Mobile communication system, user terminal, and base station
A mobile communication system according to the embodiment supports cellular communication in which a data path passes through a network and D2D communication that is direct device-to-device communication in which a data path does not pass through the network. A frequency division multiplexing scheme is applied to the cellular communication and a code division multiplexing scheme is applied to the D2D communication. The network assigns a spread code having orthogonality to a user terminal in response to a request from the user terminal. The user terminal performs the D2D communication by using the spread code assigned by the network.
1. A mobile communication system that supports cellular communication in which a data path passes through a network and D2D communication that is direct device-to-device communication in which a data path does not pass through the network, wherein
the network assigns radio resources having orthogonality to a user terminal in response to a request from the user terminal,
the user terminal performs the D2D communication by using the radio resources assigned by the network,
the radio resources include a spread code,
the network controls a code length of the spread code to be assigned to the user terminal on the basis of at least one of communication quality of the D2D communication in the user terminal and the number of user terminals performing the D2D communication in a cell to which the user terminal belongs, and
when the network determines that the code length of the spread code to be assigned to the user terminal is longer than a predetermined length, the network instructs the user terminal to switch from the D2D communication to the cellular communication.
2. The mobile communication system according to claim 1 , wherein
the user terminal retains an at least one initial spreading code having no orthogonality, and
the user terminal performs the D2D communication by using the at least one initial spreading code.
3. The mobile communication system according to claim 2 , wherein
the user terminal performing the D2D communication by using the at least one initial spreading code requests the network to assign the radio resources in response to detection of deterioration in communication quality of the D2D communication.
4. The mobile communication system according to claim 3 , wherein
when the network determines that the communication quality will improve by assigning the radio resources, the network assigns the radio resources to the user terminal.
5. The mobile communication system according to claim 2 , wherein
the user terminal performing the D2D communication by using the at least one initial spreading code performs transmission in the D2D communication on the basis of a result of monitoring an interference wave signal.
6. The mobile communication system according to claim 1 , wherein
a valid time is set for the radio resources, and
the user terminal to which the radio resources are assigned requests the network to reassign the radio resources in order to continue the D2D communication.
7. The mobile communication system according to claim 6 , wherein
the network controls the valid time on the basis of at least one of an elapsed time of the D2D communication by the user terminal, an application that the user terminal uses for the D2D communication, a billing contract of the user terminal, and movement speed of the user terminal.
8. The mobile communication system according to claim 6 , wherein
the user terminal requests the network to reassign the radio resources in response to detection of deterioration in communication quality of the D2D communication, even before the valid time expires.
9. The mobile communication system according to claim 6 , wherein
when the user terminal ends the D2D communication before the valid time expires, the user terminal notifies the network of the end of the D2D communication.
10. The mobile communication system according to claim 6 , wherein
when reassigning the radio resources, the network assigns, to the user terminal, radio resources different from the radio resources before the reassignment.
11. The mobile communication system according to claim 1 , wherein
the network assigns the radio resources to a user terminal group including the user terminal and another user terminal which is to perform the D2D communication with the user terminal.
12. The mobile communication system according to claim 11 , wherein
the user terminal transmits the request to the network on the basis of an increase and decrease in the number of user terminals included in the user terminal group.
13. The mobile communication system according to claim 11 , wherein
the network controls the number of radio resources to be assigned to the user terminal group on the basis of the number of user terminals included in the user terminal group.
14. The mobile communication system according to claim 11 , wherein
the network denies the assignment of the radio resources to the user terminal group when a user terminal under a billing contract for which the D2D communication is not permitted is included in the user terminal group.
15. The mobile communication system according to claim 1 , wherein
the network performs charging for the use of the radio resources by the user terminal.
16. The mobile communication system according to claim 1 , wherein
the network assigns, to the user terminal, radio resources for transmission in the D2D communication and radio resources for reception in the D2D communication.
17. The mobile communication system according to claim 1 , wherein
the network notifies the user terminal of transmission and reception start timing of the D2D communication by using, as a reference, timing of the cellular communication.
18. The mobile communication system according to claim 1 , wherein
the network comprises a plurality of cells, and each of the plurality of cells notifies a neighboring cell of an assignment situation of the radio resources in the self cell.
19. The mobile communication system according to claim 1 , wherein
the network assigns the radio resources to the user terminal on the basis of an identifier associated with the user terminal.
20. The mobile communication system according to claim 1 , wherein
the user terminal performing the D2D communication by using the spread code as the radio resources performs transmission by applying the spread code to each of a plurality of subcarriers.
21. The mobile communication system according to claim 1 , wherein
when the user terminal performing the D2D communication transmits data, the user terminal transmits information indicating an application corresponding to the data by adding the information to the data.
22. The mobile communication system according to claim 1 , wherein
the network comprises a server device that is shared by a plurality of communication providers and that performs assignment of the radio resources.
23. A user terminal that is used in a mobile communication system that supports cellular communication in which a data path passes through a network, and D2D communication that is direct device-to-device communication in which a data path does not pass through the network, comprising:
a controller including a processor and a memory, the controller configured to perform the D2D communication by using radio resources assigned by the network in response to a request from the user terminal, the radio resources having orthogonality, wherein
the radio resources include a spread code,
a code length of the spread code to be assigned to the user terminal is controlled by the network controls on the basis of at least one of communication quality of the D2D communication in the user terminal and the number of user terminals performing the D2D communication in a cell to which the user terminal belongs, and
the controller is further configured to switch from the D2D communication to the cellular communication upon a determination that the code length of the spread code to be assigned to the user terminal is longer than a predetermined length.
24. A base station that is used in a mobile communication system that supports cellular communication in which a data path passes through a network, and D2D communication that is direct device-to-device communication in which a data path does not pass through the network, comprising:
a controller including a processor and a memory, the controller configured to assign radio resources having orthogonality to a user terminal in response to a request from the user terminal, the radio resources being used by the user terminal to perform the D2D communication, wherein
the radio resources include a spread code, and
the controller is further configured to:
control a code length of the spread code to be assigned to the user terminal on the basis of at least one of communication quality of the D2D communication in the user terminal and the number of user terminals performing the D2D communication in a cell to which the user terminal belongs, and
instruct the user terminal to switch from the D2D communication to the cellular communication upon a determination that the code length of the spread code to be assigned to the user terminal is longer than a predetermined length.