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Impact of reflections in enclosed mmWave wearable networks
Abstract
We study the impact of signal reflections in enclosed wireless networks of wearable devices operating at mmWave frequencies. Given the radical blockage by obstacles and people (including the user's own body) at these frequencies, surface reflections are expected to be very important contributors to the collection of an adequate amount of desired signal power. At the same time, they are also expected to substantially increase the level of interference reaching any given receiver. Our objective is to understand the interplay of these two effects in relevant enclosed settings with high user densities (e.g., commuter trains, subways, airplanes, airports, or offices) in order to help assess the viability of mmWave operation in such settings.
... In this paper, we consider only first-order reflections, i.e., single bounces off each surface. 1 From each transmitter X k there are six such reflections reaching X r 0 , which are incorporated by adding six phantom transmitters. The four walls are indexed with i = 1, . . . ...
... , 6, the images of X k are located at X i,k , the corresponding angles of incidence are θ i,k , and the reflected link distances are r i,k = X i,k − X r 0 . The coordinates of the image locations and the angles of incidence can be easily obtained as functions of the coordinates of X k and X r 0 , as detailed in Appendix A. 1 We have numerically verified that higher-order reflections, which can be incorporated by placing phantom transmitters at the corresponding image locations (cf. Fig. 2), have a minor effect on the results. ...
... Noting that the projections of the cylinders are circles on X 0 , we denote the projection of X k by X k . Then, as in [1], [17], [18], the blockages can be determined by checking whether the direct path between X k and X r 0 intersects any of the circles. Applied to the corresponding phantom transmitters, this blockage model further extends to the reflected links off the four walls and an algorithm for determining such blockages is given in Appendix C. ...
This paper investigates the feasibility of mmWave frequencies for personal networks of wireless wearable devices in enclosed settings (e.g., commuter trains, subways, airplanes, airports, or offices). At these frequencies, specular reflections off surfaces are expected to contribute intended signal power and, simultaneously, to aggravate the interference at the receivers. Meanwhile, blockages by obstacles and people---including the individuals wearing the devices---are expected to shield receivers from interference. With the aid of stochastic geometry and random shape theory, we assess the interplay of surface reflections and blockages for dense deployments of wearable networks equipped with directional antenna arrays in relevant indoor settings.
... It was also noted that the existing mmWave technologies have to be enhanced to efficiently handle the scenarios where several neighboring users' networks overlap. In [14], the effect of first order reflections for mmWave signal propagation in indoor operations of wearable networks was characterized and system performances when a user is located at the center and a corner of an indoor enclosure were evaluated using simulations. ...
... The finite dimensions of the indoor environment also play a key role in the spatial non-isotropy of system performance in indoor mmWave based wearable networks [12], [32]. Another important feature in indoor mmWave wireless systems is the predominant effect of signal reflections off the wall and ceilings [12], [14], [33]. This could potentially amplify the interference signals from another user's wearable network and thus degrade the SINR in a typical user's signal receiver. ...
... The main limitation in [32] and [34] is that the effect of wall and ceiling reflections in the metallic indoor environment was not explicitly modeled. The exact effects of first order reflections from all the six faces of a cuboidal enclosure were considered for the simulation results in [14]. This provided valuable insight into the nature of surface reflections in the indoor mmWave setup. ...
Supporting high data rate wireless connectivity among wearable devices in a dense indoor environment is challenging. This is primarily due to bandwidth scarcity when many users operate multiple devices simultaneously. The millimeter-wave (mmWave) band has the potential to address this bottleneck, thanks to more spectrum and less interference because of signal blockage at these frequencies. In this paper, we explain the potential and challenges associated with using mmWave for wearable networks. To provide a means for concrete analysis, we present a system model that admits easy analysis of dense, indoor mmWave wearable networks. We evaluate the performance of the system while considering the unique propagation features at mmWave frequencies, such as human body blockages and reflections from walls. One conclusion is that the non-isotropy of the surroundings relative to a reference user causes variations in system performance depending on the user location, body orientation, and density of the network. The impact of using antenna arrays is quantified through analytic closed-form expressions that incorporate antenna gain and directivity. It is shown that using directional antennas, positioning the transceiver devices appropriately, and orienting the human user body in certain directions depending on the user location result in gigabits-per-second achievable ergodic rates for mmWave wearable networks.
... Noting that the projections of the cylinders are circles on X 0 , we denote the projection of X k by X k . Then, as in [1], [17], [18], the blockages can be determined by checking whether the direct path between X k and X r 0 intersects any of the circles. Applied to the corresponding phantom transmitters, this blockage model further extends to the reflected links off the four walls and an algorithm for determining such blockages is given in Appendix B. ...
... Fig. 6). 1 As the center of X 0 is at (0, 0, z r 0 ), the joint PDF of x k and y k is Similarly, the individual wearing the interferer at X k , represented by the corresponding circle on X 0 , has its center D/2 + r w away from the projection X k , at an angle uniform in [0, 2π). ...
This paper establishes the feasibility of mmWave frequencies for personal networks of wireless wearable devices in enclosed settings (e.g., commuter trains, subways, airplanes, airports, or offices). At these frequencies, specular reflections off surfaces are expected to contribute to the capture of intended signal power and, simultaneously, to aggravate the interference at the receivers. Meanwhile, blockages by obstacles and people---including the individuals wearing the devices---are expected to shield receivers from interference. With the aid of stochastic geometry and random shape theory, we assess the interplay of surface reflections and blockages for dense deployments of wearable networks equipped with directional antenna arrays in relevant indoor settings.
... Challenges including that the outdoor model does not incorporate (i) the first-order reflections (from walls) that can have comparable strengths with the direct paths in certain indoor scenarios [28], and (ii) the partition losses, e.g. from inner walls, that contribute to a large fraction of the overall indoor path loss [30]. In [85], [170], given the semi-specular nature of the mmWave signal propagation, the first-order reflections were taken account by considering the walls as mirrors, and modeling the images of transmitters approximately. To simplify the analysis, the locations of the image transmitters were approximated as an independent process of the original transmitters with the same density. ...
We provide a comprehensive overview of mathematical models and analytical techniques for millimeter wave (mmWave) cellular systems. The two fundamental physical differences from conventional Sub-6GHz cellular systems are (i) vulnerability to blocking, and (ii) the need for significant directionality at the transmitter and/or receiver, which is achieved through the use of large antenna arrays of small individual elements. We overview and compare models for both of these factors, and present a baseline analytical approach based on stochastic geometry that allows the computation of the statistical distributions of the downlink signal-to-interference-plus-noise ratio (SINR) and also the per link data rate, which depends on the SINR as well as the average load. There are many implications of the models and analysis: (a) mmWave systems are significantly more noise-limited than at Sub-6GHz for most parameter configurations; (b) initial access is much more difficult in mmWave; (c) self-backhauling is more viable than in Sub-6GHz systems which makes ultra-dense deployments more viable, but this leads to increasingly interference-limited behavior; and (d) in sharp contrast to Sub-6GHz systems cellular operators can mutually benefit by sharing their spectrum licenses despite the uncontrolled interference that results from doing so. We conclude by outlining several important extensions of the baseline model, many of which are promising avenues for future research.
... Thanks to the introduction of advanced communication technologies in future fifth-generation networks (5G) [4], it will be possible for a typical user to carry up to several mobile and wearable devices [5]. These high-performance wearable devices can communicate with each other while nearby using millimeter-wave radio frequency (mmWave) technology in ultra-dense networks. ...
Lately, the extremely high frequency (EHF) band has become one of the factors enabling fifth-generation (5G) mobile cellular technologies. By offering large bandwidth, New Radio (NR) systems operating in the lower part of EHF band, called millimeter waves (mmWave), may satisfy the extreme requirements of future 5G networks in terms of both data transfer rate and latency at the air interface. The use of highly directional antennas in prospective mmWave-based NR communications systems raises an important question: are conventional two-dimensional (2D) cellular network modeling techniques suitable for 5G NR systems? To address this question, we introduced a novel, three-dimensional framework for evaluating the performance of emerging mmWave band wireless networks. The proposed framework explicitly takes into account the blockage effects of propagating mmWave radiation, the vertical and planar directivities at transceiver antennas, and the randomness of user equipment (UE), base station (BS), and blocker heights. The model allows for different levels of accuracy, encompassing a number of models with different levels of computational complexity as special cases. Although the main metric of interest in this thesis is the signal-to-interference-plus-noise ratio (SINR), the model can be extended to obtain the Shannon rate of the channel under investigation. The proposed model was numerically evaluated in different deployment cases and communication scenarios with a wide range of system parameters. We found that randomness of UE and BS heights and vertical directionality of the mmWave antennas are essential for accurate evaluation of system performance. We also showed that the results of traditional 2D models are too optimistic and greatly overestimate the actual SINR. In contrast, fixed-height models that ignore the impact of height on the probability of exposure to interference are too pessimistic. Furthermore, we evaluated the models that provide the best trade-off between computational complexity and accuracy in specific scenarios and provided recommendations regarding their use for practical assessment of mmWave-based NR systems.
... With adoption of advanced communication technology in the forthcoming 5G networks [1], the wireless community envisions that multiple handheld and wearable devices are to be placed on and around user bodies [2]. These capable devices may need to cooperate in proximity while utilizing the emerging millimeter-wave (mmWave) radios in ultra-dense scenarios to enable extremely high network capacity and achieve lower latency as compared to conventional communication under 6GHz [3]. ...
Recently, new opportunities for utilizing extremely high frequencies have become instrumental in developing fifth-generation (5G) mobile technology. The use of highly directional antennas in millimeter-wave (mmWave) bands poses an important question of whether two-dimensional modeling suffices to capture the resulting system performance. Accounting for the effects of human body blockage by mmWave transmissions, in this work we compare the performance of the conventional two-dimensional and the proposed three-dimensional modeling. With our stochastic geometry based approach, we consider the aggregate interference and signal-to-interference ratio (SIR) to be the main metrics of interest. Both counterpart models attempt to capture the inherent behavior of 5G mmWave systems by incorporating the effects of human body blockage and antenna directivity. We thus deliver a realistic numerical assessment by comparing the three-dimensional modeling with its two- dimensional projection to reveal the resulting discrepancy.
... Challenges including that the outdoor model does not incorporate (i) the first-order reflections (from walls) that can have comparable strengths with the direct paths in certain indoor scenarios [28], and (ii) the partition losses, e.g. from inner walls, that contribute to a large fraction of the overall indoor path loss [30]. In [85], [170], given the semi-specular nature of the mmWave signal propagation, the first-order reflections were taken account by considering the walls as mirrors, and modeling the images of transmitters approximately. To simplify the analysis, the locations of the image transmitters were approximated as an independent process of the original transmitters with the same density. ...
We provide a comprehensive overview of mathematical models and analytical techniques for millimeter wave (mmWave) cellular systems. The two fundamental physical differences from conventional Sub-6GHz cellular systems are (i) vulnerability to blocking, and (ii) the need for significant directionality at the transmitter and/or receiver, which is achieved through the use of large antenna arrays of small individual elements. We overview and compare models for both of these factors, and present a baseline analytical approach based on stochastic geometry that allows the computation of the statistical distributions of the downlink signal-to-interference-plus-noise ratio (SINR) and also the per link data rate, which depends on the SINR as well as the average load. There are many implications of the models and analysis: (a) mmWave systems are significantly more noise-limited than at Sub-6GHz for most parameter configurations; (b) initial access is much more difficult in mmWave; (c) self-backhauling is more viable than in Sub-6GHz systems which makes ultra-dense deployments more viable, but this leads to increasingly interference-limited behavior; and (d) in sharp contrast to Sub-6GHz systems cellular operators can mutually benefit by sharing their spectrum licenses despite the uncontrolled interference that results from doing so. We conclude by outlining several important extensions of the baseline model, many of which are promising avenues for future research.
Recently, new opportunities for utilizing the extremely high frequencies have become instrumental to design the fifthgeneration (5G) mobile technology. The use of highly directional antennas in millimeter-wave (mmWave) bands poses an important question of whether 2D modeling suffices to capture the resulting system performance accurately. In this work, we develop a novel mathematical framework for performance assessment of the emerging 3D mmWave communication scenarios, which takes into account vertical and planar directivities at both ends of a radio link, blockage effects in three dimensions, and random heights of communicating entities. We also formulate models having different levels of details and verify their accuracy for a wide range of system parameters. We show that capturing the randomness of both Tx and Rx heights as well as the vertical antenna directivities becomes crucial for accurate system characterization. The conventional planar models provide overly optimistic results that overestimate performance. For instance, the model with fixed heights that disregards the effect of vertical exposure is utterly pessimistic. Other two models, one having random heights and neglecting vertical exposure and another one characterized by fixed heights and capturing vertical exposure are less computationally expensive and can be used as feasible approximations for certain ranges of input parameters.
Wearable wireless devices (WWDs) have been emerging as an important tool for future communication and control systems. When multiple uncoordinated WWD bearers exist in close proximity, the issue of interference between cochannel transmissions presents a major challenge. In this work, we exploit the molecular absorption (MA) regions of the Terahertz band (0.1-10 THz) for deploying WWDs efficiently. While such regions are not suitable for relatively long-range transmission schemes, the fast exponential decay of signal power with distance due to MA proves to be beneficial for WWD systems in limiting the cochannel interference. Our results for a symbol rate of 1 Gsymbols/s show that 95% of the users achieve a signal-to-interference-plus-noise ratio greater than 3 dB for a typical application, even in high-density user scenarios.
The global bandwidth shortage facing wireless carriers has motivated the exploration of the underutilized millimeter wave (mm-wave) frequency spectrum for future broadband cellular communication networks. There is, however, little knowledge about cellular mm-wave propagation in densely populated indoor and outdoor environments. Obtaining this information is vital for the design and operation of future fifth generation cellular networks that use the mm-wave spectrum. In this paper, we present the motivation for new mm-wave cellular systems, methodology, and hardware for measurements and offer a variety of measurement results that show 28 and 38 GHz frequencies can be used when employing steerable directional antennas at base stations and mobile devices.
Wearable wireless devices are very likely to soon move into the mainstream of our society, led by the rapidly expanding multibillion dollar health and fitness markets. Should wearable technology sales follow the same pattern as those of smartphones and tablets, these new devices (a.k.a. wearables) will see explosive growth and high adoption rates over the next five years. It also means that wearables will need to become more sophisticated, capturing what the user sees, hears, or even feels. However, with an avalanche of new wearables, we will need to find ways to supply them with low-latency highspeed data connections to enable truly demanding use cases such as augmented reality. This is particularly true for high-density wearable computing scenarios, such as public transportation, where existing wireless technology may have difficulty supporting stringent application requirements. In this article, we summarize our recent progress in this area with a comprehensive review of current and emerging connectivity solutions for high-density wearable deployments, their relative performance, and open communication challenges.
With the explosive growth of mobile data demand, the fifth generation (5G)
mobile network would exploit the enormous amount of spectrum in the millimeter
wave (mmWave) bands to greatly increase communication capacity. There are
fundamental differences between mmWave communications and existing other
communication systems, in terms of high propagation loss, directivity, and
sensitivity to blockage. These characteristics of mmWave communications pose
several challenges to fully exploit the potential of mmWave communications,
including integrated circuits and system design, interference management,
spatial reuse, anti-blockage, and dynamics control. To address these
challenges, we carry out a survey of existing solutions and standards, and
propose design guidelines in architectures and protocols for mmWave
communications. We also discuss the potential applications of mmWave
communications in the 5G network, including the small cell access, the cellular
access, and the wireless backhaul. Finally, we discuss relevant open research
issues including the new physical layer technology, software-defined network
architecture, measurements of network state information, efficient control
mechanisms, and heterogeneous networking, which should be further investigated
to facilitate the deployment of mmWave communication systems in the future 5G
networks.
Large-scale blockages like buildings affect the performance of urban cellular
networks, especially at higher frequencies. Unfortunately, such blockage
effects are either neglected or characterized by oversimplified models in the
analysis of cellular networks. Leveraging concepts from random shape theory,
this paper proposes a mathematical framework to model random blockages and
analyze their impact on cellular network performance. Random buildings are
modeled as a process of rectangles with random sizes and orientations whose
centers form a Poisson point process on the plane. The distribution of the
number of blockages in a link is proven to be Poisson random variable with
parameter dependent on the length of the link. A path loss model that
incorporates the blockage effects is proposed, which matches experimental
trends observed in prior work. The model is applied to analyze the performance
of cellular networks in urban areas with the presence of buildings, in terms of
connectivity, coverage probability, and average rate. Analytic results show
while buildings may block the desired signal, they may still have a positive
impact on network performance since they can block significantly more
interference.
In this paper, we investigate the robustness of the 60 GHz connectivity in typical indoor environments by analyzing the outage probability. We define three realistic indoor scenarios which may host the 60 GHz networks in the future and perform simulations with a verified 3D ray tracing tool on them. In the first set of simulations, we show the impact of access unit position on the connectivity. In the next step, we show that increasing the obstacle density linearly decreases the outage probability of the 60 GHz network and this decrease is found to be sharper for certain positions of the access point. In the last step, we demonstrate the direct effect of reflective surface availability on the connectivity. A 60 GHz indoor network relying solely on the reflections in the absence of line-of-sight path is very vulnerable to outages even in moderately populated indoor environments.
This paper establishes the feasibility of mmWave frequencies for personal networks of wireless wearable devices in enclosed settings (e.g., commuter trains, subways, airplanes, airports, or offices). At these frequencies, specular reflections off surfaces are expected to contribute to the capture of intended signal power and, simultaneously, to aggravate the interference at the receivers. Meanwhile, blockages by obstacles and people---including the individuals wearing the devices---are expected to shield receivers from interference. With the aid of stochastic geometry and random shape theory, we assess the interplay of surface reflections and blockages for dense deployments of wearable networks equipped with directional antenna arrays in relevant indoor settings.
The millimeter wave (mmWave) spectrum is a strong candidate carrier frequency for access channels in fifth generation cellular networks. Unfortunately, the human body heavily attenuates mmWave signals. This paper evaluates the impact of self-body blocking (the blocking of the direct link by the handset user's body) in mmWave cellular networks using a stochastic geometric network model. A mathematical model for self-body blocking is proposed, allowing for position changes, and used to compute signal-to-interference-plus-noise ratio (SINR) distributions with two possible user association rules. The results characterize how self-body blocking impacts the SINR coverage. Even including self-body blocking, mmWave cellular systems can still outperform convention systems at lower frequencies, in terms of the achievable rate, due to the larger bandwidth.
We statistically characterize received signal power variations in the time domain caused by human activity affecting 60-GHz indoor short-range wireless links. Our approach is based on propagation measurements in indoor environments considering human activity intercepting the line-of-sight (LOS) path. It has been previously shown that the ensemble of received power levels in decibel (dB) scale cannot be modeled by a Gaussian distribution, as is the case for spatial shadowing variations. In this letter, we present a theoretical stochastic approach showing that received power variations can follow a Gaussian statistical model when considered within the time intervals of similar shadowing processes. Our model is shown to have good comparison to experimental data.
The reflection characteristics and refractive indices of
construction materials in the millimeter wave bands are needed for
development of millimeter-wave application systems such as indoor
communication systems and short-range sensing systems. Because so little
experimental data of construction materials at millimeter-wave bands has
been available, the authors have measured the reflection and
transmission coefficients of a concrete plate, plasterboard, rock wool,
a floorboard, a carpet tile, at 57.5, 78.5, and 95.9 GHz. The refractive
indices of the materials that can be modeled as a homogeneous dielectric
plate with a smooth surface were estimated by the combined use of
reflection and transmission data. The refractive indices of a concrete
plate, plasterboard, a floorboard, and rock wool at 57.5 GHz were found
to be 2.55-j0.084, 1.50-j0.01, 1.98-j0.083, and 1.26-j0.005,
respectively. These indices showed little frequency dependence in the
measured frequency range, except for that of the floorboard, which
varied about 10%. The authors also measured the reflection
characteristics of materials with inhomogeneous structures or rough
surfaces, and found that the specular reflection from a concrete plate
and a floorboard can be reduced significantly by covering them with
carpet tiles with rough surfaces