在區塊衰落通道下以短長度極化碼混合式進行自動重送請求的非正交多工接取

Abstract

在本論文中，我們在物聯網架構中中考慮了一種無允諾接取的非正交多重接取系統，並於其中使用極化碼的遞增冗餘混合式自動重送請求。 在物聯網應用中，由於設備的功率限制，需要考慮短封包的傳遞；因為極化碼在短碼區域的性能優於低密度奇偶檢查碼，我們選擇極化碼而不是低密度奇偶檢查碼進行研究。 我們在本論文的模擬中設置信噪比大於零分貝，因為當信噪比小於零分貝時失效機率太高以致無法執行無允諾接取系統；而為了在該系統中實現更高的流通量，我們使用打孔極化碼來執行遞增冗餘混合式自動重送請求。 在我們的演算法中，我們將首先會通過打孔長度的錯誤機率來決定重傳長度；而我們的流通量比已被提出的算法要高，而且與其相比我們的系統更加簡單，因為我們不需要傳輸重傳長度。此外，我們考慮了加性高斯白雜訊信道和馬爾可夫模型的區塊衰落通道；而我們提出的基於等效長度的方法在衰落信道中能夠實現比既有方法更高的流通量；並且我們在這兩個系統中計算出它們的上界。 在非正交多重接取系統中，我們使用內插法來逼近我們算法中使用的參數，以防止存儲過多信噪比的參數組合。此外，我們應仔細選擇極化碼的消息集合以避免打孔具有高可靠性的位子。

In this thesis, we consider a non-orthogonal multiple access (NOMA) system for grant-free access with the polar coded incremental redundancy hybrid automatic repeat re-Quest (IR-HARQ) in the Internet of Things (IoT). In IoT applications, the short packet is considered due to the power limit of the devices. We choose polar codes rather than low-density parity-check(LDPC) codes since polar codes can outperform LDPC codes in the shortcode region. In our simulation, we set signal-to-noise ratio(SNR)$>$0dB in this thesis since the outage probability is too high when SNR$<$0dB to perform grant-free access. To achieve higher throughput in this system, we use punctured polar code to perform IR-HARQ. In our algorithms, we will first decide the re-transmission length by the error probability of punctured length. Our throughput is higher than the proposed algorithm, and we do not need to transmit the re-transmission length. Furthermore, we consider the additive white Gaussian noise (AWGN) channel and the Markov model for the block fading channel. The equivalent-length-based method is applied in our system to achieve higher throughput in fading channel. In both systems, we calculate an upper bound of them. In the NOMA system, we use interpolation to approximate parameters used in our algorithm to prevent storing too many parameters of the combination of SNR. The information bit set should be chosen carefully to avoid puncturing bits with high reliability.