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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.

Chang Z.,University of Jyvakyla | Ristaniemi T.,University of Jyvakyla | Han Z.,University of Houston
IEEE Communications Letters | Year: 2015

In this letter, we investigate the problem of spectrum access decision-making for the secondary users (SUs) in the cognitive radio networks. When the primary users (PUs) are absent on certain frequency bandwidth, SUs can formulate a queue and wait for the base station (BS) to serve. The queue of the SUs will be dismissed if the PU is emerging in the system. Leveraging the queueing game approaches, the decision-making process of the SUs that whether to queue or not is studied. Both individual equilibrium and social optimization strategies are derived analytically. Moreover, the optimal pricing strategy of the service provider is investigated as well. Our proposed algorithms and corresponding analysis are validated through simulation studies. © 1997-2012 IEEE.

Chang Z.,University of Jyvakyla | Zhang Q.,Yanshan University | Guo X.,Yanshan University | Ristaniemi T.,University of Jyvakyla
Eurasip Journal on Wireless Communications and Networking | Year: 2015

Most of the existed works on the radio resource allocation (RRA) problem commonly assume the channel-state information (CSI) can be perfectly obtained by the transmission source. However, such assumption is not practical in the realistic wireless systems. In this work, we consider the practical implementation issues of resource allocation in orthogonal frequency division multiple access (OFDMA) two-way relay networks: the inaccuracy of channel-state information (CSI) available to the source. Instead, only the estimated channel status is known by the source. In this context, a joint optimization of subcarrier pairing and allocation, relay selection, and transmit power allocation is formulated in OFDMA two-way amplify-and-forward relay networks. Moreover, the objective of this work is to minimize the energy consumption of the overall system. Further, to ensure the quality of service (QoS) or data rate requirement, the energy consumption must be minimized without compromising the QoS. Therefore, by applying convex optimization techniques, energy-efficient algorithms are developed with the objective to minimize the total transmit power with guaranteeing the required data rates. Through simulation studies, energy consumption performance of the systems under the proposed schemes is investigated. It can be observed that our proposed scheme can improve the energy consumption performance of the considered system. © 2015, Chang et al.

Rantalainen T.,Deakin University | Rantalainen T.,Lappeenranta University of Technology | Rantalainen T.,Health Science University | Rantalainen T.,University of Jyvakyla | And 7 more authors.
Journal of Musculoskeletal Neuronal Interactions | Year: 2011

Objective: Cortical porosity, particularly at the endocortical region, is recognised to play a central role in the pathogenesis of bone fragility. Therefore, the purpose of this study was to: 1) demonstrate how cortical volumetric BMD (vBMD) distribution can be analysed from (p)QCT images and 2) highlight the clinical significance of assessing regional density distribution of cortical bone. Methods: We used pQCT to compare mid-tibial cortical volumetric BMD distribution of 20 young (age 24(SD2) years, mass 77(11) kg, height 178(6) cm) and 25 elderly (72(4) years, 75(9) kg, 172(5) cm) men. Radial and polar cortical vBMD distributions were analysed using a custom built open source analysis tool which allowed the cortex to be divided into three concentric cortical divisions and in 36 cortical sectors originating from the centroid of the bone. Results: Mean vBMD did not differ between the groups (1135(16) vs. 1130(28) mg/cm, P=0.696). In contrast, there was a significant age-group by radial division interaction for radial cortical vBMD (P<0.001). Conclusions: The proposed analysis method for analysing cortical bone density distribution of pQCT images was effective for detecting regional differences in cortical density between young and elderly men, which would have been missed by just looking at mean vBMD values.

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