Patent ID: 8498329

Claim:
An apparatus comprising: a multiple-user mean-squared error (MMSE) equaliser configured to receive signals from a number of users and to equalise signals received from the users and to operate according to: {tilde over (G)} S =Mσ m,i 2 F m H F −1 [M 2 σ m,i 2 F m m H F −1 +Mσ v 2 I+W] −1 wherein {tilde over (G)} s is the equaliser, M is the total number of users, σ m,i 2 denotes a signal power of an ith transmitted block of a signal received from a mth user, F is the Fast Fourier Transform (FFT) matrix, F −1 is Inverse Fast Fourier Transform (IFFT) matrix, m is the P×P circulant matrix with its first column containing time domain channel taps of the mth user, where P is a block length, σ v 2 is the noise variance, I is the P×P identity matrix and W denotes a P×P matrix allowing to take into account Multi-User Interference (MUI) and Inter-Block Interference (IBI) due to the asynchronous reception among the users; wherein: W = FD m H ⁡ ( ∑ a = 1 N a ⁢ ( σ a , i 2 + σ a , i - 1 2 ) ⁢ ( A 4 , a ⁡ ( c a ⁢ c a H ⊗ I ) ⁢ A 4 , a H ) + ∑ b = 1 N b ⁢ ( σ b , i 2 + σ b , i + 1 2 ) ⁢ ( Δ 2 , b ⁡ ( c b ⁢ c b H ⊗ I ) ⁢ A 2 , b H ) ) ⁢ D m ⁢ F - 1 wherein: D m is the dispreading matrix for a first user; N a is the number of users from which signals arrive after an arrival of a signal from the first user; N b is the number of users from which signals arrive before the arrival of the signal from the first user; σ a,i and σ b,i denote the signal power of the ith transmitted block of the ath and bth user respectively; A 4,a is an upper triangular Toeplitz matrix with first row being [0 1×MP−(L−1+τ a −L CP ) h a (L−1) . . . h a (L CP −τ a +1)]; Δ 2,b is a lower triangular Toeplitz matrix with the first column being [0 1×MP−τ b , −h b (0), . . . , −h b (τ b −1)] T ; L is the channel length; τ a is a delay between receipt of a signal from the ath user and of a corresponding signal from the synchronized user; τ b is a delay between receipt of a signal from the bth user and of a corresponding signal from the synchronized user; L CP is the length of a cyclic prefix used; h a (i) and h b (i) denote the ith channel tap for the ath and bth user respectively; c a and c b are the spreading codes for the ath and bth users respectively; and denotes the Kronecker product.