CN113810068A

CN113810068A - AIS-MOB radio frequency signal generating circuit

Info

Publication number: CN113810068A
Application number: CN202111046083.4A
Authority: CN
Inventors: 张福洪; 袁啸天; 栾慎吉; 易志强
Original assignee: Hangzhou Dianzi University
Current assignee: Hangzhou Dianzi University
Priority date: 2021-09-07
Filing date: 2021-09-07
Publication date: 2021-12-17
Anticipated expiration: 2041-09-07
Also published as: CN113810068B

Abstract

The invention relates to an AIS-MOB radio frequency signal generating circuit, aiming at the defects of large volume, high power consumption and cost, complex debugging and the like of the existing AIS-MOB transmitting circuit, the scheme of the invention is as follows: the transmitting circuit is composed of an MCU, a DAC, a VCXO1, a VCXO2, a first NAND gate, a second NAND gate, a third NAND gate and a band-pass filter. The MCU modulates the information to be sent into digital data and sends the digital data into the DAC, and the DAC converts the digital signal into an analog signal which is matched with the VCXO1, the VCXO2 and the band-pass filter to generate GMSK signals of two transmitting frequency points. The MCU, the first NAND gate, the second NAND gate and the third NAND gate are matched to complete a channel selection function.

Description

AIS-MOB radio frequency signal generating circuit

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to an AIS-MOB radio frequency signal generating circuit.

Background

An AIS portable emergency position indicating beacon (AIS-MOB) is a small and portable distress position indicating and alarming device developed based on an Automatic Identification System (AIS) of a ship. The device is built in a Global Positioning System (GPS), and can rapidly acquire accurate position information and coordinate a Universal Time Clock (UTC). When the equipment is immersed in water or manually started, information such as the positions of the persons in danger and the like is transmitted in a broadcasting mode on 87 channels and 88 channels of a Very High Frequency (VHF) frequency band at sea, and the information can be received by an AIS base station, other ships and aircrafts equipped with AIS equipment, so that rescue workers can quickly and accurately position and rescue the persons in danger. The AIS-MOB should have the characteristics of small volume, light weight, low cost, long working time, long working distance and the like.

The existing AIS-MOB generally adopts a special baseband modulation chip or a Field Programmable Gate Array (FPGA), and cooperates with a phase-locked loop to form a transmitting circuit. The special baseband modulation chip or the FPGA encodes the information into standardized AIS data and forms modulation signal output, and the phase-locked loop circuit carries out carrier modulation on the modulation signal so as to obtain a radio frequency signal. Although the scheme reduces the development period and is flexible to realize, AIS-MOB cost and power consumption are high, and large-scale popularization and long-time work are not facilitated. The phase-locked loop generally comprises a phase discriminator, a loop filter and a voltage-controlled oscillator, the loop contains more discrete devices, the occupied space of hardware is larger, the miniaturization of AIS-MOB is not facilitated, and meanwhile, the debugging complexity is increased. Aiming at the defects, the AIS-MOB radio frequency signal generating circuit is designed, and has lower cost and power consumption and smaller circuit size on the premise of ensuring performance indexes.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides the AIS-MOB radio frequency signal generating circuit, which further reduces the cost and power consumption of the prior scheme on the premise of ensuring the performance index and reduces the volume.

The AIS signal emission process in the invention is as follows: after the equipment is started in water or manually, the MCU synchronizes by using UTC time transmitted by the GPS and performs related coding on position information transmitted by the GPS; the MCU then randomly selects 8 AIS messages for 16 consecutive seconds per minute, once every 2 seconds, each transmission lasting 26.67 milliseconds, with 8 transmission processes alternating 87, 88 channels.

The technical scheme of the invention is as follows: an AIS-MOB radio frequency signal generating circuit comprising: MCU, DAC, VCXO1, VCXO2, first NAND gate, second NAND gate, third NAND gate, band-pass filter.

The input signal includes: switching signals and GPS messages; the general IO port P1 of the MCU is connected with the SCLK pin of the DAC, the general IO port P2 is connected with the DIN pin of the DAC, and the general IO port P3 is connected with the DAC

The pins are connected, the general IO port P4 is connected with the input end A of the first NAND gate, and the general IO port P5 is connected with the input end A of the second NAND gate; the only output end of the DAC is respectively connected with the input ends of the VCXO1 and the VCXO 2; the only output end of the VCXO1 is connected with the input end B of the first NAND gate, and the only output end of the VCXO2 is connected with the input end B of the second NAND gate; the unique output end of the first NAND gate is connected with the input end A of the third NAND gate, the unique output end of the second NAND gate is connected with the input end B of the third NAND gate, and the unique output end of the third NAND gate is connected with the unique input end of the band-pass filter; the only output of the filter outputs a Gaussian Minimum Shift Keying (GMSK) radio frequency signal.

The input signal is composed of a switching signal and a GPS message. The switch signals come from a starting button, a shutdown button and a water sensor. When a starting button outside the position indicator is pressed, the power circuit is conducted, and the equipment starts to enter a working state; when a shutdown key outside the position indicator is pressed, the power circuit is disconnected, and the equipment is powered off and enters a shutdown state; the position indicating mark is provided with a water immersion sensor, when the sensor is immersed in water, a power circuit is conducted, and the equipment starts to enter a working state. The GPS message comes from a GPS positioning module, and the MCU mainly extracts longitude and latitude information and UTC time in the message.

The MCU is a signal processing core of the whole system. During each transmission, after Cyclic Redundancy Check (CRC), framing and reverse non-return to zero coding (NRZI) are carried out on transmission data inside the MCU, the transmission data are processed by a Gaussian filter with parameters meeting AIS standards to obtain digital modulation data, the digital modulation data are serially input into the DAC through a general IO port P2 of the MCU, the transmission rate of the digital modulation data is Nx 9.6kBaud (N is a digital oversampling rate), and the transmission time is 26.67 milliseconds; meanwhile, the synchronizing signal output by the P3 changes from high level to low level, and changes back to high level after being kept for 26.67 milliseconds; p1 outputs a clock signal of Nx 9.6kHz to the SCLK pin of the DAC. When the MCU selects to transmit the AIS message on the 87 channel, the general IO port P4 is controlled to output a high level signal of 26.67 milliseconds, and the P5 keeps a low level signal; when the MCU selects to transmit the AIS message on the 88 channel, the general IO port P5 is controlled to output a high level signal of 26.67 milliseconds, and the P4 keeps a low level signal; when the AIS message is not transmitted, the general IO ports P4, P5 hold a low level signal.

The DAC is used for converting the digital signals transmitted by the MCU into analog signals and sending the analog signals into voltage-controlled input ends of the VCXO1 and VCXO2 as modulation signals. The maximum and minimum voltages of the DAC output signal correspond to the highest and lowest frequencies of the VCXO generated signal, respectively, the difference between the highest and lowest frequencies being 0.96kHz, i.e. the 5 th harmonic is a GMSK signal with a frequency modulation index of 0.5.

The main frequency of the VCXO1 is 32.395MHz, and the 5 th harmonic of the signal is 161.975MHz, corresponding to the 87 channels of the marine mobile communication band.

The main frequency of the VCXO2 is 32.405MHz, and the 5 th harmonic of the signal is 162.025MHz, corresponding to 88 channels of the marine mobile communication band.

The first nand gate functions to switch the signal from the VCXO 1. The input end A of the first NAND gate receives a control signal from a general IO port P4 of the MCU, and the input end B receives a GMSK signal from the VCXO 1. The first nand gate converts the signal output by the VCXO1 into an approximately square wave or high level signal according to the control signal.

The second nand gate functions to switch the signal from the VCXO 2. The input end A of the second NAND gate receives a control signal from the general IO port P5 of the MCU, and the input end B receives a GMSK signal from the VCXO 2. The second nand gate converts the signal output by the VCXO2 into an approximately square wave or high level signal according to the control signal.

The third NAND gate is used for selectively outputting one of the output signals of the first NAND gate and the second NAND gate according to the control signal. When the AIS message is not sent, the third NAND gate continuously outputs a low level signal.

The center frequency of the band-pass filter is 162MHz, the bandwidth is 10MHz, and the band-pass filter is used for filtering out fifth harmonic signals of VCXO1 and VCXO2, namely the center frequencies are 161.975MHz and 162.025MHz, and the signals are output as AIS radio frequency signals.

The invention has the beneficial effects that: compared with a circuit scheme adopting a special modulation chip or an FPGA and a phase-locked loop, the invention uses the analog modulation signal output by the DAC and controls the VCXO to generate the AIS radio-frequency signal by matching with a corresponding logic circuit, thereby effectively reducing the cost and the power consumption of a transmitting circuit, reducing the debugging difficulty, reducing the circuit volume and being beneficial to the popularization of AIS-MOB.

Drawings

FIG. 1 is a schematic diagram of an AIS-MOB radio frequency signal generating circuit according to the present invention;

fig. 2 is a circuit of a band pass filter of the present invention.

Detailed Description

Example 1

Fig. 1 shows an AIS-MOB radio frequency signal generating circuit according to the present invention, which includes an MCU, a DAC, a VCXO1, a VCXO2, a first nand gate, a second nand gate, a third nand gate, and a band pass filter.

The pins are connected, the general IO port P4 is connected with the input end A of the first NAND gate, and the general IO port P5 is connected with the input end A of the second NAND gate; the only output end of the DAC is respectively connected with the input ends of the VCXO1 and the VCXO 2; the only output end of the VCXO1 is connected with the input end B of the first NAND gate, and the only output end of the VCXO2 is connected with the input end B of the second NAND gate; the unique output end of the first NAND gate is connected with the input end A of the third NAND gate, the unique output end of the second NAND gate is connected with the input end B of the third NAND gate, and the unique output end of the third NAND gate is connected with the unique input end of the band-pass filter; the only output of the filter outputs the GMSK radio frequency signal.

The MCU is a signal processing core of the whole system. During each transmission, after CRC (cyclic redundancy check), framing and NRZI (non-return error) coding are carried out on transmission data in the MCU, the transmission data are processed by a Gaussian filter with parameters meeting AIS (automatic identification system) standards to obtain digital modulation data, the digital modulation data are serially input into a DAC (digital-to-analog converter) through a general IO port P2 of the MCU, the transmission rate of the digital modulation data is Nx 9.6kBaud (N is a digital oversampling rate), and the transmission time is 26.67 milliseconds; meanwhile, the synchronizing signal output by the P3 changes from high level to low level, and changes back to high level after being kept for 26.67 milliseconds; p1 outputs a clock signal of Nx 9.6kHz to the SCLK pin of the DAC. When the MCU selects to transmit the AIS message on the 87 channel, the general IO port P4 is controlled to output a high level signal of 26.67 milliseconds, and the P5 keeps a low level signal; when the MCU selects to transmit the AIS message on the 88 channel, the general IO port P5 is controlled to output a high level signal of 26.67 milliseconds, and the P4 keeps a low level signal; when the AIS message is not transmitted, the general IO ports P4, P5 hold a low level signal.

Fig. 2 is a circuit of a band pass filter of the present invention. The band-pass filter has a center frequency of 162MHz and a bandwidth of 10MHz, and is used for filtering out fifth harmonic signals of VCXO1 and VCXO2, namely, the center frequencies are 161.975MHz and 162.025MHz, and the fifth harmonic signals are output as AIS radio frequency signals. The filter is of a butterworth structure type and is designed as shown in figure 2.

Claims

1. An AIS-MOB radio frequency signal generating circuit, comprising: the MCU, the DAC, the VCXO1, the VCXO2, a first NAND gate, a second NAND gate, a third NAND gate and a band-pass filter;

the input signal includes: switching signals and GPS messages;

a general IO port P1 of the MCU is connected with an SCLK pin of the DAC, a general IO port P2 is connected with a DIN pin of the DAC, a general IO port P3 is connected with a SYNC pin of the DAC, a general IO port P4 is connected with an input end A of the first NAND gate, and a general IO port P5 is connected with an input end A of the second NAND gate; the output end of the DAC is electrically connected with the input ends of the VCXO1 and the VCXO 2; the output end of the VCXO1 is connected with the input end B of the first NAND gate, and the output end of the VCXO2 is connected with the input end B of the second NAND gate; the output end of the first NAND gate is connected with the input end A of the third NAND gate, the output end of the second NAND gate is connected with the input end B of the third NAND gate, and the output end of the third NAND gate is connected with the input end of the band-pass filter; the output end of the filter outputs GMSK radio frequency signals;

the switch signals come from a starting button, a shutdown button and a water immersion sensor; the GPS message comes from a GPS positioning module, and the MCU extracts longitude and latitude information and UTC time in the GPS message;

when the MCU sends data each time, the MCU carries out CRC check, framing and NRZI coding on the sent data, the data are processed by a Gaussian filter with parameters meeting AIS standards to obtain digital modulation data, the data are serially input into the DAC through a general IO port P2 of the MCU, the transmission rate is Nx 9.6kBaud (N is a digital oversampling rate), and the transmission time is 26.67 milliseconds; meanwhile, the synchronizing signal output by the P3 changes from high level to low level, and changes back to high level after being kept for 26.67 milliseconds; p1 outputs a clock signal of Nx 9.6kHz to SCLK pin of DAC; when the MCU selects to transmit the AIS message on the 87 channel, the general IO port P4 is controlled to output a high level signal of 26.67 milliseconds, and the P5 keeps a low level signal; when the MCU selects to transmit the AIS message on the 88 channel, the general IO port P5 is controlled to output a high level signal of 26.67 milliseconds, and the P4 keeps a low level signal; when the AIS message is not transmitted, the general IO ports P4, P5 hold low level signals;

the DAC is used for converting the digital signal transmitted by the MCU into an analog signal and transmitting the analog signal serving as a modulation signal to the voltage-controlled input ends of the VCXO1 and the VCXO 2; the maximum voltage and the minimum voltage of the DAC output signal respectively correspond to the highest frequency and the lowest frequency of a VCXO generated signal, the difference between the highest frequency and the lowest frequency is 0.96kHz, namely, the 5 th harmonic is a GMSK signal with the frequency modulation index of 0.5;

the main frequency of the VCXO1 is 32.395MHz, the 5 th harmonic of the signal is 161.975MHz, and the signal corresponds to 87 channels of a maritime mobile communication frequency band;

the main frequency of the VCXO2 is 32.405MHz, the 5 th harmonic of the signal is 162.025MHz, and the signal corresponds to 88 channels of a maritime mobile communication frequency band;

the first NAND gate is used for controlling the on-off of a signal from the VCXO 1; an input end A of the first NAND gate receives a control signal from a general IO port P4 of the MCU, and an input end B receives a GMSK signal from the VCXO 1; the first NAND gate converts a signal output by the VCXO1 into an approximate square wave or a high-level signal according to a control signal;

the second NAND gate is used for controlling the on-off of a signal from the VCXO 2; an input end A of the second NAND gate receives a control signal from a general IO port P5 of the MCU, and an input end B receives a GMSK signal from the VCXO 2; the second NAND gate converts the signal output by the VCXO2 into an approximate square wave or a high-level signal according to the control signal;

the third NAND gate is used for selectively outputting one of the output signals of the first NAND gate and the second NAND gate according to the control signal; when the AIS message is not sent, the third NAND gate continuously outputs a low-level signal;