Patent ID: 8565800

Claim:
A wireless base station for performing multiple input multiple output communication with a plurality of mobile terminals, the wireless base station comprising: a selecting unit which selects a mobile terminal, wherein the selected mobile terminal realizes that a parameter satisfies a predetermined criterion, from the plurality of mobile terminals, the parameter being defined by an inverse matrix of a predetermined matrix which is used to calculate a channel capacity between the plurality of mobile terminals and the wireless base station; and an updating unit which updates the inverse matrix based on the selected mobile terminal, every time the mobile terminal is selected by the selecting unit, the selecting unit selecting new mobile terminal, wherein the new mobile terminal realizes that the parameter defined by the updated inverse matrix satisfies the predetermined criterion, from the other mobile terminals except the mobile terminal selected by the selecting unit out of the plurality of mobile terminals, every time the inverse matrix is updated by the updating unit, wherein the inverse matrix B n at the time when n (wherein n is an integer of 1 or more) mobile terminals are selected from the plurality of mobile terminals is B n =(H n H n H +γI n×Nr ) −1 , wherein γ is a value obtained by dividing the number of antennas provided for the wireless base station by a signal-to-noise ratio, I n×Nr is an identity matrix whose number of the rows is the number of antennas provided for the mobile terminal Nr×n, and H n is a channel matrix of the selected n mobile terminals, and the updating unit obtains the updated inverse matrix B n+1 based on an equation 1 when the (n+1)-th mobile terminal is newly selected by the selecting unit, B n + 1 = [ B n + U 2 H ⁢ U 3 - U 3 H - U 3 C 2 - 1 ] , [ Equation ⁢ ⁢ 1 ] wherein H(k) is a channel matrix of the selected (n+1)-th mobile terminal, U 1 =H(k)H n H , U 2 =U 1 B n , U 3 =C 2 −1 U 2 , and C 2 =G(k)−U 2 U 1 H =(H(k)H(k) H +γI)−U 2 U 1 H .