As a radio communication system, there is known a system which includes a radio terminal such as a mobile phone, a base station wirelessly communicating with the radio terminal, and a backhaul device (for example, WO 2011/096315). The backhaul device establishes a backhaul system connecting the base station with an upper-level communication network (also referred to as a core network), and relays between the base station and a management server for example. In particular, the costs are increased to install optical lines in a mountainous area and a remote island, which are separated from an urban area. Therefore, a radio backhaul device and a radio backhaul system equipped therewith are used in many cases.
After the initial installation, the radio backhaul device may be deviated in its position by earthquakes or snow fall after the installation. If so, propagation characteristics of the radio backhaul device is lowered. In such a case, a service engineer is necessarily sent to that area to quickly correct the position of the radio backhaul device. However, the radio backhaul device installed in a mountainous area or a remote island separated from the urban area as described above may be hard for the service engineer to maintain. Since it also takes a lot of time until the service engineer arrives that area, there needs a lot of time for recovery. In order to care such a case, there is disclosed an antenna adjustment method in which the direction of the antennas of transmission and reception units of the radio device is adjusted based on a received signal (for example, JP 2007-251862 A).
In the radio backhaul device and the radio backhaul system equipped therewith, it needs to transmit a large quantity of user's data handled by the base station. Therefore, a significantly high transmission rate is required. For this reason, there is used a significantly high frequency such as a millimeter wave bandwidth (30 GHz bandwidth or 80 GHz bandwidth) in which a wide range of frequency bandwidth can be secured. When a high frequency such as the millimeter wave bandwidth is used, a linearity of radio waves becomes strong, and propagation strength depends largely on directivity of the antenna.