FFT size optimization for LTE RoF in nonlinear fibre propagation

This papers investigates the performance of the fast Fourier transform (FFT) sizes- 64, 128, 256, 512 and 1024 for the orthogonal frequency division multiplexing (OFDM) scheme in 3^rd generation partnership program (3GPP)-long term evolution (LTE) and LTE-Advanced (LTE-A). This paper aims to optimize the FFT sizes with respect to quadrature phase shift keying (QPSK), 16, 64 and 256-quadrature amplitude modulation (QAM). This optimization is for the transmission of LTE signals between eNodeB (eNB) and relay node (RN) to extend the mobile coverage employing radio-over-fibre (RoF). This paper will take into account the positive frequency chirp (PFC) induced by distributed feedback laser (DFB) through direct modulation with chromatic dispersion (CD) and self phase modulation (SPM) impairments into consideration. We present the optimum optical launch power (OLP) region termed as the intermixing region between linear and nonlinear optical fibre propagation. The optimum OLP in this investigation takes place at -4 dBm which falls within the intermixing region. At the transmission rate of 200, 400, 600 and 800 Mb/s of QPSK, 16, 64 and 256-QAM, the FFT size-128 provides the optimum power penalty with average system efficiency with respect to FFT size-64 is 54% and FFT size-256 is 65%.