正交分頻多工系統中使用領航子載波於實虛部非協調與載波頻率偏移之同估測

Joint Estimation of I/Q Imbalance and Carrier Frequency Offset Using Pilot Subcarriers for OFDM Systems

簡翊帆(Yi-Fan Jian)

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(2011年)

https://doi.org/10.6342/NTU.2011.02868

摘要

正交分頻多工（OFDM）技術能夠提供良好的頻譜效益，以及避免多路徑傳輸所造成的影響。在本論文中，我們考量了兩個正交分頻多工系統中的非理想效應：載波頻率偏移(Carrier Frequency Offset)與實虛部非協調 (IQ imbalance)。此兩種非理想效應都會對系統效能產生嚴重影響。

首先我們根據領航子載波的特性，提出演算法來分別及聯合估測載波頻率偏移與實虛部非協調。接下來，根據L. Wu和 X.-D. Zhang在2009年提出盲蔽式(blind)頻率偏移估測法 [20]，我們將此方法延伸至非定值模數(Non-constant modulus)系統中。最後根據模擬結果，我們演算法的效能都比某些現存的方法還要好或是運算複雜度更低。

關鍵字

正交分頻多工 ； 實虛部非協調 ； 載波頻率偏移 ； 領航子載波

並列摘要

Recently, the direct-conversion transceiver of orthogonal frequency division multiplexing (OFDM) systems become more appealing because of its significant advantages in cost, package size, and power consumption. However, the direct-conversion receivers are very sensitive to non-idealities at analog front-end, such as in-phase and quadrature-phase (I/Q) imbalance and carrier frequency offset (CFO). These non-idealities destroy the subcarrier orthogonality of OFDM systems. As a result the performance of OFDM systems will degrade severely if these non-idealities are not properly compensated. Therefore, it is an important issue to precisely estimate and compensate these mismatches.

In this thesis, the effect of I/Q imbalance and CFO in OFDM systems are first studies, and then the estimation and compensation of these parameters are considered. The results of this thesis consist of three parts. In many practical communication systems, some carriers are not used for data transmission and instead certain signal known to the receivers are transmitted on these carriers. These subcarriers are known as pilot subcarriers. In Part I, we propose a CFO estimation method using pilot subcarriers. In Part II, we will exploit these pilot subcarriers for the joint estimation of I/Q imbalance and CFO. In Part III, first, we proposed a blind CFO estimation method in QAM-OFDM systems which can improve the bandwidth efficiency without usage of any training sequences or pilots. Next, we proposed a CM (constant-modulus) pilot-aided CFO estimator. Finally the performance of the proposed method will be compared with the other existing methods that also use pilots or being blind.

並列關鍵字

OFDM ； I/Q Imbalance ； Carrier Frequency Offset ； Pilot Subcarrier ； Pilot Symbol

參考文獻

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