This paper introduces radio over fiber (RoF) as one of enabling technologies of the fourth generation (4G) wireless communication. The RoF is a key technology to solve the problem about the high radio-wave propagation attenuation of 4G systems whose frequency band is expected to be higher than 3 GHz. In addition, this technology enables 4G systems based on pico-cells to decrease transmitting power, increase the efficiency of frequency reuse, and provide cost effective deployment.