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Tampere, Finland

Chang Z.,University of Jyvaskyla | Chang Z.,Magister Solutions Ltd | Ristaniemi T.,University of Jyvaskyla
Wireless Networks | Year: 2013

This work addresses the radio resource allocation problem for cooperative relay assisted OFDMA wireless network. The relays adopt the decode-and-forward protocol and can cooperatively assist the transmission from source to destination. Recent works on the subject have mainly considered symmetric source-to-relay and relay-to-destination resource allocations, which limits the achievable gains through relaying. In this paper we consider the problem of asymmetric radio resource allocation, where the objective is to maximize the system throughput of the source-to-destination link under various constraints. In particular, we consider optimization of the set of cooperative relays and link asymmetries together with subcarrier and power allocation. We derive theoretical expressions for the solutions and illustrate them through simulations. The results show clear additional performance gains through asymmetric cooperative scheme compared to the other recently proposed resource allocation schemes. © 2012 Springer Science+Business Media, LLC. Source


Asghar M.Z.,Magister Solutions Ltd | Hamalainen S.,Nokia Inc. | Ristaniemi T.,University of Jyvaskyla
2012 IEEE 17th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks, CAMAD 2012 | Year: 2012

Fault management is an important part of the operations and maintenance subsystem (OSS) of cellular mobile networks. Perhaps the most important reason is to reduce the number of outages and duration of outages in the network in order to meet the operator's requirements such as network availability, robustness, coverage and capacity etc. Increasing complexity of the cellular networks has significant impact on the operations and maintenance of the network. Automation is necessary to protect the operational as well as capital expenses of the cellular network. The aim of this paper is to present a self-healing framework developed for 3GPP Long Term Evolution (LTE) networks and to provide a platform where the detection and compensation of cell outages are evaluated in realistic environment. The impact of early fault detection and timely execution of compensation tasks are shown in terms of radio link failures and number of connected users. © 2012 IEEE. Source


Turkka J.,Tampere University of Technology | Nihtila T.,Magister Solutions Ltd | Viering I.,Nomor Research GmbH
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC | Year: 2011

This paper presents a performance evaluation of an uplink load balancing algorithm for Long-Term Evolution (LTE) Self-Organizing Networks (SON) in a non-regular network layout and shows how cell sizes affect the performance of the algorithm. The proposed algorithm solves local overload situations by handing over users to neighboring cells and adjusting power control settings. However, the non-regular network layout and the varying cell size can limit the expected gains of the algorithm in some situations due to the chosen uplink load balancing strategies and the limitations of the LTE uplink radio access technique. The performance evaluation is done by using a fully dynamic LTE system simulator which is capable to model user and network characteristics, mobility and radio resource management (RRM) algorithms accurately. © 2011 IEEE. Source


Chang Z.,University of Jyvakyla | Chang Z.,Magister Solutions Ltd | Ristaniemi T.,University of Jyvakyla | Niu Z.,Tsinghua National Laboratory for Information Sciences and Technology
IEEE Transactions on Wireless Communications | Year: 2014

This paper addresses the resource allocation problem in collaborative relay-assisted OFDMA networks. Recent works on the subject usually ignored either the selection of relays, asymmetry of the source-to-relay and relay-to-destination links or the imperfections of channel state information. In this article we take into account all these together and our focus is two-fold. Firstly, we consider the problem of asymmetric radio resource allocation, where the objective is to maximize the system throughput of the source-to-destination link under various constraints. In particular, we consider optimization of the set of collaborative relays and link asymmetries together with subcarrier and power allocation. Using a dual approach, we solve each sub-problem in an asymptotically optimal and alternating manner. Secondly, we pay attention to the effects of imperfections in the channel-state information needed in resource allocation decisions. We derive theoretical expressions for the solutions and illustrate them through simulations. The results validate clearly the additional performance gains through an asymmetric cooperative scheme compared to the other recently proposed resource allocation schemes. © 2014 IEEE. Source


Puttonen J.,Magister Solutions Ltd | Virtej E.,Nokia Inc. | Keskitalo I.,Nokia Inc. | Malkamaki E.,Nokia Inc.
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC | Year: 2012

In cellular networks it is envisioned an explosion of diverse data applications running in smart phones, which could increase significantly not only user plane but also control plane load in the network. Smart phones and their always-on applications introduce several challenges: From the network perspective, an increased amount of UEs/applications can increase the signaling load due to frequent state transitions and handover signaling. From the UE perspective, challenges of power consumption are evident, since UE would increasingly be in connected state. In this article we study the trade-off between releasing the UE into idle state vs. keeping the UE in connected state, in a LTE system. The results indicate that optimum performance can be achieved using UE specific RRC release timer and DRX configurations by taking advantage of traffic characteristics and UE mobility. © 2012 IEEE. Source

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