As illustrated in FIG. 2, the communication device 300 or 400 switches a beam to be formed among zeroth to fifth beam patterns 511₀ to 511₅ using an array antenna or the like. Herein, the “beam” indicates a range (communication area) in which the transmission and reception of a radio signal are possible and is formed by, for example, controlling the transmission and reception of the array antenna. The zeroth beam pattern is a non-directional beam pattern. The first to fifth beam patterns 511₀ to 511₅ are beam patterns with high directivity, which are different in beam direction.

For example, when a communication partner is positioned inside the first beam pattern 511₁, the communication device 300 or 400 performs radio communication with the communication partner by forming the first beam pattern 511₁.

Which one of the beam patterns is optimal for the radio communication with the communication partner is unknown in the initial state in which the communication is initiated. Accordingly, the communication device 300 or 400 determines a usable beam pattern for each communication partner by performing a beam forming protocol and determines the beam pattern to be used for the radio communication with the communication partner. The beam forming protocol is described in detail below.

The communication device 300 or 400 may use the same beam pattern or different beam patterns as the beam pattern at the time of transmission, also referred to as the transmission sector, and the beam pattern at the time of reception, also referred to as the reception sector.