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What Optics Products Are Needed in 5G Fronthaul?

In the past few years, Telecom operators have already upgraded their LTE networks by using additional spectrum, carrier aggregation and LTE-A, and have added Small Cell in Macrocell coverage area to drive the increasement of fronthaul bandwidth requirements. In the current, many operators and equipment vendors have standardized the multi-rate transceivers that support 10Gb/s for all fronthaul requirements. Because they are able to meet most of different transmission speed requirement by one device and decrease the complexity of the specific site design and spare part inventory. Many operators, especially those that lease their fronthaul fiber, also deployed WDM system in their fronthaul networks.

5G Fronthaul Will Need Faster Optical Products, But How Fast?

With the emergence of 5G mobile network, the fronthaul demand will also change. The target peak bandwidth of 5G is 20Gb/s, which will require a higher spectrum than LTE to realize the requirement. That is to say, the shorter wavelength can realize the smaller antenna in the millimeter wave range, thus allows the use of higher order MIMO antenna arrays. In LTE area, 4*8 and 8*8 MIMO have been top. But in 5G area, 64*64 MIMO is also possible. The number of MIMO is higher; the bandwidth required for the corresponding fronthaul link is larger. In the case that other conditions are same, the second way for 5G to increase bandwidth is to use 100 GHz frequency (LTE uses 20GHz), so that can produce a single radio transmission from cellular site to the core network for more than 5 times of bandwidth.

Given the fronthaul bandwidth required to support 5G radio may be have a substantial growth, mobile device manufacturers update the CPRI specification to „eCPRI“ (released in August 2017). One key factor of eCPRI is to transfer some physical layer signal processing from the baseband unit to the radiofrequency pull head (RRH), which in many cases reduces the fronthaul bandwidth to one in ten.

When all the different factors that influence the bandwidth of the 5G fronthaul add up (some drive its growth, some drive it down), the expected bandwidth fall in the 14 Gb/s to 30 Gb/s range, depending on the eCPRI implementation details, base stations, and etc. If the old CPRI scheme is adopted, all physical layer signal processing will remain in the baseband unit, and similar 5G network configuration will require 236Gb/s fronthaul bandwidth. As a result, the 5G base station will generate 160Gb/s or more in nominal terms, and with eCPRI, the actual fronthaul bandwidth required will be 14-30Gb/s.

Just like that 10G optical transceivers can become the actual standard for LTE fronthaul, the next generation of higher standard Ethernet speeds will be applied to 5G fronthaul, which means that 5G deployment will require a large number of 25GbE devices. Even though some components are industrial temperature and/or bidirectional versions specially designed for fronthaul application.

5G Network Will Also Need Higher-speed Optics Products( 25Gb/s or above)

Mobile fronthaul or backhaul need 50G, 100G or even 400G optical transceivers. CPRI alliance has defined fronthaul for a long time, but there is no a consistent definition for wireless backhaul. LightCounting defines the backhaul as the first optical link that begins in BBU and carries the flow from the core network. Other broader definitions include access, aggregation, and core networks. Naturally, if the data flow from BBU to the core network flows to 25Gb/s, then 50G, 10G, or even 400Gb/s transfers may be needed.

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