What does Integrated Access Backhaul mean?
Integrated Access and Backhaul (IAB) is a 5G technology that connects base stations without a dedicated fibre connection or a separate conventional microwave link at each site. IAB can interconnect mobile cells by using mobile spectrum for backhaul. This is sometimes called “self-backhauling”. Wireless backhaul bridges the link to the individual cell.
The base station that connects the IAB system to the rest of the network is called the IAB donor. It needs a high-capacity transport connection, often provided by fibre. The choice of transmission medium depends on capacity, availability and latency requirements. [1]
Two tasks within an IAB node
The access link connects the cell to user equipment. The backhaul link carries that traffic towards the donor. An IAB node contains a DU (Distributed Unit) for radio access and an MT (Mobile Termination) for the connection to its parent node. The node provides its own radio cell and forwards its traffic to the parent node. [1]
Where is IAB useful?
The technology is intended for three scenarios:
- Connecting many small outdoor cells.
- Interconnecting indoor 5G networks.
- Connecting moving base stations, for example on trains, using the Mobile IAB functions designed for this purpose.
Connecting many outdoor small cells with cables, usually fibre, can be expensive. In urban areas, where small cells are particularly useful, installing fibre infrastructure can involve substantial costs. Microwave equipment and planning also add costs.
IAB uses 5G NR technology for both access and backhaul, which can remove the need for separate backhaul equipment. It requires IAB-capable nodes and a suitably equipped donor. Power supply, mounting locations and a suitable radio path also need to be planned.
Wireless backhaul can reduce rollout costs and speed up deployment when it avoids extensive civil engineering work. The benefit depends on the site, the required capacity and the equipment. A business case weighs these requirements against the savings in excavation and connection costs.
Update on moving base stations: The original article described support for trains and other moving objects as a future standardisation step. Mobile IAB is now part of 3GPP Release 18. Deployment on trains requires the corresponding equipment in both the vehicles and the network. [4]
Mobile IAB has its own requirements. In the Release 18 specification cited here, a mobile IAB node must not serve further IAB nodes downstream. The stationary multi-hop chain in the diagram therefore cannot be applied unchanged to a chain of moving base stations. [3]
In-band and out-of-band IAB
IAB can be implemented in two ways: in-band and out-of-band backhauling differ in whether the access and backhaul links use the same or overlapping frequency resources.
- In-band backhauling covers scenarios in which the access and backhaul links overlap at least partly in frequency. The same carrier is often used for the connections to user equipment and for the wireless backhaul link. Both tasks then share radio resources. Scheduling must account for half-duplex constraints and potential mutual interference.
- Out-of-band IAB uses different, non-overlapping frequency resources for access and backhaul. This removes direct competition for the same carrier. End-to-end capacity still depends on the backhaul link and the donor’s transport connection.
Resources can be separated in time (Time Division Multiplexing, TDM). Enhanced IAB functions also support frequency division multiplexing (FDM) and spatial separation (SDM). The combinations available depend on factors such as the nodes’ duplex capabilities and radio planning. Network planners select an arrangement that suits the equipment and propagation conditions. [2]
One out-of-band IAB design could use 26 GHz spectrum for backhaul and the 3.6 GHz band for access to user equipment. This is a planning example and requires equipment that supports the relevant bands and their combination.
With in-band backhaul, part of the shared radio resources must be allocated to backhaul. Large available bandwidths, such as those in the 26 GHz range, can help. FR1 spectrum is also an option, for example n78 around 3.5 GHz. The balance between available capacity and traffic demand determines whether a design is suitable.
In-band IAB describes shared resource use between access and backhaul. Dynamic Spectrum Sharing (DSS) addresses how a carrier is shared between LTE and 5G NR.
Multi-hop connections are possible
IAB can also provide multi-hop backhaul, forwarding traffic through several small cells. This can be especially useful at higher frequencies , where propagation can be strongly affected by the surroundings. Several suitable sites can extend a connection beyond the reach of a single link. A suitable arrangement of nodes can also route around obstacles.
The radio path and equipment determine the rangeof each individual link. The chain covers the overall distance in stages. Each additional hop requires resources and can add delay. The first backhaul link at the donor is particularly important because it also carries traffic from the nodes further downstream. [5]
IAB forwards traffic using the Backhaul Adaptation Protocol (BAP). BAP maps packets to the configured routes through the IAB nodes. IAB is integrated into the radio access network. With a connection through a 5G router , a separate base station instead obtains internet access through that router. [1]
IAB can support standalone (SA) and certain non-standalone (NSA) configurations. The specification describes SA or EN-DCfor the IAB node, with EN-DC combining LTE and NR. The IAB wireless backhaul itself uses NR in these configurations. [1]
Conclusion
IAB can be a cost-effective way to connect many small mobile cells. A wired connection is not needed at every site. The donor serving the IAB nodes needs a transport connection with sufficient capacity.
Quality-of-service requirements, including latency, must be met across multiple hops. IAB can bridge links that are difficult or expensive to provide. Capacity, latency and the connection to the wider network are planned for the entire chain. [5]
Sources and technical review
Originally published on 18 January 2020. Technically reviewed and selectively updated on 26 October 2026. The original illustration was retained in the German article; this English version uses the same layout with English labels. The following primary sources were used for architecture and resource planning:
- [1] ETSI / 3GPP: 3GPP TS 38.300, Release 16, V16.8.0 – sections 4.7 and 10.9
- [2] ETSI / 3GPP: 3GPP TS 38.300, Release 17, V17.2.0 – section 10.9
- [3] ETSI / 3GPP: 3GPP TS 38.300, Release 18, V18.1.0 – sections 4.7.1 and 4.7.5
- [4] 3GPP: Mobile IAB (Integrated Access and Backhaul) for NR, Work Item 941009
- [5] Ericsson Technology Review: Integrated access and backhaul: a new option for 5G, 23 June 2020