Unequal Error Protection Raptor Codes

We design Unequal Error Protection (UEP) Raptor codes with the UEP property provided by the precode part of Raptor codes which is usually a Low Density Parity Check (LDPC) code. Existing UEP Raptor codes apply the UEP property on the Luby transform (LT) code part of Raptor codes. This approach lowers the bit erasure rate (BER) of the more important bits (MIB) of the data decoded by the LT part of the decoder of Raptor code at the expense of degrading the BER performance of Less Important Bits (LIB), and hence the overall BER of the data passed from the LT part to the LDPC part of the decoder is higher compared to the case of using an Equal Error Protection (EEP) LT code. The proposed UEP Raptor code design has the structure of UEP LDPC code and EEP LT code so that it has the advantage of passing data blocks with lower BER from the LT code part to the LDPC code part of the decoder. This advantage is translated into improved performance in terms of required overhead and achieved BER on both the MIB bits and LIB bits of the decoded data compared to UEP Raptor codes applying the UEP property on the LT part. We propose two design schemes. The first combines a partially regular LDPC code which has UEP properties with an EEP LT code, and the second scheme uses two LDPC codes with different code rates in the precode part such that the MIB bits are encoded using the LDPC code with lower rate and the LT part is EEP. Simulations of both designs exhibit improved BER performance on both the MIB bits and LIB bits while consuming smaller overheads. The second design can be used to provide unequal protection for cases where the MIB bits comprise a fraction of more than 0.4 of the source data which is a case where UEP Raptor codes with UEP LT codes perform poorly