  This paper proposes a class of rate-compatible LDPC codes, called
protograph-based Raptor-like (PBRL) codes. The construction is focused on
binary codes for BI-AWGN channels. As with the Raptor codes, additional parity
bits are produced by exclusive-OR operations on the precoded bits, providing
extensive rate compatibility. Unlike Raptor codes, the structure of each
additional parity bit in the protograph is explicitly designed through density
evolution. The construction method provides low iterative decoding thresholds
and the lifted codes result in excellent error rate performance for
long-blocklength PBRL codes. For short-blocklength PBRL codes the protograph
design and lifting must avoid undesired graphical structures such as trapping
sets and absorbing sets while also seeking to minimize the density evolution
threshold. Simulation results are shown in information block sizes of $k=192$,
$16368$ and $16384$. Comparing at the same information block size of $k=16368$
bits, the PBRL codes outperform the best known standardized code, the AR4JA
codes in the waterfall region. The PBRL codes also perform comparably to DVB-S2
codes even though the DVB-S2 codes use LDPC codes with longer blocklengths and
are concatenated with outer BCH codes.
