the following parameters: (i) location in geographical coordinates; (ii) height of the tower hosting the antennas; (iii) signal emitting power; (iv) antenna parameters such as the gain, azimuth, and tilt; (v) frequency band used; (vi) type of technology available (2G, 3G, or 4G), and; (vii) date of deployment.

Then, we calculated the coverage of each relay site using a Radio Propagation Model (RPM). RPMs are empirical mathematical models widely used by MNOs for planning the setup of their networks, allowing them to plan the location and characteristics of each relay site so as to maximize coverage and decrease costs. There are several RPMs available that are optimized for specific settings or technologies. We used an Irregular Terrain Model (ITM), also known as the Longley Rice model,<sup>10</sup> which is optimized to deliver accurate results in rural and peri-urban areas.

The ITM uses two sets of input variables. The first are the technical parameters of each individual relay site that we collected from MNOs. The second are the characteristics of the transmission medium, such as the terrain profile<sup>11</sup> and the type of vegetation in the area.<sup>12</sup> The output of the ITM model is a geocoded image showing the area covered with signal strength above a predefined threshold (see Figure 2 as an example). The predefined signal strength thresholds that we used are presented in Table 2.<sup>13</sup> Our approach is similar to that used by Yanagizawa-Drott (2014) to estimate the coverage of two radio transmitters in Rwanda, with the difference that mobile networks in Nigeria have tens of thousands of relay sites emitting in multiple frequencies that we overlaid to obtain the aggregated coverage.

Figure 3 shows the aggregated 3G coverage in Nigeria in 2010, 2012, and 2015. During this period, 3G coverage evolved from the main cities only to a large number of intermediate cities and rural areas. This represented an increase in population coverage from 21% to 57%. This variability is not observed for 2G, which for the same period increased from 83% to 89%. The main operators did not start rolling out 4G networks until 2016, when it was limited to urban areas.

By contrast, during the same period, penetration of fixed broadband internet in the country averaged around 2%, reaching just over 5% in 2016.<sup>14</sup> Mobile has therefore been the primary platform for users in Nigeria to access broadband internet services.

# Linking coverage data to each household location

Figure 4 presents the location of the enumeration areas that were surveyed in the GHS and shows which had access to 3G or 4G coverage in 2010 and 2016. We consider a household to have mobile broadband coverage when it is covered by a medium or strong signal in 3G or 4G. The two data sets 10 P.L. Rice, A.G. Longley, “Prediction of Tropospheric Radio Transmission Loss Over Irregular Terrain – A computer method 1968,” Essa Technical Report ERL 79-IT S67. Available: <u>http://www.visuallmr.com/documentation/pathlossmodels/ntis.longleyrice.676874.pdf</u> 11 - We used the SRTM 90m Digital Elevation Database created by NASA. See: https://cgiarcsi.community/data/srtm <u>90m-digital-elevation-database-v4-1/</u> 12 The vegetation profile used for Nigeria was Maritime Subtropical (West coast of Africa).

13 These thresholds were chosen to fit industry standards. For reference see: BEREC, “Common Position on information to consumers on mobile coverage”, 2018. Available at: <u>https://berec.europa.eu/eng/document_register/subject_matter/berec/download/0/8315-berec-common-position-oninformation-to-_0.pdf.</u>

> 14 Source: ITU World Telecommunication/ICT Indicators (WTI) Database 2019.

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