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This work investigates the secrecy capability of energy harvesting based overlay cognitive networks (EHOCNs). To this end, we assume that a message by a licensed transmitter is relayed by an unlicensed sender. Critically, the unlicensed sender uses energy harvested from licensed signals, enhancing the overall energy efficiency and maintaining the integrity of licensed communications. To secure messages broadcast by the unlicensed sender against the wire-tapper, full-duplex destinations - unlicensed recipient and licensed receiver - jam the eavesdropper at the same time they receive signals from the unlicensed sender. To this effect, we derive closed-form formulas for the secrecy outage probability, which then quantify the security performance of both unlicensed and licensed communications for EHOCNs with jamming-assisted full-duplex destinations, namely EHOCNwFD. In addition, optimum operating parameters are established, which can serve as essential design guidelines of such systems. acceptedVersion

In this article, we study the joint communication and sensing (JCAS) paradigm in the context of millimeter-wave (mm-wave) mobile communication networks. We specifically address the JCAS challenges stemming from the full-duplex operation and from the co-existence of multiple simultaneous beams for communications and sensing purposes. To this end, we first formulate and solve beamforming optimization problems for hybrid beamforming based multiuser multiple-input and multiple-output JCAS systems. The cost function to be maximized is the beamformed power at the sensing direction while constraining the beamformed power at the communications directions, suppressing interuser interference and cancelling full-duplexing related self-interference (SI). We then also propose new transmitter and receiver beamforming solutions for purely analog beamforming based JCAS systems that maximize the beamforming gain at the sensing direction while controlling the beamformed power at the communications direction(s), cancelling the SI as well as eliminating the potential reflection from the communication direction and optimizing the combined radar pattern (CRP). Both closed-form and numerical optimization based formulations are provided. We analyze and evaluate the performance through extensive simulations, and show that substantial gains and benefits in terms of radar transmit gain, CRP, and SI suppression can be achieved with the proposed beamforming methods.

The millimeter wave (mmWave) device-to-device air interface not only supports a direct wireless connectivity among devices, but it also offers an improved beamforming capability to obtain the direction information among the vehicles and devices for positioning. Both features serve as the key physical layer components for communications and positioning in the industrial Internet of things (IIoT) systems. Exploiting both accurate beamforming and wide bandwidth in a mmWave network, high-accuracy positioning is achievable, which can be then facilitated for location-aware communications, for instance. However, the uncertainty of anchors’ locations in the industrial environment highly degrades the achievable positioning accuracy if left without proper consideration. In order to resolve such challenge, this paper presents a cooperative positioning system (CPS), where the locations of all the vehicles and anchors can be jointly estimated based on acquired location-related measurements (LRMs). Furthermore, the positioning performance is evaluated under random trajectories and different geometric relationships between the vehicles and the anchors. We show that, the proposed positioning solution is capable of resolving the aforementioned challenge by simultaneously tracking the mobile vehicles while mapping the locations of the static anchors. Utilizing the LRMs from both time and angular domains, the achieved positioning accuracy in both 2D and vertical plane is demonstrated based on extensive numerical simulations. Last but not least, the impact of different numbers of the mobile vehicles on the overall positioning performance is also investigated. acceptedVersion

A common design of the random access procedure on the physical random access channel (PRACH) is required for the diverse usage scenarios in the fifth generation new radio (5G NR) mobile networks. Based on the latest 3GPP specifications and evaluation assumptions agreed for Release 16, the 2 step-RACH (2SR) enhancement, composed of the denoted MsgA and MsgB, not only reduces the latency but also the control-signalling overhead due to the reduced number of messages transmitted. The channel structure of MsgA comprises RACH preamble and data in the physical uplink shared channel (PUSCH) while MsgB combines the random access response and the contention resolution. This procedure should operate in local area (LA), medium range (MR) and wide area (WA) cells despite the lack of time alignment (TA) in the PUSCH part of MsgA. The demodulation performance degradation observed without time offset compensation at the base station (gNB), specially for MR or WA cells, highlight that practical gNB implementations relying in MAC control element-based TA command for PUSCH time alignment are not conceivable for 2SR. Furthermore, in the case that all preambles from multiple users (UEs) trying to perform the initial access are mapped to the same PUSCH physical resources, the associated data parts overlap and may result in unsuccessful decoding. There is therefore a trade-off between the collision probability of the PUSCH part of MsgA and the resource overhead for 2SR. This paper addresses the channel structure design of this procedure for the preamble and data parts of MsgA together with the receiver processing framework. The performance results suggest that using lower payload sizes provide higher resource utilization and allow more UEs to be multiplexed within the same PUSCH occasion. In addition, using different DMRS ports for UEs sharing same physical resources decrease the probability of failure in the decoding of the data part of MsgA while reduces the resource overhead for 2SR. acceptedVersion

In the nearest future, connected vehicles will be widely spread due to ongoing standardization activities of vehicle-to-everything communications. However, exchanging real-time traffic information is challenging in urban environments with dense traffic where the line-of-sight might be blocked. In this work, we present the measurement results of the automotive communication and radar sensing through the obstructing vehicle, when the transmitting and receiving antennas are located very close to the ground, and the radio waves propagate near-ground, i.e. between the bottom of the car and the road pavement. It is shown that communication between two vehicles is undoubtedly feasible at distances starting from 1.5 m and antenna heights of 0.3 m with 16 dB loss. Almost the same losses are observed in a radar sensing for distances larger than 2 m. acceptedVersion

The short wavelength of millimeter-waves in fifth-generation (5G) mobile communications enables the implementation of multi-element antenna arrays in relatively small space, e.g., in user devices and small base stations. Joint communication and sensing (JCAS) is a scheme which utilizes the beamsteering capabilities of the multi-element antenna arrays for simultaneously maintaining a communication link and sensing the surroundings with a radar beam and receiving it with the same device. The simultaneous transmission and reception requires a beam weighting algorithm which cancels the self-interference while at the same time maintaining the integrity of both beams. In this paper, the performance of different linear patch antenna array architectures is studied in terms of self-interference cancellation performance and obtained maximum gain in the beamsteering range. A mirror-beam problem in the self-interference cancellation algorithm for parallel arrays is studied and novel coupling randomization is introduced for the arrays to prevent the forming of the mirror beams. acceptedVersion

Integrated communications, localization and sensing is one of the most addressed technologies considered for future mobile communications systems. In this context, a user equipment (UE)-centric mobile radar has been proposed to introduce improved situational awareness, and consequently potential improvement in network performance. In this paper, we derive an extended Kalman probability hypothesis density (EK-PHD) filter with a novel feature model, for a mobile radar based environment mapping, where range-angle detections are used to track map objects over time for dynamic map construction. In order to evaluate the performance of the proposed filtering approach, we employ a realistic ray-tracing-based simulation setup, which models the full transmission chain from the transmitted IQ-samples to mapping results. Besides this, a simplified measurement model considering solely single-bounce specular reflections is exploited for providing further insight into the filter performance. The obtained results show that the proposed EK-PHD filter is able to provide high-quality mapping results, reaching around 10 cm landmark estimation accuracy in the considered millimeter wave simulation setup. acceptedVersion

This paper proposes a superposition transmission scheme for the future Radio Frequency (RF) convergence applications. The scheme is discussed under the assumption of a monostatic broadcasting channel topology. Under communications quality-of-service (QoS) constraints, the joint performance region of communications sum rate and radar estimation error variance is studied. Two radar signal waveforms, namely linear FM and parabolic FM, are used to investigate how signal shapes may influence the estimation accuracy. Both waveforms are generated with rectangular envelope. In the end, a numerical analysis is applied, which concludes that a moderate communications QoS promises a good communications fairness while with the limited radar performance degradation. acceptedVersion

Switched-capacitor power amplifier has gained popularity within the radio frequency integrated circuit community, since it is CMOS compatible offering high integration density and good performance particularly in terms of linearity. In this paper we present a study on the use of switched-capacitor power amplifier at millimeter-wave frequency range. We identify the major design challenges in this paper, and demonstrate the feasibility of switched-capacitor power amplifier with a 30-G Hz design case. Our analysis describes the effects of power amplifier device parasitics and their contribution to dynamic power consumption, revealing that these are a major factor in degradation of switched capacitor power amplifier efficiency at millimeter waves. Two circuits, one for 3 GHz and the other for 30 GHz, were designed and simulated with 28-nm bulk CMOS technology. At 3 GHz, the designed switched capacitor power amplifier structure with 6-bit resolution features maximum output power of 19.4 dBm and efficiency of 59% whereas the output power of 18.6 dBm with 21% efficiency is achieved at 30 GHz. The switched-capacitor power amplifier preserves its good linearity at higher frequencies as well, and our design demonstrates an adjacent channel leackage ratio of -34.4 dB at 30 GHz for a 100-MHz OFDM-modulated signal. acceptedVersion

Future drone delivery infrastructure and service for distributing goods to inner city and rural areas, by collaborating with the already existing transportation system, has become an important function in the semi-/full-automation process of home deliveries. This has been exacerbated by the current (and possible future) Covid-19 pandemic. This paper presents a new paradigm for a 5G enabled drone delivery system based on ground-aerial integrated mobilities called TWIN that provide a high-quality communication system for increased drone fleet service capacity. We depict the 5G architecture that supports the dual mobilities and emphasize the strategies to ensure reliable, low latency radio link, high accuracy drone positioning together with location management. The increased link level availability coupled with high accuracy location management, allows for a series of new network applications and support the fast creation of drone delivery services. We envision that logistic services on the TWIN concept will have a high societal and economic impact for both urban and rural areas. acceptedVersion

High-level synthesis (HLS) aims to improve the productivity of digital logic design over traditional register-transfer level (RTL) methods. This paper shows that HLS can replace RTL when implementing a complex data path oriented signal processing algorithm under strict throughput constraints. Our system is a nonlinear spline-based Hammerstein self-interference (SI) canceller for full-duplex transceiver capable of achieving high SI suppression, while maintaining low computational complexity. The achieved suppression of the SI is superb 45 dB, while consuming 29 026 of the available LUTs, 17992 of registers, and 655 of the DSP slices on Kintex-7 XC7K410T FPGA. Our paper also compares the usability of two commercial HLS tools that were used in this work. acceptedVersion

Future mobile networks will enable new use cases, requiring further enhanced data rates, latency, coverage, capacity, and reliability. In this article, to emphasize sustainable energy consumption and improved device battery lifetime, the concept, benefits, and challenges of utilizing wake-up radio-based access in 5G networks are reviewed and discussed. To this end, the operating principle and associated wake-up signal structures are first reviewed, together with the corresponding power consumption and buffering delay trade-offs. Then the applicability of wake-up methods at mmWave bands and beamforming systems is addressed and highlighted. Additionally, an energy-efficient mobility management procedure for wake-up radio-based devices is described and demonstrated, utilizing narrowband uplink reference signals. Overall, the article provides an overview of wake-up-based access in 5G systems as a promising power-saving mechanism, and discusses the associated prospects, benefits, and challenges. acceptedVersion

Future 5G networks will serve both terrestrial and aerial users, thanks to their network slicing and flexible numerology capabilities. The probability of Line-of-Sight (LoS) propagation will be intuitively higher for aerial users than for terrestrial users and this will provide a trade-off between increased capacity and increased interference. Our paper analyzes theoretically this trade-off and proposes solutions based on downlink multiantenna beamorming and joint optimization of the signal-to- interference ratio of multiple aerial users. It is shown that Multiple-Input-Single-Output solutions offer the most convenient tradeoff between complexity and capacity/interference performance. Simulation results are provided for mm Wave bands and low-altitude aerial vehicles. acceptedVersion

Recently, wake-up scheme has been proposed to enhance the energy-efficiency of 5G mobile devices and prolong its battery lifetime while reducing the buffering delay. The existing wake-up optimization mechanisms use off-line methods and are tied to specific traffic models. In this paper, a novel concept of wake-up scheduling is introduced to further improve the energy-efficiency of mobile devices and to deal with realistic traffic. The main idea is to use a fixed configuration of the wake-up scheme and adjust the scheduling of the wake-up signals dynamically. For this, a proactive wake-up scheduler is proposed to take online decisions based on traffic prediction. Towards this end, a framework to predict packet arrivals based on recurrent neural networks is developed. Numerical results show that for given delay requirements of video, audio streaming, and mixed traffic flow, the proactive wake-up scheduler reduces the power consumption of the baseline wake-up scheme without scheduler by up to 36%, 28% and 9%, respectively. acceptedVersion

@ IEEE. Published in 2020 IEEE International Conference on Communications Workshops (ICC Workshops). This work was supported by the project 5G-FORCE and RAAS Connectivity RTF framework. Abstract: Unmanned aerial vehicles (UAVs) can be controlled in beyond-visual-line-of-sight use cases via today’s commercial mobile network operator (MNO) deployments, such as those based on long-term evolution (LTE) technology. In order to improve the reliability of UAV connectivity, especially in more critical use cases, several MNO networks may be utilized si- multaneously. To evaluate this option in typical environments, performance measurements were conducted over two public LTE networks in urban, suburban, and rural areas in/near the city of Tampere, Finland, and at various UAV flight altitudes: 1 m, 15-20 m, and 50 m above the ground. The results indicate that there are distinct benefits in utilizing more than one MNO for improved levels of connection reliability.

Positioning is considered one of the most important features and enabler of various novel industry verticals in future radio systems. Since path loss or received signal strength-based measurements are widely available and accessible in the majority of wireless standards, path loss-based positioning has an important role among other positioning technologies. Conventionally path loss-based positioning has two phases; i) fitting a path loss model to training data, if such training data is available, and ii) determining link distance estimates based on the path loss model and calculating the position estimate. However, in both phases, the maximum measurable path loss is limited by measurement noise. Such immeasurable samples are called censored path loss data and such noisy data is commonly neglected in both the model fitting and in the positioning phase. In the case of censored path loss, the loss is known to be above a known threshold level and that information can be used in model fitting as well as in the positioning phase. In this paper, we examine and propose how to use censored path loss data in path loss model-based positioning and demonstrate with simulations the potential of the proposed approach for considerable improvements (over 30%) in positioning accuracy. acceptedVersion

openaire: EC/H2020/704947/EU//ADVANTAG5 This article presents a power amplifier (PA) design, which consists of eight class-D PA units on a single 28-nm CMOS die and a coupled-line power combiner on printed circuit board. The PA utilizes tri-phasing modulation, which combines polar and outphasing components in a way that eliminates linearity-degrading effects of multilevel outphasing while maintaining the back off efficiency. Each PA unit contains a cascoded output stage with a 3.6-V supply voltage, and multilevel operation is enabled by ON/OFF logic circuitry. Our analysis shows that the choice of power-combiner type is vital for reducing PA supply and ground ripple and thus ensuring reliable operation. Accordingly, the power combiner is implemented with extended Marchand baluns, which consist of input transmission lines and coupled-line sections. Unlike the original Marchand balun, our new topology is feasible for implementation under the layout restrictions caused by the multiple-unit PA on a single die. Measurement results show the PA achieving a peak output power of 29.7 dBm with a 34.7% efficiency, and operation with aggregated Long Term Evolution (LTE) signals at 1.7-GHz carrier frequency is verified with bandwidths up to 100 MHz.

Improved mobile device battery lifetime and latency minimization are critical requirements for enhancing the mobile broadband services and user experience. Long-term evolution (LTE) networks have adopted discontinuous reception (DRX) as the baseline solution for prolonged battery lifetime. However, in every DRX cycle, the mobile device baseband processing unit monitors and decodes the control signaling, and thus all instances without any actual data allocation leads to unnecessary energy consumption. This fact together with the long start-up and power-down times can prevent adopting frequent wake-up instants, which in turn leads to considerable latency. In this work, a novel wake-up scheme is described and studied, to tackle the tradeoff between latency and battery lifetime in future 5G networks, seeking thus to facilitate an always-available experience, rather than always on. Analytical and simulation-based results show that the proposed scheme is a promising approach to control the user plane latency and energy consumption, when the device is operating in the power saving mode. The aim of this article is to describe the overall wake-up system operating principle and the associated signaling methods, receiver processing solutions and essential implementation aspects. Additionally, the advantages compared to DRX-based systems are shown and demonstrated, through the analysis of the system energy-efficiency and latency characteristics, with special emphasis on future 5G-grade mobile devices.

There is a strong interest in utilizing commercial cellular networks to support unmanned aerial vehicles (UAVs) to send control commands and communicate heavy traffic. Cellular networks are well suited for offering reliable and secure connections to the UAVs as well as facilitating traffic management systems to enhance safe operation. However, for the full-scale integration of UAVs that perform critical and high-risk tasks, more advanced solutions are required to improve wireless connectivity in mobile networks. In this context, integrated access and backhaul (IAB) is an attractive approach for the UAVs to enhance connectivity and traffic forwarding. In this paper, we study a novel approach to dynamic associations based on reinforcement learning at the edge of the network and compare it to alternative association algorithms. Considering the average data rate, our results indicate that the reinforcement learning methods improve the achievable data rate. The optimal parameters of the introduced algorithm are highly sensitive to the donor next generation node base (DgNB) and UAV IAB node densities, and need to be identified beforehand or estimated via a stateful search. However, its performance nearly converges to that of the ideal scheme with a full knowledge of the data rates in dense deployments of DgNBs. acceptedVersion

Unmanned aerial vehicles (UAVs) are increasingly employed for numerous public and civil applications, such as goods delivery, medicine, surveillance, and telecommunications. For the latter, UAVs with onboard communication equipment may help temporarily offload traffic onto the neighboring cells in fifth-generation networks and beyond (5G+). In this paper, we propose and evaluate the use of UAVs traveling over the area of interest to relieve congestion in 5G+ systems under spontaneous traffic fluctuations. To this end, we assess two inherently different offloading schemes, named routed and controlled UAV `bridging'. Using the tools of renewal theory and stochastic geometry, we analytically characterize these schemes in terms of the fraction of traffic demand that can be offloaded onto the UAV `bridge' as our parameter of interest. This framework accounts for the unique features of millimeter-wave (mmWave) radio propagation and city deployment types with potential line-of-sight (LoS) link blockage by buildings. We also introduce enhancements to the proposed schemes that significantly improve the offloading gains. Our findings offer evidence that the UAV `bridges' may be used for efficient traffic offloading in various urban scenarios., Comment: This work has been accepted for publication in the IEEE Transactions on Vehicular Technology

This article studies advanced digital self-interference (SI) cancellation algorithms for wireless full-duplex (FD) transceivers. While the majority of works in this area consider linear SI models and corresponding cancellation algorithms, we take also both the transmitter (TX) and receiver (RX) nonlinearities into account. Specifically, we develop a Hammerstein-Wiener type of digital SI cancellation system where the two involved nonlinearities are efficiently implemented through spline-interpolated look-up tables (LUTs). Also, adaptive parameter estimation solutions are pursued and discussed, and comprehensive cancellation performance examples and processing complexity comparisons are provided. The obtained results show that taking both the TX and RX nonlinearities into account in the digital cancellation stage can be beneficial, particularly when the TX power amplifier is operating close to saturation and when the RF isolation and RF cancellation prior to the RX low-noise amplifier (LNA) is limited, such that also the LNA is distorting the SI waveform. acceptedVersion

Wireless inband full-duplex communications, where individual radio devices transmit and receive simultaneously on the same frequency band, has recently been proposed as another step towards the full utilization of the available spectral resources. This chapter concentrates on solving the greatest challenge in wireless inband full-duplex communications, i.e., the self-interference, which refers to the interference produced by the own transmitter. To this end, this chapter provides digital-domain solutions for efficient self-interference cancellation in low-cost full-duplex radios. The proposed digital cancellers are capable of modeling the most prominent radio circuit impairments, in particular the nonlinear distortion produced by the transmitter power amplifier. The digital cancellers are evaluated using an actual inband full-duplex prototype, which contains also other self-interference suppression mechanisms operating in the analog domain. The obtained measurement results show that, with the help of these digital cancellers, the self-interference can be cancelled almost perfectly, proving that true full-duplex operation is indeed possible. Altogether, the own transmit signal is shown to be suppressed in some cases by more than 100 dB, which is one of the highest reported self-interference cancellation performances to date.

This paper investigates a full-duplex base station using a generalized frequency division multiplexing (GFDM) transceiver with the radio frequency (RF) impairments phase noise, carrier frequency offset (CFO) and in-phase (I) and quadrature (Q) imbalance. To fully focus on the RF impairment issue, we study the simple configuration of single uplink user and single downlink user. They both are half duplex wireless. In the uplink, we study analog and digital self-interference (SI) cancellation and propose a complementary SI suppression method. Desired signal and residual SI powers and signal-to-interference ratio (SIR) are derived in closed form. Similarly, in the downlink, we derive desired signal power, co-channel interference signal power caused by the uplink user and SIR. The RF impairments degrade the efficiency of SI cancellation and affect GFDM more negatively than full-duplex orthogonal frequency division multiplexing (OFDM). Hence, we propose full-duplex GFDM receiver filters for maximizing the SIR for both uplink and downlink transmissions. Finally, the uplink and downlink rates and the uplink-downlink rate region are derived. Significantly, the optimal-filter based GFDM outperforms full-duplex OFDM by 25 dB higher SIR and an uplink rate increase of 500%. acceptedVersion

openaire: EC/H2020/704947/EU//ADVANTAG5 In this paper, we show that amplitude transitions that are inherent to the multilevel outphasing radio transmitter architecture distort the transmitted signal due to time-domain discontinuities. In order to address this challenge, we propose a new transmitter architecture called tri-phasing which avoids discontinuities in signal waveforms and thus achieves significantly better linearity than multilevel outphasing. The output waveform in tri-phasing can be made continuous by representing the baseband signal with three components. One of the three components is amplified by discrete amplitude steps, whereas the other two are used to compensate the instantaneous shift in the output waveform due to the discrete amplitude step and to provide fine amplitude resolution. An implementation of the tri-phasing transmitter requires three phase modulators and additional digital signal processing. The system-level simulations performed in this paper demonstrate that the ACLR of a multilevel outphasing transmitter with 4 amplitude levels and 10-bit phase resolution is limited to -48 dBc, when simulated with a 100 MHz carrier-aggregated LTE downlink signal at 2.46 GHz carrier frequency. The proposed tri-phasing transmitter achieves -58 dBc ACLR with the same simulation parameters, indicating that continuous amplitude transitions can significantly improve the transmitter linearity.

We analyze an inband full-duplex access node that is serving mobile users while simultaneously connecting to a core network over a wireless backhaul link, utilizing the same frequency band for all communication tasks. Such wireless self-backhauling is an intriguing option for the next generation wireless systems since a wired backhaul connection might not be economically viable if the access nodes are deployed densely. In particular, we derive the optimal transmit power allocation for such a system in closed form under Quality-of-Service (QoS) requirements, which are defined in terms of the minimum data rates for each mobile user. For comparison, the optimal transmit power allocation is solved also for two reference scenarios: a purely half-duplex access node, and a relay-type full-duplex access node. Based on the obtained expressions for the optimal transmit powers, we then show that the systems utilizing a full-duplex capable access node have a fundamental feasibility boundary, meaning that there are circumstances under which the QoS requirements cannot be fulfilled using finite transmit powers. This fundamental feasibility boundary is also derived in closed form. The feasibility boundaries and optimal transmit powers are then numerically evaluated in order to compare the different communication schemes. In general, utilizing the purely full-duplex access node results in the lowest transmit powers for all the communicating parties, although there are some network geometries under which such a system is not capable of reaching the required minimum data rates. In addition, the numerical results indicate that a full-duplex capable access node is best suited for relatively small cells. acceptedVersion

This paper analyzes the performance of linearly precoded time division duplex based multi-user massive MIMO downlink system under joint impacts of channel non-reciprocity (NRC) and imperfect channel state information (CSI). We consider a generic and realistic NRC model that accounts for transceiver frequency-response as well as mutual coupling mismatches at both user equipment (UE) and base station (BS) sides. The analysis covers two most prominent forms of linear precoding schemes, namely, zero-forcing (ZF) and maximumratio transmission (MRT), and assumes that only the statistical properties of the beamformed channel are used at the UE side to decode the received signal. Under the approximation of i.i.d. Gaussian channels, closed-form analytical expressions are derived for the effective signal to interference and noise ratios (SINRs) and the corresponding capacity lower bounds. The expressions show that, in moderate to high SNR, the additional interference caused by imperfect NRC calibration can degrade the performance of both precoders significantly. Moreover, ZF is shown to be more sensitive to NRC than MRT. Numerical evaluations with practical NRC levels indicate that this performance loss in the spectral efficiency can be as high as 42% for ZF, whereas it is typically less than 13% for MRT. It is also shown that due to the NRC, the asymptotic large-antenna performance of both precoders saturate to an identical finite level. The derived analytical expressions provide useful tools and valuable technical insight, e.g., into calculating the NRC calibration requirements in BSs and UEs for any given specific performance targets in terms of effective SINR or the system capacity bound. acceptedVersion

The nonlinearities of power amplifiers combined with non-contiguous transmissions found in modern, frequency-agile, wireless standards create undesirable spurious emissions through the nearby spectrum of data carriers. Digital predistortion (DPD) is an effective way of combating spurious emission violations without the need for a significant power reduction in the transmitter leading to better power efficiency and network coverage. In this paper, an iterative, multi sub-band version of the sub-band DPD, proposed earlier by the authors, is presented. The DPD learning is iterated over intermodulation distortion (IMD) sub-bands until a satisfactory performance is achieved for each of them. A sequential DPD learning procedure is also presented to reduce the hardware complexity when higher order nonlinearities are incorporated in the DPD learning. Improvements in the convergence speed of the adaptive DPD learning are also achieved via incorporating a variable learning rate and interpolation of previously trained DPD coefficients. A WarpLab implementation of the proposed DPD is also shown with excellent suppression of the targeted spurious emissions.

Traditional direction-of-arrival (DoA) estimation algorithms for multi-element antenna arrays are not directly applicable to reconfigurable antennas due to inherent design and operating differences between antenna arrays and reconfigurable antennas. In this paper, we propose novel modifications to existing DoA algorithms and show how these can be adapted for realtime DoA estimation using two-port composite right/left-handed (CRLH) reconfigurable leaky-wave antennas (LWAs). First, we propose a single/two-port multiple signal classification (MUSIC) algorithm and derive the corresponding steering vector for reconfigurable LWAs. We also present the power pattern cross correlation (PPCC) algorithm which is based on finding the maximum correlation between the measured radiation patterns and the received powers. For all algorithms, we show how to simultaneously use both ports of the two-port LWA in order to improve the DoA estimation accuracy and, at the same time, reduce the scanning time for the arriving signals. Moreover, we formulate the Cramer-Rao bound (CRB) for MUSIC-based DoA estimation with LWAs and present an extensive performance evaluation of MUSIC algorithm based on numerical simulations. Additionally, these results are compared to DoA estimation with conventional antenna arrays. Finally, we experimentally evaluate the performance of the proposed algorithms in an indoor multipath wireless environment with both line-of-sight (LoS) and non-line-of-sight (NLoS) components. Our results demonstrate that DoA estimation of the received signal can be successfully performed by using the two-port CRLH-LWA, even in the presence of severe multipath. acceptedVersion

This paper is devoted to the end-to-end performance analysis, optimal power allocation (OPA), and energy-efficiency (EE) optimization of decode-and-forward (DF)-based full-duplex relaying (FDR) and half-duplex relaying (HDR) systems. Unlike existing analyses and works that assume simplified transmission over symmetric fading channels, we consider the more realistic case of asymmetric multipath fading and shadowing conditions. To this end, exact and asymptotic analytic expressions are first derived for the end-to-end outage probabilities (OPs) of the considered DF-FDR set ups. Based on these expressions, we then formulate the OPA and EE optimization problems under given end-to-end target OP and maximum total transmit power constraints. It is shown that OP in FDR systems is highly dependent upon the different fading parameters and that OPA provides substantial performance gains, particularly, when the relay self-interference (SI) level is strong. Finally, the FDR is shown to be more energy-efficient than its HDR counterpart, as energy savings beyond 50% are feasible even for moderate values of the SI levels, especially at larger link distances, under given total transmit power constraints and OP requirements.

In this communication, the self-interference (SI) channel and the novel enabling techniques for a compact inband full-duplex relay are described and characterized in different operating environments. The full-duplex operation is based on a novel antenna design that uses wavetraps to provide passive isolation of up to 70 dB between the transmit and receive antenna ports. The passive isolation is complemented with novel active RF and digital cancellation stages that further suppress the residual SI to the receiver noise floor. Measurement results of a complete prototype implementation show that the proposed design can achieve an overall SI cancellation performance of over 100 dB even with an ambitious instantaneous bandwidth of 80 MHz. Similar results are obtained both in an anechoic chamber as well as in realistic multipath indoor environments.

Techniques for wireless energy harvesting (WEH) are being emerged as a fascinating set of solutions to extend the lifetime of energy-constrained wireless networks. They are commonly regarded as a key functional technique for almost perpetual communications. With the WEH technology, wireless devices are able to harvest energy from, e.g., different light sources or RF signals broadcast by ambient/dedicated wireless transmitters to support their operation and communications capabilities. The WEH technology will have increasingly wider range of use in upcoming applications for, e.g., wireless sensor networks, machine-to-machine (M2M) communications, and the Internet of Things (IoT). In this paper, the usability and fundamental limits of solar cell or photovoltaic harvesting-based M2M communication systems are studied and presented. The derived theoretical bounds are in essence based on the Shannon capacity theorem, combined with selected propagation loss models, assumed additional link nonidealities, as well as the given energy harvesting and storage capabilities. Fundamental performance limits and available capacity of the communicating link are derived and analyzed, together with extensive numerical results evaluated in different practical scenarios, including realistic implementation losses and the state-of-the-art printed supercapacitor performances. In particular, low-power sensor-type communication applications using passive wake-up radio (WuR)-assisted operation are addressed in this paper. The results show the benefits of using passive WuR, especially when the number of nodes is small. Moreover, the presented analysis principles and results establish clear feasibility regions and performance bounds for WEH-based low rate M2M communications in the future IoT networks.

The present work quantifies the effects of asymmetric fading conditions on differentially modulated amplify-and-forward relaying systems. To this end, novel bit error rate expressions are derived for the case that the source $-$ relay and relay $-$ destination links experience non-line-of-sight multipath fading whilst the source $-$ destination link is subject to: multipath fading, shadowing, and composite fading. Simple and tight approximate and asymptotic expressions are also derived, leading to useful insights into the system design. It is shown that the incurred performance variations range from one to few orders of magnitude compared to the standard case of symmetric Rayleigh scenarios, which verifies the importance to account for fading conditions realistically. In addition, differential phase-shift keying is shown to provide adequate performance in severe fading conditions in the moderate and high-signal-to-noise ratio regimes.

The value of the location data for the Internet of Things (IoT) devices is undisputed, and today's radio technologies provide various means to obtain these data. In this paper, we shed light on the utility of the four illustrative radio-based localization techniques, including satellite navigation and the use of BLE, LoRaWAN, and Cat-NB1 communication technologies. First, we instrument a prototype device comprising all these solutions, thus confirming the feasibility of multi-radio-enabled IoT devices supporting localization. Then, we employ this prototype to empirically assess the energy utility of different localization approaches. Our results demonstrate that in terms of energy consumption, the difference between these techniques approaches five orders of magnitude. By conducting a follow-up survey of the relevant research papers, we assess other important performance metrics, such as the operating environment and the required infrastructure, as well as their effect on the localization accuracy. By combining these results, we show that multi-radio-enabled localization solutions are more flexible than those based on a single localization solution and provide space for further optimizations, especially with regards to energy consumption. Development of such devices is an crucial step toward enabling 'anytime, anywhere' localization for IoT devices. acceptedVersion

Massive Machine Type Communication (mMTC) technologies are key to addressing communication requirements of various emerging IoT applications. In this work, a multisite mMTC test network is designed and implemented in order to investigate the long-term communication quality and sensor data of LoRa and NB-IoT. This is essential for remote network maintenance operations, because it allows distinguishing communication quality defects from software/hardware failures. Moreover, it provides additional information about the communication link quality for network management. The test network is geographically scattered over a large area in Finland and experimented both in private and public networks. Measurements on LoRaWAN test networks revealed that higher SNRs and RSSIs are generally achieved for devices with lower spreading factors. Comparison of NB-IoT and LoRaWAN shows that NB-IoT has better communication quality performance. Overall, this paper provides first long-term multi-site and multi-technology mMTC measurements and corresponding performance analysis that are not available in the existing literature.

In this study, modern machine learning (ML) methods are proposed to predict the dynamic non-linear behavior of wideband RF power amplifiers (PAs). Neural networks, k-nearest neighbor, and several tree-based ML algorithms are first adapted to handle complex-valued signals and then applied to the PA modeling problem. Their modeling performance is evaluated with measured data from two base station PAs. Gradient boosting is seen to outperform the other ML approaches and to give comparable performance to the generalized memory polynomial (GMP) reference model in terms of both the normalized mean squared error (NMSE) and adjacent channel error power ratio (ACEPR). This is the first study in the open literature to consider modern ML approaches, besides neural networks, for PA behavioral modeling. acceptedVersion

The unprecedented amount of bandwidth available at the millimeter-wave band brings new opportunities for the next-generation factory automation. By supporting these frequencies, the communication technologies may significantly improve the safety and efficiency of manufacturing processes. This paper presents channel measurement results at 28 GHz in a factory environment. The primary channel properties such as path loss, delay, and angular spread are evaluated. Additionally, the distribution of the cross-polarization ratio is shown. acceptedVersion

This paper provides experimental results regarding an emerging physical-layer concept within the field of military communications, viz. the full-duplex `radio shield', by building on the recently discovered full-duplex technology that allows an individual radio device to simultaneously transmit and receive (STAR) on the same spectrum. Its basic idea is to protect the surroundings of a radio device by broadcasting powerful jamming while successfully receiving tactical transmissions on overlapping frequencies. The jamming creates a protective dome of interference around such a military full-duplex radio (MFDR). The experimental results reported herein prove that the radio shield yields a large SINR advantage against interception, even though a fully practical full-duplex radio prototype with residual self-interference is used. Moreover, we show that the prototype radio shield is capable of preventing the control of improvised explosives or rogue drones while simultaneously receiving tactical signals. Therefore, the full-duplex radio shield can give armed forces a significant technical lead over an enemy by preventing it from using the frequency band for offensive purposes. acceptedVersion

Digital predistortion (DPD) has important applications in wireless communication for smart systems, such as, for example, in Internet of Things (IoT) applications for smart cities. DPD is used in wireless communication transmitters to counteract distortions that arise from nonlinearities, such as those related to amplifier characteristics and local oscillator leakage. In this paper, we propose an algorithm-architecture-integrated framework for design and implementation of adaptive DPD systems. The proposed framework provides energy-efficient, real-time DPD performance, and enables efficient reconfiguration of DPD architectures so that communication can be dynamically optimized based on time-varying communication requirements. Our adaptive DPD design framework applies Markov Decision Processes (MDPs) in novel ways to generate optimized runtime control policies for DPD systems. We present a GPU-based adaptive DPD system that is derived using our design framework, and demonstrate its efficiency through extensive experiments. acceptedVersion

This chapter investigates how to utilize the recently developed inband full‐duplex (IBFD) technology to further improve the efficiency of wireless self‐backhauling. In particular, it considers a scenario where one macro base station (BS) serves several densely deployed access nodes (ANs), each of which serves an individual user equipment (UE). The ANs use a wireless link to backhaul the data from the UEs to the BS and vice versa. Three different self‐backhauling strategies are evaluated under Quality‐of‐Service (QoS) requirements for the UEs by determining the minimal transmit powers with which the QoS requirements can be fulfilled. Two of these strategies rely on the IBFD technology, while one of them uses time‐division duplexing (TDD) to communicate in a traditional half‐duplex (HD) manner. In addition, these AN‐based solutions are compared to a HD reference scheme where the BS communicates directly with the UEs. acceptedVersion

We study data transfer links that would enable development of low-cost technologies for increasing safety of general aviation (GA). The solution proposed here is to supplement the existing cmWave solutions with mmWave cellular signals in order to better handle interferences and to reach lower outage probabilities and higher throughputs. Moreover, cellular solutions have the advantage of re-using existing or planned infrastructure, and thus they are expected to require minor additional investments. Our article aims both at shedding some light on the terminology in the GA field and at proposing future viable data-link solutions in GA. We also survey the existing solutions, challenges, and opportunities related to the wireless communication links in GA, and we present several case studies related to the achievable outage probabilities and throughputs under rural and urban scenarios of low-altitude GA vehicles. We conclude that supplementing the existing cmWave wireless links with mmWave wireless connections is a workable solution for affordable communication links for low-altitude GA aircraft. acceptedVersion

Fifth generation mobile networks (5G) will rather supplement than replace current 4G networks by dramatically improving their bandwidth, capacity and reliability. This way, much more demanding use cases that simply are not achievable with today's networks will become reality - from home entertainment, to product manufacturing and healthcare. However, many of them rely on Internet of Things (IoT) devices equipped with low-cost transmitters and sensors that generate enormous amount of data about their environment. Therefore, due to large scale of 5G systems, combined with their inherent complexity and heterogeneity, Big Data and analysis techniques are considered as one of the main enablers of future mobile networks. In this work, we recognize 5G use cases from various application domains and list the basic requirements for their development and realization. publishedVersion

openaire: EC/H2020/704947/EU//ADVANTAG5 This paper proposes a wideband 2-5GHz LO phase-shifting generator based on two digitally controlled delay lines. The concept is verified on a two-channel beamsteering direct conversion receiver prototype implemented in 28nm CMOS. The novel generator provides both tunable phase-shifting and generation of I/Q components, achieving picosecond time resolution. The generator consumes 4.5-11.2mW and occupies 0.021mm.sq.

The use of drone-cells in 5G wireless systems is a topic of ongoing discussions in the 3GPP standardization community. A major advantage of employing drones is that they can dynamically and timely improve the capacity and coverage of cellular networks. To address this challenge, efficient network planning tools targeting spontaneous and rapidly changing scenarios for dynamic network design need to be developed. Complementing the recent studies on the optimal static drone-cell positioning for a Poisson point process of user equipment (UE) placement, we study UE distributions with correlated mobility models. We first derive the coverage metrics for static drone-cell deployments and then proceed by developing an algorithm for adaptive drone-cell navigation. Considering the mean number of covered UEs, we show that enabling drone-cell navigation improves the overall system performance. acceptedVersion

The deployment with beamforming-capable base stations in 5G New Radio (NR) requires an efficient mobility management system to reliably operate with minimum effort and interruption. In this work, we propose two artificial neural network models to optimize the cell-level and beam-level mobility management. Both models consist of convolutional, as well as dense, layer blocks. Based on current and past received power measurements, as well as positioning information, they choose the optimum serving cell and serving beam, respectively. The obtained results show that the proposed cell-level mobility model is able to sustain a strong serving cell and reduce the number of handovers by up to 94.4% compared to the benchmark solution when the uncertainty (representing shadowing, interference, etc.) is introduced to the received signal strength measurements. The proposed beam-level mobility management model is able to proactively choose and sustain the strongest serving beam, even when high uncertainty is introduced to the measurements.

Direct-conversion architectures can offer highly integrated low-cost hardware solutions to communication transceivers. However, it has been demonstrated that radio frequency (RF) impairments such as amplifier nonlinearities, phase noise, and in-phase/quadrature-phase imbalances (IQI) can lead to severe degradation of the performance of such systems. Motivated by this, the present work is devoted to the quantification and evaluation of the effects of RF IQI on wireless communications in the context of cascaded fading channels for both single-carrier and multicarrier systems. To this end, closed-form expressions are first derived for the outage probability (OP) over $N^{\ast}$ Nakagami- $m$ channels for the cases of ideal transmitter (TX) and receiver (RX), ideal TX and IQI RX, IQI TX and ideal RX, and joint TX/RX IQI. The offered expressions, along with several deduced corresponding special cases, are subsequently employed in vehicle-to-vehicle (V2V) communications to justify their importance and practical usefulness in the context of emerging communication systems. The offered analytic results are corroborated by extensive comparisons with respective results from computer simulations. It is shown that considering non-ideal RF front-ends at the TX and/or RX introduces nonnegligible errors in the OP performance that can exceed 20% under several communication scenarios. It is further demonstrated that the effects by cascaded multipath fading conditions are particularly detrimental as they typically result in considerable performance losses of around or over an order of magnitude.

In this article, we address the challenges of transmitter-receiver isolation in \emph{mobile full-duplex devices}, building on shared-antenna based transceiver architecture. Firstly, self-adaptive analog RF cancellation circuitry is required, since the capability to track time-varying self-interference coupling characteristics is of utmost importance in mobile devices. In addition, novel adaptive nonlinear DSP methods are also required for final self-interference suppression at digital baseband, since mobile-scale devices typically operate under highly nonlinear low-cost RF components. In addition to describing above kind of advanced circuit and signal processing solutions, comprehensive RF measurement results from a complete demonstrator implementation are also provided, evidencing beyond 40~dB of active RF cancellation over an 80 MHz waveform bandwidth with a highly nonlinear transmitter power amplifier. Measured examples also demonstrate the good self-healing characteristics of the developed control loop against fast changes in the coupling channel. Furthermore, when complemented with nonlinear digital cancellation processing, the residual self-interference level is pushed down to the noise floor of the demonstration system, despite the harsh nonlinear nature of the self-interference. These findings indicate that deploying the full-duplex principle can indeed be feasible also in mobile devices, and thus be one potential technology in, e.g., 5G and beyond radio systems., Comment: 18 pages, submitted for review

Energy efficiency and its optimization constitute critical tasks in the design of low-power wireless networks. This paper is devoted to the error rate analysis and energy efficiency optimization of regenerative cooperative networks in the presence of multipath fading under spatial correlation. To this end, exact and asymptotic analytic expressions are first derived for the symbol error rate (SER) of $M$ -ary quadrature amplitude and $M$ -ary phase-shift keying modulations ( $M$ -QAM and $M$ - PSK), respectively, assuming a dual-hop decode-and-forward (DF) relay system, spatially correlated Nakagami- $m$ multipath fading, and maximum ratio combining (MRC) at the destination. The derived expressions are subsequently employed in quantifying the energy consumption of the considered system, incorporating both transmit energy and the energy consumed by the transceiver circuits, and in deriving the optimal power allocation (OPA) formulation for minimizing energy consumption under certain quality-of-service (QoS) requirements. A relatively harsh path-loss (PL) model, which also accounts for realistic device-to-device communications, is adopted in numerical evaluations, and various useful insights are provided for the design of future low-energy wireless networks deployments. Indicatively, it is shown that, depending on the degree of spatial correlation, severity of fading, transmission distance, relay location, and power allocation strategy, target performance can be achieved with much overall energy reduction compared with direct transmission (DT) reference.

Radio transmitters are evolving towards digital-intensive solutions to exploit reconfigurability and benefit from CMOS process scaling. Outphasing has been identified as a suitable candidate for digital wideband transmitters. However, with recent digital-intensive outphasing transmitters the achieved performance in terms of adjacent channel leakage ratio (ACLR) has been limited. This paper identifies the sampling images of the modulating phase signal as the main factor limiting the ACLR of digital outphasing transmitters. We present a new digital interpolating phase modulator architecture, capable of providing significantly better sampling image attenuation. When evaluated in outphasing configuration with a 100 MHz OFDM signal at the carrier frequency of 2.46 GHz, and 10-bit phase resolution, the proposed solution achieves an ACLR of $-$ 59 dBc, compared to $-$ 43 dBc achievable with the phase modulator architecture utilized in state-of-the-art digital outphasing transmitters. The proposed digital interpolating phase modulator is also capable of custom carrier generation, a straightforward method for generating an arbitrary carrier frequency up to 1.25 times the phase modulator sampling rate.

Using collaborative sensors or other observing devices equipped with sectorized antennas provides a practical and low-cost solution to direction-of-arrival (DoA) and received signal strength (RSS) estimation, as well as noncooperative transmitter (TX) localization. In this paper, we study the performance and theoretical bounds of DoA/RSS estimation and localization using sectorized antennas. We first show that the sector-power measurements at an individual sensor form a sufficient statistic for DoA/RSS estimation and TX localization. Motivated by that, we then derive the Cramer–Rao bound (CRB) on DoA/RSS estimation based on sector-powers and study its asymptotic behavior. Moreover, we derive an analytical expression for the mean square error (MSE) of a practical sectorized-antenna-based DoA estimator, compare its performance to the derived CRB, and study its asymptotic properties. Next, we derive the CRB for localization based on sector-powers. The resulting CRB is a lower bound for a localization system where the DoA/RSS estimates, obtained from sector-powers at individual sensors, are fused together into a location estimate. Moreover, the CRB also covers the more general case of a localization system where the sector-powers from individual nodes are directly fused together, without an intermediate DoA/RSS estimation step. We compare the obtained CRB to a localization approach employing an intermediate DoA/RSS estimation step and observe that skipping this intermediate processing step may result in a substantially improved localization performance. Finally, we study the influence of various important system parameters, such as the number of sensors, sectors, and measurement samples, on the achievable estimation and localization performance. Overall, this paper demonstrates and quantifies the achievable DoA/RSS estimation and localization performance of sectorized antennas and provides comprehensive design guidelines for sector-power based low-complexity localization systems.

Cooperative communication has been shown to provide significant increase of transmission reliability and network capacity while expanding coverage in cellular networks. The present work is devoted to the investigation of the end-to-end performance and power allocation of a maximum-ratio-combining based regenerative multi-relay cooperative network over non-homogeneous scattering environment, which is the realistic case in many practical wireless communication scenarios. Novel analytic expressions are derived for the end-to-end symbol-error-rate of both M -ary phase-shift keying and M -ary quadrature amplitude modulation over independent and non-identically distributed generalized fading channels are given by exact analytic expressions that involve the Lauricella function and can be readily evaluated with the aid of a proposed computing algorithm. Simple analytic expressions are also derived for the corresponding symbol-error-rate at asymptotically high signal-to-noise ratios. The derived expressions are corroborated with respective results from computer simulations and are subsequently employed in formulating a sum-power optimization problem that enhances the system performance under total sum-power constraint within the multi-relay cooperative system. It is also shown that asymptotically optimum power allocation provides substantial performance gains over the corresponding equal power allocation, particularly, when the source-relay and relay-destination paths are highly unbalanced.