Showing papers on "Multipath propagation published in 2017"

Downlink Coverage Analysis for a Finite 3-D Wireless Network of Unmanned Aerial Vehicles

Abstract: In this paper, we consider a finite network of unmanned aerial vehicles serving a given region. Modeling this network as a uniform binomial point process, we derive the downlink coverage probability of a reference receiver located at an arbitrary position on the ground assuming Nakagami- $m$ fading for all wireless links. The reference receiver is assumed to connect to its closest transmitting node as is usually the case in cellular systems. After deriving the distribution of distances from the reference receiver to the serving and interfering nodes, we derive an exact expression for downlink coverage probability in terms of the derivative of Laplace transform of interference power distribution. In the downlink of this system, it is not unusual to encounter scenarios in which the line-of-sight component is significantly stronger than the reflected multipath components. To emulate such scenarios, we also derive the coverage probability in the absence of fading from the results of Nakagami- $m$ fading by taking the limit $m \to \infty$ . Using asymptotic expansion of incomplete gamma function, we concretely show that this limit reduces to a redundant condition. Consequently, we derive an accurate coverage probability approximation for this case using dominant interferer-based approach in which the effect of dominant interferer is exactly captured and the residual interference from other interferers is carefully approximated. We then derive the bounds of the approximate coverage probability using Berry-Esseen theorem. Our analyses reveal several useful trends in coverage probability as a function of height of the transmitting nodes and the location of reference receiver on the ground.

Direct Localization for Massive MIMO

Abstract: Large-scale MIMO systems are well known for their advantages in communications, but they also have the potential for providing very accurate localization, thanks to their high angular resolution. A difficult problem arising indoors and outdoors is localizing users over multipath channels. Localization based on angle of arrival (AOA) generally involves a two-step procedure, where signals are first processed to obtain a user's AOA at different base stations, followed by triangulation to determine the user's position. In the presence of multipath, the performance of these methods is greatly degraded due to the inability to correctly detect and/or estimate the AOA of the line-of-sight (LOS) paths. To counter the limitations of this two-step procedure which is inherently suboptimal, we propose a direct localization approach in which the position of a user is localized by jointly processing the observations obtained at distributed massive MIMO base stations. Our approach is based on a novel compressed sensing framework that exploits channel properties to distinguish LOS from non-LOS signal paths, and leads to improved performance results compared to previous existing methods.

Strata: Fine-Grained Acoustic-based Device-Free Tracking

Abstract: Next generation devices, such as virtual reality (VR), augmented reality (AR), and smart appliances, demand a simple and intuitive way for users to interact with them. To address such needs, we develop a novel acoustic based device-free tracking system, called Strata, to enable a user to interact with a nearby device by simply moving his finger. In Strata, a mobile (e.g., smartphone) transmits known audio signals at inaudible frequency, and analyzes the received signal reflected by the moving finger to track the finger location. To explicitly take into account multipath propagation, the mobile estimates the channel impulse response (CIR), which characterizes signal traversal paths with different delays. Each channel tap corresponds to the multipath effects within a certain delay range. The mobile selects the channel tap corresponding to the finger movement and extracts the phase change of the selected tap to accurately estimate the distance change of a finger. Moreover, it estimates the absolute distance of the finger based on the change in CIR using a novel optimization framework. We then combine the absolute and relative distance estimates to accurately track the moving target. We implement our tracking system on Samsung Galaxy S4 mobile phone. Through micro-benchmarks and user studies, we show that our system achieves high tracking accuracy and low latency without extra hardware.

A Flexible Millimeter-Wave Channel Sounder With Absolute Timing

Abstract: This paper presents a novel ultrawideband wireless spread spectrum millimeter-wave (mmWave) channel sounder that supports both a wideband sliding correlator mode and a realtime spread spectrum mode, also known as wideband correlation or direct correlation. Both channel sounder modes are capable of absolute propagation delay (time of flight) measurements with up to 1 GHz of radio frequency null-to-null bandwidth, and can measure multipath with a 2-ns time resolution. The sliding correlator configuration facilitates long-distance measurements with angular spread and delay spread for up to 185 dB of maximum measurable path loss. The real-time spread spectrum mode is shown to support short-range, small-scale temporal, and Doppler measurements (minimum snapshot sampling interval of 32.753 μs) with a substantial dynamic fading range of 40 dB for human blockage and dynamic urban scenarios. The channel sounder uses field programmable gate arrays, analog-to-digital converters, digital-to-analog converters, and low-phase-noise rubidium standard references for frequency/time synchronization and absolute time delay measurements. Using propagation theory, several methods are presented here to calibrate and verify the accuracy of the channel sounder, and an improved diffraction model for human blockage, based on the METIS model but now including directional antenna gains, is developed from measurements using the channel sounder. The mmWave channel sounder described here may be used for accurate spatial and temporal raytracing calibration, to identify individual multipath components, to measure antenna patterns, for constructing spatial profiles of mmWave channels, and for developing statistical channel impulse response models in time and space.

Millimeter-Wave Channel Measurements and Analysis for Statistical Spatial Channel Model in In-Building and Urban Environments at 28 GHz

Abstract: The millimeter-wave (mm-wave) band will be a key component of fifth-generation (5G) wireless communication systems. This paper presents radio propagation measurements and analysis investigating the wideband directional channel characteristics of the mm-wave transmission for in-building and urban cellular communication systems in the 28-GHz band. Based on the measurements, we analyze and model the spatio-temporal channel characteristics such as multipath delay, angular statistics, and path loss. In particular we investigate the clustering of the multipath components, and investigate both the intra-cluster and inter-cluster distributions. Based on these investigations, we present a complete channel model suitable for system simulations in the in-building and urban environments.

Inverse Multipath Fingerprinting for Millimeter Wave V2I Beam Alignment

Abstract: Efficient beam alignment is a crucial component in millimeter wave systems with analog beamforming, especially in fast-changing vehicular settings. This paper proposes a position-aided approach where the vehicle's position (e.g., available via GPS) is used to query the multipath fingerprint database, which provides prior knowledge of potential pointing directions for reliable beam alignment. The approach is the inverse of fingerprinting localization, where the measured multipath signature is compared to the fingerprint database to retrieve the most likely position. The power loss probability is introduced as a metric to quantify misalignment accuracy and is used for optimizing candidate beam selection. Two candidate beam selection methods are developed, where one is a heuristic while the other minimizes the misalignment probability. The proposed beam alignment is evaluated using realistic channels generated from a commercial ray-tracing simulator. Using the generated channels, an extensive investigation is provided, which includes the required measurement sample size to build an effective fingerprint, the impact of measurement noise, the sensitivity to changes in traffic density, and beam alignment overhead comparison with IEEE 802.11ad as the baseline. Using the concept of beam coherence time, which is the duration between two consecutive beam alignments, and parameters of IEEE 802.11ad, the overhead is compared in the mobility context. The results show that while the proposed approach provides increasing rates with larger antenna arrays, IEEE 802.11ad has decreasing rates due to the larger beam training overhead that eats up a large portion of the beam coherence time, which becomes shorter with increasing mobility.

Compact Inband Full-Duplex Relays With Beyond 100 dB Self-Interference Suppression: Enabling Techniques and Field Measurements

Abstract: 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.

GNSS multipath detection using a machine learning approach

Abstract: Insufficient localization accuracy of global navigation satellite system (GNSS) receivers is one of the challenges to implement advanced intelligent transportation system in highly urbanized areas. Multipath and non-line-of-sight (NLOS) effects strongly deteriorate GNSS positioning performance. This paper aims to train a classifier by supervised machine learning to separate the type of GNSS pseudorange measurement into three categories, clean, multipath and NLOS. Several features obtained or calculated from the GNSS raw data are evaluated. This paper also proposes a new feature to indicate the consistency between measurements of pseudorange and Doppler shift. According to the experiment result, about 75% of classification accuracy can be achieved using a support vector machine (SVM) classifier trained by the proposed feature and received signal strength.

Secure Transmissions in Millimeter Wave Systems

Abstract: Exploiting millimeter wave is an effective way to meet the data traffic demand in the 5G wireless communication system. In this paper, we study secure transmissions under slow fading channels with multipath propagation in millimeter wave systems. Concerning the new propagation characteristics of millimeter wave, we investigate three transmission schemes, namely, maximum ratio transmitting (MRT) beamforming, artificial noise (AN) beamforming, and partial MRT (PMRT) beamforming. We evaluate the secrecy performance by analyzing both the secrecy outage probability (SOP) and the secrecy throughput for each scheme. Particularly, for the AN scheme, we derive a closed-form expression for the optimal power allocation ratio of the information signal power to the total transmit power that minimizes the SOP, as well as obtain an explicit solution on the optimal transmission parameters that maximize the secrecy throughput. By comparing the secrecy performances achieved by different strategies, we demonstrate that the secrecy performance of the millimeter wave system is significantly influenced by the relationship between the legitimate user’s and the eavesdropper’s spatially resolvable paths, which is different from the wireless systems with statistically independent channel models. In the absence of the common path between the legitimate user and the eavesdropper, MRT beamforming is the best scheme. In the presence of common paths, AN beamforming and PMRT beamforming show their respective superiorities depending on the transmit power and the number of common paths. Numerical results are provided to verify our theoretical analysis.

Multipath Cooperative Communications Networks for Augmented and Virtual Reality Transmission

Abstract: Augmented and/or virtual reality (AR/VR) are emerging as one of the main applications in future fifth-generation (5G) networks. To meet the requirements of lower latency and massive data transmission in AR/VR applications, a solution with software-defined networking architecture is proposed for 5G small cell networks. On this basis, a multipath cooperative route (MCR) scheme is proposed to facilitate the AR/VR wireless transmissions in 5G small cell networks, in which the delay of the MCR scheme is analytically studied. Furthermore, a service effective energy (SEE) optimization algorithm is developed for AR/VR wireless transmission in 5G small cell networks. Simulation results indicate that both the delay and SEE of the proposed MCR scheme outperform the delay and SEE of the conventional single-path route scheme in 5G small cell networks.

Analysis of the Performance Enhancement of MIMO Systems Employing Circular Polarization

Abstract: The advantages of adopting circular polarization in multiple-input-multiple-output (MIMO) systems are illustrated for both line-of-sight (LOS) and multipath propagation. More in detail, an analysis of the MIMO performance attainable by employing orthogonal circularly polarized (CP) radiators with respect to orthogonal linearly polarized (LP) ones, has been addressed. At first, an accurate analysis is presented aimed at the evaluation of the channel matrix by comprehensively including also the effects of the antenna in LOS condition. In particular, the channel matrix has been calculated as a function of the antenna parameters and orientation, demonstrating that CP radiators are capable of obtaining better average values of the matrix eigenvalues with respect to LP ones. The analysis is therefore completed by evaluating the characteristics of a CP MIMO system operating in indoor environment representing this latter a more challenging condition where multipath propagation occurs. In this latter case, some meaningful numerical experiments have been performed by using a reliable ray-tracing solver, followed by a measurements campaign conducted in a real environment for validation purposes. Measurements, which are in good agreement with simulations, confirm the benefits of adopting circular polarization in MIMO systems with respect to LP.

Achievable Rate and Energy Efficiency of Hybrid and Digital Beamforming Receivers With Low Resolution ADC

Abstract: For 5G, it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omnidirectional coverage with a similar effective antenna aperture compared with the state-of-the-art cellular systems, an antenna array is required at both the mobile and base stations. Due to the large bandwidth, the analog front-end of the receiver with a large number of antennas becomes especially power hungry. Two main solutions exist to reduce the power consumption: Hybrid BeamForming (HBF) and Digital BeamForming (DBF) with low resolution Analog to Digital Converters (ADCs). An HBF system can also be combined with low resolution ADCs. This paper compares the spectral and energy efficiency based on the RF-frontend configuration. A channel with multipath propagation is used. In contrast to previous publication, we take the spatial correlation of the quantization noise into account. We show that the low resolution ADC DBF is robust to small Automatic Gain Control (AGC) imperfections. We showed that in the low SNR regime, the performance of DBF even with 1–2 bit resolution outperforms HBF. If we consider the relationship of spectral and energy efficiency, DBF with 3–5 bit resolution achieves the best ratio of spectral efficiency per power consumption of the RF receiver frontend over a wide SNR range. The power consumption model is based on components reported in the literature.

DOA Estimation for Coherently Distributed Sources Considering Circular and Noncircular Signals in Massive MIMO Systems

Abstract: In mobile communication, the signal that a base station received cannot be regarded as a point source anymore because of the multipath propagation. A distributed source model is more suitable for the realistic scenarios. In this paper, an approach of direction-of-arrival (DOA) estimation is proposed for coherently distributed (CD) sources consisting of circular and noncircular signals in a massive or large-scale multiple-input multiple-output system. The noncircular characteristic can improve the performance of DOA estimation. However, most algorithms are not suitable for DOA estimation where circular and noncircular signals coexist. Based on the analysis of constraint conditions satisfied by the steering vector of mixed signals, a multiple signal classification (MUSIC) like approach is proposed for the DOA estimation of CD sources consisting of circular and noncircular signals. On the conditions of low signal-to-noise ratio, small snapshot numbers, and large source numbers, the pseudopeaking may appear. This phenomenon has been analyzed, and a modified MUSIC-like approach is proposed. Simulation results demonstrate that both two proposed algorithms can estimate more sources than the number of sensors. The estimation performances of the two proposed algorithms outperform the traditional MUSIC algorithm.

A Stochastic Geometric Analysis of Device-to-Device Communications Operating Over Generalized Fading Channels

Abstract: Device-to-device (D2D) communications are now considered an integral part of future 5G networks, which will enable direct communication between user equipments and achieve higher throughputs than conventional cellular networks, but with the increased potential for co-channel interference. The physical channels, which constitute D2D communications, can be expected to be complex in nature, experiencing both line-of-sight (LOS) and non-LOS conditions across closely located D2D pairs. In addition to this, given the diverse range of operating environments, they may also be subject to clustering of the scattered multipath contribution, i.e. , propagation characteristics which are quite dissimilar to conventional Rayleigh fading environments. To address these challenges, we consider two recently proposed generalized fading models, namely $\kappa$ - $\mu$ and $\eta$ - $\mu$ , to characterize the fading behavior in D2D communications. Together, these models encompass many of the most widely utilized fading models in the literature such as Rayleigh, Rice (Nakagami- $n$ ), Nakagami- $m$ , Hoyt (Nakagami- $q$ ), and One-sided Gaussian. Using stochastic geometry, we evaluate the spectral efficiency and outage probability of D2D networks under generalized fading conditions and present new insights into the tradeoffs between the reliability, rate, and mode selection. Through numerical evaluations, we also investigate the performance gains of D2D networks and demonstrate their superiority over traditional cellular networks.

Secret Key Generation Based on Estimated Channel State Information for TDD-OFDM Systems Over Fading Channels

Abstract: One of the fundamental problems in cryptography is the generation of a common secret key between two legitimate parties to prevent eavesdropping In this paper, we propose an information-theoretic secret key generation (SKG) method for time division duplexing (TDD)-based orthogonal frequency-division multiplexing (OFDM) systems over multipath fading channels By exploring physical layer properties of the wireless medium, ie, the reciprocity, randomness, and privacy features of the radio channel, an SKG method is proposed to maximize the number of secret bits given a target secret key disagreement ratio (SKDR) In the proposed SKG method, the phase information of the estimated channel state information (CSI) is distilled for SKG, and a special guard band (GB) scheme is designed to achieve the target SKDR with a small phase information loss The proposed GB consists of both the amplitude GB (AGB) and phase GB (PGB), where the AGB is determined by the average signal-to-interference plus noise ratio (SINR), whereas the PGB adapts itself to the instantaneous SINR and thus incurs a smaller phase information loss in the higher SINR region Analyses show that this GB scheme trades off a small loss of channel phase information for a better SKDR performance, and achieves a much larger number of quantization levels for a given SKDR due to the fact that the PGB decreases quickly as the SINR increases Based on the performance analysis on the SKDR, the average secret key length, the phase information loss percentage (PILP), and the optimal GB and quantization level of the adaptive quantizor are derived for a given target SKDR Both analytical and simulation results are presented to demonstrate the superiority of the proposed scheme for TDD-OFDM systems over frequency-selective fading channels

Single Anchor Localization and Orientation Performance Limits using Massive Arrays: MIMO vs. Beamforming

Abstract: Next generation cellular networks will experience the combination of femtocells, millimeter-wave (mm-wave) communications and massive antenna arrays. Thanks to the beamforming capability as well as the high angular resolution provided by massive arrays, only one single access point (AP) acting as an anchor node could be used for localization estimation, thus avoiding over-sized infrastructures dedicated to positioning. In this context, our paper aims at investigating the localization and orientation performance limits employing massive arrays both at the AP and mobile side. Thus, we first asymptotically demonstrate the tightness of the Cramer-Rao bound (CRB) in massive array regime, and in the presence or not of multipath. Successively, we propose a comparison between MIMO and beamforming in terms of array structure, time synchronization error and multipath components. Among different array configurations, we consider also random weighting as a trade-off between the high diversity gain of MIMO and the high directivity guaranteed by phased arrays. By evaluating the CRB for the different array configurations, results show the interplay between diversity and beamforming gain as well as the benefits achievable by varying the number of array elements in terms of localization accuracy.

Low altitude UAV propagation channel modelling

Abstract: The Unmanned Aerial Vehicle (UAV) is going to play an important role in fifth generation communication systems for establishing seamless coverage in various scenarios due to its low-cost and flexibility Understanding the UAV wireless channels is the basis for its application In this paper, a recently conducted measurement campaign for the UAV wireless propagation channel in a suburban scenario in Madrid is introduced Based on the Universal Software-defined Radio Peripheral (USRP) equipment, narrowband measurements at frequency of 576 GHz and broadband measurements at frequency of 1817 GHz are performed The path loss, K-factor, power delay profiles (PDPs), multipath components (MPCs) and root-mean-square (RMS) delay spreads (DSs) are presented

Impulse Radio Ultra-Wideband Communications for Localization and Tracking of Human Body and Limbs Movement for Healthcare Applications

Abstract: Accurate and precise motion tracking of limbs and human subjects has technological importance in various healthcare applications. The use of impulse radio-ultra wideband technology (IR-UWB) technology due its inherent properties is of recent interest for high-accuracy localization. This paper presents experimental investigations and analysis of indoor human body localization and tracking of limb movements in 3-D based on IR-UWB technology using compact and cost-effective body-worn antennas. The body-centric wireless channel characterization has been analyzed in detail using parameters such as path loss magnitude, number of multipath components, rms delay spread, signal amplitude, and Kurtosis with the main focus to differentiate between line-of-sight (LOS) and non-LOS situations. Fidelity of the received signal is also calculated for different activities and antenna positions to study the pulse preserving nature of the UWB antenna, when it is placed on the human body. The results reported in this paper have high localization accuracy with 90% in the range from 0.5 to 2.5 cm using simple and cost-effective techniques which is comparable to the results obtained by the standard optical motion capture system.

On the short-term temporal variations of GNSS receiver differential phase biases

Abstract: As a first step towards studying the ionosphere with the global navigation satellite system (GNSS), leveling the phase to the code geometry-free observations on an arc-by-arc basis yields the ionospheric observables, interpreted as a combination of slant total electron content along with satellite and receiver differential code biases (DCB). The leveling errors in the ionospheric observables may arise during this procedure, which, according to previous studies by other researchers, are due to the combined effects of the code multipath and the intra-day variability in the receiver DCB. In this paper we further identify the short-term temporal variations of receiver differential phase biases (DPB) as another possible cause of leveling errors. Our investigation starts by the development of a method to epoch-wise estimate between-receiver DPB (BR-DPB) employing (inter-receiver) single-differenced, phase-only GNSS observations collected from a pair of receivers creating a zero or short baseline. The key issue for this method is to get rid of the possible discontinuities in the epoch-wise BR-DPB estimates, occurring when satellite assigned as pivot changes. Our numerical tests, carried out using Global Positioning System (GPS, US GNSS) and BeiDou Navigation Satellite System (BDS, Chinese GNSS) observations sampled every 30 s by a dedicatedly selected set of zero and short baselines, suggest two major findings. First, epoch-wise BR-DPB estimates can exhibit remarkable variability over a rather short period of time (e.g. 6 cm over 3 h), thus significant from a statistical point of view. Second, a dominant factor driving this variability is the changes of ambient temperature, instead of the un-modelled phase multipath.

Indoor Multipath Assisted Angle of Arrival Localization

Abstract: Indoor radio frequency positioning systems enable a broad range of location aware applications. However, the localization accuracy is often impaired by Non-Line-Of-Sight (NLOS) connections and indoor multipath effects. An interesting evolution in widely deployed communication systems is the transition to multi-antenna devices with beamforming capabilities. These properties form an opportunity for localization methods based on Angle of Arrival (AoA) estimation. This work investigates how multipath propagation can be exploited to enhance the accuracy of AoA localization systems. The presented multipath assisted method resembles a fingerprinting approach, matching an AoA measurement vector to a set of reference vectors. However, reference data is not generated by labor intensive site surveying. Instead, a ray tracer is used, relying on a-priori known floor plan information. The resulting algorithm requires only one fixed receiving antenna array to determine the position of a mobile transmitter in a room. The approach is experimentally evaluated in LOS and NLOS conditions, providing insights in the accuracy and robustness. The measurements are performed in various indoor environments with different hardware configurations. This leads to the conclusion that the proposed system yields a considerable accuracy improvement over common narrowband AoA positioning methods, as well as a reduction of setup efforts in comparison to conventional fingerprinting systems.

Three-Dimensional End-to-End Modeling and Analysis for Graphene-Enabled Terahertz Band Communications

Abstract: Terahertz (0.1–10 THz) band communication is envisioned as a key technology to satisfy the increasing demand for ultra-high-speed wireless links. In this paper, a 3-D end-to-end model in the THz band is developed that includes the graphene-based reflectarray antenna response and the 3-D multipath propagation phenomena. In particular, the architecture of a graphene-based reflectarray antenna is investigated, and the 3-D radiation pattern is modeled. Moreover, a 3-D THz channel model based on ray tracing techniques is developed as a superposition of the line-of-sight (LoS), reflected, and scattered paths. By using the developed end-to-end model, an in-depth analysis on the 3-D channel characteristics is carried out. Specifically, the gain at the main beam of the graphene-based reflectarray antenna is 18 dB, and the 3-dB beamwidths in the elevation and the azimuth planes are $7^\circ$ and $10^\circ$ , respectively. The use of the reflectarray leads to a decrease of the delay spread from 1.23 to 0.099 ns, which suggests that the resulting coherence bandwidth reaches 2 GHz. Moreover, the root mean square (rms) angular spread in the elevation plane is less than $0.12^\circ$ , which is one tenth of that without beamforming. Furthermore, the wideband channel capacity at THz frequencies is characterized, which can be enhanced with a larger transmit power, a lower operating frequency, a larger bandwidth, and a higher beamforming gain. Finally, the beamforming gain enabled by the reflectarray antenna is compromised at the cost of the strict beam alignment, and the deviation needs to be smaller than $11^\circ$ . The provided analysis and the channel physical parameters lay out the foundation and are particularly useful for realizing reliable and efficient ultra-high-speed wireless communications in the THz band.

Using DecaWave UWB transceivers for high-accuracy multipath-assisted indoor positioning

Abstract: Robust indoor positioning and location awareness at a sub-meter accuracy typically require highly accurate radio channel measurements to extract precise time-of-flight measurements. Emerging UWB transponders like the DecaWave DW1000 chip offer to estimate channel impulse responses with reasonably high bandwidth and excellent clock stability, yielding a ranging precision below 10 cm. The competitive pricing of these chips allows scientists and engineers for the first time to exploit the benefits of UWB for indoor positioning without the need for a massive investment into experimental equipment. This work investigates the performance of the DW1000 chip concerning position related information that can be extracted from its channel impulse response measurements. We evaluate the signal-to-interference-plus-noise ratio of the line-of-sight and reflected multipath components which is a key parameter determining the Cramer-Rao lower bound on the ranging error variance. We propose a novel and highly efficient positioning algorithm, which requires information from a single anchor only. Results demonstrate reliable and robust positioning at an accuracy below 0.5 m.

Holography of Wi-fi Radiation

Abstract: Wireless data transmission systems such as wi-fi or Bluetooth emit coherent light-electromagnetic waves with a precisely known amplitude and phase. Propagating in space, this radiation forms a hologram-a two-dimensional wave front encoding a three-dimensional view of all objects traversed by the light beam. Here we demonstrate a scheme to record this hologram in a phase-coherent fashion across a meter-sized imaging region. We recover three-dimensional views of objects and emitters by feeding the resulting data into digital reconstruction algorithms. Employing a digital implementation of dark-field propagation to suppress multipath reflection, we significantly enhance the quality of the resulting images. We numerically simulate the hologram of a 10-m-sized building, finding that both localization of emitters and 3D tomography of absorptive objects could be feasible by this technique.

Programmable Radio Environments for Smart Spaces

Abstract: Smart spaces, such as smart homes and smart offices, are common Internet of Things (IoT) scenarios for building automation with networked sensors. In this paper, we suggest a different notion of smart spaces, where the radio environment is programmable to achieve desirable link quality within the space. We envision deploying low-cost devices embedded in the walls of a building to passively reflect or actively transmit radio signals. This is a significant departure from typical approaches to optimizing endpoint radios and individual links to improve performance. In contrast to previous work combating or leveraging per-link multipath fading, we actively reconfigure the multipath propagation. We sketch design and implementation directions for such a programmable radio environment, highlighting the computational and operational challenges our architecture faces. Preliminary experiments demonstrate the efficacy of using passive elements to change the wireless channel, shifting frequency "nulls" by nine Wi-Fi subcarriers, changing the 2 x 2 MIMO channel condition number by 1.5 dB, and attenuating or enhancing signal strength by up to 26 dB.

Measurement-Based Massive MIMO Channel Modeling for Outdoor LoS and NLoS Environments

Abstract: In this paper, a measurement campaign for massive multiple-input multiple-output (MIMO) channel characterization in both line-of-sight (LoS) and non-LoS outdoor environments is introduced. The measurements are conducted at the center frequency of 15 GHz with a bandwidth of 4 GHz. A virtual $40\times 40$ planar antenna array formed by stepping a vertically-polarized bi-conical omni-directional antenna (ODA) along regularly-spaced grids is used in the receiver (Rx). The transmitter is equipped with a single ODA. To investigate channel variations over the Rx array, this 1600-element Rx array is split into multiple $7\times 7$ sub-arrays, and a maximum-likelihood parameter estimation algorithm implemented using the space-alternating generalized expectation-maximization principle is applied to extracting multipath components (MPCs) from sub-array outputs. The spatial variability of $K$ -factor, composite channel spreads in delay, azimuth, and elevation of arrival are investigated. Based on the estimated MPCs’ parameters, multipath clusters are identified and associated across the array to find the so-called spatial-stationary (SS) clusters. From several hundreds of SS-clusters extracted, we establish a stochastic model for their life distances in horizontal and vertical directions, two-dimensional (2-D) life region, and variations of cluster spreads. These findings are important for massive MIMO channel modeling in the cases, where 2-D large-scale arrays are considered.

Testing vehicle-to-vehicle visible light communications in real-world driving scenarios

Abstract: Vehicle-to-vehicle (V2V) communications utilizing visible light communications (VLC) have become an attractive solution to provide a reliable and highly scalable communication link In this paper, we perform the first-ever real-world driving test of a V2V VLC prototype, with two cars driving on a highway in a car-following setting for a total of 108 kilometers Utilizing a number of software and hardware techniques and OFDM waveforms, our system can reliably achieve a working range of 45 meters Experimental results show that multipath propagation has little effects to the error performance, while the distance and the angle are the two main factors determining the received power and thus the error performance They also demonstrate extremely stable links, which generates no reception error for up to 50 seconds in many occasions Finally, we also investigate a number of specific cases which cause reception errors, such as another vehicle overtaking the receiver and interference from nearby LED signage We hope the lessons learned from this study can provide guidelines to future system designs

A Study on the Link Level Performance of Advanced Multicarrier Waveforms Under MIMO Wireless Communication Channels

Abstract: This paper studies the link level performance of orthogonal frequency division multiplexing (OFDM) and four other advanced waveforms, namely, filtered OFDM (F-OFDM), universal-filtered OFDM (UF-OFDM), filter bank multicarrier (FBMC) and generalized frequency division multiplexing (GFDM). Compared to OFDM, the two filtered variants achieve lower out-of-band (OOB) emissions and can mostly preserve the conventional OFDM-based transceiver design. For the latter two non-orthogonal waveforms, this paper proposes a low complexity implementation of minimum mean square error equalization to jointly tackle the channel and waveform-induced interference. On this basis, the benefits of FBMC and GFDM can be exploited with complexity comparable to the former (quasi-) orthogonal waveforms. The observed benefits include lower peak-to-average power ratio (PAPR) and smaller frame error rate (FER) under challenging doubly dispersive multiple-input multiple-output (MIMO) fading channels. Additionally, linear filtering of FBMC offers an ultra-low OOB emission, while a good compromise in the usage of time and frequency resources can be achieved by circular filtering of GFDM. In the comparison of offset quadrature amplitude modulation (OQAM) versus QAM for non-orthogonal waveforms, OQAM can offer lower PAPR, while smaller FERs can be achieved by QAM in rich multipath fading channels.

A Comprehensive Analysis of 5G Heterogeneous Cellular Systems Operating Over $\kappa$ – $\mu$ Shadowed Fading Channels

Abstract: Emerging cellular technologies such as those proposed for use in 5G communications will accommodate a wide range of usage scenarios with diverse link requirements. This will necessitate operation over a versatile set of wireless channels ranging from indoor to outdoor, from line-of-sight (LOS) to non-LOS, and from circularly symmetric scattering to environments which promote the clustering of scattered multipath waves. Unfortunately, many of the conventional fading models lack the flexibility to account for such disparate signal propagation mechanisms. To bridge the gap between theory and practical channels, we consider $\kappa$ – $\mu$ shadowed fading, which contains as special cases the majority of the linear fading models proposed in the open literature. In particular, we propose an analytic framework to evaluate the average of an arbitrary function of the signal-to-noise-plus-interference ratio (SINR) over $\kappa$ – $\mu$ shadowed fading channels by using an orthogonal expansion with tools from stochastic geometry. Using the proposed method, we evaluate the spectral efficiency, moments of the SINR, and outage probability of a $K$ -tier heterogeneous cellular network with $K$ classes of base stations (BSs), differing in terms of the transmit power, BS density, shadowing, and fading characteristics. Building upon these results, we provide important new insights into the network performance of these emerging wireless applications while considering a diverse range of fading conditions and link qualities.

Low Delay Random Linear Coding and Scheduling Over Multiple Interfaces

Abstract: High-performance real-time applications, expected to be of importance in the upcoming 5G era, such as virtual and augmented reality or tele-presence, have stringent requirements on throughput and per-packet in-order delivery delay . Use of multipath transport is gaining momentum for supporting these applications. However, building an efficient, low latency multipath transfer mechanism remains highly challenging. The primary reason for this is that the delivery delay along each path is typically uncertain and time-varying. When the transmitter ignores the stochastic nature of the path delays, then packets sent along different paths frequently arrive out of order and need to be buffered at the receiver to allow in-order delivery to the application. In this paper, we propose Stochastic Earliest Delivery Path First (S-EDPF), a generalization of EDPF which takes into account uncertainty and time-variation in path delays yet has low-complexity suited to practical implementation. Moreover, we integrate a novel low-delay Forward Error Correction (FEC) scheme into S-EDPF in a principled manner by deriving the optimal schedule for coded packets across multiple paths. Finally, we demonstrate, both analytically and empirically, that S-EDPF is effective at mitigating the delay impact of reordering and loss in multipath transport protocols, offering substantial performance gains over the state of the art.

Accelerating Multipath Transport Through Balanced Subflow Completion

Abstract: Simultaneously using multiple network paths (e.g., WiFi and cellular) is an attractive feature on mobile devices. A key component in a multipath system such as MPTCP is the scheduler, which determines how to distribute the traffic over multiple paths. In this paper, we propose DEMS, a new multipath scheduler aiming at reducing the data chunk download time. DEMS consists of three key design decisions: (1) being aware of the chunk boundary and strategically decoupling the paths for chunk delivery, (2) ensuring simultaneous subflow completion at the receiver side, and (3) allowing a path to trade a small amount of redundant data for performance. We have implemented DEMS on smartphones and evaluated it over both emulated and real cellular/WiFi networks. DEMS is robust to diverse network conditions and brings significant performance boost compared to the default MPTCP scheduler (e.g., median download time reduction of 33%--48% for fetching files and median loading time reduction of 6%--43% for fetching web pages), and even more benefits compared to other state-of-the-art schedulers.