In ad hoc networks, a communication link between two mobile nodes is not always bidirectional, i.e. unidirectional, since the different characters of networks and nodes. This paper studies unidirectional links which are general and universal in ad hoc networks and proposes a routing protocol LSARP (Link-State Advertisement based source Routing Protocol). LSARP can support unidirectional links to improve the routing efficiency. In LSARP, Unidirectional Link-state Advertisement Based Power Adjustment mechanism (ULABPA) is designed. ULABPA can improve the network connectivity. Simulation results show the performance of LSARP is better than the traditional routing protocols in many aspects.