CN117579445A - GMSK-based power communication method and system - Google Patents
GMSK-based power communication method and system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
- H04L27/12—Modulator circuits; Transmitter circuits
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0006—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format
- H04L1/0007—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format by modifying the frame length
- H04L1/0008—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format by modifying the frame length by supplementing frame payload, e.g. with padding bits
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0045—Arrangements at the receiver end
- H04L1/0054—Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/10—Frequency-modulated carrier systems, i.e. using frequency-shift keying
- H04L27/16—Frequency regulation arrangements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention discloses a power communication method and a power communication system based on GMSK, wherein the method comprises the steps that a receiving end receives a GMSK signal, and a periodic component is output through a baseband discriminator; performing Fourier transform on the periodic component, and performing discrete Fourier transform to obtain a frequency index corresponding to the theoretical peak value; judging whether a peak value appears at the frequency index by adopting a unit average constant false alarm detection algorithm; the receiving end adopts coherent Viterbi decoding to demodulate data, and frame data is obtained. Through adopting a unit average constant false alarm detection algorithm and Viterbi decoding to carry out data demodulation, the GMSK modulation technology can be matched with the characteristic of 230MHz frequency band frequency point dispersion of electric power, the access of mass electric power equipment is supported, and the requirement of electric power narrow bandwidth acquisition service is met.
Description
Technical Field
The invention relates to a power communication method and a power communication system, in particular to a power communication method and a power communication system based on GMSK, and belongs to the technical field of wireless communication.
Background
The novel power system needs to promote instant dynamic information of the power system for widely sensing the power generation capacity, the environment state and the power consumption requirement of the new energy of the whole network, forms a peak regulation power supply system from various power supplies through the technology of the Internet of things, forms an adjustable load system from various loads, and globally senses the internal and external environments of the power grid to develop active resource scheduling. The requirements of a plurality of links such as the source, the network, the load and the like indicate that the novel electric power system needs widely accessed Internet of things. At present, the national network company equipment department and the marketing department respectively issue narrowband internet of things standards based on LORA and ZIGBEE.
The GMSK modulation technique is a digital modulation mode developed from MSK modulation and is characterized in that a Gauss filter and a pre-modulation filter are used for pre-modulation filtering before a data stream is sent to a frequency modulator, so that jump energy during carrier switching of two different frequencies is reduced, and channel spacing can be tighter at the same data transmission rate. Because the digital signal is Gauss pre-modulation filtered before modulation, the modulated signal has continuous phase and smooth filtering at the crossover zero point, so the GMSK modulated signal has compact frequency spectrum and good error code characteristic.
Because of the characteristic that the frequency points of the 230MHz frequency band of the electric power are discrete, the large-scale access of the electric power equipment and the performance of the electric power narrow-bandwidth acquisition service cannot be met.
Disclosure of Invention
The invention aims to: the invention aims to provide a GMSK-based power communication method and a GMSK-based power communication system, which can work in a multi-frequency-point narrow-bandwidth power scene, match the characteristic of 230MHz frequency band frequency point dispersion of power, support the access of mass power equipment and meet the power narrow-bandwidth acquisition service.
The technical scheme is as follows: the power communication method based on GMSK comprises the following specific steps:
(1) The receiving end receives the GMSK signal, and outputs a periodic component through the baseband discriminator;
(2) Performing Fourier transform on the periodic component, and performing discrete Fourier transform to obtain a frequency index corresponding to the theoretical peak value;
(3) Judging whether a peak value appears at the frequency index by adopting a unit average constant false alarm detection algorithm;
(4) The receiving end adopts coherent Viterbi decoding to demodulate data, and frame data is obtained.
Further, the specific calculation of the periodic component is as follows:
the expression of the receiving end baseband signal r (t) is
Where A is the signal amplitude,is a modulated signal, τ is the frame header delay, f d Is carrier frequency offset, theta 0 Is the initial phase, n (t) is the additive white gaussian noise in the channel;
in-phase and quadrature components of the GMSK signal are represented as, respectively, ignoring noise
The in-phase component and the quadrature component of the GMSK signal pass through a baseband frequency discriminator, and the output expression phi (t) of the baseband frequency discriminator is
Wherein 2 pi f d Is a direct current component which is a direct current component,and->The derivatives of I (t) and Q (t), respectively.
Further, the calculation result of the frequency index is expressed as:
in the frame format, the training sequence is 24bit 0x555555 or 0xAAAAAA, and the period is from 2T after NRZI coding b Becomes 4T b Thus, a portion of the discriminator outputRepresented as
Wherein g (t) is the output of the gaussian filter;
fourier transform of (a) into
Wherein G (f) is the fourier transform of G (t);
due to the periodicity of the training sequence,fourier transform result F->Peaks may occur at the corresponding frequency index; when the input baseband signal is 8 times of the oversampled discrete signal x (N), the length of the training sequence is n=192, and the discrete fourier transform DFT is performed on the data with the length of N points, where the expression is
Assuming DFT operationsThe input data corresponds to the training sequence, then the periodic sequence frequency f is input i ＝1/(4T b ) Sampling rate f s ＝8/T b According to k=f i N/f s The frequency index k=6 corresponding to the theoretical peak is obtained.
Further, N reference units x are designated in the unit average constant false alarm detection CA-CFAR algorithm i Selecting a unit near the target unit as a reference unit, and obtaining noise power P by calculating a sample mean value of the reference unit n The expression is
Threshold factor a and false alarm probability P fa The reference unit sample number N is related, and the expression is
a＝N(P fa -1N -1)
The threshold T expression is as follows
T＝a·P n
From the above formula, the threshold is related to the false alarm probability and the choice of the reference cell.
Further, the step of judging whether the peak value occurs at the frequency index includes taking the frequency index k=6 as a target unit, taking 4 points forwards and 12 points backwards as reference units, taking the average value of 16 reference units as noise power, and multiplying the threshold factor and the noise power to obtain a threshold; if the training sequence exists and the power of the target unit is greater than the threshold, judging that the frame head exists, namely finding the target unit, and if the training sequence does not exist and the power of the target unit is greater than the threshold, judging that the frame head exists, namely a false alarm; if the power of the target unit exceeds the threshold, judging that a primary frame head is detected; in order to avoid incorrect judgment caused by noise at a certain time, if the threshold crossing mark is continuously detected for three times, judging that the frame head is detected, and returning to the position of the frame head to obtain the frame head time delay estimation
Further, the coherent viterbi decoding includes calculating branch metrics, updating path metrics, deriving surviving paths, and traceback decoding.
Further, the computing branch metrics includes at (k+1) T b At the moment, the currently received symbol r k+1 (t) and all branch path reference symbols s d (t) performing a correlation operation (d=1, 2,.. d ) Obtaining branch metric lambda d The expression is
Wherein T is b Is symbol time width;
the updated path metrics are included at kT b Time of day path metricsOn the basis of (k+1) T b Path metric expression of each branch at moment
Wherein n=1, 2,.. s ，i＝1,2。
Further, the survivor path is included in (k+1) T b Each state S of time n Two candidate paths are provided, and the path metrics of the two candidate paths are respectively expressed asAnd->By comparing the paths with larger path metrics to remain as surviving paths, the surviving paths are expressed as
The backtracking decoding comprises the steps of selecting a node with the maximum path metric as a backtracking starting point when the decoding depth reaches the backtracking depth which is more than 5 times of the coding constraint length, backtracking according to a surviving path route in a state grid diagram, obtaining a demodulation sequence, and finally obtaining frame data.
The GMSK-based power communication system of the invention comprises:
the sampling rate conversion module is used for performing filtering and extraction operations and reducing the sampling rate so as to facilitate the subsequent demodulation processing;
the cross-clock domain interface is an asynchronous RAM and is used for caching received data;
the scheduling module is used for controlling the cross-clock domain interface to read out data to each demodulation module;
and the demodulation module is used for carrying out burst frame detection on the sampled signal, then carrying out fine timing and frequency offset estimation, and carrying out differential demodulation decoding on the data subjected to frequency offset removal to obtain frame data.
Further, the frame comprises a rising edge, a training sequence, a start mark, data, frame verification, an end mark and buffering, wherein the default frame is 256 bits long and the maximum frame is 1024 bits long; the information bits are NRZI coded, the coded bits are GMSK modulated, the symbol rate is 9.6ksps, the modulation index is 0.4, and the information bits work on an electric power authorization frequency point of 230 MHz;
rising edge: accounting for 8 bits, the response time is reserved for automatic gain control of the radio frequency part of the receiver;
training sequence: 24 bits, which is a periodic sequence of 0, 1 alternates, in two forms, 0x555555 and 0xaaaaa, for the receiver to quickly capture GMSK signals of burst transmissions;
start flag: accounting for 8 bits, marking the beginning of the data portion;
data: the length is variable, the default occupies 168bit, and the effective data part in the frame format;
and (3) frame verification: accounting for 16 bits, and adopting a 16bit CRC check code as error detection of data transmission;
end flag: accounting for 8 bits, marking the end of the data part for the frame decoding operation of the receiver;
buffering: occupies 24 bits, wherein the 12bit distance delay is a reserved guard interval.
The beneficial effects are that: compared with the prior art, the invention has the following remarkable advantages: (1) The power supply can work in an authorized frequency band of 230MHz of power and is realized by a GMSK modulation technology; (2) The method meets the narrow bandwidth communication condition, can work in a multi-frequency-point narrow-band power acquisition scene through GMSK modulation, and supports the access of mass power equipment.
Drawings
Fig. 1 is a flow chart of a GMSK-based power communication method of the present invention;
fig. 2 is a schematic diagram of a GMSK-based power communication system of the present invention.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, an embodiment of the present invention provides a GMSK-based power communication method, including the steps of:
step 1: the receiving end receives GMSK signals, and outputs periodic components through a baseband frequency discriminator.
Since the arrival time of the preamble sequence is unknown, the detection is required by utilizing the periodicity characteristic of the training sequence, the detection range is the maximum delay length of the received signal, the detection window length is the data length of the training sequence, and the sliding detection is performed by stepping 1 data.
If the data in the detection window has periodicity, a periodic component is output through the baseband discriminator, fourier transformation is carried out on the periodic component, and finally, a constant false alarm algorithm is adopted to detect whether a peak value appears at a corresponding frequency index, so that whether a training sequence, namely a frame head, arrives or not can be judged.
The expression of the receiving end baseband signal r (t) is
Where A is the signal amplitude,is a modulated signal, τ is the frame header delay, f d Is carrier frequency offset, theta 0 Is the initial phase and n (t) is the additive white gaussian noise in the channel.
In-phase and quadrature components of the GMSK signal are represented as, respectively, ignoring noise
The in-phase component and the quadrature component of the GMSK signal pass through a baseband frequency discriminator, and the output expression phi (t) of the baseband frequency discriminator is
Wherein 2 pi f d Is a direct current component which is a direct current component,and->The derivatives of I (t) and Q (t), respectively.
Step 2: and carrying out Fourier transform on the periodic component, and then carrying out discrete Fourier transform to obtain a frequency index corresponding to the theoretical peak value.
The calculation result of the frequency index is expressed as:
in the frame format, the training sequence is 24bit 0x555555 or 0xAAAAAA, and the period is from 2T after NRZI coding b Becomes 4T b Thus, a portion of the discriminator outputRepresented as
Where g (t) is the output of the gaussian filter.
Fourier transform of (a) into
Wherein G (f) is the fourier transform of G (t).
Due to the periodicity of the training sequence,fourier transform result F->Peaks may occur at the corresponding frequency index; when the input baseband signal is 8 times of the oversampled discrete signal x (N), the length of the training sequence is n=192, and the discrete fourier transform DFT is performed on the data with the length of N points, where the expression is
Assuming that the input data of the DFT operation corresponds to a training sequence, then the periodic sequence frequency f is input i ＝1/(4T b ) Sampling rate f s ＝8/T b According to k=f i N/f s The frequency index k=6 corresponding to the theoretical peak is obtained.
In detecting whether a peak occurs at the corresponding frequency index. When detecting whether a peak value occurs at the corresponding frequency index, the problem of detection threshold selection exists, and constant false alarm detection CFAR is introduced at the moment.
The basic idea of CFAR is to change the fixed threshold into the self-adaptive threshold under the condition of ensuring the consistency of the false alarm probability, so that the size of the threshold can be adjusted in real time along with the background noise of the target unit; and comparing the power of the target unit with the adaptive threshold so as to judge whether the target unit has a target signal. The CFAR technique in this embodiment is a cell average constant false alarm detection technique CA-CFAR.
Step 3: and judging whether a peak value appears at the frequency index by adopting a unit average constant false alarm detection algorithm.
N reference units x are designated in unit average constant false alarm detection CA-CFAR algorithm i Selecting a unit near the target unit as a reference unit, and obtaining noise power P by calculating a sample mean value of the reference unit n The expression is
Threshold factor a and false alarm probability P fa The reference unit sample number N is related, and the expression is
a＝N(P fa -1/N -1)
The threshold T expression is as follows
T＝a·P n
From the above formula, the threshold is related to the false alarm probability and the choice of the reference cell.
Judging whether the peak value occurs at the frequency index comprises taking the frequency index k=6 as a target unit, wherein the interference intensity of the reference unit is required to be basically consistent with that of the target unit, so that the selected reference units are close to the target unit and the number of the reference units is not excessive, 4 points are taken forwards, 12 points are taken backwards as the reference units, the average value of 16 reference units is taken as noise power, and the threshold is obtained by multiplying the threshold factor and the noise power; if the training sequence exists and the power of the target unit is greater than the threshold, judging that the frame head exists, namely finding the target unit, and if the training sequence does not exist and the power of the target unit is greater than the threshold, judging that the frame head exists, namely a false alarm; if the power of the target unit exceeds the threshold, judging that a primary frame head is detected; in order to avoid incorrect judgment caused by noise at a certain time, if the threshold crossing mark is continuously detected for three times, judging that the frame head is detected, and returning to the position of the frame head to obtain the frame head time delay estimation
Then, adopting coherent Viterbi decoding to carry out data demodulation, wherein the Viterbi coherent demodulation process is to search a path in a state grid diagram so as to maximize the correlation value between a local modulation signal of the path and a receiving sequence; the specific flow of Viterbi coherent demodulation is as follows:
step 4: the receiving end adopts coherent Viterbi decoding to demodulate data, and frame data is obtained.
Coherent viterbi decoding includes computing branch metrics, updating path metrics, deriving surviving paths, and traceback decoding.
Calculating the branch metrics includes at (k+1) T b At the moment, the currently received symbol r k+1 (t) and all branch path reference symbols s d (t) performing a correlation operation (d=1, 2,.. d ) Obtaining branch metric lambda d The expression is
Wherein T is b Is symbol time width.
Updating path metrics included at kT b Time of day path metricsOn the basis of (k+1) T b Path metric expression of each branch at moment
Wherein n=1, 2,.. s ，i＝1,2。
The surviving path is included in (k+1) T b Each state S of time n Two candidate paths are provided, and the path metrics of the two candidate paths are respectively expressed asAnd->Preserving paths with larger path metrics as survivors by comparisonPaths, surviving paths are expressed as
The backtracking decoding comprises selecting a node with the maximum path metric as a backtracking starting point when the decoding depth reaches the backtracking depth, namely more than 5 times of the coding constraint length, backtracking according to the surviving path route in the state grid diagram, obtaining a demodulation sequence, and finally obtaining frame data.
As shown in fig. 2, the GMSK-based power communication system of the present invention includes:
the sampling rate conversion module is used for performing filtering and extraction operations and reducing the sampling rate so as to facilitate the subsequent demodulation processing;
the cross-clock domain interface is an asynchronous RAM and is used for caching received data;
the scheduling module is used for controlling the cross-clock domain interface to read out data to each demodulation module;
and the demodulation module is used for carrying out burst frame detection on the sampled signal, then carrying out fine timing and frequency offset estimation, and carrying out differential demodulation decoding on the data subjected to frequency offset removal to obtain frame data.
The frame comprises a rising edge, a training sequence, a start mark, data, a frame check, an end mark and a buffer, and a default frame is 256 bits long and 1024 bits at maximum.
Wherein, rising edge: 8 bits is used to leave the response time of the automatic gain control of the radio frequency part of the receiver.
Training sequence: accounting for 24 bits, is a periodic sequence of 0, 1 alternates, there are two forms of 0x555555 and 0xaaaaa for the receiver to quickly capture GMSK signals of burst transmissions.
Start flag: accounting for 8 bits, marks the beginning of the data portion.
Data: the length is variable, occupying 168 bits by default, the valid data portion in the frame format.
And (3) frame verification: accounting for 16 bits, a 16bit CRC check code is used as error detection for data transmission.
End flag: and 8 bits are occupied, and the mark data part is ended and is used for the frame-removing operation of the receiver.
Buffering: occupies 24 bits, wherein the 12bit distance delay is a reserved guard interval.
After NRZI encoding, the information bits are modulated in a GMSK mode, the symbol rate is 9.6ksps, the modulation index is 0.4, and the information bits work on an electric power authorization frequency point of 230 MHz; at the receiving end, firstly, the frame head detection technology is utilized to obtain the time-frequency information.
The receiving end firstly inputs the received GMSK signal into a sampling rate conversion module, and the sampling rate conversion module performs filtering and extraction operations to reduce the sampling rate so as to facilitate the subsequent demodulation processing. The cross-clock domain interface is an asynchronous RAM, which can buffer the received data, and the scheduling module controls the cross-clock domain interface to read the data to each demodulation module; the sampled signal is firstly subjected to burst frame detection, then subjected to fine timing and frequency offset estimation, and subjected to differential demodulation decoding to the data subjected to frequency offset removal, so that frame data can be obtained.
In conclusion, the invention can be matched with the characteristic of the dispersion of the frequency point of the 230MHz frequency band of the power by adopting the power communication method based on GMSK, supports the access of mass power equipment and meets the power narrow bandwidth acquisition service. The GMSK modulation has good modulation and demodulation performance, is suitable for communication with narrow bandwidth, and is very suitable for a 25kHz narrow-band channel which is scattered on an authorized frequency band of 230MHz of electric power.
Claims (10)
1. A GMSK-based power communication method, comprising the steps of:
(1) The receiving end receives the GMSK signal, and outputs a periodic component through the baseband discriminator;
(2) Performing Fourier transform on the periodic component, and performing discrete Fourier transform to obtain a frequency index corresponding to the theoretical peak value;
(3) Judging whether a peak value appears at the frequency index by adopting a unit average constant false alarm detection algorithm;
(4) The receiving end adopts coherent Viterbi decoding to demodulate data, and frame data is obtained.
2. The GMSK-based power communication method of claim 1, wherein the specific calculation of the periodic component is:
the expression of the receiving end baseband signal r (t) is
Where A is the signal amplitude,is a modulated signal, τ is the frame header delay, f d Is carrier frequency offset, theta 0 Is the initial phase, n (t) is the additive white gaussian noise in the channel;
in-phase and quadrature components of the GMSK signal are represented as, respectively, ignoring noise
The in-phase component and the quadrature component of the GMSK signal pass through a baseband frequency discriminator, and the output expression phi (t) of the baseband frequency discriminator is
Wherein 2 pi f d Is a direct current component which is a direct current component,and->The derivatives of I (t) and Q (t), respectively.
3. The GMSK-based power communication method of claim 1, wherein the calculation result of the frequency index is expressed as:
in the frame format, the training sequence is 24bit 0x555555 or 0xAAAAAA, and the period is from 2T after NRZI coding b Becomes 4T b Thus, a portion of the discriminator outputRepresented as
Wherein g (t) is the output of the gaussian filter;
fourier transform of (a) into
Wherein G (f) is the fourier transform of G (t);
due to the periodicity of the training sequence,fourier transform result F->Peaks may occur at the corresponding frequency index; when the input baseband signal is 8 times of the oversampled discrete signal x (N), the length of the training sequence is n=192, and the discrete fourier transform DFT is performed on the data with the length of N points, where the expression is
Assuming that the input data of the DFT operation corresponds to the training sequence, then the periodic sequence is inputColumn frequency f i ＝1/(4T b ) Sampling rate f s ＝8/T b According to k=f i N/f s The frequency index k=6 corresponding to the theoretical peak is obtained.
4. The GMSK-based power communication method of claim 1, wherein N reference units x are specified in the unit-average constant false alarm detection CA-CFAR algorithm i Selecting a unit near the target unit as a reference unit, and obtaining noise power P by calculating a sample mean value of the reference unit n The expression is
Threshold factor a and false alarm probability P fa The reference unit sample number N is related, and the expression is
a＝N(P fa -1/N -1)
The threshold T expression is as follows
T＝a·P n
From the above formula, the threshold is related to the false alarm probability and the choice of the reference cell.
5. The GMSK-based power communication method of claim 1, wherein determining whether a peak occurs at the frequency index comprises taking the frequency index k=6 as a target unit, taking 4 points forward and 12 points backward as reference units, taking a mean value of 16 reference units as noise power, and multiplying a threshold factor by the noise power to obtain a threshold; if the training sequence exists and the power of the target unit is greater than the threshold, judging that the frame head exists, namely finding the target unit, and if the training sequence does not exist and the power of the target unit is greater than the threshold, judging that the frame head exists, namely a false alarm; if the power of the target unit exceeds the threshold, judging that a primary frame head is detected; in order to avoid incorrect decision caused by noise at a time, if three times of threshold crossing marks are detected continuously, the decision is that the frame head is detected, and the frame head position is returned,obtaining frame header delay estimation
6. The GMSK-based power communication method of claim 1, wherein the coherent viterbi decoding comprises computing branch metrics, updating path metrics, deriving surviving paths, and traceback decoding.
7. The GMSK-based power communication method of claim 6, wherein the calculating a branch metric comprises at (k+1) T b At the moment, the currently received symbol r k+1 (t) and all branch path reference symbols s d (t) performing a correlation operation (d=1, 2,.. d ) Obtaining branch metric lambda d The expression is
Wherein T is b Is symbol time width;
the updated path metrics are included at kT b Time of day path metricsOn the basis of (k+1) T b Path metric expression of each branch at moment
Wherein n=1, 2,.. s ，i＝1,2。
8. The GMSK-based power communication method of claim 6, wherein the survivor path is included in (k+1) T b Each state S of time n Two candidate paths are provided, and the path metrics of the two candidate paths are respectively expressed asAnd->By comparing the paths with larger path metrics to remain as surviving paths, the surviving paths are expressed as
The backtracking decoding comprises the steps of selecting a node with the maximum path metric as a backtracking starting point when the decoding depth reaches the backtracking depth which is more than 5 times of the coding constraint length, backtracking according to a surviving path route in a state grid diagram, obtaining a demodulation sequence, and finally obtaining frame data.
9. A GMSK-based power communication system is characterized by comprising,
the sampling rate conversion module is used for performing filtering and extraction operations and reducing the sampling rate so as to facilitate the subsequent demodulation processing;
the cross-clock domain interface is an asynchronous RAM and is used for caching received data;
the scheduling module is used for controlling the cross-clock domain interface to read out data to each demodulation module;
and the demodulation module is used for carrying out burst frame detection on the sampled signal, then carrying out fine timing and frequency offset estimation, and carrying out differential demodulation decoding on the data subjected to frequency offset removal to obtain frame data.
10. The GMSK based power communication system of claim 9, wherein the frame comprises a rising edge, a training sequence, a start flag, data, a frame check, an end flag, and a buffer, a default frame length of 256 bits and a maximum of 1024 bits; the information bits are NRZI coded, the coded bits are GMSK modulated, the symbol rate is 9.6ksps, the modulation index is 0.4, and the information bits work on an electric power authorization frequency point of 230 MHz;
rising edge: accounting for 8 bits, the response time is reserved for automatic gain control of the radio frequency part of the receiver;
training sequence: 24 bits, which is a periodic sequence of 0, 1 alternates, in two forms, 0x555555 and 0xaaaaa, for the receiver to quickly capture GMSK signals of burst transmissions;
start flag: accounting for 8 bits, marking the beginning of the data portion;
data: occupying 168 bits, the valid data portion in the frame format;
and (3) frame verification: accounting for 16 bits, and adopting a 16bit CRC check code as error detection of data transmission;
end flag: accounting for 8 bits, marking the end of the data part for the frame decoding operation of the receiver;
buffering: occupies 24 bits, wherein the 12bit distance delay is a reserved guard interval.
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