  In their landmark paper Cover and El Gamal proposed different coding
strategies for the relay channel with a single relay supporting a communication
pair. These strategies are the decode-and-forward and compress-and-forward
approach, as well as a general lower bound on the capacity of a relay network
which relies on the mixed application of the previous two strategies. So far,
only parts of their work - the decode-and-forward and the compress-and-forward
strategy - have been applied to networks with multiple relays.
  This paper derives a mixed strategy for multiple relay networks using a
combined approach of partial decode-and-forward with N +1 levels and the ideas
of successive refinement with different side information at the receivers.
After describing the protocol structure, we present the achievable rates for
the discrete memoryless relay channel as well as Gaussian multiple relay
networks. Using these results we compare the mixed strategy with some special
cases, e. g., multilevel decode-and-forward, distributed compress-and-forward
and a mixed approach where one relay node operates in decode-and-forward and
the other in compress-and-forward mode.
