A channel demodulation method for multi-level MFSK system of power Internet of Things service

Abstract

The present invention belongs to the technical field of power distribution network, and discloses a multi-level MFSK system channelization demodulation method for power Internet of Things services, including a signal sending end adopting multiple power frequency points for communication, wherein the power frequency points send modulation signals in an MFSK manner, and a signal receiving end channelizes the received modulation signals through a multi-phase filter group to obtain channelized data, and the channelized data is demodulated by MFSK to obtain a modulated instantaneous frequency signal, thereby effectively reducing the reception complexity of the power Internet of Things services.

Description

Technical Field

[0001] The present invention relates to a channelized demodulation method for a multi - level MFSK system in power Internet of Things services, belonging to the technical field of distribution networks. Background Art

[0002] The power system can use 290 dedicated frequency points of 25 kHz in the range of 223 - 235 MHz to carry out private network applications. There are three types of interference in the commonly used 230 MHz private network frequency band: broadband full - frequency interference, narrow - band co - frequency interference, and narrow - band adjacent - frequency interference. Among them, broadband full - frequency interference is mainly caused by various LED electronic screens, electronic billboards, electronic nameplates, and spotlights or lighting lamps; narrow - band co - frequency interference is mainly caused by authorized radio stations and temporary interferences within the 230 MHz frequency band; narrow - band adjacent - frequency interference is mainly caused by other 230 MHz narrow - band communication systems using non - power frequency points.

[0003] For broadband full - band interference, technologies such as spread - spectrum communication and narrow - band transmission can be used to improve the receiving performance for countermeasures. The traditional MFSK system processes each frequency point separately. At the receiving end, if there are multiple MFSK communication frequency points, each communication frequency point needs to be orthogonally down - converted and then base - band demodulated. When there are many communication frequency points, the receiving complexity of the traditional MFSK system is relatively high. At the same time, in the local communication system of the power Internet of Things, there is an edge device for data collection of power equipment in the area. When there are many MFSK communication frequency points for simultaneous communication, if the traditional single - frequency - point independent processing is adopted, the complexity of the receiving end and the transmitting end will increase sharply with the number of frequency points. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a channelized demodulation method for a multi - level MFSK system in power Internet of Things services to reduce the receiving complexity of power Internet of Things services.

[0005] To achieve the above - mentioned purpose, the present invention is implemented by the following technical solutions:

[0006] In the first aspect, the present invention provides a channelized demodulation method for a multi - level MFSK system in power Internet of Things services, and the method includes the following steps:

[0007] The signal transmitting end uses multiple power frequency points for communication, and the power frequency points send modulated signals in the MFSK mode;

[0008] The signal receiving end channelizes the received modulated signal through a polyphase filter bank to achieve channel separation of multi - frequency - point MFSK signals, reduce the complexity of the receiving end, and obtain the channelized data;

[0009] The channelized data undergoes MFSK demodulation to obtain the modulated instantaneous frequency signal.

[0010] In combination with the first aspect, further, when there are multiple MFSK transmission frequency points at the signal sending end, sparse OFDM is used for transmission, which can meet the requirements of different power services in the power Internet of Things while reducing the implementation complexity of the multi-frequency point MFSK system.

[0011] Further, the MFSK demodulation adopts the frequency discrimination method, and the frequency discrimination method uses small-angle approximation demodulation.

[0012] Further, the calculation formula of the instantaneous frequency signal after small-angle approximation demodulation is as follows:

[0013] m f α n ∝Δθ(n) = sinΔθ(n) = Q(n)I(n - 1) - I(n)Q(n - 1);

[0014] In the formula, I(n - 1) and I(n) are the in-phase received signals at n - 1 and n moments respectively, Q(n - 1) and Q(n) are the quadrature-phase received signals at n - 1 and n moments respectively, Δθ(n) represents the phase change at n moment, m f represents the frequency modulation index, and α n represents the modulation symbol.

[0015] Further, the signal receiving end groups the received modulation signals, and each branch modulation signal after grouping is filtered by a plurality of low-pass filters to obtain the channelized data.

[0016] Further, the power frequency point is a discrete 25 kHz bandwidth, and 2FSK modulation is adopted within each 25 kHz bandwidth.

[0017] Further, the method further includes performing differential demodulation on the obtained instantaneous frequency signal and simultaneously completing the code inverse transformation.

[0018] In the second aspect, the present invention provides a channelized demodulation system for a multi - base MFSK system of power Internet of Things services, including a processor and a storage medium;

[0019] The storage medium is used for storing instructions;

[0020] The processor is used to operate according to the instructions to execute the steps of the method according to any one of the above.

[0021] The present invention also provides a computer - readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the method according to any one of the above are implemented.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention include:

[0023] The present invention realizes the transmission of different power services by using multi - frequency - point MFSK technology, and can match the requirements of different power services in the power Internet of Things;

[0024] At the transmitter, a sparse OFDM transmission scheme is adopted to reduce the implementation complexity of the multi - frequency - point MFSK system;

[0025] At the receiver, a polyphase filter bank is adopted to realize the channel separation of multi - frequency - point MFSK signals, reducing the complexity of the receiver;

[0026] The MFSK system adopted in the present invention belongs to narrow - band communication technology. Compared with the OFDM system in the prior art, this system has a low peak - to - mean value and high power amplifier efficiency, and can effectively achieve low - power consumption transmission. Description of the Drawings

[0027] Figure 1 is the schematic diagram of the power multi - frequency - point FSK technology provided by the embodiment of the present invention;

[0028] Figure 2 is the schematic diagram of channelization based on a polyphase filter bank provided by the embodiment of the present invention;

[0029] Figure 3 is the system structure diagram of the small - angle approximation demodulation method provided by the embodiment of the present invention;

[0030] Figure 4 is the schematic diagram of demodulating the DPSK sub - carrier modulation signal provided by the embodiment of the present invention. Detailed Embodiments

[0031] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0032] Embodiment 1

[0033] The present invention provides a method for channel demodulation of a multi - ary MFSK system for power Internet of Things services. The modulation process of the MFSK system is as follows:

[0034] In the frequency domain, there are M orthogonal modulation frequency points [f0...f k ...f M-1 , where M is a power of 2. According to log2(M) information bits, a frequency point k ∈ [0, M - 1] is selected through a certain mapping method, and then this frequency point is selected for modulation and transmission, that is, s(t)=cos(f c t + 2π*f k t), where f cLet \(f_c\) be the carrier frequency point, and the interval between frequency points be SCS. The duration of each M-FSK modulation symbol must be greater than 1 / SCS. According to the MFSK modulation order M and the frequency point interval SCS, the signal occupied bandwidth BW = M * SCS can be obtained.

[0035] The authorized frequency band of 230M in power is composed of 40 discrete 25kHz frequency points. In order to make full use of the power authorized frequency points and not interfere with adjacent frequency points, the present invention proposes a multi-frequency point MFSK based on power, which can use multiple power frequency points for communication, and an independent MFSK modulation method is adopted within each 25kHz.

[0036] As Figure 1 shown in the schematic diagram of the power multi-frequency point FSK technology provided by this embodiment, the power frequency points are discrete 25kHz. 2FSK modulation is adopted within each 25kHz bandwidth, and the transmission rate of each frequency point can be 12kbps (assuming the effective bandwidth is 24kHz). The data rate is increased by aggregating multiple frequency points. For example, aggregating 4 frequency points results in a rate of 48kbps, and aggregating 5 frequency points is 60kbps.

[0037] Since the 230MHz frequency band is divided with a bandwidth of 25kHz, when 2FSK modulation is adopted for each frequency point, an OFDM system with a subcarrier interval of 12.5kHz can be used for transmission, and its characteristic is that at most only one frequency point is activated among every two subcarriers.

[0038] Assume that the radio frequency bandwidth of the edge device is 3.2MHz. When the subcarrier interval is 12.5kHz, there are 256 subcarriers in total. Assume that the center frequencies of the available 25kHz frequency bands in power are f1, f2, …, f K , the correspondence between the transmitted bit b i and the frequency is:

[0039]

[0040] The data domain representation of the transmitted sparse OFDM symbol is as follows:

[0041]

[0042] Performing IFFT transformation on the sequence d1, d2, …, d 256 can obtain the multi-frequency point MFSK transmission signal of the edge device, that is:

[0043]

[0044] where represents the frequency domain data corresponding to the nth OFDM symbol, T srepresents the duration of an OFDM symbol, and g(t) is a rectangular pulse with a time width of T s That is:

[0045]

[0046] When the edge device receives a multi - frequency - point MFSK system, in order to reduce the processing complexity at the receiving end, the present invention adopts a channelization technology based on a polyphase filter bank, which can quickly realize the channelization of the received signal. In the FSK system of the present invention, this technology can be used to quickly separate and sample multiple 25 - kHz channels, and its principle is as Figure 2 shown. Polyphase filtering channelization is an improvement on the traditional channelization structure. By sharing a low - pass filter in each branch, the utilization rate of resources is improved, and at the same time, polyphase decimation is adopted to improve the operation efficiency of subsequent filtering and FFT.

[0047] During the uplink receiving process, assuming that the transmission times of different power terminals are random, when N power terminals transmit simultaneously, the received signal of the edge - side power receiving device can be expressed as:

[0048]

[0049] In the formula, w c is the carrier frequency, T n is the transmission delay from the nth terminal to the edge device, m f is the frequency - modulation index, α n (t - T n ) is the data stream transmitted by the nth terminal, and w n is the symbol rate.

[0050] The sampled data can be expressed as:

[0051]

[0052] In the formula, σ represents noise.

[0053] The receiving end uses a poly - filter bank for channelization. Assuming that the narrow - band prototype filter is:

[0054]

[0055] In the formula, the length of the narrow - band prototype filter is K. It is decomposed into D groups in the following way, and assuming that K is an integer multiple of D, the above formula is decomposed and expressed as:

[0056]

[0057] Among them

[0058] Let Then

[0059] Similarly, the received data is also grouped and multiplied in the above manner by to obtain:

[0060]

[0061] Filtering is performed for each data group, and we get:

[0062] r k = y k * E k ,

[0063] The data after channelization can be expressed as:

[0064] c = ifft([r1 r2…r D ) = (c0, c1,…, c D-1 ),

[0065] In the formula, c0 to c D-1 represent the narrowband signals of the 1st to Dth channels.

[0066] For the MFSK demodulation of each path of data after channelization by the multi-channel filter bank of the present invention, the frequency discrimination method is adopted, and the used frequency discrimination algorithm does not adopt the traditional arctangent operation for frequency discrimination, but adopts a method to avoid the arctangent operation.

[0067] The derivative of the traditional arctangent function is expressed as follows:

[0068]

[0069] In the formula, Q(n) and I(n) respectively represent the real part and the imaginary part of the received signal c k , k = 0, 1,…, D - 1 at the nth sampling moment.

[0070] From the constellation diagram, since FSK is a constant envelope modulation, that is, all points on the constellation diagram are on the unit circle, so there is:

[0071] cosθ1 = I(n - 1), sinθ1 = Q(n - 1

[0072] cosθ2 = I(n), sinθ2 = Q(n),

[0073] Then there is:

[0074] SinΔθ(n) = sin(θ2 - θ1) = sinθ2cosθ1 - cosθ2sinθ1

[0075] = Q(n)I(n - 1) - I(n)Q(n - 1),

[0076] When Δθ(n) is very small, according to the small-angle approximation rule, SinΔθ(n) is approximately equal to Δθ(n), and further simplification gives X(n), that is:

[0077] m f α n ∝Δθ(n) = SinΔθ(n) = Q(n)I(n - 1) - I(n)Q(n - 1)

[0078] In the formula, I(n - 1) and I(n) are the in-phase received signals at times n - 1 and n respectively, Q(n - 1) and Q(n) are the quadrature-phase received signals at times n - 1 and n respectively, Δθ(n) represents the phase change at time n, m f represents the frequency modulation index, and α n represents the modulation symbol.

[0079] The traditional quadrature demodulation method calculates the trigonometric function of θ(n) and cannot be approximated. Only the method of calculation or looking up the inverse trigonometric function table can be used; the advantage of the small-angle approximation demodulation method is that it calculates the trigonometric function of Δθ(n) and can be approximated.

[0080] The system structure of the small-angle approximation demodulation method used in the present invention Figure 3 As shown, the obtained result is the output of differential frequency discrimination, which is the instantaneous frequency signal of MFSK carrier modulation. According to the small-angle approximation demodulation method, the present invention obtains the simplest algorithm. Since there are only two multiplications and one subtraction, and there are no calculations such as arctangent and division, the calculation amount is greatly simplified.

[0081] Furthermore, the present invention can also adopt a higher intermediate frequency sampling rate, but it can only be applied in the case of a smaller modulation angle.

[0082] What is obtained after MFSK demodulation is the DPSK subcarrier modulation signal with stable frequency. This signal enters the differential demodulation module for demodulation. The principle of differential demodulation in the differential demodulation module is to directly compare the phase difference between the front and rear symbols, so as to restore the transmitted binary information. Since the function of code reverse transformation is completed during demodulation, there is no need for a code reverse converter in the demodulator, that is, no dedicated coherent carrier is required. The principle block diagram is as Figure 4 shown. The FFT is used at the transmitting end to generate FSK, and channelized parallel demodulation is used at the receiving end.

[0083] Embodiment 2

[0084] The present invention also provides a channelized demodulation system for a multi - level MFSK system of power Internet of Things services, including a processor and a storage medium. The storage medium is used to store instructions, and the processor is used to operate according to the instructions to execute the steps of a channelized demodulation method for a multi - level MFSK system of power Internet of Things services.

[0085] Example 3

[0086] A computer program is stored on a computer-readable storage medium. When the program is executed by a processor, it implements the steps of a channel demodulation method for a multi - level MFSK system of power Internet of Things services.

[0087] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer - available storage media (including but not limited to disk memory, CD - ROM, optical memory, etc.) containing computer - available program code.

[0088] The present application is described with reference to the flowcharts and / or block diagrams of methods, systems, and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of flows and / or blocks in the flowchart and / or block diagram can also be implemented. These computer program instructions can be provided to the processor of a general - purpose computer, a special - purpose computer, an embedded processor, or other programmable data - processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data - processing devices generate means for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0089] These computer program instructions can also be stored in a computer - readable memory that can direct a computer or other programmable data - processing device to work in a specific manner, so that the instructions stored in the computer - readable memory generate a manufactured article including instruction means, and the instruction means implements the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0090] These computer program instructions can also be loaded onto a computer or other programmable data - processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer - implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one Figure 1 flow or multiple flows and / or blocks Figure 1 block or multiple blocks.

[0091] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A channel demodulation method for a multi - base MFSK system of power Internet of Things services, characterized in that, The method includes the following steps: The signal sending end communicates using multiple power frequency points, and the power frequency points send modulated signals in the MFSK manner; when there are multiple MFSK sending frequency points at the signal sending end, sparse OFDM is used for sending; The signal receiving end channels the received modulated signal through a polyphase filter bank to obtain the channelized data; The channelized data undergoes MFSK demodulation to obtain the modulated instantaneous frequency signal; the MFSK demodulation uses the frequency discrimination method, and the frequency discrimination method uses small angle approximation demodulation.

2. The method for channelization demodulation of a multi-level MFSK system for power Internet of Things services according to claim 1, characterized in that: The calculation formula of the instantaneous frequency signal after small angle approximation demodulation is as follows: ； Wherein, and are respectively and in-phase received signals at moments, and are respectively and quadrature-phase received signals at moments, represents phase change at a moment, represents the frequency modulation index, represents the modulation symbol.

3. A channel demodulation method for a multi - base MFSK system of power Internet of Things services according to claim 1, characterized in that, The signal receiving end groups the received modulated signal, and each branch modulated signal after grouping is filtered by multiple low-pass filters to obtain the channelized data.

4. The method for channelization demodulation of a multi-level MFSK system for power Internet of Things services according to claim 1, characterized in that: The power frequency points are discrete 25 kHz bandwidths, and 2FSK modulation is used within each 25 kHz bandwidth.

5. The method for channelization demodulation of a multi-level MFSK system for power Internet of Things services according to claim 1, characterized in that: It also includes performing differential demodulation on the obtained instantaneous frequency signal and simultaneously completing code inverse transformation.

6. A channel demodulation system for a multi - base MFSK system of power Internet of Things services, characterized in that, It includes a processor and a storage medium; The storage medium is used to store instructions; The processor is used to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, the steps of the method according to any one of claims 1 to 5 are implemented.

Images