Marc Schinnenburg

Multihop Communication in Relay Enhanced IEEE 802.16 Networks

The introduction of relay stations into metropolitan area networks allows providing ubiquitous broadband access economically to everyone, even to subscribers in remote places. IEEE 802.16, also known as WiMAX, is one of the most promising technologies that currently integrate relays for multihop communication. Such a relay enhanced IEEE 802.16 network can provide ubiquitous radio coverage, achieve high QoS requirements, and it can be economically deployed and operated. This paper presents two concepts to integrate multihop communication into the IEEE 802.16 system. The first concept follows a centralized approach where the base station has full control over the relay-enhanced cell. The second concept follows a semi-distributed approach where a relay station controls the associated subscriber itself. Both concepts are standard-compliant so that legacy subscriber stations can participate without modification

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.

Performance evaluation of soft handover in a realistic UMTS network

With the operation of multiple radio links simultaneously in so-called soft handover situation, the link quality can significantly be improved. On the other hand, additional radio resources are necessary and distributed transmitters cause severe changes in a networks interference situation. This paper focuses on the effects of soft handover applied to a realistically planned UMTS network. As a result, the trade-off between interference mitigation and capacity loss is evaluated by means of dynamic simulation.

System Level Performance of Cellular WiMAX IEEE 802.16 with SDMA-enhanced Medium Access

Recent years have witnessed an ever-increasing interest in smart antenna technologies to boost the capacity of existing and future wireless systems. As one of the first standards the wireless metropolitan area network IEEE 802.16 (WiMAX) provides means to support these techniques. This paper investigates the potential of smart antenna beamforming and space division multiple access (SDMA) in the context of a cellular IEEE 802.16 deployment. It presents the system level performance evaluation of a joint TDMA/SDMA scheduling approach taking into account the influence of intra- and inter-cell interference generated by concurrent SDMA transmissions. The performance of single- and multi-user beamforming is compared with the non-beamforming reference case.

Enhanced measurement procedures for vertical handover in heterogeneous wireless systems

This paper presents an approach to realize integration of heterogeneous systems. Vertical handover thereby is seen as a key feature to allow for interoperability. In order to properly perform handover decisions, interference information with respect to the target system need to be available. For this, dedicated scanning procedures are necessary causing problems if a mobile is using continuous transmission and reception schemes like in UMTS FDD mode. To overcome this problem, different methods are mentioned, whereby a special focus is put on the compressed mode, since alternative means of making measurements are not yet considered within 3GPP. However, it is shown by means of simulations, that applying the compressed mode has a negative impact on the overall system performance. Therefore, another approach is introduced that relies on integrating measurement reports of other systems to support the VHO decision process. The proposal features by continuous operation during information gathering and facilitates reduced power consumption.

Evaluation of Grouping Strategies for an Hierarchical SDMA/TDMA Scheduling Process

Adding SDMA capabilities to modern wireless communication systems like IEEE 802.16 WiMAX promises high system capacity gains but raises the problem of combining orthogonal medium access schemes like TDMA with the non- orthogonal SDMA. In order to reduce the complexity and to improve the flexibility of a joint SDMA/TDMA scheduler, the scheduling process can be subdivided into two parts. First, a spatial grouping algorithm forms groups of users that can be co-scheduled because of their spatial separability. Then, a group scheduling algorithm allocates resources of the time domain to the spatial groups. This paper focuses on the first part of the hierarchical SDMA/TDMA scheduling process, i.e., the spatial grouping. It outlines different grouping strategies and it analyzes their computational complexity. Their respective grouping performance is evaluated according to a metric introduced in the paper. Finally, a tree-based grouping strategy is recommended based on its low complexity and good performance.

Evaluation of IMT-Advanced scenarios using the open Wireless Network Simulator

With the commence of the IMT-Advanced (IMT-A) submission and evaluation process, the vague term 4th generation wireless networks moves towards existing standards, technologies and hardware. A significant part of the evaluation process is based on the system level simulation of reference scenarios. n nIn this paper, we present how the open Wireless Network Simulator (openWNS), developed in the last 5 years at the department of Communication Networks (ComNets) at RWTH Aachen University, can be used to study protocols of wireless networks. Due to the complexity of IMT-A candidate systems, the features of openWNS are described by means of the lightweight WiFiMAC. This module provides the functions of IEEE 802.11, including amendment n. n nOn this basis, the following details of the simulator are explained: (a) the modular simulation framework for protocol stack development, (b) the WiFiMAC module, (c) simulator calibration to ensure the reliability of the results and (d) the simulation of urban-micro scenarios based on the IMT-A evaluation guidelines.

Simulative evaluation of location aided handover in wireless heterogeneous systems

This paper enquires an approach of location aided handover for next generation system integration. For the future only the combination of heterogeneous networks can fulfill the expectations of customers in the sense of ubiquity and bandwidth. Therefore, sophisticated handover and interworking strategies are necessary, in our approach a new entity, called hybrid information system (HIS), gathers status information, like C/I values or free medium capacity, of all associated networks. Thus, a terminal willing to handover has no need to scan the other systems but can simply requests the information from the HIS. To be always connected to the best network regarding the user requirements and to maximize the overall performance it is important to find efficient handover algorithms. We introduce a simulative investigation of the efficiency of a HIS enabled system compared to a legacy solution with direct scanning of potential destination networks.

A flexible protocol stack for multi-mode convergence in a relay-based radio network architecture

Wireless network of next generation will satisfy the user demand for a ubiquitous mobile broadband access. Current research efforts are targeting therefore at the efficient realization of a flexible air-interface and network architecture. The plentitude of envisaged application scenarios and the complexity of communication technology seem to prohibit a universal air-interface. Instead, many different solutions each customized to a specific communication environment are expected. Ideally, these solutions are modes of specific radio access technologies with a common functional as well as architectural basis. This paper presents the realization of relay-based wireless broadband networks benefiting from the convergence of multiple Modes. A flexible air interface considers multi-mode capability in the user and control plane of communication protocols together with the related management. The modes are used in a complementary way, taking maximum benefit of the commonalities between them. The coexistence and cooperation between multiple modes enables the efficient realization of devices supporting multiple modes with the possibility to the available spectrum in a flexible way

Hybrid information system [3G/WLAN intersystem cooperation]

This paper introduces a new concept for intersystem cooperation of heterogeneous networks. The basic idea, referred to as a hybrid information system (HIS), adopts a symbiotic approach in which measurements that are inherently available for each system are made available to heterogeneous systems as well. Thereby, mobiles benefit from other mobiles measurements provided via the HIS on the one hand, e.g. for preparation of handover, and conversely serve as measuring entities for feeding the HIS on the other hand. The presented approach does not only allow for a minimization of self-driven scanning but also allows for further improvement of existing overall network installations or even the feasibility of future location based services.