Mobile communication system

Abstract

A mobile communication system that supports Device to Device (D2D) communication comprises a user terminal that transmits a reference signal for D2D that is used for channel estimation in at least the D2D communication, and the reference signal for D2D is further used for discovering another user terminal to be a communication partner of the D2D communication.

1 . A mobile communication system that supports Device to Device (D2D) communication, comprising:
 a user terminal that transmits a reference signal for D2D that is used for channel estimation in at least the D2D communication, wherein   the reference signal for D2D is further used for discovering another user terminal to be a communication partner of the D2D communication.   
     
     
         2 . The mobile communication system according to  claim 1 , wherein a reference signal parameter different depending on each D2D group composed of a plurality of user terminals performing the D2D communication, is applied to the reference signal for D2D. 
     
     
         3 . The mobile communication system according to  claim 2 , wherein the reference signal parameter is determined in response to designation from a base station. 
     
     
         4 . The mobile communication system according to  claim 2 , wherein
 the reference signal for D2D is transmitted by using a resource element common in the respective D2D groups, and   the reference signal parameter is an orthogonal code for performing code division multiplexing on the reference signal for D2D.   
     
     
         5 . The mobile communication system according to  claim 1 , wherein, in a case in which the reference signal for D2D is transmitted within an uplink frequency band of the mobile communication system, the reference signal for D2D is arranged while avoiding a physical uplink control channel, a demodulation reference signal, and a sounding reference signal within the uplink frequency band. 
     
     
         6 . The mobile communication system according to  claim 1 , wherein, in a case in which the reference signal for D2D is transmitted within a downlink frequency band of the mobile communication system, the reference signal for D2D is arranged while avoiding a physical downlink control channel and a cell-specific reference signal within the downlink frequency band. 
     
     
         7 . The mobile communication system according to  claim 1 , wherein, in a case in which the reference signal for D2D is transmitted within a frequency band of an uplink of the mobile communication system, the reference signal for D2D is further used for detecting interference to the uplink from the D2D communication. 
     
     
         8 . The mobile communication system according to  claim 7 , wherein, in response to a reception level of the reference signal for D2D from the user terminal being higher than a threshold value, the base station transmits switching information for switching the D2D communication to the cellular communication to the user terminal. 
     
     
         9 . The mobile communication system according to  claim 7 , wherein, in response to a reception level of the reference signal for D2D from the user terminal being higher than a threshold value, the base station performs scheduling such that a radio resource is not shared between the D2D communication and the uplink. 
     
     
         10 . The mobile communication system according to  claim 7 , wherein, in response to a reception level of the reference signal for D2D from the user terminal being higher than a threshold value, the base station transmits power control information for reducing transmission power in the D2D communication to the user terminal. 
     
     
         11 . The mobile communication system according to  claim 7 , wherein, in response to a reception level of the reference signal for D2D from the user terminal being higher than a threshold value, the base station transmits power control information for increasing transmission power in the uplink or MCS control information for reducing MCS in the uplink to a cellular communication terminal to which a radio resource shared with the user terminal is assigned. 
     
     
         12 . The mobile communication system according to  claim 7 , wherein
 the user terminal performs multi-antenna transmission in the D2D communication, and   in response to the base station detecting the reference signal for D2D from the user terminal, the base station transmits, to the user terminal, setting information for setting an antenna weight by which interference applied to the base station is reduced.   
     
     
         13 . A mobile communication system, which supports cellular communication in which data communication is performed between a network and a user terminal and D2D communication in which data communication is directly performed among two or more user terminals, comprising:
 a D2D communication terminal that is a user terminal which performs the D2D communication; and   a base station that assigns a radio resource to be used in the D2D communication to the D2D communication terminal, wherein   in response to detection of interference power, the D2D communication terminal transmits interference information on interference to the base station.   
     
     
         14 . The mobile communication system according to  claim 13 , wherein the D2D communication terminal transmits the interference information to the base station when a value of the interference power is higher than a threshold value. 
     
     
         15 . The mobile communication system according to  claim 14 , wherein the threshold value is designated from the base station. 
     
     
         16 . The mobile communication system according to  claim 13 , wherein
 the D2D communication terminal transmits the interference information to the base station at a timing after a predetermined time lapses from a detection timing of the interference power, and   the interference information is information indicating that the terminal has received interference.   
     
     
         17 . The mobile communication system according to  claim 16 , wherein
 the base station manages a history of radio resource assignment, and   when the interference information is received from the D2D communication terminal, the base station estimates a user terminal being an interference source on the basis of a reception timing of the interference information and the history.   
     
     
         18 . The mobile communication system according to  claim 13 , wherein the interference information includes timing information indicating a detection timing of the interference power. 
     
     
         19 . The mobile communication system according to  claim 18 , wherein
 the base station manages a history of radio resource assignment, and   when the interference information is received from the D2D communication terminal, the base station estimates a user terminal being an interference source on the basis of the timing information included in the interference information and the history.   
     
     
         20 . The mobile communication system according to  claim 13 , wherein the interference information includes information indicating a frequency at which the interference power has been detected. 
     
     
         21 . The mobile communication system according to  claim 13 , wherein a radio resource shared with the cellular communication is assigned to the D2D communication terminal as a radio resource to be used in the D2D communication. 
     
     
         22 . The mobile communication system according to  claim 21 , wherein the D2D communication terminal detects the interference power for a reference signal in an uplink of the cellular communication. 
     
     
         23 . The mobile communication system according to  claim 22 , wherein the interference information includes information indicating a signal sequence of the reference signal or information generated from the signal sequence of the reference signal. 
     
     
         24 . The mobile communication system according to  claim 21 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station transmits switching information for switching the D2D communication to the cellular communication to the D2D communication terminal. 
     
     
         25 . The mobile communication system according to  claim 21 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station allows a radio resource to be assigned to the D2D communication terminal to differ from a radio resource to be assigned to a cellular communication terminal being an interference source. 
     
     
         26 . The mobile communication system according to  claim 21 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station transmits, to the D2D communication terminal, power control information for increasing transmission power in the D2D communication or MCS control information for reducing MCS in the D2D communication. 
     
     
         27 . The mobile communication system according to  claim 21 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station transmits power control information for reducing uplink transmission power to a cellular communication terminal being an interference source. 
     
     
         28 . The mobile communication system according to  claim 21 , wherein, when a cellular communication terminal being an interference source performs multi-antenna transmission in an uplink, the base station transmits, to the cellular communication terminal being the interference source, setting information for setting an antenna weight by which interference applied to the D2D communication is reduced, in response to reception of the interference information from the D2D communication terminal. 
     
     
         29 . The mobile communication system according to  claim 13 , wherein the D2D communication terminal transmits the interference information to the base station in response to detection of the interference power from another D2D communication terminal which is not a communication partner of the D2D communication terminal. 
     
     
         30 . The mobile communication system according to  claim 29 , wherein the D2D communication terminal detects the interference power for a reference signal for the D2D communication and/or a beacon signal for the D2D communication. 
     
     
         31 . The mobile communication system according to  claim 30 , wherein the interference information includes information indicating a signal sequence of the reference signal or information generated from the signal sequence of the reference signal. 
     
     
         32 . The mobile communication system according to  claim 29 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station transmits switching information for switching the D2D communication to the cellular communication to the D2D communication terminal or the other D2D communication terminal. 
     
     
         33 . The mobile communication system according to  claim 29 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station allows a radio resource to be assigned to the D2D communication terminal to differ from a radio resource to be assigned to the other D2D communication terminal. 
     
     
         34 . The mobile communication system according to  claim 29 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station transmits, to the D2D communication terminal and/or the other D2D communication terminal, power control information for reducing transmission power or MCS control information for reducing MCS. 
     
     
         35 . The mobile communication system according to  claim 29 , wherein, in response to reception of the interference information from the D2D communication terminal, the base station transmits setting information for setting an antenna weight, by which interference is reduced, to the D2D communication terminal and/or the other D2D communication terminal.