# Novel Baseband Equivalent Models of Quadrature Modulated All-Digital Transmitters

## TL;DR

This paper derives a comprehensive baseband equivalent model for quadrature modulated all-digital transmitters, enabling improved analysis and predistortion of nonlinearities without restrictions on digital modulation schemes.

## Contribution

It introduces a general, exact baseband equivalent model for all-digital transmitters that combines pulse encoding, Volterra series, and linear time-varying systems.

## Key findings

- Model verified through MATLAB simulations
- Enables new digital predistortion approaches
- Applicable to various digital modulation schemes

## Abstract

In this paper an exact baseband equivalent model of a quadrature modulated all-digital transmitter is derived. No restrictions on the number of levels of a digital switched-mode power amplifier (SMPA) driving input, nor the pulse encoding scheme employed, are made. This implies a high level of generality of the proposed model. We show that all-digital transmitter (ADT) can be represented as a series connection of the pulse encoder, discrete-time Volterra series model of fixed degree and memory depth, and a linear time-varying system with special properties. This result suggests a new analytically motivated structure of a digital predistortion (DPD) of SMPA nonlinearities in ADT. Numerical simulations in MATLAB are used to verify proposed baseband equivalent model.