CE-OFDM Schemes: Spectral Characterization and Optimum Performance

Abstract

Constant envelope orthogonal frequency division multiplexing (CE-OFDM) techniques have been recently proposed to allow the use of power-efficient saturated amplifiers, since those signals do not have the high peak-to-average ratio of OFDM signals, but maintain most of the OFDM advantages. However, the nonlinear nature of the phase modulation process inherent to CE-OFDM schemes gives rise to both theoretical challenges (analytical difficulties due to the nonlinear processes involved) and practical challenges (spectral widening and possible performance degradation due to nonlinear distortion effects). In this work, we present accurate expressions for the average power spectral density of CE-OFDM signals. Making use of recent results that indicate performance gains associated to the optimum detection of nonlinearly distorted multicarrier signals, we also investigate the optimum detection of CE-OFDM signals considering both additive white Gaussian noise channels and frequency-selective channels with Rayleigh fading, providing theoretical expressions for the asymptotic gains as well as the correspondent approximate bit-error-rate results.

Multiuser Equalizer for Hybrid Massive MIMO mmWave CE-OFDM Systems

“…Cleary, there is an optimal value, which is approximately 2πh = 0.9. A deeper discussion about the impact of the modulation index in the system performance can be found in [19]. Hereinafter, the results are obtained for 2πh = 0.9.…”

“…The use of mmWave bands allows larger bandwidths, but considering orthogonal frequency division multiplexing (OFDM) modulation, this leads to a higher number of subcarriers. Therefore, the use of OFDM, which is very efficient to mitigate the effects of inter-symbol interference (ISI) in frequency selective channels, results in a signal with high amplitude fluctuations, making the large peak-to-average power ratio (PAPR) a problem, which should be taken into account for mmWave mMIMO systems [19]. A high PAPR results in strong nonlinear distortions caused by the power amplifier [20], degrading the system performance.…”