Dsc modulation method based on digital communication chip

Abstract

The application discloses a DSC modulation method based on a digital communication chip, which adjusts a frequency division coefficient in real time and continuously, so as to adjust a frequency in real time and continuously, and realizes FM modulation of a DSC audio waveform, wherein the frequency division coefficient comprises an integer part and a decimal part. The application can directly realize a frequency modulation signal required by the DSC by using a traditional digital communication chip, improves utilization of the chip, realizes the frequency modulation by using a low-cost digital communication chip, greatly reduces cost, and is suitable for promotion.

Description

Technical Field

[0001] This invention belongs to the field of communication technology, specifically relating to a DSC modulation method based on a digital communication chip. Background Technology

[0002] DSC (Digital Selective Calling) is an important communication technology for maritime communication. It enables selective calling based on digital signaling and can also provide distress alerts in distress situations. It is an important technical guarantee for ensuring maritime navigation safety.

[0003] DSC technology is a subcarrier modulation technique, which first modulates the 0 and 1 sequence in the DSC message into the corresponding audio signal. According to the DSC specification, 1 bit of 1 information corresponds to a 2100Hz sine wave for 0.833ms (i.e., 1 / 1200 seconds), and 1 bit of 0 information corresponds to a 1300Hz sine wave for 0.833ms (i.e., 1 / 1200 seconds).

[0004] Traditional DSC implementation methods are mostly based on analog modulation techniques. This involves first generating a corresponding audio signal based on the DSC information, then frequency-modulating this audio signal, amplifying it, and transmitting it through an antenna. Figure 1 As shown.

[0005] Traditional DSC modulation is based on analog FM modulation, which has many problems, such as poor consistency of modulation frequency offset parameters, requiring adjustment, which is not conducive to mass production, and also not conducive to the miniaturization and low power consumption of equipment. For marine life rescue equipment, low power consumption and miniaturization are very important.

[0006] With the advancement of technology, monolithic multifunctional digital communication chips have emerged. These chips take binary or quaternary digital signals as input, and their internal circuits generate specified modulation waveforms according to certain algorithms, thereby achieving end-to-end communication.

[0007] Depend on Figure 1 The DSC modulation method shown requires the generation of a continuous analog FM signal based on the DSC audio signal. Obviously, the frequency of the output signal cannot be directly controlled using binary or quaternary communication methods. Therefore, this type of digital communication chip cannot directly realize the frequency modulation signal required by DSC. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a DSC modulation method based on a digital communication chip.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] This invention discloses a DSC modulation method based on a digital communication chip. The method utilizes the digital communication chip to adjust the frequency division coefficient in real time and continuously, thereby adjusting the frequency in real time and continuously to achieve FM modulation of the DSC audio waveform. The frequency division coefficient includes an integer part and a fractional part.

[0011] Based on the above technical solution, the following improvements can be made:

[0012] As a preferred embodiment, within a certain frequency variation range, there is a linear relationship between the frequency variation and the register configuration parameter values ​​of the digital communication chip, as shown in the following formula:

[0013]

[0014] Where: k is the linear relationship coefficient;

[0015] Δf is the change in frequency;

[0016] ΔR represents the change in the register configuration parameter value.

[0017] As a preferred approach, frequency adjustment is achieved by changing the register configuration parameter values, as shown in the following formula:

[0018] f n =f c +k×ΔR n ;

[0019]

[0020] R n =R c +ΔR n ;

[0021] Where: f c The frequency of the center point;

[0022] f n The modulation frequency;

[0023] ΔR n Modulation parameters for configuring parameter values ​​for registers;

[0024] R c Configure parameter values ​​for the register at the center frequency point;

[0025] R n Configure the parameter values ​​for the corrected registers.

[0026] As a preferred option, the modulation parameter ΔR of the register configuration parameter value is... n We obtain it from the following formula:

[0027] ΔR n =XkSn ;

[0028] Where: X is the expansion coefficient;

[0029] S n These are sampled values.

[0030] As the preferred option, S n We obtain it from the following formula:

[0031]

[0032] Δθ i =2πf m T s ;

[0033] f m The frequency corresponding to the m-th symbol;

[0034] T s The sampling period;

[0035] A m This represents the amplitude value corresponding to the m-th symbol;

[0036]

[0037]

[0038] As a preferred solution, in S n In the sequence, its value range is S n For ∈(-1.75, 1.75), FM modulation should meet the requirement that the absolute value of the modulation frequency deviation is not greater than 5kHz. X is obtained through the following formula:

[0039]

[0040] As a preferred solution, the digital communication chip is electrically connected to the MCU, and the MCU has an internal clock interrupt that can correct the register configuration parameter values ​​at equal intervals.

[0041] As a preferred option, the MCU uses a 16-bit SPI interface to be electrically connected to the digital communication chip.

[0042] This invention discloses a DSC modulation method based on a digital communication chip, which has the following characteristics:

[0043] Beneficial effects:

[0044] First, traditional digital communication chips can directly realize the frequency modulation signal required by DSC, improving chip utilization. Furthermore, frequency modulation can be achieved using low-cost digital communication chips, greatly reducing costs and making it suitable for widespread application.

[0045] Second, frequency adjustment is achieved by changing the values ​​of register configuration parameters. During signal transmission, the parameters are simply written into the corresponding registers in a timely manner. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A schematic diagram of a traditional DSC modulation method provided by existing technology.

[0048] Figure 2 The circuit diagram provided for an embodiment of the present invention.

[0049] Figure 3 This is a data reconstruction diagram provided for an embodiment of the present invention. Detailed Implementation

[0050] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0052] The expression “includes” is an “open-ended” expression, which means that there is a corresponding component or step, and should not be interpreted as excluding additional components or steps.

[0053] To achieve the objectives of this invention, in some embodiments of the DSC modulation method based on a digital communication chip, the CMT2310A is selected as the digital communication chip. However, the scope of protection of this invention is not limited to the CMT2310A. The CMT2310A chip provides digital communication functions for OOK, FSK / 4FKS, GFSK / 4GFSK, and other standards. Various communication methods can be easily implemented using this chip or a similar chip. The operating mode settings of the CMT2310A chip are shown in Table 1.

[0054] This invention discloses a DSC modulation method based on a digital communication chip. First, the digital communication chip (such as CMT2310A) is set to OOK mode, and the input modulation signal is constantly set to 1, that is, a continuous no-modulation carrier output state is maintained. The frequency division coefficient is adjusted in real time and continuously through the chip interface, thereby adjusting the frequency in real time and continuously to realize FM modulation of the DSC audio waveform. The frequency division coefficient includes an integer part and a fractional part.

[0055] Table 1. CMT2310A Operating Mode Settings

[0056]

[0057] The CMT2310A contains a digital phase-locked loop (DPLL) based on fractional frequency division.

[0058] It is worth noting that the circuit involved in this invention is as follows: Figure 2 As shown, the components include: CMT2310A chip, MCU, power amplifier, and antenna. Using the RFPDK software provided in the CMT2310A production kit, the CMT2310A configuration parameter header can be generated. By comparing the generated header file cmt2310a_params.h at different frequencies, the parameters corresponding to the frequency division coefficients can be determined.

[0059] Furthermore, within a certain frequency variation range, there is a linear relationship between the frequency variation and the register configuration parameter values ​​of the CMT2310A chip, as shown in the following formula:

[0060]

[0061] Where: k is the linear relationship coefficient;

[0062] Δf is the change in frequency;

[0063] ΔR represents the change in the register configuration parameter value.

[0064] Specifically, the relationship between frequency variation and register configuration parameter values ​​of the CMT2310A chip is shown in Table 2.

[0065] Table 2 Register configuration parameter values ​​and their variations at different frequencies

[0066] frequency Register (0x12) Register (0x11) Variation / 5kHz 156.515 0x26 0x66 ～ 156.520 0x33 0x33 0xCCD 156.525 0x40 0x00 0xCCD 156.535 0x4C 0XCC 0xCCC 156.540 0x59 0x99 0xCCD

[0067] Therefore, according to Table 2, we can obtain...

[0068]

[0069] When the center frequency is 156.525MHz, the frequency increases or decreases by 1.907Hz for every 1-bit change in the register configuration parameter value.

[0070] Frequency adjustment is achieved by changing the values ​​of register configuration parameters, as shown in the following formula:

[0071] f n =f c +k×ΔR n ;

[0072]

[0073] R n =R c +ΔR n ;

[0074] Where: f c The frequency of the center point;

[0075] f n The modulation frequency;

[0076] ΔR n Modulation parameters for configuring parameter values ​​for registers;

[0077] R c Configure the parameter value for the center frequency register. For the 156.525MHz frequency point, the value is always 0x4000.

[0078] R n Configure the parameter values ​​for the corrected registers.

[0079] According to R n =R c +ΔR n It can change the oscillation frequency of CMT2310A in real time and dynamically, thereby realizing FM modulation of arbitrary baseband waveforms, thus providing the possibility of realizing DSC modulation.

[0080] Modulation parameter ΔR of register configuration parameter value n We obtain it from the following formula:

[0081] ΔR n =XkS n ;

[0082] Where: X is the expansion coefficient;

[0083] S n These are sampled values.

[0084] Furthermore, S n We obtain it from the following formula:

[0085]

[0086] Δθ t =2nf m T s ;

[0087] f m The frequency corresponding to the m-th symbol;

[0088] T s The sampling period is, for example, 1 / 48kHz;

[0089] A m This represents the amplitude value corresponding to the m-th symbol;

[0090]

[0091]

[0092] according to The formula can be used to obtain a baseband audio signal with continuous phase and pre-emphasis, which is called the DSC audio baseband modulation signal and is used for FM modulation.

[0093] Furthermore, in S n In the sequence, in S n In the sequence, its value range is S n ∈(-1.75, 1.75), meaning the maximum value is +1.75 or -1.75. FM modulation should meet the requirement that the absolute value of the modulation frequency deviation is not greater than 5kHz. X is obtained through the following formula:

[0094]

[0095] In summary, ΔR n =XkS n =1498 × 1.907 × S n ≈2860S n .

[0096] This allows us to obtain several corresponding corrected R values. n During the transmission process, the carrier frequency can be adjusted in real time simply by writing it dynamically into the corresponding register.

[0097] Based on the above embodiments, the CMT2310A chip is electrically connected to the MCU, and the MCU has an internal clock interrupt, which can correct the register configuration parameter values ​​at equal intervals.

[0098] Theoretically, the faster the correction speed, the more ideal the FM waveform will be. When resources allow, use the highest possible clock interrupt, such as 120kHz, 96kHz, or 48kHz.

[0099] Specifically, in the case of a 48kHz interrupt, two register values ​​need to be corrected simultaneously each time, namely the 17th (0x11) and 18th (0x12) register values ​​in the CMT2310Apage1 register group. The method is as follows: take the i-th R... i The value (i = 1, 2, ..., n) is used to take the lower 8 bits of information and write them to the 17th (0x11) register. The higher 8 bits are taken and written to the 18th (0x12) register.

[0100] In the CMT2310A interface specification, the method for writing registers is to first write the address value of the register to be accessed, such as 0x11, through the 8-bit SPI interface, and then write the actual parameters through the 8-bit SPI interface. Each modification requires two SPI accesses, which greatly reduces efficiency and delays parameter configuration time, thus affecting the modulation accuracy to some extent.

[0101] Therefore, in this embodiment of the invention, the MCU uses a 16-bit SPI interface to be electrically connected to the digital communication chip, that is, 16 bits of data can be written at a time through the SPI interface.

[0102] The data is reassembled according to the CMT2310A SPI interface specification, such as... Figure 3 As shown, address information and data information are integrated into a 16-bit unit, and one correction corresponds to two 16-bit data units, or 32-bit data units.

[0103] After the data is reassembled, it can be read and written according to the standard 16-bit SPI specification, which simplifies and speeds up the read and write process, and facilitates direct DMA read and write operations, which also provides the possibility of further improving the correction speed.

[0104] This invention discloses a DSC modulation method based on a digital communication chip, which has the following characteristics:

[0105] Beneficial effects:

[0106] First, traditional digital communication chips can directly realize the frequency modulation signal required by DSC, improving chip utilization. Furthermore, frequency modulation can be achieved using low-cost digital communication chips, greatly reducing costs and making it suitable for widespread application.

[0107] Second, frequency adjustment is achieved by changing the values ​​of register configuration parameters. During signal transmission, the parameters are simply written into the corresponding registers in a timely manner.

[0108] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A DSC modulation method based on a digital communication chip for implementing maritime digital selective calling modulation, characterized in that, The application relates to a method for realizing FM modulation of a DSC audio waveform. Firstly, the digital communication chip is set to an OOK modulation mode, and an input modulation signal is constantly set to 1, so that the digital communication chip outputs a continuous unmodulated carrier; Then, on the basis, a frequency is continuously and real-timely adjusted by using the digital communication chip to continuously and real-timely adjust a frequency division coefficient, so that FM modulation of the DSC audio waveform is realized, wherein the frequency division coefficient comprises an integer part and a decimal part. The DSC audio waveform is generated according to a DSC specification, in a baseband modulation signal, binary '1' corresponds to a 2100Hz sine wave, binary '0' corresponds to a 1300Hz sine wave, each symbol lasts for 0.833ms, and an absolute value of a modulation frequency offset of the FM modulation is not greater than 5kHz. In a frequency variation range, a linear relationship exists between variation of the frequency and a register configuration parameter value of the digital communication chip, and the frequency is adjusted by using variation of the register configuration parameter value.

2. The DSC modulation method of claim 1, wherein, In a frequency variation range, a linear relationship exists between variation of the frequency and a register configuration parameter value of the digital communication chip, and the frequency is adjusted by using variation of the register configuration parameter value. Wherein, k is a linear relationship coefficient; Delta f is a variation value of the frequency; and Delta R is a variation value of the register configuration parameter value. The frequency is adjusted by using variation of the register configuration parameter value, and the frequency is adjusted by using variation of the register configuration parameter value. Wherein, X is an expansion coefficient.

3. The DSC modulation method of claim 2, wherein, The digital communication chip is electrically connected with an MCU, and the MCU has a clock interrupt inside, so that the register configuration parameter value can be corrected at equal intervals. f n = f c + k x AR n ; R n = R c + ΔR n ; wherein: f c is the frequency of the center frequency point; f n is the modulation frequency; ΔR n modulation parameters for configuring parameter values for registers; R c configuring a parameter value for a register as a center frequency point; R n is the modified register configuration parameter value.

4. The DSC modulation method of claim 3, wherein, Modulation parameter AR of the register configuration parameter value n is obtained by ΔR n = XkS n ; The MCU is electrically connected with the digital communication chip by using a 16bit SPI interface. S n is a sample value.

5. The DSC modulation method of claim 4, wherein, S n By the following formula: Δθ i = 2πf m T s ; f m is the frequency corresponding to the mth symbol; T s is the sampling period; A m Am is the amplitude value corresponding to the mth symbol; 6. The DSC modulation method of claim 5, wherein, In S n The sequence has a value range of S n The FM modulation should satisfy the requirement that the absolute value of the modulation frequency deviation is not greater than 5 kHz, and X is obtained by the following formula:

7. The DSC modulation method according to any one of claims 1 to 6, characterized in that, ​ 8. The DSC modulation method of claim 7, wherein, ​

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