The fifth generation of mobile communication is characterized by ultra-dense cellular networks, where massive small cells are deployed in hot spots to increase the network capacity. As a promising technology in the small-cell scenario, coordinated multipoint (CoMP) is proposed to improve cell-edge user throughput by converting inter-cell interference into useful signals. In this paper, we study how reconfigurable fronthaul enabled by optical networks can help improve the CoMP service. According to the baseband unit (BBU) that serves the purposes of coordination, we classify the CoMP service into intra-BBU CoMP and inter-BBU CoMP. Inter-BBU CoMP will cause data exchange between the BBUs, which requires backhaul to support a large bandwidth and low latency. Our proposal is to associate coordinated RRHs with a single BBU to reduce the data exchange. To achieve this goal, we propose two heuristic algorithms: a minimum-cut graph-based lightpath reconfiguration (MCG-LR) and a BBU weight-based lightpath reconfiguration (BW-LR). The two algorithms are emulated on a time and wavelength division multiplexing passive optical network-based fronthaul under different cell conditions. The simulation results show that the reconfigurability of fronthaul can improve the CoMP service through elastic radio resource allocation. In addition, we can observe that MCG-LR achieves a lower inter-BBU CoMP ratio and lower BBU migration than BW-LR after lightpath (wavelength) reconfiguration.
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