PLL and Costas loop based carrier recovery circuits for 4QAM: non-linear analysis and simulation

TL;DR

This paper analyzes and simulates carrier recovery circuits for 4QAM modulation, focusing on non-linear analysis of Costas loops and their modifications, including a new circuit proposal, using MATLAB Simulink models.

Contribution

It introduces a new 4QAM Costas loop circuit and provides detailed non-linear analysis and simulation models for various circuit modifications.

Findings

Non-linear analysis of Costas loops is complex but essential.

Simulation results validate the stability and performance of the proposed circuits.

The new circuit design shows improved noise robustness.

Abstract

Design of stable carrier recovery circuits are used in many applications: wireless digital communication, optical communication, microwave devices and other applications. Quadrature Phase-Shift Keying (QPSK, 4-QAM) is used as modulation technique in many of these applications, since QPSK provides double the data rate of classic Binary PSK (BPSK) modulation. Analysis of Costas loop is a hard task because of its non-linearity. In this work we consider two well-known modifications of 4QAM Costas loop circuits and discuss a new circuit proposed by J. Ladvanszky. MATLAB Simulink models of the circuits are provided and the noise analysis is performed.