Characteristics of directly modulated ROF link for wireless access

Abstract

The radio-over-fiber (ROF) link is of much interest to provide broadband wireless access. In this paper, we discuss some characteristics of a directly modulated ROF link in CDMA and FDMA environments. These RF measurement results show that, though the ROF link has adequate bandwidth to support several radio channels, nonlinear distortion and power loss, mainly due to electrical to optical conversion process and vice versa, limit the performance. Especially, the AM-PM type nonlinearity that starts at low power levels is a bigger concern. Furthermore, the spurious free dynamic range (SFDR) decreases because the increases with the bandwidth of the RF signal.

On the Equalization of an OFDM-Based Radio-over-Fiber System Using Neural Networks

“…Also, the OFDM system parameters [18] and optical subsystem parameters [3] are summarized in Tab. Number of epochs for training RBF-NN 1 000…”

“…1) includes a laser diode (LD), a 2.2 km long single-mode fiber and a photodiode (PD) [3]. The radio frequency is 1.8 GHz, however the frequency response of the optical link (centred at 1310 nm) is flat over frequencies 1.7 < f < 2.2 GHz.…”

“…is the gain of the pre-amplifier which matches the output power of the transmit RRC filter to the input power of the optical subsystem [3], P m is the maximum input RF power to the optical subsystem before the pre-amplifier, max(P RF,i ) is the (measured) maximum input RF power before the pre-amplifier, ψ x (t) is the phase of the signal x t (t), R in = R out = 50 Ω is the input/output impedance of the optical subsystem, and G out is a linear gain which sets the overall gain of the optical subsystem to unity. Also, f AM-AM (.)…”

“…Typically, the optical part is used to interconnect a central radio processing facility with a remote radio antenna, the latter providing coverage to wireless broadband users. Some of the advantages offered by a RoF system include low signal attenuation (in the fiber), improved coverage and system performance, enhanced capacity, low Radio Frequency (RF) power dissipation, reduced complexity due to the centralized processing of RF signals and ultimately low system costs [1][2][3]. However, the performance of RoF systems can be severely affected by nonlinear effects in the transmission channel.…”

Pilot‐aided estimation and equalisation of a Radio‐over‐Fibre system in Wideband Code Division Multiple Access

“…Finally, RF channel parameters [21], WCDMA system parameters [22], [23], and optical subsystem parameters [12] are summarised in Tables I, II, and III, respectively. This behavior may be explained more accurately as follows.…”