Abstract
In this paper, we present a joint time-variant carrier frequency offset (CFO) and frequency-selective channel response estimation scheme for multiple input-multiple output-orthogonal frequency-division multiplexing (MIMO-OFDM) systems for mobile users. The signal model of the MIMO-OFDM system is introduced, and the joint estimator is derived according to the maximum likelihood criterion. The proposed algorithm can be separated into three major parts. In the first part of the proposed algorithm, an initial CFO is estimated using derotation, and the result is used to apply a frequency-domain equalizer. In the second part, an iterative method is employed to locate the fine frequency peak for better CFO estimation. An adaptive process is used in the third part of the proposed algorithm to obtain the updated CFO estimation and track parameter time variations, including the time-varying CFOs and time-varying channels. The computational complexity of the proposed algorithm is considerably lower than that of the maximum likelihood-based grid search method. In a simulation, the mean squared error performance of the proposed algorithm was close to the Cramer-Rao lower bound. The simulation results indicate that the proposed novel joint estimation algorithm provides a bit error rate performance close to that in the perfect channel estimation condition. The results also suggest that the proposed method has reliable tracking performance in Jakes’ channel models.
Highlights
Many researchers regard multiple input multiple output (MIMO) as a candidate technology for fifth-generation mobile networks (5G)
Note that K is the number of subcarriers and N and M are the numbers of TX and RX antennas, respectively
By substituting (23) into (11), the channel estimation in this adaptive mode is rewritten as follows: Fig. 6 The mean squared error (MSE) performance for carrier frequency offset (CFO) estimation of the proposed algorithm compared with Cramer-Rao lower bound (CRB)
Summary
Many researchers regard multiple input multiple output (MIMO) as a candidate technology for fifth-generation mobile networks (5G). A prohibitively high computational complexity is required to obtain maximum likelihood (ML) solutions for both the frequency offset and channel impulse response (CIR) [13] These estimators in [3, 5–7, 9–13] are designed for single-input single-output OFDM systems and not MIMO-OFDM systems. Our contribution and new ideas are as follows: (a) a joint CFO and channel estimation in MIMO-OFDM systems for mobile users, (b) a new iteration algorithm with lower complexity than the grid search-based method, and (c) a newly designed mechanism with an adaptive mode to simultaneously track the time-varying CFOs and time-varying channels. Up to the present time, the proposed adaptive iteration algorithm is currently a state-of-the art approach for achieving near-optimal performance for this joint CFO and channel estimation problem.
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