Maciej Mühleisen

OpenWNS - open Wireless Network Simulator

This paper presents the open Wireless Network Simulator (openWNS). This simulation tool was developed in the last 5 years at the department of Communication Networks (ComNets) at RWTH Aachen University and has been released as open source software recently. openWNS is a dynamic event driven system level simulation platform that allows for investigation of dynamic protocol behaviour in multi-cellular scenarios with detailed interference modeling. The simulation platform follows a modular design down to protocol building blocks, which makes it possible to rapidly modify the implemented protocol stacks. openWNS currently includes models from physical to application layer. The protocol modules for IEEE 802.16m and IEEE 802.11n-draft are probably the most interesting for the wireless research community.

Analytical evaluation of LTE uplink performance in the IMT-Advanced Indoor Hotspot scenario

LTE-Advanced (LTE-A) proposed by the 3rd Generation Partnership Project (3GPP) has been accepted by the International Telecommunication Union (ITU) in 2010 as an IMT-Advanced (IMT-A) compliant 4G mobile radio system. As part of this application 3GPP has provided LTE-A system level simulation results for cell spectral efficiency and cell edge user spectral efficiency. In this work we analytically derive the uplink spectral efficiency, throughput distribution, and cell edge user spectral efficiency for LTE-A in an IMT-A scenario and validate it by comparison to system level simulation results gained from the openWNS simulator. We use the model to evaluate the impact of power control on uplink system performance.

Uplink VoIP capacity of 3GPP LTE under power control and semi-persistent scheduling

LTE-Advanced (LTE-A) standardized as Release 10 by the 3rd Generation Partnership Project (3GPP) is a packet-based 4G mobile radio system. Of specific interest is its capability to support a large number of voice calls through Voice over IP (VoIP) calls. Radio resource management for VoIP calls is challenging. Control channel limitations prevent the dynamic scheduling of every VoIP packet in each 1 ms subframe. Semi-persistent VoIP scheduling enables channel quality aware scheduling reducing load to control channels, substantially. We describe and evaluate by system level simulation a semipersistent VoIP schedulers for LTE. In addition, contributions to VoIP system capacity of power control, as applied in Soft Frequency Reuse (SFR), are evaluated. It turns out that system capacity is reduced if SFR is applied in the uplink. This unexpected result is found to be caused by performance degradation of the weakest users under SFR, limiting overall system capacity.

Uplink capacity analysis of OFDMA based cellular networks with reuse-1

OFDMA based cellular radio networks aim to operate as close as possible to frequency reuse distance of one, where the whole spectrum would be available in every cell. Modern systems are able to adjust parameters such as transmission power, modulation, and coding separately for each frequency sub-channel on a very short time scale. This way Fractional Frequency Reuse (FFR) can be applied, allowing to operate reuse-1 in the center of cells and reuse greater one at cell edges. This paper presents a novel method to analyze the Carrier to Interference Ratio (CIR) distribution and uplink capacity of a cell, from which spectral efficiency of a cellular radio network using FFR is derived. The results presented apply for OFDMA cellular networks operated in IMT-Advanced evaluation scenarios.

IEEE 802.16 coexistence through regular channel occupation

Todays radio frequency regulation is undergoing fundamental changes. There is a high demand for radio frequency spectrum for data communication but no blank spots in the frequency assignments plan. Under the approach of coexistence and cognitive radio, spectrum is made available to systems if a license holder is not using it at a given geographic location or time. In this case multiple systems can compete for spectrum access. In this paper we present an approach how multiple IEEE 802.16 systems can coexist in the same frequency band. The key idea is to define rules how the systems can schedule their transmissions to achieve more regular and therefore more predictable channel occupation. The approach does not require carrier sensing before normal data transmission. Analytic and simulation results are presented showing how systems can estimate available capacity and the impact of their behaviour to own and overall performance. Therefore results for the collision probability are derived.

Evaluation of the Aircraft Distribution in Satellite Spotbeams

Upcoming inflight entertainment and other onboard data services request broadband data connections during long- and short-haul flights all over the world. To cope with this amount of traffic, especially over oceanic areas where no ground infrastructure is available, satellite systems offer broadband satellite links for avionic purpose.

Minimising the Entry Effort in Experimenting with WSN Testbeds to Perform Heterogeneous Research

Testbeds play a crucial role in evaluating novel protocols, algorithms, and applications in controlled, but realistic environments. These testbeds are mainly used by researchers to realize diverse application environments, which are not realistic to be achieved in simulated environments (e.g., lossy channels in Wireless Sensor Networks (WSN)). Most researchers, especially bachelor or master students spend a large portion of their time familiarizing themselves and setting up test beds before performing the actual research work. This portion of time, when considering the overall time for such work (e.g., 6 months for a masters thesis), forms a major part compared to the time spent on designing and developing protocols and algorithms (i.e., the focus of research). Therefore, to minimize the aforementioned entry effort in using testbeds for experiments, we have setup a testbed called the Versatile Experiment Platform for Sensor Networks (VEPSNet), which has a common Linux based environment with a homogeneous backend to collect data and process results allowing researchers to spend their quality time in the actual research work. In this paper, we provide details of the VEPSNet highlighting how this testbed is used to perform research in the area of WSN.

openWNS—a simulation platform for IMT-advanced systems†

The open source wireless network simulator (openWNS) is presented. It has been released in January 2009 as open source software. openWNS is a dynamic event driven system level simulation platform useful for investigation of dynamic protocol behaviour in multi-cellular mobile radio network scenarios with detailed signal interference modelling. The platform follows a modular design down to atomic protocol building blocks, making possible to rapidly modify and extend a protocol stack implemented. openWNS includes models from physical to application layer and is supported by a large number of Unit Tests. The tool has been used for IMT-Advanced evaluation within the European WINNER+ evaluation group. Copyright

Capacity analysis and improvement for coexisting IEEE 802.16 systems in unlicensed spectrum

Today spectrum demand for wireless communication is tremendous and even keeps growing. In contrast, there are no blank spots in the spectrum map. Additional spectrum opportunities are available in unlicensed bands and so-called non-exclusively licensed bands which are currently made available. This non-exclusive spectrum can be exploited whenever a license holder is not active. These spectrum opportunities cannot be exclusively accessed so that multiple systems need to coexist. Existing MAC protocols need to be enhanced to allow a system to meet own Quality of Service (QoS) demands while allowing other coexisting systems to meet their QoS requirements. In this work, methods for capacity calculation known from cellular networks are extended and applied to a scenario of coexisting IEEE 802.16 (WiMAX) systems. Developed methods are used to evaluate enhancements for interference mitigation which lead to increased capacity.

Coordination across base stations for effective control of space division multiple access enhanced IEEE 802.16m systems

In recent years, smart antenna technologies are of ever-increasing interest to boost the capacity of existing and future wireless systems. Several standards support these techniques such as the wireless metropolitan area network IEEE 802.16 (WiMAX) and IMT-Advanced candidates. In applying smart antenna beamforming and Space Division Multiple Access (SDMA) techniques, adaptive antennas are able to increase cell capacity by reducing inter-cell interference and by allowing concurrent transmissions. As a downside, an SDMA enabled cell generates less predictable interference than a conventional cell, because a changing number of mobile stations (MS) are sending uplink data in parallel and downlink streams with changing direction are transmitted by the base station (BS). Thereby the SINR estimation becomes less precise and the link adaptation sub optimal. This work investigates the potential of coordination across BSs on MAC layer for further mitigation of inter-cell interference and increasing precision of SINR estimations in an SDMA enhanced system. The developed concepts are evaluated in a cellular deployment by means of system-level simulations for up-and downlink. The performance of a coordinated system is compared with a non-coordinated reference case.