CN109039972B - Method and device for estimating and compensating residual sampling frequency offset - Google Patents
Method and device for estimating and compensating residual sampling frequency offset Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
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- H04L27/261—Details of reference signals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0024—Carrier regulation at the receiver end
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Abstract
The method and the device are used for solving the problems that in the prior art, when the residual sampling frequency offset is reduced by reducing the sampling frequency offset, the sampling frequency offset can be reduced only by the iteration result of a plurality of beacon frames because the period of the beacon frames is long, so that the residual sampling frequency offset is reduced, the decoding success is ensured, and the decoding success rate is low. The method comprises the following steps: determining alternative OFDM symbols in preamble symbols of a received data frame, wherein the alternative OFDM symbols are used for residual sampling frequency offset estimation; performing residual sampling frequency offset estimation according to the alternative OFDM symbols to determine residual sampling frequency offset; and performing residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset.
Description
Technical Field
The present invention relates to the field of wireless communications, and in particular, to a method and an apparatus for estimating and compensating residual sampling frequency offset.
Background
In a Broadband Power Line Carrier (BPLC) system, a BPLC communication network is composed of a Central Coordinator (CCO), a Proxy Coordinator (PCO), and a site (Station, STA) networking shown in fig. 1, where the CCO and the PCO are responsible for completing networking control, network maintenance and management, and the STA is responsible for terminal data collection and transmission. In the BPLC communication network, the CCO, PCO, STA transmit and receive in the same frame format, and generally have 3 parts as shown in fig. 2. In the BPLC communication network, STA, PCO and CCO need to keep synchronous in time, specifically, network reference time is maintained by CCO, beacon frame is used for CCO to manage network and transmitted in form of beacon timestamp, wherein, in the central beacon, i.e., the beacon timestamp in the beacon frame sent by the CCO is the network reference time, in the proxy beacon, i.e., the beacon timestamp in the beacon frame transmitted by the PCO is the network reference time estimated by the PCO, in the discovery beacon, i.e. the timestamp in the beacon frame sent by the STA is the network reference time estimated by the STA, since the BPLC is a baseband communication system, there is a deviation in the crystal oscillators between nodes, and there is a deviation in the estimated timing, a sampling frequency offset is caused, if the duration of the transmission frame is longer, the accumulated sampling frequency offset is larger, thereby affecting the demodulation performance of FC and PL, or causing the demodulation failure of the transmission frame. Therefore, in order to ensure demodulation performance, nodes corresponding to the PCO and the STA in the BPLC communication network must perform estimation and compensation of sampling frequency offset, and although each node estimates the sampling frequency offset between the node and the CCO or the PCO through a beacon frame, it cannot be ensured that the residual sampling frequency offset between each node and the CCO or the PCO is consistent after compensation, and therefore, when any node needs to forward data to the CCO or the PCO from other nodes, a situation that demodulation of a transmission frame fails may occur.
For example, as shown in fig. 3, STA2 receives data of STA1, STA3, PCO1, and data of the next STA5 of PCO1, and even data of the next STA7 of PCO2, and data of other PCOs or data of next-level nodes of other PCOs, and particularly, in an actual BPLC network, from CCO0, through paths PCO1, PCO2, STA7, the timing of each stage is based on the network time of the previous stage, a beacon frame is transmitted, but each stage has residual sampling frequency offset, which increases in multiple stages, as shown in fig. 4, when the communication between STA7 and primary PCO2 is interrupted, STA7 needs to select a neighboring node as a relay to communicate with CCO0, and if the actual sampling frequency offset between STA2 and CCO0 is α 0, the sampling frequency offset is estimated to be α' 0, that is, Delf _ C0S2 in fig. 4, STA2 considers that the data on the transmitting side is all without sampling frequency offset from CCO0, and STA2 compensates the received data with α' 0. Under the condition that no sampling frequency offset exists between the transmitting side and the CCO0, after the STA2 compensates the received data, the sampled data still has a residual sampling frequency offset with the size Δ α 0 ═ α 0- α' 0. Actually, after performing sampling frequency offset compensation on transmission data, other STAs or PCOs also have residual sampling frequency offsets with the CCO0, for example, when the actual sampling frequency offset of the STA7 and the CCO0 is α 1, the estimated sampling frequency offset is α '1, which is the sum of Delf _ C0P1, Delf _ P1P2, and Delf _ P2S2, and after performing sampling frequency offset compensation on transmission data, the STA7 still has residual sampling frequency offsets Δ α 1 — α' 1. When STA2 receives data of STA7, the actual residual sampling frequency offset is Δ α ═ Δ α 0- Δ α 1, instead of Δ α 0, and if the signs of Δ α 0 and Δ α 1 are opposite, Δ α increases, and STA2 directly compensates for the data using α' 0, which cannot ensure successful decoding of the data sent by STA 7. Although STA2 may perform tracking estimation on the sampling frequency offset α 0 multiple-frame iteration using the beacon frame transmitted by CCO0, Δ α 0 is reduced, thereby reducing the residual sampling frequency offset Δ α between STA2 and STA 7. However, in practice, the beacon frame is transmitted periodically, and the period of transmission is at least 1 second, multiple iterations may be required to reduce Δ α 0 to an order of ensuring that STA2 correctly decodes STA7 data, and the time elapsed at this time may exceed 1 second, while the frame length of one BPLC does not exceed 28 milliseconds, and when STA7 transmits data to STA2, it is desirable that STA2 can decode successfully and forward to CCO0 immediately, but since the period of the beacon frame is relatively long and the result of multiple iterations of the beacon frame may be required to ensure successful decoding, it takes a long time for successful decoding.
In summary, how to rapidly estimate the residual sampling frequency offset of the received data, perform residual sampling frequency offset compensation on channel estimation, and improve the decoding success rate is a problem that needs to be solved at present.
Disclosure of Invention
In view of this, embodiments of the present invention provide a method and an apparatus for residual sampling frequency offset estimation and compensation, which can quickly estimate a residual sampling frequency offset of received data, perform residual sampling frequency offset compensation on channel estimation, and improve a decoding success rate.
According to a first aspect of the embodiments of the present invention, there is provided a method for estimating and compensating residual sampling frequency offset, including: determining alternative Orthogonal Frequency Division Multiplexing (OFDM) symbols in preamble symbols of a received data frame, wherein the alternative OFDM symbols are used for residual sampling Frequency offset estimation; performing residual sampling frequency offset estimation according to the alternative OFDM symbols to determine residual sampling frequency offset; and performing residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset.
In one embodiment, after performing residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset, the method further includes: determining that the data frame is a Central Coordinator (CCO) data frame; and updating the sampling frequency offset according to the residual sampling frequency offset.
In one embodiment, after determining that the data frame is a CCO data frame, the method further includes: determining that the signal quality of the CCO data frame is greater than or equal to a preset first quality threshold.
In one embodiment, determining that the data frame is a CCO data frame specifically includes: and determining the data frame as a CCO data frame according to the frame control symbol.
In an embodiment, determining candidate OFDM symbols in preamble symbols of a received data frame specifically includes: determining a preselected OFDM symbol in the preamble symbol according to the repeatability of the preamble symbol; determining the signal quality of the data frame according to the preselected OFDM symbols; and determining alternative OFDM symbols of which the signal quality is greater than or equal to a preset second quality threshold in the preselected OFDM symbols.
In an embodiment, determining a preselected OFDM symbol in the preamble symbol according to the repetition of the preamble symbol specifically includes: and determining the preselected OFDM symbols in the preamble symbols by adopting sliding autocorrelation according to the repeatability of the preamble symbols.
In an embodiment, performing residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset specifically includes: and respectively carrying out residual sampling frequency offset compensation on the frame control symbol and the service symbol in the data frame according to the residual sampling frequency offset.
In an embodiment, performing residual sampling frequency offset compensation on a frame control symbol in the data frame according to the residual sampling frequency offset specifically includes: determining a reference table of the first residual sampling frequency offset compensation and a step length table of the first residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the frame control symbol according to the reference table of the first residual sampling frequency offset compensation and the step length table of the first residual sampling frequency offset compensation.
In an embodiment, performing residual sampling frequency offset compensation on a service symbol in the data frame according to the residual sampling frequency offset specifically includes: determining a reference table of the second residual sampling frequency offset compensation and a step length table of the second residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the service symbol according to the reference table of the second residual sampling frequency offset compensation and the step length table of the second residual sampling frequency offset compensation.
According to a second aspect of the embodiments of the present invention, there is provided an apparatus for estimating and compensating residual sampling frequency offset, including: an effective data determining unit, configured to determine an alternative orthogonal frequency division multiplexing OFDM symbol in preamble symbols of a received data frame, where the alternative OFDM symbol is used to perform residual sampling frequency offset estimation; the estimation unit is used for carrying out residual sampling frequency offset estimation according to the alternative OFDM symbols to determine residual sampling frequency offset; and the compensation unit is used for carrying out residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset.
In one embodiment, the apparatus further comprises: a decoding unit for determining the data frame to be a Central Coordinator (CCO) data frame; and the updating unit is used for updating the sampling frequency offset according to the residual sampling frequency offset.
In one embodiment, the update unit is further configured to: determining that the signal quality of the CCO data frame is greater than or equal to a preset first quality threshold.
In one embodiment, the coding unit is specifically configured to: and determining the data frame as a CCO data frame according to the frame control symbol.
In one embodiment, the valid data determining unit specifically: determining a preselected OFDM symbol in the preamble symbol according to the repeatability of the preamble symbol; determining the signal quality of the data frame according to the preselected OFDM symbols; and determining alternative OFDM symbols of which the signal quality is greater than or equal to a preset second quality threshold in the preselected OFDM symbols.
In an embodiment, the valid data determining unit is specifically configured to: and determining the preselected OFDM symbols in the preamble symbols by adopting sliding autocorrelation according to the repeatability of the preamble symbols.
In one embodiment, the compensation unit is specifically configured to: and respectively carrying out residual sampling frequency offset compensation on the frame control symbol and the service symbol in the data frame according to the residual sampling frequency offset.
In one embodiment, the compensation unit is specifically configured to: determining a reference table of the first residual sampling frequency offset compensation and a step length table of the first residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the frame control symbol according to the reference table of the first residual sampling frequency offset compensation and the step length table of the first residual sampling frequency offset compensation.
In one embodiment, the compensation unit is specifically configured to: determining a reference table of the second residual sampling frequency offset compensation and a step length table of the second residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the service symbol according to the reference table of the second residual sampling frequency offset compensation and the step length table of the second residual sampling frequency offset compensation.
According to a third aspect of embodiments of the present invention, there is provided an integrated circuit comprising: a memory for storing one or more computer program instructions which, when executed by the processor, implement a method as set forth in the first aspect or any embodiment of the first aspect.
In the embodiment of the invention, firstly, an alternative Orthogonal Frequency Division Multiplexing (OFDM) symbol in a preamble symbol of a received data frame is determined, wherein the alternative OFDM symbol is used for carrying out residual sampling frequency offset estimation, then, the residual sampling frequency offset estimation is carried out according to the alternative OFDM symbol to determine the residual sampling frequency offset, and finally, the residual sampling frequency offset compensation is carried out on the data frame according to the residual sampling frequency offset. By adopting the method, after the data frame is received, the residual sampling frequency offset of the data frame can be rapidly estimated according to the preamble symbol of the current data frame, and the residual sampling frequency offset compensation is carried out on the data frame on the channel estimation, so that the decoding success rate is improved.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:
fig. 1 is a schematic diagram of a BPLC communication network according to an embodiment of the present invention;
FIG. 2 is a diagram of a frame format according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of another BPLC communication network provided by an embodiment of the present invention;
FIG. 4 is a diagram illustrating residual sampling frequency offset between stages according to an embodiment of the present invention;
FIG. 5 is a flowchart of a method for residual sampling frequency offset estimation and compensation according to an embodiment of the present invention;
fig. 6 is a schematic diagram of a preamble symbol structure according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a sliding autocorrelation of preamble symbols according to an embodiment of the present invention;
fig. 8 is a schematic flowchart of an effectiveness determination according to an embodiment of the present invention;
FIG. 9 is a flowchart of another method for residual sampling frequency offset estimation and compensation according to an embodiment of the present invention;
FIG. 10 is a diagram illustrating an apparatus for residual sampling frequency offset estimation and compensation according to an embodiment of the present invention;
fig. 11 is a schematic diagram of another apparatus for estimating and compensating residual sampling frequency offset according to an embodiment of the present invention.
Detailed Description
The present invention will be described below based on examples, but the present invention is not limited to only these examples.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
In the following detailed description of the present invention, certain specific details are set forth. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Further, in the description of the embodiments of the present invention, "a plurality" means two or more unless otherwise specified.
Fig. 5 is a flowchart of a method for estimating and compensating residual sampling frequency offset according to an embodiment of the present invention, and as shown in fig. 5, the method for compensating residual sampling frequency offset includes:
step S500, determining alternative OFDM symbols in the preamble symbols of the received data frame, wherein the alternative OFDM symbols are used for residual sampling frequency offset estimation.
Specifically, according to the repeatability of the preamble symbol, a sliding autocorrelation is adopted to determine a preselected OFDM symbol in the preamble symbol; determining the signal quality of the data frame according to the preselected OFDM symbols; and determining alternative OFDM symbols of which the signal quality is greater than or equal to a preset second quality threshold in the preselected OFDM symbols.
And S501, performing residual sampling frequency offset estimation according to the alternative OFDM symbol to determine residual sampling frequency offset.
And S502, performing residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset.
Specifically, the frame control symbol and the service symbol in the data frame are respectively subjected to residual sampling frequency offset compensation according to the residual sampling frequency offset. Performing residual sampling frequency offset compensation on a frame control symbol in the data frame according to the residual sampling frequency offset, specifically including: determining a reference table of the first residual sampling frequency offset compensation and a step length table of the first residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the frame control symbol according to the reference table of the first residual sampling frequency offset compensation and the step length table of the first residual sampling frequency offset compensation. Performing residual sampling frequency offset compensation on the service symbol in the data frame according to the residual sampling frequency offset, specifically including: determining a reference table of the second residual sampling frequency offset compensation and a step length table of the second residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the service symbol according to the reference table of the second residual sampling frequency offset compensation and the step length table of the second residual sampling frequency offset compensation.
In the embodiment of the present invention, an alternative orthogonal frequency division multiplexing OFDM symbol in a preamble symbol of a received data frame is first determined, where the alternative OFDM symbol is used to perform residual sampling frequency offset estimation, then perform residual sampling frequency offset estimation according to the alternative OFDM symbol to determine a residual sampling frequency offset, and finally perform residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset. By adopting the method, after the data frame is received, the residual sampling frequency offset of the data frame can be rapidly estimated according to the preamble symbol of the current data frame, and the residual sampling frequency offset compensation is carried out on the data frame on the channel estimation, so that the decoding success rate is improved.
After step S502, the method further includes step S503: determining that the data frame is a Central Coordinator (CCO) data frame; and updating the sampling frequency offset according to the residual sampling frequency offset.
Specifically, the data frame is determined to be a CCO data frame according to the frame control symbol.
Optionally, after determining that the data frame is a CCO data frame, the method further includes: determining that the signal quality of the CCO data frame is greater than or equal to a preset first quality threshold.
Step S500, step S501, step S502, and step 503 will be described in detail below with four specific embodiments.
The first embodiment,
By measuring Preamble of the received data frame, candidate OFDM symbols for residual sampling frequency offset estimation are determined from OFDM symbols of the Preamble, wherein a data structure of the Preamble is as shown in fig. 6 and has repeatability. Specifically, in fig. 6, the time domain length of each synchronization symbol SYNCP and SYNCM is equal to the length of an OFDM symbol in the time domain, within a certain window length, the sliding autocorrelation of two adjacent OFDM symbols is a fixed value, candidate OFDM symbols for residual sampling frequency offset estimation are searched, a Signal-to-Noise Ratio (SNR) reflecting the Signal quality is calculated according to corresponding data in the candidate OFDM symbols, and finally, the candidate OFDM symbols are determined. In the time domain, the OFDM length of the Preamble is a window length, and the sliding autocorrelation is performed on the entire Preamble, the schematic diagram of the sliding autocorrelation of the Preamble is shown in fig. 7, where a climbing interval, a flat interval, a falling interval, and a reverse interval may occur in the sliding autocorrelation.
Determining that the candidate OFDM symbol needs to determine the validity of OFDM in the current signal, that is, determining the validity of the current signal, the specific implementation steps are shown in fig. 8, and the flow is as follows:
step S800, calculating a sliding autocorrelation and an average power, specifically, performing a sliding autocorrelation according to formula (1) on the received time domain signal, and calculating an average power according to formula (2).
Wherein, AutoCor (tau) represents the value of sliding autocorrelation, N represents the number of sampling points of an OFDM, rx represents a time domain sampling signal, tau represents the index of sampling smooth autocorrelation, tau has the value range of 0-13.N-1, Pwravg (tau) represents the average power of N points from tau. For example, the length of each OFDM of the Preamble is 40.96us, and analog-to-digital (AD) sampling is performed at 25MHz, so that the OFDM length is 1024 samples, and N takes 1024 values.
Step S801, comparing the sliding self phase with the average power, specifically, setting a relative threshold factor Fac0, determining the relationship between the sliding self phase and the average power, if the formula (3) is satisfied, executing step S802, otherwise, returning to step S800.
AutoCor(τ)≥Fac0·PwrAvg(τ) (3)
Wherein the formula (3) indicates that the ratio of the value of the sliding autocorrelation to the average power needs to be greater than or equal to a relative threshold Fac0, wherein Fac0 is preset. If no interference noise exists, according to the repetition characteristic of Preamble, in a climbing interval, even if there is an influence of roll-off windowing, the value of the sliding autocorrelation and the average power should be equal, and enter a flat interval, the value of the sliding autocorrelation and the average power are always equal, but in an actual environment, because there are interference and noise, the equality relation cannot be guaranteed, so when the signal-to-noise ratio is relatively low, the signal is submerged under the noise, the average value of the power sum of the noise and the signal is calculated by formula (2), while formula (1) only contains the power of the signal, the selected target relative to the threshold factor Fac0 is to reduce the signal omission, and therefore, the setting is performed according to the signal-to-noise ratio corresponding to the probability of omission. For example, if the probability of missed detection is 1% with a signal-to-noise ratio of-6 dB, the threshold may be set to 0.25, i.e., 10-0.60.25 or determined from actual testing.
Step S802, comparing the sliding autocorrelation with an absolute threshold.
Specifically, in an actual power environment, under the condition of no signal, there may be narrowband interference and white noise, since the narrowband interference exists in a specific frequency band for a long time, there is a certain correlation in the time domain, which results in that the sliding autocorrelation value and the average power satisfy formula (3), therefore, an absolute threshold AbsThr is set, so that the sliding autocorrelation value satisfies formula (3) and formula (4) at the same time, so as to ensure accuracy, where formula (4) is as follows:
Autocor(τ)≥AbsThr (4)
if formula (4) is satisfied, step S803 is executed, otherwise, step S800 is returned to. Since the absolute threshold is set to reduce false alarm, the absolute threshold is set according to the Signal Strength corresponding to the probability of false alarm, for example, when the Received Signal Strength Indication (RSSI) of the Signal is 500, the probability of false alarm of the Signal is 1%, and the absolute threshold can be set to 500.
Step S803, a flat section starting point is calculated.
Specifically, in order to ensure the reliability of the calculated SNR, it is necessary to smooth as many OFDM as possible and adopt OFDM in a flat interval, but for Preamble of BPLC, the number of OFDM in the flat interval does not exceed 9, and it cannot be determined in the calculation process at which interval reception starts, so the maximum number of received OFDM in the flat interval maxofdnmum does not exceed 10, and it is necessary to determine the starting point of the flat interval by using 1 or more pieces of OFDM length data. The rules are as follows: when the value of the sliding autocorrelation and the average power satisfy the first point τ 0 of the formulas (3) and (4), it cannot be determined that the signal enters the climb interval or the flat interval. In order to determine the accuracy of the signal entering the flat region, the number of points Samplenum satisfying the formula (3) and the formula (4) within one OFDM length N is counted from τ 0, a relative threshold Fac1 is set, the first point of the flat region is determined by data of one OFDM length, if the formula (5) can be satisfied, the corresponding point τ 1 τ 0+ N is regarded as the first point entering the flat region, and if the formula (5) cannot be satisfied, the process returns to step S800.
Samplenum≥N·Fac1 (5)
Wherein the Fac1 reflects the percentage of (3) and (4) within the length N that satisfies the equation, Fac1 needs to be less than 1 in view of the noise and interference effects, e.g., Fac1 equals 0.8.
Step S804, the flat section signal is confirmed.
Specifically, since it cannot be determined from what section the device starts to receive data, the value of ofdm num needs to be determined by continuously deciding on data through formula (5), specifically as follows:
1) setting maxofdnmum, which cannot exceed 10, as it cannot be determined that the device can receive from the frame head of a frame and ensure the reliability of subsequent calculation, where maxofdnmum may be set to a value greater than or equal to 4 and less than 10, setting OFDM number OFDM num, which may be used for residual sampling frequency offset estimation, to 0, and setting received OFDM number recofdm number to 0.
2) Starting from τ 1, N pieces of point data are received, and the number of sampling points Samplenum satisfying equations (3) and (4) in the N sampling points is counted, and RecOFDMnum +1 is updated.
3) If Samplenum satisfies formula (5), updating OFDM number OFDM num +1 for estimation, and updating τ 1 to τ 1+ N, if Samplenum cannot satisfy formula (5), executing 5), otherwise, continuing executing 4).
4) If RecOFDMnum is less than the maximum OFDM number maxofdnmum available for residual sampling frequency offset estimation, returning to S801, continuing to process the next possible OFDM, otherwise, executing 5).
5) If the obtained OFDM number OFDM mnum available for residual frequency offset estimation is greater than the set threshold number OFDM numthr, then the subsequent SNR calculation is performed, otherwise, step S803 is executed again, since the calculation of SNR and subsequent residual sampling frequency offset requires a plurality of OFDM averages, for the reliability of the calculation, the value OFDMnumThr is selected to be greater than 2.
Step S805 calculates SNR.
The SNR calculation steps are as follows:
1) and from tau 1, taking N as length, carrying out Fast Fourier Transform (FFT) conversion on OFDMnum OFDM to obtain frequency domain data Rx (m, k) of the OFDMnum OFDM, and extracting the frequency domain data in the effective bandwidth.
Rx(m,k)＝fft(rx(n+m·N)) (6)
Wherein k is a subcarrier index, a value range is determined by a system bandwidth, such as Band0, an effective bandwidth is 80-490, m is greater than or equal to 0 and is less than or equal to OFDMnum, Ry (m, k) is used for representing the extracted frequency domain data, m is greater than or equal to 0 and is less than OFDMnum, k is greater than or equal to 0 and is less than or equal to Knum, the number of effective carriers is determined by the system bandwidth, such as Band0, and the effective bandwidth is Knum 411.
2) And averaging the signals Ry (k, m) to obtain a frequency domain signal rz (k) after noise suppression:
3) and calculating SNR:
the signal power is:
the noise power is:
the signal-to-noise ratio SNR is:
SNR＝10*log10(Pwrsig)-10*log10(Pwrnoise) (10)
step S806, determining the validity of the current signal when performing residual sampling frequency offset estimation.
Specifically, when the SNR is less than the second quality threshold SNRThr0, it is considered that the estimation of the residual sampling frequency offset using the current data is unreliable, so the estimation and compensation of the residual sampling frequency offset are abandoned, and the subsequent frequency offset updating is abandoned, and if the SNR is greater than or equal to the second quality threshold SNRThr0, the estimation process of the residual sampling frequency offset is continued. The second quality threshold SNRThr0 is set by taking the SNR corresponding to the residual sampling frequency offset estimation with Mean Square Error (MSE) not higher than a certain performance index as SNRThr 0. For example, it is desirable that the mean square error of the estimate be 5%, which corresponds to a SNR value, i.e., SNRThr 0. If the limitation of maximum 511 OFDM of PL under various bandwidths of BPLC and the repeated characteristic of data of FC and PL are considered, the index of mean square error can be properly relaxed.
The second embodiment,
And performing residual sampling frequency offset estimation according to the alternative OFDM symbol to determine the residual sampling frequency offset, performing noise suppression processing on the effective signal determined in the first embodiment, performing conjugate multiplication on the effective carrier wave with the same frequency by using the repetition characteristic between adjacent OFDM symbols, and calculating an angle according to the result of the conjugate multiplication to obtain the residual sampling frequency offset.
For example, the following steps are carried out: in the presence of a sampling frequency offset, the received signal is represented in the form of an inverse fast fourier transform IFFT:
where α represents a deviation of samples, and abs (α) <1, rx (n) represents an FFT result of rx (n) in the case where there is no sampling frequency deviation. In the case where there is no sampling variation, α is 0. After the point with the offset length of mN point,
due to the repetition of Preamble, Rx (k) and Rx (m, k) are equal, (12) can be converted into:
comparing (11) and (13), each subcarrier is affected by sampling frequency offset.
Order to
Then rx (m, n) FFT post-transform tableShown as follows:
Rx′(m,k)＝Rx′(k)exp(-j2πkmα) (14)
according to the formula (14), it can be seen that the sampling deviation α can be calculated by performing frequency domain conjugate multiplication on two OFDM symbols and corresponding subcarriers, and then taking the angle, that is, the sampling deviation α is
Wherein, arg (·) represents an arctangent function, and the value range is (-pi, + pi); l represents the number of OFDM symbols spaced apart between two OFDM symbols, for example, if two adjacent OFDM symbols are spaced apart, l is 1.
Specifically, the implementation method of the residual sampling frequency offset estimation comprises the following steps:
1) for effective frequency domain data, selecting L adjacent OFDM symbols, and continuously selecting CarrNum carriers from an effective bandwidth, wherein the selection criterion of L is to reduce the operation amount, because the quantity of OFDM used for estimation in a flat area is OFDM _ num, L is less than or equal to OFDM _ num, the selection criterion of CarrNum is also to reduce the operation amount, and CarrNum is ensured to be less than Knum; the starting carrier KestStart position needs to be selected in consideration of the fact that the bandwidth edge may be affected by the filter design, and the carrier position is selected as far as possible in the middle flat area of the bandwidth. If the starting carrier of the system bandwidth is kstart and the ending carrier is kend, the starting position KestStart of the selected carrier is:
2) in L OFDM, every two conjugate multiplication is carried out on subcarriers corresponding to CarrNum of adjacent OFDM, the angle is calculated according to the result of the conjugate multiplication, sampling frequency offset corresponding to the angle is calculated, and finally average processing is carried out on alpha obtained by a plurality of carriers and a plurality of OFDM to obtain the estimation result of residual sampling frequency offset. The calculation method is as follows:
the third concrete example,
And respectively carrying out residual sampling frequency offset compensation on the frame control symbol and the service symbol in the data frame according to the residual sampling frequency offset. Specifically, the time difference between the channel estimation data and the first OFDM symbol of the FC and the estimated residual sampling frequency offset are utilized to perform frequency domain compensation on the channel estimation result to obtain a reference table of first residual sampling frequency offset compensation, and a step size table of first residual sampling frequency offset compensation in the FC demodulation stage is calculated according to the equal interval of each OFDM symbol of the FC and the first two OFDM symbols of the PL; and taking the result of the second OFDM channel estimation compensation of the PL as a second residual sampling frequency offset compensation reference table, and calculating a step table of the second residual sampling frequency offset compensation of the PL according to the equal interval of each OFDM symbol after the second OFDM symbol of the PL. The reference table of the first residual sampling frequency offset compensation, the reference table of the second residual sampling frequency offset compensation, the step table of the first residual sampling frequency offset compensation and the step table of the second residual sampling frequency offset compensation are only effective in the receiving frame at this time and are not used for the next receiving processing.
The specific treatment process is as follows: the equalization process is that the received OFDM symbols are multiplied by the channel estimation result in a conjugate way on the corresponding subcarrier position to obtain constellation modulation symbols on the carrier; for BPLC, if the influence of sampling frequency offset and interference is not considered, it can be considered that the channel corresponding to each OFDM symbol is slowly changed or approximately equal, and the equalization only uses the channel estimated in the Preamble stage, but there is a residual frequency offset, and according to formula (14), the residual frequency offset affects each subcarrier in the frequency domain, causing the equalized constellation diagram to rotate, so that the channel used in each OFDM equalization process needs to be compensated. Assuming that the channel estimate is obtained at the ith OFDM of the received frame and the first OFDM of FC is located at the p-th OFDM symbol position of the received frame, the compensated channel estimate for the p-th OFDM can be expressed as:
h (k) represents a channel estimated according to the Preamble, k represents an index number of a carrier within an effective bandwidth, a value of the index number is determined by the effective bandwidth, for example, Band0, is 80-490, H (p, k) represents a compensation result of the channel at an OFDM symbol, and Ncp0 represents a length of a cyclic prefix of the FC OFDM symbol. Since each OFDM of FC is equally spaced and the spacing length is N + Ncp0, the spacing of the first two OFDM of PL is also N + Ncp0, therefore, for each OFDM of FC, and the first two OFDM of PL, the reference compensation table is calculated in terms of equation (18) over the bandwidth.
Calculating a compensated step size table according to the following formula:
for each OFDM processed, the channel is compensated based on the previous compensation as follows:
H(p+l,k)＝H(p+l-1,k)·CompTbl0(k) (20)
similarly, due to the equal spacing of each OFDM symbol after PL second OFDM symbol, the step size table after PL second OFDM symbol can be expressed as:
where Ncp1 represents the length of the cyclic prefix of the third OFDM and subsequent OFDM of PL, assuming that the channel estimation compensation result corresponding to the second OFDM symbol of PL obtained by iteration through equation (20) is H (p + FcNum +2, k), each time one OFDM is processed, the channel is compensated on the basis of the previous compensation, as follows:
H(p+FcNum+2+l，k)＝H(p+FcNum+2+l，k)·CompTbl1(k) (22)
where FcNum represents the number of OFDM of FCs, which is determined by the system bandwidth of BPLC, and 2 represents the first two OFDM of PLs.
The specific implementation process of the residual sampling frequency offset compensation is as follows:
1) calculating a compensation reference table of the FC stage according to formula (18); calculating a step table of FC stage compensation according to formula (19);
2) according to a formula (20), performing residual sampling frequency offset compensation on channels corresponding to each OFDM of FC and the first two OFDM of PL;
3) calculating a step length table of the residual sampling frequency offset compensation corresponding to the third and the following OFDM by taking the compensation result of the channel corresponding to the second OFDM of the PL as a reference table according to a formula (21);
4) and (4) performing residual sampling frequency offset compensation on channels corresponding to the third and later OFDM of the PL according to a formula (22).
The fourth concrete example,
And updating the sampling frequency offset according to the residual sampling frequency offset, specifically, according to a BPLC protocol, transmitting a source address of the current frame, analyzing data decoded by the FC to obtain the type of the frame and the address of a data source, and updating the frequency offset according to the source address and the signal quality.
If the currently received frame is found to be CCO data and the signal quality meets the update requirement, the frequency offset is updated, and the updated frequency offset can be used for compensating the transmitted data or the received data.
The specific implementation steps of the frequency offset update are as follows:
1) and if the FC demodulation of the current frame is successful and the current frame is data sent by the CCO, carrying out the next operation, otherwise, not carrying out the subsequent processing.
2) And if the current frame is instructed to give up frequency offset estimation when the data validity is judged, the subsequent processing is not carried out, and if not, the next processing is carried out.
3) If the SNR determined in one embodiment is greater than or equal to the first quality threshold SNRThr1, the frequency offset is updated, otherwise the process ends.
In the embodiment of the present invention, the method for setting the first quality threshold SNRThr1 and the second quality threshold SNRThr0 is the same, and the SNR corresponding to the MSE of the residual sampling frequency offset estimation not higher than a certain performance index is used as SNRThr1, in order to reduce the influence caused by estimation error, the selection index of SNRThr1 needs to be more strict than that of SNRThr0, for example, the index of SNRThr0 requires that the mean square error of estimation is up to 5%, and the index of SNRThr1 can be selected to be 1%.
Specifically, the frequency offset updating method comprises the following steps: and summing the residual sampling frequency offset and the sampling frequency offset estimated by the beacon frame, wherein the formula is as follows:
deltaF＝deltaF+α′ (23)
where deltaF is a sampling frequency offset estimated from an error between the network reference time carried by the beacon frame and the reception timing, and α' represents an estimated residual sampling frequency offset.
In the embodiment of the present invention, a method for estimating and compensating residual sampling frequency offset is described in detail with reference to fig. 9, where the specific process is as follows:
and S900, acquiring alternative OFDM symbols and calculating the signal-to-noise ratio according to the repeated characteristics of the Preamble symbol.
Step S901, determining whether the signal-to-noise ratio meets a preset threshold requirement, if so, executing step S902, otherwise, returning to step S900.
And S902, performing residual sampling frequency offset estimation according to the alternative OFDM symbol to determine residual sampling frequency offset.
And step S903, performing residual sampling frequency offset compensation on the FC and the PL according to the residual sampling frequency offset.
Step S904, the FC decoding result is analyzed, and the sampling frequency offset is updated.
Fig. 10 is a schematic diagram of an apparatus for estimating and compensating residual sampling frequency offset according to an embodiment of the present invention. As shown in fig. 10, the apparatus for estimating and compensating residual sampling frequency offset of this embodiment includes: effective data determination unit 1001, estimation unit 1002, and compensation unit 1003.
The valid data determining unit 1001 is configured to determine an alternative OFDM symbol in a preamble symbol of a received data frame, where the alternative OFDM symbol is used to perform residual sampling frequency offset estimation; an estimating unit 1002, configured to perform residual sampling frequency offset estimation according to the candidate OFDM symbol, and determine a residual sampling frequency offset; a compensating unit 1003, configured to perform residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset.
Optionally, the apparatus further comprises: a decode unit 1004 to determine the data frame to be a central coordinator CCO data frame; an updating unit 1005, configured to update the sampling frequency offset according to the residual sampling frequency offset.
Optionally, the updating unit is further configured to: determining that the signal quality of the CCO data frame is greater than or equal to a preset first quality threshold.
In an embodiment, the coding unit is specifically configured to: and determining the data frame as a CCO data frame according to the frame control symbol.
In an embodiment, the valid data determining unit specifically: determining a preselected OFDM symbol in the preamble symbol according to the repeatability of the preamble symbol; determining the signal quality of the data frame according to the preselected OFDM symbols; and determining alternative OFDM symbols of which the signal quality is greater than or equal to a preset second quality threshold in the preselected OFDM symbols.
Optionally, the valid data determining unit is specifically configured to: and determining the preselected OFDM symbols in the preamble symbols by adopting sliding autocorrelation according to the repeatability of the preamble symbols.
Optionally, the compensation unit is specifically configured to: and respectively carrying out residual sampling frequency offset compensation on the frame control symbol and the service symbol in the data frame according to the residual sampling frequency offset.
Optionally, the compensation unit is specifically configured to: determining a reference table of the first residual sampling frequency offset compensation and a step length table of the first residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the frame control symbol according to the reference table of the first residual sampling frequency offset compensation and the step length table of the first residual sampling frequency offset compensation.
In an embodiment, the compensation unit is specifically configured to: determining a reference table of the second residual sampling frequency offset compensation and a step length table of the second residual sampling frequency offset compensation; and performing residual sampling frequency offset compensation on the service symbol according to the reference table of the second residual sampling frequency offset compensation and the step length table of the second residual sampling frequency offset compensation.
In this embodiment of the present invention, the valid data determining unit 1001 may also be referred to as a data validity determiner, the estimating unit 1002 may also be referred to as a residual frequency offset estimator, the compensating unit 1003 may also be referred to as a residual frequency offset compensator, the decoding unit 1004 may also be referred to as a frame control data decoding, the updating unit 1005 may also be referred to as a frequency offset updater, and an apparatus for estimating and compensating residual sampling frequency offset may also be shown in fig. 11, where the data validity determiner 1101, the residual frequency offset estimator 1102, the residual frequency offset compensator 1103, the frame control data decoding 1104, and the frequency offset updater 1105.
An embodiment of the present invention provides an integrated circuit, including: a memory for storing one or more computer program instructions which, when executed by the processor, implement the method as described in steps S500 to S503.
As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, various aspects of the present invention may take the form of: an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit," module "or" system. Further, aspects of the invention may take the form of: a computer program product embodied in one or more computer readable media having computer readable program code embodied thereon.
Any combination of one or more computer-readable media may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of the present invention, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to: electromagnetic, optical, or any suitable combination thereof. The computer readable signal medium may be any of the following computer readable media: is not a computer readable storage medium and may communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including: object oriented programming languages such as Java, Smalltalk, C + +, and the like; and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package; executing in part on a user computer and in part on a remote computer; or entirely on a remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider).
The flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention described above describe various aspects of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.
The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (13)
1. A method for residual sampling frequency offset estimation and compensation, comprising:
determining alternative OFDM symbols in preamble symbols of a received data frame, wherein the alternative OFDM symbols are used for residual sampling frequency offset estimation;
performing residual sampling frequency offset estimation according to the alternative OFDM symbols to determine residual sampling frequency offset;
performing residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset;
determining that the data frame is a Central Coordinator (CCO) data frame;
updating the estimated sampling frequency offset according to the residual sampling frequency offset;
the determining alternative OFDM symbols in preamble symbols of a received data frame specifically includes:
calculating the sliding autocorrelation and the average power of the preamble symbols;
comparing the ratio of the sliding autocorrelation and the average power to a relative threshold;
comparing the sliding autocorrelation to an absolute threshold in response to the ratio of the sliding autocorrelation to the average power being greater than or equal to the relative threshold;
calculating a flat interval starting point in response to the sliding autocorrelation being greater than or equal to an absolute threshold;
determining a preselected OFDM symbol according to the flat interval starting point, wherein the preselected OFDM symbol is a flat interval signal;
calculating the signal-to-noise ratio of the preselected OFDM symbol;
and determining the alternative OFDM symbols according to the signal-to-noise ratio and a preset second quality threshold.
2. The method of claim 1, wherein after determining that the data frame is a CCO data frame, the method further comprises:
determining that the signal quality of the CCO data frame is greater than or equal to a preset first quality threshold.
3. The method of claim 1, wherein determining that the data frame is a CCO data frame specifically comprises:
and determining the data frame to be a CCO data frame according to the frame control symbol in the data frame.
4. The method of claim 1, wherein performing residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset specifically comprises:
and respectively carrying out residual sampling frequency offset compensation on the frame control symbol and the service symbol in the data frame according to the residual sampling frequency offset.
5. The method of claim 4, wherein performing residual sampling frequency offset compensation on the frame control symbols in the data frame according to the residual sampling frequency offset comprises:
determining a reference table of the first residual sampling frequency offset compensation and a step length table of the first residual sampling frequency offset compensation;
and performing residual sampling frequency offset compensation on the frame control symbol according to the reference table of the first residual sampling frequency offset compensation and the step length table of the first residual sampling frequency offset compensation.
6. The method of claim 4, wherein performing residual sampling frequency offset compensation on the traffic symbols in the data frame according to the residual sampling frequency offset comprises:
determining a reference table of the second residual sampling frequency offset compensation and a step length table of the second residual sampling frequency offset compensation;
and performing residual sampling frequency offset compensation on the service symbol according to the reference table of the second residual sampling frequency offset compensation and the step length table of the second residual sampling frequency offset compensation.
7. An apparatus for estimating and compensating residual sampling frequency offset, comprising:
an effective data determining unit, configured to determine an alternative orthogonal frequency division multiplexing OFDM symbol in preamble symbols of a received data frame, where the alternative OFDM symbol is used to perform residual sampling frequency offset estimation;
the estimation unit is used for carrying out residual sampling frequency offset estimation according to the alternative OFDM symbols to determine residual sampling frequency offset;
the compensation unit is used for carrying out residual sampling frequency offset compensation on the data frame according to the residual sampling frequency offset;
a decoding unit for determining the data frame to be a Central Coordinator (CCO) data frame;
the updating unit is used for updating the sampling frequency offset according to the residual sampling frequency offset;
wherein the valid data determining unit is specifically configured to:
calculating the sliding autocorrelation and the average power of the preamble symbols;
comparing the ratio of the sliding autocorrelation and the average power to a relative threshold;
comparing the sliding autocorrelation to an absolute threshold in response to the ratio of the sliding autocorrelation to the average power being greater than or equal to the relative threshold;
calculating a flat interval starting point in response to the sliding autocorrelation being greater than or equal to an absolute threshold;
determining a preselected OFDM symbol according to the flat interval starting point, wherein the preselected OFDM symbol is a flat interval signal;
calculating the signal-to-noise ratio of the preselected OFDM symbol;
and determining the alternative OFDM symbols according to the signal-to-noise ratio and a preset second quality threshold.
8. The apparatus of claim 7, wherein the update unit is further to:
determining that the signal quality of the CCO data frame is greater than or equal to a preset first quality threshold.
9. The apparatus of claim 7, wherein the decoding unit is specifically configured to:
and determining the data frame to be a CCO data frame according to the frame control symbol in the data frame.
10. The apparatus of claim 7, wherein the compensation unit is specifically configured to:
and respectively carrying out residual sampling frequency offset compensation on the frame control symbol and the service symbol in the data frame according to the residual sampling frequency offset.
11. The apparatus as claimed in claim 10, wherein the compensation unit is specifically configured to:
determining a reference table of the first residual sampling frequency offset compensation and a step length table of the first residual sampling frequency offset compensation;
and performing residual sampling frequency offset compensation on the frame control symbol according to the reference table of the first residual sampling frequency offset compensation and the step length table of the first residual sampling frequency offset compensation.
12. The apparatus as claimed in claim 10, wherein the compensation unit is specifically configured to:
determining a reference table of the second residual sampling frequency offset compensation and a step length table of the second residual sampling frequency offset compensation;
and performing residual sampling frequency offset compensation on the service symbol according to the reference table of the second residual sampling frequency offset compensation and the step length table of the second residual sampling frequency offset compensation.
13. An integrated circuit, comprising: a memory to store one or more computer program instructions, and a processor, wherein the one or more computer program instructions are executed by the processor to implement the method of any of claims 1-6.
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