Daniel Bültmann

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.

Analysis of 3GPP LTE-Advanced cell spectral efficiency

Multihop and multipoint transmissions are two of the main features towards an increased spectral efficiency for the LTE-Advanced mobile radio system. Fixed wireless relays with in-band backhauling are considered as a multihop technique in LTE-Advanced. Relays improve cell capacity and cell edge user performance depending on the deployment. In this paper, at first, results for the peak spectral efficiency of LTE-Advanced are presented and secondly, an analytical model to calculate the cell spectral efficiency of relay enhanced cell deployments in the context of the IMT-Advanced evaluation is presented. The developed model is applied to the LTE-Advanced system comparing different relay deployments with different frequency reuse schemes.

Assessing 3GPP LTE-advanced as IMT-advanced technology: the WINNER+ evaluation group approach

This article describes the WINNER+ approach to performance evaluation of the 3GPP LTE-Advanced proposal as an IMT-Advanced technology candidate. The official registered WINNER+ Independent Evaluation Group evaluated this proposal against ITU-R requirements. The first part of the article gives an overview of the ITU-R evaluation process, criteria, and scenarios. The second part is focused on the working method of the evaluation group, emphasizing the simulator calibration approach. Finally, the article contains exemplary evaluation results based on analytical and simulation approaches. The obtained results allow WINNER+ to confirm that the 3GPP LTE Release 10 & Beyond (LTE-Advanced) proposal satisfies all the IMTAdvanced requirements, and thus qualifies as an IMT-advanced system.

Channel quality indication for adaptive resource scheduling in Multihop OFDMA systems

IMT-advanced systems of the future will be based on OFDMA and frequency divicion duplex will be widely used. Multihop techniques, e.g. the use of fixed relays, are also considered a key technology. The OFDMA resources have the dimensions time, frequency and space. In all these dimensions a radio channel is variable due to fading. On the other hand a complete utilization of the channel capacity close to the Shannon bound is required. Therefore all channel adaptive modulation and coding schemes require good channel state information. For FDD this needs to be signalled back from user terminals to base stations or relays, so that the adaptive scheduling algorithms there can decide optimally. This is performed by channel quality indication. This paper discusses a multimode-capable multistage CQI concept for IMT-advanced systems, shows measurements from simulation and provides the system view including CQI.

System Level Performance Evaluation of LTE with MIMO and Relays in Reuse-1 IMT-Advanced Scenarios

Cellular radio systems of the next generation will have to comply with the IMT-Advanced guidelines. Advanced radio techniques must be integrated into wireless systems to achieve the high spectral efficiency numbers required. Multiple antenna techniques such as MIMO are beneficial in regions of high SINR and low spatial stream correlation. Multihop techniques with fixed relays increase the throughput in regions close to the cell edge where SINR is typically low. Another challenge is the reuse-1 paradigm which worsens the interference situation. In this paper a mathematical model on system level is proposed and applied which allows to calculate system performance measures such as spectral efficiency. The MIMO model allows fast system evaluation without a lot of parameters and is therefore suitable for MAC layer simulative evaluation. The paper compares performance results for these techniques.

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.

Media independent handover enabled advanced mobility management and its functional mapping

In this paper, we propose a suitable set of protocols schematically combining both radio handover and IP handover for heterogeneous network with the enhancement of relay nodes, that is considered as an important feature of the future radio network. Based on that, we develop the functional allocation of media independent handover entities for a 4G communication system developed by the European WINNER project. The allocation is suitable for decentralized radio resource and mobility management as proposed by the system architecture evolution. Performance evaluation of the handover signaling delay for media independent handover enabled relay enhanced cells is presented. Conclusions derived from this work serve as a reference for the design of future radio network and the associated protocols.

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

Performance evaluation of joint downlink scheduling in multi-cellular OFDMA systems based on IEEE 802.16a

The employment of the OFDMA transmission technique in broadband radio systems shows several benefits. Especially the exploitation of multi-user diversity with the help of sophisticated scheduling algorithms can significantly increase the system capacity. In this paper, the performance of joint scheduling of downlink data transmissions for access point sets is evaluated in a multi-cellular system. The latter is compared with an independent scheduling on orthogonal subchannel sets in the access points. The general MAC structure of the investigated system is thereby based on IEEE 802.16a. However, concerning the Physical Layer there is an important difference. In IEEE 802.16a, the exploitation of multi-user diversity is not possible since the OFDMA subchannel scheme is based on an interference and fading averaging approach. The technique examined in this paper in contrast can be regarded as an avoidance approach which is subject to diversity in the subchannel quality. A basic OFDMA scheduling algorithm, which is able to exploit multi-user diversity and provide fairness, is used both for the joint and for the independent scheme.

Link Layer Modeling

The Data Link Layer (DLL) is located above the PHY layer described in the previous chapter and below the network layer described in Chapter 16. All data received from these layers is digital. Today most parts of the DLL are implemented in software, either as device drivers running on general purpose Central Processing Units (CPUs) or as firmware running on dedicated network interface hardware.