CN1128513C - Reverse external-loop power control method - Google Patents
Reverse external-loop power control method Download PDFInfo
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- CN1128513C CN1128513C CN 01105343 CN01105343A CN1128513C CN 1128513 C CN1128513 C CN 1128513C CN 01105343 CN01105343 CN 01105343 CN 01105343 A CN01105343 A CN 01105343A CN 1128513 C CN1128513 C CN 1128513C
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Abstract
The present invention discloses a control method for reverse external-loop power. A receiver receives the rate indication and the symbol error rate of a current frame signal; an operation state is judged according to the received frame rate indication; the judged operation state is entered, and statistic is carried out to the frame error rate; the symbol error rate of a target is adjusted by the difference between the frame error rate and the frame error rate of a target under the corresponding state; the difference between the symbol error rate of the current frame and the symbol error rate of the target obtained by the receiver is compared; a threshold value of an external loop is adjusted by the obtained difference value; the threshold value of the external loop is controlled to be within the designated range by an amplitude limiter. The present invention comprehensively considers the realization of two aspects of factors of speed and control precision, and has the advantages of convenient realization and rapid speed.
Description
The present invention relates to a kind of Poewr control method of wireless telecommunication system, especially the Uplink Power Control Technology in the CDMA communication system.
Code division multiple access (CDMA) is a kind of in the mobile communication multiple access modulation technique commonly used.Fig. 1 has provided a typical C DMA cellular system structural representation.Travelling carriage (MS) 12A or 12B carry out communication by base station transceiver (BTS) 16A or 16B and base station controller (BSC) 14A, and travelling carriage may all be related with two base stations simultaneously in a certain period.Base station controller carries out network communication by mobile switching centre (MSC) and PSTN or ISDN again, and MSC also can connect other base station controller simultaneously, as BSC14B etc.
In fact, in certain sub-district, there are a plurality of mobile subscribers.If all in the sub-district are with launching with equal-wattage per family, then the travelling carriage near the base station arrives signal of base station strong (arriving BTS16B such as MS12B), away from a little less than the travelling carriage arrival signal of base station of base station (arriving BTS16B) such as MS12A, cause strong signal to cover weak signal, " near-far interference " problem in the mobile communication that Here it is.Cdma system is a self-interference system in addition, and the same frequency of the common use of all users is so " near-far interference " problem is more outstanding.The power of certain subscriber signal is stronger in the cdma system, is favourable to this user by correct the reception, but can increase the interference to other user in the frequency band of sharing, even floods other users' useful signal, the result makes other user communication quality deterioration, causes power system capacity to descend.In order to overcome near-far interference, must adjust the required power of transmitter in real time according to the difference of communication distance, this just need carry out " power control ".Because the influence of urban architecture and ground complex-terrain, the signal that receiver is received is through the result who repeatedly reflects or scattering path is propagated, its amplitude and phase place all are change at random, be referred to as " multipath signal ", the decline of multipath signal is very serious usually, also needs to carry out power control to remedy the decline of certain period.In addition, owing to run into the shade that forms electromagnetic wave propagation that stops of barriers such as high-lager building, mountain, the woods on wave path, overcoming this shadow effect also needs to carry out power control.Therefore, power control can be described as the core of all CDMA key technologies.Otherwise many advantages of cdma system just can't embody, and high power capacity, high-quality cdma system also can not be realized.
In order to realize accurate power controls, the technology that cdma system has adopted forward power control and reverse power control to combine usually.In the forward link of cdma system, introduce power control,, make the transmitting power of forward traffic channel as far as possible little under the situation that satisfies travelling carriage demodulation minimum essential requirement signal to noise ratio by adjusting the base station acc power of Traffic Channel.
The power control of reverse link generally comprises three parts: open Loop Power control, closed power control and exterior ring power control.Each travelling carriage of cdma system is calculating the path loss from the base station to the travelling carriage always, when travelling carriage receives from the very strong signal in base station, show this travelling carriage or very near from the base station, a good especially propagation path is arranged, at this moment travelling carriage can reduce its transmitted power, and the base station still can normally receive; On the contrary, when the signal that receives when travelling carriage was very weak, it just increased transmitted power, to offset attenuation, open Loop Power control that Here it is.Open Loop Power control is simple, direct, does not need exchange of control information between travelling carriage and base station, and control rate is fast simultaneously also can pare down expenses.But in the cdma system, forward direction different with the frequency that reverse transfer is used (frequency difference as the IS-95 regulation is 45MHz), frequency difference is considerably beyond the coherence bandwidth of channel, thereby can not think that forward channel fading rise characteristic equals backward channel fading rise characteristic, and this is the limitation part of open Loop Power control.
In order to overcome incoherent Rayleigh fading on forward direction and the reverse link, can be by the signal to noise ratio of base station detection from mobile station signal, and relatively it and threshold value, according to comparative result instruction to rising of travelling carriage transmitted power or power decline on forward channel, travelling carriage is regulated its transmitting power according to the instruction of receiving, closed power control that Here it is.The key that realizes closed power control is that the speed that produces, transmits, handles and carry out power control instruction wants fast, to follow the tracks of the Rayleigh fading of reverse link as far as possible.
Because under the varying environment condition, the signal-noise ratio threshold value of keeping given communication quality needs is different.Therefore in closed power control, the threshold value of signal to noise ratio neither be constant, but can be under exterior ring power control dynamic change.So-called exterior ring power control be actually a kind of occur in the base station or base station and mobile switching centre between a kind of power control process, it adjusts the signal-noise ratio threshold value with the speech quality information that receives as the input of control, thereby changes the benchmark that power control command is differentiated.
In real system, reverse power control is finished jointly by above-mentioned three kinds of power control.Promptly at first transmission power of mobile station is done open loop and estimate, estimate to do further to revise by closed power control and exterior ring power control divided ring then, try hard to accomplish accurate power controls.In this backward power control method, the outer shroud method has very big flexibility, and the quality of signal-noise ratio threshold value adjustment is determining the performance of control to a great extent.Therefore, need a kind of effective outer-loop power controlling method, when change of external conditions, revise the signal-noise ratio threshold value automatically,, the reverse link circuit quality of reception is maintained near certain desired value all the time to change the transmitting power of travelling carriage.
Present outer-loop power controlling method has multiple.Generally they can be classified as two classes: one is based on the principle of path compensation, and keeping received signal intensity is constant; One is based on the scheme of received signal quality.The former great advantage is simple, but this method in full remuneration in the path loss, almost can not obtain the increase of capacity.Some improvement projects based on this thinking have only remedied part path loss, can obtain the lifting of some capacity, but the phenomenon of dispersing of control procedure usually may occur.The latter makes all users have identical quality, divergence problem can not occur basically, and it has realized the lifting of capacity.U.S. Pat 5396516, " Method and System for the Dynamic Modification of ControlParameters in A Transmitter Power Control System ", its basic technical scheme is communication process to be divided into several states (move such as full rate, the variable bit rate operation, deletion state etc.), the threshold value step-length that descends when having received frame, the threshold value step-length that rises when receiving bad frame, but the rise and fall step-length adopts different values under different conditions.Such method can make the threshold value adjustment violent, and promptly the variance of threshold value is big, can not finely utilize power system capacity.
Another part U.S. Pat 5745520, " Method and Apparatus for Power Controlin A Spread Spectrum Communication System Using Threshold Step-down SizeAdjustment ", the method that it proposes is directly to utilize the difference of frame error rate FER and target frame error rate to adjust rising step-length or decline step-length, adjust the outer loop threshold value by this step-length, the variance of this method adjustment threshold value is still bigger than normal, influences making full use of of power system capacity.In addition, U.S. Pat 5732328 " Method forPower Control Threshold in Wireless Networks for Communication MultipleInformation Classes ", its thought is the adjustment that utilizes the difference of error sign ratio and target error sign ratio to come the control gate limit value, and the target error sign ratio is adjusted according to frame error rate again.This method realizes simpler, trades off but directly be difficult between frame error rate (FER) and the error sign ratio (SER) according to two parameters, finally also is difficult for reaching superperformance.
The objective of the invention is the contradiction that realizes in the existing outer shroud control method between difficulty, control rate, the power system capacity in order to overcome based on received signal quality, propose a kind ofly under the prerequisite that guarantees the target control quality, can improve the outer-loop power controlling method of power system capacity.
For realizing goal of the invention, the method that the present invention proposes mainly may further comprise the steps:
(1) receiver obtains the speed indication and the error sign ratio of current frame signal;
(2) according to the frame rate indication that receives, carry out the running status judgement;
(3) enter the running status that draws after the judgement and add up frame error rate;
(4) utilize the poor of target frame error rate under frame error rate and the corresponding state, adjust the target error sign ratio;
(5) the present frame error sign ratio that obtains of receiver and target error sign ratio poor relatively;
(6) adjust the outer loop threshold value with the difference that obtains in (5);
(7) control the outer loop threshold value within the scope of appointment by amplitude limiter.
In the described outer-loop power controlling method, can also may further comprise the steps between step (4) and the step (5): after obtaining the adjusted value of target error sign ratio, decimation blocks 250 is according to the sampling rate size of selecting, state to buffer area is sampled, and then sampling results is sent into the adjustment speed of accumulator 252 in order to controlled target SER value.
Adopt method of the present invention, existing relatively method has been taken all factors into consideration the realization speed and the control precision two aspect factors of outer shroud control method, the variance of control is relatively little, saved the power of transmitter, balance the quality of received signal, the service time of having improved power system capacity and battery.Below in conjunction with drawings and Examples the present invention is described in detail.
Fig. 1 is a cdma cellular mobile communcations system structure chart.Fig. 2 is the Reverse Link Close Loop Power Control schematic diagram.Fig. 3 is the flow chart of the reverse outer-loop power control method that proposes of the present invention.Fig. 4 is an embodiment of the inventive method.
The available Fig. 2 of the effect of outer shroud method of adjustment in the reverse power control process clearly represents.In reverse link, closed loop control, the base station is the next fading signal of receiving mobile antenna emission at first, finish the demodulation sign indicating number of received signal in module 200, (such as a power control group time) normalized energy of received signal or signal to noise ratio of received signal in a period of time can be obtained, the quality information (such as frame rate indication, frame check word and error sign ratio SER etc.) of current received signal frame can also be from the data field of decoding, judged.The snr value that each section received in the period is sent into comparator 270 and is carried out comparison with threshold value.Simultaneously module 220 receives the quality information of present frames, as the input of outer shroud control adjusting module 240, finishes the adjustment of signal-noise ratio threshold value at this, and will adjust the result and offer comparator 270, with the benchmark of dynamic change comparator comparison.According to the result of comparator, produce corresponding power control bit, if the signal to noise ratio of current reception greater than threshold value, produces and characterizes the control bit that power descends, characterize the control bit that power rises otherwise then in module 280, produce in module 285.Rule by the air interface protocol regulation is inserted on the power control sub-channel of corresponding forward traffic channel in module 290 then, gives travelling carriage by forward link with power control command.Travelling carriage receives the signal of forward link and detects effective power control commands (corresponding effectively emitted power control group) in module 110, by a fixed step size transmitting power is adjusted in transmitting power adjusting module 100; If travelling carriage is in soft changing state, receive a plurality of power control commands simultaneously, will carry out the order that allows its power descend as far as possible.
The outer-loop power controlling method that the present invention proposes as shown in Figure 3.At first the receiver demodulation and the received signal of decoding in 300 obtain indication of present frame speed and mistake symbolic number; In 310, carry out the running status judgement according to the frame quality indication that receives; In 320, carry out the statistics of frame error rate under the corresponding state; In 330, compare the poor of frame error rate and target frame error rate then, adjust the target error sign ratio; Error sign ratio and target error sign ratio with received frame in 340 compare, and difference is used for revising the outer loop threshold value; In 350, utilize amplitude limiter with Threshold Control Method within certain scope, be provided with too high or too low to avoid a certain user's outer loop threshold value; The adjusted outer shroud value of setting of output is carried out the differentiation of power control bit to comparator in 360 at last.
Fig. 4 has provided the detailed operation process of an embodiment of outer-loop power controlling method.
In this embodiment, travelling carriage has the vocoder of a rate-compatible, and it is rate, 1/2 speed, 1/4 speed or 1/8 speed work at full speed.Certain speed decision method is adopted by the data message that the demodulating and decoding process obtains in the base station, and the judgement of present frame speed can be provided, or produces the information of frame rate.
The at first input of received frame quality information here mainly is the frame rate that obtains of speed judgement and the error sign ratio SER of every frame.In state justify module 242,, determine the state that the present frame statistics belongs in according to speed discriminative information (comprising the four kinds of correct frame indications and the frame indication information of several mistakes).The division of this state is to carry out according to the difference to quality requirement under the different rates, and the speed that quality requirement is identical can be included into a kind of state.Select different statistics branch road a, b and c according to the state of differentiating.A is an example with the statistics branch road, at first in an annular buffer 244a, add up the frame error rate in the certain hour section (such as 360 frames), this annular buffer is followed the principle of first in first out (FIFO) and is added up interior FER of nearest a period of time, to reflect the quality of current received signal.In comparator 246a, the quality of current received signal and target communication quality compare, and are about to add up FER and target FER1 compares, and obtain the difference of communication quality, and here this difference is reflected on the difference of frame error rate FER.
After multiplier 248 utilizes conversion constant C1 to convert the difference of communication quality to the target error sign ratio adjusted value, decimation blocks 250 is according to the sampling rate size of selecting, at regular intervals the state of buffer area is sampled, then sampling results is sent into the adjustment speed of accumulator 252 in order to controlled target SER value.The sampling rate of decimation blocks 250 is compromisely on the speed of adjusting target SER value and control precision to consider.Why will carry out this extraction operation, because buffer area is to carry out work with a kind of form of circular buffer, an erroneous frame needs a period of time from producing by new frame covering, and this time is depended on the buffer area length of setting.Obviously in the maintenance process of same state, each frame is all sampled once nonsensical.Therefore, decimation blocks 250 need be sampled to " state " in the buffer area with certain ratio, the big I of sampling rate requires to decide on the adjustment of target SER as the case may be, sampling rate accelerates to increase the amplitude of each adjustment target SER, sampling rate reduces the amplitude that then can reduce at every turn to adjust target SER value, and the variation of target SER is eased up.
Adjusted target SER value is an input of device 254 as a comparison, and another input of comparator 254 is the output of receiving filter 256.The error sign ratio SER of 256 pairs of current received frames of filter carries out Filtering Processing, and this filtering can adopt the finite impulse response filter of certain exponent number to realize.In comparator 254, filtering output is compared with adjusted target error sign ratio, comparative result is delivered to multiplier 258, multiply by conversion constant C2, realization is by the conversion to signal-noise ratio threshold value correction of the error of error sign ratio, and the result of conversion delivers to signal-noise ratio threshold value accumulator 260 again and produces adjusted threshold value.
In order to limit undue the unusual of this link transmitting power that badly cause owing to certain bar link, thereby other users to whole system cause huge interference, influence the performance of whole system, effect by amplitude limiter 262, the maximum threshold (MAX_threshold) and the minimum threshold (MIN_threshold) that adopt restriction signal-noise ratio threshold value to adjust are carried out amplitude limit, and the threshold value of each output all is controlled between this bound.Through after the effect of this amplitude limiter, just obtained the adjustment result of final output signal-to-noise ratio threshold value.
This control procedure init state can be selected a state that frame rate was included into that probability of occurrence is lower.Need simultaneously three statistics FER circular buffers are carried out initialization, this process need is according to calculating the mistake frame number total time of target communication quality and statistics, be filled into equably in the buffer, make the quality of statistics in the initial time buffer just in time consistent with the target communication quality.
What provide above only is an exemplary embodiments of the present invention.Also there are other many obvious variation in the method for the invention.
Add up respectively as the state of statistics FER being divided into full rate state (promptly receiving full-rate vocoding) and sub-speed state (the reception low rate frame comprises speed such as 1/2,1/4,1/8) two states among another embodiment.Similarly, can meticulously statistic behavior be divided into four kinds of statistic behaviors, with correspondingly corresponding with four kinds of speed, this does not break away from the description of technical solution of the present invention yet.
The present invention also can take other quality information as the input information of adjusting.Such as, just can not adopt two kinds of received frame quality indication (CQI) informations in the foregoing description, promptly speed court verdict and error sign ratio SER also can adopt frame quality indicator word, even some information of other additional current link-quality, as translational speed, communication environment grade etc.
The present invention almost can without any modification be used in the link of vocoders such as adopting 8K, 13K and EVRC, as long as this reception link can provide certain quality of reception indication information.
Further expand, the present invention can be applicable in all close-loop power controlling methods, and not only is used in the back closed loop Poewr control method.Such as, also increased at reverse link under the situation of power control sub-channel, the present invention just can be used in the travelling carriage according to the communication quality of the forward link that receives and adjust the signal-noise ratio threshold value, relatively the signal to noise ratio of received signal and threshold value produce suitable power control command, on reverse power control subchannel, be sent to the base station, the base station receives and this power control command of demodulation, thereby controls the transmitting power of corresponding forward link.
In a word, the present invention adopts linear operation, and it is convenient to realize, speed is very fast, and it is less relatively to control variance simultaneously, under the prerequisite that guarantees the target control quality, can improve the capacity of self-interference system.
Claims (5)
1, a kind of method of backward external ring power control is characterized in that mainly may further comprise the steps: (1) receiver receives the speed indication and the error sign ratio of current frame signal; (2) according to the frame rate indication that receives, carry out the running status judgement; (3) enter the running status that draws according to judgement and add up frame error rate; (4) utilize the poor of target frame error rate under frame error rate and the corresponding state, adjust the target error sign ratio; (5) the present frame error sign ratio that obtains of receiver and target error sign ratio poor relatively; (6) adjust the outer loop threshold value with the difference that obtains in the step (5); (7) by the amplitude limiter adjustment outer loop threshold value is controlled within the scope of appointment.
2, the method for a kind of backward external ring power control as claimed in claim 1, it is characterized in that to comprise between step (4) and the step (5): after obtaining the adjusted value of target, decimation blocks (250) is according to the sampling rate size of selecting, state to buffer area is sampled, and then sampling results is sent into the adjustment speed of accumulator (252) in order to the controlled target error sign ratio.
3, the method for a kind of backward external ring power control as claimed in claim 1 or 2 is characterized in that the running status in the step (2) is to divide according to the difference to quality requirement under the different rates, and the speed that quality requirement is identical is included into a kind of state.
4, the method for a kind of backward external ring power control as claimed in claim 1 or 2, it is characterized in that step (4) specifically comprises: frame error rate and target frame error rate that statistics is obtained compare, obtain the difference of communication quality, in multiplier (248), utilize conversion constant C1 to convert the difference of communication quality to adjusted value then the target error sign ratio.
5, the method for a kind of backward external ring power control as claimed in claim 1 or 2, it is characterized in that step (6) comprising: result and adjusted target error sign ratio that the error sign ratio of current received frame is carried out after the Filtering Processing compare, comparative result is delivered to multiplier (258), multiply by conversion constant C2, realization is by the conversion to signal-noise ratio threshold value correction of the error of error sign ratio, and the result of conversion delivers to signal-noise ratio threshold value accumulator (260) again and produces adjusted outer loop threshold value.
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| CN 01105343 CN1128513C (en) | 2001-02-15 | 2001-02-15 | Reverse external-loop power control method |
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| CN 01105343 CN1128513C (en) | 2001-02-15 | 2001-02-15 | Reverse external-loop power control method |
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| CN1128513C true CN1128513C (en) | 2003-11-19 |
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Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1326332C (en) * | 2003-12-11 | 2007-07-11 | 上海贝尔阿尔卡特股份有限公司 | Implementation method for controlling power in external ring |
| CN1305229C (en) * | 2004-03-12 | 2007-03-14 | 中兴通讯股份有限公司 | Reverse external ring power control method |
| CN100375404C (en) * | 2005-04-20 | 2008-03-12 | 北京首信股份有限公司 | Reversed outer ring power control method in CDMA mobile communication system |
| CN101009523B (en) * | 2006-01-23 | 2011-08-10 | 中兴通讯股份有限公司 | A device and method for automatic measurement of the mobile communication terminal demodulation performance |
| CN101202571B (en) * | 2006-12-15 | 2011-05-11 | 中兴通讯股份有限公司 | Method for reducing HS-SCCH channel outer ring power control step length cumulative effect |
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