To meet the requirements of 5G mobile networks, several radio access technologies, such as millimeter wave\ncommunications and massive MIMO, are being proposed. In addition, cloud radio access network (C-RAN) architectures are\nconsidered instrumental to fully exploit the capabilities of future 5G RANs. However, RAN centralization imposes stringent\nrequirements on the transport network, which today are addressed with purpose-specific and expensive fronthaul links. As\nthe demands on future access networks rise, so will the challenges in the fronthaul and backhaul segments. It is hence of\nfundamental importance to consider the design of transport networks alongside the definition of future access\ntechnologies to avoid the transport becoming a bottleneck. Therefore, we analyze in this work the impact\nthat future RAN technologies will have on the transport network and on the design of the next generation\nfronthaul interface. To understand the especially important impact of varying user traffic, we utilize measurements from a\nreal-world 4G network and, taking target 5G performance figures into account, extrapolate its statistics to a 5G scenario.\nWith this, we derive both per-cell and aggregated data rate requirements for 5G transport networks. In addition, we show\nthat the effect of statistical multiplexing is an important factor to reduce transport network capacity requirements and\ncosts. Based on our investigations, we provide guidelines for the development of the 5G transport network architecture.
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