Andrey K. Samuylov

Analysis of human-body blockage in urban millimeter-wave cellular communications

The use of extremely high frequency (EHF) or millimeter-wave (mmWave) band has attracted significant attention for the next generation wireless access networks. As demonstrated by recent measurements, mmWave frequencies render themselves quite sensitive to “blocking” caused by obstacles like foliage, humans, vehicles, etc. However, there is a dearth of analytical models for characterizing such blocking and the consequent effect on the signal reliability. In this paper, we propose a novel, general, and tractable model for characterizing the blocking caused by humans (assuming them to be randomly located in the environment) to mmWave propagation as a function of system parameters like transmitter-receiver locations and dimensions, as well as density and dimensions of humans. Moreover, the proposed model is validated using a ray-launcher tool. Utilizing the proposed model, the blockage probability is shown to increase with human density and separation between the transmitter-receiver pair. Furthermore, the developed analysis is shown to demonstrate the existence of a transmitter antenna height that maximizes the received signal strength, which in turn is a function of the transmitter-receiver distance and their dimensions.

Vehicle-Based Relay Assistance for Opportunistic Crowdsensing over Narrowband IoT (NB-IoT)

The Internet of Things (IoT) undergoes a fundamental transformation by augmenting its conventional sensor network deployments with more advanced and mobile devices, such as connected and self-driving cars. This fusion of embedded and automotive domains promises to deliver unprecedented mutual benefits, where vehicles will receive timely updates from their proximate sensors while assisting them in delivering their sensory data to the remote network infrastructure. In this paper, we put forward the vision of opportunistic crowdsensing applications, in which the ubiquitous deployments of low-cost and battery-constrained IoT sensors take advantage of more capable and energy-abundant vehicle-mounted mobile relays. In particular, we consider the use of the emerging narrowband IoT radio technology recently ratified by 3GPP and offering efficient means for underlying wireless connectivity. Our rigorous mathematical analysis supported with comprehensive system-level evaluations reveals the effects of vehicle-based relays on the important metrics of interest, such as connection reliability, transmission latency, and communication energy efficiency. These systematic findings advocate for an extensive utilization of vehicular relays as part of the next-generation IoT ecosystem.

Direct Connection on the Move: Characterization of User Mobility in Cellular-Assisted D2D Systems

Next-generation device-to-device (D2D) communication technology, in which a cellular network assists proximal users at all stages of their interaction, is rapidly developing. Previous research has thoroughly characterized D2D performance aspects from discovery to connection establishment, security, and service continuity; however, prospective D2Denabled applications and services envision highly opportunistic device contacts as a consequence of unpredictable human user mobility. Therefore, mobilitys impact on D2D communication requires careful investigation to understand the practical operational efficiency of future cellular-assisted D2D systems. This article offers a first-hand tutorial on various implications of D2D mobility across different user movement patterns and mobility-related parameters and proposes an assessment methodology for D2D-enabled systems. The rigorous system-level evaluation conducted for this study delivers important conclusions on the effects of user mobility in emerging D2D-centric systems.

LTE performance analysis using queuing systems with finite resources and random requirements

Heavy traffic load in current LTE networks calls for effective radio resource allocation methods and tools for performance evaluation. In this work, we provide an analytical framework for LTE resource allocation in terms of queuing theory. We consider a multiservice queuing system with a finite amount of resources of several types, and allow the customers occupy a random amount of resources upon their arrival. Random resource requirements lead to more accurate performance evaluation compared to conventional multiservice models. For the considered model, we prove that the stationary probability distribution has a multiplicative form. Our findings are illustrated with a numerical example.

Analytical performance estimation of network-assisted D2D communications in urban scenarios with rectangular cells

The aggressive spatial reuse of radio resources is considered today as one of the most promising avenues to achieve significant cellular capacity improvements in future fifth-generation networks. Accordingly, device-to-device (D2D) communications are an emerging paradigm that promises to offer these much expected gains without the need for additional investments into the network infrastructure. However, before this attractive technology can be deployed ubiquitously, the research community has to fully understand the extent of its potential performance benefits across typical scenarios of interest. In this work, we consider one such use case of rectangular cells (common for offices, shopping malls, dormitories, etc.) and develop the corresponding analytical methodology for D2D performance evaluation. As our target metric, we employ the signal-to-interference (SIR) ratio experienced by a D2D user. To this end, we propose two relatively simple approximations for SIR distribution and hence capture the related parameters, including user throughput. Further, we carefully investigate the most interesting numerical results by making important conclusions on the envisioned operation of our chosen scenario. In particular, we demonstrate that under certain conditions, the SIR behaviour is insensitive to the dimensions of cells, while different propagation exponents ‘scale’ its density function thus allowing to simplify the characterisation of SIR in a wide range of input parameters. Copyright

Characterizing Spatial Correlation of Blockage Statistics in Urban mmWave Systems

Millimeter-wave (mmWave) systems suffer from a significant loss in performance when the line-of- sight (LoS) path between the transmitter and the receiver is obstructed due to blockage caused by humans or other obstacles. However, due to blocker or user motion, the mmWave receiver may transition between the LoS and non-LoS (nLoS) states. Following the recent 3GPP requirements on spatial consistency for channel modeling, this paper aims to analyze the spatial correlation of blockage statistics and characterize their evolution due to user mobility in a static field of blockers in urban mmWave systems. In particular, we derive conditional probabilities of residing in LoS or nLoS state at a given time t1, provided that a user was in LoS/nLoS state at a prior time t0. We demonstrate that for realistic values of user speed, the angle of motion, height of transmitter and receiver, as well as the density of blockers, there always is a significant correlation between user channel states at time t0 and t1, across the time scales relevant for mmWave resource scheduling. Hence, our model can serve as an important tool for optimizing system performance in the presence of blockage.

Discrete Markov chain model for analyzing probability measures of P2P streaming network

In this paper, we present a model of the data exchange process between users in P2P live streaming network with buffering mechanism - buffer occupancy model. The model is developed in terms of discrete Markov chain. We study the probability measures of the model - buffer position occupancy probability and probability of playback continuity. The model is very tractable and compacted formulas were obtained. While considering user churn in the model we examine how user departure affects buffer occupancy and playback continuity. For our numerical experiment we develop a simulation tool for the considered model.

Dynamic Multi-Connectivity Performance in Ultra-Dense Urban mmWave Deployments

Leveraging multiple simultaneous small cell connections is an emerging and promising solution to enhance session continuity in millimeter-wave (mmWave) cellular systems that suffer from frequent link interruptions due to blockage in ultra-dense urban deployments. However, the available performance benefits of feasible multi-connectivity strategies as well as the tentative service quality gains that they promise remain an open research question. Addressing it requires the development of a novel performance evaluation methodology, which should consider: 1) the intricacies of mmWave radio propagation in realistic urban environments; 2) the dynamic mmWave link blockage due to human mobility; and 3) the multi-connectivity network behavior to preserve session continuity. In this paper, we construct this much needed methodology by combining the methods from queuing theory, stochastic geometry, as well as ray-based and system-level simulations. With this integrated framework, both user- and network-centric performance indicators together with their underlying scaling laws can be quantified in representative mmWave scenarios. To ensure modeling accuracy, the components of our methodology are carefully cross verified and calibrated against the current considerations in the standards. Building on this, a thorough comparison of alternative multi-connectivity strategies is conducted, as this paper reveals that even simpler multi-connectivity schemes bring notable improvements to session-level mmWave operation in realistic environments. These findings may become an important reference point for subsequent standardization in this area.

Random Triangle: A Baseline Model for Interference Analysis in Heterogeneous Networks

In emerging heterogeneous networks (HetNets), a wide range of the underlying performance evaluation problems is related to wireless interference characterization and can be reduced to investigating the distribution of a side length in a random triangle. In this paper, we address the task of calculating the side-length distribution in such a triangle determined by the known distributions of its two other sides and the distribution of the angle between them. No restrictions on the distributions of input random variables (RVs) are imposed except for their statistical independence. Our solution delivers a crucial building block for interference analysis in multitier and multiradio HetNets, including mobile device-to-device communication as one of the most extreme interference-limited cases.

Utility function maximization problems for two cross-layer optimization algorithms in OFDM wireless networks

One of the main problems in wireless networks is optimization of radio resources allocation in down-link channel. Different traffic types transmitted over the network suggest a dynamic resource allocation in order to provide a better quality of service (QoS). There are radio resource management modules, called schedulers, which are engaged in resource planning and access priority assignment depending on the types of traffic with the specified requirements for QoS. Schedulers are developed based on algorithms derived from solving various radio resources optimization problems. Cross-layer optimization problems such as the problem of minimizing the transmission power or the problem of maximizing the transmission rate [1], in fact involve the optimization of a utility function, that describe a certain level of user satisfaction for a particular resources allocation scheme under certain restrictions. In this paper we study two cross-layer optimization algorithms that are intended to maximize the utility function under different conditions - dynamic subcarrier assignment (DSA) algorithm and adaptive power allocation (APA) algorithm.