Geometric Construction of Killing Spinors and Supersymmetry Algebras in   Homogeneous Spacetimes
  We show how the Killing spinors of some maximally supersymmetric supergravity solutions whose metrics describe symmetric spacetimes (including $AdS,AdS\times S$ and H$pp$-waves) can be easily constructed using purely geometrical and group-theoretical methods. The calculation of the supersymmetry algebras is extremely simple in this formalism. 
N. Alonso-Alberca, E. Lozano-Tellechea and T. Ortin