Abstract :
Both constant and variable forward error correcting (FEC) coding is provided by the DVB-S2 system. Variable FEC can be used to provide different levels of error protection according to applications, & may be combined with the use of return channels, to achieve adaptive coding. The novel idea explained in this paper, introduces an algebraic method for construction of well-structured low density parity check (LPDC) codes, enabling the system to switch between LDPC codes of different rates (9/10, 8/9, 5/6, 4/5,...) and perform FEC based on the required level of error protection. In this scheme instead of using different parity check matrices for the different code rates, LDPC codes of different rates are derived by structurally modifying a mother parity check matrix. It is different from the rate-compatible (J. Li, et al., 2002) code construction in the sense that the H-matrix used for different code-rates is independent of the H-matrices used for all other code-rates in the set
