Communication system and api server, headset, and mobile communication terminal used in communication system

A communication system in which a group call is performed between a plurality of clients via a VoIP server, the communication system comprising:

• an API server that manages the group call,
• wherein each client in the plurality of clients comprises:
• a mobile communication terminal that performs communication via a mobile communication network;
• and
• a headset that exchanges voice data with the mobile communication terminal by short range wireless communication,
• wherein the headset comprises:
• a speech detector that detects a speech;
• a speech emphasizer that emphasizes a speech part included in the speech detected by the speech detector relatively with respect to ambient sound;
• and
• a reproduction controller that reproduces the voice data received from the mobile communication terminal so that the speech detected by the speech detector in the speech part of the voice data is easy to be heard relatively with respect to background noise,
• wherein the mobile communication terminal comprises:
• a noise estimator that estimates noise included in the voice data received from the headset;
• a speech candidate determiner that determines a range of candidates for the speech part from the voice data on the basis of an estimation result obtained by the noise estimator;
• a speech characteristics determiner that determines a speech part of a person from the range of candidates for the speech part of the voice data determined by the speech candidate determiner;
• a voice data transmitter that transmits the part of the voice data that the speech characteristics determiner has determined to be the speech of a person to the VoIP server;
• and
• a reproduction voice data transmitter that transmits the voice data received from the VoIP server to the headset,
• wherein the API server comprises:
• a communication quality controller that notifies the clients and the VoIP server of a command related to control of a communication quality of the group call on the basis of a communication state between each of the clients and the VoIP server, and
• wherein the voice data transmitter encodes the part of the voice data that the speech characteristics determiner has determined to be the speech of a person with a communication quality based on the command notified from the communication quality controller and transmits the encoded part to the VoIP server.