Showing papers by "Preben Mogensen published in 2018"

How to Ensure Reliable Connectivity for Aerial Vehicles Over Cellular Networks

Abstract: 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.

Joint Link Adaptation and Scheduling for 5G Ultra-Reliable Low-Latency Communications

Abstract: This paper presents solutions for efficient multiplexing of ultra-reliable low-latency communications (URLLC) and enhanced mobile broadband (eMBB) traffic on a shared channel. This scenario presents multiple challenges in terms of radio resource scheduling, link adaptation, and inter-cell interference, which are identified and addressed throughout this paper. We propose a joint link adaptation and resource allocation policy that dynamically adjusts the block error probability of URLLC small payload transmissions in accordance with the instantaneous experienced load per cell. Extensive system-level simulations of the downlink performance showpromising gains of this technique, reducing the URLLC latency from 1.3 to 1 ms at the 99.999% percentile, with less than 10% degradation of the eMBB throughput performance as compared with conventional scheduling policies. Moreover, an exhaustive sensitivity analysis is conducted to determine the URLLC and eMBB performance under different offered loads, URLLC payload sizes, and link adaptation and scheduling strategies. The presented results give valuable insights on the maximum URLLC offered traffic load that can be tolerated while still satisfying the URLLC requirements, as well as what conditions are more appropriate for dynamic multiplexing of URLLC and eMBB traffic in the upcoming 5G systems.

Reliability Analysis of Uplink Grant-Free Transmission Over Shared Resources

Abstract: Uplink grant-free schemes have the promise of reducing the latency of a user-equipment-initiated transmission by avoiding the handshaking procedure for acquiring a dedicated scheduling grant. However, the possibility of successfully delivering a payload within a latency constraint may be severely compromised in case of grant-free operations over shared radio resources. In this paper, we study the performance of two different uplink grant-free schemes over shared resources recently discussed within the fifth generation new radio standardization, namely, a solution based on a stop-and-wait (SAW) protocol and a blind retransmission approach. Performance is evaluated assuming Rayleigh fading channels with a maximum ratio combining (MRC) multi-antenna receiver. Analytical results show the benefits of grant-free transmission with respect to the traditional grant-based approach for a tight latency constraint. A high-order receive diversity is beneficial to leverage the MRC gain and enables the possibility of achieving the 10−5 outage probability target set for ultra-reliable low-latency communication services. The blind retransmission approach is significantly penalized by identification and signaling errors, while a SAW solution with potentially scheduled retransmissions out of the shared bandwidth leads to the lowest outage probability, at least for frequent packet arrivals.

Beyond 5G Wireless IRT for Industry 4.0: Design Principles and Spectrum Aspects

Abstract: We present our vision for a Beyond 5G Wireless Isochronous Real Time (WIRT) system for industrial control networks, designed for supporting fast closed loop control applications. WIRT aims at ultra-reliable short range wireless links with ∼0.1 ms latencies and a wired-like 10−9 reliability. The usage of a large spectrum and frequency/interference diversity are considered fundamental components for WIRT. Ultrawideband (UWB) spectrum access and unlicensed transmission at millimeter-waves (60 GHz band) are identified as possible solutions towards ultra-reliable ultra-low latency communication. The suitability and challenges of both approaches are extensively discussed, along with the way forward for WIRT design.

Measured Uplink Interference Caused by Aerial Vehicles in LTE Cellular Networks

Abstract: 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.

5G for Ultra-Reliable Low-Latency Communications

Abstract: The articles in this special section focus on fifth generation (5G) mobile communication for ultra-reliable low-latency communications. With the expected superior performance to the current generation of mobile networks, 5G systems are poised to support new and diverse usage scenarios and applications, thus enriching the lives of citizens and the productivity of industry and public sectors. The widely accepted scenarios for 5G include enhanced mobile broadband (eMBB), addressing human-centric use cases for access to multimedia content, services and data; ultra-reliable low-latency communications (URLLC) with strict requirements, especially in terms of latency and reliability; and massive machine type communications (mMTC) for a very large number of connected devices typically transmitting a relatively low volume of non-delay-sensitive data. The articles in this section present the most relevant scenarios, prominent research outcomes, and state-of-the-art advances of 5G systems for URLLC achieving the Third Generation Partnership Project (3GPP) targets on latency and reliability requirements to successfully deliver delay-sensitive information. In 3GPP, the performance target for control plane latency is 10 ms, and for user plane latency it is 0.5 ms for downlink and uplink directions, separately.

5G Centralized Multi-Cell Scheduling for URLLC: Algorithms and System-Level Performance

Abstract: We study centralized radio access network (C-RAN) with multi-cell scheduling algorithms to overcome the challenges for supporting ultra-reliable low-latency communications (URLLC) in the fifth-generation new radio (5G NR) networks. Low-complexity multi-cell scheduling algorithms are proposed for enhancing the URLLC performance. In comparison with the conventional distributed scheduling, we show that the C-RAN architecture can significantly reduce undesirable queuing delay of URLLC traffic. The gain of user scheduling with different metrics and the benefit of packet segmentation are analyzed. The performance of the proposed solutions is evaluated with an advanced 5G NR compliant system-level simulator with high degree of realism. The results show that the centralized multi-cell scheduling achieves up to 60% latency improvement over the traditional distributed scheduling while fulfilling the challenging reliability of URLLC. It is shown that segmentation brings additional performance gain for both centralized and distributed scheduling. The results also highlight the significant impact of channel- and delay-aware scheduling of URLLC payloads.

Power control optimization for uplink grant-free URLLC

Abstract: Ultra-reliable and low latency communication (URLLC) presents the most challenging use cases for fifth generation (5G) mobile networks. Traditionally the focus for mobile broadband has been to optimize the system throughput for high speed data traffic. However the optimization criteria for URLLC should focus on achieving small packets transmissions under strict targets such as 99.999% reliability within 1 ms. Power control is one candidate technology component for improving reliability and latency. In this work we investigate the power control for grant-free URLLC transmissions through extensive system level simulations in a urban outdoor scenario. We initially compare different settings for open loop power control (OLPC) with full and with fractional path loss compensation. Then we evaluate whether power boosting the retransmission can reduce the probability of packets delays under the 1 ms constraint. We also discuss the practical implication of applying power boosting. With full path loss compensation and boosting retransmissions, we show that a URLLC load such as 1200 small packets per second per cell can be achieved in the considered scenario.

A Blind Retransmission Scheme for Ultra-Reliable and Low Latency Communications

Abstract: This work is related to 5G new radio concept design, with focus on ultra-reliable and low latency communication (URLLC) use cases. We mainly target to achieve the stringent latency and reliability requirements for transmissions over the air interface, such as 99.999% success probability within 1 ms. Meeting these requirements in an efficient way, that is, without draining the network capacity is one of the main challenges for the new radio standardization. In this work, we propose a scheme to perform blind retransmissions on shared radio resources together with the application of successive interference cancellation to receive remaining non-decoded data with low delay penalty. The method avoids control errors and extra delays existent on feedback-based retransmission schemes. The investigations also show that blind retransmission on shared resources is more resource efficient than a conservative single shot transmission, depending on the number of users sharing the resources.

LTE radio measurements above urban rooftops for aerial communications

Abstract: 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.

Radio Propagation Analysis of Industrial Scenarios within the Context of Ultra-Reliable Communication

Abstract: One of the 5G use cases, known as ultra- reliable communication (URC), is expected to support very low packet error rate on the order of $10^{-5}$ with a 1 ms latency. In an industrial scenario, this would make possible replacing wired connections with wireless for controlling critical processes. Industrial environments with large metallic machinery and concrete structures can lead to deep shadowing and severe fading in the radio propagation channel, and thus pose a challenge for achieving the outage levels in connection with URC. In this paper, we present and analyze the large-scale propagation characteristics of two different industrial environments - open production space and dense factory clutter - based on measurements conducted at 2.3 and 5.7 GHz. By including a large number of spatially distributed samples, as per our experimental approach, we show the importance of properly characterizing the large-scale fading outage for URC. For instance, we show that based on a simple one-slope distance dependent path loss model, the conventional log-normal model for large-scale shadow fading is by far too simple for this environment. Our results show that at the 10^{-4} percentile, the tail of the shadow fading distribution can deviate by up to 10-20 dB from the log-normal model with respect to the average NLOS values (around 6 dB and 8 dB at 2.3 and 5.7 GHz, respectively). The simplicity of the one-slope path loss model, and its ability as we show, to express the trends with respect to scenarios, frequencies, and antenna heights, makes it an attractable option. However, there is a need for further experimental insight, possibly in combination with deterministic analysis, to get a better understanding of the large-scale fading for the study of URC in industrial environments.

Experimental Evaluation of Multi-Antenna Receivers for UAV Communication in Live LTE Networks

Abstract: Unmanned Aerial Vehicle (UAV) communication is known to suffer from significant interference due to the clearance of the radio paths with ground base stations. Multi-antenna receive combining has the promise of alleviating the impact of interference, translating to improved connectivity performance. In this paper, we evaluate the performance of Conventional Beamforming (CB) and Maximum Ratio Combining (MRC) receivers for UAV communication based on live Long Term Evolution (LTE) networks. Our measurement setup consists of nine Universal Software Radio Peripheral (USRP) boards and a circular antenna array with sixteen elements. The LTE signals are recorded at different UAV flight heights in urban environments, and processed offline. Results show similar Signal-to-Interference-plus-Noise Ratio (SINR) performance by MRC and CB, with CB slightly outperforming MRC provided knowledge of LTE signal structure is used for the beam selection. No significant dependency from the flight height has been observed. The outage probability analysis further emphasizes the benefits of using CB in the studied scenarios.

Joint Resource Configuration and MCS Selection Scheme for Uplink Grant-Free URLLC

Abstract: Ultra-reliable and low-latency communications (URLLC) addresses the most challenging set of services for 5G New Radio. Uplink grant-free transmissions is recognized as a promising solution to meet the ambitious URLLC target (1 ms latency at a 99.999% reliability). Achieving such a high reliability comes at the expense of poor spectral efficiency, which ultimately affects the load supported by the system. This paper proposes a joint resource allocation solution including multiple modulation and coding schemes (MCSs) and power control settings for grant-free uplink transmissions on shared resources. The scheme assigns smaller bandwidths parts and higher MCS to the UEs in good average channel conditions, reducing the probability of fully overlapping transmissions. The performance analysis shows that the scheme is capable of increasing the system outage capacity by ∼90%, compared to prior art solutions using a conservative single-MCS configuration with fully overlapping transmissions.

Reducing Handover Outage for Autonomous Vehicles with LTE Hybrid Access

Abstract: Autonomous vehicle applications require sub-100 ms message latency with a high success probability. While this will be supported by upcoming fifth generation networks, hybrid access technology using multiple LTE connections, may pave the way for the autonomous vehicle applications today. In current LTE networks, handovers often lead to long data interruption. Therefore, we study the handovers and the related data interruption, and how performance can be improved through hybrid access, using redundant transmissions over multiple connections. The study is based on drive tests, where four QualiPoc measurement smartphones are connected to different LTE networks simultaneously, performing synchronized ping latency measurements, and recording handover events. The results show that a handover event during a ping measurement, prolongs the average latency from 60-80 ms to more than 200 ms. However, the handovers do not occur simultaneously in the measured LTE networks. Therefore, hybrid access with two connections is shown to reduce the handover outage by a factor 60. Furthermore, the 99.9 %-tile latency is reduced 66 %, by using two simultaneous connections, as compared to the best single network measurement.

The Gigantium Smart City Living Lab: A Multi-Arena LoRa-based Testbed

Abstract: The Wireless Communications Networks Section, from the Department of Electronic Systems at Aalborg University, Denmark, has successfully deployed, in collaboration with a number of Danish local industrial partners and the municipality of Aalborg, a LoRa network in the Gigantium multi-arena center. The initial aim of this network is to serve as an integrated multi-arena indoor environment monitoring wireless system, in contrast to the existing cabled solutions based on bus communication systems for each of the individual arenas. In addition, the network also enables usage monitoring of arenas and meeting rooms. The final setup is comprised of 33 multi-sensor nodes distributed across the multiple arenas, and 4 gateways, which provide macroscopic diversity to the wireless system, ensuring a high level of reliability. The setup is already operational, but still open for optimization. The deployed network will serve as a testbed for research in the wireless, and indoor environment domains.

Centralized Joint Cell Selection and Scheduling for Improved URLLC Performance

Abstract: A centralized joint cell selection and scheduling policy for ultra-reliable low latency communication (URLLC) is studied in this paper for the 5G new radio (NR). A low complexity cell association and scheduling algorithm is proposed, while maintaining attractive performance benefits. By being able to centrally control from which cells the different users are instantaneously scheduled, we show that the undesirable queuing delays for URLLC traffic can be significantly reduced. The proposed solution is evaluated in a realistic multi-cell, multi-user, dynamic network setting in line with the 5G NR system design specifications, and calibrated against 3GPP NR assumptions. The presented performance results show promising gains, where the proposed centralized solution can accommodate 38% higher traffic offered load than a traditional distributed network implementation, while still fulfilling the challenging reliability and latency targets for URLLC.

Multiplexing of latency-critical communication and mobile broadband on a shared channel

Abstract: This paper presents solutions for efficient multiplexing of ultra-reliable low-latency communications (URLLC) and enhanced mobile broadband (eMBB) traffic on a shared downlink channel. Such a scenario presents multiple challenges in the context of radio resource scheduling, link adaptation and inter-cell interference, which are identified and addressed throughout the paper. Specifically, a joint link adaptation and resource allocation technique is proposed that dynamically adjusts the block error probability (BLEP) of the URLLC payload transmissions in accordance with the instantaneous experienced load per cell. Extensive system-level simulations of the downlink performance show promising gains of this technique, reducing the URLLC latency from 1.3 ms to 1 ms at the 99.999% percentile, with less than 10% degradation of the eMBB throughput performance as compared to conventional scheduling policies.

An Empirical Study of Propagation Models for Wireless Communications in Open-Pit Mines

Abstract: In this paper, we investigate the suitability of the propagation models ITU-R 526, Okumura Hata, COST Hata models and Standard Propagation Model (SPM) to predict the path loss in open-pit mines. The models are evaluated by comparing the predicted data with measurements obtained in two operational iron-ore mining complexes in Brazil. Additionally, a simple deterministic model, based on the inclusion of an effective antenna height term to the ITU-R 526, is proposed and compared to the other methods. The results show that the proposed model results in root-mean-square error (RMSE) values between 5.5 dB and 9.2 dB, and it is capable of providing a close approximation of the best predictions (i.e. those with lowest RMSE) as provided by the SPM. The proposed model, however, reduces the calibration complexity considerably.

On the Achievable Rates over Collision-Prone Radio Resources with Linear Receivers

Abstract: In this paper, we discuss the achievable transmission rates over collision-prone radio resources shared by a number of devices, representative of novel Internet-of-Things (IoT) scenarios We consider Maximum Ratio Combining (MRC) and Minimum Mean Square Error (MMSE) receivers at the base station, and derive the relationship between target failure probability and saturation rate, which represents the maximum achievable rate over shared resources in the interference limited regime MRC receiver is shown to be sensitive to the presence of statistically relevant interferers operating over the same resources, rapidly leading to rate saturation The MMSE receiver adds a tier of protection to collisions thanks to its interference suppression capabilities, suffering for a rate penalty only in case of a high number of users A realistic system analysis in an indoor hotspot scenario validates the analytical trends and suggests insights on practical link adaptation strategies

The Development of the ITU-R Terrestrial Clutter Loss Model

Abstract: 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.