臺灣博碩士論文加值系統

由於科技的蓬勃發展，未來我們對無線通訊系統的容量需求漸趨嚴苛，這使得非正交多重接取 (non-orthogonal multiple access；簡稱NOMA) 開始受到重視，而在這樣的系統下，使用者之間的干擾便是其中一個我們必須去解決的問題。在論文中，基於NOMA系統的基本架構，為了更進一步提升NOMA下行系統容量，我們提出了一個多輸入多輸出非正交多重接取（multiple-input multiple-output NOMA；簡稱MIMO-NOMA）下行系統。在該系統中我們首先考慮一個基地台（base station；簡稱BS）及四個使用者，這四個使用者會被分成兩個群組，每個群組包含兩個使用者。由於BS端會將欲給兩個群組中的使用者們的訊號疊加後再廣播，因此群組間干擾必然產生。另一方面，在傳統MIMO系統中，MIMO通道的特徵值大小和整體系統容量有非常大的關係。因此，我們提出了聯合使用者分組及預編碼演算法來同時達到將群組間干擾消除及提升整體系統容量。在所提出的演算法中，我們首先利用系統全部MIMO通道的特徵空間來建立分別對應到兩個群組的預編碼器集合，並從其中選出一組可以最大化系統容量的預編碼器，同時完成使用者的分組。然而，由於所提出的聯合演算法是以窮舉搜尋的方式找出最好的一組預編碼器，以致有計算量複雜度的問題。基於如此，我們更進一步提出複雜度較低的改良式演算法。在NOMA系統中，BS端是根據使用者的通道增益來分配功率，因此在同一個群組中，通道增益差異越大的兩個使用者所分到的功率差異就會越大。基於這樣的概念，在此改良式演算法中，BS首先計算所有使用者的MIMO通道增益，接著將增益最大的使用者及增益第三大的使用者安排在同一群組，剩下的兩個使用者則安排在另外一個群組。完成使用者分組後，再根據此群組的MIMO通道建立預編碼器集合，並選出能使系統容量最大的預編碼器。相較於原本所提出之聯合演算法，改良式演算法的計算量複雜度降為其三分之一。最後我們將所提出之MIMO-NOMA系統結合正交分頻多工 (orthogonal frequency-division multiplexing；簡稱OFDM) 的概念以推廣至能夠承載多使用者的下行系統。

In this thesis, we propose a downlink multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) system. We first consider a MIMO-NOMA system with a base station and four users, where the four users are divided into two clusters and the inter-cluster interference is induced in the downlink transmission. With the fact that the eigenvalues of the channel matrix would significantly affect the capacity of a MIMO system, we then propose a joint clustering and precoding algorithm for the MIMO-NOMA system such that not only the inter-cluster interference can be effectively eliminated but also the sum capacity can be enhanced. Specifically, a set of precoder pairs (one pair having two precoders for the two clusters) are first constructed based on the eigenspaces of channel matrices, and then one of them is selected to maximize the sum capacity. Compared to a MIMO orthogonal multiple access (OMA) system, the proposed joint algorithm can provide a larger capacity gain, but involve a high complexity issue due to the need of exhaustive search for the best precoder pair. To reduce the search complexity, we further explore the channel gain of each user and construct a reduced-size precoding set for selection. The modified clustering and precoding algorithm can achieve a close sum capacity to the original one, but reduce the search complexity by a factor of about three. Combined with orthogonal frequency-division multiplexing (OFDM), the proposed MIMO-NOMA scheme can also be extended to the general multiuser case, where every four users share a subband for MIMO-NOMA transmission.

Absrtract i
Contents ii
List of Figures iii
I. Introduction 1
II. Related Work 4
A. System Model 4
B. Zero-Forcing BF in the NOMA-BF System 6
C. Received Signal to Interference plus Noise Ratio (SINR) 6
D. Clustering Algorithm 7
III. System Model 9
IV. Proposed Methods 11
A. Interference Cancellation 11
B. Joint Clustering and Precoding Algorithm 13
C. Modified Clustering and Precoding Algorithm 15
V. Extension to the General Multiuser Case 17
A. The Transmitter of the Base Station 17
1) NOMA Encoding for Each Subband 18
2) OFDM Modulation for Each Antenna 18
B. The Receiver of Each User 19
1) OFDM Demodulation for Each Antenna of Each User 19
2) NOMA Decoding 20
VI. Simulation Results 21
VII. Conclusions 27
References 28

[1] 3GPP TS36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description.
[2] 3GPP TR36.814 (V9.0.0), “Further advancements for E-UTRA physical layer aspects,” Mar. 2010.
[3] Q. Li, H. Niu, A. Papathanassiou, and G. Wu, “5G network capacity: Key elements and technologies,” IEEE Veh. Technol. Mag., vol. 9, no. 3, pp. 71–78, Mar. 2014.
[4] A. Benjebbour, Y. Saito, Y. Kishiyama, A. Li, A. Harada, and T. Nakamura, “Concept and practical considerations of non-orthogonal mutiple access (NOMA) for future radio access,” in Proc. IEEE ISPACS, Okinawa, Japan, Dec. 2013.
[5] Y. Saito, A. Benjebbour, Y. Kishiyama, and T. Nakamura, “System-level performance evaluation of downlink non-orthogonal multiple access (NOMA),” in Proc. IEEE PIMRC, London, UK, Sep. 2013.
[6] P. Wang, J. Xiao, and L. Ping, “Comparison of orthogonal and non-orthogonal approaches to future wireless cellular systems,” IEEE Veh. Technol. Mag., vol. 1, no. 9, pp. 4–11, Sep. 2006.
[7] Z. Ding, Z. Yang, P. Fan, and H. V. Poor, “On the performance of non-orthogonal multiple access in 5G systems with randomly deployed users,” IEEE Signal Process. Lett., vol. 21, no. 12, pp. 1501–1505, Dec. 2014.
[8] B. Kim, S. Lim, H. Kim, S. Suh, and J. Kwun, “Non-orthogonal multiple access in a downlink multiuser beamforming system,” in Proc. IEEE MILCOM, San Diego, CA, Nov. 2013.
[9] G. J. Foschini and M. J. Gans, “On limits of wireless communications in a fading environment when using multiple antennas,” Wireless Pers. Commun., vol. 6, pp. 311–335, Mar. 1998.
[10] E. Telatar, “Capacity of multi-antenna Gaussian channels,” European Trans. Telecommun., vol. 10, pp. 585–598, Nov. 1999.
[11] D. P. Palomar, J. M. Cioffi, and M. A. Lagunas, “Joint Tx-Rx beamforming design for multicarrier MIMO channels: A unified framework for convex optimization,” IEEE Trans. Signal Process., vol. 51, no. 9, pp. 2381–2401, Sep. 2003.
[12] L. Sanguinetti, A. A. D’Amico, and Y. Rong, “A tutorial on the optimization of amplify-and-forward MIMO relay networks,” IEEE J. Sel. Areas Commun., vol. 30, no. 8, pp. 1331–1346, Sep. 2012.
[13] Y. Lan, A. Benjebbour, X. Chen, A. Li, and H. Jiang, “Considerations on downlink non-orthogonal multiple access (NOMA) combined with closed-loop SU-MIMO,” in Proc. IEEE ICSPCS, Gold Coast, Australia, Dec. 2014.
[14] Q. Sun, S. Han, C.-L. I, and Z. Pan, “On the ergodic capacity of MIMO NOMA systems,” IEEE Wireless Commun. Lett., vol. 4, no. 4, pp. 405–408, Aug. 2015.
[15] R. van Nee and R. Prasad, OFDM for Wireless Multimedia Communications. Artech House, 2000.
[16] D. Tse and P. Viswanath, Fundamentals of wireless communication. Cambridge University Press, 2005
[17] H. Abdzadeh-Ziabari, M. G. Shayesteh, and M. Manaffar, “Robust timing and frequency synchronization for OFDM systems,” IEEE Trans. Veh. Technol., vol. 60, no. 8, pp 3646–3656, Oct. 2011.