LOON AND A TERRESTRIAL LTE NETWORK HOW LOON COVERAGE IMPACTS AN EXISTING TERRESTRIAL LTE NETWORK, THE INTERACTIONS BETWEEN THE TWO NETWORKS, AND THE LOON USER EXPERIENCE

February 2020

Prepared by Signals Research Group

www.signalsresearch.com

We conducted this benchmark study on behalf of Loon, LLC. We stand behind analysis and commentary provided in this report, which are supported by results from extensive testing done over a five-day period in a region just south of Tarapoto, Peru. In addition to providing consulting services on wireless-related topics, including performance benchmark studies, Signals Research Group is the publisher of the Signals Ahead and Signals Flash! research reports (www.signalsresearch.com). Loon is a trademark of Loon LLC. Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Key Highlights Signals Research Group (SRG) conducted a comprehensive network performance benchmark study of Loon. We collected the data over a period of ve days (September 23–27) in a region just south of Tarapoto, Peru. ‚e results presented in this paper stem from a combination of drive testing and walk testing in a very rural part of the country where terrestrial LTE coverage wasn’t always available. ‚e results and our commentary are based on the capabilities of Loon and the conguration used in this network deployment when we tested it in 2019. We recognize that these performance results do not take into consideration pending and potential improvements to the Loon system, not to mention di‰erent deployment congurations that are currently available.

We used a Rohde & Schwarz scanner to capture fundamental network parameters, including signal strength (RSRP) and signal quality (SINR) from the nearby serving cell sites (PCIs), which could be terrestrial cell sites or Loon balloons overhead. We also used a mix of smartphones, connected to Accuver America’s XCAL-M and XCAL-Solo drive test solutions, to log LTE chipset diagnostic messages. We used chipset messages to augment scanner data and to help us quantify the user experi- ence with Loon.

Key observations, which we support with test results and analysis in this paper, include the following:

Loon only has a modest detrimental impact on the existing terrestrial LTE network while improving coverage in areas where terrestrial LTE coverage does not exist. Any time a new cell site gets deployed in an LTE network it will generate at least some interference with adjacent cells. Loon is no di‰erent. However, we only detected Loon’s presence in poor terrestrial coverage areas since the Loon signal strength (RSRP) was almost always below -100 dBm. Further, self-interference between terrestrial LTE sites, which is typical in an LTE network, existed even in the absence of Loon while Loon’s contribution to interference in the LTE network was comparable to the interference generated by other terrestrial cell sites. ‚e self-interference in the terrestrial network was also present in high geometry scenarios (strong RSRP) while Loon’s impact on the terrestrial network was frequently limited to a small region of the network – outside that region Loon provided coverage where the terrestrial network coverage wasn’t adequate or the Loon signal strength was suœciently below the terrestrial network that it had minimal impact on the terrestrial LTE network.

The performance of the Loon network is somewhat comparable to a terrestrial LTE network with similar attributes. ‚e Loon network that we tested primarily used a 2x10 MHz channel in Band 28 (DL = 795.5 MHz) so comparisons with a terrestrial LTE network need to be made accord- ingly. We also brie£y tested a Loon 2x5 MHz channel bandwidth, and we know Loon can operate in other frequency bands, plus support other channel bandwidths that we did not test. Although we observed sustained data speeds in the high teens (Mbps) and a peak physical layer throughput that was just over 40 Mbps (BLER = ~10%), we believe more typical data speeds with Loon are in the mid- to high- single digits. Latency was also only modestly higher (13%) than the terrestrial LTE network. Although we didn’t analyze battery life, we noticed the transmit power of the smartphones connected to Loon was frequently 23 dBm – the highest transmit power level – even when down- loading content. ‚e Loon network we tested wasn’t optimized for handovers with the terrestrial LTE network or between di‰erent Loon cells. Nonetheless, when moving between Loon cells or between Loon and the terrestrial network (and vice versa) the smartphone does an RRC detach/attach that was fast enough it should go unnoticed by consumers. Further integration of the Loon network and the terrestrial network is possible and it should improve handovers and cell reselection, but we have not yet tested this conguration.

February 2020 Page 2 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

The user experience with Loon is surprisingly good. Separate from data speeds and latency, we also evaluated how Loon performed with popular mobile data applications, such as web browsing, video chat, YouTube, and downloading applications from Google Play. Web page load times were very comparable with Wi-Fi and LTE – sometimes a bit faster and sometimes a bit slower. Our experi- ence with streaming 360p and 720p videos was favorable with no bu‰ering although the video start times took a bit longer than the terrestrial LTE network (2x20 MHz channel bandwidth) and Wi-Fi. Likewise, the download times with Google Play took a bit longer with Loon than the terrestrial LTE network, but it is an unfair comparison since the Google Play (and YouTube) tests took place in Tarapoto where the operator has LTE deployed in Band 4 (2x20 MHz channels) and the Loon testing occurred in a region where terrestrial LTE coverage did not exist. We also successfully placed a video chat call (Google Duo) back to the United States, and while the quality of the video wasn’t as good as we experience when we use video chat applications at home, it was more than satisfactory without any observable video freezes or dropped audio.

We expand on our ndings in the next chapter and then back them up with detailed analysis of multiple test scenarios in the subsequent chapters of this paper. We include additional test results without commentary in the appendix.

February 2020 Page 3 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Table of Contents

Key Highlights …………………………………………………………………………………………………………… 2

1.0 Key Findings and Observations ………………………………………………………………………………………………………………… 7

2.0 The Impact of Loon on an Existing Terrestrial LTE Network ………………………………………………………………12 2.1 Tests 61 Through Test 71 …………………………………………………………………………………… 13 2.2 Test 87 ………………………………………………………………………………………………………… 18 2.3 Test 53 …………………………………………………………………………………………………………23 2.4 Stationary Tests with and without Loon ………………………………………………………………27

3.0 Extending Terrestrial Coverage with Loon and the Interactions between the Two Networks ……31 3.1 Test 91 …………………………………………………………………………………………………………32 3.2 Test 42 and Test 46 ……………………………………………………………………………………… 36 3.3 5 MHz and 10 MHz Loon Sensitivity ………………………………………………………………… 39 3.4 Moving between Loon and Terrestrial Cells with a Mobile Device ………………………… 42 3.5 Moving between Loon Cells with a Mobile Device ……………………………………………… 44

4.0 Loon and the User Experience………………………………………………………………………………………………………………… 47

5.0 Test Methodology …………………………………………………………………………………………………………………………………… 55

6.0 Appendix ……………………………………………………………………………………………………………………………………………………… 57

Index of Figures and Tables

Figure 1. Terrestrial LTE Network Signal Quality with and without Loon …………………………………… 8

Figure 2. Loon Performance and the User Experience …………………………………………………………… 11

Figure 3. Loon Test Area …………………………………………………………………………………………………12

Figure 4. Test 61-71 Key Metrics – geo plot …………………………………………………………………………13

Figure 5. Terrestrial and Loon RSRP Time Series ……………………………………………………………………14

Figure 6. Cumulative Distribution of Loon Signal Strength ………………………………………………………15 Figure 7. Cumulative Distribution of the Di–erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell ………………………………………………………………………………16

Figure 8. Test 87 Key Metrics – geo plot ……………………………………………………………………………18

Figure 9. Cumulative Distribution of Loon Signal Strength ………………………………………………………19 Figure 10. Cumulative Distribution of the Di–erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell …………………………………………………………………………… 20

Figure 11. SINR and RSRP Delta as a Function of RSRP ……………………………………………………………21

Figure 12. Time Series Plot of RSRP for Two Terrestrial Cell Sites …………………………………………… 22

Figure 13. Test 53 Key Metrics – geo plot ………………………………………………………………………… 23

Figure 14. Cumulative Distribution of Loon Signal Strength ………………………………………………… 24 Figure 15. Cumulative Distribution of the Di–erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell …………………………………………………………………………… 25

February 2020 Page 4 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 16. SINR and RSRP Delta as a Function of RSRP ………………………………………………………… 26

Figure 17. Test Locations ……………………………………………………………………………………………… 27

Figure 18. Network Performance Parameters with and without Loon ……………………………………… 28

Figure 19. Mobile Device Performance with and without Loon ……………………………………………… 29

Figure 20. Network Performance Parameters with and without Loon …………………………………… 30

Figure 21. Test 91 Key Metrics – geo plot ………………………………………………………………………… 32

Figure 22. Cumulative Distribution of Loon Signal Strength ………………………………………………… 33

Figure 23. Mobile Device Throughput While Changing the Loon Ground Station ……………………… 34

Figure 24. Mobile Device and Scanner RSRP Measurement Reports ……………………………………… 35

Figure 25. Mobile Device CQI and Scanner RSRP Measurement Reports ………………………………… 35

Figure 26. Test 42 and Test 46 Key Metrics – geo plot ………………………………………………………… 36

Figure 27. Test 42 RSRP for Loon and Terrestrial Cells ………………………………………………………… 37

Figure 28. Test 42 Serving Cell SINR ………………………………………………………………………………… 37

Figure 29. Test 46 Serving Cell SINR and RSRP …………………………………………………………………… 38

Figure 30. Stationary Test Locations ………………………………………………………………………………… 39

Figure 31. RSRP and SINR for Loon and Terrestrial Cells ……………………………………………………… 40

Figure 32. Serving Cell RSRP and SINR with the Introduction of a Loon 5 MHz Channel …………………41

Figure 33. Mobile RRC Reconnect when Moving from Loon to the Terrestrial Network ……………… 42 Table 1. RRC Signaling Messages When the Mobile Device Moved from Loon to the Terrestrial Network …………………………………………………………………………………………… 43

Figure 34. Serving Cell PCI and RSRP, including RSRP from Neighboring Cells …………………………… 44

Figure 35. Serving Cell PCI and RSRP, including RSRP from Neighboring Cells – Enhanced View …… 44 Table 2. RRC Signaling Messages When the Mobile Device Moved from Loon to the Terrestrial Network ……………………………………………………………………………………………… 45

Figure 36. Mobile Device Throughput ……………………………………………………………………………… 46

Figure 37. Latency and Jitter ………………………………………………………………………………………… 47

Figure 38. Web Browsing ……………………………………………………………………………………………… 49

Figure 39. YouTube ……………………………………………………………………………………………………… 50

Figure 40. YouTube – enhanced view …………………………………………………………………………………51

Figure 41. YouTube Bu–er Management …………………………………………………………………………… 52

Figure 42. Physical Layer Throughput While Downloading an Application from Google Play ……… 53

Figure 43. PUSCH Transmit Power …………………………………………………………………………………… 54

Figure 44. Scenes from the Loon Coverage Area ………………………………………………………………… 56

Figure 45. A Loon Balloon Overhead ……………………………………………………………………………… 56

Figure 46. Test 25, 26 and 30 Key Metrics – geo plot …………………………………………………………… 57 Figure 47. Cumulative Distribution of the Di–erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell – Test 25, 26 and 30 ……………………… 58

Figure 49. Cumulative Distribution of Loon Signal Strength – Test 34 and 35 …………………………… 60

February 2020 Page 5 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 50. Test 52 Key Metrics – geo plot ……………………………………………………………………………61

Figure 51. Cumulative Distribution of Loon Signal Strength – Test 52 ……………………………………… 62 Figure 52. Cumulative Distribution of the Di–erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell – Test 52 ………………………… 62

February 2020 Page 6 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

1.0 Key Findings and Observations Much of our focus while testing in Peru and the analysis phase once we returned pertained to how Loon impacted the terrestrial LTE network. Specically, we wanted to determine if Loon could be a “good neighbor” to the terrestrial network by providing adequate coverage in areas the terrestrial network did not cover and, most importantly, minimizing interference at the boundary between the two networks. Additionally, we wanted to determine how well Loon performed and the subsequent user experience. ‚e two gures in this chapter summarize our overall ndings.

To determine the impact on the terrestrial LTE network, we aggregated all relevant test results with scanner data (e.g., most of the tests provided in this paper and in the appendix). To ensure the results weren’t in£uenced by an overweighting of data points in one location versus another location (e.g., due to di‰erences in vehicular speed or the inclusion of stationary tests), we geo binned the data in 3-meter quadrants. We ltered this data (nearly 20,000 data points) into three buckets. Each bucket required the strongest cell, based on measured RSRP, to be a terrestrial cell site (PCI). ‚e rst bucket includes results where the scanner did not detect the presence of a Loon PCI in any of the top four interfering cells. We only included the top four interfering cells, plus the strongest cell, in this analysis since the relative signal strength of additional cells would be well below that of the strongest cell. ‚e second bucket includes results where the scanner detected a Loon PCI as an interfering cell in the list of top four interfering cells. ‚is bucket includes instances when there was a terrestrial cell with higher interference than the Loon cell, although the Loon cell was still present in the list of top four interfering cells. Finally, we looked at data points for those cases when Loon was the strongest interfering cell site. ‚is bucket is a subset of the second bucket since it excludes data points when Loon was the second, third or fourth strongest interfering site with terrestrial cell(s) generating more interference.

February 2020 Page 7 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

The signal quality in the terrestrial Figure 1 summarizes the results of this analysis. ‚e solid lines in the top gure show the relationship network in the absence of between the RSRP and SINR of the terrestrial cell site with the strongest signal. We calculated the Loon was no dierent than the median RSRP at each SINR value for the three previously described buckets. All three lines show an signal quality with Loon. upward trend with increasing RSRP, but the Terrestrial SINR with Loon as the Strongest Interfering Cell line is higher in absolute terms and it increases more rapidly with higher RSRP, for reasons explained in a bit. Comparing the Terrestrial SINR with Terrestrial Top Interfering Cell and Terrestrial SINR with Loon Interfering Cell(s) lines, it is evident the SINR values are quite similar – the terres- trial signal quality was slightly better with Loon as the interfering source between -90 dBm and -105 dBm and the terrestrial signal quality was modestly better without Loon’s presence when the RSRP was below -105 dBm. ‚ere were not enough data points to extend the plots below -118 dBm since frequently Loon was the dominant cell in this region of RSRP.

Figure 1. Terrestrial LTE Network Signal Quality with and without Loon

SINR (dB) 20 Terrestrial SINR with Terrestrial Top Interfering Cell (no Loon present) 15 Terrestrial SINR with Loon as the Strongest Interfering Cell (terrestrial interfering cells could be present) 10 Terrestial SINR with Loon Interfering Cell(s) (terrestrial interfering cells could be present) 5

0

-5 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 RSRP (dBm)

RSRP Delta (dB) 15 RSRP Delta with Loon as the Dominant Interfering Cell (Terrestrial Serving Cell RSRP minus Loon RSRP) 12 RSRP Delta with Loon Present (Terrestrial Serving Cell RSRP minus Interfering Cell RSRP) 9

6 RSRP Delta without Loon (Terrestrial Serving Cell RSRP minus Terrestrial Interfering Cell RSRP) 3

0 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 RSRP (dBm) Source: Signals Research Group

February 2020 Page 8 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

The median RSRP of the strongest In the detailed analysis in the next chapter we show the median and cumulative distribution of the Loon cell was frequently below Loon RSRP in the drive tests we conducted. ‚e median RSRP of the strongest Loon cell was -105 dBm if not below -110 dBm. frequently below -105 dBm if not below -110 dBm and the strongest Loon signal rarely exceeded -100 dBm. For this reason, when Loon was the dominant source of interference, its impact on the terrestrial LTE network dropped o‰ more rapidly with increasing RSRP in the terrestrial LTE network – hence the more rapid increase in the Terrestrial SINR with Loon as the Strongest Interfering Cell line. Likewise, when the LTE terrestrial network RSRP was higher than -90 dBm, there would almost always be a separation of at least 15 dB between the signal strength of the LTE network and the signal strength of Loon. In other words, Loon had no detrimental impact on the terrestrial LTE network in the higher RSRP regions of the network.

‚e second gure shows the delta between the RSRP of the terrestrial serving cell and the source of interference, which could be a Loon cell or another terrestrial cell. As expected, the scenario with Loon as the strongest interfering cell (RSRP Delta with Loon as the Dominant Interfering Cell) had the steepest increase in the RSRP delta. For example, when the terrestrial cell RSRP was -90 dBm, the median separation with the Loon cell site serving as the strongest source of interference was 14.9 dB. ‚e RSRP Delta without Loon line shows a very gradual increase in the delta with increasing RSRP. ‚is trend is due to the self-interference within the terrestrial LTE network that existed, even with very favorable RF conditions. We provide additional clarity on this point later in this paper.

In addition to analyzing the impact of Loon on a terrestrial network, we also evaluated Loon’s ability to provide cellular coverage. Due to the length of time required to drive from Tarapoto to the start of the Loon coverage area, we couldn’t test the breadth of Loon coverage in the region. However, we extended far enough into Loon-only coverage to evaluate its performance, plus we were able to evaluate how mobile devices perform when moving between the two networks as well as between di‰erent Loon cells.

Loon’s performance was somewhat comparable to a terrestrial LTE network, especially when compared with a terrestrial LTE network utilizing a single 2x10 MHz channel. Measured physical layer data speeds were typically in the mid- to high- single digits (Mbps) although we did observe sustained data speeds in the mid-teens with a peak speed of just over 40 Mbps. Loon wasn’t designed to provide in-building coverage, nor was it designed to provide in-vehicle coverage. However, we witnessed Loon sustain a video call for several kilometers without dropping the connection even though the smartphone was located within the test van. We also point out that in the region where we tested, open-air Moto taxis were the dominant form of transportation used by the locals.

Latency using Loon was only 13% Latency was another area of interest. Our results found that latency using Loon was only 13% higher higher than the terrestrial network, than the terrestrial network, based on round trip time (RTT) ping tests to a local server. ‚e Block although the transmit power was Error Rate (BLER) during FTP data transfer tests was also consistent with what we observe in frequently much higher with Loon terrestrial networks, or just under 10%. We did identify higher transmit power with Loon than with than with the terrestrial network. the terrestrial network. ‚e PUSCH transmit power with Loon was 23 dBm, including while web browsing or streaming a YouTube video. ‚ese values were much higher than what we observed with the terrestrial network while web browsing (13.3 dBm) or streaming a YouTube video (9.69 dBm). ‚e terrestrial results, in this case, stem from testing that we did in Tarapoto when the smartphone was connected to Band 4 and the serving cell site was likely nearby our location. In one of our tests in a Loon coverage area the mobile device did one FTP transfer over the terrestrial network before switching to Loon and doing a second FTP transfer. With this scenario, which represents a fairer comparison, the transmit power with Loon was only 4 dB higher than over the terrestrial network. ‚e terrestrial cell site was likely far away from our location, hence the transmit power was higher than it was in the city.

February 2020 Page 9 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

It took the mobile device just A mobile device moving between the two networks does an RRC detach from the origin network under 2 seconds to move between and then an RRC attach to the destination network. In our tests it took the mobile device just under networks and it took less than 20 2 seconds to move between the networks and it took less than 20 ms to move between Loon cells. A ms to move between Loon cells. consumer wouldn’t likely notice when the mobile device switched networks and it would seemingly be impossible to observe the mobile device moving between Loon cells without appropriate test equipment. In another test, also highlighted in this paper, we observed the Loon network can switch ground stations, which provide the S1 connection to the Loon balloons, without any meaningful disruption. We were performing a sustained FTP data transfer when the Loon engineers recong- ured the network for the new ground station, and we could barely detect the impact when analyzing the log le. Switching ground stations might be required due to poor weather conditions, which would cause impacts to the S1 connection as discussed. From the test results, this should not cause a noticeable impact to the user experience.

February 2020 Page 10 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 2 summarizes some results from the performance and user experience testing that we performed.

Figure 2. Loon Performance and the User Experience

50 14.4

40.3 40 11.6

30 8.0 8.0

20 16.4

3.4 10 2.4 2.5–5.0

0 0 0 Expected Peak Sustained Peak Data Web Browsing YouTube Media Video Buƒering Google Play Average Throughput Throughput (Observed) Speed (Observed) (Average Load Time - sec) Start Time (sec) Time (sec) Download Speed (Mbps) User Throughput User Experience

Loon (2x10 MHz) Terrestrial (2x20 MHz)

Source: Signals Research Group

Loon delivered a good user Although we observed a sustained data speed of 16.4 Mbps over a period of several minutes (peak experience with several = 40.3 Mbps), we believe an expected data speed of 2.5 to 5 Mbps is more realistic, especially when applications that was largely other people are accessing the Loon network. ‚ e user experience results also re£ ect good perfor- on par with the terrestrial mance relative to the terrestrial LTE network, even though the comparison isn’t fair since the terres- LTE network and Wi-Fi. trial LTE network used a 2x20 MHz radio channel. ‚ e terrestrial LTE user experience testing also took place in Tarapoto where we would expect much better performance than in the rural areas where we tested Loon. For web browsing, the average web page load time for some of the most popular mobile websites in Peru was 3.4 seconds with Loon and 2.4 seconds with the terrestrial network. With YouTube, the video took 3.6 seconds longer to start playing, but there wasn’t any video bu‰ ering once the video started to play. We used 360p and 720p video resolution, with the latter probably being the upper limit for typical Loon network conditions. Finally, we observed an average data speed of 8 Mbps while downloading an application from Google Play versus 14.4 Mbps with the terrestrial LTE network.

In the next three chapters we provide test results which support these observations. Chapter 3 addresses Loon’s impact on the terrestrial LTE network. Chapter 4 deals with Loon coverage and the interactions between the two networks. Finally, Chapter 5 provides the results and analysis from the user experience tests.

February 2020 Page 11 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

2.0 The Impact of Loon on an Existing Terrestrial LTE Network In this section, we include results and analysis for three sets of drive test results, which occurred on two di‰erent days in an area that started 8 kilometers south of Tarapoto and extended for an addi- tional 52 kilometers further south, not to mention along tangential roads. We also include results from two stationary tests where we turned Loon coverage on and o‰. Collecting data on di‰erent days meant the Loon balloons in the vicinity were at di‰erent positions relative to their terrestrial cell sites. We’ve selected these tests, because we could detect the presence of the Loon serving cells, even if the terrestrial network had the dominant serving cell (e.g., the strongest signal strength). In other words, these test results are ideal for determining how Loon impacted the terrestrial LTE network when the terrestrial network was providing primary coverage. In the appendix, we include some additional test results.

Figure 3 provides a geo plot of the Loon test area.

Figure 3. Loon Test Area

Source: Signals Research Group

February 2020 Page 12 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

2.1 Tests 61 Through Test 71 We combined these tests into a single study for analysis purposes, since each individual test was merely a continuation of the preceding test without any other meaningful di‰ erentiation. Figure 4 provides four key metrics in a geo plot of the 18-kilometer test. ‚ e Green-Red line identi es if the terrestrial network (Red) or Loon (Green) was providing cellular coverage, as determined by the

Figure 4. Test 61-71 Key Metrics – geo plot

Tarapoto

Overview

Focus Area – Figure 5 Focus Area – Figure 5

Top PCIs Loon RSRP

Focus Area – Figure 5 Focus Area – Figure 5

Terrestrial RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

February 2020 Page 13 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

serving cell PCI with the strongest signal (RSRP). We used the R&S scanner to make this determi- nation. ‚e gure also shows the signal strength of the strongest Loon and the strongest terrestrial PCI at each point along the route. Black indicates the scanner could not detect the presence of the pertinent network. Finally, the RSRP Delta plot shows the di‰erence in signal strength between the serving terrestrial cell site and the strongest Loon PCI. In the event Loon was the dominant cell, no colored circle is shown. ‚is attribute explains why much of this plotted line is “missing.”

There was a strong delineation Looking at the four bottom images in the gure, there are a few observations worth making. First, between the area covered by there was a strong delineation between the area covered by the terrestrial network and the area covered the terrestrial network and by Loon. Additionally, in terrestrial-covered areas the Loon signal was generally weak. or it went the area covered by Loon. undetected (black circles). Likewise, in areas where Loon was the dominant cell, the terrestrial signal strength was generally very weak and frequently below -115 dBm. It is worth noting the Loon signal rarely exceeded -105 dBm, based on scanner measurements. Lastly, the RSRP delta image shows the di‰erences between the strongest terrestrial cell and the strongest Loon cell were frequently more than 5 dB (magenta) with some limited regions where the di‰erences in signal strength were more modest, indicating an area where Loon was creating some interference with the terrestrial network.

Figure 5 shows the signal strength for the scanner-detected terrestrial and Loon cells in the high- lighted region shown in Figure 4. For the rst 200 seconds of the plot, Loon had two PCIs (42 and 62) which were approximately 20 dB higher than the two terrestrial cells, which had very low signals. In this region of the network, Loon provided coverage with inconsequential interference from the terrestrial network. From 500 seconds onward, the terrestrial network (PCI 28) had a much stronger signal than Loon (10-20 dB), indicating the terrestrial network provided coverage with Loon causing inconsequential interference to the network. Finally, between 200 and 500 seconds there was inter- ference between the terrestrial network and Loon, as well as interference between three terrestrial cell sites (PCI 425, 189 and 28). ‚e self-interference in the terrestrial network would exist with or without Loon. ‚is region of the drive route was approximately 0.4 kilometers, compared with the

Figure 5. Terrestrial and Loon RSRP Time Series

Loon Dominant Interfering Region - 0.4 km Terrestrial Dominant RSRP (dBm) (~20 dB Stronger Signal) (at least 2 Terrestrial and 2 Loon PCIs (~10 to 30 dB Stronger Signal) with Comparable Signals) -80 Terrestrial (PCI 28)

-90

-100 Terrestrial (PCI 189) Loon (PCI 62) -110

-120

-130 Loon (PCI 42)

Terrestrial (PCI 425) -140 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 Time (sec) Source: Signals Research Group

February 2020 Page 14 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

8 kilometer stretch where Loon provided the only reliable signal. We didn’t continue further down the road so we don’t know where (or even if) the terrestrial network would have resumed providing coverage.

The Loon signal strength was Figure 6 shows the cumulative distribution for the Loon signal strength (RSRP). ‚ e Top Loon plot rarely higher than -100 dBm and and median value (-108 dBm) re£ ects the distribution of the strongest detected Loon signal along frequently below -110 dBm. the route. ‚ e All Loon plot and median value (-126.5 dBm) includes all Loon signals, including the strongest Loon signal as well as all the weaker Loon signals detected by the scanner. Including both sets of values demonstrates that while the strongest Loon signal – the one likely used by a mobile device – was more than adequate for providing coverage without unnecessarily high signal levels, Loon can also extend to much lower signal levels. ‚ e latter point indicates that the potential Loon coverage area was much greater than we document in this paper.

Figure 6. Cumulative Distribution of Loon Signal Strength

Cumulative Probability Distribution (%) 100%

Top Loon PCI Median RSRP (dBm) All Loon PCIs 80% Top Loon RSRP All Loon

60%

40% -108 -126.5 20%

0% -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 -130 -135 -140 RSRP (dBm) Source: Signals Research Group

February 2020 Page 15 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Finally, Figure 7 shows the cumulative distribution of the di‰ erences in signal strength between the top terrestrial cell and the strongest interfering cell. We excluded all instances when Loon was the strongest cell since the focus of this analysis is to evaluate Loon’s impact on the terrestrial network and not to highlight Loon’s ability to extend coverage (something we do in the next two chapters).

Figure 7. Cumulative Distribution of the Diš erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell

Cumulative Probability Distribution (%) 100% Median RSRP Delta (dB)

Terrestrial to Terrestrial to Terrestrial Terrestrial 80% Terrestrial to Loon RSRP Delta RSRP Delta RSRP Delta (RSRP < -95 dBm) Terrestrial to Terrestrial RSRP Delta

60%

-2.84 -3.34 40% -5.36 Terrestrial to Loon RSRP Delta 20%

Terrestrial to Terrestrial RSRP Delta (RSRP < -95 dBm) 0% -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 RSRP Delta between Top Cell and Second Cell (dBm) Source: Signals Research Group

For this analysis, we looked at three scenarios. First, we looked at the di‰ erences in signal strength between the top terrestrial cell and the strongest interfering cell, which had to be a terrestrial cell. ‚ is relationship, labeled Terrestrial to Terrestrial RSRP Delta, serves as one benchmark we can use to evaluate Loon. With more favorable RSRP, the di‰ erences in signal strength between the stron- gest cell and the top interfering cell should be much higher than when the signal strength from the strongest cell is low, since the latter suggests an edge-of-cell location where there will be detected signals with largely comparable signal strength from multiple cell sites. High RSRP values suggest a location near the serving cell site where interference from adjacent cells should be less pronounced. Since Loon operates in a region with low signal strength from the terrestrial network, we then  ltered the terrestrial-terrestrial scenario to only include those data points when the top terrestrial cell had an RSRP below -95 dBm (labeled Terrestrial to Terrestrial RSRP Delta (RSRP < -95 dBm). ‚ is comparison is more appropriate for evaluating Loon’s impact on the terrestrial network, but we also include the Terrestrial to Terrestrial RSRP Delta scenario with all RSRP values for full transparency. Finally, we included those instances when Loon was the strongest interfering cell with the terrestrial network (labeled Terrestrial to Loon RSRP Delta).

‚ e information in Figure 7 indicates the Loon signal was -2.84 dB lower [median] than the top terrestrial cells’ signal strength, or largely comparable to the scenario when the top terrestrial cell’s signal strength was below -95 dBm and the strongest interfering cell was another terrestrial cell site. As expected, if we include all RSRP values, the di‰ erence in signal strength between the top

February 2020 Page 16 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

cell and the interfering terrestrial cell increases to 5.36 dB, since this analysis includes regions of the network where the interference was inherently lower. Looking at the distribution plot, the Terrestrial to Terrestrial RSRP Delta scenario with all RSRP values shows this scenario had the highest prob- ability of having the biggest di‰erences in signal strength [lowest interference]. ‚e plot also shows the Terrestrial to Loon RSRP Delta scenario had a slightly lower probability of having a signal strength that was within 3 dB of the strongest terrestrial cell, compared with the Terrestrial to Terres- trial (RSRP < -95) interference scenario. ‚is observation is important because comparable signal strengths indicate higher interference and a lower signal quality (SINR).

February 2020 Page 17 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

2.2 Test 87 Test 87 took place along an 11.5-kilometer drive route which began 10.5 kilometers southeast of the Test 61-71 drive route, which we analyzed in the previous section. Additionally, we conducted this test on a di‰ erent day so the locations of the Loon balloons would have been di‰ erent than with the Test 61-71 study. Figure 8 identi es the location of the drive route and it provides a geo plot of several relevant network metrics. ‚ e  gure shows that Loon had the strongest cell in the southern portion

Figure 8. Test 87 Key Metrics – geo plot

Tarapoto

Overview

Top PCIs Terrestrial RSRP Loon RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

February 2020 Page 18 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

of the test where the terrestrial coverage was generally poor with RSRP frequently below -120 dBm. As we continued further north the terrestrial network coverage improved while the signal strength from the Loon cells dropped. ‚ e RSRP delta  gure shows the relative changes in the terrestrial and Loon signal strengths.

Figure 9 provides the median values and distribution plots for the strongest Loon cell as well for all Loon cells (PCI values), regardless of whether these cells were providing the strongest Loon signal. We detected four unique Loon PCI values during this drive, but one Loon PCI was generally 3-4 dB stronger than two PCIs while the scanner only detected the fourth Loon PCI for a short period of time.

Figure 9. Cumulative Distribution of Loon Signal Strength

Cumulative Probability Distribution (%) 100%

Top Loon Median RSRP (dBm) 80% Top Loon RSRP All Loon

All Loon 60%

40%

-105.3 -112.7 20%

0% -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 -130 -135 -140 RSRP (dBm) Source: Signals Research Group

February 2020 Page 19 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 10 shows the cumulative distribution of the di‰ erences in signal strength between the top terrestrial cell and the strongest interfering cell. Our approach to this analysis is consistent with what we did in the previous section. For this test, the Terrestrial to Terrestrial Interference scenario was higher than in Test 61-71 by nearly 1 dB (5.36 versus 4.4 dB) while the Terrestrial to Loon Interfer- ence scenario was comparable. More importantly, the results indicate Loon’s potential contribution to interference with the terrestrial network was nearly identical to the self-interference that already existed within the terrestrial LTE network when the RSRP was below -95 dBm (Terrestrial to Terres- trial RSRP Delta (RSRP < -95 dBm).

Since there was a good mix of areas along this drive route where Loon was present as well as areas where we couldn’t detect Loon (or it was inconsequential), we were able to look at the measured SINR versus RSRP for the two scenarios. To ensure a meaningful set of data to analyze, we included data points in the Terrestrial SINR with Terrestrial Top Interfering Cell scenario if Loon was present, as long as the RSRP was at least 8 dB lower than the top terrestrial cell site and it wasn’t the strongest interfering site.

Figure 10. Cumulative Distribution of the Diš erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell

Cumulative Probability Distribution (%) 100% Median RSRP Delta (dB) Terrestrial to Terrestrial Terrestrial to Terrestrial to Loon Terrestrial 80% RSRP Delta RSRP Delta RSRP Delta (RSRP < -95 dBm)

60%

Terrestrial to Terrestrial RSRP Delta -2.6 -2.5 40% -4.4 Terrestrial to Loon RSRP Delta 20%

Terrestrial to Terrestrial RSRP Delta (RSRP < -95 dBm) 0% -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 RSRP Delta between Top Cell and Second Cell (dB) Source: Signals Research Group

February 2020 Page 20 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

As evident in Figure 11, when the measured RSRP from the strongest terrestrial cell was in the range of -90 to -105 dBm, the impact of Loon as an interfering cell site was very comparable to the impact of another terrestrial cell site creating interference. With higher RSRP, the scanner didn’t detect Loon’s presence or the RSRP delta was so signicant (> 20 dB) that Loon would have no impact on the terrestrial LTE signal quality. With RSRP below -105 dBm, Loon was frequently the dominant cell over the terrestrial cells so providing interference-related information for the terrestrial LTE network is not meaningful. ‚e gure also shows that the di‰erences in RSRP between the top terres- trial cell and Loon dropped signicantly, and much faster than the Terrestrial SINR with Terrestrial Top Interfering Cell scenario, as the dominant terrestrial cell’s RSRP increased.

Figure 11 also shows an interesting phenomenon between RSRP -75 and -85 dBm, which falls outside the range where Loon was detected. Specically, the di‰erences in RSRP between the top terrestrial cell and the strongest interfering terrestrial cell were much lower and the top terrestrial cell’s SINR declined. ‚is information suggests there were two cell sites providing excellent coverage to the same physical location in the network, but the strong signals from both sites negated the benet due to the increased interference.

Figure 11. SINR and RSRP Delta as a Function of RSRP

SINR (dB) RSRP Delta (dB) 16 0 Terrestrial SINR with RSRP Delta between Terrestrial Terrestrial Top Interfering Cell Serving Cell and Terrestrial Interfering Cell 14 -2 RSRP Delta between Terrestrial Serving Cell and all Loon Interfering Cells -4 12 -6 10 -8 8 -10 Drop in SINR consistent with 6 relative strength of terrestrial interfering cell -12 4 -14

2 Terrestial SINR with -16 Loon Interfering Cell(s) 0 -18 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 RSRP (dBm)

Source: Signals Research Group

February 2020 Page 21 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 12 provides a time series plot of the scanner measured RSRP for the top terrestrial cell site and the strongest interfering cell site, which was also a terrestrial cell site. Generally, there is a good separation between the two lines, especially with higher absolute RSRP values. However, starting at 700 seconds, both cells had similar RSRP values in an area of the network where the measured RSRP was very favorable. ‚is phenomenon, along with other occurrences along the route, explains the peculiar trends shown in Figure 11.

Figure 12. Time Series Plot of RSRP for Two Terrestrial Cell Sites

RSRP (dBm) -60

Top Terrestrial RSRP -70

-80

-90

-100

Top Terrestrial Interferer RSRP -110

-120 850800750700650600550500450400350300250200150100500 Time (sec) Source: Signals Research Group

February 2020 Page 22 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

2.3 Test 53 ‚ e Test 53 drive route started 7 kilometers outside of Tarapoto, winding down 35 kilometers along the major highway until the test ended 32.5 kilometers south of Tarapoto. Figure 13 shows the drive route as well as geo plots of some key performance metrics. Compared with other tests shown in this section, Loon was less frequently the dominant cell site – it provided coverage in the southern

Figure 13. Test 53 Key Metrics – geo plot

Tarapoto

Overview

Top PCIs Terrestrial RSRP Loon RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

February 2020 Page 23 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

portion of the drive route where there was poorer terrestrial coverage. However, Loon was present as a potential source of the interference with the terrestrial network for a good portion of the route.

Loon’s impact on the terrestrial Figure 14 shows the median and cumulative distribution plots for the strongest Loon cell as well as network was negligible. for all detected Loon cells. During this drive, we identi ed nine di‰ erent Loon PCI values. Given the relative di‰ erences in the signal strength between the Loon cells and the terrestrial network, which was quite good along this route, Loon’s impact on the terrestrial network was negligible, meaning that pre-existing self-interference in the terrestrial LTE was largely responsible for the interference that we observed. ‚ is statement is supported by the information in Figure 15, which shows the median delta between the terrestrial network and Loon was 9.63 dB, compared with only 5.21 dB with Terrestrial to Terrestrial interference scenario and 4.58 dB for the Terrestrial to Terrestrial (RSRP < -95 dBm) scenario.

Figure 14. Cumulative Distribution of Loon Signal Strength

Cumulative Probability Distribution (%) 100%

Top Loon RSRP Median RSRP Delta (dB) All Loon RSRP 80% Top Loon RSRP All Loon

60%

40% -103.5 -112

20%

0% -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 -130 -135 -140 RSRP Delta between Top Cell and Second Cell (dB) Source: Signals Research Group

February 2020 Page 24 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

‚ e relationships between the terrestrial SINR and the terrestrial RSRP, as well as the di‰ erences in the RSRP between the top cell and the strongest interfering cell also show that Loon had minimal impact on network quality when the terrestrial network had the dominant cell. As shown in Figure 16, the terrestrial network’s SINR was higher when there was interference from Loon (e.g., the Loon Interfering Cell(s) scenario) than in areas along the drive route where Loon didn’t generate any inter- ference (e.g., the Terrestrial Top Interfering Cell scenario) And as expected, the di‰ erences in RSRP between the terrestrial cell and the strongest Loon cell dropped o‰ more rapidly than the Terrestrial Top Interfering Cell scenario when the terrestrial’s network RSRP increased. ‚ ere weren’t enough data points to extend the Terrestrial Top Interfering Cell SINR plot below -102 dBm.

Figure 15. Cumulative Distribution of the Diš erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell

Cumulative Probability Distribution (%) 100% Median RSRP Delta (dB) Terrestrial to Terrestrial to Terrestrial to Terrestrial Terrestrial to Loon RSRP Delta 80% Terrestrial Loon RSRP Delta RSRP Delta RSRP Delta (RSRP < -95 dBm)

60% -4.58 -5.21 Terrestrial to Terrestrial RSRP Delta 40%

-8.63

20%

Terrestrial to Terrestrial RSRP Delta (RSRP < -95 dBm) 0% -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 RSRP Delta between Top Cell and Second Cell (dB) Source: Signals Research Group

February 2020 Page 25 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

‚e gure also shows two other interesting trends. First, with improving terrestrial RSRP the signal quality declined due to terrestrial to terrestrial interference. ‚is trend is evident with RSRP higher than -85 dBm. ‚e other interesting trend occurs with the Loon Interfering Cell(s) scenario with RSRP lower than -105 dBm. ‚is counterintuitive trend is due to the absence of meaningful inter- ference from the terrestrial cells when Loon was the dominant interfering source. Worth reiterating, with lower RSRP values there weren’t enough data points when Loon wasn’t present for this test, so we can’t show comparative results for the Terrestrial Top Interfering Cell scenario.

Figure 16. SINR and RSRP Delta as a Function of RSRP

SINR (dB) RSRP Delta (dB) 12 RSRP Delta between Terrestrial Serving Cell and Terrestrial Interfering Cell 0

10 -5 Higher Interference decreases signal quality -10 8 with otherwise favorable RF conditions Terrestial SINR with Loon Interfering Cell(s) Increase in SINR is due to -15 low interference from the 6 terrestrial network -20

4 -25 Terrestrial SINR with Terrestrial Top Interfering Cell 2 -30 RSRP Delta between Terrestrial Serving Cell and all Loon Interfering Cells 0 -35 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 RSRP (dBm)

Source: Signals Research Group

February 2020 Page 26 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

2.4 Stationary Tests with and without Loon In this section we include the results from two pairs of stationary tests in which we collected network performance metrics with Loon present as an interfering cell and with Loon turned o‰ . Figure 17 shows the locations where the tests took place.

Figure 17. Test Locations

Source: Signals Research Group

February 2020 Page 27 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 18 shows the SINR and the RSRP values for the serving cell and the interfering cells for Test 80 (No Loon) and Test 81 (Loon). ‚ is test occurred at the same location with approximately ten minutes separating the completion of Test 80 and the start of Test 81. We needed this time to bring up the Loon cell sites. In both cases the serving cell, based on scanner metrics, was in the terrestrial network, as was the strongest interfering cell. Loon was the second strongest interfering cell (labeled 3rd PCI (Loon) in the  gure. Although the serving cell SINR dropped by 5.4 dB with Loon present in Test 81, the results also show the signal strength from the strongest interfering cell (terrestrial) increased by 3 dB for reasons that are not entirely clear. Additionally, the Loon RSRP was 9.8 dB lower than the serving cell and 4 dB lower than the terrestrial interfering cell. ‚ erefore, although the presence of Loon likely had a negative impact on the serving cell SINR, much of the drop in SINR for the serving cell was due to changes in the terrestrial network that had nothing to do with Loon.

Figure 18. Network Performance Parameters with and without Loon

Test 80 Test 81

12 Serving PCI (28) 2nd PCI (425) Serving PCI (28) 2nd PCI (425) 3rd PCI (Loon)

6.6

-94.8 -93.6 -99.4 -102.4 -103.4

Serving PCI (Test 80) Serving PCI (Test 81) dB dBm Source: Signals Research Group

February 2020 Page 28 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 19 shows the observed physical layer (PDSCH) data speeds recorded on a smartphone using a high-bandwidth Umetrix FTP server, located in Virginia. ‚ e  gure shows we did one data speed test without Loon and two data speed tests with Loon present. In the  rst test the mobile device was obviously using the terrestrial network since Loon wasn’t present. In the second test, the smartphone used the terrestrial network for the  rst data transfer but then it switched to Loon (PCI 52) for the second data transfer.

Figure 19 also shows the median actual and RB-normalized data speeds for the three tests. ‚ e infor- mation indicates Loon delivered higher data speeds than the terrestrial network (9.7 Mbps versus 3.6 Mbps and 3.8 Mbps). However, the RB-normalized data speeds, which take into consideration network loading and channel bandwidth favor the terrestrial results, especially the Test 80 results when Loon wasn’t present. One critical piece of information, which helps explain the RB-normalized results is that the Loon channel bandwidth was 2x10 MHz (50 RBs), compared with the terrestrial channel bandwidth, which was 2x15 MHz (75 RBs). Given the disparity in channel bandwidth between the two networks, we would expect the Loon RB-normalized throughput to be lower than the terrestrial results and the comparison isn’t fair. However, we are including the information to show that the terrestrial network had lots of data traœ c from other mobile devices in the area while at the time we did this test the Loon network was lightly loaded.

Figure 19. Mobile Device Performance with and without Loon

Mbps 15 Phone on Terrestrial Phone on Loon 12

Test 80 (No Active Loon) Test 81 (Loon Active) 9

6

3

0 6050403020100 70 1601501401301201101009080 170 220210200190180 Time (sec)

46.1 20.3

17.1

9.7 10.5 16.6 13.3

3.6 3.8

Test 80 Test 81 (Terrestrial) Test 82 (Loon) Test 80 Test 81 Test 82 (Loon) Test 80 Test 81 Test 82 (Loon) (Terrestrial) (Terrestrial) RB Utilization Actual (Mbps) RB Normalized (Mbps) Source: Signals Research Group

February 2020 Page 29 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

We did another stationary test on a di‰ erent day in the general location of the previous test. ‚ e Loon cell sites had an RSRP nearly 15 dB lower than the strongest terrestrial cell at this location. ‚ ere was a 1.9 dB drop in the measured SINR with Loon present but given the huge di‰ erence in signal strength between Loon and the terrestrial network, it isn’t clear how much of this drop was due to Loon versus other factors involving the terrestrial network. We also point out that Loon’s intended coverage area was not at this location, but further outside the village. Test 42 and Test 46, in the next Chapter, show the impact of this Loon balloon on improving terrestrial coverage.

In the appendix we include results from other drive tests. ‚ ese test results, along with the test results provided in this section, are included in the analysis used to create the two summary  gures in Chapter 2.

Figure 20. Network Performance Parameters with and without Loon

PCI 28 PCI 425 PCI 29 Loon (PCI 41) Loon (PCI 43) 10 9.5

7.6 8

6

4

2 -94 -95.8 -100.9 -99.9 -112.8 -110.1 0 -118.9 -116 SINR (Pre Loon) SINR (Post Loon)

RSRP (dBm) SINR (dB)

Test 35 (pre Loon) Test 41 (post Loon) Source: Signals Research Group

February 2020 Page 30 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

3.0 Extending Terrestrial Coverage with Loon and the Interactions between the Two Networks In this chapter we show results where Loon coverage was more extensive along the drive route and we show how our mobile devices interacted with the two networks when moving between them or between di‰erent Loon cells (PCIs). Given the distance between Tarapoto and the outer boundary where Loon coverage was primarily targeted, it wasn’t logistically possible to navigate much further into the Loon coverage area in a day. However, we went far enough into the Loon coverage area to quantify Loon performance attributes and, most importantly, we were able to evaluate Loon’s impact on the terrestrial network (previous chapter) and the interactions between Loon and the terrestrial network (this chapter).

February 2020 Page 31 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

3.1 Test 91 ‚ e Test 91 drive route began just south of the end point for Test 87 (55 kilometers south of Tarapoto) and extended for an additional 2.9 kilometers. Figure 21 shows the drive route as well as geo plots of some key performance metrics. Along this route, there were three Loon PCIs (two di‰ erent balloons) that had a stronger signal than the terrestrial network at various sections along the route. In total, Loon had the dominant signal over 78% of the drive route. Figure 21. Test 91 Key Metrics – geo plot

Tarapoto

Overview

Top PCIs Terrestrial RSRP Loon RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

February 2020 Page 32 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Although three Loon PCIs shared responsibility for the top PCI, based on measured signal strength, we identi ed nine unique Loon PCIs along the drive route, coming from three di‰ erent Loon balloons. Figure 22 provides the median values and cumulative distribution plots for the top Loon RSRP as well as the RSRP values, based on including all Loon measurement values.

Figure 22. Cumulative Distribution of Loon Signal Strength

Cumulative Probability Distribution (%) 100%

Median RSRP (dBm) Top Loon All Loon 80% Top Loon RSRP All Loon

60%

40% -103.8 -110.7 20%

0% -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 -130 -135 -140 RSRP (dBm) Source: Signals Research Group

Given the limited data set when the terrestrial network had the strongest serving cell, there isn’t enough data to show how Loon impacted the terrestrial network. ‚ is information is also less mean- ingful since in most cases Loon was providing coverage. However, at the conclusion of this test (not captured in the  rst two  gures in this section), we did an additional test with the mobile device + scanner during which time Loon engineers made two changes to the Loon network con guration at our request. Since we knew that the S1 interface in Loon’s network transits across a stratospheric mesh network, comprised of point-to-point millimeter wave links that change over time, , we wanted to see the impact of changing the active ground station on Loon’s performance. Switching ground stations could be required for technical reasons or to accommodate unfavorable weather conditions.

Prior to changing the active Loon ground station, we started capturing data with the R&S scanner and a Galaxy Note 9 smartphone. We used the Umetrix data platform from Spirent Communications to generate high bandwidth throughput using the FTP protocol to the mobile device. ‚ e Umetrix server was in Virginia. Loon engineers then switched the active ground station from Yurimaguas to Iquitos. As part of this activity, Loon engineers also switched o‰ two Loon cells (PCI 81 and PCI 83) which were on the same Loon balloon as the serving cell (PCI 82) being used by the mobile device.

February 2020 Page 33 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

We observed a median Figure 23 shows the physical layer (PDSCH) throughput for the mobile device while changing the sustained data speed of 16.4 ground station and turning o‰ two Loon cells. ‚ e RSRP and SINR metrics come from the scanner Mbps (peak = 40.3 Mbps) using data. We’ve highlighted a section of the plot where the two neighboring Loon cells were momen- Loon with a BLER of 9.7%. Drops to 0 / near 0 occur tarily turned o‰ – they disappeared in the scanner data and on the mobile device – and the moment when each 30 second when they permanently disappeared. ‚ e periodic dips in the throughput were due to the Umetrix test finishes test scenario. We used a 30-second FTP data transfer which ran in a repetitive loop, albeit with very brief periods when no data was being sent. Although it isn’t shown in the  gure, the median BLER (Block Error Rate) was 9.7%, or comparable with what we would expect with a terrestrial network. Surprisingly [at least to us], it isn’t evident in the  gure when the Loon engineers changed the active ground station. Loon developed a “Temporospatial SDN” that orchestrates the backhaul network radio resource management, link hando‰ s, and routing table updates around each other to automate such events based on the forecast motion and weather, which minimizes packet loss during such events. In any event, it is very unlikely a consumer would notice the switch.

Figure 23. Mobile Device Throughput While Changing the Loon Ground Station

Mbps 50 6.1 Two Loon PCIs Median = 16.4 Mbps Two Loon PCIs Loon Terrestrial 4 momentarily turned Maximum = 40.3 turned o o Mbps Loon Terrestrial 40

30

20

10

-103.7 -110.1 0 650600550500450400350300250200150100500 700 750 900850800 RSRP (dBm) SINR (dB) Drops to 0 / Time (sec) near 0 occur when each 30 second test finishes Source: Signals Research Group

Figure 24 and Figure 25 provide additional information about the radio conditions during this stationary test. ‚ e  rst  gure shows when PCI 81 and PCI 83 were not radiating as well as the RSRP for PCI 82 (the serving cell), as measured by the mobile device and the scanner. Interestingly, the mobile device observed a meaningful drop in the PCI 82 RSRP when PCI 81 and PCI 83 were momentarily turned o‰ . In the second  gure, there is a noticeable improvement in the mobile device CQI, starting at 120 seconds when PCI 81 and PCI 83 were not active. Toward the end of the test when both Loon PCIs were turned o‰ the second time there was a modest improvement in the CQI. ‚ roughout this test the data speeds were excellent. Although turning o‰ two Loon cells helped improve radio conditions, we believe switching to the new ground station was a bigger factor in the favorable data speeds since we believe there was high packet-loss in the wired connection from the

February 2020 Page 34 -110.1 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

original ground station (external to the Loon network). ‚is observation isn’t evident in the gure and it is based on additional information that we obtained while testing in Peru.

Figure 24. Mobile Device and Scanner RSRP Measurement Reports

RSRP (dBm) -90

RSRP (dBm) -90-95

-95-100 Loon PCI 82 (Scanner)

-100-105 Loon PCI 82 (Scanner) Loon PCI 81 (Scanner) -105-110

Loon PCI 81 (Scanner) -110-115

Mobile Device Serving Loon PCI 83 (Scanner) Cell RSRP (Loon PCI 82) -115-120 650600550500450400350300250200150100500 Mobile700 Device750 Serving 850800 900 Loon PCI 83 (Scanner) Cell RSRP (Loon PCI 82) -120 Time (sec) Source: Signals Research Group 650600550500450400350300250200150100500 700 750 850800 900 Time (sec)

SINR/CQI Figure15 25. Mobile Device CQI and Scanner RSRP Measurement Reports CQI (Mobile Device) SINR/CQI 15 12 CQI (Mobile Device)

12 9

9 6

6 3

Loon PCI 82 SINR (Scanner) 3 0

Loon PCI 82 SINR (Scanner) 650600550500450400350300250200150100500 700 750 900850800 0 Time (sec) 650600550500450400350300250200150100500 700 750 900850800 Time (sec) Source: Signals Research Group

February 2020 Page 35 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

3.2 Test 42 and Test 46 ‚ese two tests occurred 30 kilometers south of Tarapoto along a rural secondary road. Test 42 (0.7 kilometers) included a mix of terrestrial and Loon cells serving as the dominant cell (primarily Loon). ‚e start of Test 46 was another 0.5 kilometers past the end point for Test 42 and extended for another 1.2 kilometers. Figure 26 shows the location for these two tests as well as other information about the RF environment.

Figure 26. Test 42 and Test 46 Key Metrics – geo plot

Overview

Top PCIs Loon RSRP

Terrestrial RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

February 2020 Page 36 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

It is clear in the geo plot that by the end point of Test 42 the terrestrial coverage was very poor. At the start point for Test 46, the terrestrial coverage was virtually nonexistent. Figure 27 shows how the RSRP for the Loon cell (PCI 43) and the two terrestrial cells changed throughout the test. Figure 28, which covers the same period, shows the SINR for the serving cell (the PCI with the strongest RSRP). ‚e serving cell in this gure alternates between PCI 189 (terrestrial) and PCI 43 (Loon) at the beginning before remaining entirely on PCI 43. Comparing the two gures, it is also evident that PCI 425 was only a factor for the rst twenty seconds of the test before its RSRP dropped below -120 dBm for the remainder of the test. ‚e improving SINR starting at ninety seconds was due to the drop in the PCI 189 RSRP shown in Figure 27.

Figure 27. Test 42 RSRP for Loon and Terrestrial Cells

RSRP (dBm) Top PCI -100 450

400 -105 PCI 189 (Terrestrial) RSRP RSRP (dBm) PCI 43 (Loon) RSRP Top PCI350 -100-110 450 300 -115 400 -105 PCI 189 (Terrestrial) 250 RSRP 350 PCI 43 (Loon) RSRP 200 -120-110 300 150 -125 -115 PCI 425 (Terrestrial) RSRP 250 100 Loon PCI -130 Top PCI 200 -120 50 150 -125-135 PCI 425 (Terrestrial) RSRP 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 100 Loon PCI Time (sec) -130 Top PCI Source: Signals Research Group50 SINR (dB) Top PCI -135 0 10 450 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 Figure 28. Test 42 Serving Cell SINR Top PCI Time (sec) 400 8 SINR (dB) Top SINR Top PCI350 10 450 300 6 Top PCI 400 250 8 350 Top SINR 200 4 300 150 6 250 2 100 200 4 50 150 0 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 2 100 Time (sec) 50

0 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 Time (sec) Source: Signals Research Group

February 2020 Page 37 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Finally, we observe in Figure 29 that by the time we reached the start point of Test 46 the terrestrial network was barely present. ‚ e strongest interfering cell, which happened to be a terrestrial cell, had a signal strength that was 16.5 dB below the serving Loon cell. ‚ is situation explains why the serving cell SINR was a very favorable 14.4 dB. All results based on scanner measurements.

Figure 29. Test 46 Serving Cell SINR and RSRP

SINR (dB) RSRP (dBm) Top Strongest 25 -60 Cell Interfering RSRP Cell RSRP 14.4 (Loon) (Terrestrial) 15 20 Top SINR 12 -80

15 9

-100 6 10

Top RSRP 3 -120 5 -111.9 0 Top Cell SINR (Loon) -128.4 Strongest Interfering Cell RSRP SINR (dB) RSRP (dBm) 0 -140 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 Time (sec) Source: Signals Research Group

February 2020 Page 38 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

3.3 5 MHz and 10 MHz Loon Sensitivity In this section we include the results from three di‰ erent network con gurations: Terrestrial Only, Loon 2x10 MHz and Loon 2x5 MHz. ‚ is test occurred near the conclusion of the drive test in the previous section (Figure 30). It isn’t clear if an operator would use Loon with a 2x5 MHz channel bandwidth but since we found these results interesting, we are including them for infor- mational purposes.

Figure 30. Stationary Test Locations

Source: Signals Research Group

February 2020 Page 39 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

With the introduction of a Loon 2x10 MHz radio channel the RSRP improved by 19 dB and the SINR improved by 17 dB, compared to the terrestrial LTE network. Switching to a 2x5 MHz radio channel with Loon improved the RSRP by an additional 2.7 dB and it improved the SINR by 5.1 dB. Figure 31 shows this information.

Figure 31. RSRP and SINR for Loon and Terrestrial Cells

No Loon 2x5 MHz Loon 2x10 MHz Loon 19.8

14.7

No Loon -107 -109.7 2x5 MHz Loon 2x10 MHz Loon -128.7 -2.3

RSRP (dBm) SINR (dB) Source: Signals Research Group

February 2020 Page 40 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Finally, Figure 32 shows a time series plot of the RSRP and SINR, as measured by the scanner for the period prior to Loon (terrestrial only), followed by the Loon cell turning on and radiating a 5 MHz channel. Although it isn’t evident in the gure, the strongest terrestrial serving cell jumped frequently between three di‰erence PCI values for that portion of the gure when Loon wasn’t present.

Figure 32. Serving Cell RSRP and SINR with the Introduction of a Loon 5 MHz Channel

Top Cell RSRP (dBm) Loon PCI -60 50

Loon PCI -70 40 -80

30 -90

-100 20

-110 Top RSRP 10 -120

-130 0 0 40 80 120 160 200 240 280 320 360 400 440 Time (sec)

Top Cell SINR (dB) Loon PCI 25 50

Loon PCI 20 40 15

30 10 Top SINR

5 20

0 10 -5

-10 0 0 40 80 120 160 200 240 280 320 360 400 440 Time (sec) Source: Signals Research Group

February 2020 Page 41 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

3.4 Moving between Loon and Terrestrial Cells with a Mobile Device Although it is possible to integrate the terrestrial network and Loon, the conguration we tested in Peru did not support this capability. ‚erefore, when a mobile device moved from Loon coverage to the terrestrial network (or vice versa) it didn’t do a traditional handover, that occurs when moving between di‰erent terrestrial cell sites. Instead, since the two networks were distinct entities, the mobile device did an RRC detach from a Loon/Terrestrial cell, followed by an RRC attach to a Terrestrial/ Loon cell. Figure 33 shows a time series plot of the RSRP for the top terrestrial and the top Loon cells as well as the strongest RSRP at each point, as captured by the mobile device. ‚e serving cell is Loon (PCI 62) at the start of the gure when Loon had the strongest signal and then it switches to a terres- trial cell (PCI 14) when the terrestrial network had the stronger signal. When Loon was the serving PCI, its RSRP was approximately 5 dB higher than the terrestrial cell. Starting at X=18 seconds PCI 14 had the stronger signal and by X=22 seconds the mobile device switched to the terrestrial network. Shortly thereafter, the mobile device couldn’t even detect the Loon PCI. Although not shown in this gure, scanner data from this test also shows the scanner stopped detecting the Loon PCIs shortly after the mobile device moved to the terrestrial network.

Figure 33. Mobile RRC Reconnect when Moving from Loon to the Terrestrial Network

Serving Cell PCI RSRP (dBm) -95 70 Serving PCI

-100 60

-105 50

-110 40

-115 30

Serving Cell Loon (PCI 62) -120 20

-125 10 Terrestrial (PCI 14)

-130 0 0 5 10 15 20 25 30 35 Time (sec) Source: Signals Research Group

February 2020 Page 42 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Table 1 shows the relevant RRC signaling messages when the mobile device moved from Loon to the terrestrial network. ‚e table shows the transition took 1.8 seconds, which for most data applications would go unnoticed by the consumer.

Table 1. RRC Signaling Messages When the Mobile Device Moved from Loon to the Terrestrial Network

EPS Serving TAU NAS NAS NAS Bearer RRC RRC RRC RRC RRC TIME_STAMP PCI Request Attach Attach Attach Setup Setup Setup Connect Connect Connect Request Accept Time Attempt Success Release

2019-09-24 18:06:53.000 62 2019-09-24 18:06:54.000 62 2019-09-24 18:06:55.000 62 2019-09-24 18:06:56.000 62 2019-09-24 18:06:57.000 62 2019-09-24 18:06:58.000 62 2019-09-24 18:06:59.000 62 2019-09-24 18:07:00.000 62 2019-09-24 18:07:01.000 62 2019-09-24 18:07:02.000 62 2019-09-24 18:07:03.000 62 2019-09-24 18:07:03.518 TA/LA updating 2019-09-24 18:07:03.518 RRC Attempt 2019-09-24 18:07:03.717 RRC Connect Setup 2019-09-24 18:07:03.725 RRC Success 2019-09-24 18:07:03.791 other 2019-09-24 18:07:03.853 EPS/IMSI attach 2019-09-24 18:07:03.854 RRC Attempt 2019-09-24 18:07:04.000 14 2019-09-24 18:07:04.030 RRC Connect Setup 2019-09-24 18:07:04.031 RRC Success 2019-09-24 18:07:05.000 14 2019-09-24 18:07:05.294 EPS/IMSI attach 2019-09-24 18:07:05.295 Attach 0.007 Complete 2019-09-24 18:07:06.000 14 2019-09-24 18:07:07.000 14 2019-09-24 18:07:08.000 14

Source: Signals Research Group

February 2020 Page 43 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

3.5 Moving between Loon Cells with a Mobile Device We also captured data which shows a mobile device moving between two Loon PCIs. Figure 34 provides a time series plot of the serving cell PCI, its RSRP and the RSRP of neighboring cells. We captured this information with the mobile device. ‚e neighboring cells include other Loon PCIs and two terrestrial PCIs. Figure 35 shows the same information but it focuses on a 200-second interval to provide additional visibility. Both gures show the mobile device barely detected the terrestrial network and when it did detect the network, the RSRP was frequently below -120 dBm. ‚e gures also show Loon PCI 61 and PCI 63 had comparable signal levels. From 0 to 300 seconds, PCI 61 had a slightly stronger signal and it was the serving cell. Starting at 300 seconds PCI 63 had a slightly stronger signal over PCI 61, although until ~425 seconds PCI 61 was the serving cell. ‚en, at X = 425 seconds, the mobile device moved from PCI 61 to PCI 63.

Figure 34. Serving Cell PCI and RSRP, including RSRP from Neighboring Cells

Serving Cell PCI RSRP (dBm) 65 -105 Serving Cell RSRP

Serving64 Cell PCI RSRP (dBm)-110 65 -105 Serving Cell RSRP 63 -115 64 -110

62 PCI 63 Neighbor RSRP -120 63 PCI 61 -115 Serving Cell PCI Neighbor 61 RSRP -125 PCI 63 Neighbor RSRP 62 PCI 190 Neighbor RSRP -120 PCI 189 Neighbor RSRP 60 PCI 61 -130 Serving Cell PCI Neighbor 61 0 50 100 150 200 250 300 350 400 450 RSRP 500 -125 Time (sec) PCI 190 Neighbor RSRP Source: Signals Research Group Serving Cell PCI PCI 189 Neighbor RSRP RSRP (dBm) 6560 -105-130 0 50 100 150 200 250 300 350 400 450 500 Figure 35. Serving Cell PCI and RSRP, including RSRP from NeighboringTime (sec) Cells – Enhanced View PCI 63 Neighbor RSRP 64Serving Cell PCI RSRP (dBm)-110 65 -105

63 -115 Serving Cell RSRP PCI 63 Neighbor RSRP 64 -110 PCI 61 Neighbor RSRP 62 -120 63 -115 Serving Cell RSRP 61 PCI 61 Neighbor -125 Serving Cell PCI RSRP 62 PCI 190 Neighbor RSRP -120 PCI 189 Neighbor RSRP 60 -130 61 300 350 400 450 500 -125 Serving Cell PCI Time (sec) PCI 190 Neighbor RSRP PCI 189 Neighbor RSRP 60 -130 300 350 400 450 500 Time (sec) Source: Signals Research Group

February 2020 Page 44 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Table 2 shows the RRC signaling messages that took place during this transition (19 ms) between Loon PCIs.

Table 2. RRC Signaling Messages When the Mobile Device Moved from Loon to the Terrestrial Network

NAS Attach Handover TIME_STAMP Serving Cell PCI RSRP SINR Complete RRC Success Duration

2019-09-24 16:30:10.000 61 -116.08 1.13 2019-09-24 16:30:11.000 61 -114.63 0.77 2019-09-24 16:30:12.000 61 -115.07 -0.09 2019-09-24 16:30:13.000 61 -114.54 2.39 2019-09-24 16:30:14.000 61 -114.76 -1.88 2019-09-24 16:30:15.000 61 -114.85 -2.72 2019-09-24 16:30:16.000 61 -114.85 -3.45 2019-09-24 16:30:17.000 61 -115.23 -2.88 2019-09-24 16:30:18.000 61 -115.37 0.04 2019-09-24 16:30:19.000 RRC Attempt 2019-09-24 16:30:18.781 RRC Success 0.019 2019-09-24 16:30:19.000 63 -112.23 0.67 2019-09-24 16:30:20.000 63 -112.24 1.47 2019-09-24 16:30:21.000 63 -112.95 0.61 2019-09-24 16:30:22.000 63 -113.28 0.55 2019-09-24 16:30:23.000 63 -113.09 0.18 2019-09-24 16:30:24.000 63 -113.25 -0.45

Source: Signals Research Group

February 2020 Page 45 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

During this test, we had the mobile device mounted to the roof of the drive test vehicle. We also used Google Drive to generate data transfers. Since we couldn’t reach the mobile device during this test, we didn’t have good visibility of the Drive application and what it was or wasn’t doing. Additionally, we later determined that Drive wasn’t a good application to generate maximum speed data trans- fers. ‚erefore, the absolute data speeds shown in Figure 36 likely understate the capabilities of the network. Additionally, during this test we believe that there was at least one other mobile device in our test van connected to the Loon network and consuming network resources. For this reason, we are including RB-normalized throughput in the gure. Both plots show inconsequential impact to the throughput when the mobile device moved between two Loon PCIs. In fact, the observed data speed improved.

Figure 36. Mobile Device Throughput

Mbps Serving Cell PCI 10 64 RB-Normalized Throughput

Serving Cell PCI 62 8 60

6 58

56 4

54

2 52 PDSCH Throughput

0 50 390 400 410 420 430 440 450 460 470 480 490 500 Time (sec) Source: Signals Research Group

February 2020 Page 46 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

4.0 Loon and the User Experience In earlier results we showed data speeds obtained with a smartphone attached to the Loon network. ‚ ose results, combined with other data we collected during the week of testing, indicate typical data speeds for a mobile device attached to the Loon network were frequently in the mid- to high-single digits (Mbps), although with good conditions they could reach into the mid-teens. We even observed a peak data speed of 40.3 Mbps with ideal conditions in a commercial network, but this speed is the exception and not the norm.

Loon delivers a comparable user In this chapter, we analyze the user experience with Loon, realizing that the user experience isn’t just experience to a terrestrial LTE impacted by data speeds and that fast data speeds do not always improve the user experience. To network with many applications summarize our  ndings, Loon delivers a comparable user experience to a terrestrial LTE network with many applications, especially an LTE network that is limited to a single 2x10 MHz channel. Comparing Loon to an LTE-Advanced network with 5-carrier carrier aggregation and 80 MHz of FDD spectrum isn’t meaningful since networks with these advanced capabilities do not exist in the regions that Loon serves. Clearly, downloading a Gigabyte  le over an LTE-Advanced network would take far less time than over Loon, but this isn’t a fair comparison, nor does it represent a likely usage scenario for a mobile subscriber living in an area served by Loon.

The latency with Loon Figure 37 shows the round-trip transfer (RTT) delay time and jitter, based on pinging a local server was 13% higher than the (Google) for 60 seconds. We did the Wi-Fi and terrestrial testing at our hotel in Tarapoto. ‚ e Loon terrestrial LTE network. testing occurred well outside of Tarapoto where terrestrial coverage did not exist. ‚ e latency for all three scenarios was higher than we are accustomed to seeing in the US, Western Europe, and devel- oped Asia, however, on a relative basis Loon’s performance was only modestly worse than the terres- trial network. Speci cally, the latency with Loon was 13% higher than the terrestrial LTE network.

Figure 37. Latency and Jitter

127

112.5

89.5

15.5 8.2 10

Median RTT (ms) Median Jitter (ms) Median RTT (ms) Median Jitter (ms) Median RTT (ms) Median Jitter (ms) Note 9 (Wi-Fi) Note 9 (Terrestrial) Note 9 (Loon)

Source: Signals Research Group

February 2020 Page 47 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Applications, such as web browsing, do not require high data speeds to provide a good user experience but they do benet from low latency due to the back-and-forth transfers of data packets and TCP acknowledgement (ACK) messages. We performed web browsing tests with a Galaxy Note 9 and a Samsung A10 smartphone. ‚e Loon testing occurred outside of Tarapoto in an area where terrestrial coverage did not exist. ‚e Wi-Fi and terrestrial network tests occurred at our hotel in Tarapoto. We point out the Note 9 used Band 4 (2x20 MHz) for these tests. ‚e Galaxy A10 used Band 28 for the terrestrial web browsing tests, although we note the channel bandwidth in the terrestrial Band 28 LTE network was 2x15 MHz, compared with 2x10 MHz in the Loon network. Figure 38 on the following page provides the results from these sets of tests.

We selected seven mobile websites that were popular in Peru. ‚e test script, which we ran through the XCAL-Solo platform, loaded each website sequentially while capturing pertinent time stamps to determine how long it took to load each web page. We repeated each test 10 times, meaning there were 70 web pages loaded for each test scenario. Excluding the A10 results with www.elcomercio.pe, a local news media portal, the di‰erences in webpage load times were inconsequential. In fact, in some cases, the results with Loon were slightly better than the terrestrial and/or Wi-Fi results. We have no reason to believe the A10 load time with this website is incorrect, but the result is an outlier. We also point out that during this test, the web page loaded in just a few seconds for the rst few times (comparable to the other results), but for the remaining tests the load times were substantially longer. ‚e A10 results with the other web pages during this test remained comparable so it is quite possible the long load times had less to do with Loon and more to do with the website. For completeness and full transparency, we are including the results in this paper.

February 2020 Page 48 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 38. Web Browsing

1.9 2.9 2.3 Google.com 2.5 2.6 2.4

2.9 3.8 4.0 Facebook.com 4.2 3.3 2.7

1.9 2.5 2.7 Google.pe 2.4 1.3 1.9

10.7 4.6 4.4 Elcomercio.pe 38.4 1.3 7.5

4.2 4.3 4.6 Movistar.com.pe 6.8 3.8 4.4

1.2 2.0 2.1 Mercadolibre.com 1.6 2.0 1.2

2.8 4.4 4.0 Sunot.gob.pe 4.0 1.3 2.6

0 5 10 15 20 25 30 35 40 Time (sec)

Note 9 (Wi-Fi) Note 9 (Terrestrial) Note 9 (Loon)

Samsung A10 (Loon) Samsung A10 (Terrestrial) Samsung A10 (Wi-Fi) Source: Signals Research Group

February 2020 Page 49 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 39 and Figure 40 show results from testing the user experience with YouTube. For this study, we used the same video (a 2:51 video entitled “Ben Fogle and Hugh Dennis – Peruvian Andes – Worlds Most Dangerous Roads – BBC”), although we did try both 360p and 720p resolutions. Figure 39 shows the timeline of events for the entire video playback and Figure 40 isolates the timeline to focus on the period prior to the video starting to play on the phone. Looking at the rst gure, it is evident the phones had downloaded the video in its entirety long before the video nished playing on the phone. ‚e 720p video took longer to download due to the le size. Additionally, YouTube uses bu‰er management to control how much video is downloaded to the phone’s bu‰er during the playback. ‚is mechanism means that the longer download time was due to the YouTube application and not to limitations with the network.

Figure 39. YouTube

99.3 71.4 Samsung 480p (Loon) 1.6 4.2 2.5 93.3 77.6 1.0 Samsung (Wi-Fi) 1.6 1.6 78.2 92.7 Samsung 720p (Loon) 3.9 2.8 6.3

99.6 71.2 Note 9 (Wi-Fi) 0.7 3.8 1.7 100.0 71.8 Note 9 (Terrestrial - Band 4) 0.7 5.1 2.2 99.0 71.7 Note 9 (Loon) 1.3 7.5 6.1

0 50 100 150 200 Time (sec)

Get URL Service Access Time Media Play Download Complete Media Play Complete

Source: Signals Research Group

1.6 Samsung 480p (Loon) 4.2 2.5

1.0 Samsung (Wi-Fi) 1.6 1.6

3.9 Samsung 720p (Loon) 2.8

February 2020 6.3 Page 50

0.7 Note 9 (Wi-Fi) 3.8 1.7

0.7 Note 9 (Terrestrial - Band 4) 5.1 2.2

1.3 Note 9 (Loon) 7.5 6.1

0 2 4 6 8 10 12 14 16 Time (sec)

Get URL Service Access Time Media Play 99.3 71.4 Samsung 480p (Loon) 1.6 4.2 2.5 93.3 77.6 1.0 Samsung (Wi-Fi) 1.6 1.6 78.2 92.7 Samsung 720p (Loon) 3.9 2.8 6.3

99.6 71.2 Note 9 (Wi-Fi) 0.7 3.8 1.7 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and100.0 the Loon user experience 71.8 Note 9 (Terrestrial - Band 4) 0.7 www.signalsresearch.com 5.1 2.2 99.0 71.7 Note 9 (Loon) 1.3As shown in Figure 40, the video playback starting times ranged from 4.2 seconds (A10 smartphone 7.5 6.1 with Wi-Fi) to 15 seconds (Note 9 smartphone with Loon). Within this range, Wi-Fi faired the best, followed by the terrestrial network and Loon, but the di‰erences between the terrestrial network and 0 Loon weren’t substantial.50 ‚e A10, for example,100 took 8.3 seconds for150 video playback to start with200 Loon, compared with 8 seconds with theTime Note (sec) 9 over the terrestrial network (Band 4).

Get URL Service Access Time Media Play Download Complete Media Play Complete Figure 40. YouTube – enhanced view

1.6 Samsung 480p (Loon) 4.2 2.5

1.0 Samsung (Wi-Fi) 1.6 1.6

3.9 Samsung 720p (Loon) 2.8 6.3

0.7 Note 9 (Wi-Fi) 3.8 1.7

0.7 Note 9 (Terrestrial - Band 4) 5.1 2.2

1.3 Note 9 (Loon) 7.5 6.1

0 2 4 6 8 10 12 14 16 Time (sec) Source: Signals Research Group Get URL Service Access Time Media Play

February 2020 Page 51 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Once the videos started to play, we generally didn’t experience any problems with video bu‰ering. ‚is statement is supported by the results in Figure 41. ‚e gure shows three sets of results involving the Note 9 playing the video over Loon, the terrestrial LTE network, and Wi-Fi. ‚e gure shows the cumulative number of downloaded bytes during the video playback as well as the amount of data in the bu‰er. ‚e gradual ramp of the downloaded bytes for all three networks illustrates the bu‰er management technique used by YouTube. If the bu‰ered bytes remain positive the video will continue to play.

Figure 41. YouTube Bušer Management

Bytes 16,000 14,000 Loon Downloaded Bytes 12,000 10,000 8,000 6,000 4,000 Loon Bu ered Bytes 2,000 0 0:00:00 0:00:31 0:01:00 0:01:32 0:02:12 0:02:53 Time Bytes 16,000 14,000 Terrestrial Downloaded Bytes 12,000 10,000 8,000 Terrestrial Bu ered Bytes 6,000 4,000 2,000 0 0:00:00 0:00:31 0:00:59 0:01:33 0:02:13 0:02:53 Time Bytes 16,000 14,000 Wi-Fi Downloaded Bytes 12,000 10,000 Wi-Fi Bu ered Bytes 8,000 6,000 4,000 2,000 0 0:00:00 0:00:30 0:00:59 0:01:32 0:02:13 0:02:53 Time

Source: Signals Research Group

February 2020 Page 52 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

We also took the opportunity to do a video chat (Google Duo) back to the United States while testing well outside of Tarapoto in an area only served by Loon. ‚e video quality wasn’t as good as it would be in a high bandwidth LTE network or over W-Fi, but it was more than acceptable. ‚e video was a bit fuzzy, suggesting a low resolution, but there wasn’t any freezing on either side and the audio quality was ne.

Downloads from Google Play were ‚e last set of results pertain to downloading an application from Google Play. Figure 42 shows the modestly slower with Loon than physical layer throughput. We don’t have Wi-Fi results because it isn’t possible to capture physical Wi-Fi and the terrestrial network, layer throughput with the drive test tool. ‚e gure plots each download sequentially – each spike but dierences in channel represents a separate download of the ~5 MB application. ‚e implied download times with the bandwidth were also a factor. Note 9 smartphone using the terrestrial LTE network were the fastest, but it is important to note the phone was using Band 4 with 2x20 MHz of spectrum. Likewise, the Samsung A10 results over the terrestrial LTE network used a 2x15 MHz channel, compared with the Loon results, which stem from using a 2x10 MHz channel. ‚e conclusion is that while the download times with Loon were modestly slower than the other networks, the di‰erences were inconsequential and largely due to the narrower channel bandwidth used by Loon.

Figure 42. Physical Layer Throughput While Downloading an Application from Google Play

Mbps 30

25

Note 9 (Terrestrial) 20 Note 9 (Terrestrial) Samsung (Terrestrial - 2x15 MHz) 15 Note 9 (Loon)

10

5

0

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400

Time (sec) Source: Signals Research Group

February 2020 Page 53 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

We also looked at mobile device transmit power during some of these tests to determine if there were di‰ erences between the mobile device using Loon and the terrestrial network. As shown in Figure 43, the mobile device transmit power when attached to Loon was frequently 22 dBm. ‚ e median values for each scenario only include data points when the mobile device was transmitting. For example, the mobile device only transmits when it is downloading the YouTube video and not when the video is playing from the phone’s bu‰ er. When connected to the terrestrial LTE network the transmit power levels were much lower. ‚ e  rst three scenarios with the terrestrial network occurred in Tarapoto on Band 4. ‚ e last scenario (Test 81, which we discussed previously in the last chapter) is a very direct comparison since the Loon and terrestrial network transmit power levels occurred at the same location. Although we didn’t quantify the impact on the user experience, we know a higher transmit power can have a negative impact on battery life. However, we know from other studies that we have done that display brightness combined with non-communications activities which trigger the display turning on, have a very meaningful impact on battery life, thereby minimizing the impact of the higher transmit power.

Figure 43. PUSCH Transmit Power

25 22.9 22.1 22.1 22

20 18

15 13.3 13

9.7 10

5

0 Terrestrial LTE Loon Terrestrial LTE Loon Terrestrial LTE Loon Terrestrial LTE Loon Web Browsing FTP Data Transfer YouTube (360p) Test 81

Source: Signals Research Group

February 2020 Page 54 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

5.0 Test Methodology SRG conducted the Loon benchmark study during the week of September 23, 2019. ‚e testing occurred in a region south of Tarapoto, Peru in the San Martin region in northern Peru. All testing occurred during daylight hours, starting around 9 AM and nishing around 5:30 PM to ensure we made it back to Tarapoto before it got dark. Given the travel time to the area where Loon was deployed to provide coverage, we couldn’t extend deep into the Loon coverage area. However, we trav- eled far enough into the Loon coverage area to collect suœcient network performance data. Further, one key focus of this study was to evaluate Loon’s impact on the terrestrial network and for this objec- tive we needed to test at the boundary between Loon and the terrestrial LTE network. If anything, we are not showing the breadth of Loon coverage throughout Peru.

Loon engineers provided critical technical support, including guiding our drive test vehicle to loca- tions where Loon coverage existed. Additionally, Loon engineers were able to turn on/o‰ the Loon cells and identify the PCI values associated with their network. SRG collected all the performance data provided in this report and we take full responsibility for the analysis of the data.

We used the TSMA scanner from Rohde & Schwarz to log network parameters in the Band 28 LTE network. ‚e scanner was in our test van with the antennas magnetically attached to the roof of the van. In addition to the scanner, we used a combination of XCAL-M and XCAL-Solo from Accuver Americas to log chipset diagnostic messages from the LTE modems in the smartphones that we used in the study. We used the Pixel 3 (Qualcomm chipset), Samsung Galaxy Note 9 (Qualcomm chipset) and a Samsung A10 (Samsung chipset) smartphones. Depending on the test, the smartphone(s) were placed inside the vehicle, mounted to the roof/side of the van, or we were holding the phone outside of the vehicle. Finally, we leveraged the Umetrix data platform from Spirent Communications to generate high bandwidth data transfers. Although the server that we used was located in Virginia, we were still able to generate very high data speeds to the mobile devices attached to Loon, suggesting the remote location of the server didn’t have a big impact on performance. We work with all three companies in our benchmark studies of LTE and 5G networks.

Since XCAL-M interfaces with the R&S scanner we were able to analyze the scanner and mobile device results with the Accuver Americas XCAP post-processing software. ‚e results presented in this paper are based on geo binning the data in three-meter quadrants. For tests involving time sensitive information or tests where geo binning doesn’t make sense (e.g., user experience tests and stationary tests), we binned the data in one-second time increments. RRC signaling messages are not time binned so we were able to extract precise time stamps for pertinent events, including web page load times and cell attach/detach times.

February 2020 Page 55 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

We are including a few pictures in this chapter to highlight the areas where we tested. Additionally, one evening we were able to view Loon balloons overhead. From the same location alongside a road we spotted three Loon balloons at di‰erent points in the sky.

Figure 44. Scenes from the Loon Coverage Area

Source: Signals Research Group

Figure 45. A Loon Balloon Overhead

Source: Signals Research Group

February 2020 Page 56 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com 6.0 Appendix We include some additional test results in the appendix. Since we explained the analysis behind each  gure in the previous chapter, we are not providing any additional commentary for these results. We included these results in the two summary  gures in Chapter 1. However, we felt other test results provided better insight into Loon’s performance and/or its impact on the terrestrial network, so we moved these results to the appendix. In these tests, Loon was barely present in the results, making them less interesting, or the drive route largely overlapped with another test shown in a previous chapter.

Figure 46. Test 25, 26 and 30 Key Metrics – geo plot

TarapotoOverview

Overview

Overview

Top PCIs Terrestrial RSRP Loon RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

February 2020 Page 57 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 47. Cumulative Distribution of the Diš erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell – Test 25, 26 and 30

Cumulative Probability Distribution (%) 100%

Median RSRP Delta (dB)

80% Terrestrial Terrestrial to Terrestrial to to Loon Terrestrial Terrestrial RSRP RSRP Delta RSRP Delta Delta (RSRP < -95 dBm) Terrestrial to Terrestrial RSRP Delta (RSRP < -95 dBm) Terrestrial to Terrestrial RSRP Delta 60%

-4.5 -5 40% -9

20%

Terrestrial to Loon RSRP Delta 0% -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 RSRP Delta between Top Cell and Second Cell (dB) Source: Signals Research Group

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Figure 48. Test 34-35 Key Metrics - geo plot

Tarapoto

Overview

Top PCIs Terrestrial RSRP Loon RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

February 2020 Page 59 Loon and a Terrestrial LTE Network How Loon coverage impacts an existing terrestrial LTE network, the interactions between the two networks, and the Loon user experience www.signalsresearch.com

Figure 49. Cumulative Distribution of Loon Signal Strength – Test 34 and 35

Cumulative Probability Distribution (%) 100%

80% Median RSRP (dBm)

60%

40% -114.8

20%

0% -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 -130 -135 -140 RSRP (dBm) Source: Signals Research Group

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Figure 50. Test 52 Key Metrics – geo plot

Tarapoto

Overview

Top PCIs Terrestrial RSRP Loon RSRP RSRP Delta

Top PCI RSRP (dBm) RSRP Delta (dB) Loon Dominant Cell X > -90 -110 <= X < -105 0 <= X < 1 4 <= X < 5 Terrestial Dominant Cell -95 <= X < -90 -115 <= X < -110 1 <= X < 2 5 < X -100 <= X < -95 -120 <= X < -115 2 <= X < 3 -105 <= X < -100 X <= -120 3 <= X < 4

Source: Signals Research Group

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Figure 51. Cumulative Distribution of Loon Signal Strength – Test 52

Cumulative Probability Distribution (%) 100%

Median RSRP (dBm) 80%

60%

-114.4

40%

20%

0% -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 -130 -135 -140 RSRP (dBm) Source: Signals Research Group

Figure 52. Cumulative Distribution of the Diš erences in Signal Strength between the Top Terrestrial Cell and the Strongest Interfering Cell – Test 52

Cumulative Probability Distribution (%) 100% Median RSRP Delta (dB) Terrestrial Terrestrial to Terrestrial to to Loon Terrestrial 80% Terrestrial RSRP RSRP Delta RSRP Delta Delta (RSRP < -95 dBm) Terrestrial to Loon RSRP Delta

60% -4.4 -4.4 Terrestrial to Terrestrial RSRP Delta (RSRP < -95 dBm)

40% -8.3

20%

Terrestrial to Terrestrial RSRP Delta 0% -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 RSRP Delta between Top Cell and Second Cell (dB) Source: Signals Research Group

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