Power budget improvement of multi-IFoF based analog indoor-distributed antenna system (DAS) with laser over-modulation

Abstract

Abstract We demonstrate the improvement of the optical power budget in multi-intermediate frequency over fiber (IFoF) based indoor-distributed antenna system (DAS) with 48 IF carriers of LTE-A signal using laser over-modulation. The laser over-modulation can improve the optical power budget by increasing the input RF power to DFB-LD until a limit of nonlinear distortion such as CTB and clipping, when the received optical power is very low. To compensate the decrease of optical power budget in analog optical link, we employ the laser over-modulation, and derive the optimum optical modulation index (OMI)/ch to enhance link budget. To investigate the effect of laser over-modulation, we analyze the noise characteristics associated with the carrier-to-noise ratio (CNR) depending on the received optical power, and compare three different optical receivers (Rx) most often used: i) PIN-photodiode (PD), ii) APD, iii) PIN-PD following an EDFA (EDFA-PIN), respectively. Using the laser over-modulation, it is experimentally observed to achieve optical power budget of 25 dB for PIN-PD, 31 dB for APD, and 33 dB for EDFA-PIN in multi-IFoF based indoor-DAS for 48 x 20 MHz LTE-A signals transmission, respectively.