LTE and Drones - Global Semiconductor Alliance...networks. We explored interference mitigation...

LTE and Drones

LTE and Drones sequans.com

2© 2018 Sequans Communications | sequans.com

Contents1. Introduction .................................................................................................................................................................................... 3

2. LTE Network Design ................................................................................................................................................................ 3

3. Exploring Interference Mitigation Improvements ......................................................................................... 8

4. Use Cases ....................................................................................................................................................................................... 12

4.1 Drone Delivery Service ............................................................................................................................................ 12

4.2 Building and Infrastructure Inspection ........................................................................................................ 12

4.3 Agricultural Inspection ............................................................................................................................................. 13

4.4 Public Safety ................................................................................................................................................................... 13

5. Conclusion ..................................................................................................................................................................................... 13

6. Footnotes ....................................................................................................................................................................................... 13



1. IntroductionAlthough drones have been in use for many years for military and intelligence gathering applications, over the last year commercial use of them has skyrocketed to the point where the Federal Aviation Administration has mandated their registration. It is estimated that seven million drones will be shipped by the end of the year 2020, and that the projected value of the drone industry will approach $90 billion by 2025. Even though there are concerns among consumers related to theft and privacy, a high number, 47 percent, are interested in drone deliveries, to highlight one key application. Beyond deliveries, drones are being used for photography, surveying, real estate and infrastructure surveillance and inspection, security, and agriculture monitoring.

Wireless communication is used in drones for two main purposes: 1) to remotely control the drone flight and convey flight control commands from the user to the drone and 2) to convey information from the drone to the user---information such as first person view (FPV) video or flight information: altitude, speed, location, and battery life. Depending on the amount and type of data to be transmitted, low latency and a high-speed connection can be required.

Typically, drone connectivity is provided by proprietary wireless technologies or, in some cases, public Wi-Fi operating in unlicensed spectrum. However for some of the more sophisticated applications being developed now that have high data usage and long-range flight requirements, or where the user and drone are not within line-of-sight of each other, the range and capability of typical wireless connectivity technologies is not sufficient. Licensed LTE cellular networks, which provide almost global coverage and a uniform quality of service, are needed.

Connecting flying objects has been discussed in documents describing the uses and evolution of LTE networks, both in 4G and in the future 5G. Moreover, a dedicated report entitled: Study On Enhanced Support for Aerial Vehicles, was approved by the 3GPP1 in March of 2017 within the context of 3GPP LTE Release 15 to identify possible issues and improvements needed in LTE to support drones and other flying devices.

Sequans, as an expert in LTE technology and a provider of optimized LTE connectivity solutions for many types of devices, including inflight devices, has devoted time and resources to investigating the use of LTE for drones to get a better understanding of the performance of drones in terrestrial networks, and the impact of drones on network performance. This white paper summarizes the key findings.

2. LTE Network DesignIn an LTE cellular network an LTE base station (eNodeB) traditionally uses three sectors and three antennas. This antenna sectorization technique ensures that sectors of the same eNodeB do not interfere with each other. The network can re-use the same frequency band in each cell (frequency re-use factor of 1) and each sector has the following general characteristics:

An azimuth plane coverage angle of 120 degrees provides sector coverage in the azimuth plane using the main antenna lobe.

An elevation plane coverage angle provides coverage in the elevation plane. The z-axis side lobes are also used for this purpose.

A mechanical tilt is used to point antennas downwards to provide better coverage in terrestrial environments.

Figure 1: Antenna TiltOnly the main antenna lobe is depicted in this figure.



In addition to antenna sectorization, LTE supports beamforming, a technique whereby the antenna beam is concentrated in a specific direction to improve the link budget and thus the connection to a given terminal (or to multiple terminals simultaneously) using space separation. It should be noted that beamforming works in both the transmit or receive paths.

Figure 2: Antenna Sectorization

Figure 3: Beamforming IllustratedBeamforming can be used to focus the antenna in the direction of interest and create a null in the direction of an interferer.

Beamforming can be used to focus the antenna pattern in a given direction and thus increase the reach by separating users in space.

Horizontal radiation pattern for 3-sector antenna.



Because of this differing geometry, we can anticipate that drones will suffer from increased interference from neighboring cells in the downlink direction, and even more interference in the uplink direction, impacting terrestrial user equipment. In order to assess the impact of drones in an LTE network, we have conducted system simulations. The key findings are highlighted in the following figures:

Figure 4: Illustration of the Cell Coverage Experienced by Aerial Vehicles

More recently, full dimension MIMO, introduced in 3GPP LTE Release 13 and improved in Release 142 3, allows generalized beamforming in the vertical axis. However, the main direction of the eNodeB antenna beam is towards the ground since LTE was originally designed to serve ground-based terminals.

The introduction of drones and other aerial devices impacts LTE network design in several ways. Drones generally fly above the base station antenna height---something that was not anticipated at first in network planning--creating unexpected coverage conditions. On the negative side, drones are covered by only the side lobes of the elevation plane and thus suffer from lower antenna gain; but on the positive side, the line of sight probability is significantly increased since direct obstacles and shadowing occur less frequently. Aerial devices are therefore visible from more cells than terrestrial devices, and when the aerial device is at the exact zenith of a base station, it may even be possible that, because of the antenna patterns, the signal from neighboring cells is stronger than the signal from the cell just below the device. First observations show that coverage geometry for objects above average antenna height is significantly different than the coverage experienced by terrestrial devices.

Figure 5: Snapshot of the System Level Simulation to Investigate Impact of Drones in LTE Network



Figures 6 and 7 show the Cumulated Density Function (CDF) of the signal to interference and noise ratio (SINR) for aerial and terrestrial devices for various penetration rates of aerial devices.

In the downlink, drones are more easily reachable from inter-cell signals and this has an average impact of -9dB on the downlink SINR compared to the downlink SINR of the terrestrial UEs with no drone presence. The downlink SINR of the terrestrial devices is not affected by the presence of drones. However, because of the degraded performance of drone UEs, the network will suffer from an overall degradation of capacity, since more resources must be allocated to drones to compensate for their lower SINR. As a result, the downlink performance of terrestrial UEs is also affected by the presence of aerials.

Figure 6: DL SINR CDF performance of terrestrial and aerial UEsShown without (solid line) and with (dashed lines) the presence of drones.

In the downlink, drone UEs suffer from a degradation of SINR compared to terrestrial UEs; signal quality of the terrestrial UE is not affected but the overall network capacity can be degraded because of the drone’s low SINR.



Figure 7: UL SINR CDF performance of terrestrial and drone UEsShown without (solid line) and with (dashed lines) the presence of aerials.

In the uplink, drones have a more dominant inter-user presence than terrestrial UEs and this has an average impact of -16dB on uplink SINR degradation for terrestrial UEs, compared to the uplink SINR performance of terrestrial UEs when aerials are not present. The uplink average SINR degradation of aerials compared to terrestrial UEs without aerial presence is not as significant. It should be noted that these results were obtained without power control.

These simulation results show that the presence of drones inside an LTE network not only results in degraded downlink connectivity for aerial devices, but also has a significant negative impact on the uplink connection of terrestrial devices.

Aerial UEs generate significant uplink interference that impacts terrestrial UE performance. Uplink performance of drone UEs are however similar to regular UE performance (without presence of drones.)



To mitigate the downlink interference, we proposed a simple adaptation of the interference mechanisms already defined in the LTE standard. These include: 1) joint transmission coordinated multipoint (JT-COMP), a technique that combines the transmissions from two or more cells (see Figure 8(a), green arrows) so that they no longer act as interfering cells but rather improve the quality of the received signal; and 2) almost blank subframe (ABS), a coordination scheme between neighboring base stations whereby certain signals are muted (see Figure 8(b), white arrows representing blanked signals).

3. Exploring Interference Mitigation Improvements

In investigating how these negative effects can be mitigated, we asked: how can we ensure that connected devices flying over an LTE network do not degrade the connectivity of the terrestrial devices? How can we ensure a consistent quality of service level for both drones and terrestrial devices?

Our study centered on investigating interference mitigation approaches both in the uplink and downlink, some that would require evolution of the LTE standard, and some that can be implemented now in a transparent manner in existing networks. We explored interference mitigation techniques for both the downlink (to protect aerial devices) and the uplink (to protect terrestrial devices).

Figure 8: Drone downlink interference mitigation using (a) JT CoMP, and (b) ABS eICICFigure (a) on the left, and figure (b) on the right.



Both approaches rely on coordination between neighboring cells, which may not be trivial and will increase the traffic on the interface between the base stations (also known as the X2 interface). Furthermore, such solutions will not necessarily improve the uplink interference issue.

Another approach relies on using sectorized antennas, or beamforming antennas on the aerial device.

For aerial UEs, the signal from the serving cell and inter-cells is very likely to arrive from line-of-site (LOS) cells. The use of omni-directional antennas allows interfering cells to pollute the serving cell’s downlink signal to the aerial, and the aerial

to pollute the uplink signal to other (terrestrial and aerial) UEs of the network, as depicted in Figure 9 (a). Thus, the use of directional antennas can be extremely useful in suppressing the interference from a large number of inter-cells. The interference suppression is dependent on the used beam width and the direction of the broadside.

The ideal solution is to be able to track the serving cell dynamically with a steerable beam (either mechanically, or electronically) to ensure maximum gain for the desired signal and maximum nulling of interfering signals. This approach works equally well for uplink and downlink.

Figure 9: Drones with and without a steerable antennaFigure (a) on the left without steerable antenna, and figure (b) on the right with steerable antenna.



Figure 10: Downlink SINR CDF performance of aerials using beamforming and beam trackingShown with various beam-widths (dashed lines) compared to the downlink of terrestrial UEs (solid line).

Figure 10 illustrates the gains possible with the use of antenna patterns of various beam widths. The narrower the beam, the better the performance. Beam width is usually defined by the angle for which the power is 3dB lower than the maximum power in the broadside of the antenna pattern.

Using a 15-degree beam width, almost all degradation seen by the aerials with omnidirectional antennas is recovered.

Similarly, Figure 11 shows the improvement seen by the terrestrial UE on the uplink when the aerials use various antenna patterns. With a 15-degree beam, the uplink performance of the terrestrial UEs is no longer degraded by the presence of aerials.

In practice, it may be difficult (and costly) to create an ideal narrow beam and maintain it in a given direction but simple approaches may be imagined and deployed on the aerial UE side. For instance, one can imagine a quadcopter drone with 4 90-degree beam width antennas, with one antenna per drone leg, and replacing the ideal beam tracking with a simple antenna switch. Overlapping antenna patterns could conceivably ease handover and avoid a possible ping-pong effect within the antenna switches. Such solutions are easily implementable on the device and would require simple customization of the UE’s modem firmware. The current discussion in the 3GPP may also extend to include aerials in the existing LTE feature that allows the network to control antenna switches on the UE.



Figure 11: UL SINR CDF performance of terrestrial UEs in the presence of aerials using omni-directional antenna or beamforming (LOS tracking) Shown with various beam widths (solid lines) compared to the uplink of terrestrial UEs without the presence of aerials (dashed line).

Several methods can be put in place that would mitigate the interference generated by the aerials in the uplink and would provide better downlink SINR to the aerials. Some approaches rely on the network but could be complex to deploy in practice. Other approaches rely on simple adaptation of the aerial device.

The 3GPP community is addressing the point and will provide technical recommendation within the Release 15 framework, by June 2018.



In the end, it may be required to adapt the standard so the network can distinguish between aerial devices and terrestrial devices. The interference mitigation schemes briefly described above would then have to be put in place only when required, e.g., when the device is flying above the usual height. In addition, mechanisms such as location, speed and angle of arrival estimations may have to be updated to include the possibility of drones. All these topics were addressed in the early discussion in 3GPP and summarized in the technical report TR 36.7771. The actual standardization process began in December 2017 and is expected to be completed in June 2018.4

4. Use Cases

4.1 Drone Delivery Service

One of the most popular applications for LTE connected drones is in retail goods delivery, which has been made public by Amazon in a big way. The service Amazon is planning to introduce, called PrimeAir is still in the planning stages, but those in the know say it is just a matter of time until Amazon delivery drones take flight for real, despite FAA regulatory hurdles. Drone flights will be automated whereby the trajectory would be pre-programmed and it is most likely that LTE will be used to connect the drone to the wide area network and to the retailer’s operations center for close monitoring of the drone’s path to ensure safe and secure delivery of goods.

Sequans’ Monarch LTE platform is an ideal solution to connect drones to the wide area network. It provides low cost, secure, and energy-efficient LTE Cat-M connectivity, as necessary to monitor and report drone flight parameters, activity and position, as well as to send commands as needed for possible emergency landings or return to home. Monarch is optimized for power and size and would not significantly increase the weight of the drone platform nor decrease the overall flight duration.

4.2 Building and Infrastructure Inspection

The inspection of buildings, such as bridges, dams, industrial towers, or public arenas, can be greatly simplified using LTE connected drones. As traditionally done, inspection of buildings and infrastructure is difficult and very costly, involving the construction of inspection towers with scaffolding and camera mounts, and the hiring of attendants. With drones performing aerial inspection and transmitting video and data to a central operations center, inspection is greatly simplified, less costly, and much easier to manage from one central location. Drones can be controlled with precision to approach the buildings or other public areas needing surveillance, and then take photos or real time video, allowing the attendant to instantly detect defects, illegal activity, or any one of a number of other things related to security or safety. Drones used for aerial inspection of buildings could also be programmed with sensors to detect motion, heat or moisture, or open/close status of doors or windows.

An LTE-connected drone has several advantages over drones connected via short-range technology such as Wi-Fi. In the case of tall industrial buildings or large monuments, the topology may be such that a drone could not be in line of sight with the operator, which would severely limit its range and utility. LTE, as a wide-area network technology, has no such limitation. Moreover, LTE can support high definition video streaming, enabling real time video monitoring of the building or monument. Sequans’ Cassiopeia LTE Cat 6 platform, with high throughput, optimized size, cost, and power consumption is ideal for this use case.

© 2018 Sequans Communications | sequans.com

Sequans, Monarch and Single SKU are trademarks or registered trademarks of Sequans Communications. All rights reserved.


4.3 Agricultural Inspection

The use of drones to aerially inspect farms and crops can be simplified with LTE-connected drones. Short range technologies are ineffective for the vast size of some farms and crop fields, and this application requires the low power, wide area capabilities of LTE. LTE-connected drones can not only monitor crop growth or areas of variability via still image or video surveillance, but they can be programmed to collect and transmit data from sensors to detect humidity, temperature, the presence of pests, or other conditions. If the type of data to be transmitted is simple, such as low resolution images to detect crop variability, narrowband LTE technology can be used, such as Sequans Monarch LTE-M technology, but if high resolution video is needed, perhaps to detect the emergence of young plants, Sequans Cassiopeia LTE Cat 6 technology can be used.

4.4 Public Safety

The use of drones for public safety is an area of key interest. Drones can be programmed to deploy quickly when an emergency, such as a traffic accident, fire, or natural disaster occurs, to fly quickly to the location, and then transmit condition reports back to the operations center. This will help first responders understand the type and amount of response needed and will be an effective aid in limiting damage. No other connectivity technology has the security, and reliability and range of LTE. Sequans’ LTE Cat 6 technology, Cassiopeia, with the high throughput needed for real-time video surveillance, secure and reliable connections, is ideal for public safety applications.

5. Conclusion

Using the LTE network to connect aerial devices will become reality in the not too distant future, and with appropriate mitigation schemes, LTE can be used to great advantage over other connectivity technologies. Without mitigation schemes, aerial UEs will suffer from higher interference than terrestrial UEs on the downlink and will degrade uplink performance of legacy UEs. However, techniques to mitigate interference are being refined and adapted to drone use; these include simple techniques such as the use of directional antennas on the aerial device, or more complex techniques, involving network adaptation and evolution of the standard.

Sequans contributed to the 3GPP Study on Enhanced Support for Aerial Vehicles1 and is monitoring the follow up work item4 to enable safe and easy communication with aerials based on LTE.

6. Footnotes [1] 3GPP TR 36.777, Study on Enhanced LTE Support for

Aerial Vehicles available at http://www.3gpp.org/ftp/Specs/archive/36_series/36.777/

[2] Elevation Beamforming/Full-Dimension (FD) MIMO for LTE, Rel. 13 Work item, see description in RM-151085 available at http://www.3gpp.org/ftp/tsg_ran/TSG_RAN/TSGR_68/Docs/RP-151085.zip

[3] Enhancements on Full-Dimension (FD) MIMO for LTE, Rel. 14 work item, see description in RP-160623 available at http://www.3gpp.org/ftp/tsg_Ran/tsg_Ran/TSGR_71/Docs/RP-160623.zip

[4] Enhanced LTE Support for Aerial Vehicles, Rel. 15 work item, see description in RP-172826, available at http://www.3gpp.org/ftp/TSG_RAN/TSG_RAN/TSGR_78/Docs/RP-172826.zip

LTE and Drones - Global Semiconductor Alliance...networks. We explored interference mitigation...

Documents

Transcript of LTE and Drones - Global Semiconductor Alliance...networks. We explored interference mitigation...