CN109525523B - Data packet detection device and detection method thereof - Google Patents
Data packet detection device and detection method thereof Download PDFInfo
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- CN109525523B CN109525523B CN201811496693.2A CN201811496693A CN109525523B CN 109525523 B CN109525523 B CN 109525523B CN 201811496693 A CN201811496693 A CN 201811496693A CN 109525523 B CN109525523 B CN 109525523B
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
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- H—ELECTRICITY
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
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Abstract
The invention discloses a data packet detection device, which comprises a packet detection FFT control module and a data packet detection state machine; the data packet detection state machine is respectively connected with the SC _ FD module, the MC _ FD module and the NBI _ DET module; the packet detection FFT control module is connected with the Fourier transform device and the autocorrelation memory; the autocorrelation memory is connected with the SC _ FD module, the MC _ FD module and the NBI _ DET module; the analog-to-digital conversion device is connected with the FFT input module and the packet detection FFT control module through the buffer; the detection method is also disclosed, the leader sequence is transformed into a frequency domain sample through Fourier transform and then is subjected to autocorrelation and cross-correlation calculation, and a data packet and the boundary thereof are output after filtering in a data packet detection state machine; combining the output of the NB _ DET module when SC _ FD and MC _ FD are calculated in the frequency domain, so that the influence of narrow-band interference is reduced, and the false alarm probability is reduced; the detection process is carried out in a frequency domain, and can be used in combination with a narrow-band interference detection technology, so that the false alarm influence of narrow-band interference on packet detection is reduced; and the symbol timing is determined while the data packet is detected, so that the cost is reduced.
Description
Technical Field
The invention belongs to the technical field of communication; in particular to a data packet detection method and a data packet detection device.
Background
In a communication system based on packet transmission, the bits transmitted by the source are coded and modulated into packets and transmitted to the sink. Packet-based communication networks can efficiently utilize the communication medium. The existing typical data includes preamble sequence, data header and data payload with different length. The preamble sequence is used to perform a series of important functions, including packet detection, frequency offset estimation, symbol timing, and channel estimation.
At present, a receiver mainly adopts a correlation method when detecting a preamble sequence. Two widely used correlators are the autocorrelator and the cross correlator, respectively. For an autocorrelator, the receiver inputs include the current received signal and the properly delayed received signal, and the two input signals are multiplied and summed. For a cross-correlator, the two input signals are the received signal and the local reference signal, respectively, and the two signals undergo multiplication and accumulation operations, the accumulation typically spanning the same duration as the symbol period.
Both correlators detect the preamble sequence by searching for peaks in the correlator output. In an actual communication scenario, if the preamble sequence is interfered by a narrowband signal or a single-frequency signal, both correlators may trigger a false alarm, that is, the receiver sends an indication that the preamble sequence is detected when the preamble sequence is not present.
Disclosure of Invention
The invention provides a data packet detection device and a detection method, wherein the whole detection process is carried out in a frequency domain, and compared with the traditional time domain coherent or incoherent detection, the data packet detection device can be used in combination with a narrow-band interference detection technology, so that the false alarm influence of narrow-band interference on packet detection is reduced; the symbol timing is determined while the data packet is detected, so that the design is simplified, and the cost is reduced; the problems in the prior art are solved.
The technical scheme of the invention is as follows: a data packet detection device comprises a packet detection FFT control module, a Fourier transform device, an SC _ FD module, an MC _ FD module, an NBI _ DET module, an autocorrelation memory, a data packet detection state machine and an analog-to-digital conversion device; the data packet detection state machine is respectively connected with the packet detection FFT control module, the SC _ FD module, the MC _ FD module and the NBI _ DET module; the packet detection FFT control module is connected with the Fourier transform device and the autocorrelation memory; the autocorrelation memory is connected with the SC _ FD module, the MC _ FD module and the NBI _ DET module; the Fourier transform device comprises an FFT input module and an FFT engine; the analog-to-digital conversion device is connected with the FFT input module and the packet detection FFT control module; a buffer is arranged between the analog-to-digital conversion device and the FFT input module;
the buffer is used for caching the preamble sequence to be processed, the packet detection FFT control module sends the preamble sequence to the buffer to be transmitted to the Fourier transform device, and the packet detection FFT control module sends a Fourier transform instruction to the Fourier transform device; the FFT is used for carrying out Fourier transform on the signal sample block and outputting a frequency domain sample block; the packet detection FFT control module sends a transmission instruction to the autocorrelation storage module; the NBI _ DET module is used for detecting a narrow-band interference signal, generating a bit sequence of an NBI Mask corresponding to each frequency domain sample block and judging whether each subcarrier in the frequency domain sample block needs to perform autocorrelation and cross-correlation calculation; the frequency domain sample block is transmitted to an SC _ FD module and an MC _ FD module, a correlation value of the two frequency domain sample blocks is calculated in the SC _ FD module, and a cross-correlation value of the frequency domain sample block and a local sample block is calculated in the MC _ FD module; the obtained autocorrelation value and the cross correlation value are transmitted to a packet detection state machine for judgment, and the packet detection state machine outputs an indication of whether a data packet exists and a boundary thereof.
The data packet detection method of the data packet detection device comprises the following steps:
step1, storing the preamble sequence processed by the analog-to-digital conversion device into a buffer as a signal sample block;
step2, the packet detection state machine sends an instruction to the buffer, the buffer transmits the signal sample block stored in the buffer to the Fourier transform device, and the signal sample block is transformed into frequency domain samples in the Fourier transform device;
step3, the module NBI _ DET detects the narrowband interference signals in the frequency domain samples and generates a bit sequence of NBI Mask corresponding to the subcarriers in each frequency domain sample; judging whether the sub-carriers in the corresponding frequency domain samples participate in the calculation of SC _ FD and MC _ FD according to the output value of the NBI Mask;
if any bit output in the NBI Mask is 1, the subcarrier in the corresponding frequency domain sample does not participate in the calculation of SC _ FD and MC _ FD;
step4, the frequency-domain autocorrelator SC _ FD calculates the correlation value between two blocks of frequency-domain samples; ,
step5, calculating a cross-correlation value of a frequency domain sample data block and a local data block by a frequency domain cross-correlator MC _ FD;
step6, under the control of the packet detection FFT control module, the packet detection state machine outputs the packet detection state, where the detection state refers to whether the packet state machine outputs a packet and the boundary of the packet, or no packet.
In Step4, the correlation value includes the self-strength value of the frequency-domain sample block and its similarity with the last frequency-domain sample block.
In Step5, the input of the frequency-domain cross correlator MC _ FD is the average of FFT output samples, and the correlation value is how similar the frequency-domain sample data block to the local data block.
The detection flow of the packet detection state machine to the packet detection state is as follows:
(a) the frequency domain autocorrelator SC _ FD calculates a frequency domain correlation value ARF0 and a mean square value ARN0 of an FFT output sample block under an initial state S0 of the packet detection state machine;
(b) the data packet detection state machine judges the relation between the frequency domain related value ARF0 and a preset threshold ArFreqTd0_ N and the relation between the mean square value ARN0 and a preset threshold SyncNormMin, and further determines that the data packet detection state machine stays in an S0 state or jumps to an S1 state;
when the ARF0 is greater than the preset threshold ArFreqTd0_ N and the ARN0 is greater than the preset threshold SyncNormMin, the packet detection state machine control state transitions to state S1; otherwise, the packet inspection state machine stops at state S0;
(c) in a state S1, the frequency domain autocorrelator SC _ FD calculates ARF1 and ARN1, and the packet inspection state machine judges the relationship between the ARF1 and a preset threshold ArFreqTd1_ N and the relationship between the ARN1 and a preset threshold SyncNormMin;
if the ARF1 is greater than the preset threshold ArFreqTd1_ N and the ARN1 is greater than the preset threshold SyncNormMin, the packet detection state machine control state transitions to state S2; if any one of the ARF1 and the ARN1 is lower than the corresponding preset threshold, the packet detection state machine control state jumps back to the start state S0;
the data packet detection state machine judges the relationship between the ARF0 and a preset threshold ArFreqTd0_ H and the relationship between the ARF1 and a preset threshold ArFreqTd1_ H;
if the ARF0 is greater than the preset threshold ArFreqTd0_ H and the ARF1 is greater than the preset threshold ArFreqTd1_ H, the packet inspection state machine control state jumps directly to state S3_ I; behavior in the S2 state is similar to that in the S1 state; namely, it is
In the S2 state, the frequency domain autocorrelator SC _ FD calculates ARF2 and ARN2, the packet detection state machine judges the relationship between the ARF2 and a preset threshold ArFreqTd2_ L and the relationship between the ARN2 and a preset threshold SyncNormMin, if the ARF1 is more than ArFreqTd1_ N or the ARF2 is more than ArFreqTd2_ N, the ARF2 is more than ArFreqTd2_ L and the ARN2 is more than the preset threshold SyncNormMin, the packet detection state machine control state jumps to S3_ I; otherwise, the control state of the packet detection state machine jumps to the state of S0;
(d) judging whether channel impact response exists or not in the S3_ I state, and determining symbol timing;
if the peak-to-average ratio PAR of the frequency domain sample output by the S3_ I is greater than a preset threshold PeakToAverTd, the channel impulse response is considered to be effective, and the control state of the data packet detection state machine jumps to the S3_ U state; otherwise, jumping to the S0 state;
(e) in the S3_ U state, the frequency domain autocorrelator SC _ FD continues to calculate the frequency domain autocorrelation value ARF4, and the packet inspection state machine judges the relationship between the ARF4 and the ArFreqTd4_ L so as to determine whether the packet inspection state machine jumps to the S _4 state or carries out overtime judgment; determining whether the packet inspection state machine stays in the S3_ U state or enters the S0 state by determining whether a timeout occurs;
if ARF4 < ArFreqTd4_ L, the packet inspection state machine jumps to the S _4 state to declare the end of packet inspection.
If ARF4 is greater than ArFreqTd4_ L, system timeout judgment is carried out, if the system timeout judgment is carried out, the data packet detection state machine jumps to an S0 state, and if the system timeout judgment is not carried out, the data packet detection state machine stays in an S3_ U state;
while SC _ FD continues to calculate the frequency domain autocorrelation value ARF4, the preamble sequence shown in fig. 8 contains a change of polarity inversion, and the frequency domain autocorrelation value should have a fast descending process, so if the frequency domain autocorrelation value ARF4 is detected to be lower than the preset threshold ArFreqTd4_ L, the packet detection state machine declares the end of packet detection by entering the S _4 state.
The initial state of the packet inspection state machine, S0, is ARN0 for monitoring the average input power, and in state S0, the input sample block of each FFT is not synchronized with the preamble sequence.
The preset threshold value ArFreqTd1_ N is greater than the preset threshold value ArFreqTd0_ N.
The preset threshold value ArFreqTd1_ H is greater than the second ArFreqTd1_ N, and the preset threshold value ArFreqTd0_ H is greater than the preset threshold value ArFreqTd0_ N;
in the detection flow (e), if ARF4 < ArFreqTd4_ L, the packet detection state machine jumps to the S _4 state to declare the packet detection to be finished;
if ARF4 > ArFreqTd4_ L, a system timeout judgment is carried out, if timeout occurs, the data packet detection state machine jumps to an S0 state, and if not, the data packet detection state machine continues to detect in an S3_ U state.
The packet inspection state machine inspecting at state S3_ I includes the steps of:
d1) accumulating and averaging sample blocks output by the FFT;
d2) calculating a frequency domain autocorrelation value in an autocorrelator, and judging whether a data packet detection state machine continuously jumps or not; if the data packet detection state machine continues to the S0 state, the following steps are carried out, otherwise, the data packet detection state machine jumps to the S0 state;
d3) calculating a frequency domain cross-correlation value in a cross-correlator;
d4) converting the frequency domain cross-correlation vector to the time domain using an inverse fourier transform;
d5) then, calculating a peak-to-average ratio (PAR), determining a symbol boundary of a leader sequence according to a peak position, judging the relation between the PAR and a preset threshold PeakToAverTd, and if the PAR is greater than the preset threshold PeakToAverTd, indicating that the data packet detection is successful and determining the reliability of symbol timing; the state of the packet detection state machine jumps to the S3_ U state otherwise, it is considered as a false alarm message and the state machine resets the S0 state.
Compared with the prior art, the invention has the beneficial effects that: the invention combines the output of the NB _ DET module when calculating SC _ FD and MC _ FD in the frequency domain, reduces the influence of narrow-band interference and improves the accuracy of detection; not only does correlation in the frequency domain, but also increases the judgment of the time domain peak-to-average ratio threshold, further reduces the probability of false alarm, and the data packet detection state machine adopts multiple threshold filtering, reduces the probability of false alarm; the whole detection process is carried out in a frequency domain, and can be used in combination with a narrow-band interference detection technology, so that the false alarm influence of narrow-band interference on packet detection is reduced; and the symbol timing is determined while the data packet is detected, so that the design is simplified and the cost is reduced.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic diagram of a frequency-domain autocorrelator according to the present invention;
FIG. 3 is a schematic diagram of a frequency cross-correlator according to the present invention;
FIG. 4 is a state transition flow diagram of the packet inspection state machine of the present invention;
FIG. 5 is a schematic flow chart of the calculation of the frequency domain autocorrelation value and the mean square value under different states;
fig. 6 is a specific operation flow in the S3_ I state;
FIG. 7 is a typical state transition process for a packet inspection state machine;
fig. 8 shows a specific preamble sequence comprising several identical symbols and one polarity change.
Detailed Description
The technical solution of the present invention is further explained with reference to the accompanying drawings and specific embodiments.
The correlator can operate in both the time domain and the frequency domain. At the input of the correlator, the N samples are grouped into a block, which is transformed into a frequency domain signal via a fourier transform, while the reference signal is also transformed into a frequency domain signal. For an autocorrelator, the reference signal is the conjugate component of the delayed signal Sk-1(0: N-1). For a cross-correlator, the reference signal is the conjugate component of the local reference signal. The correlator calculates the inner product of the two paths of frequency domain input signals.
As shown in fig. 1, a packet detection apparatus includes a packet detection FFT control module, a fourier transform device, an SC _ FD module, an MC _ FD module, an NBI _ DET module, an autocorrelation memory, a packet detection state machine, and an analog-to-digital conversion device; the data packet detection state machine is respectively connected with the packet detection FFT control module, the SC _ FD module, the MC _ FD module and the NBI _ DET module; the packet detection FFT control module is connected with the Fourier transform device and the autocorrelation memory; the autocorrelation memory is connected with the SC _ FD module, the MC _ FD module and the NBI _ DET module; the Fourier transform device comprises an FFT input module and an FFT engine; the analog-to-digital conversion device is connected with the FFT input module and the packet detection FFT control module; a buffer is arranged between the analog-to-digital conversion device and the FFT input module;
the buffer is used for caching the leader sequence to be processed; the packet detection FFT control module is a central controller; the FFT is used for carrying out Fourier transform on the signal sample block and outputting a frequency domain sample block; the SC _ FD module is used for calculating correlation values of two FFT output blocks, and the MC _ FD module is used for calculating a cross-correlation value of one data block; the NBI _ DET module is used to detect the narrowband interfering signal and generate a bit sequence of NBI Mask corresponding to each block of frequency domain samples.
A method for simultaneous packet detection and symbol timing, comprising the steps of:
step1, storing the signal sample output by the D/A converter into the buffer;
step2, under the control of the packet detection state machine, the sample block in the buffer is sent to the Fourier transform device and transformed into frequency domain samples;
step3, the frequency domain autocorrelator SC _ FD calculates the correlation value of two FFT output blocks, as shown in FIG. 2;
step4, MC _ FD calculates the cross-correlation value of a data block, as shown in fig. 3; to improve receiver sensitivity, the input to MC _ FD is the average of the FFT output samples.
Step5, detecting the narrow-band interference signal by a module NBI _ DET and generating a bit sequence of NBI Mask corresponding to each subcarrier; if any bit in the NBI Mask is set to be 1, the corresponding subcarrier does not participate in the calculation of SC _ FD and MC _ FD; this mechanism can significantly reduce false alarms caused by narrow-band interference;
step6, finally, under the control of the packet detection FFT control module, the packet detection state machine outputs a packet detection state, where the detection state refers to whether the packet state machine outputs a packet and the boundary of the packet, or no packet.
As shown in fig. 5, in different states of the packet detection state machine, the autocorrelation value and the mean square value of the frequency domain sample need to be calculated, the frequency domain samples output by the FFT are accumulated and averaged, and then the autocorrelation value and the mean square value are calculated.
The method provided by the invention can effectively reduce the false alarm probability of the system; as shown in fig. 4, the detection flow of the packet detection state machine for the packet detection state is as follows:
(a) the initial state of the packet detection state machine is S0, and the frequency domain autocorrelator SC _ FD calculates the frequency domain correlation value ARF0 and the mean square value ARN0 of the FFT output sample block; where ARN0 is used to detect the average input power, in state S0, the input sample block of each FFT is not synchronized with the preamble sequence;
(b) meanwhile, the relation between the frequency domain related value ARF0 and a preset threshold ArFreqTd0_ N and the relation between the mean square value ARN0 and a preset threshold SyncNormMin are judged,
when the ARF0 is greater than the preset threshold ArFreqTd0_ N and the ARN0 is greater than the preset threshold SyncNormMin, the packet detection state machine control state transitions to state S1; if the ARF0 > the preset threshold ArFreqTd0_ N and the ARN0 > the preset threshold SyncNormMin are not satisfied, the packet detection state machine stays in the S0 state;
(c) at state S1, SC _ FD calculates ARF1 and ARN1, and determines the relationship between ARF1 and the preset threshold ArFreqTd1_ N and the relationship between ARN1 and the preset threshold SyncNormMin,
if the ARF1 is greater than the predetermined threshold ArFreqTd1_ N and the ARN1 is greater than the predetermined threshold SyncNormMin, wherein ArFreqTd1_ N > ArFreqTd0_ N, the packet detection state machine control state transitions to state S2; if either of the ARF1 and the ARN1 is below a preset threshold, the packet detection state machine control state jumps back to the start state S0;
if ARF0 and ARF1 are both greater than an upper threshold, the packet inspection state machine control state transitions directly to state S3_ I, where ArFreqTd1_ H > ArFreqTd1_ N and ArFreqTd0_ H > ArFreqTd0_ N;
(d) in the state of S3_ I, the frequency-domain autocorrelator SC _ FD continues to calculate the frequency-domain autocorrelation value ARF3, and the packet inspection state machine determines the relationship between AFR3 and ArFreqTd3_ L and ArFreqTd3_ N, thereby determining whether to calculate the frequency-domain cross-correlation value. Aiming at the result of IFFT transformation of the frequency domain cross-correlation value, calculating peak-to-average ratio (PAR) and judging whether effective channel impact response exists or not and adjusting symbol timing according to the position of peak. As shown in fig. 6;
d1) accumulating and averaging sample blocks output by the FFT;
d2) referring to fig. 2, calculating frequency domain autocorrelation and judging whether to continue; if continuing, proceeding to step d3), if not, the data packet detection state machine jumps to the S0 state;
d3) referring to fig. 3, a frequency domain sample cross-correlation value is calculated;
d4) converting the frequency domain cross-correlation vector to the time domain using an inverse fourier transform;
d5) searching symbol timing and adjusting FFT input alignment;
searching a symbol boundary in the inverse FFT output, adjusting the position of the FFT input through a packet detection FFT control module, and positioning the symbol boundary by searching a peak value of the inverse FFT output; then, calculating the peak-to-average ratio (PAR) of the frequency domain sample block, judging the relation between the PAR and a preset threshold PeakToAverTd, if the PAR is greater than the preset threshold PeakToAverTd, indicating the success of data packet detection and determining the reliability of symbol timing, and entering S3_ U; otherwise, the state machine resets the state of S0 as the false alarm information; finally, the packet detection FFT control module adjusts the input sample block of FFT to be synchronous with the leading sequence symbol;
(e) when the control state of the packet detection state machine jumps to the state of S3_ U, the timer sync _ timer starts to time, the autocorrelator SC _ FD continues to calculate the frequency domain autocorrelation value ARF4, the frequency domain autocorrelation value should have a fast descending process, the preamble sequence shown in FIG. 8 contains a change of polarity inversion, therefore, once the frequency domain autocorrelation value ARF4 is detected to be lower than the preset threshold ArFreqTd4, the packet detection state machine declares the end of packet detection by entering the state of S _ 4.
If such a rapid drop cannot be detected, it is preferable that the timer in the state S3_ U counts 50us, the timer sync _ timer will time out, and the packet inspection state machine returns to the state S0; fig. 4 shows a typical packet detection state machine controlling the state transition process.
The system and the method are already applied to an independently developed altera fpga development board and applied to a communication chip in the future.
Example (b):
in practical applications, the preamble sequence often includes a polarity change (S +/S-), which provides a reference for subsequent packet header positioning, as shown in fig. 8.
Claims (10)
1. A data packet detection device is characterized by comprising a packet detection FFT control module, a Fourier transform device, an SC _ FD module, an MC _ FD module, an NBI _ DET module, an autocorrelation memory, a data packet detection state machine and an analog-to-digital conversion device; the data packet detection state machine is respectively connected with the packet detection FFT control module, the SC _ FD module, the MC _ FD module and the NBI _ DET module; the packet detection FFT control module is connected with the Fourier transform device and the autocorrelation memory; the autocorrelation memory is connected with the SC _ FD module, the MC _ FD module and the NBI _ DET module; the Fourier transform device comprises an FFT input module and an FFT engine; the analog-to-digital conversion device is respectively connected with the FFT input module and the packet detection FFT control module through the buffer;
the buffer is used for caching the preamble sequence to be processed, the packet detection FFT control module sends an instruction for transmitting the preamble sequence to the Fourier transform device to the buffer, and the packet detection FFT control module sends the Fourier transform instruction to the Fourier transform device; the Fourier transform device is used for carrying out Fourier transform on the signal sample block to output a frequency domain sample block; the packet detection FFT control module sends a transmission instruction to the autocorrelation storage module; the NBI _ DET module is used for detecting a narrow-band interference signal, generating a bit sequence of an NBI Mask corresponding to each frequency domain sample block and judging whether each subcarrier in the frequency domain sample block needs to perform autocorrelation and cross-correlation calculation; the frequency domain sample block is transmitted to an SC _ FD module and an MC _ FD module, the self-correlation values of the two frequency domain sample blocks are calculated in the SC _ FD module, and the MC _ FD module is used for calculating the cross-correlation value of the frequency domain sample block and a local sample block; the obtained autocorrelation value and the cross correlation value are transmitted to a packet detection state machine for judgment, and the packet detection state machine outputs an indication of whether a data packet exists and a boundary thereof.
2. The packet inspection method of the packet inspection device according to claim 1, comprising the steps of:
step1, storing the preamble sequence processed by the analog-to-digital conversion device into a buffer as a signal sample block;
step2, the packet detection state machine sends an instruction to the buffer, the buffer transmits the signal sample block stored in the buffer to the Fourier transform device, and the signal sample block is transformed into frequency domain samples in the Fourier transform device;
step3, the module NBI _ DET detects the narrowband interference signals in the frequency domain samples and generates a bit sequence of NBI Mask corresponding to the subcarriers in each frequency domain sample; judging whether the sub-carriers in the corresponding frequency domain samples participate in the calculation of SC _ FD and MC _ FD according to the output value of the NBI Mask;
if any bit output in the NBI Mask is 1, the subcarrier in the corresponding frequency domain sample does not participate in the calculation of SC _ FD and MC _ FD; if any bit output in the NBI Mask is 0, the calculation of SC _ FD and MC _ FD is participated;
step4, calculating an autocorrelation value between two frequency-domain sample blocks by the frequency-domain autocorrelator SC _ FD;
step5, calculating a cross-correlation value of a frequency domain sample data block and a local data block by a frequency domain cross-correlator MC _ FD;
step6, under the control of the packet detection FFT control module, the packet detection state machine outputs the packet detection state, where the detection state refers to whether the packet state machine outputs a packet and the boundary of the packet, or no packet.
3. The method of claim 2, wherein Step4, the correlation value includes the strength of the frequency-domain sample block and its similarity with the previous frequency-domain sample block.
4. The method of claim 2 wherein at Step5, the input of the frequency-domain cross-correlator MC _ FD is the average of FFT output samples, and the correlation value is how similar the frequency-domain sample data block is to the local data block.
5. The method of claim 2, wherein the packet inspection state machine performs the following inspection process on the packet inspection state:
(a) the frequency domain autocorrelator SC _ FD calculates a frequency domain correlation value ARF0 and a mean square value ARN0 of an FFT output sample block in an initial S0 state of the packet detection state machine;
(b) the data packet detection state machine judges the relation between the frequency domain related value ARF0 and a preset threshold ArFreqTd0_ N and the relation between the mean square value ARN0 and a preset threshold SyncNormMin, and further determines that the data packet detection state machine stays in an S0 state or jumps to an S1 state; if the mean square value ARN0 is larger than a preset threshold SyncNormMin and the mean square value ARN0 is larger than ArFreqTd0_ N, jumping to the S1 state, otherwise, the data packet detection state machine stays in the S0 state;
(c) in the S1 state, the frequency domain autocorrelator SC _ FD calculates ARF1 and ARN1, the packet detection state machine judges the relationship between the ARF1 and a preset threshold ArFreqTd1_ N and the relationship between the ARN1 and a preset threshold SyncNormMin, and further determines that the packet detection state machine returns to the S0 state or jumps to the S2 state; ARN1 > SyncNormMin and SyncNormMin > ArFreqTd1_ N, then jumping to S2 state, otherwise the packet inspection state machine returns value S0 state;
the packet inspection state machine further determines the relationship between ARF0 and a preset threshold ArFreqTd0_ H and the relationship between ARF1 and a preset threshold ArFreqTd1_ H; further determining that the packet inspection state machine enters the S2 state or jumps to the S3_ I state; ARF1 > ArFreqTd1_ H and ARF0 > ArFreqTd0_ H, the packet inspection state machine enters the S3_ I state, otherwise enters the S2 state;
in the S2 state, the frequency domain autocorrelator SC _ FD calculates ARF2 and ARN2, the packet detection state machine judges the relationship between the ARF2 and the preset thresholds ArFreqTd2_ L and ArFreqTd2_ N and the relationship between the ARN2 and the preset threshold SyncNormMin, and determines that the packet detection state machine returns to the S0 state or jumps to the S3_ I state; if ARN2 < SyncNormMin or ARF2 < ArFreqTd2_ L or (ARF 1 < ArFreqTd1_ H and ARF2 < ArFreqTd2_ N), returning to S0 state, otherwise jumping to S3_ I state;
(d) in the state of S3_ I, the frequency domain autocorrelator SC _ FD continues to calculate the frequency domain autocorrelation value ARF3, and the packet inspection state machine determines the relationship between ARF3 and ArFreqTd3_ L and ArFreqTd3_ N, thereby determining whether to calculate the frequency domain cross-correlation value; if ARN3 < SyncNormMin or ARF3 < ArFreqTd3_ L or (ARF 2 < ArFreqTd2_ L and ARF3 < ArFreqTd3_ N), returning to the S0 state, otherwise, calculating the frequency domain cross-correlation value;
aiming at the result of the IFFT of the frequency domain cross-correlation value, calculating a peak-to-average ratio (PAR) and judging whether effective channel impact response exists or not and adjusting symbol timing according to the position of a peak; entering an S3_ U state if a valid channel impulse response exists, and returning to an S0 state if the valid channel impulse response does not exist;
(e) in the S3_ U state, the frequency domain autocorrelator SC _ FD continues to calculate the frequency domain autocorrelation value ARF4, and the packet inspection state machine judges the relationship between the ARF4 and the ArFreqTd4_ L so as to determine whether the packet inspection state machine jumps to the S _4 state or carries out overtime judgment; if ARF4 < ArFreqTd4_ L, the state is entered into S _4, otherwise, the state machine is determined to stay in S3_ U state or S0 state by judging whether time is out.
6. The method of claim 5, wherein the ARN0 at S0 for the initial state of the packet inspection state machine is used to monitor the average input power, and the input sample block of each FFT is not synchronized with the preamble sequence at S0.
7. The method of claim 5, wherein the predetermined threshold ArFreqTd1_ N is greater than the predetermined threshold ArFreqTd0_ N.
8. The method of claim 5, wherein the predetermined threshold ArFreqTd1_ H is greater than ArFreqTd1_ N, and the predetermined threshold ArFreqTd0_ H is greater than the predetermined threshold ArFreqTd0_ N.
9. The method of claim 5, wherein in the detecting step (e), if ARF4 < ArFreqTd0_ L, the packet detecting state machine jumps to S _4 state to declare the packet detection is over;
if ARF4 > ArFreqTd4_ L, a system timeout judgment is carried out, if timeout occurs, the data packet detection state machine jumps to an S0 state, and if not, the data packet detection state machine continues to detect in an S3_ U state.
10. The packet inspection method of claim 5, wherein the packet inspection state machine inspecting at the state S3_ I comprises the steps of:
d1) accumulating and averaging sample blocks output by the FFT;
d2) calculating a frequency domain autocorrelation value in an autocorrelator, and judging whether a data packet detection state machine continuously jumps or not; if so, the following steps are carried out, otherwise, the data packet detection state machine jumps to an S0 state;
d3) calculating a frequency domain cross-correlation value in a cross-correlator;
d4) converting the frequency domain cross-correlation vector to the time domain using an inverse fourier transform;
d5) then, calculating a peak-to-average ratio (PAR), determining a symbol boundary of a leader sequence according to a peak position, judging the relation between the PAR and a preset threshold PeakToAverTd, and if the PAR is greater than the preset threshold PeakToAverTd, indicating that the data packet detection is successful and determining the reliability of symbol timing; the state of the packet inspection state machine jumps to the S3_ U state, otherwise, the state machine resets the S0 state, considering false alarm information.
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