Low latency mobile backhauling using optical wireless links

To overcome the ever increasing bandwidth demands of modern mobile radio applications, the use of spectral efficient modulation is necessary but not sufficient. Small cells are able to provide additional bandwidth at those locations where the traffic volume is high. Therefore, the number of small cells inside a larger macro-cell will be increased in the near future. Commonly, 10 small cells per sector are expected outdoors and 50 indoors. A major problem related to the massive use of small cells is the required backhaul. In order to increase the mobile network capacity while keeping the deployment costs low, the backhaul technology needs to be low-cost and reliable likewise. The deployment of fiber is the best choice on the long run but expensive and often impractical. As radio spectrum is restricted, optical wireless offers an attractive alternative to micro-and mm-wave technologies. Visibility measurements show that typical outdoor distances of 200 m can be covered by optical wireless links with high availability. Beside the achievable data rate, latency is an issue in the mobile backhaul. In this paper, we demonstrate experimentally that optical wireless links can meet the latency requirements for Long-Term Evolution (LTE) mobile networks of 10 ms. Moreover, using a next generation baseband chipset, end-to-end latencies below 2 ms can be achieved