CN114095327B - Frame detection and coarse synchronization method and device of wireless local area network based on frequency domain processing - Google Patents
Frame detection and coarse synchronization method and device of wireless local area network based on frequency domain processing Download PDFInfo
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- H04L27/00—Modulated-carrier systems
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- H04L27/2601—Multicarrier modulation systems
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Abstract
The frame detection and coarse synchronization method and device for the wireless local area network based on the frequency domain processing are characterized in that the method comprises the steps of obtaining time domain data of the wireless local area network; calculating power and signal-to-noise ratio estimated values of pilot frequency subcarriers and null subcarriers according to FFT results of time domain data, and carrying out narrowband interference detection according to the power of the pilot frequency subcarriers and the null subcarriers; when the signal-to-noise ratio estimated value is smaller than or equal to a preset first threshold, continuing to perform frame detection, otherwise, calculating a pilot frequency subcarrier position average value and a null subcarrier position average value according to results obtained by conjugate multiplication of two groups of continuous FFT processing results according to the same position, comparing the ratio of the powers of the two position average values with a preset second threshold, and continuing to perform frame detection when a preset condition is not met; and otherwise, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the position average value of the pilot frequency subcarriers. The method can rapidly and reliably complete frame detection, coarse timing and frequency offset estimation compensation under low signal-to-noise ratio.
Description
Technical Field
The present disclosure relates to the field of digital communications technologies, and in particular, to a method and apparatus for frame detection and coarse synchronization in a wireless local area network based on frequency domain processing.
Background
In wireless local area network communication protocols (802.11 series), conventional frame detection and coarse timing methods are typically based on time domain normalized autocorrelation: the first segment of data of the frame header of the physical layer of the wireless local area network protocol is 10 groups of the same data with the length of 16 in the time domain, so that the time domain autocorrelation with the delay length of 16 is generally adopted. When the normalized correlation value is greater than the number of times of the specified threshold, after a certain value is reached by accumulation, the frame header can be considered to be found.
Due to the size of the normalized correlation value, the fluctuation is large along with factors such as multipath, sampling error, signal-to-noise ratio, correlation window length and the like (inversely proportional to the sampling error and proportional to the signal-to-noise ratio and the correlation window length), wherein the influence of the signal-to-noise ratio is the greatest: the normalized correlation value is generally higher than 0.9 when the signal-to-noise ratio is above 15dB, and may be lower than 0.3 when the signal-to-noise ratio is close to 0dB (the threshold of the signal-to-noise ratio for the BPSK modulation mode is about 1 dB). Thus, such detection algorithms require dynamic adjustment of the decision threshold: the threshold is proportional to the signal-to-noise ratio. At low signal-to-noise ratio, the performance of frame detection, coarse synchronization is not high. Meanwhile, when single-tone interference and narrowband interference exist, a large time domain autocorrelation value can be obtained based on a time domain autocorrelation module in the processes of frame detection, coarse timing and time domain frequency offset estimation, so that false detection occurs, and a secondary detection or detection algorithm replacement is needed.
Disclosure of Invention
In view of the foregoing, it is desirable to provide a method and apparatus for frame detection and coarse synchronization in a wireless lan based on frequency domain processing, which can quickly and reliably perform frame detection and coarse timing at a low signal-to-noise ratio.
A frame detection and coarse synchronization method for a wireless local area network based on frequency domain processing, the method comprising the steps of:
s10: time domain data of the wireless local area network is obtained.
S20: and carrying out FFT processing on the time domain data according to a preset step length, and calculating according to the obtained first group of frequency domain data to obtain power and signal-to-noise ratio estimated values of pilot frequency subcarriers and null subcarriers.
S30: and carrying out narrow-band interference detection according to the power of the pilot frequency sub-carrier and the null sub-carrier to obtain the average power of the corrected signal.
S40: and comparing the signal-to-noise ratio estimated value with a preset first threshold to obtain a first comparison result.
S50: and when the first comparison result is smaller than or equal to the first comparison result, returning to the step S20, and continuing to perform frame detection on the time domain data.
S60: and when the first comparison result is larger than the first comparison result, carrying out conjugate multiplication according to the same position according to the first group of frequency domain data and the second group of frequency domain data obtained by carrying out FFT processing on the time domain data of the next step length, so as to obtain a conjugate product in the passband, wherein the conjugate product in the passband comprises a conjugate product in the passband of a pilot subcarrier and a null subcarrier.
S70: obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; and comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result.
S80: and when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, returning to the step S20 to continue frame detection.
S90: when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, the coarse timing detection is completed, and the carrier frequency offset estimation and compensation are carried out according to the pilot frequency subcarrier position average value
In one embodiment, the carrier frequency offset estimation and compensation is performed according to the pilot subcarrier average value, including:
and after the pilot frequency subcarrier position average value is phased, calculating a carrier frequency offset estimation value by combining the sampling rate and the step length, and compensating the frequency offset.
In one embodiment, step S60 specifically includes:
and when the first comparison result is larger than the first comparison result, performing FFT processing on the time domain data of the next step length to obtain a second group of frequency domain data.
And carrying out conjugate multiplication on the first group of frequency domain data and the second group of frequency domain data according to the same position to obtain a conjugate product in the passband.
And grouping the passband inner conjugate products according to the pilot frequency subcarrier and the null subcarrier according to positions to obtain the passband inner conjugate products of the pilot frequency subcarrier and the null subcarrier.
In one embodiment, the power of the null sub-carrier is noise average power; the step S30 specifically includes:
searching in the first frequency domain data to obtain the carrier wave with the maximum power.
When the maximum power carrier is a null sub-carrier, calculating the noise average power excluding the maximum power carrier; when the maximum power carrier is a pilot subcarrier, calculating the average power of the pilot carrier excluding the maximum power carrier;
when the power of the carrier wave with the maximum power is larger than the preset times of the average power of the noise, the position corresponding to the carrier wave with the maximum power has narrow-band/single-tone interference, and an interference detection mark is set to be 1.
In one embodiment, step S20 specifically includes: performing FFT processing on the time domain data according to a preset step length to obtain a first group of frequency domain data; the predetermined step size is 16 or 32 and the length of the fft is 64.
And calculating the average power of 40 empty subcarriers in the passband according to the first set of frequency domain data to obtain the average power of the empty subcarriers, wherein the average power of the empty subcarriers is the noise average power.
And calculating the average power of 12 pilot frequency subcarriers in the passband according to the first set of frequency domain data to obtain the average power of the pilot frequency subcarriers.
And subtracting the average power of the pilot frequency subcarrier from the average power of the noise to obtain the average power of the signal.
And obtaining a signal-to-noise ratio estimated value according to the signal average power and the noise power.
In one embodiment, step S70 specifically includes:
and obtaining a pilot frequency subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot frequency subcarrier and the null subcarrier.
The power of the pilot subcarrier position average and the null subcarrier position average is calculated.
And taking the ratio of the power of the obtained pilot frequency subcarrier position average value and the power of the null subcarrier position average value, and comparing the obtained ratio with a preset second threshold to obtain a second comparison result.
A frame detection and coarse synchronization apparatus for a wireless local area network based on frequency domain processing, the apparatus comprising:
and the data acquisition module is used for acquiring the time domain data of the wireless local area network.
The first stage frame detection module is used for carrying out FFT processing on the time domain data according to a preset step length, and calculating according to the obtained first group of frequency domain data to obtain power and signal-to-noise ratio estimated values of pilot frequency subcarriers and null subcarriers; carrying out narrow-band interference detection according to the power of the pilot frequency sub-carrier and the empty sub-carrier to obtain the average power of the corrected signal; comparing the signal-to-noise ratio estimated value with a preset first threshold to obtain a first comparison result; and when the first comparison result is smaller than or equal to the first comparison result, continuing to perform first-stage frame detection on the time domain data.
The second stage frame detection module is used for carrying out conjugate multiplication according to the same position according to the first group of frequency domain data and the second group of frequency domain data obtained by carrying out FFT processing on the time domain data of the next step length when the first comparison result is larger than the first comparison result, so as to obtain a conjugate product in a passband, wherein the conjugate product in the passband comprises a conjugate product in the passband of a pilot subcarrier and a null subcarrier; obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result; when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, returning to the first stage frame detection module to continue the first stage frame detection; and when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the pilot frequency subcarrier position average value.
The frame detection and coarse synchronization method and device for the wireless local area network based on the frequency domain processing are characterized in that the method comprises the steps of obtaining time domain data of the wireless local area network; and carrying out FFT processing on the signal according to a preset step length, calculating according to the obtained first group of frequency domain data to obtain power of pilot frequency sub-carriers and idle sub-carriers and signal to noise ratio estimated values, and carrying out narrow-band interference detection according to the power of the pilot frequency sub-carriers and the idle sub-carriers to obtain corrected signal average power. Comparing the signal-to-noise ratio estimation value with a preset first threshold, and continuing to perform frame detection on the time domain data when the comparison result is smaller than or equal to the preset first threshold; when the comparison result is larger than the first set of frequency domain data and the second set of frequency domain data obtained by FFT processing the time domain data of the next step length are multiplied in a conjugate way according to the same position, so as to obtain a conjugate product in the passband; obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result; when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, continuing to perform frame detection; and when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the pilot frequency subcarrier position average value. The method can rapidly and reliably complete frame detection, coarse timing and frequency offset estimation compensation under low signal-to-noise ratio.
Drawings
Fig. 1 is a flow chart of a method for frame detection and coarse synchronization of a wireless local area network based on frequency domain processing in one embodiment;
FIG. 2 is a block diagram of a frame detection and coarse synchronization apparatus for a wireless local area network based on frequency domain processing in one embodiment;
FIG. 3 is a state transition diagram of a frame detection and coarse synchronization method for a wireless local area network based on frequency domain processing in one embodiment;
FIG. 4 is a schematic diagram of a state 1 process flow in another embodiment;
FIG. 5 is a flow chart diagram of a state 2 process in another embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
In one embodiment, as shown in fig. 1, there is provided a frame detection and coarse synchronization method of a wireless local area network based on frequency domain processing, the method comprising the steps of:
s10: time domain data of the wireless local area network is obtained.
S20: and carrying out FFT processing on the time domain data according to a preset step length, and calculating according to the obtained first group of frequency domain data to obtain power and signal-to-noise ratio estimated values of the pilot frequency sub-carrier and the null sub-carrier.
At the receiving end, all data is affected by noise, and the power of the null sub-carrier is brought by the noise. The parts of the stop band and the transition band of the filter at the receiving end are excluded, 40 empty subcarriers are totally arranged in the pass band, and the average power is the noise power Pwr_noise at the receiving end. The pilot subcarrier power contains both useful signal power and noise power, and the useful signal power pwr_sig can be obtained by subtracting the noise power. The two are divided, and the quotient is multiplied by 10 to obtain the signal to noise ratio estimated value of the pilot sub-carrier.
Wherein S1 is the signal-to-noise ratio estimation value of pilot frequency subcarrier, P Pilot subcarriers For the power of pilot sub-carriers, P Null sub-carriers Is the power of the null sub-carrier.
S30: and carrying out narrow-band interference detection according to the power of the pilot frequency sub-carrier and the null sub-carrier to obtain the average power of the corrected signal.
S, 40: and comparing the signal-to-noise ratio estimated value with a preset first threshold to obtain a first comparison result.
S50: and when the first comparison result is less than or equal to the first comparison result, returning to the step S20, and continuing to perform frame detection on the time domain data.
S60: and when the first comparison result is larger than the first comparison result, carrying out conjugate multiplication according to the same position according to the first group of frequency domain data and the second group of frequency domain data obtained by carrying out FFT processing on the time domain data of the next step length, so as to obtain a conjugate product in the passband, wherein the conjugate product in the passband comprises the conjugate product in the passband of the pilot frequency subcarrier and the null subcarrier.
After conjugate multiplication is carried out on the frequency domain, the product of pilot frequency positions becomes complex numbers with basically the same phase and different amplitudes because the data of pilot frequency subcarriers are the same, and the accumulated data become large and can be used for frequency offset estimation; the data of the sub-carriers at the non-pilot positions are white noise, so that the product of the positions is white noise, and the accumulated data is smaller. The average value of the two groups of products is utilized to carry out secondary frame judgment, and more phase information is compared with the first frame judgment, so that the method is more accurate.
S70: obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; and comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result.
S80: and when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, returning to the step S20 to continue frame detection.
S90: and when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the pilot frequency subcarrier position average value.
In the frame detection and coarse synchronization method of the wireless local area network based on the frequency domain processing, the method obtains the time domain data of the wireless local area network; and carrying out FFT processing on the signal according to a preset step length, calculating according to the obtained first group of frequency domain data to obtain power of pilot frequency sub-carriers and idle sub-carriers and signal to noise ratio estimated values, and carrying out narrow-band interference detection according to the power of the pilot frequency sub-carriers and the idle sub-carriers to obtain corrected signal average power. Comparing the signal-to-noise ratio estimation value with a preset first threshold, and continuing to perform frame detection on the time domain data when the comparison result is smaller than or equal to the preset first threshold; when the first comparison result is larger than the first frequency domain data, performing FFT processing on the time domain data of the next step length to obtain second frequency domain data, and performing conjugate multiplication according to the same position to obtain conjugate product in the passband; obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result; when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, continuing to perform frame detection; and when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the pilot frequency subcarrier position average value. The method can rapidly and reliably complete frame detection, coarse timing and frequency offset estimation compensation under low signal-to-noise ratio.
In one embodiment, the carrier frequency offset estimation and compensation according to the pilot subcarrier position average value pair includes: and carrying out phase sampling on the position average value of the pilot frequency subcarrier, then carrying out calculation to obtain frequency offset, and compensating the frequency offset.
In one embodiment, step S60 specifically includes: when the first comparison result is larger than the first comparison result, FFT processing is carried out on the time domain data of the next step length, and a second group of frequency domain data is obtained; conjugate multiplying the first set of frequency domain data and the second set of frequency domain data according to the same position to obtain conjugate product in the passband; and grouping the conjugate products in the pass band according to the positions of the pilot frequency sub-carriers and the null sub-carriers to obtain the conjugate products in the pass band of the pilot frequency sub-carriers and the null sub-carriers.
In one embodiment, the power of the null sub-carriers is the noise average power; the step S30 specifically includes: searching in the first frequency domain data to obtain a carrier with the maximum power; when the maximum power carrier is a null sub-carrier, calculating the noise average power excluding the maximum power carrier; when the maximum power carrier is a pilot subcarrier, calculating the average power of the pilot carrier excluding the maximum power carrier; when the power of the maximum power carrier is larger than the preset times of the average power of the noise, the position corresponding to the maximum power carrier has narrow-band/single-tone interference, and an interference detection mark is set to be 1.
And the frequency domain detection is used, meanwhile, the narrowband interference detection is also carried out, the carrier wave which is interfered is eliminated, the influence of the narrowband interference (including direct current interference) on the signal power and the noise power estimated value is eliminated, and the detection success rate is improved. The traditional time domain autocorrelation algorithm can not eliminate the influence of single-tone interference and zero-frequency direct current interference, and is easy to misdetect.
In one embodiment, step S20 includes: performing FFT processing on the time domain data according to a preset step length to obtain a first group of frequency domain data; the predetermined step size is 16 or 32, and the length of the FFT is 64; according to the first set of frequency domain data, calculating the average power of 40 empty subcarriers in the passband to obtain the average power of the empty subcarriers, wherein the average power of the empty subcarriers is the average power of noise; according to the first group of frequency domain data, calculating the average power of 12 pilot frequency subcarriers in the passband to obtain the average power of the pilot frequency subcarriers; subtracting the average power of the pilot frequency sub-carrier from the average power of the noise to obtain the average power of the signal; and obtaining a signal-to-noise ratio estimated value according to the average power of the signal and the noise power.
In order to utilize limited (160) data, the FFT conversion is continuously performed according to a step size (16 or 32) smaller than the FFT length (64) (although input data processed by two continuous FFT processing has 64-N identical data), so that the detection frequency and the data utilization rate are improved, and the probability of missed detection is reduced.
In one embodiment, step S70 specifically includes: obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; calculating the power of the pilot frequency subcarrier position average value and the null subcarrier position average value; and taking the ratio of the power of the obtained pilot frequency subcarrier position average value and the power of the null subcarrier position average value, and comparing the obtained ratio with a preset second threshold to obtain a second comparison result.
It should be understood that, although the steps in the flowchart of fig. 1 are shown in sequence as indicated by the arrows, the steps are not necessarily performed in sequence as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least some of the steps in fig. 1 may include multiple sub-steps or stages that are not necessarily performed at the same time, but may be performed at different times, nor do the order in which the sub-steps or stages are performed necessarily performed in sequence, but may be performed alternately or alternately with at least a portion of other steps or sub-steps of other steps.
In one embodiment, as shown in fig. 2, there is provided a frame detection and coarse synchronization apparatus of a wireless local area network based on frequency domain processing, including: the system comprises a data acquisition module, a first stage frame detection module and a second stage frame detection module, wherein:
a frame detection and coarse synchronization apparatus for a wireless local area network based on frequency domain processing, the apparatus comprising:
and the data acquisition module is used for acquiring the time domain data of the wireless local area network.
The first stage frame detection module is used for carrying out FFT processing on the time domain data according to a preset step length, and calculating according to the obtained first group of frequency domain data to obtain power and signal-to-noise ratio estimated values of pilot frequency subcarriers and null subcarriers; carrying out narrow-band interference detection according to the power of the pilot frequency sub-carrier and the empty sub-carrier to obtain the average power of the corrected signal; comparing the signal-to-noise ratio estimated value with a preset first threshold to obtain a first comparison result; and when the first comparison result is smaller than or equal to the first comparison result, continuing to perform first-stage frame detection on the time domain data.
The second stage frame detection module is used for carrying out conjugate multiplication according to the same position according to the first group of frequency domain data and the second group of frequency domain data obtained by carrying out FFT processing on the time domain data of the next step length when the first comparison result is larger than the first comparison result, so as to obtain a passband inner conjugate product, wherein the passband inner conjugate product comprises a passband inner conjugate product of a pilot subcarrier and a null subcarrier; obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result; when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, returning to the first stage frame detection module to continue the first stage frame detection; and when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the pilot frequency subcarrier position average value.
In one embodiment, the second stage frame detection module is further configured to perform calculation after taking a phase of the pilot subcarrier position average value, obtain a frequency offset, and compensate the frequency offset.
In one embodiment, the second stage frame detection module is further configured to perform FFT processing on time domain data of a next step length to obtain a second set of frequency domain data when the first comparison result is greater than the first comparison result; conjugate multiplying the first set of frequency domain data and the second set of frequency domain data according to the same position to obtain conjugate product in the passband; and grouping the conjugate products in the pass band according to the positions of the pilot frequency sub-carriers and the null sub-carriers to obtain the conjugate products in the pass band of the pilot frequency sub-carriers and the null sub-carriers.
In one embodiment, the power of the null sub-carriers is the noise average power; the step S30 specifically includes: searching in the first frequency domain data to obtain a carrier with the maximum power; when the maximum power carrier is a null sub-carrier, calculating the noise average power excluding the maximum power carrier; when the maximum power carrier is a pilot subcarrier, calculating the average power of the pilot carrier excluding the maximum power carrier; when the power of the maximum power carrier is larger than the preset times of the average power of the noise, the position corresponding to the maximum power carrier has narrow-band/single-tone interference, and an interference detection mark is set to be 1.
In one embodiment, the first stage frame detection module is further configured to perform FFT processing on the time domain data according to a predetermined step length, to obtain a first set of frequency domain data; the predetermined step size is 16 or 32, and the length of the FFT is 64; according to the first set of frequency domain data, calculating the average power of 40 empty subcarriers in the passband to obtain the average power of the empty subcarriers, wherein the average power of the empty subcarriers is the average power of noise; according to the first group of frequency domain data, calculating the average power of 12 pilot frequency subcarriers in the passband to obtain the average power of the pilot frequency subcarriers; subtracting the average power of the pilot frequency sub-carrier from the average power of the noise to obtain the average power of the signal; and obtaining a signal-to-noise ratio estimated value according to the average power of the signal and the noise power.
In one embodiment, the second stage frame detection module is further configured to obtain a pilot subcarrier position average value and a null subcarrier position average value according to a passband inner conjugate product of the pilot subcarrier and the null subcarrier; calculating the power of the pilot frequency subcarrier position average value and the null subcarrier position average value; and taking the ratio of the power of the obtained pilot frequency subcarrier position average value and the power of the null subcarrier position average value, and comparing the obtained ratio with a preset second threshold to obtain a second comparison result.
The specific limitation of the frame detection and coarse synchronization device of the wireless local area network based on the frequency domain processing can be referred to as the limitation of the frame detection and coarse synchronization method of the wireless local area network based on the frequency domain processing hereinabove, and the description thereof is omitted. The above-mentioned frame detection and coarse synchronization means of the wireless local area network based on the frequency domain processing may be implemented in whole or in part by software, hardware, and combinations thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
In a specific embodiment, as shown in fig. 3, a state transition diagram of a frame detection and coarse synchronization method of a wireless local area network based on frequency domain processing is provided, where a stage 1 frame is detected as a state 1, and a stage 2 frame is detected as a state 2. The frame detection and coarse synchronization method of the wireless local area network based on the frequency domain processing specifically comprises the following processing flows:
and step one, after the system is started, continuously performing stage 1 frame detection and simultaneously performing narrowband interference detection. When the detection result DetFrm is 1, jumping to the next state; when the detection result DetFrm is 0, the current state is remained, and the frame detection is continued. The process flow for state 1 is shown in fig. 4.
In this state, detection is performed once every 32 data, and other detection values are output: noise factor, signal-to-noise ratio estimate, interference detection flag, maximum position P1, corrected signal average power or noise power.
1.1, the FFT processing with length 64 is continued with a step length of N (default 32) (N is smaller than 64, so that the input data of two successive FFT processing has 64-N identical pieces).
1.2, carrying out frequency domain SNR estimation to obtain a frequency domain signal-to-noise ratio estimation value S1 and noise average power Pwr_noise (S1 is 6.5dB larger than the time domain SNR because of only 12 non-zero subcarriers in the frequency domain), wherein the specific steps are as follows:
1.2.1 calculating the average power of 40 null sub-carriers within the passband, i.e. the noise power (i.e. noise factor) pwr_noise;
1.2.2 calculating the average power Pwr_carrier of 12 pilot subcarriers in the passband;
1.2.3 calculating the signal average power pwr_sig=pwr_carrier-pwr_noise.
1.2.4 calculating the signal to noise ratio estimate s1=10×log10 (pwr_sig/pwr_noise), i.e. s1=10×log10 (pwr_sig) -10×log10 (pwr_noise).
1.3, simultaneously carrying out narrowband interference detection, wherein the specific steps are as follows:
1.3.1 searching the carrier with the largest power, wherein the position of the carrier is P1;
1.3.2 correction of carrier power: when P1 belongs to the empty sub-carrier, indicating that the position is interference, or the signal to noise ratio of the received signal is extremely low, or is pure noise, calculating the noise average power after P1 carrier is eliminated; when P1 belongs to the pilot frequency sub-carrier wave, calculating the average power of the pilot frequency carrier wave excluding the P1 carrier wave;
1.3.3 if the P1 carrier power is greater than TH0 times the noise average power, then it is determined that narrowband/single tone interference is likely at that location.
1.4, stage 1 frame decision: when the signal-to-noise ratio estimated value S1 is larger than the threshold TH1, setting DetFrm to be 1, and jumping to the next state; otherwise, if the DetFrm is set to 0, the method stays in the current state and continues to detect the frame.
And secondly, when the detection result DetFrm is 1, performing stage 2 frame detection. When the detection result DetFrm is 2, the frame head is successfully detected, and the next state is skipped to carry out frequency offset estimation compensation; when the detection result DetFrm is 3, the last state is returned, and the frame detection is continued. The process flow for state 2 is shown in fig. 5.
And 2.1, performing FFT processing on the data of the next step.
2.2, performing conjugate multiplication (equivalent to conjugate multiplication of delay 64) on frequency domain data after two groups of FFT processing in succession according to the same position.
And 2.3, grouping conjugate products in the pass band according to positions according to the pilot frequency sub-carrier and the null sub-carrier, and calculating an average value.
2.4, performing second judgment according to the average power: if the power ratio of the two is larger than the threshold TH2 and the power of the pilot frequency average value is larger than the signal power after threshold correction (preventing false detection under pure noise), the frame detection is considered to be successful, the coarse timing detection is completed, the DetFrm is set to be 2, and the next state is entered. Otherwise, set DetFrm to 3, return to the previous state.
Thirdly, when the detection result DetFrm is 2, carrying out frequency offset estimation and compensation: the frequency offset estimation directly uses the pilot frequency position related value obtained in the last state, and the phase offset of the 32 delayed data is obtained by taking the phase, so that the frequency offset is calculated, and then the frequency offset is compensated.
After the process is completed, the frame detection and coarse synchronization process for the current frame is completed, the module returns to the IDLE state, and the system jumps to the subsequent processing module, typically at a fine timing.
Because the frequency domain data of the first field of the physical frame of the wireless local area network is only 12 nonzero, the average power of the nonzero data is 6.5dB higher than the average power of the time domain signal, so that the method of frequency domain detection (after the frequency domain data is grouped, the average power and the power of the related value are calculated and compared with the noise power to carry out twice judgment detection) is more reliable than the time domain, and frame detection, coarse timing and frequency offset estimation compensation can be rapidly completed under the condition of low signal-to-noise ratio (which can reach-2 dB).
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples merely represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.
Claims (7)
1. A frame detection and coarse synchronization method for a wireless local area network based on frequency domain processing, the method comprising the steps of:
s10: acquiring time domain data of a wireless local area network;
s20: performing FFT processing on the time domain data according to a preset step length, and calculating according to the obtained first group of frequency domain data to obtain power and signal-to-noise ratio estimated values of pilot frequency subcarriers and null subcarriers;
s30: carrying out narrow-band interference detection according to the power of the pilot frequency sub-carrier and the empty sub-carrier to obtain the average power of the corrected signal;
s40: comparing the signal-to-noise ratio estimated value with a preset first threshold to obtain a first comparison result;
s50: when the first comparison result is smaller than or equal to the first comparison result, returning to the step S20, and continuing to perform frame detection on the time domain data;
s60: when the first comparison result is larger than the first comparison result, carrying out conjugate multiplication according to the same position according to a first group of frequency domain data and a second group of frequency domain data obtained by carrying out FFT processing on time domain data of the next step length, so as to obtain a conjugate product in a passband, wherein the conjugate product in the passband comprises a conjugate product in the passband of a pilot subcarrier and a null subcarrier;
s70: obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result;
s80: when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, returning to the step S20 to continue frame detection;
s90: and when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the pilot frequency subcarrier position average value.
2. The method of claim 1 wherein performing carrier frequency offset estimation and compensation based on pilot subcarrier location averages comprises:
and after the pilot frequency subcarrier position average value is phased, calculating a carrier frequency offset estimation value by combining the sampling rate and the step length, and compensating the frequency offset.
3. The method according to claim 1, wherein step S60 specifically comprises:
when the first comparison result is larger than the first comparison result, FFT processing is carried out on the time domain data of the next step length, and a second group of frequency domain data is obtained;
conjugate multiplying the first set of frequency domain data and the second set of frequency domain data according to the same position to obtain conjugate product in the passband;
and grouping the passband inner conjugate products according to the pilot frequency subcarrier and the null subcarrier according to positions to obtain the passband inner conjugate products of the pilot frequency subcarrier and the null subcarrier.
4. The method of claim 1, wherein the power of the null sub-carriers is a noise average power, and step S30 specifically includes:
searching in the first group of frequency domain data to obtain a carrier wave with the maximum power;
when the maximum power carrier is a null sub-carrier, calculating the noise average power excluding the maximum power carrier; when the maximum power carrier is a pilot subcarrier, calculating the average power of the pilot carrier excluding the maximum power carrier;
when the power of the carrier wave with the maximum power is larger than the preset times of the average power of the noise, the position corresponding to the carrier wave with the maximum power has narrow-band/single-tone interference, and an interference detection mark is set to be 1.
5. The method according to claim 1, wherein step S20 specifically comprises:
performing FFT processing on the time domain data according to a preset step length to obtain a first group of frequency domain data; the predetermined step size is 16 or 32, and the length of the FFT is 64;
according to the first set of frequency domain data, calculating the average power of 40 empty subcarriers in a passband to obtain the average power of the empty subcarriers, wherein the average power of the empty subcarriers is noise average power;
according to the first set of frequency domain data, calculating the average power of 12 pilot frequency subcarriers in the passband to obtain the average power of the pilot frequency subcarriers;
subtracting the average power of the pilot frequency sub-carrier from the average power of the noise to obtain the average power of the signal;
and obtaining a signal-to-noise ratio estimated value according to the signal average power and the noise average power.
6. The method according to claim 1, wherein step S70 specifically comprises:
obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier;
calculating the power of the pilot frequency subcarrier position average value and the null subcarrier position average value;
and taking the ratio of the power of the obtained pilot frequency subcarrier position average value and the power of the null subcarrier position average value, and comparing the obtained ratio with a preset second threshold to obtain a second comparison result.
7. A frame detection and coarse synchronization apparatus for a wireless local area network based on frequency domain processing, the apparatus comprising:
the data acquisition module is used for acquiring time domain data of the wireless local area network;
the first stage frame detection module is used for carrying out FFT processing on the time domain data according to a preset step length, and calculating according to the obtained first group of frequency domain data to obtain power and signal-to-noise ratio estimated values of pilot frequency subcarriers and null subcarriers; carrying out narrow-band interference detection according to the power of the pilot frequency sub-carrier and the empty sub-carrier, and obtaining the average power of the corrected signal; comparing the signal-to-noise ratio estimated value with a preset first threshold to obtain a first comparison result; when the first comparison result is smaller than or equal to the first comparison result, continuing to perform first-stage frame detection on the time domain data;
the second stage frame detection module is used for carrying out conjugate multiplication according to the same position according to the first group of frequency domain data and the second group of frequency domain data obtained by carrying out FFT processing on the time domain data of the next step length when the first comparison result is larger than the first comparison result, so as to obtain a conjugate product in a passband, wherein the conjugate product in the passband comprises a conjugate product in the passband of a pilot subcarrier and a null subcarrier; obtaining a pilot subcarrier position average value and a null subcarrier position average value according to the conjugate product in the passband of the pilot subcarrier and the null subcarrier; comparing the ratio of the powers of the pilot frequency subcarrier position average value and the null subcarrier position average value with a preset second threshold to obtain a second comparison result; when the second comparison result is smaller than or equal to the second comparison result or the power of the pilot frequency subcarrier position average value is smaller than or equal to the corrected signal power, returning to the first stage frame detection module to continue the first stage frame detection; and when the second comparison result is larger than the second comparison result and the power of the pilot frequency subcarrier position average value is larger than the corrected signal power, finishing coarse timing detection, and carrying out carrier frequency offset estimation and compensation according to the pilot frequency subcarrier position average value.
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