Patent ID: 9532294
Filing Date: 2016-12-27
CPC Classification: H04L,H04W

Claim Text:
1. A mobile communication system, comprising: a first radio terminal; a second radio terminal; and a base station, wherein the first radio terminal directly transmits user data to the second radio terminal by device to device (D2D) communication, the second radio terminal transmits a first radio signal, the first radio signal indicates whether or not the second radio terminal has received the user data, the base station receives the first radio signal from the second radio terminal, the base station transmits a second radio signal to the first radio terminal in response to a reception of the first radio signal, the second radio signal indicates whether or not the second radio terminal has received the user data, the first radio terminal receives the second radio signal form the base station, and the first radio terminal determines whether to retransmit the user data to the second radio terminal on a basis of the first radio signal without use of the second radio signal in response to a communication state of the D2D communication exceeding a threshold value.