Patent ID: 8369461

Claim:
A method for providing a reliability information on information bits (b k ) transmitted in a communications network, said bits constituting a transmitted vector (s) comprising elements selected by a transmitter from a finite alphabet (S), wherein said transmitted vector is detected from an observed vector of received symbols (y) providing a log-likelihood (L), the method comprising: approximating said log-likelihood (L) by defining a number of bit terms having constant size and selecting a subset of bits and marginalizing over a selected part of said subset of bits, wherein said approximation comprises: L ⁡ ( b k | y ) ≈ log ⁡ ( ⁢ ∑ b I 1 = 0 1 ⁢ ⁢ … ⁢ ⁢ ∑ b I k - 1 = 0 1 ⁢ ∑ b I k + 1 = 0 1 ⁢ ⁢ … ⁢ ⁢ ⁢ ⁢ ∑ b I r = 0 1 ⁢ ( max b I r + 1 , ⁢ … ⁢ , b I n t ⁢ m ⁢ μ ⁡ ( b I 1 , … ⁢ , b I k - 1 , 1 , b I k + 1 , … ⁢ , b I n t ⁢ m ) ) ⁢ ∑ b I 1 = 0 1 ⁢ ⁢ … ⁢ ⁢ ∑ b I k - 1 = 0 1 ⁢ ∑ b I k + 1 = 0 1 ⁢ ⁢ … ⁢ ⁢ ⁢ ∑ b I r = 0 1 ⁢ ( max b I r + 1 , ⁢ … ⁢ , b I n t ⁢ m ⁢ μ ⁡ ( b I 1 , … ⁢ , b I k - 1 , 0 , b I k + 1 , … ⁢ , b I n t ⁢ m ) ) ) ⁢ For ⁢ ⁢ k ≤ r ⁢ L ⁡ ( b k | y ) ≈ log ⁡ ( ∑ b I 1 = 0 1 ⁢ ⁢ … ⁢ ⁢ ∑ b I r = 0 1 ⁢ ( max b I r + 1 , ⁢ … ⁢ , b I k - 1 , b I k + 1 , ⁢ … ⁢ , b I n t ⁢ m ⁢ ⁢ ⁢ μ ⁡ ( b I 1 , … ⁢ , b I k - 1 , 1 , b I k + 1 , … ⁢ , b I n t ⁢ m ) ) ∑ b I 1 = 0 1 ⁢ ⁢ … ⁢ ⁢ ∑ b I r = 0 1 ⁢ ( max b I r + 1 , ⁢ … ⁢ , b I k - 1 , b I k + 1 , ⁢ … ⁢ , b I n t ⁢ m ⁢ ⁢ ⁢ μ ⁡ ( b I 1 , … ⁢ , b I ⁢ ⁢ b I k + 1 , … ⁢ , b I n t ⁢ m ) ) ) ⁢ For ⁢ ⁢ k > r , ⁢ where ⁢ ⁢ ⁢ μ ⁡ ( b 0 , … ⁢ , b n t ⁢ m ) ⁢ = Δ ⁢ exp ⁡ ( - 1 N 0 ⁢  y - Hs ⁡ ( b 0 , … ⁢ , b n t ⁢ m )  2 ) wherein each bit in said vector (s) is enumerated as {b k } { b k } k = 1 n t ⁢ m , wherein n t is the number of transmit antennas and m the number of transmitted bits, r is a fixed integer in an interval 0≦r≦n t m−1 I is an index permutation on [1, . . . , n t m] such that b 1 , b 2 , . . . , b n t m enumerate the bits in increasing order of reliability, k is 1≦k≦n t m, and for a given k let k′ is a uniquely defined integer such that l k′ =k, s(b 0 , . . . , b ntm ) is the vector s which corresponds to the bits {b 1 , . . . , b ntm }, H is a channel matrix of dimension n r ×n 1 , where n r number of receive and n t transmit antennas, and N 0 is rower spectral density of noise.