Fiber is helping mobile network operators take advantage of LTE-Advanced technology and will be critical in “5G” network architectures, but there are challenges associated with fiber at cell towers and in distributed radio architectures. Kashif Hussain, go to market leader at Viavi Solutions, is in the business of helping operators address those challenges.
“The first challenge is how to manage fiber connectors,” Hussain said. It’s easy to assume that a cover on a fiber connector means the equipment is clean and ready to use, but Hussain said that can be a costly assumption to make.
“A micron of dirt can significantly impact your signal quality,” he said. “A lot of training had to happen for these technicians who were used to working with big coax cables. … A lot of ‘inspect before you connect’ kinds of technologies were introduced and are being practiced in the industry.”
Centralized radio access network architectures use fiber to connect radios to digital baseband units that can be up to 15 miles away. This enables operators to house the baseband in a data center or in a location that is less expensive than the radio site. It also allows them to use one centralized baseband unit to support several radios. C-RAN also facilitates LTE-Advanced.
“The biggest advantage is the LTE-Advanced features, for example coordinated multipoint,” said Hussain. “At the cell edge you can cancel the interference effects and manage data throughput through multiple sectors and multiple sites … truly implementing the heterogeneous networks, meaning you can have data provided to a mobile from a macrocell and a small cell.”
“Now the baseband units are moved into a baseband hotel and the coordination is much faster, and now instead of using just the X2 interface between the radios you are actually working within the cell site hub and your coordination is much faster and you can truly use the LTE-Advanced capabilities, so that is one of the reasons that C-RAN is getting deployed much faster,” Hussain said. “Again, the challenge with that is you have to manage your fiber interface, you have to insure the fiber links are clean and you have to do the proper testing. There are certain steps that are required for the provisioning … all the wavelengths need to be checked all the way back to the mixer. So, it offers certain advantages but also you have to be careful and everything has to be tested properly.”