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Integrated Access and Backhauling (IAB) - Today and Tomorrow

I wrote a detailed blog on The 3G4G Blog late last year about what IAB is and what will be available this year as part of Release-16 and what enhancements are planned as part of Release-17. It's available here.

In the Ericsson Technology Review last month, there is a short section on IAB which is reproduced below for anyone wishing to dig deep into this topic:
IAB provides an alternative to fiber backhaul by extending NR to support wireless backhaul. As a result, it is possible to use NR for a wireless link from central locations to distributed cell sites and between cell sites. This can simplify the deployment of small cells, for example, and be useful for temporary deployments for special events or emergency situations. IAB can be used in any frequency band in which NR can operate. However, it is anticipated that mm-wave spectrum will be the most relevant spectrum for the backhaul link. Furthermore, the access link may either operate in the same frequency band as the backhaul link (known as inband operation) or by using a separate frequency band (out-of-band operation).

Architecture-wise, IAB is based on the CU/DU split introduced in release 15. The CU/DU split implies that the base station is split into two parts – a centralized unit (CU) and one or more distributed units (DUs) – where the CU and DU(s) may be physically separated depending on the deployment. The CU includes the RRC (radio resource control) and PDC (packet data convergence) protocols, while the DU includes the RLC (radio link control) and MAC (multiple access control) protocols along with the physical layer. The CU and DU are connected through the standardized F1 interface.

Figure 2 illustrates the basic structure of a network utilizing IAB. The IAB node creates cells of its own and appears as a normal base station to UEs connecting to it. Connecting the IAB node to the network uses the same initial-access mechanism as a terminal. Once connected, the IAB node receives the necessary configuration from the donor node. Additional IAB nodes can connect to the network through the cells created by an IAB node, thereby enabling multi-hop wireless backhauling.

The lower part of the figure highlights that an IAB node includes a conventional DU part that creates cells to which UEs and other IAB nodes can connect. The IAB node also includes a mobile-termination (MT) part providing connectivity for the IAB node to (the DU of) the donor node.

PDF of the magazine is available here.
Ericsson also provides a good summary in RP-190971 regarding Release 16 IAB and Rel-17 enhancements:
  • IAB Rel-16 provide basic support for multi-hop and multi-path relaying. 
  • The solution supports 
    • QoS prioritization of traffic on the backhaul link
    • Flexible resource usage between access and backhaul
    • Topology adaptivity in case link failure
  • In Rel-17 it would be possible to further evolve the IAB solution targeting increased efficiency and support for new use cases
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