正交分頻多工與多重存取系統中載波頻率位移與符元時序偏移之盲估測

Blind Estimation of Carrier Frequency Offset and Symbol Timing Offset in OFDM and OFDMA Systems

王彥青(Yen-Chin Wang)

指導教授 ： 馮世邁

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201701808

摘要

正交分頻多工和正交分頻多重存取系統已經在許多無線通訊標準中被採用。然而，正交分頻多工取向的的系統對同步誤差如載波頻率位移與符元時序偏移相對敏感。這些同步誤差可能造成子載波間的載波間干擾或是符元信號間的符元間干擾。因此，準確的估計和補償這些同步誤差是非常重要的。在本篇論文中，我們探討正交分頻多工系統中載波頻率位移與符元時序偏移之盲估測，和上行正交分頻多重存取系統中多個載波頻率位移之盲估測。本篇論文包含三個部分。在第一部分，我們為正交分頻多工系統在定值模量調變下提出了一個新的盲蔽符元時序偏移估計器。此被提出之估計器可以在僅使用一個正交分頻多工符元的情況下估計符元時序偏移。除此之外，一個低複雜度演算法也被推導出來實現所述之估計器。在第二部分，我們延伸前述之符元時序偏移估計器至載波頻率位移與符元時序偏移之盲蔽同步估測器。在第三部分，我們為上行正交分頻多重存取系統在定值模量調變下提出一個盲蔽載波頻率位移估計器。此被提出之估計器可以在任何子載波分配設置估計多個載波頻率位移，而大部分現存的估計器只可以在交錯子載波分配設置下估計。更進一步，不像其他現存估計器只能在子載波沒有完全被使用的情況下來估計，我們提出的估計器不論子載波有無完全被使用皆可以估計多個載波頻率誤差。數值模擬結果也被附上來證明這些被提出來的方法或估計器的效能

關鍵字

正交分頻多工 ； 正交分頻多重存取 ； 載波頻率位移 ； 符元時序偏移 ； 盲估測

並列摘要

Orthogonal frequency divsion multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA)have been adopted as a modulation technique in many wireless communication standards. However, OFDM-based systems are sensitive to synchronization errors, such as symbol timing o set (STO) and carrier frequency offset (CFO). These synchronization errors may cause intercarrier interference (ICI) among all subcarriers as well as intersymbol interference (ISI) between successive OFDM symbols. Therefore, accurate estimation and compensation of these synchronization errors are important. In this thesis, we study the blind estimation of STO and CFO in OFDM systems, and the blind estimation of multiple CFOs in uplink OFDMA systems. The thesis includes three parts. In the first part, we propose a new blind STO estimator for OFDM systems with constant modulus (CM) constellation. The proposed estimators can estimate STO with only one OFDM symbol. Besides, a low complexity implementation for the proposed estimator is derived. In the second part, we extend the proposed STO estimation to the blind joint estimation of CFO and STO. In the third part, we propose a blind CFO estimatior for uplink OFDMA systems with constant modulus (CM) constellation. The proposed estimator can estimate multiple CFOs under any kinds of subcarrier assignment, while most of existing methods can only work for the interleaved subcarrier assignment scheme. Moreover, unlike the existing methods which can work for non fully-loaded systems, our methods can work for fully-loaded and non fully-loaded systems. Numerical simulations are also provided to verify the performances of the proposed methods.

並列關鍵字

OFDM ； OFDMA ； CFO ； STO ； blind estimation

參考文獻

[3] Asymmetrical Digital Subscriber Line (ADSL) Transceivers," International Telecommunications Union, ITU Recommendation G.992.1, 1999.

[4] M. M. U. Gul, X. Ma and S. Lee, "Timing and Frequency Synchronization for OFDM Downlink Transmissions Using Zado -Chu Sequences," IEEE Transactions on Wireless Communications, vol. 14, no. 3, pp. 1716-1729, Mar, 2015.

[5] A. Mohebbi, H. Abodzadeh-Ziabari and M. G. Shayesteh, "Novel Coarse Timing Synchronization Methods in OFDM Systems Using Fourth-Order Statistics," IEEE Transactions on Vehicular Technology, vol. 64, no. 5, pp. 1904-1917, May, 2015.

[7] H. T. Hsieh and W. R. Wu, "Maximum Likelihood Timing and Carrier Frequency Offset Estimation for OFDM Systems With Periodic Preambles," IEEE Transactions on Vehicular Technology, vol. 58, no. 8, pp. 4224-4237, Oct, 2009.

[8] H. Shao, Y. Li, J. Tan, Y. Xu and G. Liu, "Robust timing and frequency synchronization based on constant amplitude zero autocorrelation sequence for OFDM systems," 2014 IEEE International Conference on Communiction Problem-solving, Beijing, 2014, pp. 14-17.