A matter of particular interest after the discovery of the Higgs boson is the search for supersymmetric particles which could give answers to several important questions in particle physics. Essential for the search for these hypothetical particles at the Large Hadron Collider (LHC) are calculations of observables with the highest possible precision. To this end, higher-order corrections in the strong interaction and the resummation of logarithmically enhanced contributions via parton-shower

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... ulations have to be considered. The signatures of supersymmetric particles in detectors are significantly affected by hard jets in the final state which originate from the radiation of hard gluons and quarks. It is thus necessary to include them in higher-order calculations. The central concern of this thesis is an extensive phenomenological study of pair-production processes in the Minimal Supersymmetric Standard Model (MSSM) taking into account the radiation of hard jets. For that purpose, we calculate matrix elements at the next-to-leading order (NLO) in the strong coupling for electroweakino-pair production processes without and with a hard jet in the final state. To further refine the precision of experimentally accessible observables, the matrix elements of the hard scattering process are matched to a parton-shower Monte Carlo program via the \POWHEG{} formalism. During the implementation of the processes we do not use any simplification with regard to masses or resonance effects. The complete NLO-QCD calculation includes complicated resonance structures in the real corrections which we regularize by a suitable subtraction method. To obtain well-defined matrix elements, we use the so-called \PROSPINO{} subtraction scheme for singly resonant real-emission matrix elements. For diagrams that are doubly resonant an extended version of this method is being used. This subtraction method is the first to be applicable to processes with three final-state particles at tree level. Additionally, by using the \POWHEGBOX{} we are [...]