Patent ID: 7133642

Claim:
A base station apparatus that performs radio communication with a plurality of mobile station apparatuses concurrently, the base station apparatus comprising: a plurality of antennas provided in a greater number than the plurality of mobile station apparatuses; a receiver that receives a plurality of signals from the plurality of mobile station apparatuses via the plurality of antennas; an estimator that estimates channel estimation values between the plurality of mobile station apparatuses and the plurality of antennas using the plurality of signals; a transformer that performs linear transformation of a plurality of transmission signals using coefficients determined from the channel estimation values estimated in the estimator; and a transmitter that transmits the plurality of transmission signals subjected to linear transformation to the plurality of mobile station apparatuses via the plurality of antennas, wherein: the transformer performs linear transformation of the plurality of transmission signals in accordance with the formula: |Sig out | M×1 =|x| N×M ·|Sig in | N×1 where: N is the number of the plurality of mobile station apparatuses and M is the number of the plurality of antennas; |Sig out | M×1 is a matrix of the plurality of transmission signals subjected to linear transformation in the transformer; |x| N×M is a matrix of the coefficients; and |Sig in | N×1 is a matrix of the plurality of transmission signals before linear transformation in the transformer.