- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Adaptive Nonlinear Equalization of a Tunable Bandpass Filter
摘要： The mitigation of third-order intermodulation distortion produced by a nonlinear tunable bandpass filter (BPF) in a digital receiver channel is demonstrated. An iterative solution is proposed, in the use of the least-mean-square algorithm, as an effective way to allow the correction coefficients to adapt to the changes in the system characteristics when the center frequency is changed. Results are shown using a two-pole, varactor-loaded BPF, and an Analog Devices AD9371 transceiver.
关键词： Adaptive signal processing,nonlinear distortion and intermodulation distortion (IMD),nonlinear filters,least mean square
更新于2025-09-23 15:22:29
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Precompensation and System Parameters Estimation for Low-Cost Nonlinear Tera-Hertz Transmitters in the Presence of I/Q Imbalance
摘要： Tera-Hertz (THz) transmission can offer several attractive applications, yet developing low-cost energy-efficient THz devices is at an early stage. The most promising low-cost THz transmitter architecture in the literature is the so-called frequency-multiplier-last architecture. However, it is incapable of transmitting quadrature amplitude modulation (QAM) due to the architecture's inherent nonlinear distortions. We study such nonlinear THz communication systems by incorporating the nonlinearity aspects of the low-cost THz devices and the inphase and quadrature (I/Q) imbalance effect into the signal model. Then, we propose a precompensation scheme to compensate the nonlinearity and I/Q imbalance effects, thus enabling the QAM-capable frequency-multiplier-last architecture for THz systems. The proposed precompensation scheme requires the knowledge of the system parameters. To estimate the system parameters, we propose a maximum-likelihood estimator and its practical implementation via an alternating estimation algorithm. We also derive closed-form expressions for the Cramér–Rao lower bounds (CRLBs) of the system parameters estimation, and design the pilot sequence used in estimating the system parameters. Numerical results show that the proposed precompensation schemes overcome the prominent problems experienced in the existing THz systems, namely severe nonlinear distortions of the modulation symbols as well as spectral spreading and/or large spectrum sidelobes, and mitigate the I/Q imbalance effect.
关键词： precompensation,estimation,QAM,I/Q imbalance,nonlinear distortion,Low-cost,Tera-Hertz
更新于2025-09-23 15:22:29
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Multiple Access With Polarity Division Sparse Code for Visible Light Communication
摘要： The increasing demand of mobile internet and Internet of Things poses challenging requirements for indoor wireless communication. Visible light communication (VLC) is a promising technology to alleviate the growing traffic problem. In addition, nonlinear distortion of light emitting diodes (LEDs) results in a poor link quality. In this paper, we propose multiple access with polarity division sparse code (PDSC) for VLC, which is based on nonorthogonal multiple access and spatial characteristic of LEDs. The experimental results indicate that the PDSC significantly enhances capacity and spectral efficiency of VLC network compared with orthogonal frequency division multiple access. We also demonstrate that the PDSC can optimize the problem of nonlinear distortion with polarity division. The experimental results reveal that PDSC is a promising multiple access scheme for the indoor VLC networks.
关键词： Nonorthogonal multiple access,visible light communication,PDSC,nonlinear distortion optimization
更新于2025-09-23 15:22:29
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RoF system based on phase modulator-employing polarization for linearization
摘要： In this paper, an analytical model is represented to analyze and improve the performance of radio over fiber (RoF) links against nonlinear distortion. RoF transmission link comprised of a phase modulator, polarizer and optical filter is considered. By controlling angles of polarization, the signals are fed to the modulator. Polarizer helps to suppress intermodulation distortion along the considered link. Performance is found in terms of spurious-free dynamic range (SFDR). Results show an improvement of 7.5-dB in SFDR for a polarized link in comparison with the conventional link.
关键词： Polarizer,IMD,SFDR,RoF,Nonlinear distortion
更新于2025-09-10 09:29:36
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A High Linearity, 8-<i>GSa</i>/<i>s</i> Track-and-Hold Amplifier in GaAs HBT Technology
摘要： A high linearity full differential 8 GSa/s track-and-hold amplifier (THA) is presented in this paper. The proposed THA is designed and implemented using 2-μm GaAs HBT technology to be targeted for faster operation in sampling systems at a clock frequency of GHz. In this THA, an alternative switch emitter follower (SEF) is used as a switching stage with a Schottky diode for hold-mode isolation enhancement and high–speed operation. In conjunction with well-designed input buffer allows us to achieve high linearity and comparable dynamic performance. Measured small signal -3 dB bandwidth, and hold-mode isolation are better than 3.6 GHz and 40 dB, respectively. The prototype achieves a spurious-free dynamic range (SFDR) of 43.9 dB at 0.5 GHz and an average total harmonic distortion (THD) below -40 dBc up to a first Nyquist frequency of 4 GHz. This work has the potential for wideband, high speed and low distortion analog to digital converter (ADC) used in the future direct sampling systems.
关键词： nonlinear distortion,track-and-hold,high-speed sampling,Schottky diodes,gallium arsenide,MMICs
更新于2025-09-09 09:28:46