In ad hoc wireless networks, wireless terminals can autonomously construct and can maintain the network. They communicate with some neighbor terminals, exchange network information and determine routes for packets on the multi-hop wireless network. Flexible Radio Network (FRN), one of the ad hoc wireless network systems, adopts a proprietary protocol that provides a multiple routes management and a packet retransmission mechanism against packet transmission errors. This system is a commercial product that has been in use in a recent few years. In this paper, we first evaluate the performance through simulations for data-link protocol and routing protocol of the FRN to clarify its basic properties. Furthermore, we propose some techniques that enhance its performance and solve problems on the protocols. We show how they improve the system performance through simulations and analyses.

Robustness is one of the significant properties in wireless sensor networks because sensor nodes and wireless links are subjected to frequent failures. Once these failures occur, system performance falls into critical condition due to increases in traffic and losses of connectivity and reachability. Most of the existing studies on sensor networks, however, do not conduct quantitative evaluation on robustness and do not discuss what brings in robustness. In this paper, we define and evaluate robustness of wireless sensor networks and show how to improve them. By computer simulation, we show that receiver-initiated MAC protocols are more robust than sender-initiated ones and a simple detour-routing algorithm has more than tripled robustness than the simple minimum-hop routing algorithm.

Since a radio channel is shared among terminals in an ad hoc network, packet collisions are frequent. In case of transmitting packets especially using TCP, data and ACK packets are transmitted in opposite directions on the same radio channel. Therefore, frequent collisions are unavoidable, and this seriously degrades TCP throughput. It is possible to transmit to two or more nodes which adjoin from a certain node simultaneously on the radio channel. To reduce the likelihood of packet collisions when an intermediate node transmits both data and ACK packets, these two types of packet can be combined and transmitted at the same time to increase the efficiency of radio channel utilization. In this paper, we propose a new technique to improve TCP performance by combining data and ACK packets. Our proposed technique is applicable to generic ad hoc networks easily. By means of a simulation using networks with various topologies, we have found that throughput can be improved by up to 60% by applying our proposed technique.