5G Integrated Access and Backhaul

I’ve been discussing in this blog how I don’t believe there are any real 5G deployments yet in the US. A 5G deployment requires the implementation of the new features that are defined by the 5G specifications. To date, each of the major carriers is in the process of implementing new spectrum bands they are labeling as 5G – but the technology being delivered is still 4G that happens to use different spectrum bands. The carriers are at least a few years away from deploying any features that can be said to be 5G such frequency slicing or dynamic spectrum sharing. It’s going to be interesting to see how carriers will announce real 5G after having labeled everything else under the sun as 5G.

One of the first 5G features that will likely to be implemented is IAB – Integrated Access and Backhaul. This feature is defined in 3GPP Release 15 of the 5G specifications and will let a cell site share spectrum between connections to customers and connections to another cell site. It’s likely that the carriers will test this new feature this year and could start to deploy before the end of the year.

IAB will be useful in the deployment of small cell sites. Carriers will be able to use the bandwidth from a cell site connected to fiber to provide bandwidth for a nearby cell site – all integrated into the cell site electronics. This has several benefits for carriers:

  • This avoids needing a second set of wireless electronics to handle backhaul – and the extra antennas and power supplies needed to feed more electronics. The carriers are sensitive to the issue of reducing the profile of small cell sites and want to make them as small and unobtrusive as possible. IAB eliminates the need for extra hardware on poles.
  • It allows deployment of small cell sites before fiber is constructed to every site, and that means being able to activate small cell sites earlier. One of the primary purposes of deploying small cell sites is to offload some of the traffic that is clogging the tall tower cell sites today. Bring fiber to at least a few small cell sites in a neighborhood with IAB will allow connections to other nearby small cells before fiber is constructed everywhere.
  • It allows placing cell sites at locations that would be difficult to feed with fiber. Both Verizon and AT&T say that they view IAB in most cases as a temporary solution to use before fiber is constructed. But there will be situations where a few IAB connections could be permanent where it’s cost-prohibitive to bring fiber.
  • IAB will also provide for emergency backhaul at times when fiber to a small cell site is cut – the backhaul can be fed from nearby small cells until the fiber is repaired.

It is possible to daisy-chain multiple cell sites in a row with wireless backhaul, but that largely kills the reason for deploying small cell sites. The primary purpose of a small cell is to be a fully functional cell site that can grab traffic in a given local neighborhood to keep that traffic off the larger big tower cell sites. The physics of bandwidth is that the amount of bandwidth available for customers cuts in half at both the transmitting and receiving cell site when bandwidth is shared between two cell sites. Splitting bandwidth a second and third time further reduces the effective bandwidth available for customers at each cell site in the chain.

However, there are circumstances where splitting bandwidth is acceptable. While small cell sites are being touted as a way to beef up the 4G LTE network, the biggest use of small cell sites currently is to beam cellular signals into large buildings that have poor indoor cellular coverage. These small cells are often placed on the rooftop and beam cellular signal downward. IAB wireless backhaul could be a permanent solution to feed small cell sites that don’t need as much bandwidth as a full 5G cell site.

IAB is one of the new 5G features that will work in the background and that customers won’t notice, other than to perhaps start enjoying the benefits of small cells earlier before fiber is constructed. However, it will be one of the 5G features that will be deployed first and that will eventually enable the deployment of real 5G.