This paper presents an iterative estimation and cancellation technique for nonlinear in-band full-duplex transceivers with IQ imbalances and amplifier nonlinearities. The estimation process of the proposed scheme consists of three stages, namely, the channel response estimation, IQ imbalance estimation, and power amplifier and low-noise amplifier (LNA) nonlinearities estimation. For the estimation of the parameters and improvement of the accuracy, distortions are compensated by cancellation or inversion with the latest estimated parameters. On the one hand, the channel response is estimated on the time domain; on the other hand, the IQ imbalance and nonlinearities are estimated on the frequency domain for a more straightforward estimation and superior accuracy. In the cancellation process of the proposed scheme, the received signal is compensated with the estimated parameters of the LNA and receiver IQ imbalance before cancellation because the desired signal is received with a high-power self-interference and is distorted by the radiofrequency receiver impairments. Simulation results show that the proposed technique can achieve higher cancellation performance compared with the Hammerstein canceller when the LNA is saturated by the self-interference. Additionally, the performance of the proposed canceller converges much faster than that of the Hammerstein canceller.
This paper presents a basis function selection technique of a frequency-domain Hammerstein digital selfinterference canceller for in-band full-duplex communications. The power spectral density (PSD) of the nonlinear selfinterference signal is theoretically analyzed in detail, and a nonlinear self-interference PSD estimation method is developed. The proposed selection technique decides on the basis functions necessary for cancellation and relaxes the computational cost of the frequency-domain Hammerstein canceller based on the estimated PSD of the self-interference of each basis function. Furthermore, the convergence performance of the canceller is improved by the proposed selection technique. Simulation results are then presented, showing that the proposed technique can achieve similar cancellation performance compared with the original frequency-domain Hammerstein canceller and a time-domain nonlinear canceller. Additionally, it is shown that the proposed technique improves the computational cost and the convergence performance of the original frequency-domain Hammerstein canceller.
In-band full-duplex (IBFD) communication systems utilize self-interference cancellation to mitigate high-power selfinterference caused by simultaneous transmission and reception at the same frequency in the digital baseband domain. Self-interference is distorted by transceiver nonlinearity. Thus, the IBFD literature includes reports of nonlinear self-interference cancellers developed to achieve better cancellation performance. However, there are no detailed theoretical studies analyzing the performance of nonlinear cancellers in IBFD systems. In this work, we develop a theoretical analysis technique for IBFD systems using parallel Hammerstein self-interference cancellers. The nonlinear characteristics of the system are expanded by a generalized Fourier series using orthonormal Laguerre polynomials. Then, the canceller's performance and the system's symbol error rate (SER) are analyzed using the obtained Fourier coefficients. The analytical results are compared with simulation results, demonstrating good correlation in a wide range of situations, from extremely nonlinear cases to good linear cases. Additionally, we show that the SER of the IBFD system is reduced by moderately nonlinearizing rather than linearizing the amplifier.
In-band full-duplex communications have been spotlighted because they can double the spectral efficiency of the current wireless communication systems. However, it is necessary to mitigate the self-interference (SI). Currently, several time-domain and frequency-domain SI cancellers have been proposed. Timedomain SI cancellers are based on the parallel Hammerstein (PH) model, and they have good flexibility with high computational cost. In contrast, frequency-domain SI cancellers can achieve high cancellation performance with low computational cost but they have less flexibility than time-domain PH based SI cancellers. In this paper, we propose a frequency-domain SI canceller based on the PH model. The proposed scheme estimates the frequency response of the SI channel and regenerates SI signals by the overlap-save method. Therefore, the computational complexity of the proposed scheme is less than time-domain PH based SI canceller. The performance of the proposed scheme is assessed by equivalent baseband signal simulations of a fullduplex transceiver. As a result, the proposed scheme achieves high SI cancellation as the time-domain PH based SI canceller with low computational cost. In addition, the convergence performance of the proposed scheme is faster than the time-domain scheme.
In-band full-duplex communication, which transmits and receives simultaneously on the same frequency, causes self-interference (SI). In this paper, to cancel SI present in the radio frequency (RF) domain, we propose a novel nonlinear SI cancellation approach using an auxiliary transmitter which is effective in the presence of IQ imbalance and nonlinear distortion. The proposed approach estimates the local transceiver channel by using a time-domain least squares method and creates a signal for SI cancellation based on estimation results and a finite impulse response filter, whose coefficients are derived in this paper. Additionally, we theoretically calculate the SI cancellation limit of the proposed approach. Information about the SI cancellation limit due to phase noise is important for meeting SI cancellation requirements and being able to compare the effects of RF impairments such as IQ imbalance and nonlinear distortion. From simulation results, we show that the proposed approach outperforms the conventional approach and the case of using a general adaptive algorithm for the proposed approach. Furthermore, the SI cancellation limit is improved by adjusting the propagation delay of the SI signal and the canceling signal in addition to sharing one local oscillator in the local transceiver.
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