In a Multiple-Input Multiple-Output (MIMO) system interference channel, a preferable precoding matrix generally needs to be selected for a transmitting end to improve performance of the system. The prior art provides a precoding matrix calculation method with manual rank reduction, which may calculate the preferable precoding matrix. Specific implementation steps are as follows.
1. In a MIMO system, each receiving end performs measurement and feeds back a channel matrix to a transmitting end corresponding to the receiving end. A constraint on the maximum number of data streams simultaneously transmitted is set at each transmitting end (the maximum number of data streams simultaneously transmitted is a rank of a precoding matrix), and a precoding matrix is initialized according to the constraint and the channel matrix.
2. In the MIMO system, each transmitting end updates its own precoding matrix in turn as follows: A certain transmitting end (hereinafter referred to as a first transmitting end) obtains an autocorrelation matrix of interference generated by another transmitting end at a receiving end (hereinafter referred to as a first receiving end) corresponding to it. The information may be measured by the first receiving end and fed back by the first receiving end to the first transmitting end. Then, the first transmitting end reduces a rank of a channel matrix of a signal link (hereinafter referred to as a first link) of itself according to the constraint of itself on the maximum number of data streams simultaneously transmitted, so that a rank of the channel matrix after rank reduction is not greater than the maximum number of data streams simultaneously transmitted. Finally, the first transmitting end calculates, according to the channel matrix after rank reduction and the autocorrelation matrix of interference, a precoding matrix for maximizing channel capacity of the first link, and transmits data by using the precoding matrix.
3. Updating in step 2 is executed on each transmitting end repeatedly until convergence (that is, there are few changes between a precoding matrix after updating and the precoding matrix before updating).
However, when the foregoing precoding matrix calculation method with manual rank reduction is adopted, rank reduction may be performed on an actual channel matrix to reduce mutual interference between different links, which improves the system performance to a certain extent, but the method cannot make full use of a spatial feature of the channel matrix, therefore, the obtained system performance is still poor.