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Analog Telephone Channels and the Subscriber Loop
Published in Jerry D. Gibson, The Communications Handbook, 2018
Intermodulation distortion (IMD), also known as nonlinear distortion, is an impairment that arises due to the nonlinear characteristics of loop interfaces. IMD is the power generated at extraneous frequencies (intermodulation products) when a multi-tone signal is applied to a circuit. Loop facilities composed entirely of twisted pair cables do not contribute to IMD but the cables always are connected to interfaces. In particular, nonlinearities in the interface electronics lead to generation of undesirable sum and difference signals related to the original desired signals. As with other transmission impairments, IMD manifests itself as analog voiceband modem errors and reduced throughput or connection speed, but IMD does not significantly impair voice quality. Where there is only a single A/D - D/A conversion process in an analog circuit, the ratio of desired signal to undesired signal due to IMD is around 40 to 50 dB.
Radio Frequency Distortion Mechanisms and Analysis
Published in Jerry C. Whitaker, Electronic Systems Maintenance Handbook, 2017
The amplitude of an angle modulated wave is supposed to be constant while the information being transmitted is contained in the phase. Linear distortion can be introduced by the channel, nonideal filters and other subcircuits. In general, linear distortion results in time-variant amplitude and phase errors in the angle modulated wave. In effect, the angle modulated wave now contains both amplitude and phase modulation. Nonlinear distortion usually results from channel or power amplifier nonlinearities. Amplitude nonlinearities result in undesirable (or residual) amplitude modulation (AM), whereas phase nonlinearities result in phase distortion of the angle modulated wave. The effect of undesirable amplitude modulation resulting from linear and nonlinear distortion are discussed under separate subheadings. The effects of the time-variant phase errors resulting from linear distortion and from phase nonlinearities are discussed together under phase distortion in angle modulation.
High-Speed Directly Modulated Injection-Locked VCSELs
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
In analog links, high linearity is desirable in order to reproduce the source information with minimal distortion. The nonlinear distortion comes from several sources, including second and higher-order harmonics of the signal, and the intermodulation distortion (IMD). In actual applications of multi-channel signal transmission where baseband signals from different channels are carried by a number of well-separated high-frequency carriers, second- (or higher-) order harmonic distortions generated by signals in a channel are actually of little concern since they generally do not fall within the frequency band of that particular channel or any other channels [77]. However, the third-order intermodulation (IMD3) product of the laser transmitter (for two-tone modulation at ω1 and ω2, the IMD3 are at frequencies (2ω1–ω2 and 2ω2–ω1)) may lie within the frequency band and is thus not desirable. For device studies, the standard technique is to characterize the IMD3 using two-tone modulation. The spurious-free dynamic range (SFDR) is a useful measure to characterize how IMD3 can limit system performance [80]. It is defined as the ratio of the fundamental to the intermodulation product at the point where the system noise floor equals the intermodulation product [81].
Fractional Wavelet Transform based PAPR Reduction Schemes in Multicarrier Modulation System
Published in IETE Journal of Research, 2022
R. Ayeswarya, N. Amutha Prabha
The major drawback with the conventional MCM transmission techniques is the occurrence of high peak amplitude signals. The excursion of these signals into non-linear region of power amplifier leads to spectral spreading and nonlinear distortion [41]. In this proposal, the reductions of PAPR without any usage of CP and detailed simultaneous information of signals in both time and frequency domain by means of FrWT is considered. This motivates to obtain the results of the proposed scheme. An oversampling by a factor greater than 1 provides accuracy in the PAPR of the time domain signals.