=Paper=
{{Paper
|id=Vol-3919/short10
|storemode=property
|title=3D Photorealistic Radio Map Generation Using Gaussian Splatting toward On-site Surveys
|pdfUrl=https://ceur-ws.org/Vol-3919/short10.pdf
|volume=Vol-3919
|authors=Yuma Toyoda,Sho Maeoki,Naoya Yokono,Wataru Yamada
|dblpUrl=https://dblp.org/rec/conf/ipin/ToyodaMYY24
}}
==3D Photorealistic Radio Map Generation Using Gaussian Splatting toward On-site Surveys==
https://ceur-ws.org/Vol-3919/short10.pdf
3D Photorealistic Radio Map Generation Using
Gaussian Splatting toward On-site Surveys
Yuma Toyoda1,∗ , Sho Maeoki1 , Naoya Yokono1 and Wataru Yamada1
1
NTT DOCOMO, INC. Chiyoda-ku, Tokyo, Japan
Abstract
Thanks to mobile network operators who maintain their networks, we can communicate anywhere with
high speed and stability over them. Radio maps, data sets of radio information at each location, are
essential to maintain communication quality in cellular networks. Radio maps are typically collected
by measuring radio information and plotting locations manually in on-site surveys; however, this
investigation work is a hard burden. Although several studies have been proposed to efficiently generate
radio maps by automatically acquiring location information, those methods are limited to constructing 2D
maps or necessitate expensive equipment. This paper proposes a time-efficient and low-cost method to
generate a radio map with a 3D photorealistic map (i.e., a 3DP radio map) using an omnidirectional camera
and a smartphone. Intuitive comprehension of radio conditions and the measurement environment with
the 3DP radio map can help maintainers to analyze and improve communication states. The experiments
demonstrated the efficiency of radio map generation by the proposed method and revealed the beneficial
factors of the 3DP radio map for improving communication quality.
Keywords
Radio Map, Cellular, 3D Mapping, Gaussian Splatting, Computer Vision
1. Introduction
Mobile network operators (MNOs) maintain their networks to address the demand for high-
capacity communications using smartphones. Thanks to their constant effort, we can enjoy
high-quality and stable communication.
The MNOs collect radio maps [1], data sets of radio information at each position in measure-
ment areas, to maintain communication quality in their networks. The characteristics of radio
propagation in the cellular networks can be observed from radio maps. Based on the analysis
of radio maps, MNOs devise ways for specific purposes, such as adjusting the parameters of
existing base stations or installing new base stations.
There are two typical approaches to obtain radio maps. One is the automatic collection
of communication status from mobile devices. This approach automatically collects radio
information by monitoring the communication status between base stations and mobile devices
of massive users. Although this approach facilitates the grasp of radio conditions in large areas,
Proceedings of the Work-in-Progress Papers at the 14th International Conference on Indoor Positioning and Indoor
Navigation (IPIN-WiP 2024),October 14- 17, 2024, Hong Kong
∗
Corresponding author.
Envelope-Open yuuma.toyoda.hx@nttdocomo.com (Y. Toyoda); syou.maeoki.rz@nttdocomo.com (S. Maeoki);
naoya.yokono.kz@nttdocomo.com (N. Yokono); wataruyamada@acm.org (W. Yamada)
Orcid 0000-0002-0050-2890 (Y. Toyoda)
© 2024 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR
ceur-ws.org
Workshop ISSN 1613-0073
Proceedings
(a) Video Capturing and (b) Processing of Video Data (d) Generating 3DP Radio Map
Radio Measurement Structure Gaussian
from Motion Splatting
360-degree (SfM) 3D Sparse 3D Photorealistic 3D Photorealistic Radio Map
Omnidirectional
Camera Video Data Point Cloud Data Spatial Data (3DP Radio Map)
Camera Position
Data
Smartphone
Measurement (c) Processing of Radio Information
Device
Radio Information Radio Map
Joining Process elapsed time bands rsrp … X Y Z
• Elapsed time
・ Radio information and 2.0 [1] -97 1.19 -3.78 -0.20
・ Radio conditions are visualized
• Bands 4.0 [1] -95 1.27 -3.60 -0.19
• RSRP
position data are associated
6.0 [1] -94 … 1.33 -3.38 -0.18
• etc.
according to the elapsed time in 3D photorealistic space.
8.0 [1] -93 1.46 -3.22 -0.16
10.0 [1] -93 1.57 -3.11 -0.18
︙
Figure 1: Overview of the proposed method. Proposed method consists of four main steps.
it is not suitable for detailed analysis of a specific small area due to its inability to provide
enough data where the radio wave information is required to be collected.
The other is manual on-site surveys by MNO’s maintainers. The maintainers survey radio
conditions on site with smartphones. In a typical survey procedure, the maintainers collect
radio information at each position in the target area while manually plotting measurement
points. Although this survey is a hard burden, it is still conducted, especially for some facilities
with high priority (e.g., train stations and event venues), as it can provide detailed radio maps.
Exploring alternatives to the manual plotting approach, several studies have proposed ways
to reduce the burden of manual on-site surveys [2, 3]. For example, 2D light detection and
rangings (LiDARs) or smartphones are used to automatically plot measurement points for
radio information. Point cloud data acquired from 2D LiDARs or image data acquired from
smartphone cameras are used as input to the simultaneous localization and mapping (SLAM)
algorithm. Consequently, a 2D map and a radio map can be generated at the same time.
Moreover, a 3D LiDAR-based method [4] has also been proposed to generate radio maps.
With this method, a 3D map of the surveyed area can be obtained, which is impossible with
2D LiDAR and smartphone-based methods. With the generated 3D map, we can observe the
structure and arrangement of objects and partitions in the target area, based on which we can
analyze radio conditions without going there again. Additionally, the 3D reconstructed map
can be used to simulate radio wave propagation by ray tracing.
In spite of such advantages, unfortunately, 3D LiDAR is very expensive and specialized
equipment. For this reason, conducting large-scale and frequent on-site surveys may present
significant challenges due to the need for extensive preparation of numerous devices and the
associated high costs. Furthermore, if it is leveraged for optimizing the radio environment,
the generated 3D map is ought to be composed of photorealistic point cloud data that allows
for intuitive recognition of the target area. The acquisition of high-density point clouds for
generating 3D photorealistic data requires even more expensive 3D LiDARs.
We propose a time-efficient and low-cost method to generate a radio map and a 3D photoreal-
istic map using an omnidirectional camera and a smartphone. In this paper, the generated radio
map together with a 3D photorealistic map are referred to as the 3D photorealistic radio map
(3DP radio map) as shown in Figure 1. The proposed method initially captures 360-degree video
data and measures radio information simultaneously. A measured radio map is superimposed
on a reconstructed 3D photorealistic map. The 3D map is reconstructed by Gaussian Splatting
method [5]. The 3DP radio map provides an intuitive recognition of radio environments in the
target area; hence, it helps radio surveyors to analyze radio conditions and consider methods to
improve the quality of radio communications.
We conduct two experiments to evaluate the time-efficiency in generating a radio map and
the helpfulness in analyzing radio conditions of the proposed method. The first experiment is a
comparison of the proposed method and the manual plotting method for the same duration
of time at the same on-site survey location. The second experiment is that we interview
three experts of on-site radio surveys, where we request them to fill out questionnaires and
hold discussions regarding the effects of 3D photorealistic data under the same observing
radio conditions. The experimental results demonstrate that the proposed method can obtain
approximately 8.2 times more measurement points in the same measurement time compared to
the method of plotting locations manually. Furthermore, the 3D photorealistic information in
the measurement environment is revealed to be more expressive and suggestive in the analysis
of radio conditions using radio maps than the information simply given by a radio map based
on a 2D map.
2. Proposed Method
The proposed method overview is illustrated in Figure 1. There are primarily four main processes
in the generation of the 3DP radio map: video capturing and radio measurement, processing
of video data, processing of radio information, and generating a 3DP radio map. First, video
data and radio information are collected as illustrated in Figure 1a. Next, position data and
3D photorealistic spatial data are obtained based on the captured video data as shown in
Figure 1b. In parallel, the measured radio information is processed into a radio map as in
Figure 1c. Subsequently, a 3DP radio map is generated by combining the radio map and the 3D
photorealistic spatial data.
Video Capturing and Radio Measurement. We prepare a device that combines an omni-
directional camera and a smartphone to simultaneously capture video data and measure radio
information in the target area, as shown in Figure 1a. While holding this device, we walk
around the target area to collect video data and radio information. We slowly and carefully
move around the area during the measurement to reduce the blurring of omnidirectional videos,
which results in improving the quality of 3D reconstructed data. Note that the coordinates of
the omnidirectional camera are regarded as the position data for the radio map, because the
camera and the smartphone are fixed at close range.
Processing of Video Data. From the acquired video data, we generate position data and 3D
photorealistic spatial data (i.e. 3D reconstructed data by gaussian splatting) for the 3DP radio
map, as shown in Figure 1b. As a pre-processing step, the video captured by an omnidirectional
camera, which contains 360-degree information, is divided into eight 2D sequence images with
different angles every 45 degrees in the horizontal direction. The processed image sequence data
is fed into a structure from motion (SfM) algorithm [6, 7], and consequently camera coordinates
and sparse 3D point cloud data are generated. Then, Gaussian Splatting is performed with
the obtained camera positions and the sparse 3D point cloud as input data to reconstruct 3D
photorealistic data.
Processing of Radio Information. Combining the radio information collected from the
camera position data calculated in the previous process, we produce a radio map for the 3DP
radio map, as illustrated in Figure 1c. The radio information includes various data significant
for the analysis of radio conditions represented by RSRP, RSRQ, and bands. The elapsed time
from the start of measurement is also recorded to construct a radio map. Given the elapsed
time as a key, the radio information is joined to the position data. Note that the measurement
interval for cellular data is constrained to once per approximately two seconds due to Android
specifications.
Generating 3DP radio map. The 3DP radio map is finally generated by combining the 3D
photorealistic spatial data and the radio map, as shown in Figure 1d. The generated 3DP radio
map enables the observation of radio information in the measurement area, which is helpful for
the analysis of radio conditions.
3. Evaluation
We conducted two experiments to evaluate how much time for the on-site radio surveys can
be reduced by the proposed method and how the analysis for improvement of communication
quality can be facilitated with the 3DP radio map. The one experiment campared the number of
measurement points between the proposed method and a manual plotting method in radio map
generation. The other was a comparison of the 3DP radio map and the conventional 2D radio
map, where the radio map is visualized on a 2D map, through questionnaires and interviews
with experts involved in on-site radio surveys.
3.1. Experimental Setup
We collected data for generating a radio map by walking around in an event room approximately
10 × 20 meters, as shown in Figure 2a. The measurement was performed along a route to
cover the entire space, as illustrated in Figure 2b. The RICOH THETA X was adopted as an
omnidirectional camera for capturing 360-degree video data and the Google Pixel 8 Pro was
used as a smartphone for measuring radio information. The radio information was acquired
using the TelephonyManager class 1 provided by the Android SDK.
3.2. Measurement time in on-site radio surveys
We compared the number of measurement points of radio maps to evaluate whether the proposed
method can reduce the burdens of the manual on-site surveys. We conducted the experiment of
radio map generation to compare the measurement points collected over the same duration of
time for both the proposed method and the manual plotting method in the on-site radio survey.
1
https://developer.android.com/reference/android/telephony/TelephonyManager
(a)
(b) (c)
Measurement points are plotted
Measurement Start/End Point on a printed 2D map
Corresponding time is recorded
on a printed sheet
Figure 2: (a) Image of the measurement environment. (b) Measurement route. (c) Image of a clipboard
used for the manual plotting method.
The experiment consists of the following two steps. The first step was measurement using
the proposed method. We performed the measurement with the proposed method while slowly
moving along the route shown in Figure 2b. The measurement took 6 minutes and 40 seconds.
For the second step, we employed the manual plotting method, a typical method in on-site
radio surveys for producing a radio map. We plotted the locations at where radio information
was measured on a 2D map. The location and the corresponding time for constructing a radio
map were recorded by hand on a printed map and sheet, both of which are attached to a
clipboard during the measurement as depicted in Figure 2c. The measurement time was ensured
to be the same 6 minutes and 40 seconds as for the proposed method.
The number of measurement points obtained by the proposed method was 188, whereas
the manual plotting method resulted in 23 measurement points, as shown in Figure 3. The
experiment results demonstrate that the proposed method can obtain approximately 8.2 times
more measurement points over the same duration of time compared to the manual plotting
method. These results indicate that the proposed method can generate dense radio maps with
a greater number of measurement points in a shorter period of time compared to the manual
plotting method, resulting in a reduction of the burdens in the manual on-site surveys.
3.3. How 3DP radio map facilitates analysis and discussion
Questionnaires and interviews were conducted with on-site radio survey experts to evaluate
which aspects of the 3DP radio map are practical in the study for improving communication
(a) (b)
Number of measurement points: 188 Number of measurement points: 23
Figure 3: (a) Measurement points by the proposed method. (b) Measurement points by the manual
plotting method.
quality.
3.3.1. Settings
We asked three experts working on on-site radio surveys in the MNO to review both the
conventional 2D radio map and the 3DP radio map in terms of their advantages for analyzing
and improving radio conditions. The experts had two to five years of experience in on-site
radio surveys and analysis for communication quality improvement. As the conventional 2D
radio map, images of radio wave information and measurement location visualized on a 2D map
as illustrated in Figure 4a was shown to the experts. Subsequently, we presented the experts
with the 3DP radio map, as shown in Figure 4b. We requested the experts to complete the
questionnaire after reviewing each radio map. The questionnaire consisted of six questions in
total, including the four categories described below.
• Recognition of the survey environment appearance (Q1): Whether the experts can grasp
the appearance and the structure of the target area.
• Comprehension of radio conditions (Q2-Q4): Whether the experts can interpret the
distribution of reference signal received power (RSRP), bands, and physical cell id (PCI).
• How suggestive for improvement approaches (Q5): Whether the experts can come up
with some plans for improving radio conditions.
• Overall assessment (Q6): Which method the experts prefer to adopt for on-site radio
surveys.
Questionnaires were rated on the 5-point Likert scale. A rating closer to 1 indicates that the
conventional 2D radio map is superior, whereas a rating closer to 5 indicates that the proposed
3DP radio map is superior. After questionnaire completion, we conducted group interviews
with the three experts to explore the reasons for their responses to questionnaires, as well as
the advantages and potential improvements of the proposed method.
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(c) 3DP
radio map
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2D radio map
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Figure 4: Results of the experiments. (a) Radio map visualized on a 2D map. (b) 3DP radio map by the
proposed method. (c) Questionnaire results. Note that the RSRP visualization at each measurement
point in (a) and (b) are colored black to red.
3.3.2. Results
The results of the questionnaire regarding Q1 showed that the experts unanimously rated the
proposed method as excellent in terms of recognizing the appearance of the target environment
as shown in Figure 4c. The experts mentioned that the 3DP radio map is beneficial for their work
thanks to its intuitive visual information on the target area. According to their comments, this
could be explained that the 3DP radio map can reveal the placement and height of objects such
as desks, chairs, and partitions. We assume that the photorealistic visualization of the target
area can help analyze radio conditions without being on-site from the results and comments of
Q1.
Regarding the comprehension of radio conditions, there were different opinions between
those who responded that the proposed method is superior and those who answered that the
conventional 2D radio map is better as illustrated in Q2 and Q3 of Figure 4c. Subject C who rated
the proposed method highly appreciated the ability to visualize the strength and distribution of
radio signals in a 3D space. On the other hand, subject A, who supported the 2D radio map,
and subject B, who considered both the same, argued that even though the 3DP radio map
is preferred in terms of comprehending local radio conditions, the 2D map provides a more
holistic view of the target area that helps us comprehend the overall distribution of radio signals.
The superiority of the conventional method was also demonstrated in Q4 because the radio
map with 2D map is sufficient for comprehending the PCI distribution. As a comprehensive
insight into the interpretation of radio conditions, these results suggest that the conventional
2D map is superior to the 3DP radio map in terms of overall visibility of the radio wave situation,
whereas the 3DP radio map is superior in terms of recognizing the structure of the target area
for considering radio wave propagation and interference.
Regarding how suggestive for improving communication quality, the result showed the
superiority of the proposed method as shown in Q5 of Figure 4c. The experts evaluated that
the photorealistic 3D data, which contains the arrangement of windows and the height of
objects, is valuable for examining approaches to communication quality. Therefore, the 3DP
radio map enables the experts to analyze radio propagation and interference in the target area.
Particularly, the experts advocated that the photorealistic appearance provoked discussions
about the placement of base stations for improving radio quality.
Finally, in terms of the overall assessment, the 3DP radio maps showed a tendency to be
superior as illustrated in Figure 4c (Q6). The experts indicated that the visualization of radio
conditions on a 3D space in the measurement environment contributes to the beneficial con-
sideration of approaches for improving communication quality. These results suggest that the
intuitive comprehension of radio conditions in the target area provided by the 3DP radio map
facilitates suggestions to improve communication quality compared to conventional 2D radio
maps. We consider that combining the conventional 2D radio maps and the 3DP radio map will
be effective for analyzing radio conditions in the target area because each of them has different
effective usage scenarios. These two radio maps can be used together to help MNOs maintain
their networks in the future.
4. Conclusion
In this paper, we proposed a method for generating a 3DP radio map (i.e., a radio map with
3D photorealistic spatial data), that provides important insights into the consideration of
approaches for improving communication quality. The proposed method generates a 3DP
radio map that visually represents measured radio conditions in a photorealistic 3D data by
simultaneously capturing omnidirectional video data and collecting radio information. This
method enables efficient generation of a radio map useful for on-site radio surveys without
the need for expensive equipment. Through experiments, we demonstrated that the proposed
method is capable of efficiently generating radio maps. Moreover, the intuitive visual information
of radio conditions provided by the 3DP radio map is more effective in the analysis for improving
communication quality through the evaluation by experts of on-site radio surveys. We will
consider a measurement method that take into account the influences of orientation and
placement of a smartphone on the acquired radio information as a further study. In addition,
we will explore the application of the proposed method to automatic measurement of radio
conditions using robots and to fingerprint-based localization using measured radio information.
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