A Scalable LDPC Coding Scheme for Adaptive HARQ Techniques

In wireless communication systems, the achievable data rates are always dependent on the characteristics of the wireless channel. Although a system is designed for an expected channel link quality, the channel may deteriorate for certain periods of time due to the changing nature of the propagation environment. A weak channel may lead to transmission errors, which can be corrected by employing Hybrid Automatic Repeat Requests (HARQ). In particular, type II HARQ protocols have become an appealing option since they only involve the transmission of additional parity bits, instead of repeating the original transmission. These additional parity bits can be obtained by puncturing a low rate channel code. However, finding an optimum pattern of puncturing for a specific code is non-trivial. In this work, we propose a retransmission scheme that considers various Low-Density Parity-Check (LDPC) codes of different rates that can be concatenated to perform the encoding and decoding operations, resulting in a lower encoding overhead for successful transmissions, while maintaining efficient decoding. We show that this technique can maintain high throughput and goodput, and a low outage probability, even when the received signal power is suddenly reduced due to the loss of the Line-of-sight (LOS) component.