在5G網路下針對稀疏碼多工存取的低複雜度多用戶偵測器設計

大規模機器通信（mMTC）是5G三種主要使用場景之一。在即將到來的物聯網（IoT）時代，所有的設備都將被連接起來。目前在3GPP標準會議上有數個實現這個目標的提案。其中引起大量注意的稀疏碼多工存取(SCMA)實現了用於mMTC網絡的上行免核可非正交多工存取(Uplink Grant-Free NOMA)。SCMA源自於低密度簽記(Low Density Signature)系統，具有低的訊號傳輸成本、低傳輸延遲和高頻譜效率的優點。本論文主要在研究低複雜度與高性能的SCMA多用戶接收機設計。在第三章中，介紹了SCMA和LDS系統的原理。並對加成性白色高斯雜訊通道和上行多路徑衰減通道進行了實體層模擬。首先，我們設計了SCMA碼簿和低密度簽記，並分析了它們的BER性能和收斂行為。特別一提的是，我們也考慮了不同的擴展長度、過載程度、接收機多樣性以及遠近效應來進行分析。在第四章中，我們針對基本的SCMA系統設計了低複雜度的多用戶偵測，包括對應的因子圖和消息傳遞算法。為了提高收斂速度以及降低後面MPA迴圈的複雜度，提出了基於SINR的訊息傳遞演算法(SS-MPA)和基於碼簿基數化減的訊息傳遞演算法(CCR-MPA)。接著我們驗證這兩種方法的有效性。電腦模擬結果顯示SS-MPA在上行多徑衰落信道上的收斂速度比傳統MPA快。而CCR-MPA降低了傳統MPA複雜度的50％〜80％，其中CCR-MPA仍保留了固定複雜度的特性來增加硬體實現的可行性。在論文的最後，我們針對渦輪式稀疏碼多工存取(Turbo-SCMA)系統設計了高性價比的多用戶接收機。藉由迭代偵測和解碼以及我們提出的方法，此接收機可以達到很好的錯誤率性能，且與最先進的文獻相比，減少了大量的記憶體使用量和計算複雜度。

關鍵字

非正交多工存取；訊息傳遞演算法；多用戶偵測；稀疏碼多工存取；低密度簽記；渦輪接收機

並列摘要

Massive Machine Type Communications (mMTC) is one of the three major types of 5G use cases. In the coming era of Internet of Things (IoT), all devices will be connected. Currently there are several proposals for achieving this objective in the 3GPP standard meetings. One promising technology, called sparse code multiple access (SCMA), implements uplink grant-free non-orthogonal multiple access (NOMA) for mMTC networks. SCMA is derived from the low-density spread OFDM (LDS-OFDM) and has the advantages of low signaling overhead, low transmission latency, and high spectral efficiency. In this thesis, we focus on low complexity and high performance multiuser receiver design for SCMA systems. In the Chapter 3, we introduce the principle of SCMA and LDS systems and conduct physical layer simulation for AWGN channel and uplink multipath fading channel. To start with, we design the SCMA codebook and low-density signature (LDS) and analyze their BER performance and convergence behavior. It is worth mentioning that different spreading length, overloading ratio, receiver diversity and near-far effect are also taken into account in our analysis. In the Chapter 4, we design the low complexity multiuser detection for the basic SCMA system, including the factor graph and the message passing algorithm. To improve the convergence rate and reduce the MPA complexity of later iterations, SINR based Serial MPA (SS-MPA) and codebook cardinality reduction based MPA (CCR-MPA) are proposed. To validate the effectiveness of these two methods, we conduct simulations to show that SS-MPA converges faster than traditional methods on the uplink multipath fading channel and CCR-MPA reduces 50% to 80% complexity of conventional MPA while the characteristic of fixed complexity is retained to facilitate the realization of the hardware implementation. At the end of the thesis, we design the cost-efficient multiuser receiver for turbo sparse code multiple access (Turbo-SCMA) system. By iterative detection and decoding (IDD) and our proposed methods, the receiver achieves high BER performance and reduces a lot of memory usages and computational complexity compared with state state of the art method.

並列關鍵字

Non-Orthogonal Multiple Access (NOMA) ； Message Passing Algorithm (MPA) ； Multiuser Detection (MUD) ； Sparse Code Multiple Access (SCMA) ； Low Density Signature (LDS) ； Turbo Receiver

參考文獻

[4] L. Dai, B. Wang, Y. Yuan, S. Han, C.-I. I, and Z. Wang, “Non-orthogonal multiple access for 5G: Solutions, challenges, opportunities, and future research trends,” IEEE Commun. Mag., vol. 53, no. 9, pp. 74–81, Sep. 2015.

[5] Y. Yuan et al., “Non-orthogonal transmission technology in LTE evolution,” IEEE Commun. Mag., vol. 54, no. 7, pp. 68–74, Jul. 2016.

[6] Saito, Y. and et al., “Non-Orthogonal Multiple Access (NOMA) for Future Radio Access,” in Proc. IEEE VTC, June 2013.

[7] H. Nikopour and H. Baligh, “Sparse code multiple access,” in Proc. PIMRC, 2013, pp. 332–336.

[8] R. Hoshyar, F. P. Wathan, and R. Tafazolli, “Novel low-density signature for synchronous CDMA systems over AWGN channel,” IEEE Trans. Signal Process., vol. 56, no. 4, pp. 1616–1626, Apr. 2008.

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在5G網路下針對稀疏碼多工存取的低複雜度多用戶偵測器設計

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