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Optical Wireless Transmitter Design
Published in Roberto Ramirez-Iniguez, Sevia M. Idrus, Ziran Sun, Optical Wireless Communications, 2008
Roberto Ramirez-Iniguez, Sevia M. Idrus, Ziran Sun
Predistortion can be further divided into two subcategories: (1) digital pre-distortion (also called baseband predistortion) and (2) analog predistortion (also called RF predistortion). Digital predistortion is often based on look-up table (LUT) algorithms and enjoys well-established DSP hardware for its implementation. However, the major drawbacks of this technique include bandwidth constraints on the input signal imposed by DSP speed limitations, greater complexity and the necessity of digital baseband data, which may not be available in some systems. Analog predistortion, on the other hand, is relatively simple to implement and can handle larger signal bandwidths in adaptive architectures [128]. Analog predistortion can be performed in various ways but always involves the purposeful generation of intermodulation products with appropriate magnitude and phase to cancel the intermodulation tones created by the nonlinear transmitter. An adaptive equalizer predistortion using instantaneous digital adaptation (IDA) provides both a large signal-to-noise and distortion ratio (SNDR) and modulation depth range at the transmitter, as demonstrated by Stapleton [129]. To illustrate the concept of predistortion, consider the block diagram in Figure 6.30. Here, an input signal x(t) can be seen being predistorted to produce a signal y(t) that, when distorted by the transmitter, produces z(t), a replica (possibly scaled) of the input signal x(t). Thus, the input–output relationship from x(t) to z(t) is linear.
Predistortion Algorithms and Applications
Published in Jingchang Nan, Mingming Gao, Nonlinear Modeling Analysis and Predistortion Algorithm Research of Radio Frequency Power Amplifiers, 2021
Figure 10.17 outlines an adaptive predistortion transmitter model for the OFDM system. The TX end converts the binary digital signal to be transmitted into a mapping of subcarrier amplitude and phase. Following a serial-to-parallel conversion, it then transforms the spectral representation of digital data into the time domain using an IFFT, and performs a parallel-to-serial conversion to complete OFDM modulation. In addition, the predistorter performs nonlinear predistortion to overcome the nonlinear distortion of amplifier, and the adaptive algorithm updates the predistorter parameters.
High linear low voltage CMOS power amplifier for 2.4 GHz applications
Published in International Journal of Electronics Letters, 2023
S Manjula, P Anandan, M Suganthy
The power amplifier is linearised using the RF predistortion approach. The predistortion technique is used to suppress the out of band emissions and improves the linearity. The important linearity measure of predistortion technique is Adjacent Channel Power (ACP) or ACL (Adjacent Channel Leakage). By lowering ACL in the PA output power spectrum density, the linearisation process can improve overall system response. The spectrum of PA with /4DQPSK modulation is shown in Figure 8. The predistorter improves the ACLR when compared with ACLR without linearizer as shown in Table 2. At a frequency offset of 5 MHz, it improves ACLR by 10 dB, and at a frequency offset of 10 MHz, it improves ACLR by 21 dB. The linearisation technique provides the 3 dBm improvement in terms of output third order intercept value (OIP3) for PA1.The linearised PA1 produces 21.7 dBm of OIP3 and 9.1 dBm of OP-1 dB.
Broadband analogue predistortion using a distortion generator based on two-stage RF mixer topology
Published in International Journal of Electronics, 2018
Predistortion techniques achieve linearisation by creating the inverse of the nonlinear characteristics of the PA (Katz, Wood, & Chokola, 2016; Raab et al., 2002). The PA’s compressive gain characteristic has to be predistorted with an expansive characteristic so that the overall transfer function becomes linear as shown in Figure 1. Analogue predistortion is considered in applications where moderate improvements in linearity are required. But, compared to other linearisation techniques, it may be better suited to multiband and broadband applications (Nesimoglu, Canagarajah, & McGeehan, 2001). Here, a comparison of analogue predistortion topologies and a review on the state-of-the-art are also provided.
Stair-type parallel digital predistorter for power amplifier linearisation and harmonic reduction
Published in International Journal of Electronics Letters, 2021
Eui-Rim Jeong, Hyukjun Oh, Jingon Joung
As an essential radiofrequency (RF) component in wireless communication systems, power amplifiers (PAs) have been extensively studied considering practical characteristics such as the nonlinearity and inefficiency, according to (Joung et al., 2014). (Joung et al., 2014) demonstrated that PA nonlinearity severely degrades communication performance; hence, various techniques that compensate and/or mitigate nonlinearity are desired for reliable communication. Instead of the inherent nonlinearity caused by PA materials, signal processing that predistorts PA input signals using the inverse characteristics of a nonlinear PA, i.e. predistortion (PD), is a promising and practical technique. PD techniques can be classified into analogue (Hajipour & Mohammadi, 2012) and digital (Aggarwal & Bohara, 2019; Kwan et al., 2017; Nesimoglu, 2018; Wu et al., 2018); digital PD is more popular because of its simple implementation and superior linearisation performance. It has been extensively studied to simultaneously remove multiband cross-modulations and harmonics in concurrent dual-band (Li et al., 2017; Rawat et al., 2015) and triband (Jaraut et al., 2019) environments, and improve the linearity near the fundamental frequency of wideband signals (see (Becerra-González et al., 2017; Choi & Jeong, 2012; Huang et al., 2006; Jiang & Wilford, 2010; Zhang et al., 2017; Zhu et al., 2013) and the references therein). In addition to linearising the fundamental signal, a parallel-structured PD was proposed to eliminate the harmonics at , where is an integer greater than unity. The parallel-structured PD is composed of multiple-parallel PDs, which are upconverted to an integer multiple of (Choi et al., 2011). The computational complexity required for determining the parallel-PD parameters is considerable because multiple nonlinear equations need to be handled simultaneously; thus, its implementation is challenging.