CN107302407B - Electromagnetic spectrum signal field intensity preprocessing method based on empirical mode decomposition - Google Patents

Electromagnetic spectrum signal field intensity preprocessing method based on empirical mode decomposition Download PDF

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CN107302407B
CN107302407B CN201710504709.9A CN201710504709A CN107302407B CN 107302407 B CN107302407 B CN 107302407B CN 201710504709 A CN201710504709 A CN 201710504709A CN 107302407 B CN107302407 B CN 107302407B
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field intensity
sequence
intensity value
envelope
fading
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CN107302407A (en
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谢树果
谷晓鹏
李圆圆
郝旭春
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Beihang University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/318—Received signal strength
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/391—Modelling the propagation channel
    • H04B17/3911—Fading models or fading generators
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/08—Testing, supervising or monitoring using real traffic
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q2209/00—Arrangements in telecontrol or telemetry systems
    • H04Q2209/50—Arrangements in telecontrol or telemetry systems using a mobile data collecting device, e.g. walk by or drive by

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Abstract

The invention relates to a preprocessing method of electromagnetic spectrum signal field intensity based on empirical mode decomposition, which comprises the following steps: (1) arranging the field intensity values received in the moving mode into a field intensity value sequence according to the moving receiving sequence; (2) fitting the extreme value envelope and the mean value envelope of the field intensity value sequence in the step (1); (3) and decomposing the field intensity value sequence into a plurality of intrinsic mode functions, and removing high-frequency components to obtain the field intensity value sequence for eliminating fading.

Description

Electromagnetic spectrum signal field intensity preprocessing method based on empirical mode decomposition
Technical Field
The invention relates to a field intensity preprocessing method based on empirical mode decomposition, in particular to a method for preprocessing the field intensity of a received signal under the condition of mobile signal receiving.
Background
The road test is a common test method for wireless signals in the communication industry, and by means of mobile test, relevant data of electromagnetic spectrum signals are collected along the way, so that the conditions of field intensity coverage and the like in a test area can be accurately known, and the method is used for supporting reasonable planning and optimal configuration of an electromagnetic environment. The international union radio communication also proposes that the field intensity is monitored by using an actual path to carry out works such as regional field intensity prediction and the like. In addition, by using the mobile test, the position of the regional radiation source can be positioned through a field intensity fading model. In these applications, the accuracy of the received field strength values determines the quality of the test results. When a mobile field intensity test is carried out, due to the complexity of an urban electromagnetic environment, a received field intensity value is easily influenced by fading and is inaccurate. In the existing field intensity value application, the obtained result has low precision just because of the influence, and the field intensity value can only be used as an auxiliary reference. The invention provides a method for effectively removing fading, which enables the field intensity value received by moving to be more accurate and improves the reliability of the field intensity value.
Disclosure of Invention
The invention overcomes the defects of the prior art, provides a preprocessing method of electromagnetic spectrum signal field intensity based on empirical mode decomposition, and aims at the characteristic that the change of adjacent field intensity values in a mobile field intensity test is slow, and eliminates fading by decomposing a received field intensity value sequence in a self-adaptive manner by using the empirical mode to obtain a more accurate field intensity value.
The technical scheme of the invention is as follows: a preprocessing method of electromagnetic spectrum signal field intensity based on empirical mode decomposition comprises the following steps:
firstly, arranging the field intensity values received in a moving mode into a field intensity value sequence according to a moving receiving sequence;
secondly, finding an extreme point of the field intensity value sequence, and fitting the extreme envelope and the mean envelope of the field intensity value sequence in the first step by an interpolation fitting method; subtracting the mean envelope from the field intensity value sequence, and calculating to obtain a first modal component;
and thirdly, repeating the interpolation fitting method in the second step, decomposing the field intensity value sequence into a plurality of modal components until the remaining components are monotonous sequences, then removing high-frequency components in the modal components to obtain the field intensity value sequence for eliminating fading, and finishing the pretreatment.
The second step is specifically realized as follows:
(1) finding all maximum value points of the field intensity value sequence x (t), and interpolating and fitting a maximum value envelope line through a cubic spline function; finding all minimum value points of the sequence x (t), and interpolating and fitting a minimum value envelope line through a cubic spline function; calculating the mean of the upper and lower envelopes as the mean envelope m (t) of the sequence;
(2) subtracting the mean envelope m (t) from the original sequence x (t) to obtain h1(t) ═ x (t) -m (t), detection h1(t) whether the condition of the modal component is satisfied:
Figure BDA0001334364980000021
h(k-1)(t)、hk(t) represents two successive interpolation fitting calculations. If not, let h1(t) repeating the interpolation fitting calculation step as the data to be processed until h1(t) is a modal component, denoted c1(t)＝h1(t) of (d). T represents the time when the field strength sequence sampling starts, T is 0 as the sampling starting time, and T represents the total time.
The third step is specifically realized as follows:
(1) decomposing a first modal component c1After (t), subtracting c from x (t)1(t), obtaining a residue sequence:
x1(t)＝x(t)-c1(t)
b is x1(t) as a new original sequence, test x1(t) whether the model is monotonous or not, if not, repeating the interpolation fitting method step of the second step until the nth modal component is extracted;
(2) when the residual component becomes a monotonous function, so that the modal component can not be screened out, the last residual term r is leftn(t), it is possible to obtain:
x′(t)＝cn(t)+rn(t)
x' (t) is the sequence of field strength values to eliminate fading.
Compared with the prior art, the invention has the advantages that:
(1) aiming at the characteristic that the change of adjacent field intensity values is slow in the mobile field intensity test, the invention decomposes the sequence of the received field intensity values in a self-adaptive way by using the empirical mode, and provides a method for effectively removing fading, so that the field intensity values received by the mobile station can be more accurate, and the reliability of the field intensity values is improved.
(2) The prior art has a certain solution to both fast fading and slow fading, but does not have a solution to both fast fading and slow fading. This makes it possible in some applications for the measured field strength values to serve only as an auxiliary reference. The invention considers the fast and slow fading as the noise of the field intensity value, and eliminates the noise, so that the obtained field intensity value sequence can well meet the functional requirements of drive test, positioning and the like.
(3) The existing denoising technology generally needs to preset a denoising threshold value in advance according to a received signal and an environment, so that the technology is lack of flexibility and has great practical limitation when facing different environments and unknown signals. The denoising method of the invention does not need to set a denoising threshold in advance, and adaptive denoising is carried out according to the characteristics of the field intensity sequence. The method has better adaptability in the aspects of facing complex environment and detecting unknown signals.
Drawings
FIG. 1 is a schematic diagram of signal field strength fading;
FIG. 2 is a schematic diagram of an envelope fit;
FIG. 3 is a schematic exploded view of a sequence of field strength values;
FIG. 4 is a schematic diagram of the steps of the mobile field strength test value preprocessing method.
Detailed Description
The method is further described below with reference to the accompanying drawings.
As shown in FIG. 4, the method of the present invention implements the preprocessing of the electromagnetic spectrum signal field strength value by three steps. Arranging the field intensity values obtained by the mobile test into a sequence, and utilizing the characteristic that the adjacent field intensity values change slowly to decompose the received field intensity value sequence in a self-adaptive manner, eliminating fading and obtaining more accurate field intensity values. The invention has the following 3 processing steps:
1. and arranging the field intensity values received by the mobile terminal into a field intensity value sequence according to the mobile receiving sequence.
2. And fitting an extreme value envelope and a mean value envelope of the sequence, and subtracting the mean value envelope from the field intensity value sequence to obtain a first modal component.
3. And repeating the interpolation fitting calculation step in the second step, and decomposing the field intensity value sequence into a plurality of modal components until the residual components are monotonous sequences. And removing the high-frequency component in the modal component to obtain a field intensity value sequence for eliminating fading, and finishing the pretreatment.
The processing of each step will be described in detail below:
step 1, arranging the field intensity values received by the mobile station into a field intensity value sequence according to the mobile receiving sequence.
Electromagnetic environments are nowadays increasingly complex. In such an environment, the received signal strength may be affected by fast fading and slow fading. This effect causes the received field strength values to deviate significantly from the actual field strength values. The fast fading, also called small-scale fading, is a fast jitter of a signal caused by a multipath effect, and generally conforms to rayleigh distribution. The slow fading is called shadow fading, and is caused by shadow fading caused by emission, absorption and scattering of obstacles, and generally conforms to normal distribution. As shown in fig. 1.
As can be seen from fig. 1, when the field strength values monitored by the mobile are removed from the fast fading and the slow fading, only the path fading remains, which is correlated with the propagation loss, and the adjacent field strengths of the path fading are slowly changed. The received field intensity values are arranged into a field intensity value sequence according to the mobile receiving sequence, and the influence of fast fading and slow fading in the field intensity values can be removed by utilizing a noise elimination method.
The empirical mode decomposition method decomposes a complex signal into a plurality of mode components which are arranged according to the frequency. It is a posteriori, without the need to select basis functions in advance, but to generate suitable modal components adaptively according to the characteristics of the signal itself. According to the characteristic that each modal component after being decomposed by the empirical mode decomposition method is arranged according to the frequency, for the arranged field intensity value sequence, the complex nonlinear achievement in the envelope can be regarded as noise, and the noise can be eliminated.
And 2, fitting the extreme value envelope and the mean value envelope of the sequence, and subtracting the mean value envelope from the field intensity value sequence to obtain a first modal component.
As shown in fig. 2: in the figure, curve x (t) is the original sequence, curve a is the maximum envelope, curve B is the minimum envelope, and curve C is the envelope mean. Finding all maximum value points of the sequence x (t), and interpolating and fitting a maximum value envelope line through a cubic spline function; finding all minimum value points of the sequence x (t), and interpolating and fitting a minimum value envelope line through a cubic spline function; the mean of the upper and lower envelopes is calculated as the mean envelope m (t) of the sequence.
Subtracting the mean envelope m (t) from the original sequence x (t) to obtain h1(t) ═ x (t) -m (t), detection h1(t) whether the condition of the modal component is satisfied:
Figure BDA0001334364980000041
h(k-1)(t)、hk(t) represents two successive interpolation fitting calculations.
If not, let h1(t) repeating the interpolation fitting calculation step as the data to be processed until h1(t) is a modal component, denoted c1(t)＝h1(t)。
And 3, repeating the interpolation fitting calculation step in the second step, and decomposing the field intensity value sequence into a plurality of modal components until the residual components are monotonous sequences. And removing the high-frequency component in the modal component to obtain a field intensity value sequence for eliminating fading, and finishing the pretreatment.
And removing a plurality of high-frequency components and reconstructing the sequence by the rest components, namely, keeping the adjacent field intensity value with slow change, and eliminating the influence of fast fading and slow fading.
The specific method is shown in fig. 3: decomposing a first modal component c1After (t), subtracting c from x (t)1(t), obtaining a residue sequence:
x1(t)＝x(t)-c1(t) (2)
b is x1(t) repeating the interpolation fitting calculation step as a new 'original sequence' until the nth fundamental mode component is extracted. Until the remaining components become monotonic functions from which modal components can no longer be filtered out. The last remaining remainder rn(t) of (d). The following can be obtained:
x′(t)＝cn(t)+rn(t) (3)
x' (t) is the sequence of field strengths after noise cancellation.
The complete step diagram is shown in figure 4,
(1) an initialization sequence, i.e. a sequence of field strength values.
(2) Finding all maximum value points of the sequence x (t), and interpolating and fitting a maximum value envelope line through a cubic spline function; finding all minimum value points of the sequence x (t), and interpolating and fitting a minimum value envelope line through a cubic spline function; the mean of the upper and lower envelopes is calculated as the mean envelope m (t) of the sequence.
(3) Subtracting the mean envelope m (t) from the original sequence x (t) to obtain h1(t) ═ x (t) -m (t), detection h1(t) whether the condition of the modal component is satisfied:
Figure BDA0001334364980000051
if not, let h1(t) repeating the interpolation fitting calculation step as the data to be processed until h1(t) is a modal component, denoted c1(t)＝h1(t)。
(4) And (5) storing the satisfied modal components, checking whether the residual components satisfy monotony, repeating (3) if the residual components do not satisfy, and continuing to decompose. Until the remaining components are monotonic. By which the preprocessing is ended.
In a word, the mobile field intensity test value preprocessing method based on empirical mode decomposition can adaptively perform adaptive preprocessing on the field intensity signals of mobile measurement, eliminate noises caused by fast fading and slow fading, better restore the field intensity receiving value and provide great help for further work by utilizing the measured value. Has higher application value.
The above examples are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications can be made without departing from the spirit and principles of the invention, and are intended to be within the scope of the invention.

Claims (1)

1. A preprocessing method of electromagnetic spectrum signal field intensity based on empirical mode decomposition is characterized in that: decomposing the received field intensity value sequence by an empirical mode, performing adaptive preprocessing, eliminating noise caused by fast fading and slow fading, and well restoring the field intensity received value, wherein the steps are as follows:
firstly, arranging the field intensity values received in a moving mode into a field intensity value sequence according to a moving receiving sequence;
secondly, finding an extreme point of the field intensity value sequence, and fitting the extreme envelope and the mean envelope of the field intensity value sequence in the first step by an interpolation fitting method; subtracting the mean envelope from the field intensity value sequence, and calculating to obtain a first modal component;
thirdly, repeating the interpolation fitting method in the second step, decomposing the field intensity value sequence into a plurality of modal components until the remaining components are monotonous sequences, then removing high-frequency components in the modal components to obtain a field intensity value sequence for eliminating fading, and finishing the pretreatment;
the second step is specifically realized as follows:
(1) finding all maximum value points of the field intensity value sequence x (t), and interpolating and fitting a maximum value envelope line through a cubic spline function; finding all minimum value points of the sequence x (t), and interpolating and fitting a minimum value envelope line through a cubic spline function; calculating the mean of the upper and lower envelopes as the mean envelope m of the sequence1(t)；
(2) Subtracting the mean envelope m (t) from the original sequence x (t) to obtain h1(t)＝x(t)-m1(t), detection h1(t) whether or not the condition S for modal component is satisfiedd≤0.3：
Figure FDA0002968228930000011
h(k-1)(t)、hk(t) represents two successive interpolation fitting calculations, and if not, h is calculated1(t) repeating the interpolation fitting calculation step as the data to be processed until h1(t) is a modal component, denoted c1(t)＝h1(t)；
The third step is specifically realized as follows:
(1) decompose to obtainA modal component c1After (t), subtracting c from x (t)1(t), obtaining a residue sequence:
x1(t)＝x(t)-c1(t)
b is x1(t) as a new original sequence, test x1(t) whether the model is monotonous or not, if not, repeating the interpolation fitting method step of the second step until the nth modal component is extracted;
(2) when the residual component becomes a monotonous function, so that the modal component can not be screened out, the last residual term r is leftn(t), it is possible to obtain:
x′(t)＝cn(t)+rn(t)
x' (t) is the sequence of field strength values to eliminate fading.
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