Joint Estimation of I/Q Imbalance and Carrier Frequency Offset Using Pilot Subcarriers for OFDM Systems
Date Issued
2011
Date
2011
Author(s)
Jian, Yi-Fan
Abstract
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.
Subjects
OFDM
I/Q Imbalance
Carrier Frequency Offset
Pilot Subcarrier
Pilot Symbol
Type
thesis
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