The objective of this dissertation is to investigate incremental redundancy low-density parity-check (IR-LDPC) codes for hybrid forward error correction / automatic repeat request (HybridARQ) schemes. Powerful capacity-approaching IR-LDPC codes are one of the key functional elements in high-throughput HybridARQ schemes and provide a flexible rate-compatible structure, which is necessary for low-complexity HybridARQ schemes. This dissertation first studies the design and performance evaluation of IR-LDPC codes, which have good error rate performance at short block lengths. The subset codes of the IR-LDPC codes are compared to conventional random punctured codes and multiple dedicated codes. As a system model for this work, an adaptive LDPC coded system is presented. This adaptive system can confront the nature of time-varying channels and approach the capacity of the system with the aid of LDPC codes. This system shows remarkable throughput improvement over a conventional punctured system and, for systems that use multiple dedicated codes, provides comparable performance with low-complexity at every target error rate. This dissertation also focuses on IR-LDPC codes with a wider operating code range because the previous IR-LDPC codes exhibited performance limitation related to the maximum achievable code rate. For this reason, this research proposes a new way to increase the maximum code rate of the IR-LDPC codes, which provides throughput improvement at high throughput regions over conventional random punctured codes. Also presented is an adaptive code selection algorithm using threshold parameters. This algorithm reduces the number of the unnecessary traffic channels in HybridARQ schemes. This dissertation also examines how to improve throughput performance in HybridARQ schemes with low-complexity by exploiting irregular repeat accumulate (IRA) codes. The proposed adaptive transmission method with adaptive puncturing patterns of IRA codes shows higher throughput performance in all of operating code ranges than does any other single mode in HybridARQ schemes.

Automatic Repeat-reQuest (ARQ) schemes are extensively used in communication systems and computer networks to achieve reliable transmission. Using space-time codes (STCs) with multiple input multiple output (MIMO) or multiple input single output (MISO) systems is an effective way to combat multipath fading, which is the most severe impairment for wireless communication systems. STCs are designed to use the rich scattering multipath environment provided by using multiple transmit antennas. The work done in this thesis focuses on the use of ARQ schemes with non-orthogonal space-time block codes (NOSTBCs) based on Reed Solomon codes. The truncated-selective ARQ (TS-ARQ) scheme is considered and three novel hybrid ARQ (HARQ) schemes are proposed. Simulation results reveal that, compared to using TS-ARQ with orthogonal space-time block codes (OSTBCs), using NOSTBCs with any of the three proposed HARQ schemes can provide significant gains in terms of dropped packet rate and spectral efficiency at the cost of increased decoding complexity. The performance can be further improved by using the water filling principle to adaptively allocate transmit power among transmit antennas.