Electric power communication equipment based on GMSK

Abstract

The invention discloses a GMSK-based electric power communication device, a message frame of the device is composed of seven parts, namely a rising edge, a training sequence, a start mark, data, frame verification, an end mark and a buffer, and the default frame length is 256 bits; nRZI coding is adopted for information bits, a GMSK modulation mode is adopted for the coded bits, the symbol rate is 9.6 ksps, the modulation index is 0.4, and the system works on a 230MHz electric power authorization frequency point; and a receiving end adopts a constant false alarm detection algorithm to detect a frame header and adopts a differential mode to demodulate data. According to the GMSK-based electric power communication equipment provided by the invention, stable communication on discrete 25kHz narrow-band frequency points authorized by electric power 230MHz can be realized, and electric power frequency band resources are fully utilized.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a power communication device based on GMSK. Background Technology

[0002] The new power system needs to enhance its ability to perceive real-time dynamic information on the output of renewable energy generation, environmental conditions, and electricity demand across the entire grid. It requires leveraging IoT technology to connect various power sources into peak-shaving power systems and various loads into adjustable load systems, enabling proactive resource dispatch based on a global perception of the internal and external grid environment. These requirements across multiple links—source, grid, and load—demonstrate the need for widespread IoT connectivity in the new power system. Currently, the State Grid Corporation's Equipment Department and Marketing Department have each released narrowband IoT standards based on LoRa and Zigbee. However, these technologies rely on chips patented by US companies, posing supply chain risks for large-scale power IoT deployment. Therefore, the independent controllability of the power IoT is becoming increasingly important.

[0003] GMSK modulation is a digital modulation technique developed from MSK (Minimum Shift Keying) modulation. Its key feature is that the data stream is pre-modulated and filtered by a Gaussian filter before being sent to the frequency modulator. This reduces the transition energy during the switching between two carriers of different frequencies, allowing for closer channel spacing at the same data transmission rate. Because the digital signal undergoes Gaussian pre-modulation filtering before modulation, the modulated signal not only has continuous phase at the zero-crossing point but also exhibits smooth filtering. Therefore, GMSK modulation results in a compact signal spectrum and good bit error rate characteristics.

[0004] This invention proposes a power communication device based on GMSK, which can operate in multi-frequency narrowband power scenarios, match the discrete frequency characteristics of the 230MHz power frequency band, support the access of massive power devices, and meet the needs of power narrowband data acquisition services. Summary of the Invention

[0005] The purpose of this invention is to provide a power communication device based on GMSK to realize local communication at power licensed discrete frequency points.

[0006] The technical solution to achieve the purpose of this invention is: a power communication device based on GMSK, wherein the message frame consists of 7 parts, namely rising edge, training sequence, start flag, data, frame check, end flag and buffer, and the default frame length is 256 bits.

[0007] Furthermore, the information bits are encoded using NRZI, and the encoded bits are modulated using GMSK modulation with a symbol rate of 9.6 ksps and a modulation index of 0.4, operating on the 230 MHz power license frequency.

[0008] Furthermore, the lengths and functions of each part of the signal are as follows:

[0009] Rising edge: Occupies 8 bits, which is reserved for the automatic gain control response time of the receiver's RF section;

[0010] Training sequence: occupies 24 bits and is a periodic sequence of alternating 0s and 1s. It has two forms: 0x555555 and 0xAAAAAA. It is used by the receiver to quickly capture the burst transmission of GMSK signals.

[0011] Start flag: occupies 8 bits and marks the beginning of the data portion;

[0012] Data: 168 bits, the valid data portion of the frame format;

[0013] Frame check: occupies 16 bits, using a 16-bit CRC checksum for error detection in data transmission;

[0014] End flag: occupies 8 bits, marks the end of the data portion, and is used for receiver deframe operation;

[0015] Buffer: occupies 24 bits, of which 12 bits are reserved for protection intervals due to distance delay.

[0016] Furthermore, the receiver employs a constant false alarm rate (CFAR) detection algorithm to detect the frame header. The threshold value is related to the noise power and threshold factor α, which are derived from the sample mean of the reference cell. This is expressed as follows:

[0017]

[0018] Where N is the number of noise samples, x i Let be the power value of the i-th noise sample signal.

[0019] Furthermore, the receiver employs differential demodulation for data demodulation. The received signal r(t) is represented as r(t) = I(t) + jQ(t), where I(t) and Q(t) represent the in-phase and quadrature components of r(t), respectively. A 1-bit differential operation is performed on r(t), expressed as:

[0020]

[0021] Among them, the phase difference between adjacent symbols when At that time, the corresponding received signal bit b k The judgment is "1", when At that time, the corresponding received signal bit b k The verdict was "0".

[0022] Compared with the prior art, the significant advantages of this invention are: GMSK modulation has good modulation and demodulation performance and is suitable for narrowband communication, making it very suitable for discrete 25kHz narrowband channels operating on the 230MHz licensed power band. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the information frame composition of the power communication device based on GMSK according to the present invention.

[0024] Figure 2 This is a flowchart of the signal reception and processing of the power communication equipment based on GMSK according to the present invention. Detailed Implementation

[0025] The message frame of a GMSK-based power communication device according to this invention consists of seven parts: rising edge, training sequence, start flag, data, frame check, end flag, and buffer. The default frame length is 256 bits. The length and function of each part of the signal are as follows:

[0026] Rising edge: occupies 8 bits and is reserved for the automatic gain control response time of the receiver's RF section.

[0027] Training sequence: occupies 24 bits and is a periodic sequence of alternating 0s and 1s. It has two forms (0x555555 and 0xAAAAAA) and is used by the receiver to quickly capture burst transmissions of GMSK signals.

[0028] Start flag: occupies 8 bits and marks the beginning of the data portion.

[0029] Data: 168 bits, the valid data portion in the frame format.

[0030] Frame check: occupies 16 bits, using a 16-bit CRC checksum for error detection in data transmission.

[0031] End flag: occupies 8 bits, marks the end of the data portion, and is used for receiver deframe operation.

[0032] Buffer: occupies 24 bits, of which 12 bits are reserved for protection intervals due to distance delay.

[0033] The information bits are encoded using NRZI and then modulated using GMSK modulation with a symbol rate of 9.6 ksps and a modulation index of 0.4. At the receiver, time-frequency information is first obtained using frame header detection technology.

[0034] Since the arrival time of the preamble sequence is unknown, the periodicity of the training sequence needs to be utilized for detection. The detection range is the maximum delay length of the received signal, and the detection window length is the length of the training sequence data. Sliding detection is performed by incrementing by one data point. If the data within the detection window is periodic, a periodic component will be output after passing through the baseband discriminator. A Fourier transform is performed on this periodic component, and finally, a constant false alarm rate (CFAR) algorithm is used to detect whether a peak occurs at the corresponding frequency index. This allows determination of whether the training sequence (frame header) has arrived.

[0035] The expression for the baseband AIS signal r(t) at the receiving end is:

[0036]

[0037] Where A is the signal amplitude. It is the modulated signal, τ is the frame header delay, and f d Let θ0 be the carrier frequency offset, θ0 be the initial phase, and n(t) be the additive white Gaussian noise in the channel. Ignoring noise, the in-phase and quadrature components of the GMSK signal are expressed as follows:

[0038]

[0039]

[0040] The in-phase and quadrature components of the GMSK signal are passed through a baseband frequency discriminator, and the output is...

[0041]

[0042] Where 2πf d It is the DC component. and These are the derivatives of I(t) and Q(t), respectively. In the frame format, the training sequence is a 24-bit string of 0x555555 or 0xAAAAAA, encoded using NRZI, with a period of 2T. b Become 4T b ,therefore, It can also be expressed as

[0043]

[0044] Where g(t) is the output of the Gaussian filter, The Fourier transform is

[0045]

[0046] Where G(f) is the Fourier transform of g(t). Due to the periodicity of the training sequence, Fourier transform results A peak will appear at the corresponding frequency index. When the input baseband signal is an 8x oversampled discrete signal x(n), the length of the training sequence is N = 192. The Discrete Fourier Transform (DFT) of the N-point data is expressed as follows:

[0047]

[0048] Assuming the input data for the DFT operation corresponds to the training sequence, then the frequency f of the input periodic sequence... i =1(4T) b ), sampling rate f s =8T b According to k = f i Nf s The frequency index k = 6 corresponding to the theoretical peak value is obtained. When detecting whether a peak value appears at the corresponding frequency index, there is a problem with selecting the detection threshold. Therefore, constant false alarm rate (CFAR) detection is introduced.

[0049] CFAR (Constant False Alarm Ranging) modifies a fixed threshold to an adaptive threshold while maintaining a consistent false alarm probability. This allows the threshold to be adjusted in real-time according to the background noise of the target cell. Typically, cells near the target cell are selected as reference cells, and the noise power P is obtained by calculating the sample mean of the reference cells. n The expression is

[0050]

[0051] Threshold factor a and false alarm probability P fa The number of reference unit samples N is related to this, and the expression is as follows:

[0052] a=N(P fa -1 / N -1)

[0053] The threshold T expression is as follows:

[0054] T = a·P n

[0055] As can be seen from the above formula, the threshold and false alarm probability are related to the selection of the reference unit.

[0056] Then, differential demodulation is used for data demodulation. The received signal r(t) can be expressed as r(t) = I(t) + jQ(t), where I(t) and Q(t) represent the in-phase and quadrature components of r(t), respectively. A 1-bit differential operation is performed on r(t), expressed as follows:

[0057]

[0058] Among them, the phase difference between adjacent symbols As can be seen from the GMSK modulation principle, The decision regarding the received signal depends entirely on The positive and negative, when At that time, the corresponding received signal bit b k The judgment is "1", when At that time, the corresponding received signal bit b k The verdict was "0".

[0059] The following will refer to the appendices in the embodiments of the present invention. Figure 1 With appendix Figure 2 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] Example

[0061] In this embodiment, the message frame of the GMSK-based power communication device consists of seven parts: rising edge, training sequence, start flag, data, frame check, end flag, and buffer. The default frame length is 256 bits. The length and function of each part of the signal are as follows:

[0062] Rising edge: occupies 8 bits and is reserved for the automatic gain control response time of the receiver's RF section.

[0063] Training sequence: occupies 24 bits and is a periodic sequence of alternating 0s and 1s. It has two forms (0x555555 and 0xAAAAAA) and is used by the receiver to quickly capture burst transmissions of GMSK signals.

[0064] Start flag: occupies 8 bits and marks the beginning of the data portion.

[0065] Data: 168 bits, the valid data portion in the frame format.

[0066] Frame check: occupies 16 bits, using a 16-bit CRC checksum for error detection in data transmission.

[0067] End flag: occupies 8 bits, marks the end of the data portion, and is used for receiver deframe operation.

[0068] Buffer: occupies 24 bits, of which 12 bits are reserved for protection intervals due to distance delay.

[0069] The information bits are encoded using NRZI and then modulated using GMSK modulation with a symbol rate of 9.6 ksps and a modulation index of 0.4. At the receiver, time-frequency information is first obtained using frame header detection technology.

[0070] The receiver first inputs the received GMSK signal into the sampling rate conversion module. This module performs filtering and decimation operations to reduce the sampling rate for subsequent demodulation processing. The cross-clock domain interface is an asynchronous RAM that buffers the received data. The scheduling module controls the cross-clock domain interface to read data and distribute it to each demodulation module. The sampled signal first undergoes burst frame detection, followed by precise timing and frequency offset estimation. Differential demodulation decoding is then performed on the frequency offset-reduced data to obtain the frame data.

[0071] Since the arrival time of the preamble sequence is unknown, the periodicity of the training sequence needs to be utilized for detection. The detection range is the maximum delay length of the received signal, and the detection window length is the length of the training sequence data. Sliding detection is performed by incrementing by one data point. If the data within the detection window is periodic, a periodic component will be output after passing through the baseband discriminator. A Fourier transform is performed on this periodic component, and finally, a constant false alarm rate (CFAR) algorithm is used to detect whether a peak occurs at the corresponding frequency index. This allows determination of whether the training sequence (frame header) has arrived.

[0072] The expression for the baseband AIS signal r(t) at the receiving end is:

[0073]

[0074] Where A is the signal amplitude. It is the modulated signal, τ is the frame header delay, and f d Let θ0 be the carrier frequency offset, θ0 be the initial phase, and n(t) be the additive white Gaussian noise in the channel. Ignoring noise, the in-phase and quadrature components of the GMSK signal are expressed as follows:

[0075]

[0076]

[0077] The in-phase and quadrature components of the GMSK signal are passed through a baseband frequency discriminator, and the output is...

[0078]

[0079] Where 2πf d It is the DC component. and These are the derivatives of I(t) and Q(t), respectively. In the frame format, the training sequence is a 24-bit string of 0x555555 or 0xAAAAAA, encoded using NRZI, with a period of 2T.b Become 4T b ,therefore, It can also be expressed as

[0080]

[0081] Where g(t) is the output of the Gaussian filter, The Fourier transform is

[0082]

[0083] Where G(f) is the Fourier transform of g(t). Due to the periodicity of the training sequence, Fourier transform results A peak will appear at the corresponding frequency index. When the input baseband signal is an 8x oversampled discrete signal x(n), the length of the training sequence is N = 192. The Discrete Fourier Transform (DFT) of the N-point data is expressed as follows:

[0084]

[0085] Assuming the input data for the DFT operation corresponds to the training sequence, then the frequency f of the input periodic sequence... i =1(4T) b ), sampling rate f s =8T b According to k = f i Nf s The frequency index k = 6 corresponding to the theoretical peak value is obtained. When detecting whether a peak value appears at the corresponding frequency index, there is a problem with selecting the detection threshold. Therefore, constant false alarm rate (CFAR) detection is introduced.

[0086] The basic idea of ​​CFAR is to change a fixed threshold to an adaptive threshold while ensuring a consistent false alarm probability. This allows the threshold to be adjusted in real time according to the background noise of the target cell. The target cell power is compared with the adaptive threshold to determine whether a target signal exists in the target cell. Currently, the most widely used CFAR technique is Cell Average Constant False Alarm Detection (CA-CFAR). The CA-CFAR algorithm requires specifying N reference cells x. i Typically, a cell near the target cell is selected as a reference cell, and the noise power P is obtained by calculating the sample mean of the reference cell. n The expression is

[0087]

[0088] Threshold factor a and false alarm probability P fa The number of reference unit samples N is related to this, and the expression is as follows:

[0089] a=N(P fa -1N -1)

[0090] The threshold T expression is as follows:

[0091] T = a·P

[0092] As can be seen from the above formula, the threshold and false alarm probability are related to the selection of the reference unit.

[0093] Using frequency index k=6 as the target unit, and considering that the interference intensity of the reference units should be roughly the same as that of the target unit, the selected reference units should be near the target unit and their number should not be excessive. Therefore, 4 points forward and 12 points backward are selected as reference units, and the average of the 16 reference units is used as the noise power. The threshold is obtained by multiplying the threshold factor and the noise power. If the training sequence exists and the target unit power is greater than the threshold, it is determined that a frame header has been detected, i.e., the target has been found. If the training sequence does not exist and the target unit power is greater than the threshold, it is determined that a frame header has been detected, i.e., a false alarm. If the power of the target unit exceeds the threshold, it is determined that a frame header has been detected. To avoid false detections due to noise, it is stipulated that if three consecutive threshold-crossing flags are detected, a frame header is detected, and the frame header position is returned to obtain the frame header delay estimate.

[0094] Then, differential demodulation is used for data demodulation. The received signal r(t) can be expressed as r(t) = I(t) + jQ(t), where I(t) and Q(t) represent the in-phase and quadrature components of r(t), respectively. A 1-bit differential operation is performed on r(t), expressed as follows:

[0095]

[0096] Among them, the phase difference between adjacent symbols As can be seen from the GMSK modulation principle, The decision regarding the received signal depends entirely on The positive and negative, when At that time, the corresponding received signal bit b k The judgment is "1", when At that time, the corresponding received signal bit b k The verdict was "0".

[0097] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A power communication device based on GMSK, characterized in that, A message frame consists of 7 parts: rising edge, training sequence, start flag, data, frame check, end flag, and buffer. The default frame length is 256 bits.

2. The GMSK-based power communication equipment according to claim 1, characterized in that, The information bits are encoded using NRZI, and the encoded bits are modulated using GMSK modulation with a symbol rate of 9.6 ksps and a modulation index of 0.4, operating on the 230 MHz power license frequency.

3. The GMSK-based power communication equipment according to claim 2, characterized in that, The lengths and functions of each part of the signal are as follows: Rising edge: Occupies 8 bits, which is reserved for the automatic gain control response time of the receiver's RF section; Training sequence: occupies 24 bits and is a periodic sequence of alternating 0s and 1s. It has two forms: 0x555555 and 0xAAAAAA. It is used by the receiver to quickly capture the burst transmission of GMSK signals. Start flag: occupies 8 bits and marks the beginning of the data portion; Data: 168 bits, the valid data portion of the frame format; Frame check: occupies 16 bits, using a 16-bit CRC checksum for error detection in data transmission; End flag: occupies 8 bits, marks the end of the data portion, and is used for receiver deframe operation; Buffer: occupies 24 bits, of which 12 bits are reserved for protection intervals due to distance delay.

4. The GMSK-based power communication equipment according to claim 3, characterized in that, The receiver uses a constant false alarm rate (CFAR) detection algorithm to detect the frame header. The threshold value is related to the noise power and threshold factor α, which are derived from the sample mean of the reference cell. This is expressed as follows: Where N is the number of noise samples, x i Let be the power value of the i-th noise sample signal.

5. The GMSK-based power communication device according to claim 4, characterized in that, The receiver uses differential demodulation for data demodulation. The received signal r(t) is represented as r(t) = I(t) + jQ(t), where I(t) and Q(t) represent the in-phase and quadrature components of r(t), respectively. A 1-bit differential operation is performed on r(t), and the expression is: Among them, the phase difference between adjacent symbols when At that time, the corresponding received signal bit b k The judgment is "1", when At that time, the corresponding received signal bit b k The verdict was "0".

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