No abstract

This paper presents a new technique to improve the performance of OFDM systems with nonlinear amplifiers. This method aims to achieve good balances between PAPR and BER at low computer cost. A performance and complexity comparison with known techniques for BER reduction is presented. The results show that the proposed method has lower computational complexity (about 33% fewer multiplications), similar BER performance and better PAPR performance than the other techniques here evaluated.

Resumo-Este trabalho investiga a aplicac ¸ão de equalizacão turbo a canais de HF. Propõe-se dois algoritmos de equalizac ¸ão linear baseados no critério MMSE (Minimum Mean-Square Error), obtidos a partir de modificacões num esquema MMSE anteriormente proposto por outros autores. São apresentados resultados de avaliac ¸ão de desempenho via simulac ¸ão computacional, usando como referência o padrão MIL-STD-188-110A/B, que prevê formas de onda para modems seriais em HF. A análise destes resultados mostra que não ocorre degradac ¸ão significativa de desempenho com as modificac ¸ões introduzidas. Por outro lado, uma análise comparativa de complexidade computacional mostra que uma das propostas aqui apresentadas produz significativa reduc ¸ão na complexidade do equalizador. Palavras-Chave-Equalizac ¸ão turbo, canais de HF, equalizadores turbo de baixa complexidade, equalizadores turbo MMSE, estimac ¸ão de canal.

This work proposes a new technique to be used in orthogonal frequency division multiplexing (OFDM) systems subject to nonlinear power amplification, aiming to obtain better bit error rate (BER) performance with reduced computational complexity and low peak-to-average power ratio (PAPR). The core of the proposed technique is a new metric to choose a modified OFDM symbol to be transmitted among several alternatives with the aim of reducing the deleterious effects of nonlinear amplification. The proposed metric is independent of a power amplifier model and may be associated with different approaches to generate the modified OFDM symbols. Simulation results are presented, using a Partial Transmit Sequence (PTS) approach, which show that the proposed scheme provides BER performance similar to other known techniques at a significantly lower computational cost (about 33% less real multiplications and 66% less real additions). Estimates of the PAPR complementary cumulative distribution function (CCDF) are also presented and show that the proposed method does not degrade this performance index substantially compared to those techniques. Keywords-bit error rate (BER) performance, orthogonal frequency division multiplexing (OFDM), peak-to-average power ratio (PAPR), solid state power amplifier (SSPA), partial transmit sequence (PTS).