A system comprising: a parity bit encoder configured to encode successive blocks of n-3 bits with three parity bits to provide successive blocks of n bits; a Gray mapper coupled to said parity bit encoder and configured to map each one of said blocks of n bits to three associated quadrature amplitude modulated (QAM) symbols; a modulator coupled to said Gray mapper and configured to modulate an optical signal in response to an output of said Gray mapper to provide a modulated optical signal comprising said three associated QAM symbols; a detector for receiving said modulated optical signal and providing an electrical signal representative of said optical signal; and a de-mapper configured to provide a de-mapper output representative of said blocks of n-3 bits in response to said electrical signal, wherein said parity bit encoder is configured to position said three parity bits within said n bits according to the following: P 1 is positioned anywhere in the first 2 n / 3 bits; P 2 is positioned anywhere between the 2 n / 3 + 1 th bit and the 5 n / 6 th bit; and P 3 is positioned anywhere between the 2 n / 3 + 1 th and the n th bits that is different from the position of P 2 , where P 1 , P 2 , and P 3 , are first, second and third ones of said three parity bits, respectively, and wherein said three parity bits are calculated according to the following equations: P 1 = XOR x 1 , x 2 , ... , x 2 ⁢ n 3 − 1 ̅ ; P 2 = XOR x i + j , ∀ i , j where j ∈ 0 , n 3 , 2 ⁢ n 3 , i ∈ { 1 , ... n 6 for j ∈ 0 , n 3 1 , ... n 6 − 1 for j = 2 ⁢ n 3 ; and P 3 = XOR x 1 , x 2 , ... , x n − 3 , P 1 , P 2 ̅ , where x 1 , x 2 , ... x n- 3 , are the n-3 bits, respectively. a parity bit encoder configured to encode successive blocks of n-3 bits with three parity bits to provide successive blocks of n bits; a Gray mapper coupled to said parity bit encoder and configured to map each one of said blocks of n bits to three associated quadrature amplitude modulated (QAM) symbols; a modulator coupled to said Gray mapper and configured to modulate an optical signal in response to an output of said Gray mapper to provide a modulated optical signal comprising said three associated QAM symbols; a detector for receiving said modulated optical signal and providing an electrical signal representative of said optical signal; and a de-mapper configured to provide a de-mapper output representative of said blocks of n-3 bits in response to said electrical signal, wherein said parity bit encoder is configured to position said three parity bits within said n bits according to the following: P 1 is positioned anywhere in the first 2 n / 3 bits; P 2 is positioned anywhere between the 2 n / 3 + 1 th bit and the 5 n / 6 th bit; and P 3 is positioned anywhere between the 2 n / 3 + 1 th and the n th bits that is different from the position of P 2 , where P 1 , P 2 , and P 3 , are first, second and third ones of said three parity bits, respectively, and P 1 is positioned anywhere in the first 2 n / 3 bits; P 2 is positioned anywhere between the 2 n / 3 + 1 th bit and the 5 n / 6 th bit; and P 3 is positioned anywhere between the 2 n / 3 + 1 th and the n th bits that is different from the position of P 2 , where P 1 , P 2 , and P 3 , are first, second and third ones of said three parity bits, respectively, and wherein said three parity bits are calculated according to the following equations: P 1 = XOR x 1 , x 2 , ... , x 2 ⁢ n 3 − 1 ̅ ; P 2 = XOR x i + j , ∀ i , j where j ∈ 0 , n 3 , 2 ⁢ n 3 , i ∈ { 1 , ... n 6 for j ∈ 0 , n 3 1 , ... n 6 − 1 for j = 2 ⁢ n 3 ; and P 3 = XOR x 1 , x 2 , ... , x n − 3 , P 1 , P 2 ̅ , where x 1 , x 2 , ... x n- 3 , are the n-3 bits, respectively. <EOS>