Konstantinos Kontodimas

A simulation framework for LTE-A systems with femtocell overlays

The use of femtocells is an efficient way to improve coverage and quality of service while on the other side the deployment cost for the service provider is kept in extremely low level. Long Term Evolution Advanced (LTE-A) systems with femtocell overlays aim to provide better indoor voice and data coverage and to increase network capacity. One of the major technical challenges that femtocell networks are facing nowadays, is the cross-tier interference, i.e., the interference between the femto base stations and the macrocell infrastructure. To this direction, we have designed and implemented a framework that simulates femtocell overlays integrated over LTE-A macrocellular systems. This framework focuses on the impact of cross-tier interference and furthermore is able to estimate the throughput at every point of integrated femtocell/macrocell LTE-A networks. In this paper, we present the design and implementation of this simulation framework and we provide significant experimental results obtained with the aid of this system.

A Simulation Framework for Evaluating Interference Mitigation Techniques in Heterogeneous Cellular Environments

Femtocells present an attractive solution for the improvement of a mobile network’s services providing better data rates and coverage. Since their deployment results to a heterogeneous network where two layers must utilize the available spectrum, issues of interference arise. A method to address this challenge, is investigating the locations of the newly installed FBS, and enforcing a power controlled transmission of all FBSs that achieves optimal and fair overall performance. Another option that becomes available in inter-cell interference cancellation (ICIC) macrocell environments, is utilizing the available spectrum to complete or partly avoid co-channel operation. In this work, we provide a simulation framework that allows the creation of custom, high configurable, user defined topologies of femtocells with power control and frequency allocation capabilities. It allows the investigation of the margin of improvement in interference when these methods are applied and may work as a decision tool for planning and evaluating heterogeneous networks. To showcase the framework’s capabilities, we evaluate and study the behaviour of custom deployed femtocells/macrocells networks and examine the cross-tier interference issues. Facilitated by the framework, we enforce and evaluate each interference mitigation technique for different femtocells’ deployment densities. Finally, we compare the results of each method in terms of total throughput, spectral efficiency and cell-edge users’ performance.

Interference behavior of integrated femto and macrocell environments

Femtocells are data access points installed by the subscribers to provide better indoor voice and data coverage and to increase system capacity. The integrated femtocell/macrocell networks offer an efficient way to increase access capacity by improving coverage and quality of service while on the other side the deployment cost for the service provider is kept in extremely low levels. One of the major technical challenges that femtocell networks are facing is their interference behavior when they are placed within macrocells. The study presented in this paper focuses on the impact of integrating femtocells in macrocell networks in terms of adjacent cell interference that the macrocell environment adds to users served by a femto base station and vice versa. To this direction, we have designed and implemented a simulation testbed that estimates the cross-tier interference and the throughput in every point of an integrated femtocell/macrocell Long Term Evolution-Advanced (LTE-A) network.

Bandwidth allocation in the NEPHELE hybrid optical interconnect

The NEPHELE network is divided into pods of racks and relies on hybrid electro-optical top-of rack switches that access an all-optical network. To enable dynamic and efficient sharing of the optical resources and a collision-free network operation, the NEPHELE network is envisioned to be operated in a slotted TDMA manner with a software-defined-network (SDN) based control plane. We describe the NEPHELE resource allocation problem and present a number of algorithmic solutions suitable to tackle different traffic scenarios.

Efficient bandwidth allocation in the NEPHELE optical/electrical datacenter interconnect

The NEPHELE data center interconnection network relies on hybrid electro-optical top-of-rack switches to interconnect servers over multi-wavelength optical rings. The bandwidth of the rings is shared, and an efficient utilization of the infrastructure calls for coordination in the time, space, and wavelength domains. To this end, we present offline and incremental dynamic resource assignment algorithms. The algorithms are suitable for implementation in a software defined network control plane, achieving efficient, collision-free, and on demand capacity use. Our simulation results indicate that the proposed algorithms can achieve high utilization and low latency in a variety of traffic scenarios that include hot spots and/or rapidly changing traffic.

Making P-Space Smart: Integrating IoT Technologies in a Multi-office Environment

Internet of Things technologies are considered the next big step in Smart Building installations. Although such technologies have been widely studied in simulation and experimental scenarios it is not so obvious how problems of real world installations should be dealt with. In this work we deploy IoT devices for sensing and control in a multi-office space and employ technologies such as CoAP, RESTful interfaces and Semantic Descriptions to integrate them with the Web. We report our research goals, the challenges we faced, the decisions we made and the experience gained from the design, deployment and operation of all the hardware and software components that compose our system.

Analysis and Evaluation of Scheduling Policies for Consolidated I/O Operations

Hypervisors’ smooth operation and efficient performance has an immediate effect in the supported Cloud services. We investigate scheduling algorithms that match I/O requests originated from virtual resources, to the physical CPUs that do the actual processing. We envisage a new paradigm of virtualized resource consolidation, where I/O resources required by several Virtual Machines (VMs) in different physical hosts, are provided by one (or more) external powerful dedicated appliance(s), namely the I/O Hypervisor (IOH). For this reason I/O operations are transferred from the VMs to the IOH, where they are executed. We propose and evaluate a number of scheduling algorithms for this hypervisor model, concentrating on providing guaranteed fairness among the virtual resources. A simulator has been built that describes this model and is used for the implementation and the evaluation of the algorithms. We also analyze the performance of the different hypervisor models and highlight the importance of fair scheduling.

Collisions free scheduling in the NEPHELE hybrid electrical/optical datacenter interconnect

The NEPHELE datacenter network is divided into pods/clusters of racks and relies on hybrid electro-optical top-of rack switches that access an all-optical network consisting of WDM rings. To enable dynamic and efficient sharing of the optical resources and a collision-free network operation, the NEPHELE network is designed to operate in a slotted manner with a software-defined-network (SDN) based control plane. We describe the NEPHELE resource allocation problem, consider the wavelength conflicts on the shared WDM rings, translate them into resource allocation constraints and investigate the effect of these constraints on network performance. To do so, we define the worst-case traffic pattern and perform simulations to evaluate performance for the average traffic. Finally, we propose a variation to the NEPHELE architecture that reduces the effects of these wavelength conflict constraints on performance.