CN1937430A - Muti-path detecting method for CDMA communication system - Google Patents
Muti-path detecting method for CDMA communication system Download PDFInfo
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- CN1937430A CN1937430A CNA2005100374246A CN200510037424A CN1937430A CN 1937430 A CN1937430 A CN 1937430A CN A2005100374246 A CNA2005100374246 A CN A2005100374246A CN 200510037424 A CN200510037424 A CN 200510037424A CN 1937430 A CN1937430 A CN 1937430A
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Abstract
During the system running stage, this method calculates at real time the absolute threshold of the super strong path (SSP), reads the relative threshold of the system design stage, judges the SSP. If the multipath energy is greater than the absolute energy threshold and the ratio of multipath recent energy to historical energy is greater than the ratio threshold n, and if the multipath energy is greater than the energy of the adjacent path by 1/2 code bit, then judges it as a SSP and adopts a new SSP filter coefficient to realize the IIR filter against SSP. According to the power delay function after filtering, this method calculates the multipath threshold, makes multipath selection and completes the multipath management post-processing. Comparing with the recent technique, the multipath testing method introduces a SSP multipath test method against the multipath searching progress. The method improves feature of demodulation and the method is proved in practical system testing.
Description
Technical field
The present invention relates to the multi-path detecting method in a kind of code division multiple access (CDMA:Code-Division Multiple-Access) communication system, in particular, thus a kind ofly adopt superpower path processing method to improve multipath to detect the method that performance improves the performance of receiver.
Background technology
In the prior art, code division multiple access (CDMA) is a kind of multiple access method, and it is based on spread spectrum, and recent another multi-address method that is applied to communication system except that existing frequency division multiple access and time division multiple access method that become.Compared with former technology, CDMA has many advantages, for example availability of frequency spectrum height, good confidentiality etc.Adopt the system of CDMA method to mainly contain at present: the narrowband CDMA system, wideband CDMA system, the CDMA2000 system, TD-SCDMA system etc., adopt many yards spread spectrums in these systems or claimed double-deck spreading code distribution technology, that is to say in these cdma systems, the spread spectrum mode of the reverse link from mobile subscriber to the base station can be divided into for two steps, the first step is that cross-correlation is zero orthogonal function (Walsh function when aliging with time delay, ovsf code) as the channel code spread spectrum, the recovery process of corresponding receiving terminal is called despreading; Second step was used the auto-correlation and all reasonable pseudo noise code (the PN sequence of cross-correlation performance of the unique distribution of each user, the M sequence, the Gold sequence) and signal multiplication, the recovery process of corresponding receiving terminal is called descrambling, above-mentioned pseudo noise code is called scrambler, distinguish different mobile subscribers with scrambler, a numerical value also is chip (chip) in the scrambler sequence.Equally, the spread spectrum mode of the forward link in these systems from the base station to mobile subscriber is also divided the two same steps, and unique difference is that the scrambler in the forward link is used for distinguishing base station or sub-district.The scrambler difference of different base stations or sub-district.In addition, also adopted CDMA technology in the satellite communication system that has.
In general mobile telecommunication channel, the characteristics of radio propagation are the decay of multiple reflection, diffraction and signal energy.This is the obstacle that will inevitably exist by in some air, causes as building, hill etc., so the signal between base station and the travelling carriage is propagated along the some paths between the Receiver And Transmitter.Because the difference of different propagation path, it is also different that the different multipath compositions that arrive the same signal of receivers along different paths arrive the propagation delay of receivers, thereby cause multipath to disturb and signal fadeout etc.
The receiver that uses in present cdma system is a kind of receiver of multiple-branching construction, and wherein the time delay of each branch is basic identical with the propagation delay of a corresponding multipath.Each branch is an independent receiver element, and its function is a demodulation expectation received signal component, merges the different receivers element signal, those delays, the concentration of energy of dispersion is got up.This receiver also is Rake (Rake) receiver, can be superimposed the multipath energy of same user's different delay by certain rule, thereby improve receptivity.
Spreading code is the prerequisite of proper communication in the cdma system synchronously in local spreading code and the received signal, if can not obtain sign indicating number synchronously, just correctly despreading can't correctly solve raw information.Sign indicating number is accurate more synchronously, and demodulation performance is just good more.Multipath searching is exactly to detect the multipath signal propagation delay from received signal, with adjust local spreading code make it with received signal in the spreading code of each multipath information keep synchronously.If Multipath searching can not accurately search multidiameter delay, the Rake receiver demodulation performance of back will have loss.
In existing Multipath searching algorithm, with scrambler and the received signal correlation intergal of sliding, obtain the plural correlation function CRF (Complex Relation Function) of desired user signal, get the quadratic sum of plural correlation function real part and imaginary part then, obtain power time delay function (PDP:Power DelayProfile).For the value stationarity of guaranteed output time delay function at each sample point, reduce sudden noise and worsen in the receptivity that specific time delay point causes, before carrying out Multipath searching, the power time delay function is carried out IIR filtering.Each system is the 1 rank IIR filtering methods that adopt in reality realizes more, under reasonably filter factor is provided with, give the correct time when burst noise has on the strong energy, and wave energy effectively reduces noise effect after filtration.After the IIR filtering, carry out follow-up Multipath searching according to the power time delay function after the filtering again.
Multipath searching is equivalent to each different time delay is carried out descrambling with scrambler, usually to carry out descrambling to hundreds of delay positions, and real multi-path location generally has only wherein several (generally being less than 10) position, follow-up Rake receiver only need carry out demodulation to a few position and get final product.Therefore, whether Multipath searching can accurately search out real multipath, abandons false footpath, and reducing The noise to greatest extent is key one ring that influences in the Rake receptivity.In present Multipath searching algorithm, IIR filtering has suppressed reporting of false footpath preferably, and at specific time delay point, sudden noise process IIR filtering often can be abandoned below multi-path threshold.But IIR filtering has simultaneously also influenced the timely distribution in true footpath down of specific wireless communication environments, has caused the loss of effective energy, the reduction of demodulation performance.As giving birth under the environment that goes out, the position in true footpath is quick saltus step, IIR filtering filtering the part effective energy, can cause true footpath to delay effectively to be detected.
In addition, application number is in the patent " multipath searching method in the code division multiple access system and device " of CN02147425, in the process that superpower footpath is judged, this superpower footpath also is the multipath that sign mutation produces, what adopt in this patent is IIR filtering multipath energy before, and the multipath energy fluctuation ratio before the filtering is bigger, if adopt the result before the filtering, can't correctly detect superpower footpath better, make superpower footpath detect probability of successful and reduce.This patent application simultaneously has too much false footpath and reports and cause the multipath detection probability to reduce, and false-alarm raises.
Therefore, there is defective in prior art, and awaits improving and development.
Summary of the invention
The object of the present invention is to provide the multi-path detecting method in a kind of code division multiple address communication system, technical problem to be solved is: cause multipath to detect decreased performance in order to overcome the burst saltus step of giving birth to multipath under the environment that goes out in the Multipath searching process, thereby cause the shortcoming of base band demodulating decreased performance.
The present invention solves the problems of the technologies described above the technical scheme that is adopted to be:
Multi-path detecting method in a kind of code division multiple address communication system, it comprises:
At system design stage, determine the relative threshold in superpower footpath, the ratio thresholding n of promptly current energy and historical energy;
In system's operation phase, may further comprise the steps:
A: the absolute thresholding that calculates superpower footpath in real time;
B: the relative threshold of reading system design phase, the ratio thresholding n of promptly current energy and historical energy;
C: judge superpower footpath, if multipath energy greater than the ratio of absolute energy thresholding and current energy of multipath and historical energy greater than described ratio thresholding n, if this multipath energy is above the energy in footpath on 1/2 chip position about it simultaneously, judge that then this directly is superpower footpath;
D:, then adopt conventional filter factor to carry out conventional IIR filtering if not superpower footpath;
E: if superpower footpath then adopts new superpower footpath filter factor to realize the IIR filtering of superpower footpath, described superpower footpath filter factor is bigger than described conventional filter factor to the weights of current energy;
F: the power time delay function later according to filtering calculates multi-path threshold, carries out multipath and chooses, and finishes follow-up multipath management processing.
Described method, wherein, in the process in the superpower footpath of judgement of described step C, what the historical energy of multipath adopted is through the later multipath energy of IIR filtering.
Described method, wherein, described absolute energy thresholding is calculated as:
Absolute energy thresholding Threshold=PDPMean+m*PDPStedv, wherein PDPMean is historical average energy value, and PDPStedv is that historical energy scale is poor, and m＞1 is a weighted value.
Described method, wherein, the judgement in described superpower footpath is by relatively the current energy and the historical energy of this multipath are judged, when PDPNew/PDPHistory＞n (n＞1), and PDPNew＞Threshold, satisfy PDPNew (i)＞PDPNew (i-1) and PDPNew (i)＞PDPNew (i+1) simultaneously, judge that then this directly is superpower footpath, wherein PDPNew is the current energy of multipath, PDPHistory is the historical energy of multipath, Threshold is the absolute energy thresholding, and PDPNew (i-1) and PDPNew (i+1) are respectively about PDPNew (i) energy in footpath on 1/2 chip position.
Described method, wherein, the filter factor in described definite superpower footpath is:
The filter factor in superpower footpath is bigger than conventional IIR filter factor to the weights of the current energy of multipath in the IIR Filtering Processing of superpower footpath, and the current energy filter coefficient in superpower footpath must be greater than historical energy filter coefficient.
Multi-path detecting method in a kind of code division multiple address communication system provided by the present invention, compared with prior art, the Multipath searching process has been done a kind of special superpower footpath multi-path detecting method, improved demodulation performance, in the real system test, shown that method of the present invention is significantly improved to systematic function.
Description of drawings
Fig. 1 is a kind of typical C DMA receiving system structure chart of the inventive method;
Fig. 2 is the flow chart that the multipath of the no superpower footpath detection of prior art detects;
Fig. 3 is the multipath testing process figure that has superpower footpath to detect in the inventive method;
Fig. 4 is the implementing procedure figure that the superpower footpath of the inventive method is detected;
Fig. 5 is the performance chart that actual measurement is handled in the superpower footpath of the inventive method.
Embodiment
Below in conjunction with accompanying drawing, will be described in further detail technical scheme of the present invention, according to following described embodiment, the technical staff in same field can be easy to realize the present invention.
Multi-path detecting method in the code division multiple address communication system of the present invention is a kind of method of discerning superpower footpath and special processing being carried out in superpower footpath, and its basic technical scheme is:
At system design stage, determine the relative threshold in superpower footpath, the ratio n of promptly current energy and historical energy.
In system's operation phase, each following step of main branch of handling is carried out:
The first step is calculated the absolute thresholding in superpower footpath in real time.
Second step, relative threshold---the ratio thresholding n of current energy and historical energy during the reading system design.
The 3rd step: judge superpower footpath.If multipath energy greater than the ratio of absolute energy thresholding and current energy of multipath and historical energy greater than ratio thresholding n, if this multipath energy surpasses the energy in footpath on the 1/2chip position, its left and right sides simultaneously, judge that then this directly is superpower footpath, enters for the 5th step, otherwise enters for the 4th step.
The 4th step: conventional IIR filtering.If do not detect superpower footpath, then adopt conventional filter factor to carry out IIR filtering, entered for the 6th step then.
The 5th step: superpower footpath IIR filtering.Detect after the superpower footpath, adopt new superpower footpath filter factor to realize the IIR Filtering Processing, entered for the 6th step then.Superpower footpath filter factor is bigger than conventional filter factor to the weights of current energy.
The 6th step: the power time delay function later according to filtering calculates multi-path threshold, carries out multipath and chooses.Finish follow-up multipath management processing.
In the process in the superpower footpath of described judgement of the inventive method, what the historical energy of multipath adopted is through the later multipath energy of IIR filtering, can improve the detection probability in superpower footpath like this.Because the multipath energy fluctuation ratio before the filtering is bigger, if adopt the result before the filtering, can't correctly detect superpower footpath better, make superpower footpath detection probability reduce.Therefore in judging superpower footpath process, adopt filtering multipath energy afterwards can avoid above-mentioned situation to occur.
In addition in judging superpower footpath process, increased the judgement of multipath secondary lobe,, then it has been compared judgement if stronger with the multipath energy of superpower footpath adjacent spaces closer (being made as 1/2chip), avoid these secondary lobes are judged into superpower footpath, cause too much false footpath to report.This processing method can improve the detection probability in superpower footpath effectively, has reduced false-alarm.
Be a kind of typical C DMA receiving system structure chart as shown in Figure 1, form transmitting station by a signal source 101, emission filtration module 102, rf modulations module 103, antenna 104.Here it should be noted that before rf modulations signal also can be called pulse shaping filter (Pulse Shaping Filter) through the emission filter 102 of a base band.The effect of this filter is that the digital signal after the spread spectrum is converted to the signal that is fit to rf modulations.The characteristic of this filter is generally fixed, and such as the travelling carriage for the WCDMA system, stipulates in the standard that this filter is that rolloff-factor (roll-offfactor) is 0.22 root raised cosine filter (RRC:root-raised cosine filter).At receiving terminal, form by antenna 105, radio-frequency channel 106, Multipath searching module 107, multipath administration module 108 and Rake receiver.The Rake receiver is made up of a plurality of relatively independent receiver elements 109,110,111 etc. again.Each rake receiver element comprises time delay adjusting module 109.1 again, early road demodulation module 109.2, middle road demodulation module 109.3, late road demodulation module 109.4 are formed.As can be seen from the figure, morning, noon and afternoon three tunnel demodulation result need feed back to time delay adjusting module 109.1, constitutes a feedback loop here.Time delay adjusting module 109.1 also needs the information of multipath administration module 108, and gives multipath administration module 108 feedback information that time delay is adjusted, and also constitutes a feedback loop here.These feedback loops all make algorithm design become complicated.It is Multipath searching module 107 that the multipath that the present invention proposes detects the position of superpower path processing method in system construction drawing.
Be the flow chart that the multipath that handles in the no superpower footpath of prior art detects as shown in Figure 2.At first carry out descrambling and de-spreading, and carry out integration, report data processing module behind the integration, adopt the first order IIR filtering method that all power time delay function PDP are carried out filtering by the integration lengths that is disposed to receiving data.Carry out choosing of multipath then, finish subsequent treatment.
Be the multipath testing process figure that has superpower footpath to handle of the present invention as shown in Figure 3.Handling process among this figure is identical with handling process shown in Figure 2, handles but increased superpower footpath.Because it is very fast to give birth to the saltus step speed of multipath under the environment that goes out, the current energy in this footpath is high and historical energy is low, therefore considers this class directly is called superpower footpath.In the multipath management algorithm is handled, generally speaking, detect multipath and carry out the IIR Filtering Processing later on, in the processing procedure, if do not consider to give birth to the situation in the footpath of burst saltus step environment under of going out, may cause new footpath energy after IIR filtering of producing weakened and can not be gone down by distribution correctly.Therefore need carry out special processing to superpower footpath, in case detect superpower footpath, then revise the IIR filter factor, the current energy filter coefficient of detected multipath is provided with a higher value, can not weaken the energy in this footpath after the assurance filtering, it can correctly be distributed down.If detected is not superpower footpath, then handle by ordinary circumstance.
Be the implementing procedure figure of the superpower footpath processing of the inventive method as shown in Figure 4.
The concrete multipath of carrying out detects superpower path processing method, can be divided into following step:
1. the absolute energy thresholding calculates;
Be used as judging a standard in superpower footpath by energy threshold.Because the historical high energy of multipath energy and the not stationarity of historical low energy value, the average of energy and standard deviation then are the typical statistical values that is of universal significance, and therefore adopt these two values to carry out thresholding and calculate.
Absolute energy thresholding Threshold=PDPMean+m*PDPStedv (m＞1), wherein PDPMean is historical average energy value, PDPStedv is that historical energy scale is poor.
2. judge superpower footpath;
Superpower footpath is that the energy changing in footpath is very big owing to burst saltus step directly produces, and therefore compares the current energy of multipath and another standard that historical energy is used as judging superpower footpath.When PDPNew/PDPHistory＞n (n＞1), and PDPNew＞Threshold, satisfy PDPNew (i)＞PDPNew (i-1) and PDPNew (i)＞PDPNew (i+1) simultaneously, judge that then this directly is superpower footpath.Wherein PDPNew is the current energy of multipath, and PDPHistory is the historical energy of multipath, and Threshold is the absolute energy thresholding, and PDPNew (i-1) and PDPNew (i+1) are respectively the energy in footpath on the 1/2chip position, PDPNew (i) left and right sides.
3. determine the filter factor in superpower footpath;
In the conventional IIR Filtering Processing, if the filter factor of current energy is designated as a, the filter factor of historical energy is designated as 1-a, and the weights to the current energy of multipath are bigger than conventional IIR filter factor generally speaking for the filter factor in superpower footpath in the IIR Filtering Processing of superpower footpath.For example: the filter factor a of the historical energy of conventional filtering can be 0.875,0.75,0.625 equivalence, and the filter factor of current energy is (1-a); The filter factor a of historical energy can be 0.125,0.25,0.375 equivalence in the filtering of superpower footpath, the filter factor of current energy is (1-a), current energy filter coefficient 1-a must be greater than historical energy filter coefficient a, but can not be too big to avoid the multipath that other energy is more weak to lose.
Be that the present invention adopts superpower footpath to handle the performance chart of back actual measurement gained as shown in Figure 5, the demodulation performance that detects with no superpower footpath compares, and it is example that this figure gives birth to the communication environments that goes out with the 12.2k business.The processing method that superpower as can be seen from the figure footpath is detected has obvious gain, and demodulation performance is significantly improved.Adopting superpower footpath to handle under other service environment equally also makes moderate progress to demodulation performance.
The inventive method and application number are that the patent " multipath searching method in the code division multiple access system and device " of CN02147425 compares, and the inventive method has been improved some defectives of technical existence better.In the process that superpower footpath is judged, this superpower footpath just application number is the multipath that the patent of the CN02147425 sign mutation in described produces, what the historical energy of multipath adopted among the present invention is through the later multipath energy of IIR filtering, has improved the detection probability in superpower footpath.So the technology of the inventive method, the multipath energy after judging the process employing filtering of superpower footpath can be avoided the defect problem of prior art.
In addition, the present invention has increased the judgement of multipath secondary lobe in judging superpower footpath process, if it is stronger with the multipath energy of superpower footpath adjacent spaces closer (being made as 1/2chip), then it is compared judgement, avoid these secondary lobes are all judged into superpower footpath, cause too much false footpath to report.This processing method can improve the detection probability in superpower footpath effectively, has reduced false-alarm, is a better multipath searching method.
Should be understood that above-mentioned description at specific embodiment is comparatively concrete, can not therefore be interpreted as the restriction to scope of patent protection of the present invention, scope of patent protection of the present invention should be as the criterion with claims.
Claims (5)
1, the multi-path detecting method in a kind of code division multiple address communication system, it comprises:
At system design stage, determine the relative threshold in superpower footpath, the ratio thresholding n of promptly current energy and historical energy;
In system's operation phase, may further comprise the steps:
A: the absolute thresholding that calculates superpower footpath in real time;
B: the relative threshold of reading system design phase, the ratio thresholding n of promptly current energy and historical energy;
C: judge superpower footpath, if multipath energy greater than the ratio of absolute energy thresholding and current energy of multipath and historical energy greater than described ratio thresholding n, if this multipath energy is above the energy in footpath on 1/2 chip position about it simultaneously, judge that then this directly is superpower footpath;
D:, then adopt conventional filter factor to carry out conventional IIR filtering if not superpower footpath;
E: if superpower footpath then adopts new superpower footpath filter factor to realize the IIR filtering of superpower footpath;
F: the power time delay function later according to filtering calculates multi-path threshold, carries out multipath and chooses, and finishes follow-up multipath management processing.
2, method according to claim 1 is characterized in that, in the process in the superpower footpath of judgement of described step C, what the historical energy of multipath adopted is through the later multipath energy of IIR filtering.
3, method according to claim 1 is characterized in that, described absolute energy thresholding is calculated as:
Absolute energy thresholding Threshold=PDPMean+m
*PDPStedv, wherein PDPMean is historical average energy value, and PDPStedv is that historical energy scale is poor, and m＞1 is a weighted value.
4, method according to claim 3, it is characterized in that, the judgement in described superpower footpath is by relatively the current energy and the historical energy of this multipath are judged, when PDPNew/PDPHistory＞n (n＞1), and PDPNew＞Threshold, satisfy PDPNew (i)＞PDPNew (i-1) and PDPNew (i)＞PDPNew (i+1) simultaneously, judge that then this directly is superpower footpath, wherein PDPNew is the current energy of multipath, PDPHistory is the historical energy of multipath, Threshold is the absolute energy thresholding, and PDPNew (i-1) and PDPNew (i+1) are respectively about PDPNew (i) energy in footpath on 1/2 chip position.
5, method according to claim 1 is characterized in that, the filter factor in described definite superpower footpath is:
The filter factor in superpower footpath is bigger than conventional IIR filter factor to the weights of the current energy of multipath in the IIR Filtering Processing of superpower footpath, and the current energy filter coefficient in superpower footpath must be greater than historical energy filter coefficient.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102142860A (en) * | 2010-01-29 | 2011-08-03 | 上海摩波彼克半导体有限公司 | System and method for multi-path combining control of RAKE receiver in third-generation mobile communication system |
| CN102201835A (en) * | 2011-05-16 | 2011-09-28 | 中兴通讯股份有限公司 | Interference cancellation multi-path selection method, device, and interference cancellation system |
| CN102611663A (en) * | 2011-01-20 | 2012-07-25 | 上海贝尔股份有限公司 | Communication method, equipment and system based on downlink channel adaptability |
| CN106302267A (en) * | 2015-05-11 | 2017-01-04 | 联芯科技有限公司 | A kind of single strong footpath channel detection method and device |
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2005
- 2005-09-23 CN CNA2005100374246A patent/CN1937430A/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102142860A (en) * | 2010-01-29 | 2011-08-03 | 上海摩波彼克半导体有限公司 | System and method for multi-path combining control of RAKE receiver in third-generation mobile communication system |
| CN102142860B (en) * | 2010-01-29 | 2014-01-29 | 上海摩波彼克半导体有限公司 | Method for multi-path combining control of RAKE receiver in third-generation mobile communication system |
| CN102611663A (en) * | 2011-01-20 | 2012-07-25 | 上海贝尔股份有限公司 | Communication method, equipment and system based on downlink channel adaptability |
| CN102611663B (en) * | 2011-01-20 | 2016-06-29 | 上海贝尔股份有限公司 | Based on method, equipment and system that down channel self adaptation communicates |
| CN102201835A (en) * | 2011-05-16 | 2011-09-28 | 中兴通讯股份有限公司 | Interference cancellation multi-path selection method, device, and interference cancellation system |
| CN102201835B (en) * | 2011-05-16 | 2016-09-07 | 中兴通讯股份有限公司 | A kind of interference eliminates method, device and the interference cancelling system that multipath selects |
| CN106302267A (en) * | 2015-05-11 | 2017-01-04 | 联芯科技有限公司 | A kind of single strong footpath channel detection method and device |
| CN106302267B (en) * | 2015-05-11 | 2019-05-28 | 辰芯科技有限公司 | A kind of strong diameter channel detection method of list and device |
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