Preamble design for joint estimation of channel and I/Q imbalance in MIMO-OFDM systems (original) (raw)
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Preamble Design for Joint estimation of Channel, CFO and Receiver I/Q-Imbalance in OFDM Systems
Proceedings of the ISCIE International Symposium on Stochastic Systems Theory and its Applications, 2013
In this paper, preamble design for estimation of frequency selective channels, carrier frequency offset (CFO) and inphase/quadrature-phase (I/Q) imbalance in orthogonal frequency division multiplexing (OFDM) systems is proposed. First we utilize convex optimization to optimize power of all active subcarriers, then we employ adaptive Markov chain Monte Carlo (AMCMC) techniques to select preamble sequence that minimizes the channel estimate mean squared error (MSE) while suppressing the effect of the I/Q mismatch. To estimate CFO, maximum likelihood (ML) based scheme that utilizes two successive OFDM preambles is employed. The CFO is estimated by considering the phase rotation between two consecutive received OFDM preambles. Numerical simulations are provided to verify the efficacy of the proposed design.
2012 International Symposium on Signals, Systems, and Electronics (ISSSE), 2012
MIMO OFDM is a key technique for achieving high data rate in future wireless communication systems. The desired low-cost, low-power and fully integrated implementation of MIMO OFDM systems leads to the application of direct (up/down) conversion architecture, whose performance can be seriously limited by I/Q-imbalance. Thus, the compensation of I/Q-imbalance is a crucial issue in the implementation of MIMO OFDM systems, which requires reliable parameter estimation. In this paper, an efficient scheme is proposed for the joint estimation of the MIMO channel and frequency-selective I/Qimbalance both at the transmitter and the receiver. First, a multi-functional preamble is presented, which not only fulfills the optimal design rules for joint estimation but can also be used for both parameter estimation and frame detection/time synchronization, allowing low overhead. Furthermore, low Crest-Factor (CF) of the preamble is achieved. Based on this preamble, a low complexity estimator is developed, which can achieve performance close to the Cramer-Rao Lower Bound (CRLB). Numerical simulation results and complexity analysis have verified the advantages of the proposed estimation scheme over the existing schemes.
Estimation of MIMO Channel Response for OFDM System with I/Q Imbalance and CFO
In this project, we analyze the joint estimation of inphase and quadrature-phase (I/Q) imbalance and carrier frequency offset (CFO), and channel response for multiple-input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems using training sequences. A new concept called channel residual energy (CRE) is introduced. We show that by minimizing the CRE, we can jointly estimate the I/Q imbalance and CFO without knowing the channel response. The proposed method needs only one OFDM block for training and the training symbols can be arbitrary. Moreover when the training block consists of two repeated sequences, a low complexity two-step approach is proposed to solve the joint estimation problem. Simulation results show that the mean-squared error (MSE) of the proposed method is close to the Cramer-Rao bound (CRB).
2010 IEEE Wireless Communication and Networking Conference, 2010
MIMO OFDM is a very promising technique for high-speed wireless transmission. By applying the Direct Conversion Architecture (DCA), low-cost, low-power and fully integrated implementation of such systems is enabled. However, the performance of DCA may be seriously limited by I/Q-imbalance, which shows frequency selectivity in broadband systems. In this paper, we consider an indoor scenario and present effective preamble based joint compensation of the MIMO wireless channels (block fading) and the TX-and RX-frequency-selective I/Q-imbalance. Two low overhead preambles are proposed, which are constructed in time-and frequency domain, respectively. Both of them have their own advantages. Compared to the literature, our paper considers more practical issues and shows how to choose the adequate preamble design according to system parameters to achieve the best performance with relatively low computational complexity. Effectiveness of the proposed schemes is verified by numerical simulation. † and N indicate complex conjugate, modulo by N operation, the largest integer smaller than c, the pseudo-inverse operator and circular convolution with block length N , respectively. Subscripts "re" and "im" indicate the real and imaginary parts of a signal, respectively. The superscripts (i), r and r, i correspond to the i th TX, the r th RX and the path between the i th TX and the r th RX, respectively. The subscript h D;I indicates h D or h I (Subscripts D and I correspond to "direct" and "image" parts, respectively). The notation {a : d : b} indicates an arithmetic sequence from integer a to an integer This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2010 proceedings.
Effect of I/Q Imbalance on Pilot Design for MIMO OFDM Channel Estimation
GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009
Efficient pilot designs are vital as they improve system performance and resource utilization, especially in multiinput multi-output (MIMO) orthogonal frequency divison multiplexing (OFDM) systems. Most of the existing pilot designs do not consider in-phase and quadrature (I/Q) imbalance whose detrimental effects become more severe since the technology and applications are pushing towards smaller semiconductor node, smaller chip, cheaper equipment, and larger modulation order. This paper studies the impact of I/Q imbalance on the pilot designs, and presents several new pilot designs for equivalent channel estimation of MIMO OFDM systems with frequencydependent I/Q imbalances. Advantages of the proposed designs are illustrated through simulation and analytical results in terms of estimation accuracy, error rate, overhead efficiency, and generality with the transmission formats (preamble-based or pilot-data-multiplexed systems, with or without null guard tones).
Optimized Channel Estimation for OFDMA Uplink with Frequency-Dependent I/Q Imbalance
2014 IEEE 79th Vehicular Technology Conference (VTC Spring), 2014
I/Q imbalance (IQI) is one of the major front-end imperfections affecting the performance of communication systems. Due to frequency-dependent (FD) IQI, channel is elongated and is split into direct and image channels. We consider the problem of joint estimation of the channel and I/Q parameters for OFDM based systems. Time-domain estimation of the effective channel taps poses a question-what is the optimal number of taps that need to be estimated for the best estimation performance? More the estimated taps, more is the noise contribution to the estimator. Lesser the estimated taps, less is the precision due to unestimated taps. In this paper, we address this issue by deriving analytic expressions for mean squared errors (MSE) of estimates of the effective channels and conditions for their optimization. In the absence of channel knowledge, we propose a choice of number of taps to improve estimation performance.
EM-Based Joint Channel Estimation and IQ Imbalances for OFDM Systems
IEEE Transactions on Broadcasting, 2000
The imbalances between the In-phase (I) and Quadrature-phase (Q) branches represent a significant source of impairment in the orthogonal frequency division multiplexing (OFDM) systems. Recently, it has been shown that the unwanted IQ imbalances can be actually exploited to achieve a diversity gain. In this contribution, by taking into account the diversity gain resulting from the IQ imbalances, we develop a novel algorithm to jointly estimate the channel impulse response and IQ imbalances occurring at both the transmitter and receiver. Starting from the Maximum Likelihood (ML) principle, we derive an estimation algorithm based on the expectation maximization (EM) algorithm, which exploits information from the pilot symbols and detected data symbols in a systematic fashion. To reduce the complexity of the estimation algorithm, a sub-optimal scheme is also introduced. The results indicate that the proposed algorithms achieve a significant improvement in the bit error rate (BER) performance after three iterations as compared to conventional data-aided algorithms.
IJERT-Extimation if I/Q Imblance in Mimo OFDM System
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/extimation-if-iq-imblance-in-mimo-ofdm-system https://www.ijert.org/research/extimation-if-iq-imblance-in-mimo-ofdm-system-IJERTV2IS100489.pdf In this paper, we study the joint estimation of in phase and quadrature-phase (I/Q) imbalance, carrier frequency offset (CFO), and channel response for multiple-input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems using training sequences. A new concept called channel residual energy (CRE) is introduced. We show that by minimizing the CRE, we can jointly estimate the I/Q imbalance and CFO without knowing the channel response. The proposed method needs only one OFDM block for training and the training symbols can be arbitrary. Moreover when the training block consists of two repeated sequences, a low complexity two-step approach is proposed to solve the joint estimation problem. Simulation results show that the mean-squared error (MSE) of the proposed method is close to the Cramer-Rao bound (CRB).
Preamble-based SNR estimation algorithm for wireless MIMO OFDM systems
2009
Orthogonal frequency division multiplexing (OFDM) offers high data rates and robust performance in frequency selective channels by link adaptation utilizing information about the channel quality. Combined with multipleinput multiple-output (MIMO) technique it provides improved link reliability and increased data rate. A crucial parameter required for adaptive transmission is the signal-to-noise ratio (SNR). In this paper, we propose a novel SNR estimation algorithm for wireless 2 × 2 MIMO OFDM systems based on the reuse of the synchronization preamble. The periodic structure of the preamble is utilized for the computationally efficient estimation of average SNR and SNRs per subcarrier, based on the second-order moments of received preamble samples. The performance of the proposed algorithm is assessed for channels with different levels of frequency selectivity. Simulation results show robust performance of proposed algorithm even in strong frequency selective channels.