1. A computer system comprising: a central processing unit; a detection module coupled to the central processing unit for detecting a plurality of base stations (i=1−n) neighboring the computer system; and a storage device coupled to the central processing unit for storing a programming code, and the programming code is utilized to instruct the central processing unit to process a method for a wireless communication system comprising a mobile device and the plurality of base stations, the method comprising: obtaining a geometric matrix as H = [ e 11 e 12 e 13 1 e 21 e 22 e 23 1 ⋮ ⋮ ⋮ ⋮ e n ⁢ ⁢ 1 e n ⁢ ⁢ 2 e n ⁢ ⁢ 3 1 ] according to a plurality of relative distances between the mobile device and the plurality of base stations, wherein e i ⁢ ⁢ 1 = x ^ - X i r ^ i , e i ⁢ ⁢ 2 = y ^ - Y i r ^ i , e i ⁢ ⁢ 3 = z ^ - Z i r ^ i , ( X i , Y i , Z i ) represents a position coordinate of the i th base station, ({circumflex over (x)},ŷ,{circumflex over (z)}) is utilized as a simplified position coordinate, and e i1 2 +e i2 2 +e i3 2 =1 is satisfied; obtaining a weighted matrix as W = [ 1 / σ 1 2 0 0 0 0 0 1 / σ 2 2 0 0 0 0 0 1 / σ 3 2 0 0 0 0 0 ⋱ 0 0 0 0 0 1 / σ n 2 ] = [ k 1 0 0 0 0 0 k 2 0 0 0 0 0 k 3 0 0 0 0 0 ⋱ 0 0 0 0 0 k n ] according to the mobile device and the plurality of base stations, wherein σ i represents a covariance related to a corresponding one of the plurality of base stations, and k i represents a reciprocal value of each corresponding covariance; obtaining a weighted geometric dilution of precision (WGDOP) as WGDOP=√{square root over (tr(H T WH) −1 )} according to the weighted matrix and the geometric matrix, so as to obtain a WGDOP closed form; and choosing a plurality of selected base stations from the plurality of base stations according to the WGDOP closed form, so as to position the mobile device.