Ahmed A Zewail - Academia.edu (original) (raw)

Papers by Ahmed A Zewail

arXiv (Cornell University), Dec 13, 2017

This paper considers a two-hop network architecture known as a combination network, where a layer... more This paper considers a two-hop network architecture known as a combination network, where a layer of relay nodes connects a server to a set of end users. In particular, a new model is investigated where the intermediate relays employ caches in addition to the end users. First, a new centralized coded caching scheme is developed that utilizes maximum distance separable (MDS) coding, jointly optimizes cache placement and delivery phase, and enables decomposing the combination network into a set virtual multicast sub-networks. It is shown that if the sum of the memory of an end user and its connected relay nodes is sufficient to store the database, then the server can disengage in the delivery phase and all the end users' requests can be satisfied by the caches in the network. Lower bounds on the normalized delivery load using genie-aided cut-set arguments are presented along with second hop optimality. Next recognizing the information security concerns of coded caching, this new model is studied under three different secrecy settings: 1) secure delivery where we require an external entity must not gain any information about the database files by observing the transmitted signals over the network links, 2) secure caching, where we impose the constraint that end users must not be able to obtain any information about files that they did not request, and 3) both secure delivery and secure caching, simultaneously. We demonstrate how network topology affects the system performance under these secrecy requirements. Finally, we provide numerical results demonstrating the system performance in each of the settings considered. Index Terms Combination networks with caching relays, coded caching, maximum distance separable (MDS) codes, secure delivery, secure caching.

arXiv (Cornell University), Feb 27, 2018

This paper considers heterogeneous coded caching where the users have unequal distortion requirem... more This paper considers heterogeneous coded caching where the users have unequal distortion requirements. The server is connected to the users via an error-free multicast link and designs the users' cache sizes subject to a total memory budget. In particular, in the placement phase, the server jointly designs the users' cache sizes and the cache contents. To serve the users' requests, in the delivery phase, the server transmits signals that satisfy the users' distortion requirements. An optimization problem with the objective of minimizing the worst-case delivery load subject to the total cache memory budget and users' distortion requirements is formulated. The optimal solution for uncoded placement and linear delivery is characterized explicitly and is shown to exhibit a threshold policy with respect to the total cache memory budget. As a byproduct of the study, a caching scheme for systems with fixed cache sizes that outperforms the state-of-art is presented.

This paper considers a Gaussian multiple access channel aided by a relay. Specifically, the relay... more This paper considers a Gaussian multiple access channel aided by a relay. Specifically, the relay facilitates communication between multiple sources and a destination to which the sources have no direct link. In this set up, the relay node is considered to be untrusted, i.e., honest but curious, from whom the source messages need to be kept secret. We identify an achievable secrecy rate region utilizing cooperative jamming from the destination, and using compress-and-forward at the relay. Additionally, an outer bound on the secrecy rate region is derived. Numerical results indicate that the outer bound is tight in some cases of interest.

IEEE Transactions on Information Forensics and Security, Sep 1, 2017

We consider a two-source two-destination two-hop relay network, where all data communication must... more We consider a two-source two-destination two-hop relay network, where all data communication must be kept secret from the relay node. The model considered is the simplest primitive that embodies a multi-transmitter multi-receiver network that needs to communicate sharing an untrusted relay node. We focus on two scenarios. In the first scenario, each source aims to send two messages to be kept secret from the relay: a common message that should be decoded by both destinations, and a private message that should be decoded by the first destination while kept secret from the second one. We define an achievable rate region by utilizing stochastic encoding at the sources, the Gaussian noise cooperative jamming from the destinations, and compress-and-forward at the relay. In the second scenario, each source aims to send a confidential message to its intended destination, which should be kept secret from the other one as well as the relay. We define an achievable rate region using a combination of nested lattice codes and random binning at the sources, structured cooperative jamming from destinations, and scaled compute-and-forward at the relay. We also derive genie-aided outer bounds on the secrecy rate regions. We present numerical results that demonstrate the performance of the proposed achievable schemes. Overall, this paper provides insights into how to utilize an untrusted relay to communicate to destinations with different levels of security clearance, and how intentional interference is an enabler of communication.

This paper considers a device-to-device (D2D) coded caching system where the users have differing... more This paper considers a device-to-device (D2D) coded caching system where the users have differing cache sizes. During low traffic hours, the server places subsets of the files at the users' cache memories, in a manner that enables serving the users' requests via D2D transmissions during peak traffic hours. The objective is to jointly design the users' cache contents and the D2D transmissions in order to minimize the D2D delivery load. In particular, we seek to identify the optimal uncoded placement and linear delivery schemes. We propose a novel lower bound on the D2D delivery load under uncoded placement, which enables us to explicitly characterize the minimum D2D delivery load under uncoded placement for several cases of interest.

IEEE Journal on Selected Areas in Communications, Jun 1, 2018

This paper considers a two-hop network architecture known as a combination network, where a layer... more This paper considers a two-hop network architecture known as a combination network, where a layer of relay nodes connects a server to a set of end users. In particular, a new model is investigated where the intermediate relays employ caches in addition to the end users. First, a new centralized coded caching scheme is developed that utilizes maximum distance separable (MDS) coding, jointly optimizes cache placement and delivery phase, and enables decomposing the combination network into a set virtual multicast sub-networks. It is shown that if the sum of the memory of an end user and its connected relay nodes is sufficient to store the database, then the server can disengage in the delivery phase and all the end users' requests can be satisfied by the caches in the network. Lower bounds on the normalized delivery load using genie-aided cutset arguments are presented along with second hop optimality. Next recognizing the information security concerns of coded caching, this new model is studied under three different secrecy settings: 1) secure delivery where we require an external entity must not gain any information about the database files by observing the transmitted signals over the network links, 2) secure caching, where we impose the constraint that end users must not be able to obtain any information about files that they did not request, and 3) both secure delivery and secure caching, simultaneously. We demonstrate how network topology affects the system performance under these secrecy requirements. Finally, we provide numerical results demonstrating the system performance in each of the settings considered.

We study a two-hop cache-aided network, where a layer of relay nodes connects a server and a set ... more We study a two-hop cache-aided network, where a layer of relay nodes connects a server and a set of end users, i.e., a combination network. We consider the case where both the relay nodes and the end users have caching capabilities. We provide upper and lower bounds which are applicable to any combination network, noting that previous work had focused on models where the relays do not have caches as well as schemes that were suitable for a special class of combination networks. Utilizing maximum distance separable (MDS) codes, we jointly optimize the placement and the delivery phases, demonstrating the impact of cache memories in alleviating the delivery load over the two hop communications. Moreover, we show how cooperation between the relay nodes and the end users can effectively replace the server during the delivery phase whenever the total memory at each end user and its connected relay nodes is sufficient to store the database.

This paper investigates the performance of cacheaided systems with heterogeneous caches and secur... more This paper investigates the performance of cacheaided systems with heterogeneous caches and secure delivery. In particular, we consider users with unequal caches and assume the signals transmitted during the delivery phase to be overheard by an external eavesdropper which must not gain any information about the system's files. We study server-based delivery and device-to-device-based delivery where the server does not participate in the delivery phase. For each scenario, assuming uncoded placement and linear delivery schemes, we provide an optimization framework to minimize the secure delivery load. We show that the secure delivery requirement can be satisfied by modifying the memory capacity constraints in the non-secure framework to take into account the cost of caching keys. In addition, we show that the cost of secure delivery is negligible for caching systems with large number of files.

2014 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM 2014), Aug 1, 2014

Online social communities often exhibit complex relationship structures, ranging from close frien... more Online social communities often exhibit complex relationship structures, ranging from close friends to political rivals. As a result, persons are influenced by their friends and foes differently. Network applications can benefit from accompanying these structural differences in propagation schemes. In this paper, we study the optimal influence propagation policies for networks with positive and negative relationship types. We tackle the problem of minimizing the end-to-end propagation cost of influencing a target person in favor of an idea by utilizing the relationship types in the underlying social graph. The propagation cost is incurred by social and physical network dynamics such as frequency of interaction, the strength of friendship and foe ties, propagation delay or the impact factor of the propagating idea. We extend this problem by incorporating the impact of message deterioration and ignorance. We demonstrate our results in both a controlled environment and the Epinions dataset. Our results show that judicious propagation schemes lead to a significant reduction in the average cost and complexity of influence propagation compared to naïve myopic algorithms. Index Terms-Socially aware physical systems, network propagation for social media, signed networks, recommender systems.

IEEE Journal of Selected Topics in Signal Processing, Mar 1, 2015

Online social communities often exhibit complex relationship structures, ranging from close frien... more Online social communities often exhibit complex relationship structures, ranging from close friends to political rivals. As a result, persons are influenced by their friends and foes differently. Future network applications can benefit from integrating these structural differences in propagation schemes through socially aware sensors. In this paper, we introduce a propagation model for such social sensor networks with positive and negative relationship types. We tackle two main scenarios based on this model. The first one is to minimize the end-to-end propagation cost of influencing a target person in favor of an idea by utilizing sensor observations about the relationship types in the underlying social graph. The propagation cost is incurred by social and physical network dynamics such as propagation delay, frequency of interaction, the strength of friendship/foe ties or the impact factor of the propagating idea. We next extend this problem by incorporating the impact of message deterioration and ignorance, and by limiting the number of persons influenced against the idea before reaching the target. Second, we study the propagation problem while minimizing the number of negatively influenced persons on the path, and provide extensions to elaborate on the impact of network parameters. We demonstrate our results in both an artificially created network and the Epinions signed network topology. Our results show that judicious propagation schemes lead to a significant reduction in the average cost and complexity of network propagation compared to naïve myopic algorithms.

Communication networks are linked to and influenced by human interactions. Socially-aware systems... more Communication networks are linked to and influenced by human interactions. Socially-aware systems should integrate these complex relationship patterns in the network design. This paper studies the impact of friendship and antagonistic relationships between individuals on optimal network propagation policies. We develop a network propagation model for signed networks, and determine the optimal policies to influence a target node with an opinion while minimizing the total number of persons against it. We also provide extensions to this problem to elaborate on the impact of network parameters, such as minimum-delay propagation, while limiting the number of persons influenced against the idea before reaching the target. We provide numerical evaluations in a synthetic setup as well as the Epinions online social dataset. We demonstrate that propagation schemes with social and influence-centric constraints should take into account the relationship types in network design.

This paper investigates the impact of cooperation with an untrusted relay in multi-source multi-d... more This paper investigates the impact of cooperation with an untrusted relay in multi-source multi-destination networks. The set up considered is one where the relay is the only means of communications due to the absence of direct links between the sources and the destinations. Since the relay is untrusted, all messages from the sources need to be kept secret from the relay. Furthermore, the destinations are assumed to have different levels of security clearance, i.e., some private messages should only be decoded by their intended receiver and should be kept secret from other destinations. An achievable secure rate region is found by using random binning at the sources, cooperative jamming from the destinations, and compress-andforward at the relay. Additionally, a genie aided outer bound on the secure rate region is derived. Comparison of inner and outer bounds are provided.

In this paper, we study a cache-aided combination network, where a layer of relay nodes connects ... more In this paper, we study a cache-aided combination network, where a layer of relay nodes connects a server to a set of end users, under three different secrecy requirements. Both the relays and the end users are equipped with caches. First, we consider secure delivery where we require that an external entity must not gain any information about the database files by observing the transmitted signals over the network links. Second, we consider secure caching where we require that an end user must not be able to obtain any information about a file that he did not request. Last, we consider both of these requirements simultaneously. We jointly optimize the cache placement and delivery phases in order to minimize the delivery load over each of the two hops, and demonstrate the impact of the network topology on the system performance under these secrecy requirements.

We consider information theoretic security in a twohop combination network where there are groups... more We consider information theoretic security in a twohop combination network where there are groups of end users with distinct degrees of connectivity served by a layer of relays. The model represents a network set up with users having access to asymmetric resources, here the number of relays that they are connected to, yet demand security guarantees uniformly. We study two security constraints separately and simultaneously: secure delivery where the information must be kept confidential from an external entity that wiretaps the delivery phase; and secure caching where each cache-aided end-user can retrieve the file it requests and cannot obtain any information on files it does not. The achievable schemes we construct are multi-stage where each stage completes requests by a class of users.

This work considers a network consisting of a server and a layer of relay nodes equipped with cac... more This work considers a network consisting of a server and a layer of relay nodes equipped with cache memories which aim to deliver content to end nodes that also have cache memories. The server and the end nodes consider the intermediate relay caches to be untrusted with the content. As a result, the server must design strategies to place content in relay caches not only to serve end users, but also to ensure that any a subset of them, even when colluding, cannot gain any information about the contents of the server database. The end users randomly connect to a subset of these untrusted caches at the beginning of the delivery phase via multicast links. For this network model, a coded caching scheme is developed by jointly optimizing the cache placement and delivery phases using secure regenerating codes. In addition, the scheme is extended to the setup of combination networks with untrusted relays, where the untrusted relays are connected to the end users via unicast links. The study highlights the benefits of cooperating with untrusted caches by designing the end users' caches to provide multicast opportunities in order to minimize the delivery load.

This paper considers the two-user interference relay channel where each source wishes to communic... more This paper considers the two-user interference relay channel where each source wishes to communicate to its destination a message that is confidential from the other destination. Furthermore, the relay, that is the enabler of communication, due to the absence of direct links, is untrusted. Thus, the messages from both sources need to be kept secret from the relay as well. We provide an achievable secure rate region for this network. The achievability scheme utilizes structured codes for message transmission, cooperative jamming and scaled computeand-forward. In particular, the sources use nested lattice codes and stochastic encoding, while the destinations jam using lattice points. The relay decodes two integer combinations of the received lattice points and forwards, using Gaussian codewords, to both destinations. The achievability technique provides the insight that we can utilize the untrusted relay node as an encryption block in a two-hop interference relay channel with confidential messages.

In this work, we consider a cache-aided network where the users share the end-caches. In particul... more In this work, we consider a cache-aided network where the users share the end-caches. In particular, a user has access to only one of the caches and the number of caches is less than the number of users. We propose a coded placement scheme that exploits the asymmetry in the number of users associated with each cache. Some of the signals sent to the overloaded caches facilitate the decoding of the coded subfiles stored at the underloaded caches. We present an explicit caching scheme and fully characterize the coded placement gain for two-cache systems. Then, we generalize our scheme to larger networks, where the optimal parameters are characterized by solving a linear program. We observe that, with the proposed scheme, as the asymmetry in the users' connectivity increases, the gain from coded placement is more evident.

arXiv (Cornell University), Nov 9, 2018

In this work, we study coded placement in caching systems where the users have unequal cache size... more In this work, we study coded placement in caching systems where the users have unequal cache sizes and demonstrate its performance advantage. In particular, we propose a caching scheme with coded placement for three-user systems that outperforms the best caching scheme with uncoded placement. In our proposed scheme, users cache both uncoded and coded pieces of the files, and the coded pieces at the users with large memories are decoded using the unicast/multicast signals intended to serve users with smaller memories. Furthermore, we extend the proposed scheme to larger systems and show the reduction in delivery load with coded placement compared to uncoded placement.

arXiv (Cornell University), Mar 19, 2019

This paper considers a cache-aided device-to-device (D2D) system where the users are equipped wit... more This paper considers a cache-aided device-to-device (D2D) system where the users are equipped with cache memories of different size. During low traffic hours, a server places content in the users' cache memories, knowing that the files requested by the users during peak traffic hours will have to be delivered by D2D transmissions only. The worst-case D2D delivery load is minimized by jointly designing the uncoded cache placement and linear coded D2D delivery. Next, a novel lower bound on the D2D delivery load with uncoded placement is proposed and used in explicitly characterizing the minimum D2D delivery load (MD2DDL) with uncoded placement for several cases of interest. In particular, having characterized the MD2DDL for equal cache sizes, it is shown that the same delivery load can be achieved in the network with users of unequal cache sizes, provided that the smallest cache size is greater than a certain threshold. The MD2DDL is also characterized in the small cache size regime, the large cache size regime, and the three-user case. Comparisons of the server-based delivery load with the D2D delivery load are provided. Finally, connections and mathematical parallels between cache-aided D2D systems and coded distributed computing (CDC) systems are discussed.

IEEE journal on selected areas in information theory, Dec 1, 2021

This paper considers a cache-aided network where the users have access to helper-caches with hete... more This paper considers a cache-aided network where the users have access to helper-caches with heterogeneous sizes. First, coded placement schemes are proposed that exploit the heterogeneity in cache sizes when one user is connected to each cache. In the proposed scheme, the unicast/multicast signals intended to serve users connected to small memories are utilized in decoding the contents of the larger memories. A reduction in delivery load with coded placement is shown compared to uncoded placement for three-user systems with arbitrary cache sizes and larger systems in the small total memory regime. Next, systems with equal-size caches where multiple users are associated with each cache are considered. It is shown that coded placement outperforms the best uncoded placement scheme. In the proposed scheme, the unicast/multicast signals sent to the overloaded helper-caches facilitate the decoding of the coded subfiles stored at the underloaded helper-caches. The gain from coded placement is explicitly characterized for two-cache systems. For larger systems, the parameters of the coded placement scheme are obtained by optimization. It is observed that the gain from coded placement becomes more evident with increasing asymmetry in users’ connectivity. Finally, a unified coded placement scheme for two-cache systems that exploits the asymmetry in both the cache sizes and the connectivity pattern is presented.

arXiv (Cornell University), Dec 13, 2017

This paper considers a two-hop network architecture known as a combination network, where a layer... more This paper considers a two-hop network architecture known as a combination network, where a layer of relay nodes connects a server to a set of end users. In particular, a new model is investigated where the intermediate relays employ caches in addition to the end users. First, a new centralized coded caching scheme is developed that utilizes maximum distance separable (MDS) coding, jointly optimizes cache placement and delivery phase, and enables decomposing the combination network into a set virtual multicast sub-networks. It is shown that if the sum of the memory of an end user and its connected relay nodes is sufficient to store the database, then the server can disengage in the delivery phase and all the end users' requests can be satisfied by the caches in the network. Lower bounds on the normalized delivery load using genie-aided cut-set arguments are presented along with second hop optimality. Next recognizing the information security concerns of coded caching, this new model is studied under three different secrecy settings: 1) secure delivery where we require an external entity must not gain any information about the database files by observing the transmitted signals over the network links, 2) secure caching, where we impose the constraint that end users must not be able to obtain any information about files that they did not request, and 3) both secure delivery and secure caching, simultaneously. We demonstrate how network topology affects the system performance under these secrecy requirements. Finally, we provide numerical results demonstrating the system performance in each of the settings considered. Index Terms Combination networks with caching relays, coded caching, maximum distance separable (MDS) codes, secure delivery, secure caching.

arXiv (Cornell University), Feb 27, 2018

This paper considers heterogeneous coded caching where the users have unequal distortion requirem... more This paper considers heterogeneous coded caching where the users have unequal distortion requirements. The server is connected to the users via an error-free multicast link and designs the users' cache sizes subject to a total memory budget. In particular, in the placement phase, the server jointly designs the users' cache sizes and the cache contents. To serve the users' requests, in the delivery phase, the server transmits signals that satisfy the users' distortion requirements. An optimization problem with the objective of minimizing the worst-case delivery load subject to the total cache memory budget and users' distortion requirements is formulated. The optimal solution for uncoded placement and linear delivery is characterized explicitly and is shown to exhibit a threshold policy with respect to the total cache memory budget. As a byproduct of the study, a caching scheme for systems with fixed cache sizes that outperforms the state-of-art is presented.

This paper considers a Gaussian multiple access channel aided by a relay. Specifically, the relay... more This paper considers a Gaussian multiple access channel aided by a relay. Specifically, the relay facilitates communication between multiple sources and a destination to which the sources have no direct link. In this set up, the relay node is considered to be untrusted, i.e., honest but curious, from whom the source messages need to be kept secret. We identify an achievable secrecy rate region utilizing cooperative jamming from the destination, and using compress-and-forward at the relay. Additionally, an outer bound on the secrecy rate region is derived. Numerical results indicate that the outer bound is tight in some cases of interest.

IEEE Transactions on Information Forensics and Security, Sep 1, 2017

We consider a two-source two-destination two-hop relay network, where all data communication must... more We consider a two-source two-destination two-hop relay network, where all data communication must be kept secret from the relay node. The model considered is the simplest primitive that embodies a multi-transmitter multi-receiver network that needs to communicate sharing an untrusted relay node. We focus on two scenarios. In the first scenario, each source aims to send two messages to be kept secret from the relay: a common message that should be decoded by both destinations, and a private message that should be decoded by the first destination while kept secret from the second one. We define an achievable rate region by utilizing stochastic encoding at the sources, the Gaussian noise cooperative jamming from the destinations, and compress-and-forward at the relay. In the second scenario, each source aims to send a confidential message to its intended destination, which should be kept secret from the other one as well as the relay. We define an achievable rate region using a combination of nested lattice codes and random binning at the sources, structured cooperative jamming from destinations, and scaled compute-and-forward at the relay. We also derive genie-aided outer bounds on the secrecy rate regions. We present numerical results that demonstrate the performance of the proposed achievable schemes. Overall, this paper provides insights into how to utilize an untrusted relay to communicate to destinations with different levels of security clearance, and how intentional interference is an enabler of communication.

This paper considers a device-to-device (D2D) coded caching system where the users have differing... more This paper considers a device-to-device (D2D) coded caching system where the users have differing cache sizes. During low traffic hours, the server places subsets of the files at the users' cache memories, in a manner that enables serving the users' requests via D2D transmissions during peak traffic hours. The objective is to jointly design the users' cache contents and the D2D transmissions in order to minimize the D2D delivery load. In particular, we seek to identify the optimal uncoded placement and linear delivery schemes. We propose a novel lower bound on the D2D delivery load under uncoded placement, which enables us to explicitly characterize the minimum D2D delivery load under uncoded placement for several cases of interest.

IEEE Journal on Selected Areas in Communications, Jun 1, 2018

This paper considers a two-hop network architecture known as a combination network, where a layer... more This paper considers a two-hop network architecture known as a combination network, where a layer of relay nodes connects a server to a set of end users. In particular, a new model is investigated where the intermediate relays employ caches in addition to the end users. First, a new centralized coded caching scheme is developed that utilizes maximum distance separable (MDS) coding, jointly optimizes cache placement and delivery phase, and enables decomposing the combination network into a set virtual multicast sub-networks. It is shown that if the sum of the memory of an end user and its connected relay nodes is sufficient to store the database, then the server can disengage in the delivery phase and all the end users' requests can be satisfied by the caches in the network. Lower bounds on the normalized delivery load using genie-aided cutset arguments are presented along with second hop optimality. Next recognizing the information security concerns of coded caching, this new model is studied under three different secrecy settings: 1) secure delivery where we require an external entity must not gain any information about the database files by observing the transmitted signals over the network links, 2) secure caching, where we impose the constraint that end users must not be able to obtain any information about files that they did not request, and 3) both secure delivery and secure caching, simultaneously. We demonstrate how network topology affects the system performance under these secrecy requirements. Finally, we provide numerical results demonstrating the system performance in each of the settings considered.

We study a two-hop cache-aided network, where a layer of relay nodes connects a server and a set ... more We study a two-hop cache-aided network, where a layer of relay nodes connects a server and a set of end users, i.e., a combination network. We consider the case where both the relay nodes and the end users have caching capabilities. We provide upper and lower bounds which are applicable to any combination network, noting that previous work had focused on models where the relays do not have caches as well as schemes that were suitable for a special class of combination networks. Utilizing maximum distance separable (MDS) codes, we jointly optimize the placement and the delivery phases, demonstrating the impact of cache memories in alleviating the delivery load over the two hop communications. Moreover, we show how cooperation between the relay nodes and the end users can effectively replace the server during the delivery phase whenever the total memory at each end user and its connected relay nodes is sufficient to store the database.

This paper investigates the performance of cacheaided systems with heterogeneous caches and secur... more This paper investigates the performance of cacheaided systems with heterogeneous caches and secure delivery. In particular, we consider users with unequal caches and assume the signals transmitted during the delivery phase to be overheard by an external eavesdropper which must not gain any information about the system's files. We study server-based delivery and device-to-device-based delivery where the server does not participate in the delivery phase. For each scenario, assuming uncoded placement and linear delivery schemes, we provide an optimization framework to minimize the secure delivery load. We show that the secure delivery requirement can be satisfied by modifying the memory capacity constraints in the non-secure framework to take into account the cost of caching keys. In addition, we show that the cost of secure delivery is negligible for caching systems with large number of files.

2014 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM 2014), Aug 1, 2014

Online social communities often exhibit complex relationship structures, ranging from close frien... more Online social communities often exhibit complex relationship structures, ranging from close friends to political rivals. As a result, persons are influenced by their friends and foes differently. Network applications can benefit from accompanying these structural differences in propagation schemes. In this paper, we study the optimal influence propagation policies for networks with positive and negative relationship types. We tackle the problem of minimizing the end-to-end propagation cost of influencing a target person in favor of an idea by utilizing the relationship types in the underlying social graph. The propagation cost is incurred by social and physical network dynamics such as frequency of interaction, the strength of friendship and foe ties, propagation delay or the impact factor of the propagating idea. We extend this problem by incorporating the impact of message deterioration and ignorance. We demonstrate our results in both a controlled environment and the Epinions dataset. Our results show that judicious propagation schemes lead to a significant reduction in the average cost and complexity of influence propagation compared to naïve myopic algorithms. Index Terms-Socially aware physical systems, network propagation for social media, signed networks, recommender systems.

IEEE Journal of Selected Topics in Signal Processing, Mar 1, 2015

Online social communities often exhibit complex relationship structures, ranging from close frien... more Online social communities often exhibit complex relationship structures, ranging from close friends to political rivals. As a result, persons are influenced by their friends and foes differently. Future network applications can benefit from integrating these structural differences in propagation schemes through socially aware sensors. In this paper, we introduce a propagation model for such social sensor networks with positive and negative relationship types. We tackle two main scenarios based on this model. The first one is to minimize the end-to-end propagation cost of influencing a target person in favor of an idea by utilizing sensor observations about the relationship types in the underlying social graph. The propagation cost is incurred by social and physical network dynamics such as propagation delay, frequency of interaction, the strength of friendship/foe ties or the impact factor of the propagating idea. We next extend this problem by incorporating the impact of message deterioration and ignorance, and by limiting the number of persons influenced against the idea before reaching the target. Second, we study the propagation problem while minimizing the number of negatively influenced persons on the path, and provide extensions to elaborate on the impact of network parameters. We demonstrate our results in both an artificially created network and the Epinions signed network topology. Our results show that judicious propagation schemes lead to a significant reduction in the average cost and complexity of network propagation compared to naïve myopic algorithms.

Communication networks are linked to and influenced by human interactions. Socially-aware systems... more Communication networks are linked to and influenced by human interactions. Socially-aware systems should integrate these complex relationship patterns in the network design. This paper studies the impact of friendship and antagonistic relationships between individuals on optimal network propagation policies. We develop a network propagation model for signed networks, and determine the optimal policies to influence a target node with an opinion while minimizing the total number of persons against it. We also provide extensions to this problem to elaborate on the impact of network parameters, such as minimum-delay propagation, while limiting the number of persons influenced against the idea before reaching the target. We provide numerical evaluations in a synthetic setup as well as the Epinions online social dataset. We demonstrate that propagation schemes with social and influence-centric constraints should take into account the relationship types in network design.

This paper investigates the impact of cooperation with an untrusted relay in multi-source multi-d... more This paper investigates the impact of cooperation with an untrusted relay in multi-source multi-destination networks. The set up considered is one where the relay is the only means of communications due to the absence of direct links between the sources and the destinations. Since the relay is untrusted, all messages from the sources need to be kept secret from the relay. Furthermore, the destinations are assumed to have different levels of security clearance, i.e., some private messages should only be decoded by their intended receiver and should be kept secret from other destinations. An achievable secure rate region is found by using random binning at the sources, cooperative jamming from the destinations, and compress-andforward at the relay. Additionally, a genie aided outer bound on the secure rate region is derived. Comparison of inner and outer bounds are provided.

In this paper, we study a cache-aided combination network, where a layer of relay nodes connects ... more In this paper, we study a cache-aided combination network, where a layer of relay nodes connects a server to a set of end users, under three different secrecy requirements. Both the relays and the end users are equipped with caches. First, we consider secure delivery where we require that an external entity must not gain any information about the database files by observing the transmitted signals over the network links. Second, we consider secure caching where we require that an end user must not be able to obtain any information about a file that he did not request. Last, we consider both of these requirements simultaneously. We jointly optimize the cache placement and delivery phases in order to minimize the delivery load over each of the two hops, and demonstrate the impact of the network topology on the system performance under these secrecy requirements.

We consider information theoretic security in a twohop combination network where there are groups... more We consider information theoretic security in a twohop combination network where there are groups of end users with distinct degrees of connectivity served by a layer of relays. The model represents a network set up with users having access to asymmetric resources, here the number of relays that they are connected to, yet demand security guarantees uniformly. We study two security constraints separately and simultaneously: secure delivery where the information must be kept confidential from an external entity that wiretaps the delivery phase; and secure caching where each cache-aided end-user can retrieve the file it requests and cannot obtain any information on files it does not. The achievable schemes we construct are multi-stage where each stage completes requests by a class of users.

This work considers a network consisting of a server and a layer of relay nodes equipped with cac... more This work considers a network consisting of a server and a layer of relay nodes equipped with cache memories which aim to deliver content to end nodes that also have cache memories. The server and the end nodes consider the intermediate relay caches to be untrusted with the content. As a result, the server must design strategies to place content in relay caches not only to serve end users, but also to ensure that any a subset of them, even when colluding, cannot gain any information about the contents of the server database. The end users randomly connect to a subset of these untrusted caches at the beginning of the delivery phase via multicast links. For this network model, a coded caching scheme is developed by jointly optimizing the cache placement and delivery phases using secure regenerating codes. In addition, the scheme is extended to the setup of combination networks with untrusted relays, where the untrusted relays are connected to the end users via unicast links. The study highlights the benefits of cooperating with untrusted caches by designing the end users' caches to provide multicast opportunities in order to minimize the delivery load.

This paper considers the two-user interference relay channel where each source wishes to communic... more This paper considers the two-user interference relay channel where each source wishes to communicate to its destination a message that is confidential from the other destination. Furthermore, the relay, that is the enabler of communication, due to the absence of direct links, is untrusted. Thus, the messages from both sources need to be kept secret from the relay as well. We provide an achievable secure rate region for this network. The achievability scheme utilizes structured codes for message transmission, cooperative jamming and scaled computeand-forward. In particular, the sources use nested lattice codes and stochastic encoding, while the destinations jam using lattice points. The relay decodes two integer combinations of the received lattice points and forwards, using Gaussian codewords, to both destinations. The achievability technique provides the insight that we can utilize the untrusted relay node as an encryption block in a two-hop interference relay channel with confidential messages.

In this work, we consider a cache-aided network where the users share the end-caches. In particul... more In this work, we consider a cache-aided network where the users share the end-caches. In particular, a user has access to only one of the caches and the number of caches is less than the number of users. We propose a coded placement scheme that exploits the asymmetry in the number of users associated with each cache. Some of the signals sent to the overloaded caches facilitate the decoding of the coded subfiles stored at the underloaded caches. We present an explicit caching scheme and fully characterize the coded placement gain for two-cache systems. Then, we generalize our scheme to larger networks, where the optimal parameters are characterized by solving a linear program. We observe that, with the proposed scheme, as the asymmetry in the users' connectivity increases, the gain from coded placement is more evident.

arXiv (Cornell University), Nov 9, 2018

In this work, we study coded placement in caching systems where the users have unequal cache size... more In this work, we study coded placement in caching systems where the users have unequal cache sizes and demonstrate its performance advantage. In particular, we propose a caching scheme with coded placement for three-user systems that outperforms the best caching scheme with uncoded placement. In our proposed scheme, users cache both uncoded and coded pieces of the files, and the coded pieces at the users with large memories are decoded using the unicast/multicast signals intended to serve users with smaller memories. Furthermore, we extend the proposed scheme to larger systems and show the reduction in delivery load with coded placement compared to uncoded placement.

arXiv (Cornell University), Mar 19, 2019

This paper considers a cache-aided device-to-device (D2D) system where the users are equipped wit... more This paper considers a cache-aided device-to-device (D2D) system where the users are equipped with cache memories of different size. During low traffic hours, a server places content in the users' cache memories, knowing that the files requested by the users during peak traffic hours will have to be delivered by D2D transmissions only. The worst-case D2D delivery load is minimized by jointly designing the uncoded cache placement and linear coded D2D delivery. Next, a novel lower bound on the D2D delivery load with uncoded placement is proposed and used in explicitly characterizing the minimum D2D delivery load (MD2DDL) with uncoded placement for several cases of interest. In particular, having characterized the MD2DDL for equal cache sizes, it is shown that the same delivery load can be achieved in the network with users of unequal cache sizes, provided that the smallest cache size is greater than a certain threshold. The MD2DDL is also characterized in the small cache size regime, the large cache size regime, and the three-user case. Comparisons of the server-based delivery load with the D2D delivery load are provided. Finally, connections and mathematical parallels between cache-aided D2D systems and coded distributed computing (CDC) systems are discussed.

IEEE journal on selected areas in information theory, Dec 1, 2021

This paper considers a cache-aided network where the users have access to helper-caches with hete... more This paper considers a cache-aided network where the users have access to helper-caches with heterogeneous sizes. First, coded placement schemes are proposed that exploit the heterogeneity in cache sizes when one user is connected to each cache. In the proposed scheme, the unicast/multicast signals intended to serve users connected to small memories are utilized in decoding the contents of the larger memories. A reduction in delivery load with coded placement is shown compared to uncoded placement for three-user systems with arbitrary cache sizes and larger systems in the small total memory regime. Next, systems with equal-size caches where multiple users are associated with each cache are considered. It is shown that coded placement outperforms the best uncoded placement scheme. In the proposed scheme, the unicast/multicast signals sent to the overloaded helper-caches facilitate the decoding of the coded subfiles stored at the underloaded helper-caches. The gain from coded placement is explicitly characterized for two-cache systems. For larger systems, the parameters of the coded placement scheme are obtained by optimization. It is observed that the gain from coded placement becomes more evident with increasing asymmetry in users’ connectivity. Finally, a unified coded placement scheme for two-cache systems that exploits the asymmetry in both the cache sizes and the connectivity pattern is presented.