CN102076006A - Method for detecting PRACH preamble signal - Google Patents

Method for detecting PRACH preamble signal Download PDF

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CN102076006A
CN102076006A CN2011100312207A CN201110031220A CN102076006A CN 102076006 A CN102076006 A CN 102076006A CN 2011100312207 A CN2011100312207 A CN 2011100312207A CN 201110031220 A CN201110031220 A CN 201110031220A CN 102076006 A CN102076006 A CN 102076006A
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false
sequence
alarm
false alarm
thresholding
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刘可文
李平安
方秋巳
柯勇
祁万军
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Wuhan University of Technology WUT
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Abstract

The invention discloses a method for detecting a physical random access channel (PRACH) preamble signal, which mainly aims at the situation that four antennae are adopted for receiving in an uplink of a long term evolution (LTE) system. The method comprises the following steps of: determining an approximate straight line representing a relationship between a false alarm probability and a false alarm threshold; for the given false alarm probability, resolving a false alarm threshold T which is not corrected according to the approximate straight line; selecting a group of sequence z(n) with the length of Ns in output signals which are obtained through incoherent combination of signals received by a receiver, and removing a few maximum values in the sequence z(n) according to simulation experience to obtain a result sequence in which the length Ns is a time slot length, or a sub-frame length or length of a plurality of sub-frames; resolving the corrected false alarm threshold according to a correction relationship of the false alarm threshold, and determining that a random access request exists in a received signal when a value which is greater than the corrected false alarm threshold exists in the sequence z(n). Through the method, the effective false alarm threshold can be easily and quickly acquired.

Description

A kind of method that detects the PRACH targeting signal
Technical field
The present invention relates to the 3rd third-generation mobile communication Long Term Evolution (LTE) system, adopt at the LTE system up-link and to adopt in 4 reception antennas or the follow-up evolution system more under the multiple receive antenna situation, in the method that detects LTE ascending physical signal Random Access Channel (PRACH) targeting signal.
Background technology
In the 3rd third-generation mobile communication Long Term Evolution (LTE) system, the user is after system synchronization is finished in start, when connecting system, go up targeting signal that produces by Zadoff-Chu sequence (generally also be called for short the ZC sequence, the document 3GPP TS 36.211V8.5.0 of 3GPPLTE standard is seen in its detailed explanation) cyclic shift of emission to receiver in ascending physical signal Random Access Channel (PRACH).Receiver has judged whether that by detecting the PRACH targeting signal user asks to insert in the signal of receiving.
The process of receiver detection PRACH targeting signal supposes to have a plurality of reception antennas, reception antenna T as shown in Figure 1 iThe baseband signal x that receives iAt first reduce sampling rate through low-pass filtering and extraction, (result of related operation is one group of sequence of complex numbers to carry out related operation with local ZC sequence in correlator then, the detailed content of related operation does not belong to content of the present invention), the result of related operation is asked behind the absolute value square again output power stage range signal y iAfter then each road power level magnitudes signal being carried out incoherent merging, output power stage amplitude sequence, the threshold value of this amplitude sequence and receiver setting compares, if the threshold value that has a peak value to be provided with greater than receiver in this amplitude sequence, then judging has the user to ask to insert.
To the situation of single antenna and the reception of 2 antennas, being provided with of receiver threshold value is fairly simple, and the present invention does not relate to.The setting of receiver threshold when the present invention relates generally to the uplink random access signal that adopts 4 antennas receptions.When the following describes in the prior art for 4 antennas, how receiver is provided with thresholding.
When 4 antennas receive, behind 4 road absolute values again square after the power level magnitudes signal y of output 1, y 2, y 3, y 4In contained white Gaussian noise be plural number, real part and imaginary part satisfy independent Gaussian respectively and distribute, real part quadratic sum imaginary part square and to satisfy the degree of freedom be 2 Chi square distribution.The power level magnitudes signal y of 4 tunnel outputs 1, y 2, y 3, y 4Carry out incoherent merging, following formula is adopted in incoherent merging:
y＝y 1+y 2+y 3+y 4 (1)
(1) in the formula, y represents the output after the incoherent merging, and its sample sequence is the power level magnitudes sequence.
Containing under the situation about transmitting, the additive white Gaussian noise power level magnitudes sequence that comprises in this sequence, representing the stochastic variable y of this sequence to satisfy the degree of freedom is 8 Chi square distribution;
Do not containing under the situation about transmitting, the sample sequence of y is the white Gaussian noise sequence, and representing the stochastic variable y of this sequence amplitude to satisfy the degree of freedom is 8 Chi square distribution.
The degree of freedom is that the probability density function of the stochastic variable y of k is defined as:
f ( y ; k ) = 1 2 k / 2 Γ ( k / 2 ) y k / 2 - 1 e - y / 2 - - - ( 2 )
(2) in the formula, f (y; K) the expression degree of freedom is the probability density function of the stochastic variable y of k, and e is the substrate of natural logrithm, and Г () is a gamma function.For the receiving system of 4 antennas, k=8.
The cumulant distribution function of corresponding (2) formula is:
F(y，k)＝1-P fa(y，k) (3)
(3) in the formula, y is identical with the definition in (2) with k, P Fa(y is that the degree of freedom is the false alarm probability of the stochastic variable y of k k).
The degree of freedom is the false alarm probability P of the stochastic variable y of k Fa(y, calculating formula k) is:
P fa ( y , k ) = Σ i = 0 k / 2 - 1 ( y / 2 ) i i ! e - y / 2 - - - ( 4.1 )
(4.1) in the formula, "! " computing of expression factorial.When k=8, can get by (4.1):
P fa(y，8)＝e -y/2(1+y/2+y 2/8+y 3/48) (4.2)
If not relevant the merging adopts:
z＝(y 1+y 2+y 3+y 4)/4＝y/4 (5.1)
Then, (4.2) formula can be rewritten into following (5.2) formula:
P fa(z，8)＝e -2z(1+2z+2z 2+4z 3/3) (5.2)
False alarm probability P for system's expectation Fa(z, 8) separate (5.2) formula and can obtain the z value as the false-alarm thresholding, and finding the solution of (5.2) formula need be separated a nonlinear equation, the amount of calculation complexity.Because whether judge in the signal that receiver receives has the request of access at first to need to calculate the false-alarm thresholding, the method for therefore existing detection PRACH targeting signal is too complicated, with so be necessary to provide a kind of method of the simple PRACH of detection targeting signal.
Summary of the invention
The method that the purpose of this invention is to provide a kind of PRACH of detection targeting signal can be obtained the false-alarm thresholding quickly and easily, makes according to this false-alarm thresholding to judge in the signal that receiver receives whether have the request of access comparatively simple.
To achieve these goals, the invention provides a kind of method of the PRACH of detection targeting signal, comprise the steps:
(1) to the relational expression P of false alarm probability and false-alarm thresholding Fa(z)=e -2z(1+2z+2z 2+ 4z 3/ 3) take the logarithm in both sides, obtains both logarithmic relationship formulas, wherein P Fa(z k) is false alarm probability, and z is the false-alarm thresholding;
(2) determine the near linear of the curve that the logarithmic relationship formula of false alarm probability and false-alarm thresholding is represented;
(3), find the solution the preceding false-alarm thresholding of correction according to described near linear to given false alarm probability;
(4) get that length is N in the output signal of signal after incoherent merging that receiver receives sOne group of sequence z (n), remove several maximums among the sequence z (n) according to the emulation experience, obtain sequence as a result
Figure BDA0000045760140000041
Length N wherein sSize be a slot length or a subframe lengths or a plurality of subframe lengths;
(5) according to the correction relational expression of false-alarm thresholding
Figure BDA0000045760140000042
Find the solution revised false-alarm thresholding, wherein T is the false-alarm thresholding before revising, T FaBe revised false-alarm thresholding;
(6) when the value that has among the described sequence z (n) greater than described revised false-alarm thresholding, judging has the request that inserts at random in the received signal.
In one embodiment of the invention, take the logarithm in the described step (1) to be specially and take from right logarithm or common logarithm.
Compared with prior art, the method that the present invention detects the PRACH targeting signal obtains the near linear of false alarm probability and false-alarm thresholding relation by step (1) and step (2), like this for set false alarm probability, it is very simple to find the solution the false-alarm thresholding, make according to this false-alarm thresholding judge whether have in the signal that receiver receives insert ask comparatively simple.
In addition, this method is revised the false-alarm thresholding by the correction relational expression of step (5), with the actual noise (variance of real part and imaginary part differs and is decided to be 1) of the relevant output of satisfying receiver reception antenna correspondence, has improved the accuracy that this method detects.
By following description also in conjunction with the accompanying drawings, it is more clear that the present invention will become, and these accompanying drawings are used to explain embodiments of the invention.
Description of drawings
Fig. 1 is the schematic diagram of LTE downlink physical layer processing procedure.
Fig. 2 has showed that the present invention detects theoretical logarithm false alarm probability curve and near linear in the method for PRACH targeting signal.
Fig. 3 detects the flow chart of the method for PRACH targeting signal for the present invention.
Embodiment
With reference now to accompanying drawing, describe embodiments of the invention, the similar elements label is represented similar elements in the accompanying drawing.
Before explanation false-alarm thresholding computational methods of the present invention, false-alarm thresholding calculating principle of the present invention is described earlier.
By common logarithm is got on formula (5.2) both sides, can get
log 10P fa(z，8)＝log 10[e -2z(1+2z+2z 2+4z 3/3)] (6)
Log in (6) formula of picture 10P Fa(z, 8) see the curve among Fig. 2 with respect to the curve chart of z, this curve in a very big interval, log 10P Fa(z, 8) are almost the linear function of z, and for the LTE system, the false alarm probability P of its system's expectation Fa(z, 8) are general all in the part of the near linear of this curve.
Like this, select two points of near linear part, come the curve of approximate expression (6) expression as straight line, the straight line that we adopt is:
log 10(P fa(T))＝-0.6421T+1.1059 (7)
(7) in the formula, T represents false-alarm thresholding, P Fa(T) expression false alarm probability.
The straight line of the formula of drawing in Fig. 2 (7) expression, as Fig. 2 cathetus, as can be seen, this straight line is in a very big zone of the curve of formula (6) expression, curve that can approximant well (6) expression.Therefore, for a given false alarm probability P Fa, can calculate log earlier 10P Fa, ask T as the false-alarm thresholding by (7) again, obviously calculate very simple.
Because the false-alarm thresholding T that asks by formula (7) is after supposing the relevant output of each antenna correspondence, the real part of its noise and the variance of imaginary part are 1, noise is not necessarily to satisfy this hypothesis in the reality, so we adopt following formula to revise, the reason of revising is because thresholding T supposes that the variance of noise is 1, but actual noise variance is unknown, but can use
Figure BDA0000045760140000061
Estimate.
T fa = 0.5 T 1 N s Σ n = 0 N s - 1 z ~ ( n ) - - - ( 8 )
In the output z of incoherent merging, getting length is N sOne group of sequence z (n), length N wherein sSize be a slot length or a subframe lengths or a plurality of subframe lengths, in (8) formula
Figure BDA0000045760140000072
For remove among the sequence z (n) sequence remaining after several peak-peaks according to the emulation experience, the purpose of removing peak-peak is because when the signal emission is arranged, peak-peak is the sampling of useful signal correspondence, removes these value backs result just for white Gaussian noise, satisfies above-mentioned series of theories.If several maximums are removed in the no signal emission, remaining sequence still is the white Gaussian noise sequence.Wherein, the factor 0.5 is that denominator is 4, rather than the degree of freedom 8 because of the mean time of asking z from y.Like this, ask after the false-alarm thresholding T, ask T according to (8) formula again according to (7) formula FaFalse-alarm thresholding as last application.
Need to prove, be the situation that common logarithm is got on (5.2) formula both sides above, also can take from right logarithm to (5.2) formula here.
In addition, to the degree of freedom greater than 8 Chi square of stochastic variable, except the straight line according to formula (7) expression comes the curve of approximant (6) expression, other 2 points in the curve of all right modus ponens (6) expression on the near linear part, obtain other approximate straight lines, thereby obtain corresponding false-alarm thresholding according to these other near linears.
In addition, the denominator of the incoherent merging of formula (1) comprises other positive integer except that 4, and the factor 0.5 in this up-to-date style (8) need change the corresponding constant coefficient factor into.For example, the denominator of the incoherent merging of formula (5.1) changes 8 into by 4, and the factor 0.5 in the formula (8) need change 1 into; The denominator of the incoherent merging of formula (5.1) changes 1 into by 4, and the factor 0.5 in the formula (8) need change 1/8 into.
Calculate principle based on top false-alarm thresholding, describe the method that the false-alarm thresholding that utilizes this principle to calculate detects the PRACH targeting signal below in detail, comprise the steps:
Step S1 is to the false alarm probability P of system's expectation Fa, calculate log 10P Fa, ask the preceding false-alarm thresholding T of correction according to the straight-line formula (7) of false alarm probability and false-alarm thresholding;
Step S2, to having the receiver of 4 antennas, (targeting signal is that transmitter is upward launched one by the sequence behind the Zadoff-Chu sequence cyclic shift in ascending physical signal Random Access Channel (PRACH) to the targeting signal of receiver/transmitter simultaneously, its specific definition is seen the document 3GPP TS 36.211V8.5.0 of 3GPP LTE standard), the targeting signal that receiver receives is through the pre-process of Fig. 1 (low-pass filtering and extraction, take absolute value ask square) and press z=(y 1+ y 2+ y 3+ y 4Obtain exporting z after the incoherent merging of)/4=y/4, getting length in the output z of incoherent merging is N sOne group of sequence z (n), length N wherein sSize be a slot length or a subframe lengths or a plurality of subframe lengths;
Step S3 removes a small amount of several maximums among the sequence z (n) according to the emulation experience, such as 3, obtains sequence as a result
Figure BDA0000045760140000081
Step S4, the sequence as a result that obtains according to step S 3
Figure BDA0000045760140000082
The length N of sequence z among the step S2 (n) s, the false-alarm thresholding T before the correction that obtains of step S1, utilize the correction relational expression (8) of false alarm probability and false-alarm thresholding to obtain revised false-alarm thresholding T Fa
Step S5 judges not remove whether the false-alarm thresholding T that obtains greater than step S4 is arranged among the peaked sequence z (n) FaValue, if having, then have in the targeting signal that receiver receives and insert request at random, if do not have, then insert request at random in the targeting signal that receiver receives.
Above invention has been described in conjunction with most preferred embodiment, but the present invention is not limited to the embodiment of above announcement, and should contain various modification, equivalent combinations of carrying out according to essence of the present invention.

Claims (2)

1. a method that detects the PRACH targeting signal comprises the steps:
(1) to the relational expression P of false alarm probability and false-alarm thresholding Fa(z)=e -2z(1+2z+2z 2+ 4z 3/ 3) take the logarithm in both sides, obtains both logarithmic relationship formulas, wherein P Fa(z k) is false alarm probability, and z is the false-alarm thresholding;
(2) determine the near linear of the curve that the logarithmic relationship formula of false alarm probability and false-alarm thresholding is represented;
(3), find the solution the preceding false-alarm thresholding of correction according to described near linear to given false alarm probability;
(4) get that length is N in the output signal of targeting signal after incoherent merging that receiver receives sOne group of sequence z (n), remove maximum among the sequence z (n) according to the emulation experience, obtain sequence as a result
Figure FDA0000045760130000011
Length N wherein sSize be a slot length or a subframe lengths or a plurality of subframe lengths;
(5) according to the correction relational expression of false-alarm thresholding
Figure FDA0000045760130000012
Find the solution revised false-alarm thresholding, wherein T is the false-alarm thresholding before revising, T FaBe revised false-alarm thresholding;
(6) when the value that has among the described sequence z (n) greater than described revised false-alarm thresholding, judging in the targeting signal that receiver receives has the request that inserts at random.
2. the method for detection PRACH targeting signal as claimed in claim 1 is characterized in that, takes the logarithm in the described step (1) to be specially and takes from right logarithm or common logarithm.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102843328A (en) * 2012-08-02 2012-12-26 北京中科晶上科技有限公司 Method for detecting PRACH (Physical Random Access Channel) sequence in TDD LTE (Time Division Duplex Long Term Evolution) system
CN104618936A (en) * 2015-02-11 2015-05-13 大唐联仪科技有限公司 Method and system for detecting LTE (Long Term Evolution) preamble signal
US9954633B2 (en) 2015-06-18 2018-04-24 Nxp Usa, Inc. Apparatus and method of performing a decimation on a signal for pattern detection
WO2018130037A1 (en) * 2017-01-11 2018-07-19 中兴通讯股份有限公司 Detection method and apparatus for identifying false detection caused by interference, and base station

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101873681A (en) * 2009-04-22 2010-10-27 大唐移动通信设备有限公司 Method and device for adjusting received target power of PRACH (Physical Random Access Channel) signal
CN101873619A (en) * 2009-04-22 2010-10-27 大唐移动通信设备有限公司 Method and device for adjusting preamble sequence number

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101873681A (en) * 2009-04-22 2010-10-27 大唐移动通信设备有限公司 Method and device for adjusting received target power of PRACH (Physical Random Access Channel) signal
CN101873619A (en) * 2009-04-22 2010-10-27 大唐移动通信设备有限公司 Method and device for adjusting preamble sequence number

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102843328A (en) * 2012-08-02 2012-12-26 北京中科晶上科技有限公司 Method for detecting PRACH (Physical Random Access Channel) sequence in TDD LTE (Time Division Duplex Long Term Evolution) system
CN102843328B (en) * 2012-08-02 2014-11-26 北京中科晶上科技有限公司 Method for detecting PRACH (Physical Random Access Channel) sequence in TDD LTE (Time Division Duplex Long Term Evolution) system
CN104618936A (en) * 2015-02-11 2015-05-13 大唐联仪科技有限公司 Method and system for detecting LTE (Long Term Evolution) preamble signal
CN104618936B (en) * 2015-02-11 2018-04-27 大唐联仪科技有限公司 A kind of detection method and system of Long Term Evolution LTE targeting signals
US9954633B2 (en) 2015-06-18 2018-04-24 Nxp Usa, Inc. Apparatus and method of performing a decimation on a signal for pattern detection
WO2018130037A1 (en) * 2017-01-11 2018-07-19 中兴通讯股份有限公司 Detection method and apparatus for identifying false detection caused by interference, and base station

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