Wireless LAN

Wireless Local Area Network [ waɪəlɪs ləʊkl ɛəɹɪə nɛtwɜ ː k] ( German literally means " wireless local area network " - Wireless LAN, W- LAN, WLAN ) refers to a wireless local area network, usually a standard of IEEE 802.11 family is meant. For this narrower meaning in some countries ( eg USA, UK, Canada, Netherlands, Spain, France, Italy) is widely or well used interchangeably, the term Wi -Fi. The term is often also used misleading as a synonym for Wi-Fi hotspots or wireless Internet access.

In contrast to the Wireless Personal Area Network ( WPAN) WLANs have larger transmission power and range and generally offer higher data transfer rates. WLANs represent adjustments to the layer 1 and 2 of the OSI reference model, whereas in WPANs eg via an opening provided in network protocol emulation of the serial interface and PPP or SLIP a network connection is established. For WLAN OFDM modulation technique is used today mostly.

Card with Wi-Fi coverage in a university library

Wi -marked at Vienna Airport

Mapping of Wi-Fi in Seattle through wardriving with NetStumbler, 2004

In this place, in Estonia there is a free Wi-Fi (or Wi -Fi).

World map with Wi-Fi, data collected from 2007

2.1 data transfer rates 2.1.1 Transmission mode: single-carrier (DSSS)
2.1.2 Mode of transmission: multi-carrier (OFDM, 20 MHz channel width )

2.2.1 channel widths, non-overlapping channels and spectral masks 2.2.1.1 802.11
2.2.1.2 802.11a and 802.11b
2.2.1.3 802.11g
2.2.1.4 802.11n
2.2.1.5 802.11ac
2.2.1.6 802.11ad

3.1 radiation power
3.2 Transmission power

4.1 encryption
4.2 authentication
4.3 Basic Safety Measures

Operating mode

WLANs can - depending on the hardware configuration and needs of the operators - operate in different modes:

Infrastructure mode

The infrastructure mode is similar in structure to the mobile network: A wireless access point or a wireless router takes over the coordination of all client and sends in adjustable intervals (usually ten times per second), small packets of data, called " beacons" ( engl. " beacon ", see ger " Bake " ), to all stations in the lobby. The Beacons, inter alia, include the following information:

Network name ("Service Set Identifier ", SSID)
List of supported transfer rates,
Type of encryption.

This " beacon " makes the connection quite considerably, because the clients only need to know the network name, and optionally some parameters for encryption. At the same time the constant sending of beacon packets allows monitoring of signal quality - even when no user data is sent or received. Beacons are always sent with the lowest transfer rate ( 1 Mbit / s), the successful reception of the " beacon " so there's no stable connection to the network.

The SSID transmission (broadcasting) can be turned off, as a rule, even if this violates the actual standard. Thus, the router itself is invisible. However, the clients make in this variant active the connection by, if there is no connection at all times actively search for all stored network name " hidden" networks. The problem is that this information can be easily exploited for an attack on the terminal by the presence of the access point is simulated by the attacker.

Since Fi on the data link layer ( layer 2 in the OSI model ) uses the same addressing as Ethernet, can be produced via a wireless access point with an Ethernet connection easily connect to wired networks ( WLAN jargon " Distribution System ", DS). Consequently An Ethernet network card can not distinguish whether it is communicating with another Ethernet network card or ( via an access point ) with a wireless card. However, it must be converted between 802.11 ( WLAN) and 802.3 ( Ethernet).

The construction of larger WLANs with multiple base stations and uninterrupted switching clients between the different base stations is provided in the standard. In practice, however, it comes to problems:

The frequency ranges of base stations overlap and cause interference.
Because - unlike in cellular networks - the entire "intelligence" is in the client, there is no real handover between different base stations. A client will look normally only after a new base station when the contact to the previous is already canceled.

One solution to this problem lies in the decentralization of control functions in the base stations or the network: a central instance can frequencies, transmit power etc. better control and for example also initiate a handover. Since the base stations in such a scenario, lose some of their functionality and can communicate directly with the central instance have to be worked on relevant device classes ( Lightweight Access Point ) and protocols. Proprietary solutions already exist for several years, open standards (such as the Lightweight Access Point Protocol ), however, are still in the works. Discussions ignite especially on the question of which device to take over the functions.

Ad -hoc mode

In the ad hoc mode, no station is particularly excellent, but all are equivalent. Ad hoc networks can be quickly and easily set up, for the less spontaneous networking devices other techniques (Bluetooth, infrared), however, are rather common.

The conditions for the ad hoc mode are the same as for the infrastructure mode, all stations use the same network name ("Service Set Identifier ", SSID ) and, optionally, the same encryption settings. Since there are in an ad -hoc network is no central instance (Access Point ), whose coordinating role must be taken from the terminals. A forwarding of data packets between the stations is not intended and in practice not readily possible, because in ad-hoc mode, no information is exchanged, which could give the individual stations with an overview of the network. For these reasons, the ad-hoc mode is suitable only for a very small number of stations, which also must be physically located close to each other because of the limited range of the transmitter. If this is not the case, it may happen that a station can not communicate with all the other stations, and there just received this no signal.

To resolve this problem, the participating stations can be equipped with routing capabilities so that they are able to pass data between devices that are not located within the transmission range to each other. Collection and exchange of routing information is part of the appreciation of an ad hoc network for mobile ad -hoc network: software components on each station collect data (eg, the " visibility " of other stations, connection quality, etc.), they exchange among themselves and make decisions for the transmission of user data. The research in this area is not yet complete and in addition to a long list of experimental protocols ( AODV, OLSR, WITH RoofNet, BATMAN, etc.) and standardization proposals ( Hybrid Wireless Mesh Protocol, 802.11s ) and some commercial solutions (eg Adaptive Wireless Path Protocol produced by Cisco). See in this context also: Free radio network.

Wireless Distribution System (WDS) and Repeating

Increase the range of existing wireless networks or connecting with wired networks using a wireless ( bridging), there are various methods, see Wireless Distribution System.

Frequencies

Two license-free frequency blocks have yet been released from the ISM bands for wireless networks:

The channel bandwidth is 802.11a, b, g and h are 20 MHz, 40 MHz and 802.11n 802.11ac 80 MHz respectively (optional) 160 MHz.

Data transfer rates

When considering the data transfer rates must be considered that all devices in the network share the bandwidth for upload and download. Furthermore, the specified data transfer rates gross values , and even under optimal conditions, the achievable net data transfer rate only slightly more than half of this information. In the mixed mode (802.11b g) the transmission rate compared with the pure 802.11g operation can significantly break. The following net data transfer rates are realistically achievable under optimum conditions in practice:

Transmission mode: single-carrier (DSSS)

At the following rates of both frequency and code spreading is employed. The rates with PBCC are optional extensions and are usually not supported.

Transmission: multi-carrier (OFDM, 20 MHz channel width )

At the following rates, a convolutional code is employed with an information rate of 1/2. The information rate 2/3 and 3/4 come about by subsequent puncturing of the previously generated bit stream at the information rate of 1 /2, that is, the redundancies are partially deleted.

Frequencies and channels

Template: Future / In 5 years

The range 5150-5350 MHz may be used in Germany only in closed rooms. The range 5470-5725 MHz can with an equivalent isotropic radiated power ( EIRP) of up to 1.0 W may be used when the automatic power control ( TPS) and the dynamic frequency selection method (DFS ) can be used. In Austria, there are further restrictions on the radiation power at "indoor " applications. There, the maximum radiated transmit power of 200 mW EIRP must not be exceeded.

Channel widths, non-overlapping channels and spectral masks

In accordance with the requirements of the Standards Institute ETSI WLAN application is available in the 2.4 GHz band a total bandwidth of 83.5 MHz is available ( with minor differences in the individual countries of the EU).

802.11

The original, no longer in use WLAN standard 802.11 in 1997 provided for two types of transmission. One was the frequency hopping (FHSS), wherein the spectrum is used is divided into many small channels. Transmitter and receiver jumping synchronously according to predefined sequences from channel to channel. This reduces the sensitivity to disturbance significantly. The other was DSSS transmission, a single -carrier method, wherein the transmission power is distributed to a wide frequency range. Narrowband interference - such as by Bluetooth, ZigBee or model airplane - can be practically "swallowed ". The signal in a DSSS channel covers 22 MHz. The disturbing foothills of the modulation at the top and bottom of the channel must be damped. This results in a channel spacing of 22 MHz also, if the transport used for signal ranges should not overlap. In the U.S. and Europe three non-overlapping channels were thus possible, in Japan four. Commonly used to the channels 1, 6 and 11, and in Japan in addition channel 14 With performance degradation, operation with low channel spacing was possible.

802.11a and 802.11b

In the development of 802.11a and 802.11b was the technical aspects of OFDM modulation is the first choice. It is a multi-carrier method. Channels of 20 MHz width It was decided to use. A channel consists of 52 subcarriers (English sub - carrier), each 0.3125 MHz, for a total of 16.25 MHz, which are actually used for the signal. Four of these subcarriers are pilot carriers, ie not transmit any data. For the robustness of the signal, the method subcarrier interleaving, scrambling and convolutional code contribute. Subcarrier interleaving is a frequency hopping method at the level of sub-carriers.

Since OFDM was not yet approved for the 2.4 GHz band as 802.11a (5 GHz) and 802.11b ( 2.4 GHz) were designed and standardized, it was necessary for 802.11b DSSS back on with 22 MHz channel width recourse but could also be increased by a new coding type with DSSS transmission rate.

802.11g

After OFDM was also released for 2.4 GHz, has transferred the 20 - MHz channel scheme of 802.11a (5 GHz) to 2.4 GHz. In 2003 published standard 802.11g also a compatibility mode for 802.11b devices was built. In Europe now due to the lower channel width 4 instead of 3 non-overlapping channels in the 2.4 GHz band possible (1, 5, 9 and 13). This channel scheme is also supported by the Austrian Broadcasting and Telecommunications Regulatory GmbH (RTR ) is recommended. In Japan, channel has been waived, 14 release for OFDM, so that with the decrease in the use of the now-obsolete Transmission DSSS channel 14 is free for other uses again.

802.11n

With 802.11n 802.11a and g have been extended so that now a company with a channel spacing of 40 MHz and a signal width of 33.75 MHz is alternatively possible. The signal continues in this mode from 108 sub-carriers to turn 0.3125 MHz together. Six of these carriers are pilot carriers. This results in an increase in maximum gross transfer rate of 600 Mbit / s, but halved the number of non-overlapping channels.

802.11ac

In 2014, the new standard 802.11ac to be adopted, the opposite 802.11n faster data transfer with a gross data rate of 1.3 Gbit / s. Net create good equipment but at least three times the 3 -stream MIMO devices. The data transfer is done exclusively in the 5 GHz band and calls for a larger channel width of 80 MHz, optionally, a channel width of 160 MHz.

Similarly, as already 802.11n predecessor first products are already long before the official adoption of the standards available, based on a preliminary draft of the standard. As long as the standard has not yet officially adopted, to be reckoned with but with different interpretations by the manufacturer. Thus, the mid-2012 available 802.11ac devices show differences in speed and compatibility. This manifests itself, for example, that on 5 GHz practically only one channel is used, and as with all predecessors, thus interfering with neighboring networks that use the same channels ( shared medium ), resulting in a greatly reduced data rate.

802.11ad

The earliest from 2014 s can be achieved at distances of some meters without obstacles in the line connecting the IEEE 802.11ad standard in the 60 GHz range up to 7 Gb /. The high data rates in the 60 GHz range are possible through there, compared to the 5 - GHz range, very wide channels. The devices that are planned for the 60 - GHz range should be able to go for long distances at a reduced data rate in the 5 - GHz or 2.4 - GHz range.

Comments

It should be noted that the Wi-Fi channels 9 and 10 near the peak of the leak frequency standard household microwave ovens ( 2.455 GHz ) and are thus a strong disturbance of these channels is possible.

The frequency allocations in the 2.4 GHz band and the 5 GHz band can be found in the website of the broadcasting and telecommunications regulatory GmbH for Germany the website of the Federal Network Agency and for Austria.

Range and antennas

Radiation power

The permissible equivalent isotropic radiated power ( EIRP ) of 100 mW ( 2.4 GHz) and 500 mW expect (5 GHz) commercial 802.11 devices can be 30 to 100 meters range in open field. Some wireless devices allow you to connect an external antenna. With external omni-directional antennas can be bridged 100 to 300 meters in line of sight outdoors. In special cases, you can even reach 90 meters through closed spaces. The range depends on the obstacles and the nature and form of the buildings.

Lightweight walls reduce the range due to attenuation and can - depending on the used (metal) Trägerbau and the nature of the film - to be a major obstacle. Attenuate particular stone and concrete exterior walls, especially by moisture conditioned, strong - as well as metallized glass doors or fire protection constructions. Metals are not penetrated. The greater the electrical conductivity of the material, the stronger the attenuation.

Surfaces can also act as a reflector to " auszuspiegeln " dead spots - the higher the conductivity and the larger the area the better. Conductive objects in the vicinity of antennas may influence their directivity strong. Leafy trees also attenuate the signal strength for wireless connections.

WLAN according to IEEE 802.11h ( up to 54 Mbit / s gross ) operates in the 5 GHz band in which a larger frequency range ( 455 MHz bandwidth ) is available and thus 19 non-overlapping frequencies are used without a license ( in Germany ). (See also: U- NII ) In normal operation, are in buildings IEEE 802.11h 200 mW equivalent isotropic radiated power ( EIRP) allowed. However, only a small part of the frequency range is available without stringent conditions ( TPC Transmitter Power Control and DFS, Dynamic Frequency Selection). Outdoors only a small frequency range with TPC and DFS is also allowed. In this higher equivalent isotropic radiated power levels up to 1 watt EIRP are allowed. TPC and DFS is to ensure that satellite connections and radar devices are not disturbed ( World Radio Conference 2003). The cause and the higher cost of hardware due to the higher frequency that 802.11a / h has not yet been enforced against 802.11b or g.

With special directional antennas can be several kilometers bridge on sight. Therefore some records will be set with connections up to one hundred kilometers, where no transmission repeaters are used, but only high-gain antennas. However, this only works for quasi - optical sight and free as possible from the first Fresnel zone. The permissible equivalent isotropic radiated power is there but usually exceeded significantly.

Antennas bring both a transmit and a receive gain ( antenna gain, expressed in dBi ), by pooling electromagnetic waves. Therefore, the so-called equivalent isotropic radiated power ( EIRP) to be used instead of the restriction of the transmission power.

In Germany, the effective isotropic radiated power of Wi-Fi equipment to 100 mW (= 20 dBm) EIRP ( at 2.4 GHz ), 200 mW ( = 23 dBm) EIRP ( at 5.15-5.35 GHz 5.25 GHz with TPC and DFS ) and 1000 mW (= 30 dBm) EIRP ( limited at 5.47-5.725 GHz with TPC and DFS).

Meanwhile, there is no official reporting requirement for more land border radio equipment. The employer has the responsibility to ensure that his system does not exceed the prescribed limits. In Germany also home-built antennas may be used without restriction. But no license is required. The Federal Network Agency, formerly Regulatory Authority for Telecommunications and Post ( Regulatory Authority ), earlier Federal Office for Post and Telecommunications ( BAPT ), has provided the appropriate frequency ranges in a general allocation license. Regulated is thus merely the transmission path. At the receiving side there are no restrictions. Therefore, in case of insufficient transmission power of the remote terminal on the receiving side, a high antenna gain can be arbitrarily used, if, for example, allows the access point solutions with separate transmit and receive antennas of different gain.

Calculated the effective isotropic radiated power ( EIRP) ( in dBm ) of a wireless device:

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Transmission power

Integrated Wi-Fi devices for 2.4 GHz have transmission power of 13-16 dBm (20-40 mW). As 20 dBm (100 mW) are allowed EIRP, has the use of a dipole antenna (2 dBi ), the possibility of increasing the transmission power up to about 60 mW without exceeding, the EIRP limit. This goes for some access points with adjustable transmission power.

You can also use omni antenna with gain ( vertical bundling) or directional antennas. Minus the cable loss they may have 5 to 10 dBi gain and cause an amplification of the radio field in one direction at the expense of other directions. Here, however, may exceed the allowable EIRP. In this way it is possible, for example, with 6 dB gain ( four times EIRP) double the range.

Some wireless devices they also have an antenna diversity mode. For two antennas must be connected to the device. Transmission errors caused by interference can be reduced, then, by switching constantly between the two antennas and that is used, which provides the stronger signal. The two antenna ports can be used in a bi-static configuration may be used in the transmitting and receiving antennas separated. This has the advantage of being able to use a higher gain antenna for the reception, with the permitted emission levels would be exceeded when transmitting.

For connecting a wireless device with an associated antenna coaxial connectors are used. In the WLAN is mainly the RP -TNC and RP- SMA connector otherwise rarely used. The FCC ordered for WLAN to the use of special coaxial connectors, to prevent ( accidental ) connection of non- imaginary for WLAN antennas by the end user. Meanwhile, however, have adapters for all types of antennas on the market.

The cable attenuation plays a significant role in the frequencies used. Thus, for example, low loss H155 cable at 2.4 GHz has an attenuation of 0.5 dB / m.

Data Security

Without measures to increase the information security wireless local area networks are subject to attacks, such as Snarfing or man-in- the-middle attacks. It is therefore necessary to prevent that by appropriate means, in particular through the use of encryption and passwords ( authentication) or at least considerably more difficult.

Encoding

Part of the WLAN standard IEEE 802.11 Wired Equivalent Privacy ( WEP), a security standard that includes the RC4 algorithm. The encryption contained therein with only 40 bits ( 64 bits called ) or 104 bits ( 128 bits ), and in ( called 256 -bit) with some manufacturers even 232 bit long but static key is not enough to secure sufficient WLAN. By collecting key pairs known-plaintext attacks are possible. There are free programs available that provided even without a complete package run, a fast computer that can decrypt the password. Each user of the network can read all the traffic also. The combination of RC4 and CRC is considered to be cryptographically insecure.

For these reasons, technical supplements have been developed, such WEPplus, Wi -Fi Protected Access (WPA) 802.11i as anticipation and subset, Fast Packet Keying, Extensible Authentication Protocol (EAP), Kerberos, or High Security Solution, all more or less well reduce the problem of security of WLAN.

The successor of WEP is the new security standard 802.11i. It offers an increased security with Advanced Encryption Standard (AES ) ( WPA2 ) and is currently seen as not decipherable, as long as no trivial passwords are used, which can be cracked via a dictionary attack. As a recommendation can apply to create a password generator passwords containing uppercase and lowercase letters, numbers and special characters and not be shorter than 32 characters.

WPA2 is the equivalent of the Wi-Fi Alliance to 802.11i that uses the encryption algorithm AES (Advanced Encryption Standard with key lengths of 256 bits) and is used in most newer devices support. Some devices can be upgraded by replacing the firmware with WPA2 support. However, here the encoding is usually done without hardware acceleration, so that the gain in security is achieved through a strong loss in transmission rate.

An alternative approach is to move the entire encryption on the IP level. In this case, the traffic will be protected, for example by using IPsec or through a VPN tunnel. Especially in free radio networks are the incompatibility of various hardware bypassed a central user administration avoided and protected from the open nature of the network.

On the legal situation see below.

(By car wardriving called or when shutting down entire neighborhood) The so-called " warwalking " are searched with a wireless -enabled laptop or PDA open WLANs. This can be marked with chalk ( Warchalking ). The goal is to uncover vulnerabilities and to report to the operator and to investigate the proliferation of Wi-Fi, or this for their own benefit ( surf for free and under an assumed name ) exploit.

Authentication

Extensible Authentication Protocol is a protocol for authenticating clients. It can fall back to user management on the RADIUS server. EAP is used primarily within EPA for larger WLAN installations.

Authentication is possible via the MAC address of the wireless network adapter. The MAC address is a hardware identifier by which each attached network adapters can be identified. Most access points or routers provide the ability to allow access only to specified MAC addresses. All non-authorized MAC addresses is then assigned an IP address, or access to the access point is blocked. However, a sole backup using MAC address filtering is not secure, since such addresses can be set easily. Valid MAC addresses can be found for example, by the eavesdropping of the data traffic of other users. But encryption can be cracked in this way.

Basic safety measures

This includes some basic settings on the router or access point:

Enabling encryption with a secure encryption method, ie at least WPA, WPA2 better; this note specific instructions for safety of the selected encryption method in the related article
Award of a secure network key
Replacing the factory default router or access point passwords because these eg Arcadyan (some Easybox and port speed models) can be calculated using the BSSID
Disable Wi -Fi Protected Setup, if the function is not (more ) is required
Changing the factory default SSID name, so that no conclusions on the hardware being used, purpose of use, or are possible ( minimal gain in safety as the basis of the BSSID can usually be drawn to the hardware conclusions )
Deactivating the remote configuration of the router (and especially in private households )
Make configuration of the access point if possible only through wired connections or disable configuration by WLAN
Turning off wireless devices, as long as they are not used ( time management)
Regular firmware updates to the Access Point to obtain security-related improvements
Separation of the access point from the rest ( wired ) network part using VLANs and simultaneous use of a firewall between the network components

Social significance

The proliferation of wireless networks in recent years underlines the trend towards greater mobility and flexible working conditions. As early as 2005 in the European Union more notebooks sold than desktop computers, most of them with built-in Wi-Fi chip. Public and commercial wireless access point with Internet access, so-called "hot spots" that allow access to the worldwide web in many places. For private users usually find broadband access devices with built-in Access Point that offer telecommunications providers often cheaper along with the Internet connection.

Other applications

Wi-Fi can also be used as a platform to locate in cities and buildings. Since early 2008, is to run from the Fraunhofer Institute for Integrated Circuits on an area of 25 square kilometers in Nuremberg a test environment. After a first phase of operation, the system should be extended to other German and European cities such as Berlin, Munich, Frankfurt, London, Paris and Milan.

Google and Apple use the data from WLAN to locate the user and thus provide an alternative to localization by GPS.

It is intensively investigated the extent to which Wi-Fi can also be used on public roads to increase traffic safety.

Legal situation in Germany

Controversial has been the extent to which the owner of a Wi-Fi connection is liable for infringement of third parties which are committed under the IP address of the connection owner. In this context, there is also the question of law which safeguards a port owner has to take at all and where, if necessary terminate reasonable protective measures.

The Hanseatic Higher Regional Court ruled that a custodial parent is liable as spoilers for copyright infringements committed by its children. The parents it is reasonable to take technical measures to prevent the use of illegal filesharing (acceleration v. 11 October 2006 - 5 W 152/ 06). Also, the Higher Regional Court of Cologne saw the liability for copyright infringement, not only for a limited liability company as connecting Owner as given, but also condemned the directors of the company to personal liability from the viewpoint of disturbance liability (acceleration v. 8 May 2007 - 6 metro 244/ 06 ).

The opposite view was of the Higher Regional Court of Frankfurt am Main. The Frankfurt judges ruled that the owner of an Internet connection in principle not liable as an interferer for the unauthorized use of a wireless connection by unauthorized third parties, which in no way affiliated With It ( Urt v. 1 Juli 2008-11 U 52/ 07). In the view of the District Court of Munich I, however, shall not be liable to a radio station for the crimes committed by a volunteer law violations because no company can comply with limitless employee monitoring obligations (Case v. 4 October 2007 - 7 O 2827/ 07).

This lack of uniformity meant that such a case was now pending before the Federal Court, which on 12 May 2010 a fundamental decision on the liability issues announced (Case No. I ZR 121/ 08). Individuals may thus an injunction, on the other hand not be liable for damages claim if you do not adequately secured wireless connection is being used by unauthorized third parties for copyright infringement on the Internet. This was decided by the responsible inter alia for the First Civil Division of the Federal copyright law.

In addition, the question arises whether one who unjustifiably uses an open, alien -Fi, makes punishable. This unauthorized use is called partly in allusion to " dodging " as " Black Surfing". The District Court of Wuppertal in 2007 decided that a " Black Surfer" for breach of § § 89, pp. 1, 148 I 1 the Act and § § 44, 43 BDSG II No. 3 makes punishable. According to a recent decision of the District Court Wuppertal " Black Surfing" should no longer be subject to penalty. The District Court of Wuppertal upheld that decision. Black surfing is punishable under any legal theory.

Discussion of health effects

The radio frequencies used by wireless devices will be around 2.4 GHz and 5.4 GHz, ie in the microwave range. WLAN is therefore discussed in connection with possible health effects of electromagnetic pollution and in terms of electrical sensitivity. After several studies, including the Federal Office for Radiation Protection (BfS ), there is within the statutory exposure limits according to the current state of science no evidence that these high-frequency electromagnetic fields pose health risks.

According to the Federal Office for Radiation Protection can not ionizing radiation have health consequences: To avoid potential health risks, the BfS recommends to minimize personal exposure to radiation through their own initiative.

An effect of electromagnetic fields is heating of tissue. The associated process is called dielectric heating. Be particularly at risk compared to the thermal effect, the eye lens and other weak perfused tissues are, for additional heat can only be removed by reduced blood vessels there. WLAN generated but at the maximum allowable radiation powers (see above under EIRP) even in the immediate vicinity of the antenna power densities that are below the exposure limits, for example, according to BGV B11. A significant warming can therefore not be obtained.

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