Patent ID: 8811506

Claim:
A base station apparatus communicating with a user terminal in a multi-input multi-output (MIMO) mobile communication system using precoding, the base station apparatus comprising: a receiving unit configured to receive a precoding matrix indicator (PMI) from the user terminal, the PMI indicating a specific precoding vector; a determination unit configured to determine a value of a flag indicator that indicates whether the precoding vector specified by the PMI is to be used for downlink communications; a control signal generation unit configured to generate a downlink control signal including the flag indicator; and a transmission unit configured to transmit a signal including the downlink control signal in a downlink, wherein, when the precoding vector specified by the PMI is not used in the downlink communications, a default vector that is already known by the base station apparatus and the user teuninal is used as the precoding vector in the downlink communications, wherein the flag indicator is expressed in a plurality of bits and designates any one of a plurality of default vectors, wherein the control signal generation unit is configured to perform channel coding on an information part as a coding unit, the information part including control information, the flag indicator, and error detection information, and wherein the error detection information is derived by performing a predetermined calculation on a calculation target including the control information and the flag indicator.