=Paper= {{Paper |id=Vol-1730/p09 |storemode=property |title=WiFi Field Monitoring for E-Pollution Detection |pdfUrl=https://ceur-ws.org/Vol-1730/p09.pdf |volume=Vol-1730 |authors=Tatjana Sidekerskiene,Robertas Damaševičius |dblpUrl=https://dblp.org/rec/conf/system/SidekerskieneD16 }} ==WiFi Field Monitoring for E-Pollution Detection== https://ceur-ws.org/Vol-1730/p09.pdf
          WiFi Field Monitoring for E-Pollution Detection

                       Tatjana Sidekerskienė                                               Robertas Damaševičius
                Department of Applied Mathematics                                     Department of Software Engineering
                 Kaunas University of Technology                                       Kaunas University of Technology
                         Kaunas, Lithuania                                                     Kaunas, Lithuania
                   tatjana.sidekerskiene@ktu.lt                                          robertas.damasevicius@ktu.lt


    Abstract— The paper presents an outline of the development          systems, can penetrate thick concrete block walls. People
of WiFi field monitoring maps using the Internet-of-Things (IoT)        working in offices or students studying in schools are exposed
technology. The negative impacts of signals generated by the            to 1600 hours of WiFi radiation during an academic year. This
WiFi access points on health and measurement metrics are                value is larger than the 1640 hours of cell phone use in the
discussed. The experimental system for collecting WiFi signal           INTERPHONE study associated with a 40% increase in brain
data is presented. Finally, the construction of WiFi signal             tumors (glioma) [3]. In 2011, the radio frequencies of EMF
strength heatmap is discussed and some preliminary results using        were qualified by IARC and WHO as possibly increasing the
a combination of real worlds and simulated data are presented.
                                                                        risk of malignant brain tumor [4]. Rats exposed to pulsed
                                                                        digital WiFi frequencies (2.4 GHz) for a long-term (25
   Keywords—WiFi; field monitoring, e-health, m-health, s-
health, e-pollution.
                                                                        months), had a higher rate of both primary and metastatic
                                                                        cancers [5] though other studies did not confirm these findings
                                                                        [6, 7].
                          I.   INTRODUCTION1
                                                                            WiFi has been linked to electromagnetic hypersensitivity
    Recently there has been a significant increase of the
                                                                        or ‘idiopathic environmental intolerance to electromagnetic
availability of wireless broadband internet access in public
                                                                        fields’ (IEI-EMF). People suffering from IEI-EMF usually
spaces. Providers and points of access take the form of
                                                                        have a diverse range of nonspecific physical symptoms (e.g.,
municipal WiFi networks, community wireless networks,
                                                                        burning skin, headache, dizziness) that they attribute to their
advanced mobile phone networks (e.g. 4G), and WiFi cafes,
                                                                        exposure to the EMF emitted by, e.g., mobile phones, mobile
restaurants, bookstores and related spaces. The ubiquitous
                                                                        phone base stations, power lines and WiFi [8]. There is some
availability of wireless Internet access encourage greater
                                                                        evidence of potential adverse effects including headaches,
participation in public spaces such as cafes [1] as free WiFi
                                                                        increased     blood    pressure,      and    disturbances    to
hotspots attract people. The problem is also important in the
                                                                        electroencephalographic (EEG) activity during sleep [9].
domain of Ambient Assisted Living (AAL) and other similar
                                                                        Several papers have been discussing             the effects of
domains such as Smart Homes to avoid negative impact of
                                                                        radiofrequency radiation (RFR) [10, 11, 12]. In 2011, the
massive use of wireless transceivers for Body Area Networks
                                                                        WHO's International Agency for Research on Cancer (IARC)
(BAN), Personal Area Networks (PAN), etc. in terms of daily
                                                                        reclassified RF-EMR as potentially carcinogenic to humans
electromagnetic     (EM)      exposure   to    radiofrequency
                                                                        [13]. Also the EM radiation has been called as the fourth
electromagnetic radiation (RF-EMR), ranging between 0 Hz
                                                                        pollution source besides air, water and noise [14].
and 300 GHz in frequency, as well as interference emission
compliance. In this context the Wi-Fi devices generally work                However, long-time effects of these electromagnetic fields
in close proximity to persons, which can lead to higher risks           on human and animal health are still unknown. Several studies
related to electromagnetic field (EMF) exposure [2].                    conducted on the effects of RFR on human health have
                                                                        provided contradictory and inconsistent findings regarding the
    Electromagnetic fields (EMF) of all frequencies is one of
                                                                        actual health risks associated with RFR [15-22].
the most fastest growing environmental pollutant. All people
are now exposed to varying degrees of EMF, and the levels                   Summarizing, when considering the health-related risks of
are expected continue to increase in future. Wireless access            the use of WiFi technology in public spaces there is the need
points (APs) and wireless laptops are also often close to               to perform modeling of the locations of WiFi access points in
humans. WiFi enabled tablets such as iPads or SmartPhones               public buildings as well as in private houses to evaluate and
are handheld and thus provide more radiation directly into              minimize the exposure of people to EM radiation while
human body. The exposure in public spaces and buildings can             ensuring the quality and signal strength of WiFi connections.
be even worse than in homes as hundreds of people are                   Proposing the computational intelligence methods that allow
simultaneously connecting to the internet.                              to minimize the effects of e-pollution is a growing research
                                                                        stream [23-29].
   EMF radiation form industrial grade WiFi systems, which
are more than 10 times more powerful as domestic WiFi                       This paper presents an initial research towards developing
                                                                        such system using Wireless Sensor Network (WSN) and the
1
    Copyright © 2016 held by the authors.                               Internet-of-Things (IoT) technology.

                                                                   51
                    II. RELATED WORKS                                   development of wireless technology, including mobile phones,
    A number of systems were developed to support the                   Wi-Fi, and various kinds of inter-connected devices making
measurement of WiFi fields both in outside environment as               up the Internet-of-Things. Biologic material readily interferes
well as in buildings. For example, Bell and Jung [30] used              with HF-EMF in a way that depends upon its shape, the
Netstumbler 0.4.0 for detecting available WLAN service and              conductivity and density of the tissue, and the frequency and
collecting WiFi signal strength data. Netstumbler observes all          amplitude of the EMF leading to an elevation of the tissue
APs within the wireless card’s visible range. Spatial and signal        temperature and thermal-associated metabolic responses [35].
strength data were integrated after data was collected. Chan et             When RF exposures are taken into account, the main
al. [31] detect the IEEE 802.11b Wi-Fi signal strength and              mechanism to be considered is the ability of RF fields to
collect into a database. They also create a fuzzy color map to          increase an average temperature through the vibration of
visualize the distribution of Wi-Fi signal. StumbVerter [32] is         atoms and molecules in the biological tissue. The heat effect
a wireless visualization tool that relies on Microsoft’s                depends on water content of the biological target material, as
MapPoint mapping library. It plots wireless transmitters on a           well as on the frequency and intensity of the electromagnetic
street map using color to indicate signal strength. However, it         (EM) radiation. The characteristic quantity is the Specific
lacks signal range mapping and it does not provide imagery              Absorption Rate (SAR) [36]. SAR can be calculated as
data. Rensburg [33] use of GPS (Global Positioning System)              follows [2]:
device, PDA and a tool to measure wireless signal
characteristics. Rose [34] describe Argos, the urban-scale                          σ 2
                                                                            SAR =     E
WSN designed explicitly to support measurement of ambient                           ρ
WiFi traffic across an entire city. Argos allows urban-scale
monitoring of wireless networks. To achieve high spatial                    here σ = 10.18 m/s is skin conductivity, ρ =1043 kg/m3
coverage, this requires multiple sensor nodes deployed                  is skin density, and E is the electric field strength.
throughout a city that can capture ambient wireless network
traffic.                                                                    Exposure to RF radiation (mainly from mobile phones) has
                                                                        been postulated to trigger a variety of neurological effects,
   Several large-scale WiFI databases exist, which could be             including headaches, changes in sleep pattern, modification in
used for researching the harms of exposure to WiFi fields:              the neuronal electrical activity, and disturbance in the
                                                                        neurotransmitter release [37]. Increasing evidence indicates
   •    Wigle (http://wigle.net/): a website for collecting
                                                                        that oxidative stress may be involved in the adverse effects in
        information about the different wireless hotspots
                                                                        the nervous system. Ilhan et al. [38] reported a marked
        around the world;
                                                                        oxidative damage in brain tissues of rats exposed to 900 MHz
   •    IGiGLE: Irongeek's WiGLE: WiFi Database to                      signal for GSM (Global System for Mobile communications)
        Google Earth Client for Wardrive Mapping                        (SAR of 2 Wkg−1 in the brain) for 7 days.
        (http://www.irongeek.com/);                                         The SAR values are not directly measurable and depend on
   •    Skyhook      (http://www.skyhookwireless.com): a                the frequency. Therefore, so-called reference levels have been
        database containing unique IDs of more than 16                  defined that are comparatively easy to measure. For the
        million wireless routers and their locations.                   frequency range 0.8–2.8 GHz, the reference levels are
                                                                        approximately 33–62 Vm−1 (general public) and 49–92 Vm−1
                                                                        (occupational) [39]. Mobile phones are legally limited to a
          III. CHARACTERISTICS OF WIFI SIGNALS
                                                                        specific absorption rate (SAR) of 2.0 W/kg [40], while most
    Usually Wi-Fi systems are based on the IEEE Standards               have a SAR of ~1.4 W/kg [41].
802.11b and 802.11g and operate in the 2.4 GHz frequency
band. According to the various local legislations and                     IV. DEVELOPMENT OF WIFI FIELD MONITORING SYSTEM
regulations, Wi-Fi devices which are designed for private
(domestic) use should emit low power (less than 20 dBm or                  The system is implemented the following technologies and
100 mW) and should work in a frequency band also used by                methods:
other communication devices (such as cordless phones). Wi-Fi                1) Internet-of-Things: smart things and devices (e.g.
devices based on the IEEE Standard 802.11a operate in the               smartphones) that have necessary means to measure WIFI
frequency band of 5.8 GHz and are suitable to be used in                field intensity.
public environment. The IEEE Standard 802.11n works in
both frequency bands of 2.4 and 5.8 GHz. Tthe most                         2) Web services. Availability of free web services to
commonly used technologies are 802.11b and 802.11g (2.4                 share data.
GHz, maximum output power 100 mW) and the 802.11a (5.8                     3) Crowdsourcing. A community based effort using
GHz, maximum output power 1 W).                                         contribution of multiple users which
    High frequency (i.e., frequencies from 300 MHz to 3 GHz)               We use a standard three-tiered architecture consisting of:
electromagnetic fields are mainly human-produced,
nonionizing electromagnetic radiations that do not naturally               1) Data gathering layer: a potentially large number of
occur in the environment, excluding the cosmic radiation. HF-           devices that gather information about Wi-Fi field strength and
EMF are present in the environment because of the active                sense it with geodata to the data feeds.


                                                                   52
    2) Data feed layer that publishes gathered data online                here: d - distance, f - frequency, K - constant that depends
for further use by anyone including any applications beyond            on the units used for d and f. If d is measured in kilometers, f
Wi-Fi mapping.                                                         in MHz, then K=32.44.
    3) Data aggregator layer that aggregates and integrates               From Eq. (1), we can find out the distance as follows:
all data from data feeds and represents it as a map.
    We used Litepoint IQView equipment to measure WiFi                      d ( km ) = 10 ( FSPL – 32.44 – 20log10 ( f ) ) / 20     (2)
signal strength. A LitePoint IQview 802.11a/b/g WLAN tester
was used to sample the ISM band at 66 M/s, centered around
2.412 GHz (WLAN channel 1). The Litepoint IQView device                     The Fresnel Zone is the area around the visual line-of-sight
digitizes the received signal and records the data onto the            that radio waves spread out into after they leave the antenna.
laptop using UDP transfer connection. The results were                 You want a clear line of sight to maintain strength, especially
processed using Matlab 8.1 (R2013a) to generate heat map of            for 2.4GHz wireless systems. This is because 2.4GHz waves
signal strength.                                                       are absorbed by water, like the water found in trees. The rule
                                                                       of thumb is that 60% of Fresnel Zone must be clear of
    A computer is connected with the measurement device via            obstacles. Typically, 20% Fresnel Zone blockage introduces
UTP cables. Communication with these devices is performed              little signal loss to the link. Beyond 40% blockage the signal
using the TCP / IP protocol. RF connectors are connected to            loss will become significant.
the measuring device using special RF cables. The computer is
running agent software for communications with the
measuring device and the RF transmitter adjusting system.                                  FSPLr = 17.32 d / 4 f                    (3)
The system deployment diagram is shown in Fig. 1.
                                                                          here: d - distance [km], f - frequency [GHz], r - radius [m].
                                                                           Following the model proposed by Ocana et al. [Ocana], the
                                                                       WiFi map can be calculated using a radio propagation model.
                                                                       This model is difficult to obtain for indoor environments, due
                                                                       to multipath effects and temporal variability of the WiFi
                                                                       signal.


                                                                                     RSL = TSL + GTX + GRX +
                                                                                                                                    (4)
                                                                                     20log ( 4λ ) − 10nWlog ( d ) − X a

                                                                           here RSL is the received signal level, TSL is the transmitted
                                                                       signal level, GTX and GRX are the transmitter and receiver
Fig. 1. Package diagram of an experimental system                      antennas gain respectively, λ is the wavelength (12.5cm for the
                                                                       2.4GHz of the WiFi signal), nW is a factor that depends on the
                                                                       walls effect, Xa is a random variable and d is the distance
                      V. MEASURED VALUES                               between the emitter and the receiver [42].
    Using the developed system prototype we measure: 1) The
number of access points visible from a device. 2) The signal                           VI. CREATION OF WIFI MAPS
strength of the strongest field. 3) Aggregate signal strength.
                                                                           Creating a WiFi signal coverage map for a given
    Attenuation can be defined as the decrease of the                  transmitter using this approach involves: (1) fitting a
amplitude of a signal between its transmission and reception           semivariogram function, which describes the amount of
points. As the radio waves propagate through the air it loses          expected variation as a function of distance between
power over a distance. Therefore signal strength is less. The          measurements and (2) predicting the value at each unmeasured
loss a signal will undergo between the transmitter and receiver        location (pixel).
is referred to as Free Space Path Loss (FSPL). FSPL can be
understood as power lost as energy disperses into the air.                 Wi-Fi mapping is based on the signal scanning in different
FSPL depends on two parameters: the frequency of radio                 places at different times. Ideally, measuring the signal strength
signals and the wireless transmission distance. The following          of all possible points at the same time allows to obtain the
formula can reflect the relationship between them:                     perfect Wi-Fi access point (Access Point, AP) map. However,
                                                                       in practice signal values are measured only in a number of
                                                                       selected location points, while in other points the signal values
       FSPL ( dB ) = 20log10 ( d ) + 20log10 ( f ) + K      (1)        are interpolated
                                                                                     α +toβ create
                                                                                             = χ. large (1)areas (1)
                                                                                                                  of maps. Such WiFi
                                                                       mapping has many uses such as for open access points search;
                                                                       signal versus time comparison; finding the signal problem
                                                                       areas; and optimizing the coverage area.


                                                                  53
    Time signal detection and interpretation must be carried              assess dynamical changes of AP coordinates at some point in
out within the time for all supported frequency band. In order            time.
to evaluate the signal quality is assessed the following
                                                                              • Radio map (radio-map) constructs a map by measuring
parameters Signal to Noise Ratio (SNR), and Signal to
Interference Ratio (SIR). Since packet data networks are                  the signal strength to a number of points. This technique is
                                                                          used for internal mapping and usually requires 2 stages. The
prevalent in wireless networks therefore one needs to assess
and receive data transmission at higher layers. Since the                 first stage is to collect AP signal strength at predetermined
                                                                          points of location and save them to the database. In the second
higher layers are analyzed to transmit data, so they need to be
checked for each channel or frequency after they arrive.                  stage, the signals are compared and the most likely signal at
                                                                          each site used as a good signal for display.
Wireless networks have different frequencies each with the
further frequency width, which may be 5, 10, 20 or 40 MHz                     After collecting the data described above is possible the
wide. In assessing signal quality is necessary to take into               data shown on the map in different ways:
account these parameters. Wi-Fi mapping is necessary to
evaluate the signal in different places, and to do so at different            1. Survey Map - signal analysis map to display data
frequencies.                                                              collection points and signal strength in these points.

    The WiFi signal detection procedure is shown in Fig. 2.                  2. AP Signal heatmap – shows signal strength variation in
The data collected can include SSID: Service Set Identifier;              space except only at one selected access point, and all other
MAC address: AP identifier; Signal strength: the access point             access points are ignored. Interpolation is used to obtain full
signal strength; Quality: the strength of the surrounding access          map coverage.
points; set of parameters describing the connection quality;                 3. Signal heatmap - displays the total number of access
Longitude and Latitude of AP coordinates.                                 points and variation of the signal strength in space.
                                                                             4. AP Coverage – the map divided into zones, featuring
                                                                          dominating point. Also signal strengths are measured,
                                                                          assessing all the signals with a power greater than 70dBm.
                                                                              5. Frequency, data speeds and other parameters of signal
                                                                          strength maps representative of two or more of the selected
                                                                          attributes dominance zones and overlapping areas in assessing
                                                                          the strength of the signals which exceed the predetermined
                                                                          values.

                                                                                        VII. RESULTS IN WIFI MONITORING
                                                                              Due to the small number of transmitting devices in the
                                                                          area, it is not possible to apply simple propagation models,
                                                                          such as free space, to relate the received power to distance.
                                                                          For this reason, we need to consider more complex
                                                                          propagation models accounting for the geometry of the
                                                                          environment. Here we consider the multiwall path loss model
                                                                          [43] which accounts for propagation at 2.4 GHz. It is based on
                                                                          generalization of the classical one slope loss model including
                                                                          an additional attenuation term due to losses introduced by the
                                                                          walls and floors encountered by the direct path between the
                                                                          transmitter and the receiver. The signal power is defined as:
                                                                                          I         Nd         N fd
                                                                              M w = lc + ∑ kwi li + ∑ χ n ld + ∑ λn l fd ,                (5)
Fig. 2. Algorithm of WiFi signal capture
                                                                                         i =1       n =1       n =1

    After collecting this data, WiFi maps can be formed in                     where lc is a constant, kwi is the number of penetrated walls
many ways, such as maximum bandwidth, minimum delay,                      of type i, li is the attenuation due to the wall of type i, i = 1, 2,
the best coverage, etc. Wi-Fi detection techniques can be                 . . . , I, Nd and Nfd are the numbers of normal and thick doors
divided into two groups:                                                  encountered by the direct path, and χn(λn) are binary variables
                                                                          accounting for the state (opened or closed) of the n-th door.
    • Model-based (model-based) uses the detected signals AP
locations and radio frequency measurement model as                            The data was obtained by the authors within the office
triangulation help from all the points determined by the access           building of Kaunas University of Technology (KTU). The
point location. This technique has the great advantage of the             experimental results of modeling the SAR values of WiFi
external mapping. Mapping is a long process, and using this               signals are presented in Figs. 3, 4 & 5, respectively.
technique, a small amount is sufficient to find enough points
with precise AP coordinates. However, the model is unable to


                                                                     54
                                                                               most by the features of the building thus provided safer
                                                                               locations for office workers, e.g., for placing permanent work
                                                                               places such as office desks (see Fig. 5, see a lighter shaded
                                                                               area at the top right corner of the building).

                                                                                                         VIII. CONCLUSIONS
                                                                                   WiFi needs to be used intelligently due to health concerns.
                                                                               This involves limiting the spatial range of exposure,
                                                                               establishing WiFi-free areas, providing wired access to those
                                                                               who choose not to use wireless, and limiting the duration of
                                                                               exposure in public spaces. The developed prototype allows
                                                                               measuring the WiFi field strength and constructing WiFi
                                                                               signal maps in public spaces. Using such maps one can plan
                                                                               the layout of work desks in offices, or tables in cafes to
                                                                               minimize prolonged exposure to high frequency EM radiation.
                                                                                  Future work will involve expanding the prototype system
Fig. 3. Example of WiFi signal strength map (with walls)                       with the GSM module to allow sending SMS to people’s
                                                                               phones to anyone registered, who want to avoid the WiFi
                                                                               hotspots with high levels of EM radiation.

                                                                                                         ACKNOWLEDGEMENT
                                                                                   The authors would like to acknowledge the contribution of
                                                                               the COST Action IC1303 – Architectures, Algorithms and
                                                                               Platforms for Enhanced Living Environments (AAPELE).

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