  In this paper, we study the secure transmission in multihop wireless networks
with randomize-and-forward (RaF) relaying, in the presence of randomly
distributed eavesdroppers. By considering adaptive encoder with on-off
transmission (OFT) scheme, we investigate the optimal design of the wiretap
code and routing strategies to maximize the secrecy rate while satisfying the
secrecy outage probability (SOP) constraint. We derive the exact expressions
for the optimal rate parameters of the wiretap code. Then the secure routing
problem is solved by revising the classical Bellman-Ford algorithm. Simulation
results are conducted to verify our analysis.
