# Impact of Non-Linear High-Power Amplifiers on Cooperative Relaying Systems

## TL;DR

This paper analyzes how non-linear high-power amplifiers affect cooperative relay systems, revealing performance degradation at high data rates and deriving analytical expressions validated by simulations.

## Contribution

It introduces a comprehensive analysis of non-linear amplifier effects on relay systems, including closed-form expressions and high SNR asymptotes.

## Key findings

- Performance loss is small at low rates but significant at high rates.
- Outage probability and BER saturate at high rates due to non-linear distortion.
- Capacity is limited by a ceiling proportional to impairment parameters.

## Abstract

In this paper, we investigate the impact of the high-power amplifier non-linear distortion on multiple relay systems by introducing the soft envelope limiter, traveling wave tube amplifier, and solid-state power amplifier to the relays. The system employs amplify-and-forward either fixed or variable gain relaying and uses the opportunistic relay selection with outdated channel state information to select the best relay. The results show that the performance loss is small at low rates; however, it is significant for high rates. In particular, the outage probability and the bit error rate are saturated by an irreducible floor at high rates. The same analysis is pursued for the capacity and shows that it is saturated by a detrimental ceiling as the average signal-to-noise ratio becomes higher. This result contrasts the case of the ideal hardware where the capacity grows indefinitely. Moreover, the results show that the capacity ceiling is proportional to the impairment's parameter and for some special cases the impaired systems practically operate in acceptable conditions. Closed-forms and high SNR asymptotes of the outage probability, the bit error rate, and the capacity are derived. Finally, analytical expressions are validated by the Monte Carlo simulation.

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Source: https://tomesphere.com/paper/1902.03176