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Hier finden Sie wissenschaftliche Publikationen aus den FraunhoferInstituten. Impact of interference coupling  Loss of convexity
 Institute of Electrical and Electronics Engineers IEEE; IEEE Communications Society: IEEE Global Communications Conference, GLOBECOM 2009 : Honolulu, HI, US, 30 Nov4 Dec, 2009 Piscataway: IEEE, 2009 ISBN: 9781424456260 ISBN: 9781424441471 ISBN: 9781424441488 6 pp. 
 Global Telecommunications Conference (GLOBECOM) <2009, Honolulu/Hawaii.> 

 English 
 Conference Paper 
 Fraunhofer HHI () 
Abstract
In interference coupled wireless systems, where it is not possible to "orthogonalize" all the users in the system, we characterize the impact of interference coupling on the convexity of certain utility functions and problems. We introduce a general class of competitive user utility functions and natural competitive user utility functions. We further introduce the signaltointerference based utility functions, which are based on physical layer parameters in wireless systems. We prove the conditions, which when satisfied result in a competitive user utility function being a signaltointerference ratio based utility function. We further show that there exists no natural competitive user utility function, which is convex or concave. Furthermore, we show that a sum of weighted combination of natural competitive user utility functions is not convex or concave. Such functions are commonly encountered in wireless communication systems, e.g. rate or MMSE as a function of signaltointerference ratio. We show that such rate maximization or MMSE minimization problems are not convex programs under our specified conditions.