Constrained Deployment Optimization in Integrated Access and Backhaul Networks 1stCharitha Madapatha

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Constrained Deployment Optimization in Integrated

Access and Backhaul Networks

1st Charitha Madapatha

Dept. of Electrical Engineering

Chalmers University of Technology

Gothenburg, Sweden

charitha@chalmers.se

2nd Behrooz Makki

Ericsson Research

Ericsson AB

Gothenburg, Sweden

behrooz.makki@ericsson.com

3rd Hao Guo

Dept. of Electrical Engineering

Chalmers University of Technology

Gothenburg, Sweden

hao.guo@chalmers.se

4th Tommy Svensson

Dept. of Electrical Engineering

Chalmers University of Technology

Gothenburg, Sweden

tommy.svensson@chalmers.se

Abstract—Integrated access and backhaul (IAB) is one of

the promising techniques for 5G networks and beyond (6G),

in which the same node/hardware is used to provide both

backhaul and cellular services in a multi-hop fashion. Due to

the sensitivity of the backhaul links with high rate/reliability

demands, proper network planning is needed to make the IAB

network performing appropriately and as good as possible. In

this paper, we study the effect of deployment optimization on

the coverage of IAB networks. We concentrate on the cases

where, due to either geographical or interference management

limitations, unconstrained IAB node placement is not feasible in

some areas. To that end, we propose various millimeter wave

(mmWave) blocking-aware constrained deployment optimization

approaches. Our results indicate that, even with limitations on

deployment optimization, network planning boosts the coverage

of IAB networks considerably.

Index Terms—Integrated access and backhaul, IAB, Topology

optimization, Densiﬁcation, millimeter wave (mmWave) com-

munications, 3GPP, Coverage, Wireless backhaul, 5G NR, 6G,

Blockage, Machine learning, Network planning.

I. INTRODUCTION

The data trafﬁc and the users’ rate/reliability demands

continue to steadily increase in 5G and beyond (6G) [1]. In

order to meet such demands, network densiﬁcation, i.e, the

deployment of many base stations (BSs) of different types is

one of the key enablers. These increasing number of BSs,

however, need to be connected to the core network using the

transport network.

According to [2], the backhaul technology varies across

different regions. However, optical ﬁber and microwave links

have been globally the dominating media for the backhaul.

Recently, ﬁber deployments have increased due to their re-

liability, and have demonstrated Tbps-level data rates. On

the other hand, due to low initial investment and installation

time, wireless backhaul comes with considerably lower price,

ﬂexibility and time-to-market, at the cost of low peak rate.

Typical wireless backhaul technologies are mainly based on

1) point-to-point line-of-sight (LoS) communications in the

range of 10-80 GHz, 2) non-standardized solutions, and 3)

accurate network planning such that the interference to/from

the backhaul transceivers is minimized. With 5G, however,

access communication, i.e., the communication between the

gNB and the user equipments (UEs), moves to the millimeter

wave (mmWave) band, i.e., the band which was previously

used for backhauling. Thus, there will be conﬂict of interest

between access and backhaul, which requires coordination.

Also, considering small access points on, e.g., lamppost, one

needs to support NLoS (N: non) communication in (possibly,

unplanned) backhaul networks. These are the main motivations

for the so called integrated access and backhaul (IAB) where

the operators can use portion of the radio network resources

for wireless backhaul. That is, IAB provides not only access

link cellular service but also backhaul using the same node.

IAB has been standardized for 5G NR in 3GPP Release-16,

Release-17 [3], [4] and, the standardization will be continued

in Release-18 [5]–[7].

IAB network supports multi-hop communication in which

an IAB donor, connected to the core network via, e.g., a

ﬁber link, includes a central unit (CU) for the following

concatenated IAB nodes which are connected to IAB donor in

a multi-hop fashion (see Fig. 1). Each IAB node consists of

two modules, namely, mobile termination (MT) and distributed

unit (DU). The DU part of an IAB node is used to serve UEs

or the MT part of child IAB nodes. The MT part of the IAB

is used to connect the IAB node to its parent IAB-DU in

the multi-hop chain towards the IAB donor. In general, the

DU part has similar gNB functionalities, although there may

arXiv:2210.05253v1 [cs.NI] 11 Oct 2022

be IAB-speciﬁc differences. The IAB-MT part, on the other

hand, may have different capabilities, although in general it

acts not differently from a UE from the point-of-view of its

parent IAB.

In practice, IAB networks may face deployment constraints,

where the nodes can not be deployed in some locations. Such

constraints may come from two reasons: On one hand, de-

pending on the location and regulatory restrictions in protected

areas, it may not be possible/allowed to have the IAB nodes

in, e.g., some areas. Although these restrictions vary based on

the country and locality, all provinces have their own building

and landscape protection laws. Additionally, federal laws have

to be obeyed and permissions under these laws, if applicable,

have to be obtained (e.g. air trafﬁc safety, forest protection,

listed buildings etc.). On the other hand, network planning may

impose constraints on IAB nodes placement, e.g., to limit the

interference. For instance, 3GPP has deﬁned two categories of

IAB nodes, namely, wide- and local-area IAB, with distinct

properties [8], [9]. The main differences between these two

categories are in the nodes capabilities and the level of required

network planning.

Wide-area IAB-node can be seen as an independent IAB-

node providing its own coverage, with possibly long backhaul

link to connect to its parent IAB-node. Here, the goal is to

extend the coverage. Due to radio frequency properties, wide-

area IAB-node deployment are well-planned, by operators. For

these type of IAB-nodes, the MT part of the IAB node looks

like a normal gNB, in terms of, e.g., high transmit power,

beamforming or antenna gains. In wide-area IAB networks,

one may consider a minimum distance between the nodes with,

e.g., LOS connections. On the other hand, the use-case for the

local-area IAB-node is to boost the capacity within an already

existing cell served by an IAB donor or parent IAB-node.

With local-area IAB networks, the transmit power of the MT

part may range between those of UEs and gNBs. Also, the

network may be fairly unplanned, while geographical-based

constraints may still prevent unconstrained IAB installation in

different places.

In this paper, we study the effect of network planning on

the service coverage of IAB networks. We present different

algorithms for constrained deployment optimization, with the

constraints coming from either inter-IAB distance limitations

or geographical restrictions. Moreover, we study the effect

of different parameters on the network performance. As we

show, even with constraints on deployment optimization, the

coverage of IAB networks can be considerably improved via

proper network planning.

Note that the problem of topology optimization in differ-

ent IAB or non-IAB networks have been previously studied

in, e.g., [10]–[15]. However, compared to the literature, we

present different algorithms for deployment optimization, con-

sider different types of constraints and study the performance

of IAB networks with various parameter settings, which makes

our paper different from the previous works.

Fig. 1: An illustration of the IAB netowrk. Subplot (a): An IAB

network with a minimum required distance between the IAB

nodes and the IAB-MTs having gNB-like capabilities. Subplot

(b): An IAB network with geographical constraints on node

placement and the IAB-MT being less capable compared to

an gNB.

II. SYSTEM MODEL

Consider downlink communication in a two-hop IAB net-

work, where the IAB donor and its child IAB nodes serve

multiple UEs [16]–[20] (see Fig. 1). Since in-band communi-

cation offers proper ﬂexibility for resource allocation, at the

cost of co-ordination complexity, we consider an in-band setup

where both access and backhaul links operate over the same

mmWave band.

In one scenario as shown in Fig. 1a, the IAB nodes with

gNB-like IAB-MT capabilities maintain a minimum distance

rth between each other, i.e., the distance between every two

node sshould be s>rth where rth is a threshold distance

considered by the network designer, when there is no blockage

in the links between IAB nodes. In another scenario shown in

Fig. 1b, while the IAB nodes can be in different distances to

each other, due to geographical or regulatory restrictions, it

may not be possible to have the nodes in some speciﬁc areas.

We use the germ grain model [21, Chapter 14] to model the

blockings which provides accurate blind spot prediction. Par-

ticularly, a ﬁnite homogeneous poisson point process (FHPPP)

is used to model the blockings in an area with the blocking

density λbl. The blockings are considered to be walls of length

lbl and orientation θbl.

Using the state-of-the-art mmWave channel model, e.g.,

[22], [23], the received power at each node can be described

Pr=Ptht,rLtrGt,r ||xt−xr||−1.(1)

Here, Ptstands for the transmit power, ht,r denotes the small-

scale fading of the link, Lt,r is the path loss according to 5GCM

UMa close-in model described in [24], and Gt,r denotes the

combined antenna gain of the transmitter and receiver in the

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ConstrainedDeploymentOptimizationinIntegratedAccessandBackhaulNetworks1stCharithaMadapathaDept.ofElectricalEngineeringChalmersUniversityofTechnologyGothenburg,Swedencharitha@chalmers.se2ndBehroozMakkiEricssonResearchEricssonABGothenburg,Swedenbehrooz.makki@ericsson.com3rdHaoGuoDept.ofElectricalEngin...

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