Patent ID: 8477881

Claim:
A method of determining receiver beam forming vectors for a plurality of receivers in a MIMO system, wherein each receiver comprises a plurality of receiver antennae and wherein the MIMO system comprises a plurality of transmitter antennae, the method comprising: quantifying the characteristics of the channels of the MIMO system in a channel property matrix Ψ including interference between individual channels, performing Cholesky decomposition of the channel property matrix row-by-row into a lower triangular matrix with unit elements along its diagonal, a diagonal matrix and the Hermitian transpose of the lower triangular matrix, comprising determining, when performing a step of the Cholesky decomposition for a row, a receiver beam forming vector associated with the row that maximises the component of the diagonal matrix in the row; wherein the matrix quantifying the characteristics of said channel is: H i ⁢ H i H + γ ⁢ ⁢ I N r - ∑ j = 1 i - 1 ⁢ s ij ⁢ s ij H ⁢ q j for i rows/steps of the Cholesky decomposition for i>0, wherein H i is the channel matrix of the receiver associated with a current row/step of the Cholesky decomposition, H i H is the Hermitian transpose of H i , γ is the expectation of noise that will be received I Nr is an N r ×N r identity matrix, wherein N r is the number of receiver antennae of the receiver, s ij is s ij = { H i ⁢ h ⋒ i H q 1 if ⁢ ⁢ j = 1 ( H i ⁢ h ⋒ j H - ∑ n = 1 j - 1 ⁢ s i ⁢ ⁢ n ⁢ l jn * ⁢ q n ) q j if ⁢ ⁢ j > 1 ĥ j H is the Hermitian transpose of r j H j , wherein r j is the receiver beam forming vector associated with the j-th element of the diagonal matrix, H j is the channel matrix associated with the j-th element of the diagonal matrix, q i is: q i = Ψ ii - ∑ k i - 1 ⁢ l ik ⁢ l ik * ⁢ q k wherein: l ij = 1 q j ⁢ ( Ψ ij - ∑ n j - 1 ⁢ l i ⁢ ⁢ n ⁢ l jn * ⁢ q n ) , for ⁢ ⁢ i > j l ij = 1 , for ⁢ ⁢ i = j l ij = 0 , for ⁢ ⁢ i < j Ψ ii = h ⋒ i ⁢ h ⋒ i H + γ ⁢ ⁢ and ⁢ ⁢ ⁢ Ψ ij = h ⋒ i ⁢ h ⋒ j H h ⋒ i = r i ⁢ H i s ij H is the Hermitian transpose of s ij , l jn * is the conjugate of l jn .