CN1124715C - Multi-path search method and device of CDMA communication system - Google Patents
Multi-path search method and device of CDMA communication system Download PDFInfo
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Abstract
The present invention discloses a multi-path search method and a multi-path search device of a CDMA communication system. The multi-path search method carries out alpha filtering for a multi-path search energy window output by a matching correlator and then adopts a dual-gate noise threshold and the strongest multi-path threshold together for the search energy window to carry out multi-path judgment. A searcher is composed of the matching correlator, an alpha filter of the search energy window, a double-threshold multi-path judger, a search window slide device and a multi-path distributor. The searcher has strong multi-path capture capability, can save the hardware cost of the matching correlator and can be suitable for the environments of different multi-path channels. Regardless of indoor channels or vehicle-carried channels, the present invention has good multi-path capture performance.
Description
The present invention relates to code division multiple access (CDMA) mobile communication system, more particularly, be meant a kind of multipath searching method and device thereof of code division multiple address communication system.
The principal character of land mobile channel is a multipath transmisstion.Because CDMA mobile communication systems has adopted the spread-spectrum signal in broadband, it is little a lot of that code-element period is compared the multidiameter delay expansion of mobile channel, therefore has many distinguishable multipath signals at receiving terminal.Because these multipath signals are to arrive receiver through different propagation paths, therefore they are the fading signals that are mutually independent, utilize the RAKE receiver of multipath signal can significantly improve receptivity under the multipath channel, and the Multipath searching of accurately catching and lock multipath signal is the key component of RAKE receiver.
In code division multiple access (CDMA) spread spectrum communication, existingly generally acknowledge that multipath searching method is as follows preferably: adopt the coupling correlator to carry out related calculation with local PN sign indicating number to received signal, obtain one group of correlation energy value, constitute the search energy window corresponding to each search phase place of search energy window; Then at multipath in the update cycle, search energy window that current related operation is obtained and the search energy window of last time are done same-phase and are added up (noncoherent accumulation), obtain being used for the search energy window of multi-path judging; The average noise level of multi-path judging unit estimation search energy window, and further obtain noise gate, with this noise gate the multipath of search energy window is once adjudicated then, obtain one group of candidate's multipath; The search window sliding unit obtains the search window slip signals according to the distribution of candidate's multipath; The multipath allocation units are assigned to each bar branch road that RAKE receives with candidate's multipath;
In the land mobile channel, not only the Strength Changes of multipath is violent, and the position of multipath also can change relative to moving of base station because of travelling carriage.The acute variation of multipath intensity can significantly reduce the multi-path resolved ability of search energy window, though the method for existing noncoherent accumulation can overcome the influence of multipath intensity acute variation to the resolution capability of search energy window to a certain extent, but there is following defective: one, because noncoherent accumulation must be finished in the update cycle at a multipath, therefore the noncoherent accumulation number of times is limited, thereby limit of the improvement of this method to multi-path resolved ability, they are two years old, the method of noncoherent accumulation requires to finish repeatedly coherent accumulation computing in the update cycle at a multipath, the frequency height of related operation is bigger to hardware resource consumption.And in the multi-path judging unit, existing noise estimation method seems coarse, reason is: because Noise Estimation is to carry out before threshold judgement, the candidate's multipath information that will get rid of during Noise Estimation is inaccurate, so the accuracy of Noise Estimation can be influenced.Existing multi-path judging unit adopts single noise gate to carry out multi-path judging, when the multipath energy distribution disperses in the channel, this method is suitable, but when the distribution of the multipath energy in the channel concentrates on the minority multipath, single noise gate judgement can be exported noise as candidate's multipath, thereby reduce the performance that RAKE receives, the channel adaptive capacity of therefore single noise gate judgement is relatively poor.
For this reason, the objective of the invention is the problems referred to above at the multipath searching method existence of existing code division multiple address communication system, the multipath searching method of the code division multiple address communication system of a kind of novelty that proposes is with advancing to provide a kind of for implementing the multipath searching device that this method is used
To achieve these goals,
The multipath searching method that the present invention adopts is: the search energy window to the output of coupling correlator carries out α filtering earlier; Carry out multi-path judging with the dual-threshold judgement method search energy window that filtering obtains to α then; Candidate's multipath one tunnel of multi-path judging output obtains multipath output via the multipath distribution, slides via search window and obtain the search window slip signals in another road; At last this signal feedback is arrived coupling correlator and α filter unit to adjust search window position.
The multipath searching device that the present invention adopts comprises α filter unit, double threshold multi-path judging unit, multipath allocation units, the search window sliding unit of coupling correlator unit, search energy window, wherein:
The coupling correlator unit is carried out related operation to input signal and local PN sign indicating number, to obtain the last set energy window corresponding to each search phase place of search window;
The α filter unit of search energy window carries out α filtering to the search energy window of input, to obtain the filtered search energy window of α;
Double threshold multi-path judging unit filters out candidate's multipath from the filtered search energy window of α;
The multipath allocation units are distributed to each bar branch road that RAKE receives with candidate's multipath;
The search window sliding unit calculates the search window slip signals according to candidate's multipath of input.
Method of the present invention and have following advantage for executing the device that this method adopts:
The first, the present invention's employing improves the multi-path resolved ability of searching for energy window to the method that the Multipath searching energy window carries out α filtering, compare the method for existing noncoherent accumulation, this method is not subjected to the restriction of multipath update cycle on the one hand, therefore can access multi-path resolved ability better searches for energy window, this method can also reduce the frequency of related operation on the other hand, thereby saves the related operation resource.
The second, in the Noise Estimation of Multipath searching energy window, adopted and recalled mode.The result of multi-path judging is used for Noise Estimation, therefore can gets rid of candidate's multipath comparatively exactly, obtain Noise Estimation comparatively accurately.
Three, the employing of the mode of dual-threshold judgement.Be provided with most powerful path thresholding than the low fixed decibel number of the strongest multipath, then the noise gate that obtains in most powerful path thresholding and the Noise Estimation is compared, from two thresholdings, select bigger one to be used for multi-path judging as decision threshold, so both keep the advantage that existing single noise gate is adjudicated, also remedied the deficiency of noise gate single when multipath energy concentrates on the minority multipath simultaneously.
Below in conjunction with drawings and Examples, method and apparatus of the present invention is described in further detail:
Fig. 1 is a multipath searching device schematic block diagram of the present invention.
Fig. 2 recalls the workflow schematic diagram of the average noise of search energy window for the present invention adopts.
Fig. 3 adopts the dual-threshold judgement principle schematic for the present invention.
This method is carried out α filtering to the search energy window of coupling correlator output earlier; Carry out multi-path judging with the dual-threshold judgement method search energy window that filtering obtains to α then; Candidate's multipath one tunnel of multi-path judging output obtains multipath output via the multipath distribution, slides via search window and obtain the search window slip signals in another road; At last this signal feedback is arrived coupling correlator and α filter unit to adjust search window position.
This method further comprises following steps:
A. with the coupling correlator input signal and local PN sign indicating number are carried out related operation, obtain one group of correlation energy value, be the search energy window corresponding to each search phase place of search window;
B. the search energy window to the output of coupling correlator carries out α filtering, to obtain the filtered search energy window of α;
C. when multipath upgrades, from the filtered search energy window of up-to-date α, seek the strongest multipath of correlation energy maximum, to obtain the strongest multi-path threshold;
D. seek the strongest multipath of N bar energy as one group of candidate's multipath from the filtered search energy window of α, the value of N should be not less than the bar number of RAKE receiving branch;
E. estimate the average noise of the filtered search energy window of α, to obtain noise gate;
F. two thresholdings that utilize step c and step e to obtain, the N bar multipath that steps d is obtained carries out the double threshold multi-path judging, to obtain one group of new candidate's multipath;
G. the one group of new candidate's multipath that step f is obtained is used for the average noise of step e and estimates, repeating step e and step f carry out recalling for M time, estimate and one group of candidate's multipath with the average noise that obtains final search energy window, and incite somebody to action the α filter unit that the average noise that wherein finally obtain estimates to feed back to the search energy window, one group of candidate's multipath that will finally obtain is again delivered to multipath and is distributed and the search window sliding unit;
H. candidate's multipath that step f is obtained is distributed to each bar branch road that RAKE receives;
I. final search window sliding unit candidate's multipath that step f is obtained slip signals of obtaining search window feeds back to the α filter unit of coupling correlator and search energy window, with the slip of control search window.
When the search energy window of among the described step b coupling correlator being exported carries out α filtering, follow formula (1-α) * A+ α * B, the energy value of each phase place of the search energy window that historical α filtering is exported all is set to 0 earlier;
Then all phase places of the search energy window of each coupling correlator output are all carried out α filtering;
Again the filtered search energy window of the α that obtains is delivered to multi-path judging on the one hand, the search energy window of the historical α filtering output of storage conduct α filtering next time is used for α filtering next time on the other hand.
If the correlation energy of i phase place of the search energy window of note coupling correlator input is A, and the correlation energy of corresponding phase place with it of remembering the search energy window of historical α filtering output is B, B is determined by following method: suppose the relative historical search energy window of current search energy window x the phase place of having slided, then when the historical search energy window comprises (x+i) individual phase place, B is exactly the correlation energy value on the individual phase place of historical search energy window (x+i), otherwise the B value is the average noise of current defeated people's search energy window.
Then the correlation energy of corresponding i the phase place of the filtered search energy window of α is (1-α) * A+ α * B, and α wherein is the α filter factor, and the α value is between 0.8～1.
Among the described step c obtaining of the strongest multi-path threshold be the maximum of from the filtered search energy window of α, selecting correlation energy, will be than the correlation energy value of the low R decibels of this correlation energy value as the strongest multi-path threshold, the value of R is between 8～12.
Candidate's multipath is determined as follows in the described steps d:
Be provided with at first that all phase places are effective phase place in the filtered search energy window of α;
From effective phase place of the filtered search energy window of α, seek the phase place of energy maximum again, with this phase place as candidate's multipath, then this phase place and about each r chip be set to invalid phase place with interior phase place, the value of r is between 0.75～1;
Repeat previous step at last suddenly up to finding N bar candidate multipath;
The estimation of average noise determines to remove earlier the phase place in each chip about the phase place of the candidate's multipath in the filtered search energy window of α and each bar candidate multipath among the described step e, and then the correlation energy value that will search for other phase places in the energy window is average, has promptly obtained average noise.
Noise gate is estimated a high fixing decibels than average noise among the described step e, and the value of this decibels is between 2～4.
The double threshold multi-path judging is at first to select the greater in the strongest multi-path threshold and the noise gate as decision threshold among the described step f, again the resulting N bar of steps d candidate multipath is compared with this decision threshold respectively, if be higher than this decision threshold, then as new candidate's multipath, otherwise not as new candidate's multipath.
In the described step g, the number of times of recalling repetition is M, and the value of M is between 1～3 time.The purpose of recalling is to estimate in order to obtain more accurate average noise, the retrogressive method that adopts in the average noise estimation that Here it is.The value of bigger M can obtain average noise estimation more accurately on the one hand, thereby obtains noise gate more accurately, can increase calculation resources on the other hand.Take all factors into consideration from two aspects,
The search window slip signals is to select two candidate's multipaths of phase phasic difference maximum from candidate's multipath in the described step I, calculates the average phase of these two candidate's multipaths then, deducts the phase value of the center of search window with this average phase.
See also shown in Figure 1, multipath searching device of the present invention comprise the coupling correlator unit, the search energy window α filter unit, double threshold multi-path judging unit, multipath allocation units, search window sliding unit, wherein:
The coupling correlator unit is done the related operation of matched filtering mode, the search energy window that output is made of the correlation energy value on the difference search phase place respectively to the defeated people's signal of antenna and local PN sign indicating number in the search window scope.
The α filter unit of search energy window is done α filtering to the search energy window, the filtered search energy window of output α.
Double threshold multi-path judging unit obtains the search energy window of up-to-date α filtering output every a multipath update cycle from the α filter unit of search energy window, through judgement back output candidate multipath.
The search window sliding unit is accepted the defeated people of candidate's multipath, obtains the search window slip signals after treatment, and this signal feedback is used for the slip scan energy window to follow the tracks of the multipath drift to the α filter unit of coupling correlator unit and search energy window.
The multipath allocation units are assigned to each multipath branch road that RAKE receives with candidate's multipath.
The course of work of the α filter unit of search energy window is:
At first define the search energy window that the historical search energy window is last time α filtering output, owing to also there is not α filtering output, the energy value of each phase place of the historical search energy window of this moment all is set to 0 during initialization.α filtering is to carry out at the phase place of the search energy window of current input, remember that the correlation energy on certain phase place of energy window of current input is A, and the correlation energy on the corresponding phase of note historical search energy window is B, then the correlation energy of this phase place is (1-α) * A+ α * B in Shu Chu the search energy window, α wherein is the α filter factor, and value is between 0.8～1.All phase places in the search energy window of input are all carried out α filtering, and the search energy window that will obtain is as the historical search energy window of next α filtering.
Because the search energy window of current input historical search energy window relatively has slip, therefore before carrying out α filtering, the historical search energy window must be alignd with current defeated people's search energy window, concrete way is: the relative historical search energy window of search energy window of supposing current defeated people x the phase place of having slided, then the phase place with the corresponding historical search energy window of the phase place i of current search energy window is (x+i), when the historical search energy window comprises phase place (x+i), energy on this phase place will be used for the α filtering of phase place i of current defeated people's search energy window, when the historical search energy window did not comprise phase place (x+i), the value of the energy on this phase place was the average noise of the search energy window of current input.
See also shown in Figure 2ly, the average noise that adopts retrogressive method to be searched for energy window more accurately in the double threshold multi-path judging unit estimates that the course of work is as follows:
At first the search energy window according to input obtains one group of the strongest multipath of energy, and should organize multipath as candidate's multipath, obtain searching for the average noise estimation of energy window then according to candidate's multipath, and further obtain noise gate, carry out the double threshold multi-path judging then, the new candidate's multipath that obtains is used for average noise with feedback and estimates.Wherein, the average noise estimation approach of search energy window is as follows: according to candidate's multipath information, remove the phase place of candidate's multipath in the search energy window, and remove about each candidate's multipath phase place in (between 0.75～1 chip) among a small circle, with the phase place of phase place remaining in the search energy window as noise, on average the energy on all noise phase obtains searching for the average noise estimation of energy window.
In the average noise of search energy window is estimated, candidate's multipath information directly influences the accuracy of Noise Estimation, candidate's multipath that the method for recalling that the present invention adopts has utilized the double threshold multi-path judging to obtain is estimated average noise, consider that the candidate's multipath that obtains through dual-threshold judgement is comparatively accurately, therefore average noise is estimated correspondingly comparatively accurate, further can obtain comparatively accurate noise gate, and more accurate noise gate can improve the performance of double threshold multi-path judging, thereby obtain candidate's multipath information comparatively accurately, and candidate's multipath information can be improved the average noise estimation accurately.According to the analysis of front as can be known, retrogressive method not only can improve the average noise of search energy window to be estimated, and can improve the performance of multi-path judging.
See also shown in Figure 3ly, when carrying out multi-path judging, adopted two decision thresholds jointly multipath to be adjudicated.These two decision thresholds are respectively noise gate 1 and the strongest multi-path threshold 2, noise gate 1 is wherein estimated to obtain by the average noise of search energy window, it is than the high fixing decibels of average noise of search energy window, typical value is 2～4 decibels, and the strongest multi-path threshold 2 is determined by the strongest multipath in the search energy window, it is than low fixing decibels of energy value of the strongest multipath, and typical value is 8～12 decibels.During multi-path judging, at first from the search energy window, find one group of the strongest multipath of energy, be called the set of primary election candidate multipath, then according to noise gate 1 and the strongest multi-path threshold 2, the phase place of selecting to be higher than two thresholdings from the set of primary election candidate multipath is as candidate's multipath, and other multipath is not then as candidate's multipath.
Be subjected to the influence of the retrogressive method in the average noise estimation, the double threshold multi-path judging can carry out repeatedly, and each noise gate all will improve, thereby makes the judgement performance better.
The method that adopts double threshold in the multi-path judging is based on following consideration:
The first, the channel circumstance that the most powerful path thresholding is mainly used in one of existence or seldom several strong direct projection (or reflection) multipath is set.In this channel circumstance, there is the very strong multipath of less energy, with the energy of the resulting most of candidate's multipaths of noise gate far below most powerful path, and when the energy of candidate's multipath the most powerful path energy-the not contribution of performance improvement that almost RAKE merged when 10dB is following, and because low noise gate may be introduced the noise multipath, the performance that RAKE receives can descend on the contrary.By being set, the most powerful path thresholding just can address this problem.
The second, under the channel circumstance that does not have strong direct projection (or reflection) multipath, what work mainly is noise gate.Noise gate is the cancelling noise multipath well, obtains rational candidate's multipath.
Therefore, the binding energy of noise gate and most powerful path thresholding improves the ability that Multipath searching adapts to different channel circumstances.
Adopt multipath searching method of the present invention and device in the wideband CDMA up link, to pass through analogue simulation, emulation platform is the system emulation software Cossap of Synopsis company, simulation result has been verified validity of the present invention: under the prerequisite of acquisition and existing multipath searching device best performance, multipath searching device of the present invention is saved 2/3 coupling related operation resource than existing multipath searching device.
Claims (11)
1, a kind of multipath searching method of code division multiple address communication system is characterized in that: this method is carried out α filtering to the search energy window of coupling correlator output earlier; Carry out multi-path judging with the dual-threshold judgement method search energy window that filtering obtains to α then; Candidate's multipath one tunnel of multi-path judging output obtains multipath output via the multipath distribution, slides via search window and obtain the search window slip signals in another road; At last this signal feedback is arrived coupling correlator and α filter unit to adjust search window position.
2, the multipath searching method of code division multiple address communication system as claimed in claim 1 is characterized in that, this method further comprises following steps:
A. with the coupling correlator input signal and local PN sign indicating number are carried out related operation, obtain one group of correlation energy value, be the search energy window corresponding to each search phase place of search window;
B. the search energy window to the output of coupling correlator carries out α filtering, to obtain the filtered search energy window of α;
C. when multipath upgrades, from the filtered search energy window of up-to-date α, seek the strongest multipath of correlation energy maximum, to obtain the strongest multi-path threshold;
D. seek the strongest multipath of N bar energy as one group of candidate's multipath from the filtered search energy window of α, the value of N should be not less than the bar number of RAKE receiving branch;
E. estimate the average noise of the filtered search energy window of α, to obtain noise gate;
F. two thresholdings that utilize step c and step e to obtain, the N bar multipath that steps d is obtained carries out the double threshold multi-path judging, to obtain one group of new candidate's multipath;
G. the one group of new candidate's multipath that step f is obtained is used for the average noise of step e and estimates, repeating step e and step f carry out recalling for M time, estimate and one group of candidate's multipath with the average noise that obtains final search energy window, and incite somebody to action the α filter unit that the average noise that wherein finally obtain estimates to feed back to the search energy window, one group of candidate's multipath that will finally obtain is again delivered to multipath and is distributed and the search window sliding unit;
H. candidate's multipath that step f is obtained is distributed to each bar branch road that RAKE receives;
I. final search window sliding unit candidate's multipath that step f is obtained slip signals of obtaining search window feeds back to the α filter unit of coupling correlator and search energy window, with the slip of control search window.
3, the multipath searching method of code division multiple address communication system as claimed in claim 2, it is characterized in that, when the search energy window of among the described step b coupling correlator being exported carries out α filtering, follow formula (1-α) * A+ α * B, the energy value of each phase place of the search energy window that historical α filtering is exported all is set to 0 earlier, wherein, A is the correlation energy value of i phase place of the search energy window of coupling correlator input, and B is the correlation energy value of corresponding phase place with it of the search energy window of historical α filtering output;
Then all phase places of the search energy window of each coupling correlator output are all carried out α filtering;
Again the filtered search energy window of the α that obtains is delivered to multi-path judging on the one hand, the search energy window of the historical α filtering output of storage conduct α filtering next time is used for α filtering next time on the other hand.
4, the multipath searching method of code division multiple address communication system as claimed in claim 2, it is characterized in that, among the described step c obtaining of the strongest multi-path threshold be the maximum of from the filtered search energy window of α, selecting correlation energy, will be than the strongest multi-path threshold of correlation energy value conduct of the low R decibels of this correlation energy value, the value of R is between 8～12.
5, the multipath searching method of code division multiple address communication system as claimed in claim 2 is characterized in that, candidate's multipath is determined as follows in the described steps d:
Be provided with at first that all phase places are effective phase place in the filtered search energy window of α;
From effective phase place of the filtered search energy window of α, seek the phase place of energy maximum again, with this phase place as candidate's multipath, then this phase place and about each r chip be set to invalid phase place with interior phase place, the value of r is between 0.8～1;
Repeat previous step at last suddenly up to finding N bar candidate multipath.
6, the multipath searching method of code division multiple address communication system as claimed in claim 2, it is characterized in that, the estimation of average noise determines to remove earlier the phase place in each chip about the phase place of the candidate's multipath in the filtered search energy window of α and each bar candidate multipath among the described step e, and then the correlation energy value that will search for other phase places in the energy window is average, has promptly obtained average noise.
As the multipath searching method of claim 2 or 6 described code division multiple address communication systems, it is characterized in that 7, noise gate is estimated a high fixing decibels than average noise among the described step e, the value of this decibels is between 2～4.
8, the multipath searching method of code division multiple address communication system as claimed in claim 2, it is characterized in that, the double threshold multi-path judging is at first to select the greater in the strongest multi-path threshold and the noise gate as decision threshold among the described step f, again the resulting N bar of steps d candidate multipath is compared with this decision threshold respectively, if be higher than this decision threshold, then as new candidate's multipath, otherwise not as new candidate's multipath.
9, the multipath searching method of code division multiple address communication system as claimed in claim 2 is characterized in that, the value of recalling number of times M in the described step g is between 1～3 time.
10, the multipath searching method of code division multiple address communication system as claimed in claim 2, it is characterized in that, the search window slip signals is to select two candidate's multipaths of phase phasic difference maximum from candidate's multipath in the described step I, calculate the average phase of these two candidate's multipaths then, deduct the phase value of the center of search window with this average phase.
11, a kind of multipath searching device of code division multiple address communication system is characterized in that,
This device comprises α filter unit, double threshold multi-path judging unit, multipath allocation units, the search window sliding unit of coupling correlator unit, search energy window, wherein:
The coupling correlator unit is carried out related operation to input signal and local PN sign indicating number, to obtain the last set energy window corresponding to each search phase place of search window;
The α filter unit of search energy window carries out α filtering to the search energy window of input, to obtain the filtered search energy window of α;
Double threshold multi-path judging unit filters out candidate's multipath from the filtered search energy window of α;
The multipath allocation units are distributed to each bar branch road that RAKE receives with candidate's multipath;
The search window sliding unit calculates the search window slip signals according to candidate's multipath of input.
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| US7894508B2 (en) | 2001-08-27 | 2011-02-22 | Broadcom Corporation | WCDMA terminal baseband processing module having cell searcher module |
| CN100527654C (en) * | 2003-05-28 | 2009-08-12 | 华为技术有限公司 | Method for determining first path precisively in CDMA mobile communiation system |
| CN100438385C (en) * | 2003-06-03 | 2008-11-26 | 华为技术有限公司 | Baseband receiving synchronous acquiring method and apparatus for CDMA system |
| US7680083B2 (en) | 2005-07-28 | 2010-03-16 | Broadcom Corporation | Rake receiver architecture within a WCDMA terminal |
| CN100426691C (en) * | 2005-05-25 | 2008-10-15 | 上海华为技术有限公司 | RAKE receiving method and RAKE receiver using the method |
| US7620099B2 (en) | 2005-07-28 | 2009-11-17 | Broadcom Corporation | WCDMA terminal baseband processing module having multi-path scanner module |
| CN1925470B (en) * | 2005-08-29 | 2011-03-02 | 中兴通讯股份有限公司 | Multi-path judging method for time-division duplex mobile communication system |
| CN102315859B (en) * | 2011-09-23 | 2014-01-22 | 华为技术有限公司 | Multi-path search method and device |
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