Remote Beamforming Scheme With Fixed Wavelength Allocation for Radio-Over-Fiber Systems Employing Single-Mode Fiber

This paper presents a remote beamforming scheme with fixed wavelength allocation for radio-over-fiber (RoF) systems employing single-mode fiber (SMF). In the proposed scheme, wavelengths with equal narrow spacing are fixedly assigned to each antenna element to equalize the time delay differences between adjacent wavelengths caused by chromatic dispersion. The beam direction of base station (BS) is controlled only by phase control at central station (CS). This offers efficient wavelength utilization and completely remote beam control without information of optical fiber length, and supports systems employing high carrier frequency and long optical fiber. The beamforming performance of the scheme is evaluated theoretically and experimentally. It is shown that the beam pattern depends on optical intensity modulation frequency instead of radiated frequency. Simulations indicate that the required wavelength spacing to obtain a desired beam pattern becomes narrower as more wavelengths are used or intensity modulation frequency becomes higher. Finally, to evaluate the feasibility of the scheme, experiments are conducted under the condition of intensity modulation frequency of 10 GHz, 10 km SMF, and four element array antenna. The results substantially agree with the simulation results, and the main lobe level decrease is within 0.04 dB at wavelength spacing of 50-400 GHz (0.39-3.13 nm on average in C band). The results confirm that the scheme can achieve almost ideal beam patterns and realize beamforming and beamscanning.