Tree-based protocol for ad hoc networks constructed with data transmission modems

This paper presents a communication protocol for an ad hoc network constructed with 429 MHz data transmission modems. It is expected that the signal attenuation caused by rainfall is smaller for the 429 MHz band than for the 2.4 or 5 GHz band, which is used in wireless LANs and ZigBee. Additionally, since the signal diffraction is greater for this frequency than for higher frequencies, the signal is less attenuated by obstacles. Hence, the 429 MHz modem is suitable for networks with long-distance wireless transmission. However, the modem does not support network functions such as packet collision avoidance and routing. Thus, the paper presents a new simple protocol that avoids packet collisions and performs routing. The proposed protocol is essentially a token passing method that utilizes a rooted tree structure in a mesh network. In this method, the order of token passing is determined by a depth-first search in the tree. With this scheme, it is possible for the protocol to avoid packet collisions. In addition, routing is performed with very limited information stored at each node. This paper details the proposed token-based protocol and describes how the token and data packets circulate in the network. It also presents a distributed algorithm that finds a rooted tree in a mesh network. The proposed method was implemented on a prototype network. The feasibility of the method was confirmed through an experiment. The characteristic of a tree obtained by the tree construction algorithm is also clarified.