The unsung hero of wireless connectivity has always been backhaul, the link from the base station to the network switch. A panel at the recent AGL Virtual Summit, moderated by Chris Pearson, president of 5G Americas, discussed recent developments in this key link in attaining the high speeds and low latency required for 5G wireless communications.
One of the newest developments is integrated access backhaul (IAB), which allows the carrier to use the same radio-frequency spectrum it uses for access to the radio access network (RAN) to backhaul the signal from the cell tower. IAB was made possible by the standard protocols contained in Release 16 of the Third Generation Partnership Project (3GPP) 5G standard.
“Fiber is the ideal backhaul for any 5G network, but if there is no fiber availability, IAB gives the provider another tool to quickly set up a backhaul connection,” said Scot Bohaychyk, the carrier market manager at Clearfield. “It can be used for hot spots and small cells, too. IAB is a complement to fiber, more than it is competition. It is a good choice for backhaul, especially for events where you need a quick setup and teardown.”
Release 16 of the 5G standard does not mandate which frequencies are used for IAB, low-band, mid-band or high-band spectrum. Technically, IAB has become possible because of the large swathes of spectrum that have been made available for 5G, especially in the high-band, the emergence of small cell sites and advances in multiplex technology, according to Ranjeet Bhattacharya, a principal solutions director for 5G network evolution in the North American market area for Ericsson. He said the challenge that being studied by the carriers is how to multiplex the spectrum in the right way and avoid interference.
“The question of which spectrum makes sense to multiplex between the end-user communications and backhaul for IAB,” Bhattacharya said. “The discussion is currently favoring high-band frequencies for end-user and backhaul signals. Because it is such a wide swathe of spectrum, it would allow the carriers to avoid interference. There are ways to multiplex either in a frequency domain, time domain or spatial domain, but you lose a little bit of capacity using IAB.”
Although IAB provides a fast time to market, it can pose a challenge from the capacity standpoint. Moreover, because the backhaul signal is relayed from one site to another site to another site, latency issues can arise.
“Without sufficient capacity in backhaul, things fall apart quickly,” Bohaychyk said. “IAB is a good idea to a certain capacity threshold. From there, you have to get on fiber for backhaul. What it provides you is a manner to get coverage quickly and easily. There are sites out there that don’t have the usage where IAB is the perfect solution.”
Verizon Tests IAB in the Field
Last summer, Verizon and Ericsson completed a proof-of-concept trial using integrated access backhaul technology to deploy Verizon’s 5G service, using wireless technology instead of fiber. The carrier is looking to use IAB technology along with portable power generators to create a totally self-contained mobile cell site, not reliant on commercial power or a fiber connection.
In addition to bringing new cell sites on air more efficiently, this proof-of-concept trial showed that mobile cell sites can also be connected using IAB, which becomes a critical asset for first responders and public safety agencies who need temporary cell coverage for search and rescue operations, disaster recovery efforts or other emergency situations.
Verizon owns a fleet of mobile cell sites that are regularly deployed in public safety situations. However, until recently they have required a fiber connection to carry data, restricting where they can be deployed, or a satellite connection, which are limited and costly. With IAB technology, coupled with portable generators for power, cell sites can be deployed more rapidly and to a wider range of locations.