Communication system and control method

1. A communication system comprising:

a plurality of sensor terminals each including a clock indicating an individual time and configured to detect sensing information related to a user and an information detection time at which the sensing information has been detected;

a management terminal configured to retain a reference time and adapted to communicate with the plurality of sensor terminals; and

a relationship analysis unit configured to analyze a relationship among users of the plurality of sensor terminals, wherein

the management terminal acquires the sensing information and the information detection time from each of the plurality of sensor terminals and corrects the information detection time acquired from each of the plurality of sensor terminals based on a lag between the individual time acquired from a corresponding sensor terminal and the reference time,

when a radio field intensity of radio waves of radio communication emitted by the sensor terminal is greater than or equal to a threshold value, a set of the individual time and the reference time is recorded,

when the radio field intensity of the radio waves of the radio communication emitted by the sensor terminal is less than the threshold value, the acquired individual time is discarded, and

the relationship analysis unit analyzes the relationship using the sensing information and the corrected information detection time.

2. The communication system according to claim 1 , wherein the plurality of sensor terminals start detection of the sensing information and the information detection time before establishing communication with the management terminal.

3. The communication system according to claim 1 , wherein the management terminal updates the lag between the individual time and the reference time on a real-time basis.

4. The communication system according to claim 1 , wherein when communication with at least one of the plurality of sensor terminals is disconnected and thereafter restored, the management terminal updates the lag between the individual time and the reference time at the at least one of the plurality of sensor terminals where the communication has been disconnected.

5. A method of controlling a communication system that comprises:

a plurality of sensor terminals each including a clock indicating an individual time and configured to detect sensing information related to a user and an information detection time at which the sensing information has been detected;

a management terminal configured to retain a reference time and adapted to communicate with the plurality of sensor terminals; and

a relationship analysis unit configured to analyze a relationship among users of the plurality of sensor terminals,

the method comprising:

acquiring, at the management terminal, the individual time from each of the plurality of sensor terminals;

acquiring, at the management terminal, the sensing information and the information detection time from each of the plurality of sensor terminals;

correcting, at the management terminal, the information detection time acquired from each of the plurality of sensor terminals based on a lag between the individual time acquired from a corresponding sensor terminal and the reference time, wherein

when a radio field intensity of radio waves of radio communication emitted by the sensor terminal is greater than or equal to a threshold value, a set of the individual time and the reference time is recorded, and

when the radio field intensity of the radio waves of the radio communication emitted by the sensor terminal is less than the threshold value, the acquired individual time is discarded; and

analyzing, at the relationship analysis unit, the relationship using the sensing information and the corrected information detection time.

6. A non-transitory computer readable medium storing a computer program for causing a computer to perform the method according to claim 5 .