An ad hoc wireless network is a self-organized network system. In this system, wireless terminals autonomously construct a multi-hop network which maintains its structural information by exchanging network information with some neighbor terminals. In such a network, the network topology changes frequently due to an unsettled wireless environment. Flexible Radio Network (FRN), one of the products applying ad hoc wireless network system, adopts an original protocol that provide a multiple routes management and a packet retransmission ability against packet transmission errors. This system has been in use in recent years. In this paper, we first evaluate its performance through simulations of data-link protocol and routing protocol to clarify its basic properties, and then we discover some problems on these protocols that degrade the performance. Furthermore, we propose some performance improvement techniques, simulate them, and then show how they improve the system performance.