本文選題：5G + 多用戶檢測�。� 參考：《電子科技大學(xué)》2017年碩士論文

【摘要】：稀疏碼分多址(Sparse Code Multiple Access,SCMA)技術(shù)是一種面向第五代移動通信(Fifth Generation,5G)系統(tǒng)的新型非正交多址技術(shù)。相對于傳統(tǒng)的正交多址技術(shù),其擁有更高的頻譜利用率和更大的網(wǎng)絡(luò)承載能力,因而成為未來5G空口技術(shù)的研究熱點。與低密度信號(Low Density Signature,LDS)不同,在發(fā)送端,SCMA把星座點映射和擴頻相結(jié)合,直接將二進制比特數(shù)據(jù)映射成多維復(fù)碼字。多維復(fù)星座圖帶來的成型增益使SCMA性能相比于LDS有很大的提升。在接收端,由于碼字稀疏性,SCMA接收機可以利用消息傳遞算法(Message Passing Algorithm,MPA)進行多用戶檢測(Multi-user Detection,MUD),即使在系統(tǒng)嚴重過載的情況下也能獲得很好的性能。MPA算法是一種基于因子圖求邊緣概率分布的迭代算法,該算法中外信息在變量節(jié)點(Variable Node,VN)和函數(shù)節(jié)點(Function Node,FN)之間不斷的傳遞,最后獲得一個穩(wěn)定的概率分布作為判決量,最終最優(yōu)的判決量對應(yīng)的碼字即為判決輸出結(jié)果。相對于聯(lián)合最優(yōu)最大后驗概率(Maximum-a-posteriori,MAP),MPA是一種次優(yōu)的方法,但是MPA利用了碼本的稀疏性,極大地降低了多用戶檢測的復(fù)雜度。雖然MPA算法的復(fù)雜度相對于最優(yōu)的MAP有所降低,但是在系統(tǒng)嚴重過載或碼本尺寸過大的情況下,硬件實現(xiàn)仍然很困難。目前降低MPA復(fù)雜度的方法有很多,如加權(quán)消息傳遞算法(Weighted Message Passing Algorithm,WMPA),串行消息傳遞算法(Shuffled Message Passing Algorithm,SMPA),低映射點的碼本設(shè)計等,這些方法歸結(jié)起來可以分為兩類:一類是改進算法本身,一類是優(yōu)化碼本。本文主要通過改進MPA算法來降低復(fù)雜度,針對上行和下行鏈路分別提出了改進方案。本文的主要工作如下:(1)在上行SCMA系統(tǒng)中,提出了一種基于門限的低復(fù)雜度MPA算法。其基本思路是:在每次迭代完成后,利用門限來選擇置信度高的碼字進行譯碼。由于碼本具有串行干擾消除(Success Interference Cancellation,SIC)特性,相互疊加的用戶中能量大的用戶會很容易被檢測出來。與原始MPA相比,在信噪比較高的情況下,所提算法中絕大多數(shù)用戶不需要迭代到最大迭代步數(shù)就被譯碼,整個譯碼過程中用戶的平均迭代步數(shù)減少,系統(tǒng)復(fù)雜度降低。同時,在門限設(shè)置合適的情況下,可以獲得與原始MPA相當(dāng)?shù)南到y(tǒng)性能。(2)在SMPA基礎(chǔ)上,提出了一種基于壓縮碼本的改進SMPA算法。該算法的主要思想是:利用SMPA的快速收斂特性,及時對發(fā)送概率極低的碼字進行舍棄,從而縮小后續(xù)迭代過程中單個消息更新所需的搜索范圍,進而達到進一步降低SMPA復(fù)雜度的目的。(3)針對下行SCMA系統(tǒng),提出了一種改進的MPA算法。該算法從單個用戶角度考慮,只關(guān)注與該用戶相關(guān)頻點在內(nèi)的部分頻點,在因子圖中消息僅沿著少量的邊進行傳遞。相對于原始的多用戶聯(lián)合檢測MPA算法而言,每次迭代的復(fù)雜度減少,同時,相對于不迭代的MPA所提算法的性能有所提升,因為在迭代后碼字概率分布優(yōu)于初始化的概率分布。
[Abstract]:Sparse Code Multiple Access (SCMA) technology is a new non orthogonal multiple access technology for the fifth generation Fifth Generation (5G) system. Compared with the traditional orthogonal multiple access technology, it has higher spectrum utilization and larger network carrying capacity, thus becoming the research heat of the future 5G empty technology. Different from the low density signal (Low Density Signature, LDS), at the sending end, SCMA combines the constellation point mapping and the spread spectrum to map the binary bit data directly into a multidimensional complex code. The multidimensional complex constellation can improve the SCMA performance greatly compared to the LDS. At the receiver, the SCMA receiver can be a SCMA receiver due to the codeword sparsity. Message Passing Algorithm (MPA) is used to carry out multiuser detection (Multi-user Detection, MUD), even if the system is seriously overloaded, the.MPA algorithm is an iterative algorithm based on the factor graph to calculate the edge probability distribution. The information in this algorithm is in the variable node (Variable Node, VN). The continuous transmission between the function node (Function Node, FN), and finally a stable probability distribution as the judgment, the final optimal decision word is the result of the decision output. Relative to the joint optimal maximum posterior probability (Maximum-a-posteriori, MAP), MPA is a suboptimal method, but MPA uses the thinning of the codebook. The complexity of multiuser detection greatly reduces the complexity of multiuser detection. Although the complexity of the MPA algorithm is lower than the optimal MAP, the hardware implementation is still difficult when the system is seriously overloaded or the size of the codebook is too large. At present, there are many ways to reduce the MPA complexity, such as the weighted message transfer algorithm (Weighted Message Passing). Algorithm, WMPA), the serial message transfer algorithm (Shuffled Message Passing Algorithm, SMPA), the codebook design of low mapping points, and so on. These methods can be divided into two categories: one is to improve the algorithm itself and the other is the optimization of the codebook. This paper is mainly to reduce the complexity by improving the MPA algorithm, and propose to the uplink and downlink respectively. The main work of this paper is as follows: (1) a low complexity MPA algorithm based on threshold is proposed in the uplink SCMA system. The basic idea is that after each iteration is completed, the threshold is used to select a codeword with high confidence level. Because the codebook has a series line interference cancellation (Success Interference Cancellation, SIC) Compared with the original MPA, the majority of the users in the proposed algorithm do not need to be iterated to the maximum number of iterations, and the average iteration number of the user is reduced and the system complexity is reduced in the whole decoding process. Under the appropriate circumstances, the performance of the system equivalent to the original MPA can be obtained. (2) an improved SMPA algorithm based on the compression codebook is proposed on the basis of SMPA. The main idea of this algorithm is to use the fast convergence property of SMPA, to abandon the very low transmission probability in time, and to reduce the single message in the subsequent iteration process. Update the required search range to further reduce the SMPA complexity. (3) an improved MPA algorithm is proposed for downlink SCMA systems. This algorithm is considered from a single user angle, focusing only on the frequency points associated with the user, and the message is transmitted only along a small edge in the factor graph. As far as the initial multiuser joint detection MPA algorithm is concerned, the complexity of each iteration is reduced, while the performance of the algorithm compared with the non iterative MPA is improved because the probability distribution of the codeword probability is better than that of the initialized probability distribution after the iteration.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN929.5

【參考文獻】

相關(guān)期刊論文 前5條

1 文磊;雷菁;魏急波;王建新;;多載波碼分多址在低密度二分圖上的建模與分析[J];國防科技大學(xué)學(xué)報;2016年03期

2 TAO Yunzheng;LIU Long;LIU Shang;ZHANG Zhi;;A Survey: Several Technologies of Non-Orthogonal Transmission for 5G[J];中國通信;2015年10期

3 Lei Wang;Xiuqiang Xu;Yiqun Wu;Shuangshuang Xing;Yan Chen;;Sparse Code Multiple Access-Towards Massive Connectivity and Low Latency 5G Communications[J];電信網(wǎng)技術(shù);2015年05期

4 尤肖虎;潘志文;高西奇;曹淑敏;鄔賀銓;;5G移動通信發(fā)展趨勢與若干關(guān)鍵技術(shù)[J];中國科學(xué):信息科學(xué);2014年05期

5 許耀華;胡艷軍;;基于擬生態(tài)優(yōu)化算法的CDMA多用戶檢測方法[J];電子與信息學(xué)報;2006年11期

，

本文編號：2079175