Transmission power control method and transmission power controller

Technical Field

0001This invention relates to a transmission power control method and transmission power control device in a CDMA mobile communication system. In particular, this invention relates to a transmission power control method and transmission power control device which control the uplink transmission power of a mobile station such that a target SIR is obtained for signals received from the mobile station on the mobile network side, and which also control the target SIR based on the quality of the transmission path.

Background Art

0002<patcit id="pcit0001" dnum="JP2000307511A"><text>JP2000307511 A</text></patcit> refers to a mobile communication system of code division multi-dimensional connection type. An error detection part inspects CRC of a reception signal that is base band-processed and it is informed to a reference value setting part. When it is OK, it is detected whether Sref speedily increases or not within a prescribed period. A difference between Sref whose number of increase times counted within the prescribed period is the first time and reception SIR is compared with the difference between Sref at present time and reception SIR. When it is not less than a prescribed value, Sref is reduced in a large step as a speedy increase. If not, Sref is reduced in a small step. A transmission power control part generates a TPC bit instructed by a transmission power by Sref updated by outer loop control and reception SIR measured by an SIR measurement part.

0003<patcit id="pcit0002" dnum="US6628924B1"><text>US6628924 B1</text></patcit> refers to a CDMA mobile communications system. A method for controlling a reference SIR used for a closed loop control in a CDMA mobile communications system is disclosed. When an uplink channel has insufficient communication quality, the reference SIR is increased by a predetermined increase amount. When the uplink channel has sufficient communication quality, it is determined whether the base station is involved in the closed loop control. When the base station in involved in the closed loop control, the reference SIR in decreased by a predetermined first decrease amount. When the bane station is not involved in the closed loop control, the reference SIR is decreased by a predetermined second decrease amount which is greater than the predetermined first decrease amount.

(1) Transmission Power Control of the Prior Art

0004In mobile communication systems conforming to 3GPP specifications, transmission power control is executed such that prescribed error rates are obtained on the network side and on the mobile station side, and such that the transmission power does not become excessive. <figref idref="f0010">Fig. 12</figref> explains transmission power control, and shows a case in which the mobile station uplink transmission power is controlled on the network side.

0005Signals transmitted from a mobile station 1 are demodulated by the demodulator 2a of the base station 2, and then decoded by the error-correcting decoder 2b. Then CRC error detection is performed for each transport block TrBk in the CRC detector 2c. The error detection result for a transport block TrBk is conveyed to the target SIR control portion 3a of the base station control device 3. The target SIR control portion 3a reduces the target SIR if there are no errors in a prescribed observation interval, and if there are errors, increases the target SIR based on the block error rate, and sets the target SIR in the storage portion 2d of the base station 2. The comparator 2e compares the target SIR with the measured SIR of received signals, measured by the SIR measurement portion 2f, and based on the comparison result creates a TPC bit to control the transmission power of the mobile station 1, and transmits the TPC bit to the mobile station 1. That is, if the measured SIR is greater than the target SIR, a TPC bit is created so as to lower the transmission power by a fixed amount, and if the measured SIR is less than or equal to the target SIR, a TPC bit is created so as to raise the transmission power by a fixed amount; the TPC bit is then transmitted to the mobile station over a dedicated physical control channel DPCCH. The mobile station 1 controls its own transmission power according to the received TPC bit. The feedback loop ILP which controls the uplink transmission power of the mobile station is called the inner loop; the base station 2 performs inner loop transmission power control. The feedback loop OLP which controls the target SIR is called the outer loop; the base station control device performs outer loop transmission power control.

0006In uplink outer loop transmission power control, when the base station 2 transmits data received from the mobile station 1 to the base station control device 3, information on the quality over the wireless interval (between the mobile station and base station) is appended to the data. Here, quality information are parameters added to the Iub frame protocol in the 3GPP system, and are (1) QE (Quality Estimates), which are error correction information (for example, error correction rates) over the wireless interval, and (2) a CRCI (CRC Indicator), which is the result of judgment of the CRC appended to each transport block TrBk. The base station control device 3 measures the quality of received data over a fixed length of time based on this quality information.

0007As stated above, quality information includes CRCI and QE; when using CRCI, the base station control device 3 computes the BLER (block error rate) from the CRCI, and uses a comparison of the BLER representing the measured quality and a BLER given as the target quality to compute the uplink target SIR used in inner loop transmission power control. When using QE, the base station control device 3 converts the QE into a BER (bit error rate), computes the average value of the BER over a measurement interval, and uses a comparison of the BER representing the measured quality and a BER given as the target quality to compute the uplink target SIR used in uplink inner loop transmission power control. Computation of the target SIR may be performed in units of received frames, or a measurement interval may be set and computation performed after the measurement interval has expired. If the target SIR obtained in this way differs from the previous value at the end of the measurement time, the new target SIR is input to the base station 2.

(2) Transmission power control during handover

0008The above is a case in which one mobile station communicates with one base station; during handover, as shown in <figref idref="f0011">Fig. 13</figref>, the mobile station 1 communicates simultaneously with two base stations 2, 2'. In this case, the base station control device 3 employs the data selection portion 3b to select the uplink data received from the plurality of base stations 2, 2', as shown in <figref idref="f0011">Fig. 14</figref>, the data with better quality (for example, the data with better quality according to comparison of QE, CRCI, or similar), and the target SIR control portion 3a (<figref idref="f0010">Fig. 12</figref>) performs quality measurement of the selected data and determines the target SIR. Selection of the data with better quality is called selective diversity, and control at the time of handover is called DHO (Diversity Hand Over). Because quality is improved as a result of selective diversity, the gain resulting from selective diversity is called the diversity gain. In the case of a connection with a single base station, there does not exist other selectable data, selective diversity is not possible, and so diversity gain is not obtained.

0009The base station control device 3 notifies all base stations 2, 2' for which a connection exists with the mobile station 1 shown in <figref idref="f0011">Fig. 14</figref> of the target SIR (Eb/No) computed based on the above data after selection, in conformance with the interface Iub between the base station and the base station control device, and each base station performs inner loop transmission power control based on the target SIR thus received.

(3) Problems

0010During handover, the DHO (Diversity Hand Over) control explained in <figref idref="f0011">Fig. 14</figref> is performed. Hence a target SIR computed for the quality obtained by the diversity gain due to selective diversity is set simultaneously in all base stations, and all base stations perform inner loop transmission power control based on this same value for the target SIR (see <figref idref="f0011">Fig. 15</figref>). Consequently, in conventional outer loop transmission power control, there is the problem that quality states for each of the transmission paths are not taken into consideration in handover states having a plurality of transmission paths to base stations. In <figref idref="f0011">Fig. 15</figref>, the polygonal line ZZL is the measured SIR, and the dashed line DL is the target SIR. Uplink transmission power control is performed based on the magnitude relation between the measured SIR and target SIR, and the measured SIR changes, as shown by the polygonal line, as a result. The target SIR is updated in each measurement interval.

0011Specific problems are explained below, but the following points (1) through (4) must be taken into consideration. <ol id="ol0001" compact="compact" ol-style=""><li>(1) The quality obtained by the diversity gain of selective diversity is better, in the DHO state, than the quality of data transmitted from individual base stations.</li><li>(2) Further, in conventional methods, upon entering the DHO state (at the start of handover), the uplink target SIR values set in base stations 2, 2' may not be the same for all base stations. (3) In addition, the result obtained may not necessarily indicate that the uplink target SIR in inner loop transmission power control and the quality of data actually received (or the reception SIR) are equal. (4) Further, due to the nature of outer loop control, because the update interval of the target SIR used in inner loop control is extremely long compared with inner loop control, insofar as possible an appropriate target SIR value must be set. If an inappropriate target SIR value were set, transmission power control will be performed according to this inappropriate update value until the time of the next update.</li></ol>

• Non-DHO state/initial DHO state

0012When the mobile station 1 and the base station 2 are communicating one-to-one, the uplink target SIR value sent to the base station 2 (<figref idref="f0011">Fig. 13</figref>) and the reference SIR in uplink outer loop transmission power control coincide (see <figref idref="f0012">Fig. 16</figref>). At this time, the DHO state has not yet been entered, and so there is no need to consider diversity gain due to selective diversity. Hence due to uplink outer loop transmission power control, the updated SIR value (the target SIR value after updating) may be larger than, equal to, or smaller than the reference SIR (the uplink target SIR of the base station 2), depending on the reception quality (see <figref idref="f0012">Fig. 16</figref>).

0013Thereafter, upon entering the DHO state, as shown in <figref idref="f0012">Fig. 17</figref>, the uplink target SIR for inner loop transmission power control set in the newly added base station 2' may be different from that in the base station 2. This is because the conditions of the wireless interval differ for the base stations 2 and 2', so that the values need not be the same. After entering this DHP state, when outer loop transmission power control is executed, the updated SIR is computed for the quality obtained through the diversity gain of selective diversity, as explained above. At this time, the uplink target SIR value set in base station 2 is used as reference, and so the uplink SIR value set in base station 2' is not taken into consideration (<figref idref="f0012">Fig. 17</figref>).

0014Normally the reference SIR value used in outer loop transmission power control must be used to determine the updated SIR based on the virtual SIR due to the DHO effect, taking into account the value set in the base station 2', as shown in <figref idref="f0012">Fig. 18</figref>. The above is a problem in the initial DHO state.

• Problems in the DHO state

0015Quality judgments performed in outer loop transmission power control are determined by received data error rates and other quality information. However, the average reception level over a short time used in transmission power control does not necessarily correspond to the received data error rate. This is because the received data error rate is not determined only by the reception level, but is also affected by the period of fading and delay profile conditions. Hence the uplink target SIR value set in the newly added base station during DHO cannot be easily inferred from the reception quality; that is, cases are possible in which the average reception level is high and the SIR value is high even when quality is poor. Below, examples of the problem are explained in light of these considerations.

(a) Example of a case in which quality of different transmission paths is poor, but with selective diversity the target quality or better is obtained:

0016As shown in <figref idref="f0013">Fig. 19</figref>, there are cases in which the quality of individual transmission paths is worse than the quality target value, but with selective diversity, quality equal to or exceeding the target quality is obtained. That is, even if the quality for the base stations 2, 2' (indicated by black circles) is below the target quality (BER = 1/100 or above), upon entering the DHO state, the quality resulting from selective diversity (black circle) may be equal to or above the target quality (BER less than 1/100). In this case, the initially calculated updated SIR value is smaller than the uplink target SIR value at the current base station 2. With respect to base station 2', if the target SIR value were lower than the target value set in the current base station 2, and also lower than the updated SIR value, then rather than lowering the SIR values of the base stations 2, 2', an operation is instead performed to unnecessarily raise the target SIR value for the base station 2'.

0017By this means the transmission path quality for base station 2' is improved, and there is the possibility that the quality with selective diversity may be excess quality. And in communications with other mobile stations (in particular, mobile stations served by the base station 2' and similar), noise, that is interference, will be increased, possibly leading to degraded quality.

(b) Example of a case in which quality varies for different transmission paths, and quality is poor even with diversity gain:

0018As shown in <figref idref="f0013">Fig. 20</figref>, there are cases in which the quality of each transmission path is poor, and the quality with selective diversity is also lower than the target quality. That is, there are cases in which the quality (black circles) of the base stations 2, 2' is lower than the target quality (BER = 1/100 or higher), and when the DHO state is entered, the quality (black circle) due to selective diversity is also lower than the target quality (BER = 1/100 or higher). In such cases, upon entering the DHO state, the initially calculated updated SIR value is higher than the uplink target SIR value of the current base station 2. With respect to base station 2', if the uplink target SIR value is higher than the value set for the current base station 2, and is also higher than the updated SIR value, then rather than raising the separate SIR values, an operation is instead performed to lower the value for the base station 2'. As a result there is the possibility that the transmission quality for the base station 2' is worsened, an appropriate diversity gain cannot be obtained, and the quality with selective diversity is worsened.

(c) Excessive increase in SIR value

0019As shown in <figref idref="f0013">Fig. 21</figref>, there are cases in which the quality of each transmission path is poor, and the quality with selective diversity is also below the target quality. That is, there are cases in which the quality (black circles) of the base stations 2, 2' is lower than the target quality (BER = 1/100 or higher), and when the DHO state is entered, the quality (black circle) due to selective diversity is also lower than the target quality (BER = 1/100 or higher). Suppose that in such a case, cause of poor reception quality, the SIR value of base station 2 is the highest value for obtaining the required target quality through power control up to immediately before the DHO state. If at this time the uplink target SIR value set in the newly added base station 2' is low, and moreover data quality is poor, the updated SIR value will be higher than the value set in base station 2. Consequently the amount of change in the target SIR value at base station 2' is be extremely large, prompting an increase in power, and power control will result which intensifies interference with other mobile stations.

0020In light of the above, an object of this invention is to enable power control which takes into consideration the diversity gain of selective diversity. By means of such power control, unnecessary noise (interference) in wireless intervals can be reduced, wireless resources can be secured, that is, the number of users accommodated in a cell (cell capacity) can be increased, and there is also the advantage that power consumption of mobile stations is reduced. This is because it is sufficient to request quality for transmission path data from mobile stations which takes diversity gain into account. Moreover, by means of this invention a number of devices which heretofore had been necessary become unnecessary, leading to cost decreases and reductions in the scale of circuits.

Disclosure of the Invention

0021This invention relates to transmission power control in a CDMA mobile communication system, in cases in which a mobile station transmits and receives the same data with a plurality of base stations simultaneously, during handover or at other times. The essence of this transmission power control is that the uplink transmission power of the mobile station is controlled so as to obtain the target SIR, and in addition the target SIR is controlled based on the quality of the transmission path.

0022In an aspect of the invention, (1) when a mobile station transmits and receives the same data simultaneously with a plurality of base stations, the data received via the transmission path with the best quality, obtained by monitoring quality of each transmission path is selected, and for each transmission path, the selectivity for data sent is calculated; (2) based on the data quality after data selection, the target SIR is updated; and, (3) the target SIR after updating is multiplyied by the selectivity of each transmission path, and the result is taken to be the actual target SIR for each base station of each transmission path.

0023Through the above aspect, power control which takes into consideration the diversity gain due to selective diversity can be executed.

Brief Description of the Drawings

0024<ul id="ul0001" list-style="none"><li><figref idref="f0001">Fig. 1</figref> is a drawing of the configuration of a preferred embodiment of a transmission power control device;</li><li><figref idref="f0002">Fig. 2</figref> is an example of the configuration of the data selection portion;</li><li><figref idref="f0003">Fig. 3</figref> shows the processing flow of the target SIR update portion;</li><li><figref idref="f0004">Fig. 4</figref> explains the target SIR of each base station in the preferred embodiment;</li><li><figref idref="f0004">Fig. 5</figref> explains a modified example of the preferred embodiment;</li><li><figref idref="f0004">Fig. 6</figref> is a drawing of the configuration of the base station-specific target SIR calculation portion of the modified example;</li><li><figref idref="f0005">Fig. 7</figref> is a drawing of the configuration of a first example of a transmission power control device;</li><li><figref idref="f0006">Fig. 8</figref> is a drawing of the configuration of a second example of a transmission power control device;</li><li><figref idref="f0007">Fig. 9</figref> is a modified example of the second example;</li><li><figref idref="f0008">Fig. 10</figref> is a drawing of the configuration of a third example of a transmission power control device;</li><li><figref idref="f0009">Fig. 11</figref> is a modified example of the third example;</li><li><figref idref="f0010">Fig. 12</figref> explains basic transmission power control in a CDMA mobile communication system;</li><li><figref idref="f0011">Fig. 13</figref> is a drawing of the connection relation between a mobile station, two base stations, and a base station control device at the time of handover;</li><li><figref idref="f0011">Fig. 14</figref> explains selective diversity in the base station control device;</li><li><figref idref="f0011">Fig. 15</figref> explains inner loop transmission power control;</li><li><figref idref="f0012">Fig. 16</figref> is a drawing of SIR correlation in a non-DHO state;</li><li><figref idref="f0012">Fig. 17</figref> is a drawing of SIR correlation in an initial DHO state;</li><li><figref idref="f0012">Fig. 18</figref> is a drawing of SIR correlation taking the DHO effect into account;</li><li><figref idref="f0013">Fig. 19</figref> explains an example of an operation to raise the SIR regardless of excess quality;</li><li><figref idref="f0013">Fig. 20</figref> is an explanatory drawing showing a case in which the SIR is lowered regardless of quality degradation; and,</li><li><figref idref="f0013">Fig. 21</figref> is an explanatory drawing showing a case resulting in an inadvertent increase in SIR value.</li></ul>

Best Mode for Carrying Out the Invention

(A) Preferred Embodiment

0025<figref idref="f0001">Fig. 1</figref> is a drawing of the configuration of a preferred embodiment of a transmission power control device, provided within a base station control device (a higher-level device relative to a base station). A summary of the preferred embodiment is as follows.

0026Due to the diversity gain obtained as a result of selective diversity (see <figref idref="f0011">Fig. 14</figref>) in the base station control device, the data received from individual base stations does not necessarily satisfy the target quality. In other words, it is sufficient that the quality resulting from diversity satisfy the target quality. Because only selected data contributes to this target quality, the target quality is thought to be maintained according to the following equation: <maths id="math0001" num=""><math display="block"><mrow><mi>target quality</mi><mo>=</mo><mi>target quality</mi><mo>×</mo><mfenced separators=""><mi>first base station selectivity</mi><mo>+</mo><mi>second base station selectivity</mi></mfenced></mrow></math><img file="EP1548960B1_D0001.tif" /></maths>

0027Therefore, in the preferred embodiment, the data selectivities s1, s2 of each of the transmission paths are multiplied by the updated target SIR value based on the data quality after diversity, and the target SIR thus obtained is taken to be the true target SIR value in each of the base stations. The above is a summary of the preferred embodiment; below, overall operation is explained referring to <figref idref="f0001 f0002 f0003">Fig. 1 through Fig. 3</figref>.

0028At the time of handover, the mobile station transmits and receives the same data simultaneously with a plurality of base stations (in the drawing, the two base stations 10a, 10b). Upon receiving data from the mobile station, each of the base stations 10a and 10b detects errors in the received data, appends a quality identifier (in the case of 3GPP specifications, QE (Quality Estimates) and CRCI (CRC Indicator)) to the received data, in for example transport block units or frame units, and sends the data to the base station control device 20.

0029The data selection portion 21 of the base station control device 20 references the quality identifier appended to the received data, selects data with the best quality in each frame, and outputs this data as data after diversity processing. The data selection portion 21 also calculates and outputs, for each transmission path, the selectivities s1, s2 of data sent via the transmission path. The target SIR update portion 22 uses the quality identifier appended to the selected data to measure the quality after data selection, compares the measured quality with the quality target value, and updates the target SIR based on the comparison result. For example, if the measured quality is worse that the quality target value, a prescribed increase step amount ΔUP is added to the reference SIR (the target SIR set in the base station which had been communicating before the handover) to update the target SIR, and if the measured quality is better than the quality target value, a prescribed decrease step amount Δdown is subtracted from the reference SIR to update the target SIR. The target SIR after updating becomes the next reference SIR. Upon receiving data from the mobile station, each of the base stations 10a and 10b detects errors in the received data, appends a quality identifier (in the case of 3GPP specifications, QE (Quality Estimates) and CRCI (CRC Indicator)) to the received data, in for example transport block units or frame units, and sends the data to the base station control device 20.

0030The data selection portion 21 of the base station control device 20 references the quality identifier appended to the received data, selects data with the best quality in each frame, and outputs this data as data after diversity processing. The data selection portion 21 also calculates and outputs, for each transmission path, the selectivities s1, s2 of data sent via the transmission path. The target SIR update portion 22 uses the quality identifier appended to the selected data to measure the quality after data selection, compares the measured quality with the quality target value, and updates the target SIR based on the comparison result. For example, if the measured quality is worse that the quality target value, a prescribed increase step amount ΔUP is added to the reference SIR (the target SIR set in the base station which had been communicating before the handover) to update the target SIR, and if the measured quality is better than the quality target value, a prescribed decrease step amount Δdown is subtracted from the reference SIR to update the target SIR. The target SIR after updating becomes the next reference SIR.

0031The target SIR calculation portion 23 comprises two multipliers 23a, 23b; the target SIR after updating is multiplied by the selectivities s1, s2 of each of the transmission paths to calculate the actual target SIRs of the respective transmission paths (see <figref idref="f0004">Fig. 4</figref>), which are respectively set in the base stations 10a, 10b. Here, as a method of reflecting the selectivity, as the selection condition, in the target quality (SIR), the target SIR is multiplied by each of the selectivities; but various methods of reflecting the selection condition are conceivable, such as increasing the degree of control on the more-selected side, or setting a higher target SIR on the more-selected side.

0032<figref idref="f0002">Fig. 2</figref> is an example of the configuration of the data selection portion 21; the quality information extraction portions 21a, 21b extract quality information from the data series input from the base stations 10a, 10b, and input the quality information to the quality decision portion 21c. The quality decision portion 21c decides on the best-quality data for each frame, and inputs this data to the selector 21d. The selector 21d selects the good-quality data which is temporarily stored in the buffer 21e, and outputs this as diversity data. Also, for each frame the quality decision portion 21c inputs to the selectivity calculation portion 21f information indicating which of the base stations has input data of good quality. The selectivity calculation portion 21f counts the number of times data has been input from each of the base stations, and calculates and outputs the data selectivities s1, s2 for each base station.

0033<figref idref="f0003">Fig. 3</figref> shows the processing flow of the target SIR update portion 22.

0034At the start of control, the target SIR update portion 22 sets initial values of the observation interval T, increase/decrease steps ΔUP/Δdown, quality target value Q_T, and reference SIR (=SIR_R) (step 101). The observation interval T is input as a number of blocks or as a number of frames; the quality target value Q_T is input as a block error rate BELR. The initial value of the reference SIR (=SIR_R) is the target SIR set in the base station which had been communicating prior to the handover.

0035Upon input of data from the data selection portion 21, the target SIR update portion 22 references the CRCI and counts the number of errors for each transport block TrBk (steps 102 to 104), increments the number of blocks received (step 105), checks whether the number of blocks received has reached the number of blocks of the observation interval (step 106), and if the number of received blocks has not reached the number of blocks of the observation interval, performs the processing of step 102 and later, but if the number of blocks received has reached the number of blocks of the observation interval, calculates the reception quality Q_M (block error rate) from the number of block errors and the number of received blocks (step 107). Then, the measured quality Q_M is compared with the target quality Q_T (step 108).

0036If the measured quality Q_M is better than the target quality Q_T, the equation <maths id="math0002" num=""><math display="block"><mrow><msub><mi mathvariant="normal">SIR</mi><mi mathvariant="normal">R</mi></msub><mo>=</mo><msub><mi mathvariant="normal">SIR</mi><mi mathvariant="normal">R</mi></msub><mo>-</mo><mi mathvariant="normal">Δdown</mi></mrow></math><img file="EP1548960B1_D0002.tif" /></maths> is used to compute the target SIR (step 109). That is, if the conditions of the transmission path are good and the quality of the received data is good, the target SIR is reduced by the amount Δdown. On the other hand, if the measured quality Q_M is worse than the target quality Q_T, the equation <maths id="math0003" num=""><math display="block"><mrow><msub><mi mathvariant="normal">SIR</mi><mi mathvariant="normal">R</mi></msub><mo>=</mo><msub><mi mathvariant="normal">SIR</mi><mi mathvariant="normal">R</mi></msub><mo>+</mo><mi mathvariant="normal">ΔUP</mi></mrow></math><img file="EP1548960B1_D0003.tif" /></maths> is used to compute the target SIR (step 110). That is, if the conditions of the transmission path are poor and the quality of the received data is poor, the target SIR is increased by the amount ΔUP.

0037Then, SIR_R is taken to be the target SIR after updating, and is input to the base station-specific target SIR calculation portion 23 (<figref idref="f0001">Fig. 1</figref>) (step 111). The target SIR after updating becomes the next reference SIR.

0038However, in an extreme case in the preferred embodiment, one of the selectivities may be too great and the other selectivity may be too small, so that the target SIR may be too low. Hence means are provided in the last stage of the target SIR calculation portion 23 to set a minimum value for the target SIR and execute control such that the target SIR does not become smaller than this minimum value. Or, a minimum value for the selectivity can be set, and the selectivity determined so as never to be smaller than the minimum value. For example, if the minimum value is smin (&lt;1.0) and the actual selectivities are s1 and s2, then the selectivities S1, S2 are determined using the equations <maths id="math0004" num=""><math display="block"><mrow><mi mathvariant="normal">S</mi><mo>⁢</mo><mn mathvariant="normal">1</mn><mo>=</mo><mfenced separators=""><mn mathvariant="normal">1</mn><mo>-</mo><mi mathvariant="normal">smin</mi></mfenced><mo>×</mo><mi mathvariant="normal">s</mi><mo>⁢</mo><mn mathvariant="normal">1</mn><mo>/</mo><mfenced separators=""><mi mathvariant="normal">s</mi><mo>⁢</mo><mn mathvariant="normal">1</mn><mo>+</mo><mi mathvariant="normal">s</mi><mo>⁢</mo><mn mathvariant="normal">2</mn></mfenced><mo>+</mo><mi mathvariant="normal">smin</mi></mrow></math><img file="EP1548960B1_D0004.tif" /></maths><maths id="math0005" num=""><math display="block"><mrow><mi mathvariant="normal">S</mi><mo>⁢</mo><mn>2</mn><mo>=</mo><mfenced separators=""><mn mathvariant="normal">1</mn><mo>-</mo><mi mathvariant="normal">smin</mi></mfenced><mo>×</mo><mi mathvariant="normal">s</mi><mo>⁢</mo><mn mathvariant="normal">2</mn><mo>/</mo><mfenced separators=""><mi mathvariant="normal">s</mi><mo>⁢</mo><mn mathvariant="normal">1</mn><mo>+</mo><mi mathvariant="normal">s</mi><mo>⁢</mo><mn mathvariant="normal">2</mn></mfenced><mo>+</mo><mi mathvariant="normal">smin</mi></mrow></math><img file="EP1548960B1_D0005.tif" /></maths>

0039According to the preferred embodiment described above, transmission power control which takes into consideration the diversity gain of selective diversity can be performed. By means of the preferred embodiment, if instructions are given to increase (or decrease) the target SIR, the target SIR values of each of the base stations can be controlled to reliably increase (or decrease), and moreover the control width of the target SIR can be made small. As a result, unnecessary noise (interference) in wireless intervals can be reduced, and wireless resources can be secured, that is, the number of users accommodated in a cell (cell capacity) can be increased. Further, power consumption by the mobile station can be reduced.

0040<figref idref="f0004">Fig. 5</figref> explains a modified example of the preferred embodiment. In the preferred embodiment, the target SIR determined from the data quality after diversity processing was multiplied by the data selectivities of the respective transmission paths (here, s1&lt;s2), and the results are used as target SIR values for the respective transmission paths. However, it is necessary to taken into consideration that (1) SIR value and reception quality are not necessarily equal, and (2) data selectivity is always changing. Hence in this modified example, as shown in <figref idref="f0004">Fig. 5</figref>, by adding a margin value ΔUP to the target SIRs for each transmission path obtained in the preferred embodiment, problems arising from the factors (1) and (2) can be eliminated. ΔUP is the same as the increase step amount used in the target SIR update portion 22.

0041<figref idref="f0004">Fig. 6</figref> is a drawing of the configuration of the target SIR calculation portion 23 of the modified example; addition portions 23c, 23d are newly added. These addition portions 23c, 23d add the margin value ΔUP to the outputs of the multipliers 23a, 23b, and output the addition result as the true target SIR for the respective base stations 10a, 10b.

(B) First example

0042<figref idref="f0005">Fig. 7</figref> is a drawing of the configuration of a first example of a transmission power control device, provided within the base station control device. In the first example, portions which are the same as in the preferred embodiment are assigned the same symbols. A difference is that in the preferred embodiment, the data quality after selective diversity processing is measured, whereas in the first example, data quality is measured for the different data prior to selective diversity processing.

0043The target SIR update portion 24 measures the quality of data input from the base station 10a before selective diversity processing, updates the target SIR of the base station 10a based on the measured quality, and inputs the updated target SIR to the multiplier portion 23b of the target SIR calculation portion 23. The target SIR update portion 24 performs update processing according to the processing flow of <figref idref="f0003">Fig. 3</figref>, but the reference SIR value is the same as the target SIR value set in the base station 10a.

0044The target SIR update portion 25 measures the quality of data input from the base station 10b before selective diversity processing, updates the target SIR of the base station 10b based on the measured quality, and inputs the updated target SIR to the multiplier portion 23a of the target SIR calculation portion 23. The target SIR update portion 25 performs update processing according to the processing flow of <figref idref="f0003">Fig. 3</figref>, but the reference SIR value is the same as the target SIR value set in the base station 10b.

0045The multiplier portion 23b of the target SIR calculation portion 23 multiplies the target SIR of the base station 10a after updating by the selectivity s1 to calculate the actual target SIR of the base station 10a, and sets the result in the base station 10a. The calculation portion 23a multiplies the target SIR of the base station 10b after updating by the selectivity s2 to calculate the actual target SIR of the base station 10b, and sets the result in the base station 10b.

0046According to the transmission power control of the first example as described above, the target SIR of a base station is calculated based on the data quality before diversity processing, and multiplies this target SIR by the selectivity to obtain the actual target SIR. Hence the actual target SIR value to attain the quality target value can be made small, transmission power control which takes into consideration the diversity gain of selective diversity can be performed, and the transmission power of the mobile station can be reduced.

(C) Second example

0047<figref idref="f0006">Fig. 8</figref> is a drawing of the configuration of a second example of a transmission power control device; portions which are the same as in the preferred embodiment of <figref idref="f0001">Fig. 1</figref> are assigned the same symbols.

0048During handover, the mobile station transmits and receives the same data simultaneously with a plurality of base stations (in the drawing, two base stations). Each of the base stations 10a, 10b, upon receiving data from the mobile station, detects errors in the received data, appends a quality identifier to the received data, in for example transport block units or frame units, and sends the data to the base station control device 20. In <figref idref="f0006">Fig. 8</figref>, the quality identifier appending portion, received data transmission portion, and other portions in the base station are omitted.

0049The data selection portion 21 of the base station control device 20 references the quality identifier appended to the received data, selects the data with the best quality in each frame, and outputs the data as data after diversity processing. The data selection portion 21 calculates and outputs, for each transmission path, the selectivities s1, s2 of data sent over the transmission path.

0050The target SIR update portion 22 measures the quality after data selection using the quality identifier appended to the selected data, according to the processing flow of <figref idref="f0003">Fig. 3</figref>, compares the measured data with the quality target value, and updates the target SIR based on the comparison result. For example, if the measured quality is worse that the quality target value, a prescribed increase step amount ΔUP is added to the reference SIR (the target SIR set in the base station communicating before the handover) stored in register 31 to update the target SIR, and if the measured quality is better than the quality target value, a prescribed decrease step amount Δdown is subtracted from the reference SIR to update the target SIR. The target SIR after updating becomes the next reference SIR.

0051The difference calculation portion 32 calculates the difference ΔSIR between the target SIR value after updating, and the reference SIR value SIR_R which is the previously updated SIR value. The difference SIR calculation portion 33 multiplies this difference ΔSIR by the selectivities s1, s2 of each of the transmission paths to compute the increase or decrease s1×ΔSIR, s2×ΔSIR in the target SIR for each of the transmission paths, and sends the results to the respective base stations 10a, 10b.

0052The addition portion AD in each of the base stations 10a, 10b adds the respective increase/decrease s1×ΔSIR, s2×ΔSIR in the target SIR received from the base station control device 20 to the current target SIR1, SIR2 set in the register RG, for use as the new target SIR. Subsequently, the base stations 10a, 10b execute transmission power control for the mobile station based on the new target SIR values.

0053<figref idref="f0007">Fig. 9</figref> is a modified example of the second example. In the second example, the new target SIR values for the base stations 10a, 10b are calculated by the base stations; in the modified example, the base station control device calculates the new target SIR values for the base stations 10a, 10b and sends them to the base stations.

0054The difference SIR calculation portion 33 multiplies the difference value ΔSIR by the selectivities s1, s2 of each of the transmission paths, and inputs the increase/decrease amounts s1×ΔSIR, s2×ΔSIR in the target SIR values for each transmission path to the addition portions 41, 42. The addition portion 41 adds the reference SIR (the target SIR set in the base station 10a before handover) stored in the register 43 and the increase/decrease amount s1×ΔSIR, and sends the result to the base station 10a. And, the addition portion 42 adds the reference SIR (the target SIR set in the base station 10b before handover) stored in the register 31 and the increase/decrease amount s2×ΔSIR, and sends the result to the base station 10b. The base stations 10a, 10b subsequently execute transmission power control for the mobile station based on the new target SIR values which have been sent. The target SIR values output by the addition portions 41, 42 become the next reference SIR values.

0055According to the second example described above, the target SIR for each base station is made to reflect the difference between the target SIR determined based on the data quality after diversity processing and the previous target SIR, according to the selectivity; hence the target SIR values for each base station can be controlled gradually, and more finely-tuned transmission power control can be executed, taking into account the diversity gain of selective diversity. By means of the second example, the base station target SIR can be kept from becoming too small even when the selectivity is small, and large fluctuations in the target SIR can be eliminated.

(D) Third example

0056<figref idref="f0008">Fig. 10</figref> is a drawing of the configuration of a third example of a transmission power control device; portions which are the same as in the second example of <figref idref="f0006">Fig. 8</figref> are assigned the same symbols. A difference is that in the second example, the data quality after selective diversity processing is measured and the increase or decrease in target SIR is calculated, whereas in the third example the data quality is measured for the different data prior to selective diversity processing, and the increase or decrease in the target SIR is calculated.

0057At the time of handover, the mobile station transmits and receives the same data simultaneously with a plurality of base stations (in the drawing, two base stations). Upon receiving data from the mobile station, each of the base stations 10a, 10b detects errors in the received data, appends a quality identifier to the received data in for example transport block units or frame units, and sends the data to the base station control device 20. In <figref idref="f0008">Fig. 10</figref>, the quality identifier appending portion, received data transmission portion, and other portions in the base stations 10a, 10b are omitted.

0058The data selection portion 21 of the base station control device 20 references the quality identifier appended to the received data, selects the data with the best quality in each frame, and outputs this data as data after diversity processing. The data selection portion 21 also calculates and outputs, for each transmission path, the selectivities s1, s2 of the data sent over the transmission path.

0059The target SIR update portion 51 uses the quality identifier appended to the data to measure the quality of data prior to data selection, compares the measured quality and the quality target value, and based on the comparison result updates the target SIR of the base station 10a, according to the processing flow of <figref idref="f0003">Fig. 3</figref>. For example, if the measured quality is worse than the quality target value, a prescribed increase step amount ΔUP is added to the reference SIR (the target sir set in the base station 10a prior to handover) stored in register 52 to update the target SIR, and if the measured quality is better than the quality target value, a prescribed decrease step amount Δdown is subtracted from the reference SIR to update the target SIR. The target SIR after updating becomes the next reference SIR.

0060The difference calculation portion 53 calculates the difference ΔSIR1 between the target SIR value after updating and the reference SIR value SIR_R1 which is the previous updated SIR value, and inputs the result to the difference SIR calculation portion 54 and switching portion 55. The difference SIR calculation portion 54 multiplies the difference value ΔSIR₁ by the selectivity s1 of the transmission path to calculate the increase or decrease s1×ΔSIR₁ in the target SIR, which is input to the switching portion 55.

0061When the difference ΔSIR₁ is negative and the target SIR value has fallen, the transmission path satisfies the target quality. Hence the switching portion 55 transmits the difference ΔSIR₁ without modification to the base station 10a as the difference with the current target SIR. However, if the difference ΔSIR₁ is positive and the target SIR value has risen, the switching portion 55 transmits s1×ΔSIR₁ to the base station 10a as the difference with the current target SIR.

0062The addition portion AD of the base station 10a adds the increase or decrease in target SIR received from the base station control device 20 to the current target SIR1 set in the register RG, and uses the result as the new target SIR. Subsequently, the base station 10a executes transmission power control for the mobile station based on the new target SIR. The adder 56 adds the output of the switching portion 55 to the current reference SIR, and stores the addition result in the register 52 as the new reference SIR.

0063The above explanation is for a case in which the target SIR of the base station 10a is updated; the target SIR of the base station 10b is similarly updated by the target SIR update control portion 57.

0064<figref idref="f0009">Fig. 11</figref> is a modified example of the third example; whereas in the third example the new target SIR values of the base stations 10a, 10b are calculated by the base stations, in the modified example the base station control device calculates the new target SIR values for the base stations 10a, 10b, and transmits the results to the base stations.

0065The adder 58 adds the reference SIR stored in register 52 and the increase or decrease in target SIR output from the switching portion 55, and transmits the addition result to the base station 10a as the target SIR, while also updating the reference SIR value of the register 52 with the addition result. The base station 10a executes transmission power control for the mobile station based on the new target SIR value thus sent. Similarly, the target SIR update control portion 57 updates the target SIR for the base station 10b, and the base station 10b executes transmission power control for the mobile station based on the updated target SIR.

0066According to the transmission power control of the third example described above, the target SIR of a base station is calculated based on the data quality before diversity processing, and the target SIR of the base station is made to reflect the difference between the target SIR and the previous target SIR according to the selectivity, so that the target SIR value of each base station can be controlled gradually, and more finely-tuned transmission power control can be executed, taking into account the diversity gain of selective diversity.