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Online Antenna Tuning in Heterogeneous Cellular Networks with Deep Reinforcement LearningMar 15 2019We aim to jointly optimize the antenna tilt angle, and the vertical and horizontal half-power beamwidths of the macrocells in a heterogeneous cellular network (HetNet) via a synergistic combination of deep learning (DL) and reinforcement learning (RL). ... More

Connectivity of Millimeter Wave Networks with Multi-hop RelayingDec 21 2014This paper presents a novel stochastic geometry approach to the connectivity of milimeter wave (mmWave) networks with multi-hop relaying. The random positions and shapes of obstacles in the radio environment are modeled as a Boolean model, whose germs ... More

Uplink Capacity and Interference Avoidance for Two-Tier Femtocell NetworksFeb 23 2007Feb 05 2009Two-tier femtocell networks-- comprising a conventional macrocellular network plus embedded femtocell hotspots-- offer an economically viable solution to achieving high cellular user capacity and improved coverage. With universal frequency reuse and DS-CDMA ... More

Transmission capacity of wireless networksJan 03 2012Transmission capacity (TC) is a performance metric for wireless networks that measures the spatial intensity of successful transmissions per unit area, subject to a constraint on the permissible outage probability (where outage occurs when the SINR at ... More

An Analytical Framework for Multi-Cell Cooperation via Stochastic Geometry and Large DeviationsApr 14 2012Dec 06 2012Multi-cell cooperation (MCC) is an approach for mitigating inter-cell interference in dense cellular networks. Existing studies on MCC performance typically rely on either over-simplified Wyner-type models or complex system-level simulations. The promising ... More

Deep Learning-Based Channel Estimation for High-Dimensional SignalsApr 19 2019We propose a novel deep learning-based channel estimation technique for high-dimensional communication signals that does not require any training. Our method is broadly applicable to channel estimation for multicarrier signals with any number of antennas, ... More

Joint Resource Partitioning and Offloading in Heterogeneous Cellular NetworksMar 28 2013Aug 21 2013In heterogeneous cellular networks (HCNs), it is desirable to offload mobile users to small cells, which are typically significantly less congested than the macrocells. To achieve sufficient load balancing, the offloaded users often have much lower SINR ... More

Spectrum Allocation in Two-Tier NetworksMay 08 2008Nov 24 2008Two-tier networks, comprising a conventional cellular network overlaid with shorter range hotspots (e.g. femtocells, distributed antennas, or wired relays), offer an economically viable way to improve cellular system capacity. The capacity-limiting factor ... More

Downlink Cellular Network Analysis with Multi-slope Path Loss ModelsAug 03 2014Mar 15 2015Existing cellular network analyses, and even simulations, typically use the standard path loss model where received power decays like $\|x\|^{-\alpha}$ over a distance $\|x\|$. This standard path loss model is quite idealized, and in most scenarios the ... More

A Stochastic-Geometry Approach to Coverage in Cellular Networks with Multi-Cell CooperationMar 22 2011Multi-cell cooperation is a promising approach for mitigating inter-cell interference in dense cellular networks. Quantifying the performance of multi-cell cooperation is challenging as it integrates physical-layer techniques and network topologies. For ... More

Coverage in Multi-Antenna Two-Tier NetworksFeb 18 2009May 04 2009In two-tier networks -- comprising a conventional cellular network overlaid with shorter range hotspots (e.g. femtocells, distributed antennas, or wired relays) -- with universal frequency reuse, the near-far effect from cross-tier interference creates ... More

Bandwidth Partitioning in Decentralized Wireless NetworksNov 02 2007Apr 02 2008This paper addresses the following question, which is of interest in the design of a multiuser decentralized network. Given a total system bandwidth of W Hz and a fixed data rate constraint of R bps for each transmission, how many frequency slots N of ... More

Fractional Power Control for Decentralized Wireless NetworksJul 03 2007Apr 28 2008We consider a new approach to power control in decentralized wireless networks, termed fractional power control (FPC). Transmission power is chosen as the current channel quality raised to an exponent -s, where s is a constant between 0 and 1. The choices ... More

Open vs Closed Access Femtocells in the UplinkFeb 15 2010Femtocells are assuming an increasingly important role in the coverage and capacity of cellular networks. In contrast to existing cellular systems, femtocells are end-user deployed and controlled, randomly located, and rely on third party backhaul (e.g. ... More

On the Role of Mobility for Multi-message GossipApr 13 2012Feb 07 2013We consider information dissemination in a large $n$-user wireless network in which $k$ users wish to share a unique message with all other users. Each of the $n$ users only has knowledge of its own contents and state information; this corresponds to ... More

Multi-Antenna Communication in Ad Hoc Networks: Achieving MIMO Gains with SIMO TransmissionSep 29 2008Dec 24 2009The benefit of multi-antenna receivers is investigated in wireless ad hoc networks, and the main finding is that network throughput can be made to scale linearly with the number of receive antennas nR even if each transmitting node uses only a single ... More

An overview of the transmission capacity of wireless networksAug 29 2008Mar 30 2010This paper surveys and unifies a number of recent contributions that have collectively developed a metric for decentralized wireless network analysis known as transmission capacity. Although it is notoriously difficult to derive general end-to-end capacity ... More

Spectrum Sharing for Device-to-Device Communication in Cellular NetworksMay 18 2013Sep 23 2014This paper addresses two fundamental and interrelated issues in device-to-device (D2D) enhanced cellular networks. The first issue is how D2D users should access spectrum, and we consider two choices: overlay (orthogonal spectrum between D2D and cellular ... More

Performance Analysis of Asynchronous Multicarrier Wireless NetworksOct 14 2014This paper develops a novel analytical framework for asynchronous wireless networks deploying multicarrier transmission. Nodes in the network have different notions of timing, so from the viewpoint of a typical receiver, the received signals from different ... More

Modeling, Analysis and Design for Carrier Aggregation in Heterogeneous Cellular NetworksNov 16 2012Jun 22 2013Carrier aggregation (CA) and small cells are two distinct features of next-generation cellular networks. Cellular networks with small cells take on a very heterogeneous characteristic, and are often referred to as HetNets. In this paper, we introduce ... More

SINR and Throughput of Dense Cellular Networks with Stretched Exponential Path LossMar 23 2017Nov 20 2017Distance-based attenuation is a critical aspect of wireless communications. As opposed to the ubiquitous power-law path loss model, this paper proposes a stretched exponential path loss model that is suitable for short-range communication. In this model, ... More

Stability and Metastability of Traffic Dynamics in Uplink Random Access NetworksJun 11 2019We characterize the stability, metastability, and the stationary regime of traffic dynamics in a single-cell uplink wireless system. The traffic is represented in terms of spatial birth-death processes, in which users arrive as a Poisson point process ... More

Joint Rate and SINR Coverage Analysis for Decoupled Uplink-Downlink Biased Cell Associations in HetNetsDec 05 2014Mar 24 2015Load balancing by proactively offloading users onto small and otherwise lightly-loaded cells is critical for tapping the potential of dense heterogeneous cellular networks (HCNs). Offloading has mostly been studied for the downlink, where it is generally ... More

Throughput Maximization for Delay-Sensitive Random Access CommunicationNov 06 2017Jun 05 2018Future 5G cellular networks supporting ultra-reliable, low-latency communications (URLLC) could employ random access communication to reduce the overhead compared to scheduled access techniques used in 4G networks. We consider a wireless communication ... More

A Unified Asymptotic Analysis of Area Spectral Efficiency in Ultradense Cellular NetworksDec 20 2017Apr 11 2018This paper studies the asymptotic properties of average area spectral efficiency (ASE) of a downlink cellular network in the limit of very dense base station (BS) and user densities. This asymptotic analysis relies on three assumptions: (1) interference ... More

On Association Cells in Random Heterogeneous NetworksOct 04 2013Characterizing user to access point (AP) association strategies in heterogeneous cellular networks (HetNets) is critical for their performance analysis, as it directly influences the load across the network. In this letter, we introduce and analyze a ... More

The effect of fading, channel inversion, and threshold scheduling on ad hoc networksJul 24 2007This paper addresses three issues in the field of ad hoc network capacity: the impact of i)channel fading, ii) channel inversion power control, and iii) threshold-based scheduling on capacity. Channel inversion and threshold scheduling may be viewed as ... More

Transmission Capacity of Ad Hoc Networks with Spatial DiversityFeb 08 2007Aug 11 2008This paper derives the outage probability and transmission capacity of ad hoc wireless networks with nodes employing multiple antenna diversity techniques, for a general class of signal distributions. This analysis allows system performance to be quantified ... More

Modeling Non-Uniform UE Distributions in Downlink Cellular NetworksDec 23 2012A recent way to model and analyze downlink cellular networks is by using random spatial models. Assuming user equipment (UE) distribution to be uniform, the analysis is performed at a typical UE located at the origin. While this method of sampling UEs ... More

On the Throughput Cost of Physical Layer Security in Decentralized Wireless NetworksDec 21 2010Jun 06 2011This paper studies the throughput of large-scale decentralized wireless networks with physical layer security constraints. In particular, we are interested in the question of how much throughput needs to be sacrificed for achieving a certain level of ... More

Spatially Correlated Content Caching for Device-to-Device CommunicationsSep 01 2016We study optimal geographic content placement for device-to-device (D2D) networks in which each file's popularity follows the Zipf distribution. The locations of the D2D users (caches) are modeled by a Poisson point process (PPP) and have limited communication ... More

An Overview on 3GPP Device-to-Device Proximity ServicesOct 01 2013Device-to-device (D2D) communication will likely be added to LTE in 3GPP Release 12. In principle, exploiting direct communication between nearby mobile devices will improve spectrum utilization, overall throughput, and energy consumption, while enabling ... More

An Analytical Framework for Modeling a Spatially Repulsive Cellular NetworkJan 09 2017Sep 30 2017We propose a new cellular network model that captures both deterministic and random aspects of base station deployments. Namely, the base station locations are modeled as the superposition of two independent stationary point processes: a random shifted ... More

Spatially Correlated Content Caching for Device-to-Device CommunicationsSep 01 2016Oct 03 2017We study optimal geographic content placement for device-to-device (D2D) networks in which each file's popularity follows the Zipf distribution. The locations of the D2D users (caches) are modeled by a Poisson point process (PPP) and have limited communication ... More

Optimizing Content Caching to Maximize the Density of Successful Receptions in Device-to-Device NetworkingAug 28 2016Device-to-device (D2D) communication is a promising approach to optimize the utilization of air interface resources in 5G networks, since it allows decentralized opportunistic short-range communication. For D2D to be useful, mobile nodes must possess ... More

Towards Understanding the Fundamentals of Mobility in Cellular NetworksApr 16 2012Jan 16 2013Despite the central role of mobility in wireless networks, analytical study on its impact on network performance is notoriously difficult. This paper aims to address this gap by proposing a random waypoint (RWP) mobility model defined on the entire plane ... More

Network Coding with Two-Way Relaying: Achievable Rate Regions and Diversity-Multiplexing TradeoffsFeb 13 2009This paper addresses the fundamental characteristics of information exchange via multihop network coding over two-way relaying in a wireless ad hoc network. The end-to-end rate regions achieved by time-division multihop (TDMH), MAC-layer network coding ... More

A Tractable Approach to Coverage and Rate in Cellular NetworksSep 02 2010Feb 21 2011Cellular networks are usually modeled by placing the base stations on a grid, with mobile users either randomly scattered or placed deterministically. These models have been used extensively but suffer from being both highly idealized and not very tractable, ... More

Limited Feedback Beamforming Over Temporally-Correlated ChannelsJun 06 2006May 02 2008Feedback of quantized channel state information (CSI), called limited feedback, enables transmit beamforming in multiple-input-multiple-output (MIMO) wireless systems with a small amount of overhead. Due to its efficiency, beamforming with limited feedback ... More

High-SIR Transmission Capacity of Wireless Networks with General Fading and Node DistributionOct 08 2010In many wireless systems, interference is the main performance-limiting factor, and is primarily dictated by the locations of concurrent transmitters. In many earlier works, the locations of the transmitters is often modeled as a Poisson point process ... More

Load-Aware Modeling and Analysis of Heterogeneous Cellular NetworksApr 04 2012Mar 21 2013Random spatial models are attractive for modeling heterogeneous cellular networks (HCNs) due to their realism, tractability, and scalability. A major limitation of such models to date in the context of HCNs is the neglect of network traffic and load: ... More

A Primer on Cellular Network Analysis Using Stochastic GeometryApr 12 2016Oct 05 2016This tutorial is intended as an accessible but rigorous first reference for someone interested in learning how to model and analyze cellular network performance using stochastic geometry. In particular, we focus on computing the signal-to-interference-plus-noise ... More

Reinforcement Learning for Self-Organization and Power Control of Two-Tier Heterogeneous NetworksDec 23 2018Self-organizing networks (SONs) can help manage the severe interference in dense heterogeneous networks (HetNets). Given their need to automatically configure power and other settings, machine learning is a promising tool for data-driven decision making ... More

Broadcast Channels with Delayed Finite-Rate Feedback: Predict or Observe?May 18 2011Most multiuser precoding techniques require accurate transmitter channel state information (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in time-varying channels because the CSIT is inherently imperfect ... More

Statistical Modeling and Probabilistic Analysis of Cellular Networks with Determinantal Point ProcessesDec 05 2014Although the Poisson point process (PPP) has been widely used to model base station (BS) locations in cellular networks, it is an idealized model that neglects the spatial correlation among BSs. The present paper proposes the use of determinantal point ... More

Series Expansion for Interference in Wireless NetworksJan 20 2011The spatial correlations in transmitter node locations introduced by common multiple access protocols makes the analysis of interference, outage, and other related metrics in a wireless network extremely difficult. Most works therefore assume that nodes ... More

Offloading in Heterogeneous Networks: Modeling, Analysis, and Design InsightsAug 09 2012Apr 15 2013Pushing data traffic from cellular to WiFi is an example of inter radio access technology (RAT) offloading. While this clearly alleviates congestion on the over-loaded cellular network, the ultimate potential of such offloading and its effect on overall ... More

Analysis of Non-Coherent Joint-Transmission Cooperation in Heterogeneous Cellular NetworksFeb 12 2014Feb 17 2014Base station (BS) cooperation is set to play a key role in managing interference in dense heterogeneous cellular networks (HCNs). Non-coherent joint transmission (JT) is particularly appealing due to its low complexity, smaller overhead, and ability for ... More

Distributed Resource Allocation in Device-to-Device Enhanced Cellular NetworksMay 20 2014Dec 15 2014Cellular network performance can significantly benefit from direct device-to-device (D2D) communication, but interference from cochannel D2D communication limits the performance gain. In hybrid networks consisting of D2D and cellular links, finding the ... More

SINR and Throughput Scaling in Ultradense Urban Cellular NetworksJul 02 2015We consider a dense urban cellular network where the base stations (BSs) are stacked vertically as well as extending infinitely in the horizontal plane, resulting in a greater than two dimensional (2D) deployment. Using a dual-slope path loss model that ... More

Success Probability and Area Spectral Efficiency in Multiuser MIMO HetNetsJun 17 2015Feb 06 2016We derive a general and closed-form result for the success probability in downlink multiple-antenna (MIMO) heterogeneous cellular networks (HetNets), utilizing a novel Toeplitz matrix representation. This main result, which is equivalently the signal-to-interference ... More

Unified Analysis of HetNets using Poisson Cluster Process under Max-Power AssociationDec 05 2018Owing to its flexibility in modeling real-world spatial configurations of users and base stations (BSs), the Poisson cluster process (PCP) has recently emerged as an appealing way to model and analyze heterogeneous cellular networks (HetNets). Despite ... More

Random Access Transport CapacitySep 28 2009We develop a new metric for quantifying end-to-end throughput in multihop wireless networks, which we term random access transport capacity, since the interference model presumes uncoordinated transmissions. The metric quantifies the average maximum rate ... More

Modeling, Analysis and Optimization of Multicast Device-to-Device TransmissionSep 06 2013Multicast device-to-device (D2D) transmission is important for applications like local file transfer in commercial networks and is also a required feature in public safety networks. In this paper we propose a tractable baseline multicast D2D model, and ... More

Fundamentals of Inter-cell Overhead Signaling in Heterogeneous Cellular NetworksJun 29 2011Heterogeneous base stations (e.g. picocells, microcells, femtocells and distributed antennas) will become increasingly essential for cellular network capacity and coverage. Up until now, little basic research has been done on the fundamentals of managing ... More

Guard Region Model for Pilot Reuse Analysis in Uplink Massive MIMO SystemsMay 13 2016Massive multiple-input multiple-output (MIMO) are expected to significantly enhance the spectrum efficiency (SE) and energy efficiency (EE) of future cellular systems. Since the performance gain of massive MIMO is fundamentally limited by pilot contamination, ... More

On the Feasibility of Sharing Spectrum Licenses in mmWave Cellular SystemsDec 04 2015May 01 2016The highly directional and adaptive antennas used in mmWave communication open up the possibility of uncoordinated sharing of spectrum licenses between commercial cellular operators. There are several advantages to sharing including a reduction in license ... More

Fundamental Limits of CooperationMar 30 2012Cooperation is viewed as a key ingredient for interference management in wireless systems. This paper shows that cooperation has fundamental limitations. The main result is that even full cooperation between transmitters cannot in general change an interference-limited ... More

A Tractable Model for Non-Coherent Joint-Transmission Base Station CooperationJul 31 2013Jul 16 2014This paper presents a tractable model for analyzing non-coherent joint transmission base station (BS) cooperation, taking into account the irregular BS deployment typically encountered in practice. Besides cellular-network specific aspects such as BS ... More

Spatial Intercell Interference Cancellation with CSI Training and FeedbackMay 21 2011We investigate intercell interference cancellation (ICIC) with a practical downlink training and uplink channel state information (CSI) feedback model. The average downlink throughput for such a 2-cell network is derived. The user location has a strong ... More

Directional Cell Search Delay Analysis for Cellular Networks with Static UsersSep 04 2017Cell search is the process for a user to detect its neighboring base stations (BSs) and make a cell selection decision. Due to the importance of beamforming gain in millimeter wave (mmWave) and massive MIMO cellular networks, the directional cell search ... More

Reinforcement Learning for Self-Organization and Power Control of Two-Tier Heterogeneous NetworksDec 23 2018Mar 17 2019Self-organizing networks (SONs) can help manage the severe interference in dense heterogeneous networks (HetNets). Given their need to automatically configure power and other settings, machine learning is a promising tool for data-driven decision making ... More

Open, Closed, and Shared Access Femtocells in the DownlinkSep 17 2010A fundamental choice in femtocell deployments is the set of users which are allowed to access each femtocell. Closed access restricts the set to specifically registered users, while open access allows any mobile subscriber to use any femtocell. Which ... More

Inter-Operator Base Station Coordination in Spectrum-Shared Millimeter Wave Cellular NetworksSep 19 2017We characterize the rate coverage distribution for a spectrum-shared millimeter wave downlink cellular network. Each of multiple cellular operators owns separate mmWave bandwidth, but shares the spectrum amongst each other while using dynamic inter-operator ... More

Mode Switching for MIMO Communication Based on Delay and Channel QuantizationJul 22 2008Dec 17 2008This paper has been withdrawn by the author as a major revision is made and a new version is uploaded at arXiv:0812.3120

Tractable Model for Rate in Self-Backhauled Millimeter Wave Cellular NetworksJul 21 2014Mar 19 2015Millimeter wave (mmW) cellular systems will require high gain directional antennas and dense base station (BS) deployments to overcome high near field path loss and poor diffraction. As a desirable side effect, high gain antennas provide interference ... More

Performance of Orthogonal Beamforming for SDMA with Limited FeedbackJun 29 2006May 03 2008On the multi-antenna broadcast channel, the spatial degrees of freedom support simultaneous transmission to multiple users. The optimal multiuser transmission, known as dirty paper coding, is not directly realizable. Moreover, close-to-optimal solutions ... More

On/Off Macrocells and Load Balancing in Heterogeneous Cellular NetworksMay 24 2013The rate distribution in heterogeneous networks (HetNets) greatly benefits from load balancing, by which mobile users are pushed onto lightly-loaded small cells despite the resulting loss in SINR. This offloading can be made more aggressive and robust ... More

A Comparison of MIMO Techniques in Downlink Millimeter Wave Cellular Networks with Hybrid BeamformingOct 09 2015Mar 02 2016Large antenna arrays will be needed in future millimeter wave (mmWave) cellular networks, enabling a large number of different possible antenna architectures and multiple-input multiple-output (MIMO) techniques. It is still unclear which MIMO technique ... More

Downlink Coordinated Multi-Point with Overhead Modeling in Heterogeneous Cellular NetworksOct 19 2012Coordinated multi-point (CoMP) communication is attractive for heterogeneous cellular networks (HCNs) for interference reduction. However, previous approaches to CoMP face two major hurdles in HCNs. First, they usually ignore the inter-cell overhead messaging ... More

A Distributed Auction Policy for User Association in Device-to-Device Caching NetworksOct 13 2017We propose a distributed bidding-aided Matern carrier sense multiple access (CSMA) policy for device-to-device (D2D) content distribution. The network is composed of D2D receivers and potential D2D transmitters, i.e., transmitters are turned on or off ... More

Optimizing The Spatial Content Caching Distribution for Device-to-Device CommunicationsAug 28 2016We study the optimal geographic content placement problem for device-to-device (D2D) networks in which the content popularity follows the Zipf law. We consider a D2D caching model where the locations of the D2D users (caches) are modeled by a Poisson ... More

Optimizing Data Aggregation for Uplink Machine-to-Machine Communication NetworksMay 04 2015Nov 22 2015Machine-to-machine (M2M) communication's severe power limitations challenge the interconnectivity, access management, and reliable communication of data. In densely deployed M2M networks, controlling and aggregating the generated data is critical. We ... More

Macro diversity in Cellular Networks with Random BlockagesJan 09 2017Blocking objects (blockages) between a transmitter and receiver cause wireless communication links to transition from line-of-sight (LOS) to non-line-of-sight (NLOS) propagation, which can greatly reduce the received power, particularly at higher frequencies ... More

The Interplay between Massive MIMO and Underlaid D2D NetworkingSep 09 2014Jan 28 2015In a device-to-device (D2D) underlaid cellular network, the uplink spectrum is reused by the D2D transmissions, causing mutual interference with the ongoing cellular transmissions. Massive MIMO is appealing in such a context as the base station's (BS's) ... More

User Arrival in MIMO Interference Alignment NetworksJun 26 2011In this paper we analyze a constant multiple-input multiple-output interference channel where a set of active users are cooperating through interference alignment while a set of secondary users desire access to the channel. We derive the minimum number ... More

MIMO Interference Alignment Over Correlated Channels with Imperfect CSIOct 13 2010Interference alignment (IA), given uncorrelated channel components and perfect channel state information, obtains the maximum degrees of freedom in an interference channel. Little is known, however, about how the sum rate of IA behaves at finite transmit ... More

Space Division Multiple Access with a Sum Feedback Rate ConstraintSep 07 2006On a multi-antenna broadcast channel, simultaneous transmission to multiple users by joint beamforming and scheduling is capable of achieving high throughput, which grows double logarithmically with the number of users. The sum rate for channel state ... More

Resource Optimization in Device-to-Device Cellular Systems Using Time-Frequency HoppingSep 16 2013May 07 2014We develop a flexible and accurate framework for device-to-device (D2D) communication in the context of a conventional cellular network, which allows for time-frequency resources to be either shared or orthogonally partitioned between the two networks. ... More

Cortical Brain Computer Interface for Closed-Loop Deep Brain StimulationDec 05 2016Essential Tremor is the most common neurological movement disorder. This progressive disease causes uncontrollable rhythmic motions -most often affecting the patient's dominant upper extremity- that occur during volitional movement and make it difficult ... More

Cortical Brain Computer Interface for Closed-Loop Deep Brain StimulationDec 05 2016Jun 01 2017Essential Tremor is the most common neurological movement disorder. This progressive disease causes uncontrollable rhythmic motions -most often affecting the patient's dominant upper extremity- that occur during volitional movement and make it difficult ... More

Should the democrats move to the left on economic policy?Jul 25 2008Dec 09 2013Could John Kerry have gained votes in the 2004 Presidential election by more clearly distinguishing himself from George Bush on economic policy? At first thought, the logic of political preferences would suggest not: the Republicans are to the right of ... More

Cell-Edge-Aware Precoding for Downlink Massive MIMO Cellular NetworksJul 07 2016We propose a cell-edge-aware (CEA) zero forcing (ZF) precoder that exploits the excess spatial degrees of freedom provided by a large number of base station (BS) antennas to suppress inter-cell interference at the most vulnerable user equipments (UEs). ... More

Dual-Branch MRC Receivers under Spatial Interference Correlation and Nakagami FadingDec 20 2013May 08 2014Despite being ubiquitous in practice, the performance of maximal-ratio combining (MRC) in the presence of interference is not well understood. Because the interference received at each antenna originates from the same set of interferers, but partially ... More

Analytical Evaluation of Fractional Frequency Reuse for OFDMA Cellular NetworksJan 26 2011Fractional frequency reuse (FFR) is an interference management technique well-suited to OFDMA-based cellular networks wherein the cells are partitioned into spatial regions with different frequency reuse factors. To date, FFR techniques have been typically ... More

On the Optimal Feedback Rate in Interference-Limited Multi-Antenna Cellular SystemsNov 23 2015May 09 2016We consider a downlink cellular network where multi-antenna base stations (BSs) transmit data to single-antenna users by using one of two linear precoding methods with limited feedback: (i) maximum ratio transmission (MRT) for serving a single user or ... More

Outage of Periodic Downlink Wireless Networks with Hard DeadlinesJun 25 2018We consider a downlink periodic wireless communications system where multiple access points (APs) cooperatively transmit packets to a number of devices, e.g. actuators in an industrial control system. Each period consists of two phases: an uplink training ... More

Modeling and Analyzing the Coexistence of Wi-Fi and LTE in Unlicensed SpectrumOct 05 2015Feb 19 2016We leverage stochastic geometry to characterize key performance metrics for neighboring Wi-Fi and LTE networks in unlicensed spectrum. Our analysis focuses on a single unlicensed frequency band, where the locations for the Wi-Fi access points (APs) and ... More

Power Control in Two-Tier Femtocell NetworksOct 21 2008May 13 2009In a two tier cellular network -- comprised of a central macrocell underlaid with shorter range femtocell hotspots -- cross-tier interference limits overall capacity with universal frequency reuse. To quantify near-far effects with universal frequency ... More

Physical Layer Security in Downlink Multi-Antenna Cellular NetworksJul 27 2013In this paper, we study physical layer security for the downlink of cellular networks, where the confidential messages transmitted to each mobile user can be eavesdropped by both (i) the other users in the same cell and (ii) the users in the other cells. ... More

User Association and Interference Management in Massive MIMO HetNetsSep 25 2015Feb 06 2016Two key traits of 5G cellular networks are much higher base station (BS) densities - especially in the case of low-power BSs - and the use of massive MIMO at these BSs. This paper explores how massive MIMO can be used to jointly maximize the offloading ... More

Design and Analysis of Initial Access in Millimeter Wave Cellular NetworksSep 19 2016Initial access is the process which allows a mobile user to first connect to a cellular network. It consists of two main steps: cell search (CS) on the downlink and random access (RA) on the uplink. Millimeter wave (mmWave) cellular systems typically ... More

Downlink and Uplink Cell Association with Traditional Macrocells and Millimeter Wave Small CellsJan 20 2016Millimeter wave (mmWave) links will offer high capacity but are poor at penetrating into or diffracting around solid objects. Thus, we consider a hybrid cellular network with traditional sub 6 GHz macrocells coexisting with denser mmWave small cells, ... More

Cell-Edge-Aware Precoding for Downlink Massive MIMO Cellular NetworksJul 07 2016Oct 11 2016We propose a cell-edge-aware (CEA) zero forcing (ZF) precoder that exploits the excess spatial degrees of freedom provided by a large number of base station (BS) antennas to suppress inter-cell interference at the most vulnerable user equipments (UEs). ... More

Multi-mode Transmission for the MIMO Broadcast Channel with Imperfect Channel State InformationMar 30 2009Mar 13 2010This paper proposes an adaptive multi-mode transmission strategy to improve the spectral efficiency achieved in the multiple-input multiple-output (MIMO) broadcast channel with delayed and quantized channel state information. The adaptive strategy adjusts ... More

An Overview of Load Balancing in HetNets: Old Myths and Open ProblemsJul 30 2013Matching the demand for resources ("load") with the supply of resources ("capacity") is a basic problem occurring across many fields of engineering, logistics, and economics, and has been considered extensively both in the Internet and in wireless networks. ... More

Spatial search and the Dirac equationMay 20 2004We consider the problem of searching a d-dimensional lattice of N sites for a single marked location. We present a Hamiltonian that solves this problem in time of order sqrt(N) for d>2 and of order sqrt(N) log(N) in the critical dimension d=2. This improves ... More

Are We Approaching the Fundamental Limits of Wireless Network Densification?Dec 01 2015May 28 2016The single most important factor behind the data rate increases experienced by users of wireless networks over the past few decades has been densification, namely adding more base stations and access points and thus getting more spatial reuse of the spectrum. ... More

Fundamentals of Heterogeneous Cellular Networks with Energy HarvestingJul 05 2013We develop a new tractable model for K-tier heterogeneous cellular networks (HetNets), where each base station (BS) is powered solely by a self-contained energy harvesting module. The BSs across tiers differ in terms of the energy harvesting rate, energy ... More

Downlink Multi-Antenna Heterogeneous Cellular Network with Load BalancingOct 25 2013Nov 03 2014We model and analyze heterogeneous cellular networks with multiple antenna BSs (multi-antenna HetNets) with K classes or tiers of base stations (BSs), which may differ in terms of transmit power, deployment density, number of transmit antennas, number ... More