Fronthaul evolution: From CPRI to Ethernet

• Extensively referenced requirements (using key standards) for future fronthaul.
• Covers advantages and challenges of using Ethernet in the fronthaul.
• Ethernet-based “fronthaul lite” proposed to meet 5G demands.
• Proposals for new functional split between baseband unit and radio head.
• Caters for both co-ordinated multipoint and massive MIMO.

It is proposed that using Ethernet in the fronthaul, between base station baseband unit (BBU) pools and remote radio heads (RRHs), can bring a number of advantages, from use of lower-cost equipment, shared use of infrastructure with fixed access networks, to obtaining statistical multiplexing and optimised performance through probe-based monitoring and software-defined networking. However, a number of challenges exist: ultra-high-bit-rate requirements from the transport of increased bandwidth radio streams for multiple antennas in future mobile networks, and low latency and jitter to meet delay requirements and the demands of joint processing. A new fronthaul functional division is proposed which can alleviate the most demanding bit-rate requirements by transport of baseband signals instead of sampled radio waveforms, and enable statistical multiplexing gains. Delay and synchronisation issues remain to be solved.