Adaptive time frame threshold value judgment method based on filtering and index descent search, medium and device

Abstract

The invention provides a self-adaptive time frame threshold value judgment method, medium and device based on filtering and index descent search, and the method comprises the steps: filtering an OFDM signal obtained through sampling, and obtaining a basic envelope of a signal frame; setting a cardinal number of an index and a search order; setting a search threshold value according to the cardinal number of the index, polling the basic envelope, finding starting points and ending points of all signal frames under the condition of the threshold value, counting the number of the ending points of the signal frames, and obtaining a number vector of the ending points of the signal frames according to the search order; and searching a time frame judgment threshold value according to the signal frame end point number vector. According to the method, the situation that an appropriate threshold value is set by manually observing an envelope curve can be avoided, OFDM signals with different powers and different subcarrier distribution conditions can be adapted through an index searching method, and the effect of adaptively judging the time frame threshold is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of mobile communication signal processing, and in particular to an adaptive time frame determination threshold value method, medium and device based on filtering plus exponential descent search. Background Art

[0002] OFDM is often used as a modulation style in various independent communication systems due to its multi-carrier orthogonal characteristics. In addition, most current communication systems have the function of adaptively selecting channels to avoid interference. Combined with the allocation of multiple subcarriers, the frequency of the signal frame changes. In blind analysis, it is necessary to accurately estimate the frequency of each frame in order to perform further symbol-level analysis, so it is necessary to accurately locate the signal frame in time.

[0003] The traditional engineering method is to draw an envelope of the amplitude of the time domain signal, view the envelope curve, set the appropriate threshold value, and determine the start and end position of the signal time frame. However, in different electromagnetic environments, the signal power generated by different communication devices will change, and the noise power is also different. Therefore, the threshold value for determining the signal time frame cannot be set to a fixed value or a fixed ratio, but needs to be adjusted accordingly. Summary of the invention

[0004] For the time domain processing of OFDM signals, it is necessary to set an adaptive threshold value to determine the starting position of the signal time frame. The present invention provides an adaptive time frame determination threshold value method, medium and device based on filtering plus exponential descent search. The method does not require manual viewing of graphics to set a suitable threshold. The machine can automatically search for the determination threshold, thereby adaptively searching the time frame position of the signal.

[0005] The present invention provides an adaptive time frame determination threshold value method based on filtering plus exponential descent search, comprising the following steps:

[0006] Step 1: Filter the sampled OFDM signal Sig to obtain the basic envelope Sig_Env of the signal frame;

[0007] Step 2: Set the base of the index and the order of the search;

[0008] Step 3: Set the threshold value of the first search as Th according to the base number Base of the index, poll the basic envelope Sig_Env, compare it with the threshold value Th, find out the starting point and ending point of all signal frames under the threshold value Th, and count the number of signal frame ending points, which is set as n1;

[0009] Step 4: Start the second to order search, set the corresponding threshold value Th, and repeat step 3 to record the number of frame end points n. 2～order ;

[0010] Step 5: According to the order search, the number vector of signal frame end points (n1, n2...n order ), search out the time frame determination threshold value.

[0011] Furthermore, in step 1, the filtering is to perform low-pass filtering on the amplitude of the sampled OFDM signal Sig.

[0012] Furthermore, in step 2, the base of the index and the order of the search are adjusted according to different experimental environments.

[0013] Furthermore, Base<1.

[0014] Furthermore, the threshold value is Th = max(abs(Sig))*Base k , k represents the order of the current search, k = 1, 2, ..., order.

[0015] Furthermore, in step 3, the basic envelope Sig_Env is polled and compared with the threshold value Th, including:

[0016] Assume i=1:length(Sig_Env), when Sig_Env(i)<Th and Sig_Env(i+1)≥Th, it is considered that under the threshold value Th, i+1 is the starting point of the signal frame, and the signal frame start flag Frame_Start_Flag=1 is set;

[0017] Continue polling. When Sig_Env(i)≥Th, Sig_Env(i+1)<Th and Frame_Start_Flag=1, it is considered that i is the end point of the signal frame under the threshold value Th, and then Frame_Start_Flag=0;

[0018] Continue polling until the start and end points of all signal frames under the threshold value Th are found.

[0019] Furthermore, in step 5, the number vector of signal frame end points (n1, n2...n order ), search for the minimum point, and its corresponding threshold value is the required time frame judgment threshold value.

[0020] Furthermore, when the values ​​of multiple consecutive points are all minimum values, the threshold value corresponding to the last point is taken as the desired time frame determination threshold value.

[0021] The present invention also provides a computer terminal storage medium storing computer terminal executable instructions, wherein the computer terminal executable instructions are used to execute the above-mentioned adaptive time frame determination threshold value method based on filtering plus exponential descent search.

[0022] The present invention also provides a computing device, comprising:

[0023] At least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the above-mentioned adaptive time frame determination threshold value method based on filtering plus exponential descent search.

[0024] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0025] The present invention targets OFDM burst signals, obtains the signal amplitude envelope by low-pass filtering, and then searches for the number of signal frame end points obtained under different threshold values ​​through exponential descent, and the corresponding threshold value when the minimum value is obtained is the actual time frame determination threshold value. The present invention can avoid artificially observing the envelope curve to set a suitable threshold value, and can adapt to OFDM signals with different powers and different subcarrier allocations through the exponential search method, so as to achieve the effect of adaptively determining the time frame threshold. The signal frame obtained by the method of the present invention can contain all real signal frames, and only contains very few noise signals before and after, which is more convenient for subsequent symbol-level analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 FIG. 4 is a signal time domain diagram of an example in an embodiment of the present invention.

[0027] Figure 2 This is a diagram of envelope threshold signal frame determination results of an example in an embodiment of the present invention.

[0028] Figure 3 FIG. 4 is a signal time domain diagram of another example in an embodiment of the present invention.

[0029] Figure 4 This is another example of an envelope threshold signal frame determination result diagram in an embodiment of the present invention.

[0030] Figure 5 The flowchart of the method for adaptive time frame threshold determination based on filtering plus exponential descent search in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example

[0034] like Figure 5 As shown, this embodiment proposes an adaptive time frame determination threshold value method based on filtering plus exponential descent search, which can perform adaptive time frame determination on OFDM sampling signals for subsequent frame-by-frame analysis. Specifically, it includes the following steps:

[0035] Step 1: For the sampled OFDM signal Sig, since the envelope of the signal amplitude changes slowly relative to the signal amplitude itself and belongs to the low-frequency component, a 0.2% low-pass filter is performed on its amplitude to obtain the basic envelope Sig_Env of the signal frame.

[0036] Step 2: Set the base of the index Base, Base < 1 and the order of the search; in practical applications, the base of the index Base and the order of the search can be adjusted according to different experimental environments.

[0037] Step 3: Set the threshold value of the first search to Th = max(abs(Sig))*Base according to the base number of the index. 1, poll the basic envelope Sig_Env, compare it with the threshold value Th, set i=1:length(Sig_Env), when Sig_Env(i)<Th and Sig_Env(i+1)≥Th, it is considered that under the threshold value Th, i+1 is the starting point of the signal frame, and the signal frame start flag Frame_Start_Flag=1 is set; continue to poll, when Sig_Env(i)≥Th, Sig_Env(i+1)<Th and Frame_Start_Flag=1, it is considered that under the threshold value Th, i is the end point of the signal frame, and then set Frame_Start_Flag=0; continue to poll until the starting point and end point of all signal frames under the threshold value Th are found. In order to avoid the sampling start time in a certain signal frame, the number of signal frame end points is counted and set to n1;

[0038] Step 4: Start the second to order searches, with the threshold values ​​Th = max(abs(Sig))*Base 2～order , repeat step 3 and record the number of frame end points n 2～order .

[0039] Step 5: Search the signal frame end point vector (n1, n2...n order ), search for the minimum point, and its corresponding threshold value is the required time frame determination threshold value. When the values ​​of multiple consecutive points are all minimum values, the threshold value corresponding to the last point is taken as the required time frame determination threshold value.

[0040] Explanation of the mechanism of step 5: When the index drops to a certain level, the threshold value can intersect with the noise floor amplitude range. At this time, the calculated value of the signal frame end point will be very large. Therefore, for (n1, n2...n order ) The corresponding threshold value obtained by searching the minimum point is the reasonable threshold value. If multiple consecutive values ​​are minimum values, the last point is taken to make the threshold value small enough to ensure that the signal is completely in the intercepted signal frame.

[0041] Example:

[0042] The OFDM signal of a USRP device in practice is sampled with a sampling rate of 245.76 MHz, a sampling duration of 0.1 s, and the settings of Base = 0.8 and order = 10.

[0043] The first group: The time domain diagram of the sampled OFDM signal is as follows Figure 1 As shown, the envelope threshold signal frame is determined as follows Figure 2 The number of signal frame end points is shown in Table 1.

[0044] Table 1, the number of end points of the first group of signal frames:

[0045] Serial number 1 2 3 4 5 6 7 8 9 10 Number of frame end points 3760 220 12 15 16 17 17 17 17 448

[0046] Example 2:

[0047] The second group: The time domain diagram of the sampled OFDM signal is as follows Figure 3 As shown, the envelope threshold signal frame is determined as follows Figure 4 The number of signal frame end points is shown in Table 2.

[0048] Table 2, the number of end points of the second group of signal frames:

[0049] Serial number 1 2 3 4 5 6 7 8 1 2 Number of frame end points 625 561 21 15 17 18 25 1311 625 561

[0050] It can be seen from the above two groups of effect diagrams that the method of this invention can accurately detect the start and end positions of each signal frame without missed detection or false detection.

[0051] In addition, in some embodiments, a computer terminal storage medium is provided, which stores computer terminal executable instructions, and the computer terminal executable instructions are used to execute the adaptive time frame determination threshold value method based on filtering plus exponential descent search as described in the above embodiments. Examples of computer storage media include magnetic storage media (e.g., floppy disks, hard disks, etc.), optical recording media (e.g., CD-ROMs, DVDs, etc.) or memories, such as memory cards, ROMs or RAMs, etc. Computer storage media can also be distributed on network-connected computer systems, such as application stores.

[0052] In addition, in some embodiments, a computing device is proposed, comprising: at least one processor; and a memory connected to the at least one processor in communication; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the adaptive time frame determination threshold value method based on filtering plus exponential descent search as described in the above embodiment. Examples of computing devices include PCs, tablet computers, smart phones, or PDAs.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An adaptive time frame determination threshold value method based on filtering plus exponential descent search, characterized in that: The steps include: Step 1: Filter the sampled OFDM signal Sig to obtain the basic envelope Sig_Env of the signal frame; Step 2: Set the base of the index and the order of the search; Step 3: Set the threshold value of the first search as Th according to the base number Base of the index, poll the basic envelope Sig_Env, compare it with the threshold value Th, find out the starting point and ending point of all signal frames under the threshold value Th, and count the number of signal frame ending points, which is set as n1; Step 4: Start the second to order search, set the corresponding threshold value Th, and repeat step 3 to record the number of frame end points n. 2～order ; Step 5: According to the order search, the number vector of signal frame end points (n1, n2...n order ), search out the time frame determination threshold value.

2. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 1 is characterized in that: In step 1, the filtering is to perform low-pass filtering on the amplitude of the sampled OFDM signal Sig.

3. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 1 is characterized in that: In step 2, the base of the index and the order of the search are adjusted according to different experimental environments.

4. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 3 is characterized in that: Base<1.

5. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 1 is characterized in that: The threshold value is Th = max (abs (Sig)) * Base k , k represents the order of the current search, k = 1, 2, ..., order.

6. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 1 is characterized in that: In step 3, the basic envelope Sig_Env is polled and compared with the threshold value Th, including: Assume i=1:length(Sig_Env), when Sig_Env(i)<Th and Sig_Env(i+1)≥Th, it is considered that under the threshold value Th, i+1 is the starting point of the signal frame, and the signal frame start flag Frame_Start_Flag=1 is set; Continue polling. When Sig_Env(i)≥Th, Sig_Env(i+1)<Th and Frame_Start_Flag=1, it is considered that i is the end point of the signal frame under the threshold value Th, and then Frame_Start_Flag=0; Continue polling until the start and end points of all signal frames under the threshold value Th are found.

7. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 1 is characterized in that: In step 5, the number vector of signal frame end points (n1, n2...n order ), search for the minimum point, and its corresponding threshold value is the required time frame judgment threshold value.

8. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 7 is characterized in that: When the values ​​of multiple consecutive points are all minimum values, the threshold value corresponding to the last point is taken as the required time frame determination threshold value.

9. A computer terminal storage medium storing computer terminal executable instructions, characterized in that: The computer terminal executable instructions are used to execute the adaptive time frame determination threshold value method based on filtering plus exponential descent search as described in any one of claims 1-8.

10. A computing device, characterized in that: include: at least one processor; And a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the adaptive time frame determination threshold value method based on filtering plus exponential descent search as described in any one of claims 1-8.

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