通用濾波正交分頻多工(Universal Filtered-Orthogonal Frequency Division
Multiplexing, UF-OFDM)透過將每一個資源區塊經過濾波器濾波後來降低帶外輻
射(Out-of-band radiation)以增加頻譜效益，同時也具有不需要循環前綴的優點，
因此 UF-OFDM 也被認為是第五代行動通訊系統(5G)中的候選波形技術。
在多用戶上傳系統中，基地台會因為傳送端與接收端之間的振盪器(Local
Oscillator, LO)不匹配造成頻率的誤差以及每位用戶端受到都卜勒效應的影響程
度不相同，因此不同用戶端會有相異的載波頻率偏移(Carrier Frequency Offset,
CFO) ， 而 這些 相 異的 載 波頻 率偏 移會產 生 載波 間互 相干擾 (Inter-Carrier Interference, ICI)面臨多用戶存取干擾(Multiple Access Interference, MAI)的問題，使系統的表現受到影響。
本論文中提出一個新穎的載波頻率偏移估計方法，降低進行頻率搜索時所花
費的複雜度，同時提升頻率估計的精確程度。所提出的方法為利用前導碼
(Preamble)與濾波器進行摺積後的特性，在此特性下前導碼會被分為許多區段，
而不同區段間會有對應的頻率估計範圍，利用每個區段間有不同的頻率估計範圍
的特性，來進行相位的重疊確認，藉此搜索正確的載波頻率偏移量，並使用多級
平均的方法，提升估計的準確性，完成載波頻率偏移的補償。
本論文中也結合光纖無線通訊系統(Radio Over Fiber, RoF)實驗架構，展示
UF-OFDM 在單用戶以及多用戶上傳時之間的差異，並比較不同的載波頻率偏移
估計方法與接收光功率(Receive Optical Power, ROP)的表現。

Universal Filtered-Orthogonal Frequency Division Multiplexing (UF-OFDM)
increases spectral efficiency by filtering each resource block and then reducing out-ofband radiation. It also has the advantage of not requiring a cyclic prefix, so UF-OFDM
is considered as a candidate waveform in the fifth-generation mobile communication
system (5G).
In the multi-user uplink system, the base station will cause frequency offset due to
the mismatch of the Local Oscillator (LO) between the transmitter and the receiver, and
each user is affected by the different degrees of Doppler effect. Therefore, users will
have different Carrier Frequency Offset (CFO), it will cause Inter-Carrier Interference
(ICI) and face multi-user access interference (Multiple Access Interference, MAI),
which affects the performance of the system.
In this paper, a novel carrier frequency offset estimation method is proposed,
which reduces the complexity of frequency search and improves the accuracy of
frequency offset estimation. The proposed method utilizes the characteristic of the
preamble and the filter. By this characteristic, the preamble will be divided into many
sections, and there will be corresponding frequency estimation ranges between different
sections. There are different frequency estimation ranges between each section to
perform phase overlap confirmation, thereby searching for the correct carrier frequency
offset, and using the multi-level averaging method to improve the accuracy of the
estimation.
This paper also combines the experimental architecture of Radio Over Fiber (RoF)
to demonstrate the difference between UF-OFDM in single-user and multi-user,
compare different carrier frequency offset estimation methods and Receive Optical
Power (ROP) performance.

[1] G. Wunder, M. Kasparick, S. ten Brink, F. Schaich, T. Wild, I. Gaspar, E. Ohlmer,
S. Krone, N. Michailow, A. Navarro, G. Fettweis, D. Ktenas, V. Berg, M.Dryjanski,
S. Pietrzyk, and B. Eged, “5gnow: Challenging the lte design paradigms of
orthogonality and synchronicity,’’ in Vehicular Technology Conference(VTC
Spring), 2013 IEEE 77th, June 2013, pp. 1-5.
[2] G. Wunder, P. Jung, M. Kasparick, T Wild, F. Schaich, Y. Chen, S.Brink, I. Gaspar,
N. Michailow, A. Festag, L. Mendes, N. Cassiau, D. Ktenas, M. Dryjanski, S.
Pietrzyk, B. Eged, P. Vago, and F. Wiedmann, “5gnow: non-orthogonal,
asynchronous waveforms for future mobile applications,” Communications
Magazine, IEEE, vol. 52, no. 2, pp97-105, February 2014.
[3] M. Shafi et al., “5G: A Tutorial Overview of Standards, Trials, Challenges,
Deployment, and Practice," IEEE Journal on Selected Areas in Communications,
vol. 35, no. 6, pp. 1201-1221, 2017.
[4] Frank Schaich;Thorsten Wild, “Relaxed synchronization support of universal
filtered multi-carrier including autonomous timing advance”, International
Symposium on Wireless Communications Systems (ISWCS), pp.203-208, 2014.
[5] Vida Vakilian, Thorsten Wild, Frank Schaich, Stephan tenBrink, Jean-Francois
Frigon, “Universal-filted multi-carrier technique for wireless systems beyond
LTE”, IEEE Globecom Workshops(GC Wkshps), pp.223-228, 2013.
[6] PETER LYNCH, “The Dolph–Chebyshev Window: A Simple Optimal Filter”, 7
American Meteorological Society, pp.655-660, 1997.
[7] C. Lim, A. Nirmalathas, Yizhuo Yang, D. Novak and R. Waterhouse, "Radiooverfiber systems," 2009 Asia Communications and Photonics conference and
Exhibition (ACP), Shanghai, 2009, pp. 1-10
[8] L. Gui, B. Liu, W. Ma, and B. Song, “A novel method of frequencyoffset
estimation using time domain PN sequences in OFDM systems,” IEEE Trans.
Broadcast., vol. 54, no. 1, pp. 140–145, Mar. 2008.
[9] T. C. Lin and S. M. Phoong, “A new cyclic-prefix based algorithm for blind CFO
estimation in OFDM systems,” IEEE Trans. Wireless Commun., vol. 15, no. 6, pp.
3995–4008, Jun. 2016
64
[10] T.M. Schmidl, D.C. Cox, “Robust frequency and timing synchronization for
OFDM”, IEEE Transactions on Communications, pp.1613-1621, 1997.
[11] P. Moose, “A technique for orthogonal frequency division multiplexing frequency
offset correction,” IEEE Trans. Commun., vol. 42, pp. 2908–2914, Oct. 1994.
[12] Y. Li, B. Tian, K. Yi, and Q. Yu, “A novel hybrid CFO estimation scheme for
UFMC-based systems,” IEEE Commun. Lett., vol. 21, no. 6, pp. 1337–1340, Jun.
2017.
[13] K. Shi, E. Serpedin, "Coarse frame and carrier synchronization of OFDM systems:
a new metric and comparison," in IEEE Transactions on Wireless Communications,
vol. 3, no. 4, pp. 1271-1284, July 2004.
[14] J.J. Van de Beek, P.O.Borjesson, D. Landstram, J.M. Areans P.Odling, C. Ostberg,
M. Wahlqvist, S. K. Wilson, “A time and frequency synchronization scheme for
OFDMA”, IEEE J. Select. Area Commun., vol. 17, pp.1900-1914, Nov.1999.