Joint Synchronization and Channel Response Estimation for MIMO OFDM and SC-FDMA Systems
Date Issued
2010
Date
2010
Author(s)
Hsu, Cheng-Yi
Abstract
In this thesis, the features and techniques of LTE system are first illustrated. In order to achieve high frequency efficiency, high system performance and lower cost, LTE adopt SC-FDMA as its uplink transmission technique and OFDMA as its downlink transmission scheme. Based on the specification of LTE and channel model specified by ITU-R, we consider three front-end non-idealities including CFO, SCO and IQ imbalance as well as channel estimation in LTE system. We propose an efficient synchronization and channel estimation procedure in the system design point of view. Based on the proposed procedure, CFO, SCO, IQ imbalance and channel impulse response are scheduled to be jointly and efficiently estimated by our proposed estimation method both in downlink and uplink, respectively.
First we propose a time domain extended Kalman filtering based joint carrier frequency offset, sampling clock offset and channel estimation algorithm in MIMO OFDMA downlink. Unlike previous works, where the frequency induced ICI term is neglect and the algorithm is developed in the frequency domain, our method is based on time domain approach without ignore the ICI term. From the simulation result, our proposed time domain EKF approach is robust in medium to high SNR values compared with conventional frequency domain RLS method, where the error floor occurs due to residual frequency offsets and ICI effect.
Second, we propose a low complexity joint estimator of carrier frequency offset and channel impulse response for SC-FDMA uplink. Unlike conventional method, which is computational exhausting, our proposed scheme is based on cyclic shifted Zadoff-Chu sequences and modified time domain parallel interference cancellation scheme, which provide simple and low-complexity solution for both CFO and channel estimation. The computational complexity of channel estimation is greatly reduced since no matrix inversion is involved. Furthermore, a multiuser interfered channel estimation MSE lower bound is derived. Simulation results show that our proposed algorithm is more robust when CFO is large, has faster convergence rate and achieves the derived lower bound in acceptable iteration numbers.
Finally, based on the proposed algorithm, we take transmitter IQ imbalance into consideration and propose a joint estimator of CFO, IQ imbalance and channel impulse response for SC-FDMA in uplink. We make use of the modified time domain parallel interference cancellation for MUI cancellation and of the simplified low complexity Kalman filtering for channel estimation. Simulation results show that our proposed algorithm is very robust in highly frequency selective channel over previous work. The channel MSE is close to the derived lower bound in a few iterations.
Subjects
long term evolution (LTE)
orthogonal frequency division multiplexing(OFDM)
single carrier frequency division multiple access (SC-FDMA)
carrier frequency offset (CFO)
sampling clock offset (SCO)
IQ imbalance
extended Kalman filter (EKF)
Type
thesis
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