Incremental redundancy hybrid automatic repeat request (IR-HARQ) based on
quasi-cyclic (QC) low density parity check (LDPC) codes can improve transmission
robustness with a trade-off of additional latency. This thesis proposes an IR-HARQ
with a packet combining scheme, called superposed IR-HARQ (SIR-HARQ), for
the fifth telecommunication generation (5G) new radio (NR) communications and
beyond. The proposed SIR-HARQ can maximize data rate such that number of
required slots for re-transmission can be minimized to support ultra reliable and
low latency communications (URLLC) applications. The proposed SIR-HARQ performs
a packet combining of two packets, i.e., (i) the parity of unrecoverable packets
and (ii) the parity of new packet to be transmitted together using XOR operations,
following LDPC rules.
This thesis performs a series of computer simulations to evaluate bit-error-rate
(BER) performances and decoding behavior of the proposed SIR-HARQ scheme
under Additive White Gaussian Noise (AWGN), slow Rayleigh fading, and fast
Rayleigh fading channels. Extrinsic information transfer (EXIT) chart analysis is
also performed in this thesis to evaluate the decoding behavior of the codes.
This thesis has revealed the IR mechanism of 5G NR QC-LDPC codes due to
the use of extended parity (EP), such that, 5G NR QC-LDPC codes should be made
rateless to support IR-HARQ. From the obtained results, this thesis found that the
proposed SIR-HARQ requires signals having mutual information (MI) beyond 0.5
to effectively decode the packet, which is still practical since the MI can be estimated
even only using the log-likelihood ratio without knowing the information.
This thesis found that SIR-HARQ based on MI can outperform the conventional
IR-HARQ in terms of BER performances and data rate. The proposed SIR-HARQ
is expected to be used for ultra reliable low latency communication (URLLC) and
enhanced mobile broadband (EMBB).
Keywords: 5G NR QC-LDPC codes, EXIT Analysis, Superposed codes, IRHARQ.