Ness B. Shroff

• The Ohio State University

We study the stochastic multi-armed bandit (MAB) problem in the presence of side-observations across actions that occur as a result of an underlying network structure. In our model, a bipartite graph captures the relationship between actions and a common set of unknowns such that choosing an action reveals observations for the unknowns that it is c...

Each individual’s usage behavior on mobile devices depend on a variety of factors such as time, location, and previous actions. Hence, context-awareness provides great opportunities to make the networking and the computing capabilities of mobile systems to be more personalized and more efficient in managing their resources. To this end, we first re...

In this paper, we aim to obtain the optimal delay-power tradeoff and the corresponding optimal scheduling policy for arbitrary i.i.d. arrival process and adaptive transmissions. The number of backlogged packets at the transmitter is known to a scheduler, who has to determine how many backlogged packets to transmit during each time slot. The power c...

We propose a hybrid RF/millimeter wave (mmWave) architecture for 5G cellular systems. Communication in the mmWave band faces significant challenges due to variable channels, intermittent connectivity, and high energy usage. Moreover, speeds for electronic processing of data is of the same order as typical rates for mmWave interface. Therefore, the...

The problem of reducing the age-of-information has been extensively studied in the single-hop setting. In this paper, we minimize the age-of-information in general multihop networks. We first prove that for exponential packet transmission times, a preemptive Last Generated First Served (LGFS) policy results in smaller age processes at all nodes of...

Cybersecurity is increasingly threatened by advanced and persistent attacks. As these attacks are often designed to disable a system (or a critical resource, e.g., a user account) repeatedly, it is crucial for the defender to keep updating its security measures to strike a balance between the risk of being compromised and the cost of security updat...

The last decade has seen an unprecedented growth in the demand for wireless services. These services are fueled by applications that often require not only high data rates, but also very low latency to function as desired. However, as wireless networks grow and support increasingly large numbers of users, these control algorithms must also incur on...

A vehicle-to-vehicle network is one type of mobile ad-hoc network. Due to mobility, the topology in a vehicle-to-vehicle network is time-varying, which complicates the analysis and evaluation of network performance. In this paper, we model the network as geometric elements of lines and points and analyze connectivity and capacity of the network usi...

Usage patterns of mobile devices depend on a variety of factors such as time, location, and previous actions. Hence, context-awareness can be the key to make mobile systems to become personalized and situation dependent in managing their resources. We first reveal new findings from our own Android user experiment: (i) the launching probabilities of...

For a multicast group of n receivers, existing techniques either achieve high throughput at the cost of prohibitively large (e.g., O(n)) feedback overhead, or achieve low feedback overhead but without either optimal or near-optimal throughput guarantees. Simultaneously achieving good throughput guarantees and low feedback overhead has been an open...

In recent years, there have been significant efforts on the research and development of Massive MIMO (M-MIMO) technologies at the physical layer. So far, however, the understanding of how M-MIMO could affect the performance of network control and optimization algorithms remains rather limited. In this paper, we focus on analyzing the performance of...

In modern computer systems, long-running jobs are divided into a large number of short tasks and executed in parallel. Experience in practical systems suggests that task service times are highly random and the job service latency is bottlenecked by the slowest straggling task. One common solution for straggler mitigation is to replicate a task on m...

In this work, we consider an information-update system where a source sends update packets to a remote monitor via multiple network servers. An important metric of data freshness at the monitor is the age-of-information, or simply age, which is defined as the time elapsed since the freshest packet at the monitor was generated. Recent studies on inf...

There have been recent attempts to develop scheduling schemes for downlink transmission in a single cell of a multi-channel (e.g., OFDM-based) cellular network. These works have been quite promising in that they have developed low-complexity index scheduling policies that are delay-optimal (in a large deviation rate-function sense). However, these...

In this work we study how to manage the freshness of status updates sent from a source to a remote monitor via a network server. A proper metric of data freshness at the monitor is the status update age, which is defined as how old the latest update is since the moment this update was generated at the source. A logical policy is the zero wait polic...

Video streaming generates a substantial fraction of the traffic on the Internet. The demands of video streaming also increase the workload on the video server, which in turn leads to substantial slowdowns. In order to resolve the slowdown problem, and to provide a scalable and robust infrastructure to support on-demand streaming, helper-assisted vi...

This paper introduces the vector sparse matrix transform (vector SMT), a new decorrelating transform suitable for performing distributed processing of high dimensional signals in sensor networks. We assume that each sensor in the network encodes its measurements into vector outputs instead of scalar ones. The proposed transform decorrelates a seque...

In this paper we characterize the mean and the distribution of the first exit time of a Lévy flight from a bounded region in N -dimensional spaces. We characterize tight upper and lower bounds on the tail distribution of the first exit time, and provide the exact asymptotics of the mean first exit time for a given range of step-length distribution...

Stealthy attacks are a major threat to cyber security. In practice, both attackers and defenders have resource constraints that could limit their capabilities. Hence, to develop robust defense strategies, a promising approach is to utilize game theory to understand the fundamental trade-offs involved. Previous works in this direction, however, main...

Distributed joint congestion control and routing optimization has received a significant amount of attention recently. To date, however, most of the existing schemes follow a key idea called the back-pressure algorithm. Despite having many salient features, the first-order subgradient nature of the back-pressure based schemes results in slow conver...

Cognitive radio networks allow unlicensed users to access licensed spectrum opportunistically without disrupting primary user (PU) communication. Developing a distributed implementation that can fully utilize the spectrum opportunities for secondary users (SUs) has so far remained elusive. Although throughput optimal algorithms based on the well-kn...

We study opportunistic multiuser scheduling in downlink networks with Markov-modeled outage channels. We consider the scenario that the scheduler does not have full knowledge of the channel state information, but instead estimates the channel state by exploiting the memory inherent in the Markov channels along with Automatic-Repeat-reQues-styled-st...

In this paper, we focus on a mobile wireless network comprising a powerful communication center and a multitude of mobile users. We investigate the propagation of latency-constrained content in the wireless network characterized by heterogeneous (time-varying and user-dependent) wireless channel conditions, heterogeneous user mobility, and where co...

One key requirement for storage clouds is to be able to retrieve data quickly. Recent system measurements have shown that the data retrieving delay in storage clouds is highly variable, which may result in a long latency tail. One crucial idea to improve the delay performance is to retrieve multiple data copies by using parallel downloading threads...

Predicting spreading patterns of information or virus has been a popular research topic for which various mathematical tools have been developed. These tools have mainly focused on estimating the average time of spread to a fraction (e.g., ) of the agents, i.e., so-called average -completion time E(T). We claim that understanding stochastic confide...

The smart grid is envisioned to significantly enhance the efficiency of energy consumption, by utilizing two-way communication channels between consumers and operators. For example, operators can opportunistically leverage the delay tolerance of energy demands in order to balance the energy load over time, and hence, reduce the total operational co...

In this paper, we study the scheduling problem for downlink transmission in a multichannel (e.g., OFDM-based) wireless network. We focus on a single cell, with the aim of developing a unifying framework for designing low-complexity scheduling policies that can provide optimal performance in terms of both throughput and delay. We develop new easy-to...

The problem of online packet scheduling with hard deadlines has been studied extensively in the single-hop setting, whereas it is notoriously difficult in the multihop setting. This difficulty stems from the fact that packet scheduling decisions at each hop influence and are influenced by decisions on other hops, and only a few provably efficient o...

Smart mobile devices are generating a tremendous amount of data traffic that is putting stress on even the most advanced cellular networks. Delayed offloading has recently been proposed as an efficient mechanism to substantially alleviate this stress. The idea is simple. It allows a mobile device to delay transmission of data packets for a certain...

Link adaptation technologies, such as Adaptive Modulation and Coding (AMC) and Multiple-Input–Multiple-Output (MIMO), are used in advanced wireless communication systems to achieve high spectrum efficiency. Communication performance can be improved significantly by adaptive transmissions based on the quality of received signals, i.e., the signal-to...

In this paper, we consider the problem of distributed load shedding optimization for disaster recovery in smart grids. We develop distributed second-order interior-point based load shedding algorithms that enjoy a fast quadratic convergence rate. Our main contributions are two-fold: (i) We propose a rooted spanning tree based reformulation that ena...

We study the stochastic multi-armed bandit (MAB) problem in the presence of side-observations across actions. In our model, choosing an action provides additional side observations for a subset of the remaining actions. One example of this model occurs in the problem of targeting users in online social networks where users respond to their friends'...

We study the stochastic multi-armed bandit (MAB) problem in the presence of side-observations across actions. In our model, choosing an action provides additional side observations for a subset of the remaining actions. One example of this model occurs in the problem of targeting users in online social networks where users respond to their friends'...

In this paper, we consider the problem of distributed load shedding optimization for disaster recovery in smart grids. We develop distributed second-order interior-point based load shedding algorithms that enjoy a fast quadratic convergence rate. Our main contributions are two-fold: (i) We propose a rooted spanning tree based reformulation that ena...

The accelerated adoption of EVs in the last few years has raised concerns that the power grid can get overloaded when a large number of EVs are charged simultaneously. A promising direction is to implement large scale automated scheduling of EV charging at public facilities, by exploiting the time elasticity of charging requests. In this work, we s...

Many opportunistic scheduling techniques are impractical because they require accurate channel state information (CSI) at the transmitter. In this paper, we investigate the scheduling of unicast and multicast services in a downlink network with a very limited amount of feedback information. Specifically, unicast users send imperfect (or no) CSI and...

In this paper, we study the problem of reducing the delay of downloading data from cloud storage systems by leveraging multiple parallel threads, assuming that the data has been encoded and stored in the clouds using fixed rate forward error correction (FEC) codes with parameters (n, k). That is, each file is divided into k equal-sized chunks, whic...

A major challenge of wireless multicast is to be able to support a large number of users while simultaneously maintaining low delay and low feedback overhead. In this paper, we develop a joint coding and feedback scheme called Moving Window Network Coding (MWNC) that successfully addresses this challenge. In particular, we show that our scheme simu...

Recent breakthroughs in wireless communication show that by using new signal processing techniques, a wireless node is capable of transmitting and receiving simultaneously on the same frequency band by activating both of its RF chains, thus achieving full-duplex communication and potentially doubling the link throughput. However, with two sets of R...

In a wireless network, the efficiency of scheduling algorithms over time-varying channels depends heavily on the accuracy of the Channel State Information (CSI), which is usually quite ``costly'' in terms of consuming network resources. Scheduling in such systems is also subject to stringent constraints such as power and bandwidth, which limit the...

In this work, we investigate the use of epidemic routing in energy constrained Delay Tolerant Networks (DTNs). In DTNs, connected paths between source and destination rarely materialize due to the mobility and sparse density of nodes. Epidemic routing is well-suited for these environments due to its simplicity and fully distributed implementation....

We introduce a new approach to channel access for ad hoc networks that utilize multiple heterogeneous channels. The radios of the ad hoc networks we investigate are frequency-agile allowing them the ability to change their carrier frequency and transmission ...

We investigate the problem of minimizing the sum of the queue lengths of all the nodes in a wireless network with a forest topology. Each packet is destined to one of the roots (sinks) of the forest. We consider a time-slotted system and a primary (or one-hop) interference model. We characterize the existence of causal sample-path optimal schedulin...

Retransmissions serve as the basic building block that communication protocols use to achieve reliable data transfer. Until recently, the number of retransmissions was thought to follow a geometric (light-tailed) distribution. However, recent work shows that when the distribution of the packet sizes have infinite support, retransmission-based proto...

In this paper, we study the problem of simultaneous information and power transfer in a wireless multi-user, single hop network. Specifically, we develop an optimal resource allocation algorithm that maximizes the long term average rate of the network while harvesting energy from both the received signal and the interference. We focus on receivers...

We consider a degraded block-fading broadcast channel, in which we treat each user as an “internal eavesdropper” for the information transmitted to another user. We addressed the problem of maximizing cumulative network utility, which is a function instantaneous rate of confidential data served for all users. Then, we propose a low complexity, prov...

We consider the decision problem of an external agent choosing to execute one of M actions for each user in a social network. We assume that observing a user's actions provides valuable information for a larger set of users since each user's preferences are interrelated with those of her social peers. This falls into the well-known setting of the m...

The smart grid is expected to be the next generation of electricity grid. It will enable numerous revolutionary features, that allow end-users, such as homes, communities, or businesses, to harvest renewable energy and store the energy in a local battery, which could act as a microgeneration unit. In addition, the customers could be provided with d...

In an unreliable single-hop broadcast network setting, we investigate the throughput and decoding-delay performance of random linear network coding as a function of the coding window size and the network size. Our model consists of a source transmitting packets of a single flow to a set of n users over independent time-correlated erasure channels....

A major challenge in OFDMA cellular networks is to efficiently allocate scarce channel resources and optimize global system performance. Specifically, the allocation problem across cells/base-stations is known to incur extremely high computational/communication complexity. Recently, Gibbs sampling has been used to solve the downlink inter-cell allo...

We consider a single-user, single-hop wireless communication system, in which data packets arrive at a data queue to be transmitted to a receiver over a block fading channel, privately from an eavesdropper. We assume that the eavesdropper listens to the transmitter over another independently fading channel and that the transmitter only has knowledg...

Developing scheduling mechanisms that can simultaneously achieve throughput optimality and good delay performance often require solving the Maximum Independent Weighted Set (MWIS) problem. However, under most realistic network settings, the MWIS problem can be shown to be NP-hard. In non-fading environments, low-complexity scheduling algorithms hav...

The smart grid is the new generation of electricity grid that can efficiently utilize new distributed sources of energy (e.g., harvested renewable energy), and allow for dynamic electricity price. In this paper, we investigate the cost minimization problem for an end-user, such as a home, community, or a business, which is equipped with renewable e...

In this paper, we study distributed scheduling in multihop multiple-input-multiple-output (MIMO) networks. We first develop a “MIMO-pipe” model that provides the upper layers a set of rates and signal-to-interference-plus-noise ratio (SINR) requirements that capture the rate-reliability tradeoff in MIMO communications. The main thrust of this paper...

We study the problem of maximizing the information in a wireless sensor network with unreliable links. We consider a sensor network with a tree topology, where the root corresponds to the sink, and the rest of the network detects an event and transmits data to the sink. We formulate a combinatorial optimization problem that maximizes the informatio...

WiFi usage significantly reduces the battery lifetime of handheld devices such as smartphones and tablets, due to its high energy consumption. In this paper, we propose "Life-Add": a Lifetime Adjustable design for WiFi networks, where the devices are powered by battery, electric power, and/or renewable energy. In Life-Add, a device turns off its ra...

A new precoding-based intersession network coding (NC) scheme has recently been proposed, which applies the interference alignment technique, originally devised for wireless interference channels, to the 3-unicast problem of directed acyclic networks. The main result of this work is a graph-theoretic characterization of the feasibility of the 3-uni...

With the rapidly growing challenges of big data analytics, the need for efficient and distributed algorithms to optimize cloud computing performances is unprecedentedly high. In this paper, we consider how to optimally deploy a cloud computing programming framework (e.g., MapReduce and Dryad) over a given underlying network hardware infrastructure...

Due to the rapidly growing scale and heterogeneity of wireless networks, the design of distributed cross-layer optimization algorithms has received significant interest from the networking research community. So far, the standard distributed cross-layer approach in the literature is based on the first-order Lagrangian dual decomposition and the sub...

In this paper, we focus on the issue of stability in multihop wireless networks under flow-level dynamics, and explore the inefficiency and instability of the celebrated Back-Pressure algorithms. It has been well-known that the Back-Pressure (or Max-Weight) algorithms achieve queue stability and throughput optimality in a wide variety of scenarios....

With the rapid increase in size and number of jobs that are being processed in the MapReduce framework, efficiently scheduling jobs under this framework is becoming increasingly important. We consider the problem of minimizing the total flowtime of a sequence of jobs in the MapReduce framework, where the jobs arrive over time and need to be process...

Wireless network scheduling and control techniques (e.g., opportunistic scheduling) rely heavily on access to Channel State Information (CSI). However, obtaining this information is costly in terms of bandwidth, time, and power, and could result in large overhead. Therefore, a critical question is how to optimally manage network resources in the ab...

The problem of online job or packet scheduling with hard deadlines has been studied extensively in the single hop setting, whereas it is notoriously difficult in the multihop setting. This difficulty stems from the fact that packet scheduling decisions at each hop influences and are influenced by decisions on other hops and only a few provably effi...

In this paper, we focus on mobile wireless networks comprising of a powerful communication center and a multitude of mobile users. We investigate the propagation of deadline-based content in the wireless network characterized by heterogeneous (time-varying and user-dependent) wireless channel conditions, heterogeneous user mobility, and where commu...

Regulating the ISPs to adopt more security measures has been proposed as an effective method in mitigating the threats of attacks in the Internet. However, economic incentives of the ISPs and the network effects of security measures can lead to an under-investment in their adoption. We study the potential gains in a network's social utility when a...

This paper investigates the distributed power allocation problem for coordinated multipoint (CoMP) transmissions in distributed antenna systems (DAS). Traditional duality based optimization techniques cannot be directly applied to this problem, because the non-strict concavity of the CoMP transmission's achievable rate with respect to the transmiss...

In this paper we quantify the efficiency of parallelism in systems that are prone to failures and exhibit power law processing delays. We characterize the performance of two prototype schemes of parallelism, redundant and split, in terms of both the power law exponent and exact asymptotics of the delay distribution tail. We also develop the optimal...

In this paper, we study the scheduling problem for downlink transmission in a multi-channel (e.g., OFDM-based) wireless network. We focus on a single cell, with the aim of developing a unifying framework for designing low-complexity scheduling policies that can provide optimal performance in terms of both throughput and delay. We develop new easy-t...

A variety of mathematical tools have been developed for predicting the spreading patterns in a number of varied environments including infectious diseases, computer viruses, and urgent messages broadcast to mobile agent (e.g., humans, vehicles, and mobile devices). These tools have mainly focused on estimating the average time for the spread to rea...

In this paper, we focus on the scheduling problem in multi-channel wireless networks, e.g., the downlink of a single cell in fourth generation (4G) OFDM-based cellular networks. Our goal is to design efficient scheduling policies that can achieve provably good performance in terms of both throughput and delay, at a low complexity. While a recently...

In this paper, we focus on the scheduling problem in multi-channel wireless networks, e.g., the downlink of a single cell in fourth generation (4G) OFDM-based cellular networks. Our goal is to design practical scheduling policies that can achieve provably good performance in terms of both throughput and delay, at a low complexity. While a class of...

The smart grid is the new generation of electricity grid that can efficiently facilitate new distributed sources of energy (e.g., harvested renewable energy), and allow for dynamic electricity price. In this paper, we investigate the cost minimization problem for an end-user, such as a home, community, or a business, which is equipped with renewabl...

The security of the Internet can be significantly improved if Internet Service Providers adopt firewalls to monitor traffic entering and leaving access networks. But this process suffers due to 'free-riding', and hence, regulatory requirements and 'seeding' strategies are required to influence the adoption process. In this paper, we analytically de...

The smart grid is envisioned to significantly enhance the efficiency of energy consumption, by utilizing two-way communication channels between consumers and operators. For example, operators can opportunistically leverage the delay tolerance of energy demands in order to balance the energy load over time, and hence, reduce the total operational co...

In Cognitive Radio Networks (CRNs), unlicensed users are allowed to access the licensed spectrum when it is not currently being used by primary users (PUs). In this paper, we study the throughput maximization problem for a multi-channel CRN where each SU can only sense a limited number of channels. We show that this problem is strongly NP-hard, and...

We consider the problem of minimizing the total flow-time of multiple jobs in a pool of multiple homogeneous machines, where the jobs arrive over time and have to be served with phase precedence. This is a common occurrence in job scheduling for the increasingly popular data center oriented systems, where jobs need to be processed through Map and R...

The smart grid is envisioned to significantly enhance the efficiency of energy consumption, by utilizing two-way communication channels between consumers and operators. For example, operators can opportunistically leverage the delay tolerance of energy demands in order to balance the energy load over time, and hence, reduce the total operational co...

Due to the rapidly growing scale and heterogeneity of wireless networks, the design of distributed cross-layer optimization algorithms have received significant interest from the networking research community. So far, the standard distributed cross-layer approach in the literature is based on first-order Lagrangian dual decomposition and the subgra...

This paper considers reliable communications over a multiple-input multiple-output (MIMO) Gaussian channel, where the channel matrix is within a bounded channel uncertainty region around a nominal channel matrix, i.e., an instance of the compound MIMO Gaussian channel. We study the optimal transmit covariance matrix design to achieve the capacity o...

In this paper, we characterize the throughput of a broadcast network with n receivers using rateless codes with block size K. We assume that the underlying channel is a Markov modulated erasure channel that is i.i.d. across users, but can be correlated in time. We characterize the system throughput asymptotically in n. Specifically, we explicitly s...

In Cognitive Radio Networks (CRNs), secondary users (SUs) are allowed to opportunistically access the unused/under-utilized channels of primary users (PUs). To utilize spectrum resources efficiently, an auction scheme is often applied where an operator serves as an auctioneer and accepts spectrum requests from SUs. Most existing works on spectrum a...

In the literature, scaling laws for wireless mobile networks have been characterized under various models of node mobility and several assumptions on how communication occurs between nodes. To improve the realism in the analysis of scaling laws, we propose a new analytical framework. The framework is the first to consider a L\'{e}vy flight mobility...

We investigate the downlink scheduling problem under Markovian ON/OFF fading channels, where the instantaneous channel state information is not directly accessible, but is revealed via ARQ-type feedback. The scheduler can exploit the temporal correlation/channel memory inherent in the Markovian channels to improve network performance. However, desi...

We study the utility maximization problem for data collection in sensor networks subject to a deadline constraint, where the data on a selected subset of nodes are collected through a routing tree rooted at a sink subject to the 1-hop interference model. Our problem can be viewed as a Network Utility Maximization (NUM) problem with binary decisions...

We consider a cooperative relay network where a source node communicates to a destination node with the help of multiple relay nodes (RNs). RNs are assumed to be able to work in either active mode or sleep mode. To minimize the total energy consumption, working modes of RNs and power allocation need to be optimized. Based on the time scales of mode...

Renewable energy sources can be attached to sensor nodes to provide energy replenishment for extending the battery life and prolonging the overall lifetime of sensor networks. For networks with replenishment, conservative energy expenditure may lead to missed recharging opportunities due to battery capacity limitations, while aggressive usage of en...