Performance Analysis of Nonlinear Distortions of RF Signal in Wireless CDMA Downlink with Quadrature Amplitude Modulation
Abstract
Purpose: In this paper, we consider digital direct-sequence spread-spectrum multiple-access communication systems with CDMA technology and QAM modulation. Non-linear distortion of a grouped signal in these systems lead to a higher probability of digital errors and worse quality of individual subscriber's channels. The aim of this research is to find out how the digital error probability depends on the non-linear distortion of grouped video and radio signals. We need to know this dependence to substantiate the demands on the amplitude characteristics of the amplifiers in multiple-duct video and radio channels. Methods: A real grouped signal is represented as a sum of three components: the non-distorted part of the signal, the correlated multiplicative distortion and uncorrelated additive distortion. A computer model of the transmitted signal is built and used, taking into account, unlike the conventional methods, not only statistical but also combinatorial properties of a complex grouped signals with code division. An admissible error of estimated noise immunity is obtained by the approximation of real distribution of the signal and noise mixture, using Hermite polynomials and Gram-Charlier series. Results: It is shown that the usual Gaussian representation of the noise and the linearization of non-linear elements characteristics lead to overestimating the noise immunity. Analyzing the combinatorics of the grouped signal has helped to estimate both separate and combined impact of each parameter of nonlinear channels upon the real noise immunity of the system. The laws of distribution of the mixture of Rademacher - Walsh functions with a noise in a nonlinear channel are represented analytically and graphically, along with the calculated error probabilities. Practical relevance: Our recommendations about technical demands on grouped channels for systems with code division can improve the noise stability. They can be used in theoretical research, technical development, production and application of new high-speed digital transmission systems.Published
2015-10-20
How to Cite
Gurevich, V., & Egorov, S. (2015). Performance Analysis of Nonlinear Distortions of RF Signal in Wireless CDMA Downlink with Quadrature Amplitude Modulation. Information and Control Systems, (5), 106-115. https://doi.org/10.15217/issn1684-8853.2015.5.106
Issue
Section
Information channels and medium