Patent ID: 8234549

Claim:
A method comprising the steps of: estimating quadrature amplitude modulated QAM symbols in an LDPC encoded OFDM signal for transmission; performing channel estimation to determine channel estimates in reception of the LDPC encoded OFDM signal; and obtaining channel information for use in detection and decoding of the LDPC encoded signal, wherein the estimated QAM symbols are related to the channel distortion introduced by fiber optical signals, phase shift of the QAM symbols due to chromatic dispersion and self-phase modulation and wherein a λ-configuration, denoted as t-(v,k,{0, 1, . . . λ}), is a collection of k-subsets (blocks) of a v-set V such that every t-subset of V is contained in at most λ of the blocks and let λ 1 - and λ 2 -configurations, denoted as t-(v 1 ,k 1 ,{0, 1, . . . , λ 1 }) and t-(v 2 ,k 2 ,{0, 1, . . . , λ 2 }) be given, denote the number of blocks in λ 1 - and λ 2 -configurations by b 1 and b 2 , respectively; and the corresponding set of blocks by B 1 and B 2 , respectively, the v 1 v 2 -elements in the product configuration are ordered pair of elements (e 1 ,e 2 ), with e 1 belonging to B 1 and e 2 belonging to B 2 , b=└b 1 /k 1 ┘·└b 2 /k 2 ┘ blocks of a product configuration are obtained as follows, with └ ┘ denoted the largest integer less than or equal to the enclosed quantity, let the blocks from B 1 be grouped into └b 1 /k 1 ┘ classes of k 1 blocks each, the first block in a product configuration is obtained as a k 1 k 2 -block of ordered pair of elements ((α 1 ,β 1 ), . . . , (α 1 ,β k2 ), . . . , (α k1 ,β 1 ), . . . , (α k1 ,β k2 )), with α i (i=1, . . . , k 1 ) belonging to the first block of B 1 , and B i (i=1, . . . , k 2 ) belonging to the first block in B 2 and the LDPC encoding comprises a first class code rate obtained by taking one block from the first class in B 1 at the time and one block in B 2 out of the first k 2 blocks and creating a product block.