Extensions of linking systems with p-group kernel

We study extensions of p-local finite groups where the kernel is a p-group. In particular, we construct examples of saturated fusion systems F which do not come from finite groups, but which have normal p- subgroups A del F such that F/A is the fusion system of a finite group. One of the tools used to do this is the concept of a "transporter system", which is modelled on the transporter category of a finite group, and is more general than a linking system.