類循環低密度偶校碼(quasi-cyclic low-density parity-check codes)是一種具代數結構的低密度偶校碼，在硬體實現及分析上的複雜度皆可大幅降低。有非均等錯誤保護(unequal error protection)的類循環低密度偶校碼，可以依據其偶校矩陣將其碼字元(codeword bit)分成多個部分，各自有著不同的改錯能力，藉此加強保護較重要的訊息。
混合式自動重傳請求(hybrid automatic repeat request)機制常被使用於變動頻繁的通道，藉此減少重傳的次數。而其中一種增量冗餘(incremental redundancy)的混合式自動重傳請求機制是透過適應通道狀況決定要額外多傳冗餘字元的數量來增加流通量(throughput)。在增量冗餘的混合式自動重傳請求機制中，通常是使用有相容碼率能力(rate-compatibility)的錯誤更正碼。
在此篇論文中，我們使用非均等錯誤保護類循環低密度偶校碼，並且採用穿刺(puncturing)的技術來適應所需的碼率。我們提出了一個混合式自動重傳請求機制是應用非均等錯誤保護類循環低密度偶校碼來進行錯誤偵測及更正。電腦模擬結果中可以發現，應用非均等錯誤保護類循環低密度偶校碼之混合式自動重傳請求機制相較於傳統應用有相容碼率能力的低密度偶校碼，在低訊噪比(signal-to-noise ratio)區域有較好的表現。我們也有提出方法去分析所設計機制的流通量。

Quasi-cyclic low-density parity-check (QC-LDPC) codes with structured parity-check matrices have attracted considerable research interest as low-complexity hardware can be implemented for encoding and decoding efficiently. QC-LDPC codes with unequal error protection (UEP) properties have different levels of error-correcting capabilities for each level of subcodewords.
Hybrid automatic repeat request (HARQ) schemes are usually used in applications with fluctuating channel conditions within a certain range of signal-to-noise ratios (SNRs) to reduce the number of retransmissions. The throughput efficiency of the incremental redundancy HARQ (IR-HARQ) scheme can be increased by adapting its additional redundancy to different channel conditions. Rate-compatible (RC) codes have many applications in packet data transmission where adaptive coding and UEP are required. Hence, RC codes are commonly employed in IR-HARQ schemes.
Since UEP QC-LDPC codes already have UEP properties, we adopt puncturing techniques to adapt UEP QC-LDPC codes to the required coding rates. We propose a modified IR-HARQ scheme that uses UEP QC-LDPC codes for error correction and detection. Simulation results show that the proposed scheme with UEP QC-LDPC codes have advantages over those using conventional RC-LDPC codes at low SNR regimes. Furthermore, the cor-responding throughput performance is also analyzed.

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