Real-Time Power Allocation on Non-Orthogonal Multiple Access Downlink

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Title:	Real-Time Power Allocation on Non-Orthogonal Multiple Access Downlink
Authors:	王一融;Wang, I-Jung
Contributors:	通訊工程學系
Keywords:	非正交多重存取技術;功率分配;用戶分群;Non-orthogonal mutiple access;Power allocation;User grouping
Date:	2019-07-24
Issue Date:	2019-09-03 15:23:09 (UTC+8)
Publisher:	國立中央大學
Abstract:	近年來，隨著行動通訊技術的演進，行動裝置使用者的人數愈來愈多，尤其是物聯網的加入，更增數倍，所需傳送的資料量也越來越大，因此在有限的頻譜下，最大化資料的傳送量，是目前通訊領域極其重要的一環。現行的長期演進技術 (Long Term Evolution, LTE)下行鏈路採用的是正交分頻多重存取技術 (orthogonal frequency division multiple access, OFDMA)，在對抗多路徑干擾時有較好的表現，並且透過循環前綴 (cyclic prefix, CP)降低符元間干擾(inter-symbol interference, ISI)和載波間干擾 (inter-carrier interference, ICI)。OFDMA是將每一個使用者的資料分配在不同載波上來傳送，但如此一來每個使用者皆使用固定的頻段來接收資料，降低頻譜的使用效率。為了解決頻譜使用效率低的問題，在第五代行動通訊上，各界學者們持續尋找解決辦法，其中一項方案便是非正交多重存取技術 (non-orthogonal multiple access, NOMA)，運用功率域的角度，使用者分別使用不同的功率來乘載，並疊加在一起傳送，如此一來，在同一頻段中即可同時傳送多個使用者資料，大大提升頻譜使用效率。然而在使用NOMA時，接收端必須考慮到消除干擾的問題，目前較常見的方法有連續消除干擾 (successive interference cancellation, SIC)和聯合偵測 (joint-detection)，不管使用哪種方法都會增加接收端的運算複雜度且更加耗電，其中SIC對使用者的傳送功率由為敏感，假若使用者的功率相當，SIC就很難運作，正常的消除干擾。因此本文提出即時功率分配演算法 (real-time power allocation, RTPA)，來提升在使用者功率相當時的傳送品質，模擬結果顯示，在運用RTPA演算法後，可以在不變動系統通道容量的前提下，降低接收的錯誤率，改善SIC因為使用者功率差，所造成的位元錯誤率 (bit error rate, BER)提升。 ;For the past few years, mobile communication develops very fast. The more mobile devices are increasing, the more data are transmitted. Especially the Internet of Things, everything can access to the Internet. Therefore, under the limited spectrum, to maximize the base station throughput is now become the most important issue in the future. Long Term Evolution downlink uses Orthogonal Frequency Division Multiple Access (OFDMA) to transmit signal to UEs, which brings some benefits. OFDMA has better performance to defense multipath interference. In the meantime, cyclic prefix can not only reduce inter-symbol interference but also inter-carrier interference. The data of every UE are transmitted by their own subcarrier from a base station. However, every single UE uses the fixed spectrum to receive signal. It makes the efficient of spectrum become lower. To solve this problem, in the fifth-generation mobile communication, researchers are finding solutions. One of the solutions is Non-Orthogonal Multiple Access (NOMA). To transmit each UE’s signal, the base station uses different transmission power and add them together which method is also known as power domain. Hence, every UE’s data can be transmitted in the same spectrum at the same time. But with NOMA, receivers have to face interference cancellation problem. Currently, the common method to solve the problem are successive interference cancellation (SIC) and joint-detection. No matter which method you use, they always increase the computation complexity of receiver side and consume more electricity. SIC is very sensitive to transmission power. If the transmission power of each UE is almost equivalent, SIC cannot cancel interference completely. In this paper, we propose a real-time power allocation (RTPA) algorithm to improve the transmission performance when UEs’ transmission power is almost equivalent. Simulation results show that after introduce RTPA algorithm, it can reduce error rate at receiver side and improve SIC performance without changing any system channel capacity.
Appears in Collections:	[Graduate Institute of Communication Engineering] Electronic Thesis & Dissertation

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