A technique regarding organizing a convoy of vehicles, in which a train of vehicles keep a certain inter-vehicle distance and follow a lead vehicle, is disclosed in, for example, Japanese Patent Laid-Open No. 2009-278536 (JP '536). The technique of JP '536 provides for wireless communication between terminals disposed in each of the vehicles of the convoy (i.e., vehicle-to-vehicle communication). That is, when traveling as a convoy, or as a group of vehicles, each of the vehicles of the convoy, except for the last vehicle, transmits position information of the vehicle and other information to a following vehicle at regular intervals, since each vehicle may possibly serve as a lead vehicle (i.e., a pace vehicle) in the convoy. The information received by the following vehicle is utilized for the travel of the following vehicle itself, for organizing the convoy.
However, the technique of JP '536 is problematic in terms of suffering from congestion of transmitted information. In other words, the technique may cause congestion of transmitted information from each of the convoy vehicles, because each of the convoy vehicles transmits, at regular intervals through vehicle-to-vehicle communication, information such as a vehicle position and the like, and each of the transmitted information occupies a certain bandwidth, which increases the possibility of congestion of the transmitted information, especially when many vehicles are organized as one convoy.
If a longer transmission cycle (i.e., a longer transmission interval) is used in the vehicle-to-vehicle communication, it may prevent an increase of the bandwidth of each of the transmitted information, thereby making it less possible to cause congestion. However, under such circumstance, if the convoy vehicle needs to receive the transmitted information very frequently, the longer transmission cycle of the vehicle-to-vehicle communication may cause a problem in such information-demanding vehicle.