A power control method in a wcdma mobile communication system

Field of The Invention

0001The present invention relates to WCDMA mobile communication technologies, and more particularly, to a method for uplink power controlling in a WCDMA mobile communication system.

Background of The Invention

0002The uplink of the WCDMA system is interference limited. For a certain User Equipment (UE) in the system, the transmitting power of other UE is its interference. Some UE locate near to the base station and some locate far away from the base station due to the random distribution of the UEs in an area. Therefore, the SIR of a remote UE received by the base station is very weak, which results in great bit error and Near-Far Effect, in case that the same transmitting power is employed for all UEs. Furthermore, the mobile users are usually affected by Doppler Shift and Rayleigh Fading of the wireless link which is of wide and dynamic frequency range. In these cases, it requires prompt and accurate power control for the uplink of the WCDMA system to guarantee Quality of Service (Qos) for the users.

0003Performing an uplink Inner Loop Power Control can adjust the transmitting power of each UE and decrease the influence of Near-Far Effect to ensure that the power of each UE received by the base station is equal and to make up the effect of Doppler Shift and Rayleigh Fading, so that each user meets the Qos of transmitting service. An Inner Loop Power Control method is presented in 3GPP TS 25.214: for the uplink, the base station measures Signal to Interference Ratio (SIR = E_b/N₀) for each received wireless link and then compares the received SIR with the Signal to Interference Ratio target (SIR_target) the service need to meet. If the SIR>=SIR_target, a transmitting power control instruction with the bit value of 1 is sent to the UE in the downlink control channel; if SIR<SIR_target, a transmitting power control instruction with the bit value of 0 is sent to the UE in the downlink control channel. The UE increases or decreases the transmitting power according to the received transmitting power control instruction and power control algorithm specified by the network layer. However, along with the variation of the mobile communication environment and the moving speed, the SIR_target need to be varied as well. And the initially assigned value of uplink SIR_target, specified by the network, might be of a great difference with the actual SIR_target value. In this case, transmitting power control, performed according to the initially assigned SIR_target in this circumstance, will not be accurate. Thus the SIR_target value should be adjusted in accordance with the service quality while performing Inner Loop Power Control. And this can be achieved by Outer Loop Power Control, i.e., Outer Loop Power Control is the assistant of Inner Loop Power Control, and the basis to adjust the transmitting power by Inner Loop Power Control method.

0004It is considered that the real time channel characteristics cannot be reflected completely due to the delay caused by the loop, which is a result of fast variation of wireless channel fading in urban environment in Chinese patent application No. CN1270459A "Improving Channel Adaptive Fast Power Control in CDMA". So different Inner Loop Power Control algorithms will be adopted according to different communication environments (urban area, suburban area or countryside) to perform Inner Loop Power Control, and achieved in hardware. Although the above patent considers the problem that channel characteristics cannot be tracked in time due to the loop delay and solves this problem by selecting different Inner Loop Power Control algorithms which take SIR_target as the benchmark, the required SIR_target will also be varied to meet the service quality if the UE speed or other communication environments vary. Thus, it is not enough to only select different Inner Loop Power Control methods to overcome channel fading. When the user's moving speed is promoted very quickly, the SIR_target required by the service will increase. Thus non-adjusting the SIR_target will result in bad communication quality and call failure. As for the situation that the user's moving speed varies from a high speed to a low speed, the SIR_target required by the service will decrease, and the user's transmitting power will be greater than the required transmitting power which will increase the interference among users and finally influences the uplink capacity of the cell.

0005Generally speaking, the existing power control methods cannot adjust the SIR_target adaptively according to actual communication, which leads to failure of accurate transmitting power control.

Summary of The Invention

0006What is needed of the present invention is to provide a method for power controlling in a WCDMA mobile communication system. The adjusting period of SIR_target can be determined according to the Qos level met by different service, and the SIR_target is adaptively adjusted according to the current actual communication quality to ensure the transmitting power of all kinds of services under all kinds of environments can be converged rapidly.

0007The theme of the method for power controlling of the present invention is: the base station measures the SIR of each wireless link, compares it with the SIR_target set according to Qos requirements, controls the SIR of each link converging to the SIR_target and also adjusts the SIR_target according to the quality information obtained by the measurements so that the service quality will not vary with the variation of wireless environments and the communication quality will maintain relatively stable.

0008The present invention provides a method for power controlling in a WCDMA mobile communication system, wherein it includes the steps of: determining user's initial transmitting power and initial uplink SIR_target; performing normal Outer Loop Power Control; measuring SIR of each wireless uplink; judging whether a link SIR_error exceeds an error threshold; if not, keeping on the normal Outer Loop Power Control; or else; pausing the normal Outer Loop Power Control and triggering an Outer Loop Power Control with high priority; performing the High Priority Outer Loop Power Control, and returning an performance result; keeping on the normal Outer Loop Power Control.

0009The present invention rapidly adjusts the SIR_target according to the link SIR_error, normal Outer Loop Power Control should be performed when the link SIR_error does not exceed the threshold, and a High Priority Outer Loop Power Control will be adopted when the link SIR_error exceeds the threshold; it ensures the rapid convergence of power control by two-level Outer Loop Power Control; the High Priority Outer Loop Power Control will be adopted when the difference between the assigned SIR_target and the actually measured SIR is big so that the transmit service can rapidly meet the service quality requirement; slightly adjust the SIR_target by using threshold report cyclic check when the difference between the assigned SIR_target and the actually measured SIR is small to ensure rapid and accurate convergence of the actual SIR, which substantially makes the communication quality meet the service quality rapidly. The present invention also determines the adjusting period of SIR_target according to different Qos levels met by different services, and the power control can be converged more rapidly by the method of adaptively adjusting step length according to the current actual communication quality status. The present invention considers the problem of power control convergence in the aspects of Qos level of the transmit service, mobile communication environment, real-time communication quality, etc., which has practical application value. Generally speaking, adopting the two-level Outer Loop Power Control method can guarantee the rapid convergence of user transmitting power to ensure the service quality of the transmission and improve the capacity of the system.

Brief Description of The Drawings

0010<ul id="ul0001" list-style="none" compact="compact"><li>Fig.1 is the general flow chart of the method for power controlling in WCDMA mobile communication system in accordance with the preferred embodiment of the present invention;</li><li>Fig.2 is the flow chart of normal Outer Loop Power Control in the present invention;</li><li>Fig.3 is the flow chart of High Priority Outer Loop Power Control in the present invention;</li><li>Fig.4 is the sketch map of practical application in WCDMA communication system in accordance with the present invention.</li></ul>

Detailed Description of The Preferred Embodiments:

0011Now, the present invention will be described in details with reference to the attached figures and instances.

0012The basic principle of realizing two-level Outer Loop Power Control is: performing normal Outer Loop Power Control when threshold triggered measurement report is not received; starting uplink High Priority Outer Loop Power Control when the threshold triggered measurement report is received, and pausing the normal Outer Loop Power Control process; carrying on the normal Outer Loop Power Control after finishing the High Priority Outer Loop Power Control.

0013Since the loop delay needs 4-5 frames, i.e., the effect of upwardly adjusting SIR_target can only be reflected after 4-5 frames, a shielding period is set before performing the normal Outer Loop Power Control and after upwardly adjusting the SIR_target, and in the shielding period, error blocks will not be counted for the normal Outer Loop Power Control process.

0014Normal Outer Loop Power Control can be performed when there is correspondence context between the user and Node B in the WCDMA system. And during the period of normal Outer Loop Power Control, High Priority Outer Loop Power Control is started if the measurement report triggered according to the SIR_error is received.

0015As shown in Fig. 1, the general steps of the method for power controlling in a WCDMA communication system includes: first, determining user's initial transmitting power and initial uplink SIR_target, starting Close Loop Power Control including Inner Loop Power Control, which is performed in Node B, and normal Outer Loop Power Control, which is performed in Radio Network Controller (RNC) in WCDMA system. RNC performs normal Outer Loop Power Control for the uplink, and during the controlling process, if the measurement report triggered by the SIR_error is received from Node B, normal Outer Loop Power Control is paused, the High Priority Outer Loop Power Control is triggered and the performance result is returned to. Node B will act according to the performance result: if the performance result is not to perform the Outer Loop Power Control, a timer is started which functions to ensure the Inner Loop Power Control converging time, and when the timer expires, the RNC for normal Outer Loop Power Control is started; if the performance result is a new SIR_target value, a shielding period is set to avoid loop delay so that cyclic check CRCI indication error occurring in the shielding period will not be processed when normal Outer Power Control is on, then normal Outer Loop Power Control is carried on by the RNC repeatedly.

0016In the present invention, the normal Outer Loop Power Control adopts a method of threshold report on cyclic check triggering. The principle is: continuously monitoring if there is Cyclic Redundancy Check (CRC ) error, and counting error data block number within an allowance period assigned to error blocks . Upwardly adjusting the SIR_target to a higher value when the error block number counted in the allowance period for error blocks exceeds error block threshold, wherein the allowance period for error blocks is a data transmission window for counting the error block number with the starting point of the first monitored data block with CRC error when the allowance period for error blocks is 0. Reset the allowance period for error blocks when the allowance period for error blocks expires. Because there are at least 4-5 frames loop delay, i.e., the upwardly adjusting effect can only be reflected after 4-5 frames. Therefore within 4-5 frames after the SIR_target is upwardly adjusted, it need not to be readjusted if CRC indication error appears again, which is achieved by setting the shielding period; the CRC indication error occurring in the shielding period will not be counted, and adjust the SIR_target only when the CRC indication error still exists after the shielding period expires. At the moment, adjusting step length should be increased because such a great probability of error appears in such a short time, so that the power control can be converged quickly to meet the requirement of service quality rapidly. The principle for downward adjustment is to downwardly adjust the SIR_target when there is no CRC error in downward adjusting period. The determination of downward adjusting period reflects the requirements of service quality for different services. In the present invention, the downward adjusting period is determined according to BLER_target (Block Error Ratio target) of different services, wherein the downward adjusting period is M× (1/BLER_target), and M is an adjustable value ranging from 1 to 3. And the step length for downward adjusting will not be adjusted because it is initially assigned.

0017Fig.2 shows a detailed process of a normal Outer Loop Power Control. First of all, relative thresholds are configured in advance, such as error block threshold, allowance period for error blocks, shielding period and downward adjusting period. A receiver receives data every Transmission Timing Interval (TTI), so it should be performed every TTI to judge if the received data is correct. When data transmission interval expires, it needs to judge whether any data block with CRC indication error exists in the data blocks received in the TTI. Since several data blocks can be received in each TTI, it indicates that the data block is error if the CRC indication of any data block is 'error'. If there is an error data block among the received data blocks, a correct block counter needs to be cleared to 0, furthermore it needs to judge whether it is within the shielding period currently, i.e., whether the shielding period is set. If it is within the shielding period currently, it is not needed to deal with the error block number but returns to wait for the expiration of data transmission interval and repeats the above step. If it is not within shielding period currently, the error blocks should be counted received in the TTI, i.e., the number of error blocks received in the TTI is added to an error block counter as well as a total number of the data blocks received in the TTI to an error block allowance counter. Judge whether a value of the counter for error block allowance is greater than or equal to the allowance period for error blocks. If the value is less than the allowance period for error blocks, it needs to return to wait for the expiration of data transmission interval and repeat the above step. If the value of the counter for error block allowance is greater than or equal to the error allowance period, it needs to judge whether the value of the counter for error block is greater than or equal to the error block threshold, and if the value is less than the error block threshold, it needs to return to wait for the expiration of data transmission interval and repeat the above step. If the value of the counter for error block is greater than or equal to the error block threshold, which indicates that the current SIR_target should be adjusted upwardly, the counter for error block and the counter for error block allowance should be cleared to 0 for the determination and adjustment of next round. Then the upward adjusting step length is determined, and the present invention employs a method of adaptively adjusting step length, i.e., the times of continuously upward adjusted SIR_targe are recorded _t, it is ensured that the upward adjusting step length is in direct proportion to the number of times of continuously upwardly adjusting SIR_target; the number of times of upwardly adjusting SIR_target recorded previously is cleared when the SIR_target is adjusted downwardly. The SIR_target is adjusted Upwardly according to the upward adjusting step length, i.e., the adjusting step length is added to the current SIR_target as the new SIR_target and then the new SIR_target is informed to Node B. Finally a shielding period is set, i.e., a timer is set, the error block occurring in the shielding period will not be counted, and the shielding function will be stopped when the timer expires, then it needs to return to wait for the expiration of data transmission interval and repeat the above steps.

0018If there isn't any error data block in the received data blocks within one TTI, the total number of the data blocks received within the TTI is added to the correct data block counter. It needs to judge whether the current error block allowance counter is 0, if not, it needs to return to perform the step of adding the total number of the data blocks received within the TTI into the counter for error block allowance and the subsequent. If yes, it needs to judge whether the correct block counter is greater than or equal to the set downlink adjusting period. It needs to return to wait for the expiration of data transmission interval and repeat the above step if the counter is less than the downward adjusting period. Otherwise the correct block counter should be cleared to 0, the SIR_target is adjusted downwardly according to the initially assigned adjusting step length, the new SIR_target is informed to Node B and it needs to return to wait for the expiration of data transmission interval and repeat the above step.

0019In actual communication, the SIR meeting the transmit service needs to be changed due to the variation of the mobile communication environment and the moving speed. In case of the link SIR_error exceeding the error threshold, the High Priority Outer Loop Power Control is adopted in order to speed up the power control convergence.

00203GPP TS 25.215 Protocol mentions that a link SIR_error should be measured at UTRAN (UMTS Terrestrial Radio Access Network) side, and the SIR_error is the difference between the SIR measured at the current time and SIR_target-ave, average of the SIR_target in a certain period, i.e., SIR_error=SIR-SIR_target-ave, in which the average of SIR_target in the period of 80ms is selected in this example. The SIR_error is also closely related to power control. Outer Loop Power Control is adopted according to the value of SIR_error in the case that there is much difference between the initially assigned SIR_target value and the actual SIR_target and the case that there is much difference between the SIR_target and the actual SIR_target due to the variation of moving speed,.

0021Table 1 shows the nine possible situations which might occur in actual communication together with the adjusting method of SIR_target correspondingly. In the table, SIR_{error-threshold} is a judging threshold for triggering special measurement report of Node B SIR_error. When the absolute value of SIR_error is greater than the SIR_{error-threshold}, Node B sends the measurement report and starts the High Priority Outer Loop Power Control. <tables id="tabl0001" num="0001"><img file="EP1583256A1_D0001.tif" /></tables>

0022The 9 situations in table 1 will be described in details as below:

0023Situation 1: SIR_error is greater than SIR_{error_threshold}, and the actually measured BLER cannot meet the BLER_target, which indicates that the present SIR_target cannot meet the requirement of current service. And the SIR_target should be adjusted upwardly within the extent of SIR_error.

0024Situation 2: SIR_error is greater than SIR_{error_threshold,} and the actually measured BLER just meets the BLER_target, which indicates that the present SIR_target should be adjusted upwardly within the extent of SIR_error.

0025Situation 3: SIR_error is greater than SIR_{error_threshold}, and the actually measured BLER is much less than the BLER_target, and the communication quality is pretty good, so the Outer Loop Power Control needs not to be carried out; however Inner Loop Power Control is necessary to directly decrease the transmitting power for lower BLER by considering the present actually measured SIR has not been converged to SIR_target. Even in the situation that the assigned SIR_target is much less than the actually measured SIR, it can be transformed to be situation 1 or 2, so as to SIR_target is adjusted upwardly.

0026Situation 4: The absolute value |SIR_error| is less than or equal to SIR_{error-threshold}, which indicates that the configured SIR_target is within the allowance scope, and only normal Outer Loop Power Control is needed at the time. And the situations 5 and 6 are identical with situation 4.

0027Situation 7: The actually measured SIR is less than SIR_{target_ave} where the difference is equal to or greater than SIR_{error_threshold}, and the actually measured BLER cannot meet the BLER_target, and the communication quality is bad. So by considering the present actually measured SIR has not been converged to SIR_target, the Inner Loop Power Control is necessary to directly increase the transmitting power for lower BLER and the Outer Loop Power Control needs not to be carried out. Even in the situation that the assigned SIR_target is much greater than the actually measured SIR, it can be tra nsformed to situation 8 or 9, so as to SIR_target is adjusted downwardly.

0028Situation 8: The actually measured SIR is less than SIR_{target_ave} where the difference is equal to or greater than SIR_{error_threshold,} and the BLER just meets the BLER_target. So the SIR_target should be adjusted downwardly within the extent of SIR_error at this time to meet the requirement, and then normal Outer Loop Power Control is carried out.

0029Situation 9: The actually measured SIR is less than SIR_{target_ave} where the difference is equal to or greater than SIR_{error_threshold,} and the actually measured BLER is much less than the BLER_target, which indicates that the present SIR_target is much greater than the required SIR_target, and the SIR_target should be adjusted downwardly within the extent of SIR_error so as to increase the capacity of the system, and then normal Outer Loop Power Control is carried out.

0030In the foregoing 9 situations, SIR_{error_threshold} can be selected to be 1dB. It can be understood that SIR_error triggering condition |SIR_error|>SIR_{error_threshold} should be considered while performing Outer Loop Power Control. This triggering condition has the highest priority, i.e., special measurement report information is triggered when the condition is met, and the RNC carries out High Priority Outer Loop Power Control after the information is received.

0031Fig.3 is a flow chart of a High Priority Outer Loop Power Control. Firstly, the BLER in the sliding window with the size of <i>M</i> × <maths id="math0001" num=""><math display="inline"><mrow><mfrac><mrow><mtext>1</mtext></mrow><mrow><msub><mrow><mtext mathvariant="italic">BLER</mtext></mrow><mrow><mtext mathvariant="italic">target</mtext></mrow></msub></mrow></mfrac></mrow></math><img file="EP1583256A1_D0002.tif" /></maths> and the ratio of the actual BLER to BLER_target need to be calculated, which is defined as Diff_Value, Diff_Value=BLER/BLER_target. Secondly it needs to judge whether the SIR_error is greater than 0, and if yes, it means that the measured SIR is much greater than the SIR_target. And then it needs to judge whether the Diff_Value is greater than the assigned threshold A, which is less than 1, the maximum value in representing good communication quality. It represents the present communication quality can barely meet the communication quality requirements or cannot meet the communication quality requirements when Diff_Value is greater than the threshold A. This is the case that the actual SIR is much greater than the SIR_target at this time, so the SIR_target needs to be adjusted upwardly, and the adjusting step length is configured as: adjustment coefficient × SIR_error. And the adjustment coefficient is determined by the relation between the SIR_error and the required adjusting step length in actual measurement, which will not be changed once it is determined. The SIR_target is adjusted upwardly, and it needs to return the new SIR_target, which is the sum of the primary SIR_target and the adjusting step length, to Node B. It represents that the present communication quality is pretty good when Diff_Value is less than or equal to the threshold A. However, since the actual SIR has not been converged to the SIR_target, Outer Loop Power Control is not necessary at this time. It needs to wait for the Inner Loop Power Control to adjust the transmitting power and return the sign of not performing Outer Loop Power Control to Node B.

0032It shows that the actually measured SIR is much less than the SIR_target if the SIR_error is less than 0,it needs to judge whether the Diff_Value is greater than the assigned threshold B, which is greater than 1, the minimum value in representing poor communication quality. It means that the present communication quality is poor when Diff_Value is greater than the threshold. However, since the actual SIR has not been converged to the SIR_target, Outer Loop Power Control is not necessary at this time, it needs to wait for the Inner Loop Power Control to adjust the transmitting power and return the sign of not performing Outer Loop Power Control to Node B. It shows that the present communication quality meets the requirement when Diff_Value is less than or equal to the threshold B, and the SIR_target needs to be adjusted downwardly; the adjusting step length is configured as: adjusting coefficient × SIR_error, and obtaining a new SIR_target by subtracting the adjusting step length from the current SIR_target, and returning the new SIR_target to Node B.

0033Fig.4 shows a detailed application of the method for employing two-level Outer Loop Power Control of present invention in a WCDMA communication system. In the uplink direction, RNC can send measurement control information to Node B and inform Node B about the measurement parameters, reporting method, etc. after the establishment of the correspondence context between Node B and the user and data transmission are completed. At this moment, Node B and RNC carry out the task of its own module respectively. Period measurement will be taken for each received wireless link SIR in Node B and periodically calculate the SIR_{target_ave} by selecting the measurement period of 80ms to obtain SIR_error=SIR-SIR_{target_ave}. Afterwards, Node B judges whether the absolute value of SIR_error exceeds SIR_{error-tnresnold}. If yes, it meets the triggering condition for submitting the measurement report, and Node B sends the measurement report to RNC. Otherwise Node B keeps on measuring SIR without sending the measurement report to RNC. In RNC, normal Outer Loop Power Control is performed in the beginning. RNC obtains CRCI (CRC Instruction) of each transmission data block from the data frames transmitted by Node B so as to count the BLER of each wireless link. Then a new SIR_target is gained by Outer Loop Power Control, Node B performs Inner Loop Power Control according to the new SIR_target from the data frames transmitted by RNCand adjusts the user's transmitting power.

0034When the triggering condition of SIR_error is metmet, Node B triggers RNC pause normal Outer Loop Power Control by the measurement report and perform the High Priority Outer Loop Power Control so that the SIR_target can be converged to the value meeting the service quality more rapidly. After the accomplishment of the High Priority Outer Loop Power Control, the adjusted SIR_target is transmitted to Node B by data frames, and normal Outer Loop Power Control is restarted. Normal Outer Loop Power Control will be kept on going as long as there is the correspondence context between Node B and the user and data are transmitted in the channel with Closed Loop Power Control. High Priority Outer loop power control will be performed only if the triggering condition is met and exit after the accomplishment. And then corresponding process will be followed in accordance with the sign returned by the High Priority Outer Loop Power Control: the timer is started if the returned sign is to pause Outer Loop Power Control, and normal Outer Loop Power Control is started if the timer expires; normal Outer Loop Power Control is started at once if the returned is a new uplink SIR_target.

0035It will be understood that the above embodiments are used only to explain but not to limit the present invention. In despite of the detailed description of the present invention with referring to above preferred embodiments, it should be understood that various modifications, changes or equivalents can be made by those skilled in the art without departing from the spirit and scope of the present invention. All of these modifications, changes or equivalent replacements should be covered in the scope of accompanying claims of the application.