-receiver wiretap broadcast channel where Kw receivers are weak and have cache memories and Ks receivers are strong and have no cache memories. We derive an upper bound on the secrecy rate-memory tradeoff under a joint secrecy constraint and under decentralized caching. In contrast to previous works, prefetching in our scheme is purely decentralized and receivers randomly sample from a random key stream available at the transmitter and from the files in a library. For small cache sizes, the performance of our scheme improves with increasing length of the random key stream. For moderate and large cache sizes, a small key stream suffices to perform close to the information-theoretic limit of the system.

2017 IEEE Global Conference on Signal and Information Processing (GlobalSIP), 2017

This paper investigates the energy consumption minimization for resource scheduling in a wireless... more This paper investigates the energy consumption minimization for resource scheduling in a wireless communication. We propose to take into account a strict delay constraint for each queued packet rather than an average delay constraint, in addition to a buffer overflow constraint. The associated optimization problem can be modeled as Constraint Markov Decision Problem where the actions are the number of packets sent on the known channel at each slot. The optimal random policy is exhibited through the resolution of standard linear programming. We show the gain in energy is substantial compared to naive policy.

Cellular networks are evolving to an increasing numb er of applications ranging from simple voice... more Cellular networks are evolving to an increasing numb er of applications ranging from simple voice calls to video streaming and data transfer. Recently, it has been suggested t o xtend theses networks to short range communicati ons using device to device links. The aim of such type of operation is to alleviate t h data traffic load on cellular networks, and also to provide an alternative option for public safety communications. This paper presents a overview of the potential applications of device to device links in cellular networks and also presents the technical challenges and the potential solutions to implement this feat ure in near future standards.

2021 IEEE Information Theory Workshop (ITW), 2021

Cascaded binary hypothesis testing is studied in this paper with two decision centers at the rela... more Cascaded binary hypothesis testing is studied in this paper with two decision centers at the relay and the receiver. All terminals have their own observations, where we assume that the observations at the transmitter, the relay, and the receiver form a Markov chain in this order. The communication occurs over two hops, from the transmitter to the relay and from the relay to the receiver. Expected rate constraints are imposed on both communication links. In this work, we characterize the optimal type-II error exponents at the two decision centers under constraints on the allowed type-I error probabilities. Our recent work characterized the optimal type-II error exponents in the special case when the two decision centers have same type-I error constraints and provided an achievability scheme for the general setup. To obtain the exact characterization for the general case, in this paper we provide a new converse proof as well as a new matching achievability scheme. Our results indicate that under unequal type-I error constraints at the relay and the receiver, a tradeoff arises between the maximum type-II error probabilities at these two terminals. Previous results showed that such a tradeoff does not exist under equal type-I error constraints or under general type-I error constraints when a maximum rate constraint is imposed on the communication links. Index Terms-Multi-hop, distributed hypothesis testing, error exponents, expected rate constraints, variable-length coding,

The 2012 International Conference on Advanced Technologies for Communications, 2012

A Two-Way Relay Channel (TWRC) in which duplex transmission between two users via a relay station... more A Two-Way Relay Channel (TWRC) in which duplex transmission between two users via a relay station is considered. A physical layer network coding strategy based on compressand-forward relaying scheme for the TWRC is proposed. In the underlying coding strategy, we use nested lattices for Wyner-Ziv coding and decoding. The relay uses the weaker side information available at the receivers from the first transmission phase to broadcast a common quantized version of its received signal. We characterize the achievable rate region of the presented scheme. Then we show that lattice codes can achieve random coding rates.

2008 IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications, 2008

Distributed space-time codes over two asynchronous relays are considered. First, we show that the... more Distributed space-time codes over two asynchronous relays are considered. First, we show that the space-time code proposed in [1] is suitable for asynchronous transmission over two relays. Using tools from division algebra, we study the quadratic form resulting from its determinant and we prove that this code has a non-vanishing determinant over all constellations carved from Zopf[i], and thus is optimal in the sense of diversity-multiplexing tradeoff [2]. Then, we propose a delay-tolerant code based on the Golden code [3] the full-rate full-diversity information lossless space-time code proposed for the MIMO channel, and we deduce the convenient unitary matrices to obtain the modified code. Applying these matrices to other MIMO codes, namely Tirkkonen-Hottinen [4] and Sezginer-Sari code [5], we infer new delay-tolerant codes. In addition of being suitable for asynchronous relay transmission, all the new codes have the same determinants as the old ones.

IEEE Transactions on Information Theory, 2011

Perfect Space-Time Codes (STC) are optimal codes in their original construction for Multiple Inpu... more Perfect Space-Time Codes (STC) are optimal codes in their original construction for Multiple Input Multiple Output (MIMO) systems. Based on Cyclic Division Algebras (CDA), they are full-rate, full-diversity codes, have Non-Vanishing Determinants (NVD) and hence achieve Diversity-Multiplexing Tradeoff (DMT). In addition, these codes have led to optimal distributed space-time codes when applied in cooperative networks under the assumption of perfect synchronization between relays. However, they loose their diversity when delays are introduced and thus are not delay-tolerant. In this paper, using the cyclic division algebras of perfect codes, we construct new codes that maintain the same properties as perfect codes in the synchronous case. Moreover, these codes preserve their full-diversity in asynchronous transmission.

annals of telecommunications - annales des télécommunications, 2013

Recently, energy-efficient (EE) communications have received increasing interest specially in cel... more Recently, energy-efficient (EE) communications have received increasing interest specially in cellular networks. Promising techniques, such as multiple input multiple output (MIMO) and base station (BS) cooperation schemes, have been widely studied in the past to improve the spectral efficiency and the reliability. Nowadays, the purpose is to investigate how these techniques can reduce the energy consumption of the systems. In this paper, we address for a single-user scenario, the energy efficiency of two BSs cooperation under limited backhaul capacity. In order to evaluate the EE metric, we provide first an information-theoretical analysis based on the outage probability, for a quantization model over the backhaul. Then, we extend this EE analysis to a more practical approach with data transmission over the backhaul. For both approaches, we identify by numerical/simulation results the cooperation scenarios that can save energy depending on the backhaul capacity.

2017 IEEE International Conference on Communications (ICC), 2017

We derive upper and lower bounds on the secure capacity-memory tradeoff of the K-user (K ≥ 2) wir... more We derive upper and lower bounds on the secure capacity-memory tradeoff of the K-user (K ≥ 2) wiretap erasure broadcast channel where Kw receivers are weak and have cache memories of equal size, and Ks receivers are strong and have no cache. The bounds coincide for small and large cache memories. The lower bound also exhibits that cache memories provide larger gains under a secrecy constraint than without such a constraint. Moreover, we show for the two-user scenario that in the regime of small cache memories, the capacity-memory tradeoff is larger when only the weaker receiver has cache memory than when this cache memory is split equally among the two receivers. The lower bound is based on a joint cache-channel coding scheme that simultaneously exploits the cache contents and the channel statistics.