United States Patent (19)
`Bodin et al.
`
`US00539.0338A
`Patent Number:
`Date of Patent:
`
`(11)
`45
`
`5,390,338
`Feb. 14, 1995
`
`54 METHOD OF CONTROLLING OUTPUT
`POWER IN A MOBILE RADO
`COMMUNICATION SYSTEM
`75 Inventors: Stig R. Bodin, Spanga; Karl R. V.
`Forsselius, Bromma, both of Sweden
`73 Assignee: Telefonaktiebolaget LM Ericsson,
`Stockholm, Sweden
`(21) Appl. No.: 225,940
`(22
`Filed:
`Apr. 11, 1994
`
`63
`
`Related U.S. Application Data
`Continuation of Ser. No. 763,231, Sep. 20, 1991, aban
`doned.
`Foreign Application Priority Data
`(30)
`Oct. 5, 1990 SE Sweden .............................. 90031964
`51 Int. Cl........................... H04B 1/00; H04Q7/00
`52 U.S. C. .................................. 455/33.1; 455/54.1;
`455/67.6; 455/69; 379/63
`58 Field of Search ....................... 455/33.1, 54.1, 63,
`455/67.6, 69, 126, 127; 379/59-60, 63
`References Cited
`U.S. PATENT DOCUMENTS
`3,732,496 5/1973 Boyer .................................... 455/69
`4,495,648 1/1985 Giger ........
`... 455/73
`4,613,990 9/1986 Halpern................................. 455/69
`4,811,421 3/1989 Havel et al. ......
`... 455/126
`5,003,619 3/1991 Morris et al. ......................... 455/69
`5,056,109 10/1991 Gilhousen et al. ................. 455/33.1
`5,129,098 7/1992 McGirr et al....................... 455/126
`5,204,970 4/1993 Stengal et al. ...................... 455/126
`P. (dBm)
`
`56)
`
`FOREIGN PATENT DOCUMENTS
`0392078 10/1990 European Pat. Off. .
`0392079 10/1990 European Pat. Off. .
`2229609 9/1990 United Kingdom .
`WO86/00486 1/1986 WIPO .
`Primary Examiner-Edward F. Urban
`Assistant Examiner-Andrew Faile
`Attorney, Agent, or Firm-Burns, Doane, Swecker &
`Mathis
`ABSTRACT
`57
`The invention relates to a method of controlling, in a
`cellular mobile radio communication system, the output
`power of radio signals transmitted from a transmitter to
`a receiver located in the same cell as the transmitter.
`The method comprises controlling the output power of
`the transmitter in dependence of a parameter, that is
`characteristic of the distance between transmitter and
`receiver, to approximately follow, from a predeter
`mined maximum output power that is transmitted when
`the distance between the transmitter and receiver is the
`maximum within the cell, a first function that monotoni
`cally decreases with decreasing distance and ap
`proaches a predetermined minimum output power as
`the distance approaches zero, so that the power of the
`transmitted radio signals as received by the receiver
`from a minimum received power, that is received when
`the distance between transmitter and receiver is the
`maximum within the cell, approximately follows a sec
`ond function that monotonically increases with decreas
`ing distance and approaches a maximum received
`power as the distance approaches zero.
`
`14 Claims, 3 Drawing Sheets
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`
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`7000
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`1000
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`ZTE, Exhibit 1008-0001
`
`

`

`U.S. Patent
`
`Feb. 14, 1995
`
`Sheet 1 of 3
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`5,390,338
`
`
`
`BS1
`
`BS2 O
`CO MS 1
`MS2 O Fig. 2
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`ZTE, Exhibit 1008-0002
`
`

`

`U.S. Patent
`
`Feb. 14, 1995
`
`Sheet 2 of 3
`
`5,390,338
`
`P. (dBm)
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`1 000
`
`
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`7OOO
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`1000
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`7000
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`ZTE, Exhibit 1008-0003
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`

`

`U.S. Patent
`
`Feb. 14, 1995
`
`Sheet 3 of 3
`
`5,390,338
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`P. (dBm)
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`f OOO
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`P. (dBm)
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`7OOO
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`f000
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`7000
`
`ZTE, Exhibit 1008-0004
`
`

`

`1.
`
`METHOD OF CONTROLLING OUTPUT POWER
`N A MOBILE RADIO COMMUNICATION
`SYSTEM
`
`This application is a continuation of application Ser.
`No. 07/763,231, filed Sep. 20, 1991, abandoned.
`TECHNICAL FIELD
`The present invention relates to a method for control
`ling, in a cellular mobile radio communication system,
`the output power of radio signals transmitted from a
`transmitter to a receiver that is located in the same cell
`as the transmitter.
`
`5
`
`10
`
`20
`
`5,390,338
`2
`mately follow, from a predetermined maximum output
`power that is transmitted when the distance between
`the transmitter and receiver is the maximum within the
`cell, a first function that monotonically decreases with
`decreasing distance and approaches a predetermined
`minimum output power as the distance approaches
`zero, so that the power of the transmitted radio signals
`as received by the receiver from a minimum received
`power, that is received when the distance between
`transmitter and receiver is the maximum within the cell,
`approximately follows a second function that monotoni
`cally increases with decreasing distance and approaches
`a maximum received power as the distance approaches
`Zero.
`The transmitter can comprise either a mobile station
`in the current cell or the base station of the same cell.
`SHORT DESCRIPTION OF DRAWINGS
`The invention, further objects and advantages ob
`tained by the invention are best understood by reference
`to the following description and the accompanying
`drawings, in which:
`FIG. 1 shows a cellular mobile telephone system;
`FIG. 2 shows a number of cells in this cellular mobile
`telephone system of which two use for instance the
`same radio frequency or radio channel;
`FIG.3 shows the output power P, of the radio signal
`transmitted from a mobile station as a function of the
`distance D between mobile station and base station in
`the method in accordance with the present invention;
`FIG. 4 shows the power P, of the radio signal re
`ceived by the base station as a function of the distance D
`between mobile station and base station when the out
`put power of the radio signal transmitted by the mobile
`station is controlled in accordance with the curve in
`FIG. 3; and
`FIGS. 5(a) and 5(b) illustrates a preferred embodi
`ment of the method in accordance with the present
`invention.
`PREFERRED EMBODIMENT
`FIG. 1 shows, as an example of a mobile radio com
`munication system, the structure of an embodiment of a
`cellular mobile telephone system. Such a system com
`prises a number of cells, each cell in this embodiment
`including one base station BS. For reasons of simplicity
`only a number of such base stations BS are shown in the
`figure. Base stations BS are in radio contact with a
`number of mobile stations MS, of which only one is
`shown in the figure. Mobile station MS generally com
`municates with the base station BS of that cell in which
`it currently is located.
`FIG. 2 shows a number of cells in a cellular mobile
`telephone system. A mobile MS1 is in radio contact
`with base station BS1 in a first cell. In the second cell,
`separated from the first cell, there is another mobile
`MS2 in radio contact with base station BS2. If the load
`on the radio communication system is heavy and the
`distance between the first and the second cell is suffi
`ciently large, both radio connections may use the same
`communication channel, for instance the same radio
`frequency or time slots for the same radio frequency.
`However, this implies that the output power transmit
`ted from the base stations to the respective mobile sta
`tions should be sufficiently low to avoid interference
`between the cells. On the other hand, the power cannot
`be too low, since this would jeopardize the radio con
`nection between the respective mobile and base station.
`
`15
`
`PRIOR ART
`A cellular mobile radio communication system com
`prises a number of cells, each containing a base station.
`These base stations communicate with mobile stations
`that can nove freely within and between the cells.
`Since the number of available frequencies for the total
`system is limited, frequencies are reused for cells that
`are sufficiently separated from each other.
`However, in such reuse of radio frequencies there is a
`risk that a radio connection is disturbed by signals in
`25
`tended for another radio connection using the same
`frequency. Thus, it is desirable to control the output
`power from, for instance, a mobile station in such a way
`that sufficient output power is transmitted to guarantee
`that the quality of the radio connection is maintained at
`30
`the same time as the output power is limited so as to not
`unnecessarily disturb other radio connections that may
`use the same frequency.
`In U.S. Pat. No. 4,485,486 it has been suggested to
`control the output power of the mobile station in such a
`35
`way that the signal received by the base station has
`constant power irrespective of the distance between
`mobile station and base station. A drawback of this
`previously known method is that C/I, that is the ratio
`between the power received at the base station of the
`carrier transmitted by the mobile station and the power
`of interfering signals, on the average is lower than is
`actually permissible. This is due to the fact that the
`output power of the mobile station at small distances,
`where a further reduction of the output power from an
`45
`already low level has a very small influence on the
`disturbance on other radio connections, is reduced to an
`extent uncalled for. On the other hand this further re
`duction can increase the risk of jeopardizing the mobile
`stations own radio connection.
`50
`SUMMARY OF THE INVENTION
`An object of the present invention is to provide a
`method for controlling the output power from a mobile
`station and/or a base station in a cellular analog or
`55
`digital mobile radio communication system in depen
`dence of the distance between the base station and mo
`bile station in such a way that the variation in transmit
`ted power and received power is distributed in a more
`optimal way.
`60
`Accordingly the invention relates to a method of
`controlling, in a cellular mobile radio communication
`system, the output power of radio signals transmitted
`from a transmitter to a receiver, which is located in the
`same cell as the transmitter. This method comprises
`65
`controlling the output power of the transmitter in de
`pendence on a parameter, that is characteristic of the
`distance between transmitter and receiver, to approxi
`
`ZTE, Exhibit 1008-0005
`
`

`

`P(D)=min (POD), Pina)
`
`can be mentioned, where the function P(D) is given by:
`POD)=Pini, 10 log (DP-DLC"P-DP/P
`
`5,390,338
`3
`4.
`FIGS. 3 and 4 show transmitted and received power,
`the risk of interference with other cells that use the
`respectively, as functions of the distance D between
`same radio channel.
`mobile station and base station, on the one hand, for the
`As an example of a suitable controlled curve the
`control method in accordance with the above U.S. Pat.
`function:
`No. 4,785,486 (dashed curves) and, on the other hand,
`for the method in accordance with the present inven
`tion (solid curves). In the following description it is
`assumed that P(FIG. 3) is the power transmitted by the
`mobile station and that P (FIG. 4) is the power re
`ceived by the base station. However, this assumption is
`10
`made only to facilitate the description. P. could instead
`represent the power transmitted by the base station. Pr.
`would then represent the power received by the mobile
`station.
`As is apparent from the dashed curve in FIG. 4 the
`power P transmitted by the mobile station in accor
`dance with the previously known method is controlled
`from the base station in such a way that the power P.
`received by the base station is maintained as constant as
`possible irrespective of where the mobile station is lo
`20
`cated within the current cell. Thus, Pin this case essen
`tially has no variation; the dynamic range is zero. Con
`trolling transmission power in this way leads to he
`power transmitted from the mobile station (measured in
`dBm) from a minimum output power Po will vary lin
`25
`early with the logarithm of the distance between mobile
`station and base station up to a maximum output power
`Pinax at the outer regions of the cell, in accordance
`with the dashed curve in FIG. 3. Thus, P in this case
`has the dynamic range Pinax-Po.
`At small distances between the mobile station and its
`own base station, this control method, however, leads
`to a reduction in the power P transmitted by the mobile
`station even when the power level already is so low that
`the risk of disturbing remote base stations is practically
`negligable. The reason for this is that the control
`method assumes that the received power Pralso should
`be constant in this region. Therefore the known method
`leads to a relatively large dynamic range of the trans
`mitted signal, while the received signal is essentially
`conStant.
`The present invention is based on the insight that a
`better utilization of the radio connection can be ob
`tained by distributing the variation (dynamic range)
`between the transmitted signal and the received signal.
`45
`An example of the control method in accordance with
`the invention is shown by the solid curves in FIGS. 3
`and 4. In accordance with the invention the transmitted
`power P is not controlled on the basis of a constant
`received power that is independent of the distance,
`50
`rather the transmitted power Priscontrolled to follow a
`function that monotonically decreases with the distance
`between mobile station and base station from a maxi
`mum value Pima, that is appropriate when the mobile
`station is located at the outer regions of the cell, and for
`instance asymptotically approaches a minimum value
`Pnin as the distance approaches zero. The dynamic
`range for Prin this case is only Pima-Pamin. Such a con
`trol method results in the solid curve in FIG. 4 for the
`received power P. It should be noted that the received
`signal power in this case steadily increases from a value
`Prmin to a value Prmax as the distance between mobile
`station and base station decreases within the cell. The
`dynamic range for the received signal in this case is
`Prma-Pnin. By this distribution of the variation in the
`65
`radio connection such that both the transmitted and
`received signals have varying power within the cell,
`C/I of the connection is improved without increasing
`
`In these formulas:
`D designates the distance between mobile station and
`base station;
`DL designates a characteristic distance that defines
`the location of the "knee' of the curve;
`p designates a parameter that controls how smooth
`the transition between the flattened and steeper parts of
`the curve is (a large presults in a sharp transition);
`nm designate further parameters that control the
`shape of the curve.
`Exemplifying values for the different parameters are:
`DL=2000 m
`p=3
`m=0
`n=2.8
`Pinax=38 dBm
`Pinin=28 dBm
`In practice the control method is not realized with a
`continuous function, but with stepped functions that
`approximate this continuous function. A suitable num
`ber of levels for such stepped functions has proven to be
`about ten levels. The value of a stepped function for a
`given distance D can then easily be obtained from a
`table.
`FIGS. 5a and 5b illustrate a preferred embodiment of
`the method in accordance with the present invention.
`The stepped functions a and b shown in FIGS. 5a-b for
`sake of clearness comprise only a few levels. FIG. 5a
`shows a step function a that approximates the solid
`control curve of FIG. 3 and that is appropriate when
`the mobile station leaves the base station. Correspond
`ingly, FIG.5b shows a stepped function b that approxi
`mates the solid control curve of FIG. 3 and that is ap
`propriate when the mobile station approaches the base
`station. The stepped function a shown in 5a has been
`dashed in FIG. 5b. From FIG. 5b it is noted that the
`functions a and b have the same levels, but that the steps
`are mutually displaced along the distance axes. This
`results in a certain “hysteresis effect', which will be
`further described below when the control method in
`accordance with the preferred embodiment of the in
`vention is described.
`The control method is realized in the following way:
`At each measurement instance the new measured
`distance is compared to the previous distance.
`If the new distance is larger than the previous dis
`tance, an adjustment is to be performed in accor
`dance with stepped function a and therefore the
`new desired value for the output power P is re
`trieved from the corresponding table for function
`a.
`If the new distance is smaller than the previous dis
`tance, an adjustment is to be performed in accor
`dance with stepped function b and therefore the
`new desired value for the output power P is re
`trieved from the corresponding table for function
`b.
`
`15
`
`30
`
`35
`
`55
`
`ZTE, Exhibit 1008-0006
`
`

`

`10
`
`5,390,338
`5
`6
`trolled in dependence on a parameter, said parameter
`The result of this control method in accordance with
`the preferred embodiment is that if the mobile station
`being a function of distance between said transmitter
`happens to be near a step and alternately exceeds and
`and said receiver wherein said output power of said
`underpasses, respectively, this step distance, a jumping
`transmitter is proportional to said distance between said
`desired value is avoided. This is due to the fact that a
`transmitter and said receiver and approaches a predeter
`transition from for instance a distance that is larger than
`mined minimum output power as said distance ap
`the step distance to a distance that is smaller than this
`proaches zero and received power from said transmitter
`distance also leads to a change of step function from a to
`is inversely proportional to said distance between said
`b. However, the new step function b has a smaller step
`transmitter and said receiver when said distance ap
`distance than the previous function. Therefore a larger
`proaches zero.
`distance reduction is required before the desired value is
`2. The method of claim 1, wherein said transmitter is
`reduced. This feature can be considered as a sort of
`in a mobile station.
`"hysteresis effect”.
`3. The method of claim 2, wherein said transmitter is
`The regulation described above is commanded by the
`controlled by a base station in a same cell as said mobile
`base station, and the required calculations can be per
`15
`station.
`formed either in the base station or its control unit or
`4. The method of claim 1, wherein said transmitter is
`even in the mobile services switching center to which
`in a base station.
`the base station is connected.
`5. The method of claim 4, wherein said transmitter is
`In the above description the control method has been
`controlled by said base station.
`described as a function of the distance between nobile
`6. The method of claim 1, wherein said parameter
`station and base station in the current cell. However,
`comprises the path loss between said transmitter and
`normally the exact distance is not known, which means
`said receiver.
`that in practice a measure of or a parameter that de
`7. The method of claim 1, wherein said parameter
`pends on this distance is used. An example of such a
`comprises the time delay of said radio signals transmit
`measure is:
`25
`ted and received between said transmitter and said re
`The path loss between mobile station and base station.
`ceiver.
`Since the base station over the control channel
`8. The method of claim 1, wherein said received
`continuously commands the mobile station to
`power from said transmitter monotonically increases
`transmit with a certain output power, this com
`with decreasing distance between said transmitter and
`manded output power can be compared to the
`30
`said receiver when said distance approaches zero.
`actually received power. From this information the
`9. The method of claim 1, wherein said received
`damping of the signal along the path between mo
`power from said transmitter monotonically increases
`bile station and base station can be calculated. This
`with decreasing distance between said transmitter and
`path loss is then an approximate measure of the
`said receiver when said distance approaches zero, said
`distance between the two stations.
`35
`received power approaching a maximum received
`The time delay between mobile station and base sta
`power as said distance substantially reaches zero.
`tion for transmitted and received radio signal.
`10. The method of claim 1, wherein said output
`Since the mobile station transmits information at
`power of said transmitter monotonically decreases with
`predetermined moments, which are controlled by
`decreasing distance between said transmitter and said
`the base station, the time delay between these mo
`receiver and approaches said predetermined minimum
`ments and the actual moments of receipt can be
`output power as said distance decreases to zero.
`used for calculating an approximate measure of the
`11. The method of claim 10, wherein said monotoni
`distance between mobile station and base station.
`cally decreasing output power is approximated by a first
`As has been mentioned above it is also possible to
`and a second step function, each having a predeter
`control the output power from the base station in accor
`45
`mined number of discrete power output levels, said first
`dance with the described principles. However, the con
`step function being appropriate for increasing distances
`trol curve Pt does not have to be identical to the corre
`and said second step function being appropriate for
`sponding curve for a mobile station. For instance the
`decreasing distances.
`curve can have other maximum and minimum values
`12. The method of claim 11, wherein each of said step
`and/or another "knee point”. However the general
`shape of the curve is the same in both cases.
`functions have ten discrete levels.
`The man skilled in the art appreciates that different
`13. The method of claim 11, wherein said first and
`second step functions have substantially similar power
`changes and modifications of the invention are possible
`without departure from the scope of the invention,
`output levels but have transitions from one level to the
`which is defined by the attached patent claims.
`next located at different distances, depending on
`whether the distance between said receiver and said
`We claim:
`transmitter is increasing or decreasing.
`1. In a cellular mobile radio communications system,
`a method of controlling the output power of radio sig
`14. The method of claim 13, wherein each of said step
`nals transmitted from a transmitter to a receiver,
`functions have ten discrete levels.
`wherein said output power of said transmitter is con
`60
`2
`s
`t
`r
`
`50
`
`55
`
`65
`
`ZTE, Exhibit 1008-0007
`
`