Energy-efficient dynamic lightpath adjustment in a decomposed AWGR-based passive WDM fronthaul

To cope with the explosion of mobile traffic demand, cloud radio access networks (C-RAN) have been recently proposed. In C-RANs, the two main elements of traditional base stations (BSs), i.e., the baseband unit (BBU) and the remote radio head (RRH), are separated, and the BBU can be virtualized and located in a remote location together with BBUs of other BSs. High-bandwidth digitized baseband signals must be exchanged between BBUs and RRHs through a large-capacity fronthaul network. Wavelength division multiplexing (WDM) technology is an efficient solution to provide sufficient fronthaul bandwidth with a large number of optical transceivers. With the fixed connections between BBUs and RRHs in the traditional C-RAN, the utilization of optical transceivers as well as BBUs is inefficient. In this paper, we propose a decomposed arrayed waveguide grating router (AWGR)-enabled passive WDM fronthaul, and we formulate the minimal energy consumption problem as integer linear programming, with the objective of minimizing the energy consumption caused by optical transceivers and BBUs, etc. We also design two dynamic lightpath adjustment heuristics by light-path reconfiguration to improve energy efficiency. In addition, we take AWGR decomposition into consideration to reduce the tuning range of tunable transceivers and free spectrum range of AWGR, hence lowering the deployment cost of transport network components. Numerical evaluation shows that our proposed schemes achieve significant energy savings compared to fixed lightpath allocation.