DE10258805A1 - Mobile phone antenna radiated power reduction procedure iteratively modifies antenna characteristics with radiated power measurement used for control - Google Patents

Abstract

A mobile phone antenna radiated power reduction procedure iteratively modifies antenna characteristics including tilt, radio interface, gain and vertical position to support subscriber cell changes and reduces the radiated power so that the power at the edge of the service area remains constant and measures it to control the next characteristic change with procedure stop when a threshold value is achieved.

Description

The invention relates to a method to reduce the amount of interference caused by an antenna in a radio system Radiation exposure.

In radio communication systems Information (e.g. language, image information, video information, SMS (Short Message Service) or other data) with the help of electromagnetic Waves over transmit a radio interface between the sending and receiving station. The The electromagnetic waves are emitted at carrier frequencies, which in the for the respective system provided frequency band. A radio communication system includes subscriber stations, e.g. Mobile stations, base stations, with UMTS (Universal Mobile Telecommunications System) e.g. node Called B's, as well other network-side facilities.

For a comprehensive coverage with mobile To achieve radio applications, the areas are divided into radio cells, each of which is supplied by a base station. In particular there is now a well-developed area in densely populated areas Supply with small cell networks. The transmit power of the antenna the base station depends, among other things, on the size of the respective radio cell and the number of subscriber stations, which simultaneously with the base station communicate.

The total intensity of high-frequency electromagnetic Fields is taking off through the rapid expansion of nationwide radio communication systems to. This means that radiation protection measures are becoming increasingly important. This is how the Federal Office for Radiation protection in Germany Limit values for fixed radio transmitters in the regulation on electromagnetic fields based on the Federal Immission Control Act.

High-frequency fields, such as Radio-, TV, cell phone and microwave radiation, are from human body absorbed and lead for warming of body tissue. Experiments have shown that health effects are high-frequency Radiation can occur when individual areas of the body or the entire body tissue warmed by more than one degree Celsius. This is called the thermal effect. About other harmful effects, which are non-thermal is controversial.

• – Sendeleistung: Steigende Sendeleistungen bedeuten höhere Immissionen.
• – Abstand: Mit steigendem Abstand zur Antenne sinken die Immissionen.
• – Räumliches Abstrahlungsmuster der Antenne Die Antennen von Basisstationen strahlen in der Regel nicht in alle Richtungen gleich stark. Dies wird durch den Antennengewinn ausgedrückt, welcher durch die Richtcharakteristik einer Antenne bestimmt wird. Für die Angabe des Antennengewinns dient der isotrope Kugelstrahler als Vergleich, so dass der Antennengewinn in dBi (dB isotrop) angegeben wird. Je größer der Gewinn einer Antenne ist, desto mehr ist die abgestrahlte Energie der Antenne auf eine schmale Hauptkeule konzentriert. Die Intensität außerhalb dieser Hauptkeule verschwindet zwar nicht vollständig, ist aber stark reduziert.
• – Mauerwerke und Dächer: Sie schwächen die Strahlung ab, die von außen auf ein Gebäude trifft.

The radiation that strikes a person is called immission. For base stations, a number of factors determine the level of immissions at a person's location:

• - Transmission power: Increasing transmission power means higher immissions.
• - Distance: With increasing distance from the antenna, the immissions decrease.
• - Spatial radiation pattern of the antenna As a rule, the antennas of base stations do not emit the same intensity in all directions. This is expressed by the antenna gain, which is determined by the directional characteristic of an antenna. The isotropic omnidirectional radiator is used as a comparison to indicate the antenna gain, so that the antenna gain is given in dBi (dB isotropic). The greater the gain of an antenna, the more the radiated energy of the antenna is concentrated on a narrow main lobe. The intensity outside of this main lobe does not completely disappear, but is greatly reduced.
• - Masonry and roofs: They attenuate the radiation that strikes a building from the outside.

Responsible for compliance with legal Limit values is for radio towers and transmission masts usually the operator. Every location one Transmitting radio system is e.g. in Germany by the regulatory authority for telecommunications and Post are assigned an individual safety distance. Outside of the safety distance are harmful effects due to high-frequency No radiation expected from the transmitting antenna. Usually lies the safety distance for pure mobile radio transmitters in the direction of radiation the antenna in the order of magnitude of a few meters. Thus, at the previous level of the limit values just be careful that the main beam direction of the antenna close the masts are not at head height down to a person standing on the roof of the building, that contains the location.

In practice, the vertical is determined Position of the antennas from the geometric dimensions and the number of antennas taking into account the limit values. The output power of the base station and the gain of the Antennas are chosen so that at the border of the coverage area of the antenna a sufficient signal strength is obtained.

The legal determination of the limit values for electromagnetic Radiation is based on the recognized state of scientific Research. New medical knowledge or additional political precaution can lower the limit values in the short or medium term. An additional one to be considered The growing opposition in the population is a factor against other locations for Transmit antennas because the traditional radio network planning is fast for more locations.

If the legal limit values are reduced, for example, by 20 dB, the problem arises in mobile telephony: comprehensive coverage without radiation holes at the edges of the radio cells to be maintained from the existing antenna locations, ie avoiding the creation of new antenna locations.

The invention is therefore the object to demonstrate a method of the type mentioned at the beginning, which is an effective reduction in the radiation exposure of an antenna allows without the desired one Coverage area of the antenna is limited.

This task is solved by a method with the features of claim 1.

Refinements and training are the subject of the subclaims.

• (a) Modifikation einer ersten Eigenschaft der Antenne,
• (b) Reduzierung der Sendeleistung der Antenne in einem derartigen Ausmaß, dass die Strahlungsleistung am Rand des Versorgungsgebietes der Antenne gegenüber derjenigen vor der Modifikation der ersten Eigenschaft der Antenne im wesentlichen unverändert ist,
• (c) Ermittlung der durch die Antenne hervorgerufenen Strahlenbelastung,
• (d) abhängig von dem Ergebnis der Ermittlung Modifikation einer zweiten Eigenschaft der Antenne und Wiederholung des Verfahrensschrittes (b) in Bezug auf die Modifikation der zweiten Eigenschaft der Antenne.

According to the invention, the method comprises the method steps

• (a) modification of a first property of the antenna,
• (b) reducing the transmission power of the antenna to such an extent that the radiation power at the edge of the coverage area of the antenna is essentially unchanged from that before the modification of the first property of the antenna,
• (c) determining the radiation exposure caused by the antenna,
• (d) depending on the result of the determination, modification of a second property of the antenna and repetition of method step (b) with respect to the modification of the second property of the antenna.

Under the coverage area of the antenna understood the geographic area in which the radiation the antenna is used as intended can be. The radiation exposure is advantageously determined in the place that is usually to check the radiation limit values is used. This place can e.g. with the kind, the lineup and the use of the antenna, as well as with the radiation limit to be checked vary. Any properties modified in the process the antenna relate to those related to the antenna Parameters that depend on the type and intensity of the radiation the antenna, as well as spatial Properties of the radiation of the antenna. A modification In practice, this often becomes a property of the antenna realized that the antenna for reasons of economy is exchanged for another antenna instead of the required To carry out work on the antenna. The term antenna is used understood here the radiating unit at a certain location, so swapping one antenna for another in the same location is the modification of a property of the antenna.

The method according to the invention allows iterative Procedure: after a modification of a property of the considered The radiation exposure is determined by the antenna. Is the value of this Radiation exposure too high can be another property of Antenna can be modified. Another modification of the same Property of the antenna can be carried out. After another exam The radiation exposure can be different, or one of the first two properties of the antenna can be modified. advantageously, becomes the determined radiation exposure with a limit or threshold value compared to a decision to conduct To take modification steps. This procedure can be continue until the result of the determination of the radiation exposure certain conditions are sufficient.

Regarding a radio communication system, to which the invention can be applied there is the advantage that low limits for that electromagnetic radiation from a base station can be observed can, without additional To have to build base stations. In doing so, the nationwide Maintain radio coverage in the radio communication system and there are no dead spots between the radio cells.

• – wird vor der Durchführung des Verfahrensschrittes (a) eine Modifikation von mindestens einem Parameter zur Unterstützung eines Zellwechsels einer Teilnehmerstation des Funkkommunikationssystems durchgeführt,
• – erfolgt eine Reduzierung der Sendeleistung der Antenne,
• – erfolgt eine Ermittlung der durch die Antenne hervorgerufenen Strahlenbelastung,
• – hängt die Durchführung der Verfahrensschritte (a) bis (d) von dem Ergebnis der Ermittlung ab.

In a further development of the invention

• A modification of at least one parameter to support a cell change of a subscriber station of the radio communication system is carried out before carrying out method step (a),
• - the transmission power of the antenna is reduced,
• - the radiation exposure caused by the antenna is determined,
• - The implementation of process steps (a) to (d) depends on the result of the determination.

Before modifying a property the antenna becomes a parameter to support a cell change Subscriber station of the radio communication system, i.e. a handover Parameters, changed. A handover parameter becomes a relevant one for a handover process Understood parameters. In particular, there is a reduction here to think of a handover parameter. Handover parameters often hang on the transmission power of the antenna, so that after modification of the handover parameter reduces the transmission power of the antenna can be done without the handover in the radio communication system to endanger. When reducing the transmission power of the antenna should, however, be careful care must be taken that the transmission power of the antenna is only in one is reduced to such an extent that the coverage area of the antenna does not differ reduced to a certain extent. Determining the radiation exposure reveals that this is not a sufficient value has been reduced, the method steps according to the invention can the modification of one or more properties of the antenna.

An embodiment of the invention according to

• - becomes after performing of method step (c) a modification of at least one Support parameters a cell change of a subscriber station of the radio communication system carried out,
• - he follows a reduction in the transmission power of the antenna,
• - becomes process step (c) is repeated,
• - and process step (d) is carried out.

The modification of a handover parameter can also after a modification of a property of the antenna carried out become. Decisive for the implementation the modification of a handover parameter is again in this case the determination of the radiation exposure of the antenna.

• – wird nach der Durchführung des Verfahrensschrittes (d) eine Modifikation von mindestens einem Parameter zur Unterstützung eines Zellwechsels einer Teilnehmerstation des Funkkommunikationssystems durchgeführt,
• – erfolgt eine Reduzierung der Sendeleistung der Antenne,
• – wird der Verfahrensschritt (c) wiederholt,
• – erfolgt abhängig von dem Ergebnis der Ermittlung aus Verfahrensschritt (c) eine Modifikation einer dritten Eigenschaft der Antenne und eine Wiederholung des Verfahrensschrittes (b) in Bezug auf die Modifikation der dritten Eigenschaft der Antenne.

According to another embodiment of the invention

• A modification of at least one parameter to support a cell change of a subscriber station of the radio communication system is carried out after carrying out method step (d),
• - the transmission power of the antenna is reduced,
• Step (c) is repeated,
• - Depending on the result of the determination from method step (c), a modification of a third property of the antenna and a repetition of method step (b) is carried out with respect to the modification of the third property of the antenna.

• – der Reduzierung des vertikalen Neigungswinkels der Hauptstrahlrichtung der Antenne,
• – der Erhöhung des Antennengewinns der Antenne,
• – der Erhöhung der vertikalen Position der Antenne.

The modification of the first and / or optionally the second and / or optionally the third property of the antenna advantageously comprises one of the steps

• - the reduction of the vertical angle of inclination of the main beam direction of the antenna,
• - increasing the antenna gain of the antenna,
• - increasing the vertical position of the antenna.

The process according to the invention is as follows based on an embodiment explained. Show

1 : an antenna and its coverage area,

2 a first modification according to the invention of a property of the antenna,

3 a second modification according to the invention of a property of the antenna,

4 a third modification according to the invention of a property of the antenna,

5a : the first part of a flow chart of the inventive method, and

5b : the second part of a flow chart of the method according to the invention.

1 shows schematically an antenna A, which is located on the roof of a house, for example. The highest electromagnetic power density accessible to humans usually occurs where the main beam of antenna A strikes the head of an upright person who is on the roof of the house on which antenna A is installed. The circle around antenna A indicates the edge V of the coverage area of antenna A. In a cellular radio communication system, coverage areas of other antennas adjoin the edge V of the coverage area of the antenna A. The coverage areas of different antennas usually overlap in the area of their edges. A determination M of the radiation exposure caused by the antenna A is carried out at a suitable location P.

As a concrete example, one Antenna A for considered mobile communications, the focus of which is in an urban Environment one meter above the head height a person standing upright on the roof. The antenna gain is 15.5 dBi at an output power of 10 W, i.e. 40 dBm. Four carrier frequencies are bundled onto this antenna A. and the antenna A has a vertical electrical tilt angle (down tilt) from six degrees. With this configuration the maximum electromagnetic flux density 9.85 dB below the current valid Limit values and 10.15 dB above possible future limit values.

The course of a method according to the invention is shown by the related 5a and 5b , Before the method according to the invention for reducing the electromagnetic radiation exposure begins, the current power flux density and thus the current radiation exposure caused by the antenna are determined (“determination of radiation exposure”). By comparison with the limit value to be observed (“limit value?”) It can be determined whether and by how much the signal strength of antenna A has to be reduced. If the limit value is already observed ("yes"), the process can be terminated ("Stop"). In the event that the limit value is exceeded (“no”), it is first checked whether the angle of inclination of antenna A can be reduced (“angle of inclination?”). If this can be answered in the affirmative (“yes”), the vertical angle of inclination of the antenna A is reduced (“reduction of the vertical angle of inclination”). In the event that the angle of inclination cannot be reduced (“no”), the method is continued with a variation of parameters of the radio interface (“radio interface parameter”). After reducing the vertical angle of inclination (“reducing vertical angle of inclination”), the output power of the base station is adjusted in such a way that the signal strength at the edge of the coverage area remains approximately constant. If the vertical angle of inclination is reduced, for example to zero degrees, the output power can base station by 0.08 dB. In principle, the reduction of a vertical angle of inclination can be achieved by electrical or mechanical modification. This measure reduces the radiation exposure by 6.16 dB for the most exposed area. A reduction in the vertical angle of inclination of the main lobe of antenna A is exemplified in 2 shown.

Now in 5a again checked whether the limit value can be maintained after the vertical inclination angle of antenna A has been reduced (“limit value?”). If the answer is affirmative (“yes”), no further measures are necessary and the process for reducing the radiation exposure can be terminated ("Stop"). If this is not the case ("no"), parameters of the radio interface are modified in the second step ("radio interface parameters"). The parameter for initiating a handover is advantageously reduced. An example of this is the parameter RXLEVMIN (Receive Level Minimum) within the GSM (Global System for Mobile Communication) system, eg this value can be set from –104 dBm to –110 dBm.

This results in handover operations can only be triggered at lower reception powers on the subscriber device than before the modification. Then the static Base station output power reduced by the same amount.

With regard to the variation of parameters of the radio interface, it can also be checked beforehand whether such a variation is possible. If it is not possible or sensible, you can continue with the next step of modifying the antenna gain ("antenna gain") (in the 5a and 5b not shown for reasons of clarity). In the calculation example considered, it is assumed that the parameters of the radio interface have already been optimally used, so that a modification of the parameters cannot bring about a reduction in the radiation exposure.

If a new limit value check ("limit value?") In 5b shows that there is still a need to reduce radiation exposure ("no"), the third step is to increase the antenna gain ("antenna gain"). Otherwise ("yes") the process can be stopped again ("stop"). Again, a check can be carried out regarding the feasibility of increasing the antenna gain (in the 5b Not shown). In the event that an increase in antenna gain can be carried out, antenna A is implemented, as exemplified in 3 shown replaced by an antenna A with greater profit. The output power of the base station is then adjusted in such a way that the signal strength at the edge of the coverage area remains approximately constant. The output power of the base station can be reduced because the larger antenna gain avoids radiation losses towards the sky, for example. The higher gain corresponds to a stronger bundling of the main lobe of antenna A. In the specific case, the 15.5 dBi antenna A is replaced by an antenna A with a gain of 17 dBi. This step reduces the radiation exposure by an additional 1.32 dB due to the lower output power of the base station.

Now it is checked again whether the limit value can be maintained after the antenna gain has been increased ("limit value?"). If the answer is affirmative ("yes"), no further measures are necessary and the procedure for reducing the radiation exposure can be terminated (" Stop "). However, if this is not the case, the height of antenna A is varied in the fourth step (" vertical position "). The antenna A is mounted higher on the mast, as exemplified in 4 shown. This process step can also be queried beforehand with regard to its feasibility (in 5b not shown). A larger height of antenna A leads to less attenuation of the radio signal. The output power of the base station can therefore be reduced in order to keep the signal strength constant at the edge of the coverage area. The amount by which the output power is reduced can be determined in accordance with the radio propagation formula from M. Hata, IEEE Transactions on Vehicle Technology, Vol. VT. -29, No. 3, August 1980. In the specific calculation example, increasing the vertical position of antenna A by 50 cm results in an improvement in radiation exposure of 4.28 dB.

Now you can check again whether the limit value can be met ("limit value?") Procedure can be canceled ("Stop"). However, it is in certain circumstances also possible, to perform one or more of the steps described again in order to to achieve a further reduction in radiation exposure.

An addition of the reductions of the Radiation exposure resulting from the steps described, results in an 11.76 dB improvement in radiation exposure. This is enough to for to comply with the given case limit values which are 20 dB below the current values. A further reduction in Radiation exposure can e.g. achieved by a larger height of the transmission antennas become. If antenna A is raised by a total of five meters, it lowers the radiation exposure by a further 13.29 dB. Overall, therefore a reduction in radiation exposure of 25.05 dB was achieved become.

In particular, the process steps for modifying the properties of the antenna, namely reducing the angle of inclination of the main beam direction, increasing the antenna gain and increasing the vertical position of the antenna, are particularly suitable for densely built-up or populated areas, such as urban areas, where the greatest contribution on the signal strength at the edge of the supply area An antenna is spread over the roof of the house with subsequent diffraction into the individual streets. The subscriber stations in buildings on the edge of the cell are also supplied via this propagation path. The diffraction into the individual streets cancels the effect that, due to the modifications to the properties of the antenna, the beam direction points less towards a participant on the ground compared to the state before the modifications.

However, the method can also be used reduced effectiveness applied in less densely populated areas.

Claims (7)

Method of reducing through an antenna (A) radiation exposure caused by a radio system, comprising the procedural steps (a) Modification of a first property the antenna (A), (b) Reduction of the transmitting power of the antenna (A) to such an extent that the radiant power at the edge (V) of the coverage area opposite the antenna (A) that before the modification of the first property of the antenna (A) essentially unchanged is and (c) Determination (M) of those caused by the antenna (A) Radiation exposure (d) dependent from the result of the determination (M) modification of a second property the antenna (A) and repetition of process step (b) in relation to the modification of the second property of the antenna (A). The method of claim 1, which is based on a cellular Radio communication system is applied. The method of claim 2, wherein - before the execution of method step (a) a modification of at least one Support parameters a cell change of a subscriber station of the radio communication system carried out becomes, - one The transmission power of the antenna (A) is reduced, - an investigation (M) the radiation exposure caused by the antenna (A) he follows, - and the implementation of process steps (a) to (d) from the result of the determination (M) depends. The method of claim 2 or 3, wherein - after execution of method step (c) a modification of at least one Support parameters a cell change of a subscriber station of the radio communication system carried out becomes, - one The transmission power of the antenna (A) is reduced, - the procedural step (c) is repeated, - and process step (d) is carried out. Method according to one of claims 2 to 4, in which - after execution of method step (d) a modification of at least one Support parameters a cell change of a subscriber station of the radio communication system carried out becomes, - one The transmission power of the antenna (A) is reduced, - the procedural step (c) is repeated, - and dependent one of the result of the determination (M) from method step (c) Modification of a third property of the antenna (A) and one Repetition of process step (b) with regard to the modification the third property of the antenna (A). Method according to one of claims 1 to 5, in which the modification the first and / or optionally the second and / or optionally the third property of the antenna (A) one of the steps - the reduction the vertical angle of inclination of the main beam direction of the antenna (A), - the increase the antenna gain of the antenna (A), - increasing the vertical position the antenna (A) includes. Method according to one of claims 3 to 5, wherein the modification the at least one parameter to support a cell change of a subscriber station of the radio communication system a reduction in this parameter includes.