Radio terminal apparatus, radio base station apparatus, and radio communication method

1. A radio terminal apparatus for communicating with a radio base station apparatus, the radio terminal apparatus comprising:

a transmitter configured to transmit a signal to the radio base station apparatus;

a receiver configured to receive a signal from the radio base station apparatus; and

a controller configured to control the transmitter and the receiver, wherein

the controller is capable of selecting at least a grant-based scheme or a grant-less communication scheme in a case of a transmission of user data,

the user data and information necessary to allocate a radio resource are transmitted in a case that the grant-less communication scheme is selected to perform a transmission,

the information necessary to allocate a radio resource is signaled by prescribed identifier, and

in a case of receiving a NACK and radio resource allocation information after the transmission of the user data by using the grant-less communication scheme,

the controller is configured to use the radio resource allocation information to retransmit the user data by using the grant-based scheme.

2. A radio terminal apparatus for communicating with a radio base station apparatus, the radio terminal apparatus comprising:

a transmitter configured to transmit a signal to the radio base station apparatus;

a receiver configured to receive a signal from the radio base station apparatus; and

a controller configured to control the transmitter and the receiver, wherein

the controller is capable of selecting at least a grant-based scheme or a grant-less communication scheme in a case of a transmission of user data,

the user data and information necessary to allocate a radio resource are transmitted in a case that the grant-less communication scheme is selected to perform a transmission, and

the information necessary to allocate the radio resource is a session identifier for identifying a connection between the radio base station apparatus and the radio terminal apparatus.

3. The radio terminal apparatus according to claim 2 , wherein

the controller is configured to manage at least two modes that include a connected state and an idle state,

a connection with the radio base station apparatus is temporarily halted to switch to the idle state,

in a case of resuming the connection along with the transmission of the user data from the idle state, the transmission of the user data is performed by using the grant-less communication scheme, and

in a case of the transmission of the user data, an identifier for identifying the connection with the radio base station apparatus is added and transmitted.

4. The radio terminal apparatus according to claim 2 , wherein

in a case that the grant-less communication scheme is selected to perform the transmission, and that the user data and the information necessary to allocate the radio resource are transmitted,

in a case that a size of the user data is greater than a predetermined value, the controller is configured to perform the transmission in which data for indicating whether subsequent data exists is included.

5. A radio communication method to be used in a radio terminal apparatus for communicating with a radio base station apparatus, the radio communication method comprising:

selecting at least a grant-based scheme or a grant-less communication scheme in a case of transmitting user data; and

transmitting the user data and information necessary to allocate a radio resource in a case of selecting the grant-less communication scheme, wherein

the information necessary to allocate the radio resource is a session identifier for identifying a connection between the radio base station apparatus and the radio terminal apparatus.

6. A radio communication method to be used in a radio base station apparatus for communicating with a radio terminal apparatus, the radio communication method comprising:

selecting at least a grant-based scheme or a grant-less communication scheme in a case of communicating with the radio terminal apparatus;

receiving a signal that includes a first portion including a session identifier and a second portion including user data, the signal being transmitted by the radio terminal apparatus by using the grant-less communication scheme;

in a case that the first portion is received without error and an error in receiving the second portion exists,

allocating to the radio terminal apparatus, a radio resource to be used in the grant-based scheme, and

transmitting to the radio terminal apparatus, a NACK and the radio resource allocated; and

in a case that no error in receiving the first portion and the second portion exists, and that the signal received includes information for indicating that subsequent data exists,

allocating to the radio terminal apparatus, a radio resource to be used in the grant-based scheme, and

transmitting to the radio terminal apparatus, an ACK and the radio resource allocated.

7. A radio base station apparatus for communicating with a radio terminal apparatus, the radio base station apparatus comprising:

a transmitter configured to transmit a signal to the radio terminal apparatus;

a receiver configured to receive a signal from the radio terminal apparatus; and

a controller configured to control the transmitter and the receiver, wherein

the controller is capable of selecting at least a grant-based scheme or a grant-less communication scheme in a case of communication with the radio terminal apparatus,

in a case of receiving a signal that includes a first portion including a session identifier and a second portion including user data, the signal being transmitted by the radio terminal apparatus by using the grant-less communication scheme,

in a case that the first portion is received without error and an error in receiving the second portion exists,

the controller allocate, to the radio terminal apparatus, a radio resource to be used in the grant-based scheme, and

a NACK and the radio resource allocated are transmitted to the radio terminal apparatus,

in a case that no error in receiving the first portion and the second portion exists, and that the signal received includes information for indicating that subsequent data exists,

a radio resource to be used in the grant-based scheme is allocated to the radio terminal apparatus, and

an ACK and the radio resource allocated are transmitted to the radio terminal apparatus.