Construction and performance analysis of moderate-length rate-compatible LDPC codes

Rate-compatible coding is appropriate for communication systems that may experience a range of operating SNRs but that seek to adhere to a single underlying codec structure. This paper proposes two special and efficient approaches: extending and information-nulling, to build low rate codes from high rate LDPC codes (mother codes) of moderate length (10³<N< 10⁴). Both the two proposed approaches result in better performances than punctured RC-LDPC codes at low code-rates. Extending leads to good performance at rate about 0.4-0.6, but which has not so good performance at high rates (about 0.6-0.8). The threshold of extended code rates is pointed out for the first time, which rests with the code-rate of the mother code. Information-nulling, which results in acceptable performance at high rates, and also good performance at low rates without any threshold of code rates, is confirmed to have a wider rate range and lower computation complexity than extending.