To reduce or compensate the nonlinear distortion from a nonlinear system is becoming an important need in many areas. Here a wide class of nonlinear systems adaptive digital predistortion techniques are presented. For estimating the coefficients of the predistorter, different learning architectures like theDLA( Direct Learning Architecture) and ILA(Indirect Learning Architecture) are considered. In the DLA approach, we propose a new adaptation algorithm – the Nonlinear Filtered of x Prediction Error Method (NFxPEM) algorithm, which can work for much better completion and much faster convergence in contrast to the traditional Nonlinear Filtered of x Least Mean Squares algorithm. All of these time domain adaptive algorithms require accurate system identification of the nonlinear system.
Signal Processing for Ultra Wideband Transceivers
Here standardized and non-standardized UWBS and its implementation approaches are presented. These implementation approaches comprises The signal processing algorithms(SPA) to achieve the processing of ultra wide-band systems signals for transceiver front-ends as well as digital back-ends . With hybrid filterbank transceivers parallel position in frequency-domain can be achieved. The systematized for MB-OFDM signaling strategy permits parallelization in the frequency domain by dispersing the OMM(orthogonal multicarrier modulation) to the multiple units.Moreover, the response of the channel to the wideband signals has been parallelized in the frequency domain and the consequences of the parallelization have been scrutinized. The declining of slight performance are observed, where the limiting effects are shortened sidelobes and filter discrepancy in analog front-ends. Performance losses measurement have been defined. For UWB signal generation, a novel broadband signal generation attitude is presented.
ISDB T Digital TV Modulator With Adaptive NonLinear Digital Pre-distortion:
Integrated Service Digital Broadcasting (ISDB)-T Digital TV modulator is evolved to conform terrestrial digital television of various countries like Japan,Argentina,Brazil and different South American country. The channel of modulator can be encoding and ARIB STD-B31 standard can be fully accordance in modulation mode.. This ISDB-T modulator can assists single frequency network, four ASI hot backup input and multi-frequency network. For improving transmitter’s output performance, the ISDB-T modulator concurrently supports for layered transmission, adaptive digital pre-distortion of nonlinear systems and three transmission modes. Moreover, this device can be improved and managed along network system, which can be extensively used in ISDB-T digital broadcasting network’s setting up and set-top box design’s production and test.
Adaptive LINEAR Digital Pre-Distortion:
In Digital Pre-Distortion ,a Digital Pre-Distortion can adapt to receive a digital input signal and output .An adaptive Pre-distorted digital signal, the digital predistorter comprising the followings:
An input coupled to receive the digital input signal;
A first signal path coupled to the input;
The second signal path of Adaptive digital distortion coupled with the parallel input with the above said first signal path, encompassing a first digital predistorter circuit yielding a first predistortion signal. Whereas first digital predistorter circuit comprises a detector providing a signal related to the magnitude of the digital input signal and a Look Up Table of gain error corrections indexed by said signal related to the magnitude of the digital input signal;
The third signal path, connected in a pair to the parallel input with the above said first as well as second signal path, incorporated with the second digital predistorter circuit bestowing with a polynomial based predistortion operation on the input signal and supplying a second predistortion signal;
Acombiner circuit which receives and combines the outputs of the first and second digital predistorter circuits with the output of the first signal path to provide a Pre-distorted digital output signal.
An adaptively linear Pre-Distortion system, Incorporated:
An input adapted to receive a digital input signal;
A digital predistorter connected in a pair to the input and receiving the digital input signal and getting output in a Pre-distorted digital signal, the digital predistorter contains a hierarchical filter, inclusive of a fixed coefficient filter and an adaptive coefficient filter coupled in series, to compensate for memory effects of the transmission system ;
A DAC(Digital to Analog Converter) coupled to receive the Pre-distorted digital signal output of the digital predistorter and provide an analog signal;
An up converter for receiving the analog signal from the digital to analog converter and converting it to an RF analog signal;
A power amplifier receiving the RF analog signal and providing an amplified RF output signal;
An output sampling coupler coupled to sample the analog RF output signal from the power amplifier;
A feedback circuit mesh, connected in a pair to the output sampling coupler, embracing a down converter and an analog to digital converter converting the sampled RF
output signal to a digital sampled signal representative of the RF output signal;
A forward gain mapping circuit connected in parallel to accept the input signal and providing a model of the effect of the digital predistorter and power amplifier to the input signal;
An error generator circuit coupled to collect the output of the forward gain mapping circuit and the digital sampled signal from the feedback circuit path and supplying a digital error signal from the contrast of the signals; and an adaptive coefficient estimator circuit connected in parallel to collect the digital signal input as well as the digital error signal and providing updated predistortion coefficients to the adaptive filter in said digital predistorter.