Adaptive time frame determination threshold method, medium and device based on filtering plus exponential descent search

Abstract

The present invention provides a method, medium, and device for adaptive time frame determination thresholds based on filtering and exponential descent search. The method comprises: filtering a sampled OFDM signal to obtain a basic envelope of the signal frame; setting an exponential base and a search order; setting a search threshold based on the exponential base, polling the basic envelope to find the start and end points of all signal frames under the threshold, counting the number of signal frame end points, and obtaining a signal frame end point count vector based on the search order; and searching for a time frame determination threshold based on the signal frame end point count vector. The present invention avoids manually observing the envelope curve to set an appropriate threshold. Through the exponential search method, the method can adapt to OFDM signals with different powers and different subcarrier allocations, achieving the effect of adaptive time frame threshold determination.

Description

Technical Field

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

[0002] Due to its multi-carrier orthogonality, OFDM is often used as a modulation scheme in various independent communication systems. Furthermore, most current communication systems include adaptive channel selection to avoid interference. Combined with the allocation of multiple subcarriers, the frequency of signal frames varies. Blind analysis requires precise frequency estimation of each frame for further symbol-level analysis, thus requiring accurate time positioning of signal frames.

[0003] Traditional engineering methods plot the amplitude of a time-domain signal as an envelope. This envelope curve can then be viewed and appropriate thresholds set to determine the start and end positions of the signal's time frame. However, in different electromagnetic environments, the signal power and noise power generated by different communication devices vary. Therefore, the thresholds for determining signal time frames cannot be set to fixed values ​​or ratios but must be adjusted accordingly. Summary of the Invention

[0004] For 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 a method, medium and device for adaptive time frame determination threshold value based on filtering and exponential descent search. This method does not require manual observation of graphics to set the appropriate threshold. The machine can automatically search for the determination threshold, thereby adaptively searching the signal time frame position.

[0005] The present invention provides an adaptive time frame threshold determination method based on filtering and 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 first search threshold value Th according to the base number of the index Base, poll the basic envelope Sig_Env, compare it with the threshold value Th, find the start and end points of all signal frames under the threshold value Th, and count the number of signal frame end points, which is set to 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: 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.

[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 set 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 further 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 to enable the at least one processor to 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. After obtaining the signal amplitude envelope using low-pass filtering, it uses an exponential descent search to find the number of signal frame end points obtained under different threshold values. The threshold corresponding to the minimum value is the actual desired time frame determination threshold. This method avoids the need to manually observe the envelope curve to set the appropriate threshold. The exponential search method can adapt to OFDM signals with different power and subcarrier allocations, achieving the effect of adaptive time frame threshold determination. The signal frame obtained by the method of the present invention can contain all true signal frames and only contain minimal noise signals before and after, which is more convenient for subsequent symbol-level analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This 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 time domain diagram of a signal 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 Flowchart of a method for adaptive time frame threshold determination based on filtering plus exponential descent search in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only 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 herein 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 as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall 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 method based on filtering plus exponential descent search, which can perform adaptive time frame determination on OFDM sampling signals to facilitate subsequent frame-by-frame analysis. Specifically, the method 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 number of the index (Base, Base<1) and the order of the search. In practical applications, the base number 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, then 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; continue polling, when Sig_Env(i) ≥ Th, Sig_Env(i+1) < Th and Frame_Start_Flag = 1, then 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 polling 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 ​​being Th = max(abs(Sig))*Base 2～order Repeat step 3 to record the number of frame end points n 2～order .

[0039] Step 5: Search the number vector of signal frame end points obtained by order times (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 threshold value obtained by searching for the minimum point is the reasonable threshold value. If multiple consecutive values ​​are all minimum values, the last point is selected to make the threshold value small enough to ensure that the signal is completely within the intercepted signal frame.

[0041] Example:

[0042] The OFDM signal of a real USRP device 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] As can be seen from the two sets of effect diagrams above, 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, storing computer terminal executable instructions for executing the adaptive time frame determination threshold method based on filtering and 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 memory such as memory cards, ROM, or RAM. Computer storage media can also be distributed across networked computer systems, such as in an application store.

[0052] In addition, some embodiments provide a computing device comprising: 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 to enable the at least one processor to perform the adaptive time frame determination threshold method based on filtering and exponential descent search as described in the above embodiments. Examples of computing devices include a PC, a tablet computer, a smartphone, or a PDA.

[0053] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An adaptive time frame determination threshold method based on filtering plus exponential descent search, characterized in that: The steps include: Step 1: Sample the OFDM signal Perform filtering to obtain the basic envelope of the signal frame ; Step 2: Set the base of the index and the order of the search ; Step 3: Based on the base of the index Set the threshold for the first search to , for the basic envelope Polling, and threshold value Compare and find the threshold value The starting and ending points of all signal frames under the condition are counted, and the number of signal frame end points is set as ; The threshold value is , Indicates the order of the current search, ; Step 4. Start Search and set the corresponding threshold value , and repeat step 3 to record the number of frame end points n 2～order ; Step 5: According to The number vector of signal frame end points obtained by searching , 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 sample the OFDM signal The amplitude is low-pass filtered.

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

4. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 3, characterized in that: 。 5. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 1, characterized in that: In step 3, the basic envelope Polling, and threshold value In comparison, including: set up ,when and When the threshold conditions, Set the signal frame start flag as the starting point of the signal frame ; Continue polling, when 、 and , then it is considered that at this threshold conditions, is the end point of the signal frame, and then set ; Continue polling until the threshold is found The start and end points of all signal frames under the condition.

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

7. The adaptive time frame determination threshold value method based on filtering plus exponential descent search according to claim 6, 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.

8. 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 method based on filtering plus exponential descent search as described in any one of claims 1 to 7.

9. 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 to 7.

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