Abstract: A beacon device includes a transmitter, a receiver, and a controller. The transmitter transmits a beacon signal. The receiver is capable of receiving an emergency signal from a wireless device. The controller changes the setting of the transmission of a beacon signal from the transmitter based on whether or not the receiver has received an emergency signal. The transmitter transmits a beacon signal according to the setting made by the controller.

Abstract: A user terminal has reception directivity, and includes a beacon reception unit that receives a beacon signal transmitted by anther user terminal, a received signal strength indicator measurement unit that measures a received signal strength indicator of the received beacon signal, and a contact confirmation unit that evaluates the degree of contact with the other user terminal based on a total value of a received signal strength indicator measured in a predetermined period. The beacon reception unit is worn on a predetermined position of a person wearing the user terminal to have reception directivity corresponding to the direction in which the person wearing the user terminal faces.

Abstract: A position estimation system includes a beacon transmitter that transmits a beacon signal, a mobile station that receives the beacon signal from the beacon transmitter and transmits positioning data including ID information of the received beacon signal, and a position information server that estimates a position of the mobile station based on the positioning data transmitted from the mobile station, in which the mobile station includes a plurality of transmission means, and switches the transmission means for transmitting the positioning data based on the received beacon signal.

Abstract: A beacon device includes a transmitter, a receiver, and a controller. The transmitter transmits a beacon signal. The receiver is capable of receiving an emergency signal from a wireless device. The controller changes the setting of the transmission of a beacon signal from the transmitter based on whether or not the receiver has received an emergency signal. The transmitter transmits a beacon signal according to the setting made by the controller.

Abstract: A location information server includes: an acquisition unit configured to acquire received signal strengths of radio signals transmitted from a transmitter and received at a receiver; an estimation unit configured to estimate a location of the transmitter or receiver, using at least the top three received signal strengths among the acquired received signal strengths; and a reliability calculation unit configured to calculate a reliability of the location estimation based on the received signal strengths that have been used.

Abstract: A location information server including: an acquisition unit configured to acquire, from each of a plurality of receivers, a received signal strength of a radio signal transmitted from a transmitter; an estimation unit configured to estimate a location of the transmitter based on the received signal strengths of the first to the third highest among the acquired received signal strengths; and a correction unit configured to correct, when the difference between a received signal strength based on at least one of the received signal strengths of the first to the third highest and a received signal strength of the fourth highest is smaller than a predetermined value, the estimated location of the transmitter based on the received signal strength of the fourth highest.