On the design of optical fiber based wireless access systems

Abstract

Optical fiber based wireless access schemes receive renewed attention with the popularity of hot-spots. They increase capacity, QoS and support wideband multimedia services and have the possibility of utilizing existing fiber infrastructure. However, link design in a fiber-wireless system needs careful consideration of many factors. There are two signal to noise ratios involved, the optical SNR (OSNR) and the electrical SNR. These two form the cumulative SNR in the concatenated fiber-wireless channel. The OSNR is a function of the modulation index m, E/O, O/E conversion losses and, the fiber length. There is a 39 dB loss due to E/O and O/E conversion only in resistively matched wideband links and the OSNR rapidly decreases with fiber length. The cumulative SNR at the mobile unit decides the QoS and cell size. This SNR depends on OSNR, wireless channel path loss and the optical receiver amplifier gain. In this paper, we study the relationships between critical design parameters, such as maximum radio and optical link losses, cumulative and optical SNR and, optical amplifier gain in a fiber-based wireless system.