Because of the gains like diversity, throughput, and the coverage extension provided by the multiple-input multipleout (MIMO) systems, it has been part of the various wireless communications standards. However, to reap the benefits offered by MIMO systems in size-constrained nodes, used in wireless communications, has been a challenging issue. To address this challenge, cooperative communications has been introduced as an implementable way to exploit the multi-antenna (MIMO) gains in small size nodes. Various schemes or protocols have been devised to address the way by which cooperative communications actually takes place. In this article, we propose and investigate a novel scheme which provides a way to combine the benefits of space-time codes and network coding for cooperative communications. In this scheme, the cooperating users using space-time codes are assisted by the availability of a fixed relay node proposed for the future wireless networks. We compare our scheme with cooperative communications using Alamouti scheme and non-cooperative communications. With analytical results, we prove that the proposed scheme offers diversity gain of order three while cooperative communications using Alamouti scheme offers two and non-cooperative communications offers diversity order of one only. Moreover, the proposed relay assisted scheme outperforms by 15% in terms of multiplexing gain, the cooperative communications scheme being compared.

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Abstract. Models defined using the Unified Modeling Language (UML) are nowadays common parts of software documentations, specifications and sometimes even implementations. However, there is a broad variety of how UML is used. Reasons can be found, for example, in the lack of generally accepted modeling norms and guidelines, the semi-formal semantics of UML, or the complexity of the language. In practice, these factors inevitably lead to quality problems in UML models that need to be addressed. We investigate and discuss existing work in the field of quality assessment and improvement of UML models and present how we envision an integrated approach to quality assessment and improvement of UML models. We assess a model with a Factor-Criteria-Metrics (FCM) based quality model, detect issues by finding smells and violated metric thresholds in UML models, and improve UML models by applying refactorings using model-to-model transformations.

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