Base station apparatus, terminal device, transmission method, and reception method
Good transmission performance is obtained even when the difference between the number of transmit antennas and the number of receive antennas is small. A modulation symbol is subjected to spreading and code multiplexing in a receive antenna direction of a terminal device, is subjected to precoding, and is transmitted. A spreading ratio of a spreading code for performing the spreading in the receive antenna direction is equal to the number of receive antennas of the terminal device. Spreading code multiplexing is performed in the receive antenna direction. Thus, it is possible to provide a base station apparatus and a terminal device providing good transmission performance by changing the number of multiplexing operations even when the difference between the number of transmit antennas and the number of receive antennas is small.
1. A base station apparatus that communicates with a terminal device, comprising:
modulation circuitry that generates modulation symbols from a bit sequence;
code multiplexing circuitry that performs spreading and code multiplexing; and
precoding circuitry that performs precoding from an output from the code multiplexing circuitry; wherein
a maximum spreading ratio of a spreading code with which a spreading in a receive antenna direction is performed is equal to a number of receive antennas of the terminal device.
2. The base station apparatus of claim 1 , wherein the base station apparatus determines a number of operations of the code multiplexing based on information representing the number of the operations of the code multiplexing fed back from the terminal device.
3. The base station apparatus of claim 1 , wherein a weighting matrix of the precoding is selected from a preset codebook.
4. The base station apparatus of claim 1 , wherein the base station apparatus performs a transmission by using a plurality of polarized wave antennas.
5. The base station apparatus of claim 1 , wherein the base station apparatus performs spreading in a time direction in addition to the receive antenna direction.
6. The base station apparatus of claim 1 , wherein the base station apparatus performs spreading in a frequency direction in addition to the receive antenna direction.
7. A terminal device that communicates with a base station apparatus, comprising:
wireless receive circuitry that receives reception signals; and
despreading circuitry that performs despreading in a receive antenna direction on reception signals each received by a corresponding receive antenna; wherein
a maximum spreading ratio of a spreading code with which the despreading in a receive antenna direction is performed is equal to a number of receive antennas.
8. The terminal device of claim 7 , wherein the terminal device feeds back information representing a number of code multiplexing operations to the base station apparatus.
9. The terminal device of claim 7 , wherein the terminal device selects a precoding matrix from a codebook for each of the receive antennas and feeds back information representing the precoding matrix to the base station apparatus.
10. The terminal device of claim 7 , further comprising:
a plurality of polarized wave antennas, wherein
the despreading is performed in a direction of the plurality of polarized wave antennas.
11. A communication method in a base station apparatus that communicates with a terminal apparatus, comprising:
a modulation step of generating modulation symbols from a bit sequence;
a code multiplexing step of performing spreading and code multiplexing; and
a precoding step of performing precoding from output of the code multiplexing step, wherein
a maximum spreading ratio of a spreading code with which the spreading in a receive antenna direction is performed is equal to a number of receive antennas of the terminal apparatus.
12. A communication method in a terminal apparatus that communicates with a base station apparatus, comprising:
a wireless receive step of receiving reception signals; and
a despreading step of performing despreading in a receive antenna direction on reception signals each received by a corresponding receive antenna, wherein
a maximum spreading ratio of a spreading code with which the despreading in the receive antenna direction is performed is equal to a number of receive antennas.