Wideband OFDM Systems Research Articles

Unit Cell Phase-Frequency Profile Optimization in RIS-Assisted Wide-Band OFDM Systems

Unit Cell Phase-Frequency Profile Optimization in RIS-Assisted Wide-Band OFDM Systems

Channel prediction of wideband OFDM systems in a millimeter-wave band based on multipath delay estimation

Channel prediction of wideband OFDM systems in a millimeter-wave band based on multipath delay estimation

Research on Consistency Enhancement of Wireless Channel Key Against RF Fingerprint

The development of the physical layer key extraction technology provides a new type of encryption mechanism that uses the reciprocity and time varying of wireless channels to generate keys. This encryption mechanism can achieve informational security. However, the wireless channels in the real environment are not completely reciprocal, which results in low consistency in generating the keys. In this paper, we study the influence of RF fingerprint on channel reciprocity, and propose a calibration matrix algorithm resist the RF fingerprint effect. Based on the RF fingerprinting model established previously, we propose two calibration methods from the perspective of RF gain and I/Q gain. The superiority of the two calibration methods is proved by the average system capacity and the linear quantification error rate. Next, we extend the calibration matrix algorithm of narrowband systems to wideband OFDM systems. The applicability of the calibration matrix algorithm in OFDM systems is proved by the linear quantification error rate of the uplink and downlink channels. In order to prove the reliability of the algorithm in the real environment, we use a USRP to collect multiple sets of measured data, and analyse the data through the calibration algorithm. The final result shows that this algorithm makes the uplink and downlink channel reciprocity compensated.

Variable step-size MLMS algorithm for digital predistortion in wideband OFDM systems

As one of the most promising linearization techniques, adaptive Digital Predistortion (PD) has been widely utilized in modern wireless communication systems for improving the efficiency of Power Amplifier (PA). In view of the non-stationary signal environment for the wideband PAs, an efficient indirect learning adaptive PD is proposed in the paper based on the Memory Polynomial Model (MPM). The coefficients of the proposed PD can be effectively identified by the Modified Least Mean Square (MLMS) learning algorithm. In addition, more stable convergence and lower steady-state error can be achieved simultaneously for the PAs with deep memory effects by adopting the variable step-size parameter. Theoretical analysis results regarding the learning stability, convergence behavior, and selection criteria of initial settings are derived. Simulations demonstrate that MLMS outperforms traditional LMS, Normalized LMS (NLMS), and Generalized Normalized Gradient Descent (GNGD) algorithms in terms of the Normalized Mean Square Error (NMSE) and out-of-band Power Spectral Density (PSD) under the noisy feedback condition for the wideband PAs1.

A novel distortion elimination method of power amplifier in wideband OFDM system

The nonlinear, memory and saturate distortion caused by power amplifier lead to low BER performance and low power efficiency in wideband OFDM system. To solve the related problems, a novel power amplifier based on combined amplification with multi power amplifiers is proposed in this paper. In addition, a novel simplified filter look-up table predistorter is proposed. The novel predistorter connects to a memoryless predistorter subsystem with an adaptive filter subsystem in cascade, and can eliminate the nonlinear memory distortion effectively. The simulation results indicate that the power efficiency and BER performance will be improved by using the novel amplifier structure together with the novel predistorter.

An efficient compensation of TWTA's nonlinear distortion in wideband OFDM systems

A multi-stage approach is presented for efficient compensation of TWTA's nonlinear distortion (which belongs to Wiener systems) in wideband OFDM systems. In stages 1 and 2, TWTA's memory effects and memoryless nonlinear distortion are separately modeled, which leads to very fast modeling convergence. Then, TWTA's nonlinear distortion is completely compensated based on the models in stage 3.

Fast Fourier Transform Algorithm for Low-Power and Area-Efficient Implementation

This paper proposes the new radix-2 4 FFT algorithm and an efficient pipeline FFT architecture based on the algorithm for wideband OFDM systems. The proposed pipeline architecture has the same number of multipliers as that of the radix-2 2 algorithm. However, the multiplication complexity is reduced more than 30% by using the newly proposed CSD constant multipliers instead of the programmable multipliers. From the synthesis simulations of a standard 0.35μm CMOS SAMSUNG process, the proposed CSD constant complex multiplier achieved a reduction of more than 60% of the power consumption/area when compared with the conventional programmable complex multiplier.

Low complexity channel estimation for space~time coded wideband ofdm systems

In this article, channel estimation for space-time coded orthogonal-frequency division multiplexing (OFDM) systems is considered. By assuming that the channel frequency response is quasi-static over two consecutive OFDM symbols, we develop channel parameter estimators based on the use of space-time block coded (STBC) training blocks. Using an STBC training pattern, a low-rank Wiener filter-based channel estimator with a significant complexity reduction is proposed. A simplified approach for the optimal low-rank estimator is also proposed to further reduce the estimator complexity while retaining an accurate frequency domain channel estimation. Numerical results are provided to demonstrate the performance of the proposed low complexity channel estimators for space-time trellis coded OFDM systems.