Preamble Based Channel and CFO Estimation for MIMO-OFDM Systems with Null Subcarriers

Abstract

In this paper, challenges regarding the provision of channel state information (CSI) and carrier frequency synchronization for orthogonal frequency division multiplexing (OFDM) systems with null subcarriers are addressed. We propose novel maximum likelihood (ML) based schemes that estimate the aggregate effects of the CFO and channel by using two successive OFDM preambles. In the presented scheme, CFO is estimated by considering the phase rotation between two consecutive received OFDM preambles. Both single input single output (SISO) as well as multiple input multiple output (MIMO) OFDM systems are considered. The mean squared errors (MSE) of the channel and CFO are used to evaluate the performance of our proposed scheme. By using two successive OFDM preambles, the estimation of channel and the estimation of CFO are decoupled, which leads to a simple estimation method. Simulation results show that the BER performance of the proposed estimators is comparable to that of known channel state information and the CFO MSE performance achieves the Cramer-Rao bound (CRB) of the fully loaded OFDM system.

Preamble Design for Joint estimation of Channel, CFO and Receiver I/Q-Imbalance in OFDM Systems

“…To formulate reasonable constraints for the preamble design, we consider a noise free frequency selective fading channel and no phase errors, that is, when = 0. Frequency domain representation of the received signal y m without phase errors can be written as [7] …”

“…We utilize some criteria to design preamble that minimizes the channel estimate MSE while suppressing the interference replica caused by the I/Q imbalances. To estimate the residual CFO, we adopt an ML estimator in [7] that utilizes two consecutive OFDM preambles.…”

“…Most of the existing schemes are based on the estimation and compensation for individual I/Q imbalance and CFO by using specific preamble [1,[7][8][9]. In [7][8][9], CFO estimation schemes using the preamble with repeated pattern have been proposed. The preambles in [7][8][9] provide promising CFO performance in the absence of I/Q imbalance.…”

“…In [7][8][9], CFO estimation schemes using the preamble with repeated pattern have been proposed. The preambles in [7][8][9] provide promising CFO performance in the absence of I/Q imbalance. However, these preamble structures are not efficient for CFO estimation in the presence of I/Q imbalance and may not provide simple and accurate estimations of I/Q imbalance.…”

Pilot symbol assisted channel estimation for OFDM-based cognitive radio systems

“…In multiple input multiple output (MIMO) scenario where disjoint pilot symbols are utilized for each transmit antenna, the CE-based algorithm can efficiently design pilot placement for each antenna by adopting the algorithm in [24].…”