Adaptive compensation of frequency selective IQ imbalance and carrier frequency offset for OFDM based receivers

Direct conversion architectures are currently receiving a lot of interest in OFDM based wireless transmission systems. However such systems are very sensitive to front-end non-idealities such as in- phase/quadrature-phase (IQ) imbalances and carrier frequency offset. In this paper the joint effect of frequency selective IQ imbalance at the receiver under carrier frequency offset is studied. We also consider the case when the cyclic prefix is not sufficiently long to accommodate the channel impulse response combined with the receiver filter, which results in inter-block-interference (IBI) between the OFDM symbols. We propose a frequency domain per-tone equalizer (PTEQ) based receiver structure obtained by transferring a time domain equalizer (TEQ) to the frequency domain. In addition to the frequency domain PTEQ design procedure, a training-based RLS type initialization scheme for direct per-tone equalization is proposed. The algorithm involved provides a very efficient post-FFT adaptive equalization and front-end compensation performance which is shown to be close to the ideal case.Anglai

Low-complexity estimation of CFO and frequency independent I/Q mismatch for OFDM systems

CFO and I/Q mismatch could cause significant performance degradation to OFDM systems. Their estimation and compensation are generally difficult as they are entangled in the received signal. In this paper, we propose some low-complexity estimation and compensation schemes in the receiver, which are robust to various CFO and I/Q mismatch values although the performance is slightly degraded for very small CFO. These schemes consist of three steps: forming a cosine estimator free of I/Q mismatch interference, estimating I/Q mismatch using the estimated cosine value, and forming a sine estimator using samples after I/Q mismatch compensation. These estimators are based on the perception that an estimate of cosine serves much better as the basis for I/Q mismatch estimation than the estimate of CFO derived from the cosine function. Simulation results show that the proposed schemes can improve system performance significantly, and they are robust to CFO and I/Q mismatch

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Cognitive radio systems evaluation: measurement, modeling, and emulation approach

No abstract available.publishe

Power amplifier linearization technique with IQ imbalance and crosstalk compensation for broadband MIMO-OFDM transmitters

The design of predistortion techniques for broadband multiple input multiple output-OFDM (MIMO-OFDM) systems raises several implementation challenges. First, the large bandwidth of the OFDM signal requires the introduction of memory effects in the PD model. In addition, it is usual to consider an imbalanced in-phase and quadrature (IQ) modulator to translate the predistorted baseband signal to RF. Furthermore, the coupling effects, which occur when the MIMO paths are implemented in the same reduced size chipset, cannot be avoided in MIMO transceivers structures. This study proposes a MIMO-PD system that linearizes the power amplifier response and compensates nonlinear crosstalk and IQ imbalance effects for each branch of the multiantenna system. Efficient recursive algorithms are presented to estimate the complete MIMO-PD coefficients. The algorithms avoid the high computational complexity in previous solutions based on least squares estimation. The performance of the proposed MIMO-PD structure is validated by simulations using a two-transmitter antenna MIMO system. Error vector magnitude and adjacent channel power ratio are evaluated showing significant improvement compared with conventional MIMO-PD systems.Peer reviewe