90 research outputs found
Average Rate of Downlink Heterogeneous Cellular Networks over Generalized Fading Channels - A Stochastic Geometry Approach
In this paper, we introduce an analytical framework to compute the average
rate of downlink heterogeneous cellular networks. The framework leverages
recent application of stochastic geometry to other-cell interference modeling
and analysis. The heterogeneous cellular network is modeled as the
superposition of many tiers of Base Stations (BSs) having different transmit
power, density, path-loss exponent, fading parameters and distribution, and
unequal biasing for flexible tier association. A long-term averaged maximum
biased-received-power tier association is considered. The positions of the BSs
in each tier are modeled as points of an independent Poisson Point Process
(PPP). Under these assumptions, we introduce a new analytical methodology to
evaluate the average rate, which avoids the computation of the Coverage
Probability (Pcov) and needs only the Moment Generating Function (MGF) of the
aggregate interference at the probe mobile terminal. The distinguishable
characteristic of our analytical methodology consists in providing a tractable
and numerically efficient framework that is applicable to general fading
distributions, including composite fading channels with small- and mid-scale
fluctuations. In addition, our method can efficiently handle correlated
Log-Normal shadowing with little increase of the computational complexity. The
proposed MGF-based approach needs the computation of either a single or a
two-fold numerical integral, thus reducing the complexity of Pcov-based
frameworks, which require, for general fading distributions, the computation of
a four-fold integral.Comment: Accepted for publication in IEEE Transactions on Communications, to
appea
Modeling Heterogeneous Network Interference Using Poisson Point Processes
Cellular systems are becoming more heterogeneous with the introduction of low
power nodes including femtocells, relays, and distributed antennas.
Unfortunately, the resulting interference environment is also becoming more
complicated, making evaluation of different communication strategies
challenging in both analysis and simulation. Leveraging recent applications of
stochastic geometry to analyze cellular systems, this paper proposes to analyze
downlink performance in a fixed-size cell, which is inscribed within a weighted
Voronoi cell in a Poisson field of interferers. A nearest out-of-cell
interferer, out-of-cell interferers outside a guard region, and cross-tier
interference are included in the interference calculations. Bounding the
interference power as a function of distance from the cell center, the total
interference is characterized through its Laplace transform. An equivalent
marked process is proposed for the out-of-cell interference under additional
assumptions. To facilitate simplified calculations, the interference
distribution is approximated using the Gamma distribution with second order
moment matching. The Gamma approximation simplifies calculation of the success
probability and average rate, incorporates small-scale and large-scale fading,
and works with co-tier and cross-tier interference. Simulations show that the
proposed model provides a flexible way to characterize outage probability and
rate as a function of the distance to the cell edge.Comment: Submitted to the IEEE Transactions on Signal Processing, July 2012,
Revised December 201
Outage Analysis of Uplink Two-tier Networks
Employing multi-tier networks is among the most promising approaches to
address the rapid growth of the data demand in cellular networks. In this
paper, we study a two-tier uplink cellular network consisting of femtocells and
a macrocell. Femto base stations, and femto and macro users are assumed to be
spatially deployed based on independent Poisson point processes. We consider an
open access assignment policy, where each macro user based on the ratio between
its distances from its nearest femto access point (FAP) and from the macro base
station (MBS) is assigned to either of them. By tuning the threshold, this
policy allows controlling the coverage areas of FAPs. For a fixed threshold,
femtocells coverage areas depend on their distances from the MBS; Those closest
to the fringes will have the largest coverage areas. Under this open-access
policy, ignoring the additive noise, we derive analytical upper and lower
bounds on the outage probabilities of femto users and macro users that are
subject to fading and path loss. We also study the effect of the distance from
the MBS on the outage probability experienced by the users of a femtocell. In
all cases, our simulation results comply with our analytical bounds
Modeling and Analysis of Cellular Networks Using Stochastic Geometry: A Tutorial
This paper presents a tutorial on stochastic geometry (SG)-based analysis for cellular networks. This tutorial is distinguished by its depth with respect to wireless communication details and its focus on cellular networks. This paper starts by modeling and analyzing the baseband interference in a baseline single-tier downlink cellular network with single antenna base stations and universal frequency reuse. Then, it characterizes signal-to-interference-plus-noise-ratio and its related performance metrics. In particular, a unified approach to conduct error probability, outage probability, and transmission rate analysis is presented. Although the main focus of this paper is on cellular networks, the presented unified approach applies for other types of wireless networks that impose interference protection around receivers. This paper then extends the unified approach to capture cellular network characteristics (e.g., frequency reuse, multiple antenna, power control, etc.). It also presents numerical examples associated with demonstrations and discussions. To this end, this paper highlights the state-of-the-art research and points out future research directions
Performance analysis of reconfigurable intelligent surface assisted wireless communications
The advent of the smart radio environment has challenged traditional wireless communication systems, and reconfigurable intelligent surfaces (RIS) have emerged as a promising solution to enhance the performance limits of wireless communications. This thesis aims to study RIS technology in future networks by examining the performance of four typical RIS-assisted communication systems, each featuring unique models and practical RIS characteristics. The research begins with the performance analysis of RIS-assisted wireless communication systems with phase errors in both line-of-sight (LoS) and Rayleigh fading scenarios. It investigates the impact of different types of phase errors and other system parameters on system performance. Next, the impact of channel correlations on RIS-assisted communication systems is examined by deriving closed-form expressions of outage probability and average achievable rates for both correlated Rayleigh fading and correlated Nakagami-m fading models. The relationship between RIS size and performance degradation caused by channel correlations is explored. The study further investigates the application of RIS technology in more intricate wireless communication systems, specifically focusing on two spectrum efficiency techniques: non-orthogonal multiple access (NOMA) and full-duplex (FD) communications. For RIS-assisted NOMA, the research derives closed-form expressions for the outage probability of users with strong and weak channel conditions, while for RIS-assisted FD systems, the research proposes a setup where an FD transceiver serves uplink and downlink users simultaneously with two dedicated RISs and examines the impact of residual self-interference (SI). Finally, the performance of a RIS-assisted largescale network is examined through stochastic geometry, assessing coverage probability and average achievable rate. The research discusses two association strategies: nearest and fixed association, and investigates the effects of increasing transmitter (TX) density and RIS association probability on system performance. This thesis provides valuable analytical resources on RIS-assisted wireless communications performance, laying a foundation for future research and application of RIS technology
Performance Analysis of Indoor Wireless Communications in Dense Cellular Networks
The current decades have witnessed the explosive increase of traffic-data demand. It is predicted that indoor wireless communications will be one of the fastest growing markets, since the vast majority (over 80%) of data demand occurs in indoors. Facing such a huge data demand, the dense deployment of small cells (SCs) in indoor environments is boosted, which brings breakthroughs of throughput for in-building communications. However, the densification of indoor small-cell (SC) networks also poses new challenges, such as complex propagating environments, severe blockage effects and short link distances, which significantly influence the evaluation of network performance. This thesis mainly investigates the performance analysis of indoor dense SC networks.
Firstly, the probability of Line-of-Sight (LOS) propagation is crucial to model the real signal propagation channels and to evaluate the performance of cellular networks. However, existing LOS probability models are oversimplified to provide the exact LOS probability in indoor scenarios. By considering the realistic layout of building structures, this thesis proposes a novel and analytical LOS probability model for downlink radio propagations in typical indoor scenarios, which have rectangular rooms and corridors. Through the proposed model, the LOS probability can be calculated directly without the measurement and simulation.
Next, in terms of the impact of LOS and Non-Line-of-Sight (NLOS) transmissions, the traditional works do not distinguish them, which is not practical for dense cellular networks. Thus, a tractable path loss model considering both LOS and NLOS propagations is proposed for the performance analysis of indoor dense SC networks. Based on the theory of stochastic geometry, the performance metrics, such as coverage probability, spectral
efficiency (SE) and area spectral efficiency (ASE), are analytically derived. The analytical results provide insights into the design of indoor dense SC networks in the future.
Thirdly, regarding the severe effects of blockages in indoor environments, the traditional approach that simply considers it as a log-normal shadowing is too simple. Therefore, a wall blockage model is developed to characterize the impact of blockages based on the stochastic geometry. Furthermore, the mathematical expression of coverage probability for the case of impenetrable blockages is derived, which employs a path loss model incorporating both the blockage-based and distance-based path loss
Ultra Reliable Communication in 5G Networks: A Dependability-based Availability Analysis in the Space Domain
Master's thesis Information- and communication technology IKT591 - University of Agder 2017As our daily life is becoming more dependent on wireless and mobile services, seamless
network connectivity is of utmost importance. Wireless networks are expected to handle the
growing demand for applications which require higher capacity, without failure. Therein,
wireless connectivity is regarded as an essential requirement for a wide range of applications
in order to support
exible and cost-e ective services. As part of the fth generation (5G)
communication paradigm, ultra reliable communication (URC) is envisaged as an important
technology pillar for providing anywhere and anytime services to end users. While most existing
studies on reliable communication are not pursued from a dependability perspective,
those dependability based studies tend to de ne reliability merely in the time domain.
The main objective of this thesis work is to advocate the concept of URC from a dependability
perspective in the space domain. Accordingly, we de ne cell availability, system
availability, and guaranteed availability for cellular networks. Poisson point process (PPP)
and Voronoi tessellation are adopted to model the spatial characteristics of cell deployment
in cellular networks. The spatially modeled cellular networks are used to analyze availability
and initiate de nitions on cell availability and system availability. Correspondingly, the availability
as well as the probability of providing a guaranteed level of availability in a network
are analyzed both/either cell-wise and/or system-wise. From this perspective, we investigate
in depth the relationship between the signal to interference noise ratio (SINR), capacity or
user requirement and achievable availability levels.
Extensive simulations are performed for various network scenarios and cell deployments
to obtain numerical results based on the cell and system availability de nitions. For SINRbased
and capacity-based studies, threshold contours are identi ed in each case in order to
further study cell availability under di erent conditions. The importance of deploying di erent
types of cells for a cellular network is also highlighted by studying the tradeo between
the required transmission power and the obtained system availability. Moreover, de nitions
are developed for availability from users' perspective concerning PPP distributed users as well.
In a nutshell, this thesis proposes a novel concept referred to as space domain availability
as a contribution to the ongoing research activities on URC for future 5G networks.
Key words: 5G and URC, dependability and availability, space domain analysis, PPP and
Voronoi tessellation, simulations
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