For many years, Radio-over-Fiber (RoF) Systems are extremely interesting and evolving technology for its applications in wireless broadband communication. The need for today is to develop low-cost base stations (BS) for RoF systems to make them practical for commercial deployment. The proposed scheme in this work solves this issue in which FSK signal is generated in the down-link very efficiently by using couplers and laser sources. The generated signal is of very high frequency and simplifies the architecture, as no electrical oscillator is required. Before that signal generation in ASK...