非正交多工接取下考慮混合式自動重送請求之子頻帶排程技術

Subband Allocation for Non-Orthogonal Multiple Access with Hybrid ARQ

王鈞(Chun Wang)

指導教授 ： 謝宏昀

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201904095

摘要

在本篇論文中，我們研究了非正交多工接取（NOMA）系統下，子頻帶公平排程技術的系統級效能表現。非正交多工的主要核心概念是在發射端波束中，重疊多個用戶信號，並且在接收端使用連續解碼干擾消除（SIC）技術，基站在傳送端會對不同的使用者分配不同的訊號功率，達成將一個資源分配給多個使用者，來獲取系統最大的效能增益。這種下行鏈路傳輸系統可用於增進，符合LTE標準的效能表現。此外，混合式自動重送請求（HARQ）是鏈路適應的重要組成部分，它在現今的無線通信系統中也發揮著重要作用。HARQ的基本概念是透過重新發送未成功解碼的數據分組來獲得信道編碼增益，進而減少用戶的中斷概率，因此可以提高系統的可靠性。為了在傳輸之前降低複雜度和計算資源，在模擬方面，我們使用迭代的演算法來實現在子頻帶排程下，公平分配資源的環境，其目標是尋找最佳的排程，包括各個子頻帶的使用者配對，以及其功率分配係數。為求最大化系統總吞吐量和使用者的公平性，我們採用比例公平演算法（PF）模型，引入最佳化分析方法評估下行NOMA系統的性能。然而在NOMA系統中實行HARQ，比起傳統的OMA寬頻帶系統，NOMA系統下的子頻帶排程更具挑戰性。因為當同時進行複數子頻帶的使用者以及功率分配係數的排程時，在傳輸過程中有使用者以及功率分配的限制。為了解決上述問題，我們提出了一種基於交叉熵方法的啟發式算法解決子頻帶使用者對和功率分配的最佳化問題 PF排程，並用HARQ實現滿足中斷機率的限制。與其他子頻帶排程演算法，如傳統貪婪式演算法和序列貪婪式演算法的性能相比，我們提出的演算法能夠提升約50％的整體資料量。

關鍵字

非正交多工接取 ； 混合式自動重送請求 ； 子頻帶 ； 排程 ； 資源管理

並列摘要

This thesis investigates the system-level performance of non-orthogonal multiple access (NOMA) system. The main concept of NOMA is to transmit composition of multi-user signals in a beam at the transmitter and decode with successive interference cancellation (SIC) at the receiver, which is a promising downlink multiple access scheme for further LTE enhancement. Hybrid automatic repeat request (HARQ) is an essential part of link adaptation, and it is also playing important roles in modern wireless communication system. System with HARQ has channel coding gain by re-transmitting data packets which decoded unsuccessfully. Thus, reliability of system can be improved by reducing outage probability of users. In order to reduce complexity and computing resources before transmission, we simulate the environment which implemented with iterative subband allocation scheduling for user pairs and power allocation coefficient to research the effect of scheduling algorithms. In order to maximize total throughput and fairness, the proportionally fair (PF) scheduling model is adopted, and optimization analysis methods are introduced to evaluate downlink NOMA system performance. However, implementation of HARQ is more challenging in NOMA system with subband scheduling scenario than in traditional OMA widebannd system, because of constraints for scheduling users and power within multiple subbands in the same time. We propose a heuristic algorithm based on cross entropy method to solve the optimization problem about user pair and power allocation for subband PF scheduling, and implement with HARQ in order to meet outage probability constraint and discuss about its benefits and trade-off. Compared with other sub- band allocation algorithms, Simulation results show that proposed algorithm have about 50% performance gain of baseline traditional method and sequential greedy approach.

並列關鍵字

NOMA ； HARQ ； Subband ； Scheduling ； Resource allocation

參考文獻

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