Determining first modulation and coding scheme applied to signal based on predicted communication quality of signal when transmitted and retransmitted
[Problem] According to conventional techniques, a modulation class is determined on the basis of past communication environment information stored at a base station, and the modulation class cannot be determined with consideration of a communication environment in which a signal is retransmitted. Thus, with the conventional techniques, a modulation and coding scheme cannot be determined with consideration of the communication environment in which the signal is retransmitted. [Solution] An embodiment of this communication system has a control unit that determines a first modulation and coding scheme to be applied to a signal on the basis of information about predicted first communication quality when a signal is transmitted at a first timing and information about predicted second communication quality when the signal is retransmitted at a second timing.
1. A base station device comprising:
a control unit implemented at least in hardware comprising a processor and memory, for determining a first modulation and coding scheme to be applied to a signal, based on information on predicted first communication quality when the signal is transmitted at a first timing and information on predicted second communication quality when the signal is retransmitted at a second timing; and
a transmission unit implemented at least in the hardware, for transmitting information on the first modulation and coding scheme to the terminal device, wherein
when the information on the first communication quality is a first value and the information on the second communication quality is a second value, the control unit determines the first modulation and coding scheme, based on a value obtained by adding an offset value to the first value, the offset value being determined based on a difference between the first value and the second value.
2. The base station device according to claim 1 , wherein when the second communication quality is lower than the first communication quality, the control unit determines the first modulation and coding scheme, based on the information on the second communication quality.
3. The base station device according to claim 1 , wherein when the information on the first communication quality is a first value and the information on the second communication quality is a second value, the control unit determines the first modulation and coding scheme, based on an average value of the first value and the second value.
4. The base station device according to claim 1 , wherein when the second communication quality is lower than the first communication quality, the control unit determines a modulation and coding scheme, in which a number of bits transmittable per one symbol is smaller than a number of bits of the second modulation and coding scheme determined based on the first information, as the first modulation and coding scheme.
5. The base station device according to claim 1 , wherein the base station device is a small cell base station device and a neighboring base station device adjacent to the base station device is a macro cell base station device,
an almost blank subframe (ABS) subframe and a non-ABS subframe are set in the macro cell base station device,
the first timing is a timing of the ABS subframe,
the second timing is a timing of the non-ABS subframe,
the information on the first communication quality is information on communication quality when the signal is transmitted between a terminal device and the small cell base station device at the timing of the ABS subframe, and
the information on the second communication quality is information on communication quality when the signal is transmitted between the terminal device and the small cell base station device at the timing of the non-ABS subframe.
6. A terminal device comprising:
a reception unit implemented at least in hardware including a processor and memory, for receiving, from a base station device, information on a first modulation and coding scheme determined based on first information on predicted first communication quality when a signal is transmitted at a first timing and second information on predicted second communication quality when the signal is retransmitted at a second timing; and
a transmission unit, implement at least in the hardware, for transmitting the signal to the base station device, based on the information on the first modulation and coding scheme, wherein
when the information on the first communication quality is a first value and the information on the second communication quality is a second value, the first modulation and coding scheme are determined based on a value obtained by adding an offset value to the first value, the offset being determined based on a difference between the first value and the second value.
7. A communication system comprising a base station device and a terminal device, wherein
the base station device comprises:
a control unit implemented at least in hardware including a processor and memory, for determining a first modulation and coding scheme to be applied to a signal, based on information on predicted first communication quality when the signal is transmitted at a first timing and information on predicted second communication quality when the signal is retransmitted at a second timing;
a transmission unit implemented at least in the hardware, for transmitting information on the first modulation and coding scheme to the terminal device, wherein
when the information on the first communication quality is a first value and the information on the second communication quality is a second value, the first modulation and coding scheme are determined based on a value obtained by adding an offset value to the first value, the offset being determined based on a difference between the first value and the second value, and
the terminal device
receives the information on the first modulation and coding scheme from the base station device.