Mobility performance is at the heart of each cellular technology, including omni-present LTE networks. It becomes even more significant when such system is supposed to reliably support state-of-the-art devices, such as Unmanned Aerial Vehicles (UAVs), emerging at rapid pace in our surroundings. Contemporary network deployments, addressing mainly the needs of terrestrial users, were not optimized to serve UAVs moving below and above the typical cellular antenna heights. Thus, it is worth checking how they can handle these novel and distinctive services, also with respect to mobility robustness. This paper elaborates on the challenges ahead which must be tackled to make existing LTE networks sufficiently capable of accommodating Aerial Vehicles. We present simulation results in various environments, obtained for different user equipment's (UE's) heights and velocities. Furthermore, we describe and analyze the identified issues. Finally, we also suggest potential optimizations and future research goals.

This paper focus on the investigation of aerial communications for drones connected to cellular networks in urban areas. Most of the previous measurement based channel models for urban environments do not extend to users located at heights above rooftops. On the other hand, UAVs are expected to fly at the very low level (VLL) airspace, in heights much lower than those covered by previous air-to-ground models. By means of field measurements, this paper presents height-dependent closed form expressions for the urban channel model (path loss slope and shadowing) extending to heights up to 40 m and compares the observed results with 3GPP reference models and previous studies. Measurements were conducted by a radio scanner attached to a construction-lift to measure the radio signal from three different live LTE networks (800, 1800, and 2600 MHz). Results suggest radio path clearance increases with height. As a consequence, it leads to an increase in number of cells in the detectable range and in the set of neighbors within 3 dB of the serving cell in the receiver, indicating neighbor cells are closer to each other in the power domain.

ITU-R has recently published a new Recommendation giving methods for the estimation of clutter loss at frequencies between 30 MHz and 100 GHz. This paper provides an overview of the methods. In particular, the derivation and form of the new clutter model for terrestrial paths is described in detail and remaining work is pointed out.

Widely deployed cellular networks are an attractive solution to provide large scale radio connectivity to unmanned aerial vehicles. One main prerequisite is that co-existence and optimal performance for both aerial and terrestrial users can be provided. Today's cellular networks are, however, not designed for aerial coverage, and deployments are primarily optimized to provide good service for terrestrial users. These considerations, in combination with the strict regulatory requirements, lead to extensive research and standardization efforts to ensure that the current cellular networks can enable reliable operation of aerial vehicles in various deployment scenarios. In this paper, we investigate the performance of aerial radio connectivity in a typical rural area network deployment using extensive channel measurements and system simulations. First, we highlight that downlink and uplink radio interference play a key role, and yield relatively poor performance for the aerial traffic, when load is high in the network. Second, we analyze two potential terminal side interference mitigation solutions: interference cancellation and antenna beam selection. We show that each of these can improve the overall, aerial and terrestrial, system performance to a certain degree, with up to 30% throughput gain, and an increase in the reliability of the aerial radio connectivity to over 99%. Further, we introduce and evaluate a novel downlink inter-cell interference coordination mechanism applied to the aerial command and control traffic. Our proposed coordination mechanism is shown to provide the required aerial downlink performance at the cost of 10% capacity degradation in the serving and interfering cells.

Aerial users, such as unmanned aerial vehicles (UAVs), experience different radio propagation conditions than users on the ground. This is a concern regarding the integration of such users into cellular networks in the near future. This letter investigates the impact of uplink transmissions from an aerial user equipment. Full buffer transmissions were performed by a device at ground level and also flying attached to a UAV at 100 m height. The field measurements show a higher number of cells affected by the aerial transmission, with an increase of up to 7.7 dB in the interference over thermal noise in cells within 15 km of the test location. This letter also assesses two strategies to reduce the uplink interference caused by aerial users: 1) UAV’s cruise height control and 2) directional transmissions. Results show the directional transmission is a more promising technique, and has the advantage of not reducing the uplink received power.

Indoor deployments for providing coverage and capacity inside buildings is an attractive option for cellular network operators as most of the traffic in today's cellular networks is generated indoors. This paper studies the benefit of indoor traffic offloading on the overall network capacity using a new method that allows assessing the network performance gains considering different levels of traffic offloading without the need to decide beforehand which buildings to deploy the indoor solutions in or the exact type of indoor solution used in each building. Using this method, we evaluate the impact of different amounts of indoor traffic offload and the performance of three different indoor deployment strategies on a study case network selected as a typical real world ultra dense urban area. The results show that choosing the most cost-effective buildings (lowest cost per traffic offload) first in the indoor deployment plan leads to highest network capacity gains for the same level of investment.

The main goal of this letter is to obtain models for path loss exponents and shadowing for the radio channel between airborne unmanned aerial vehicles (UAVs) and cellular networks. In this pursuit, field measurements were conducted in live LTE networks at the 800 MHz frequency band, using a commercial UAV. Our results show that path loss exponent decreases as the UAV moves up, approximating freespace propagation for horizontal ranges up to tens of kilometers at UAV heights around 100 m. Our findings support the need of height-dependent parameters for describing the propagation channel for UAVs at different heights.

In this paper we set out to analyze the indoor capacity under a realistic high-rise building scenario. The study takes into consideration the number of indoor cells deployed per floor, different inter-site distances (ISDs), transmit power settings and outdoor macro interference levels. The outcome shows large variation in performance gain just by optimizing indoor cell locations, highlighting the need for thorough indoor radio planning. Investing into more indoor cells helps to increase capacity, and also to cope better with outdoor interference, but the gain tends to be diminishing due to the increase of inter-cell interference (ICI). Increasing transmit power brings largest gain when the density of indoor cell is low, and the noise and/or outdoor interference is the dominant source of performance degradation. When analyzing performance gain of an ideal receiver-side Interference Cancellation (IC) algorithm, the study also shows that, if the Dominant Interferer Removal (DIR) rate is below 50%, doubling the number of indoor cells would bring better capacity gain than investing into such an IC receiver.

This paper presents enhancements for lowering the handover interruption time in future wireless networks. We propose a selective data forwarding for the handover preparation phase, and the integration of the make-before-break procedure with the synchronous random access-less handover. To evaluate our proposals, we analyze the handover timing for typical and variable values of the user equipment and e-NodeB processing times, and X2 interface latencies. Our results show that the processing delays, reconfiguration times, and the X2 latency should be simultaneously reduced to minimize the data interruption time. Selective data forwarding during the handover preparation reduces the data interruption time by 18 % compared to the basic random access less handover with typical network delays. Make-before-break is the most suitable handover type for future low-latency applications, as it achieves zero data interruption independent of the latency of handover steps.

In this paper we investigate the ability of Long- Term Evolution (LTE) network to provide coverage for Unmanned Aerial Vehicles (UAVs) in a rural area, in particular for the Command and Control (C2) downlink. The study takes into consideration the dependency of the large-scale path loss on the height of the UAV, which is derived from actual measurements, and a real-world cellular network layout and configuration. The results indicate that interference is the dominant factor limiting the cellular coverage for UAVs in the downlink: outage level increases from 4.2% at 1.5m height to 51.7% at 120m under full load condition. Lower network loads or larger inter-site distances reduces the interference and thus improves the coverage significantly: outage at 120m is reduced to only 1.9% under network load of 25% for example. Similar effects are expected to be achievable by static or dynamic interference coordination schemes. In addition, ideal Interference Cancellation (IC) scheme with ability to remove completely the dominant interferer shows less effective for UAVs than for users on the ground. On the other hand, macro network diversity has very good potential for drones, as not only it improves the coverage, but also the reliability of the C2 link.

Unmanned Aerial Vehicles (UAVs) are expected to be connected through cellular networks. As the radio characteristics are different for airborne UEs compared to terrestrial UEs, it is beneficial to identify whether a UE is airborne (on a UAV) or on the ground, such that interference and mobility management can be optimized for UAVs separately from terrestrial UEs. In this paper, we present a classification algorithm using existing LTE UE radio measurements to identify whether a UE is airborne or terrestrial. The method is verified with LTE measurements made in a rural area at different heights, including terrestrial measurements and it is shown that the method in 3 out of the 4 different measurement cases can detect a UE to be airborne with 99% likelihood, while the fourth case still can classify a UE correctly in 95% of the cases. The right classification can further be improved by taking multiple consecutive samples into account before making a classification decision.

In this simulation work the coverage of GPRS, Narrowband-IoT, LoRa, and SigFox is compared in a realistic scenario, covering 7800 km2 and using Telenor's commercial 2G, 3G, and 4G deployment. The target is to evaluate which of the four technologies provides the best coverage for Internet of Things devices, which may be located deep indoor. The results show that Narrowband-IoT, having the best Maximum Coupling Loss performance of 164 dB, also provides the best coverage. This is despite the fact that LoRa and SigFox deployments with omnidirectional antennas are found to provide 3 dB lower link loss on average. In the deployment 11 % of the geographical area contains devices, located both in rural and urban areas. The NB-IoT has an outage below 1 % for locations experiencing 20 dB indoor penetration loss in addition to the outdoor path loss. SigFox performs similarly, while LoRa cannot provide coverage for 2 % of those locations. For the challenging deep indoor case, where 30 dB additional penetration loss is expected, NB-IoT has 8 % outage while SigFox and LoRa is unable to cover 13 % and 20 % of the locations. The four technologies may not be deployed at all existing site locations and therefore the work also includes a study of the coverage as a function of the minimum Inter-Site Distance, where sites closer than 2, 4, and 6 km are filtered out. The results show that SigFox and NB-IoT have outage probabilities below 5 % even though sites closer than 4 km are removed from the simulations.

In this paper the coverage and capacity of SigFox, LoRa, GPRS, and NB-IoT is compared using a real site deployment covering 8000 km2 in Northern Denmark. Using the existing Telenor cellular site grid it is shown that the four technologies have more than 99 % outdoor coverage, while GPRS is challenged for indoor coverage. Furthermore, the study analyzes the capacity of the four technologies assuming a traffic growth from 1 to 10 IoT device per user. The conclusion is that the 95 %-tile uplink failure rate for outdoor users is below 5 % for all technologies. For indoor users only NB-IoT provides uplink and downlink connectivity with less than 5 % failure rate, while SigFox is able to provide an unacknowledged uplink data service with about 12 % failure rate. Both GPRS and LoRa struggle to provide sufficient indoor coverage and capacity.

The use of Unmanned Aerial Vehicles (UAV) for civilian and commercial services has experienced a significant increase in the past couple of years. Emerging UAV enabled services, however, require extended beyond-visual-line-of-sight geographical range. One key regulatory requirement for these services is that the radio communication link must reliably cover a wide(er) area, when compared to the visual-line-of-sight range radio links currently used. Standardized cellular systems such as Long Term Evolution UMTS (LTE), are an obvious candidate to provide the radio communication link to UAVs. In this paper, we use empirical measurements in live rural LTE networks to assess the impact of uplink and downlink radio interference on the UAV radio connectivity performance. Further, we provide a baseline analysis on the potential of interference mitigation schemes, needed to provide a reliable radio connectivity to the UAVs.

In this measurement study the signal activity and power levels are measured in the European Industrial, Scientific, and Medical band 863-870 MHz in the city of Aalborg, Denmark. The target is to determine if there is any interference, which may impact deployment of Internet of Things devices. The focus is on the Low Power Wide Area technologies LoRa and SigFox. The measurements show that there is a 22-33 % probability of interfering signals above -105 dBm within the mandatory LoRa and SigFox 868.0-868.6 MHz band in a shopping area and a business park in downtown Aalborg, which thus limits the potential coverage and capacity of LoRa and SigFox. However, the probability of interference is less than 3 % in the three other measurement locations in Aalborg. Finally, a hospital and an industrial area are shown to experience high activity in the RFID subband 865-868 MHz, while the wireless audio band 863-865 MHz has less activity.

The overall cellular network performance can be optimized for both ground and aerial users, if different treatment is given for the two user classes. Airborne UAVs experience different radio conditions that terrestrial users due to clearance in the radio path, which leads to strong desired signal reception, but at the same time increases the interference. Based on this, one can for instance use different interference coordination techniques for aerial users as for terrestrial user and/or use specific mobility settings for each class. This paper compares three different classification algorithms, which use standard LTE measurements from the UE as input, for detecting the presence of airborne users in the network. The algorithms are evaluated based on measurements done with mobile phones attached under a flying drone and on a car. Results are discussed showing the advantages and drawbacks for each option regarding different use cases, and the compromise between specificity and sensibility. For the collected data results show reliability close to 99% in most cases and also discuss how waiting for the final decision can even improve this accuracy to values close to 100%.

In this measurement study the signal activity and power levels are measured in the European Industrial, Scientific, and Medical band 863-870 MHz in the city of Aalborg, Denmark. The target is to determine if there is any interference, which may impact deployment of Internet of Things devices. The focus is on the Low Power Wide Area technologies LoRa and SigFox.The measurements show that there is a 22-33% probability of interfering signals above -105 dBm within the mandatory LoRa and SigFox 868.0-868.6 MHz band in a shopping area and a business park in downtown Aalborg, which thus limits the potential coverage and capacity of LoRa and SigFox. However, the probability of interference is less than 3% in the three other measurement locations in Aalborg. Finally, a hospital and an industrial area are shown to experience high activity in the RFID subband 865-868 MHz, while the wireless audio band 863-865 MHz has less activity.

In this paper we analyze and discuss the coverage and capacity of Sigfox and LoRaWAN in a large scale urban environments covering 150 km(2) in Northern Denmark.First, the study measures and analyzes interference in the European 868 MHz license free industrial, scientific, and medical band, creating a model for the interference. The measured interference in downtown Aalborg has an occurrence rate of 22% and a generalized extreme value distributed power level.Next, the study compares the coverage of the two Internet of Things network solutions using the existing Telenor cellular site grid both with and without interference from the measured external sources. The study concludes that without interference, both LoRaWAN and Sigfox provides very good indoor coverage of more than 99%. Furthermore, Sigfox and LoRaWAN can provide uplink and downlink failure rates of less than 1% for the 95 percentile of the devices for all cells without external interference. Adding the external interference results in an outdoor coverage of 90-95% and indoor coverage of 50-80%. Finally, the uplink and downlink 95 percentile failure rate increases significantly to 50% for LoRaWAN and exceeds 60% for Sigfox.

This paper compares three candidate large-scale propagation path loss models for use over the entire microwave and millimeter-wave (mmWave) radio spectrum: the alpha-betagamma (ABG) model, the close-in (CI) free-space reference distance model, and the CI model with a frequency-weighted path loss exponent (CIF). Each of these models has been recently studied for use in standards bodies such as 3rd Generation Partnership Project (3GPP) and for use in the design of fifth-generation wireless systems in urban macrocell, urban microcell, and indoor office and shopping mall scenarios. Here, we compare the accuracy and sensitivity of these models using measured data from 30 propagation measurement data sets from 2 to 73 GHz over distances ranging from 4 to 1238 m. A series of sensitivity analyses of the three models shows that the four-parameter ABG model underpredicts path loss when relatively close to the transmitter, and overpredicts path loss far from the transmitter, and that the physically based two-parameter CI model and three-parameter CIF model offer computational simplicity, have very similar goodness of fit (i. e., the shadow fading standard deviation), exhibit more stable model parameter behavior across frequencies and distances, and yield smaller prediction error in sensitivity tests across distances and frequencies, when compared to the four-parameter ABG model. Results show the CI model with a 1-m reference distance is suitable for outdoor environments, while the CIF model is more appropriate for indoor modeling. The CI and CIF models are easily implemented in existing 3GPP models by making a very subtle modification-by replacing a floating non-physically based constant with a frequency-dependent constant that represents free-space path loss in the first meter of propagation. This paper shows this subtle change does not change the mathematical form of existing ITU/3GPP models and offers much easier analysis, intuitive appeal, better model parameter stability, and better accuracy in sensitivity tests over a vast range of microwave and mmWave frequencies, scenarios, and distances, while using a simpler model with fewer parameters.

This letter presents an empirical multifrequency outdoor-to-indoor path loss model. The model is based on measurements performed on the exact same set of scenarios for different frequency bands ranging from traditional cellular allocations below 6 GHz (0.8, 2, 3.5, and 5.2 GHz), up to centimeter (cm)-wave frequencies (10, 18, and 28 GHz). The model has applicability similar to the typical 3GPP and ITU-R outdoor-to-indoor simplified models, including the multifrequency formulation recently included in the 3GPP TR 38.900. This letter highlights some of the details behind these simplified models and provides additional modeling for internal multiwall attenuation and associated shadow fading.