WO2022262023A1 - Cdma安全编码、解码方法及系统 - Google Patents

Cdma安全编码、解码方法及系统 Download PDF

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Publication number
WO2022262023A1
WO2022262023A1 PCT/CN2021/105123 CN2021105123W WO2022262023A1 WO 2022262023 A1 WO2022262023 A1 WO 2022262023A1 CN 2021105123 W CN2021105123 W CN 2021105123W WO 2022262023 A1 WO2022262023 A1 WO 2022262023A1
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Prior art keywords
signal
cdma
baseband
unit
coded
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PCT/CN2021/105123
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English (en)
French (fr)
Inventor
王国英
杨光伦
叶峰
孙国营
张夫松
李雪健
孙振宇
吕咸亮
张生文
丁欢
陈�光
许燕文
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北京全路通信信号研究设计院集团有限公司
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Priority to EP21751949.5A priority Critical patent/EP4131789A4/en
Publication of WO2022262023A1 publication Critical patent/WO2022262023A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
    • H04B1/3822—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving specially adapted for use in vehicles
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K1/00—Secret communication
    • H04K1/02—Secret communication by adding a second signal to make the desired signal unintelligible
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
    • H04B1/40—Circuits

Definitions

  • the invention belongs to the technical field of railway communication, and in particular relates to a CDMA safe encoding and decoding method and system.
  • China's train control system In order to adapt to the rapid development of China's high-speed railways and passenger dedicated lines and to ensure the safety of railway transportation, my country has successfully developed China's train control system, which is divided into application levels according to functional requirements and configurations. China's train control systems are divided into levels 0-4.
  • the present invention provides CDMA security encoding, decoding methods and systems, which can meet the interconnection and interoperability of European railway operation control systems, and solve the problem that existing European train operation control systems use FSK, PSK and other signal systems. Poor anti-interference performance, only suitable for short-distance transmission, high bit error rate, high reception sensitivity threshold, and lack of multi-path reception.
  • the present invention realizes through following technical scheme:
  • the invention provides a CDMA secure coding method, comprising the steps of:
  • CDMA coding is performed on the baseband coded signal to obtain a CDMA coded signal.
  • the coded digital signal is received, and the coded digital signal is monitored. If the result of the monitoring shows that the coded digital signal is a short-circuit signal, the output of the analog signal and the coded digital signal is turned off.
  • performing CDMA encoding on the baseband encoded signal to obtain a CDMA encoded signal specifically includes the following steps:
  • the carrier frequency signal is subjected to power amplification and filtering processing to obtain a CDMA coded signal.
  • a phase-locked loop receives the baseband coded signal
  • the phase-locked loop controls the frequency and phase of differential bi-phase decoding, Barker decoding, differential modulation and address code generation processes to be synchronized with the frequency and phase of the baseband encoded signal according to the baseband encoded signal.
  • the present invention also provides a CDMA secure coding system, including a baseband signal generating device, a baseband coding device, and a CDMA coding device; unit and coupling unit;
  • the digital-to-analog conversion unit is configured to receive the first clock signal and convert the first clock signal to obtain an analog signal
  • the differential biphase encoding unit is configured to receive a data signal and a second clock signal, and perform differential biphase encoding on the data signal to obtain an encoded digital signal;
  • the conditioning and amplifying unit performs conditioning and amplification on the analog signal to obtain a conditioning and amplifying analog signal
  • the coupling unit is configured to perform coupling processing on the conditioned and amplified analog signal and the encoded digital signal to obtain the required baseband signal;
  • the baseband encoding device is configured to encode the baseband signal to obtain a baseband encoded signal
  • the CDMA encoding device is configured to perform CDMA encoding on the baseband encoded signal to obtain a CDMA encoded signal.
  • the baseband signal generation device also includes a recovery unit, a processing unit, a comparison unit, and a control unit;
  • the recovery unit is used to recover the coded digital signal
  • the processing unit is used to decode the retrieved coded digital signal to obtain a decoded digital signal
  • a comparison unit configured to compare the decoded digital signal with the data signal, and if the decoded digital signal is inconsistent with the data signal, the control unit controls to turn off the output of the encoded digital signal
  • the encoded digital signal is output through the differential bi-phase encoding unit.
  • the baseband signal generating device further includes a data monitoring unit; before the coupling unit performs coupling processing on the conditioned and amplified analog signal and the coded digital signal to obtain a baseband signal,
  • the data monitoring unit receives the coded digital signal, monitors the coded digital signal, and if the monitoring result shows that the coded digital signal is a short-circuit signal, then turns off the output of the analog signal and the coded digital signal.
  • the CDMA encoding device includes a differential biphase decoding unit, a Barker decoding unit, a differential modulation unit, a spread spectrum modulation unit, a carrier modulation unit, and a signal amplification and filtering unit;
  • the spread spectrum modulation unit includes a spread spectrum code trigger module and a CDMA modulation module;
  • the carrier modulation unit includes a carrier signal source and a BPSK modulation module
  • the differential biphase decoding unit performs differential biphase decoding on the baseband coded signal to obtain an initial decoded signal
  • the Barker decoding unit is used to perform Barker decoding on the initial decoded signal to obtain a baseband decoded signal
  • the differential modulation unit is configured to perform differential modulation on the baseband decoded signal to obtain a differential modulation signal
  • the spread spectrum code trigger module is used to generate an address code for spread spectrum modulation
  • the CDMA modulation module is used to perform direct sequence spread spectrum modulation on the differential modulation signal and the address code to obtain a spread spectrum modulation signal;
  • the carrier signal source is used to generate a carrier for carrier modulation
  • the BPSK modulation module is used to carry out carrier modulation to the spread spectrum modulation signal and the carrier, so that the spread spectrum modulation signal is subjected to N times spread spectrum to obtain the carrier frequency signal;
  • the signal amplification and filtering unit is used to amplify and filter the carrier frequency signal to obtain a CDMA coded signal.
  • the CDMA coding unit also includes a phase-locked loop unit
  • the phase-locked loop unit is used to receive the baseband coded signal, and control the frequency and phase of the differential biphase decoding, Barker decoding, differential modulation and address code generation process and the frequency, phase, and frequency of the baseband coded signal according to the baseband coded signal. phase synchronization.
  • the present invention also provides a CDMA secure decoding method corresponding to the above-mentioned CDMA secure encoding method, comprising the following steps:
  • a bandpass filter receives the CDMA coded signal, and performs filtering processing on the CDMA coded signal to obtain a filtered signal;
  • the A/D module receives the filtered signal, performs intermediate frequency band-pass sampling on the filtered signal, and obtains an intermediate frequency digital signal;
  • the digital down-conversion module receives the intermediate frequency digital signal, down-converts the intermediate frequency signal to a baseband signal, and performs interference processing on the intermediate frequency signal to obtain a CDMA baseband coded signal;
  • the baseband signal interference processing module receives the CDMA baseband coded signal, eliminates adjacent channels and monotone interference signals in the CDMA baseband coded signal, and obtains the processed CDMA baseband coded signal;
  • the demodulation module receives the processed CDMA baseband coded signal, restores the processed CDMA baseband coded signal according to the known address spreading code number, and obtains a CDMA decoded signal.
  • the present invention also provides a CDMA secure decoding system corresponding to the above-mentioned CDMA secure encoding method, including a bandpass filter, an A/D module, a digital down-conversion module, a baseband signal interference processing module, a demodulation module, and a digital down-conversion module. module;
  • a bandpass filter configured to receive the CDMA coded signal, suppress out-of-band noise and interference signals in the CDMA coded signal, and obtain a filtered signal
  • the A/D module is configured to receive the filtered signal, perform intermediate frequency band-pass sampling on the filtered signal, and obtain an intermediate frequency digital signal;
  • a digital down-conversion module configured to receive the intermediate-frequency digital signal, down-convert the intermediate-frequency signal to a baseband signal, and perform interference processing on the intermediate-frequency signal to obtain a CDMA baseband coded signal;
  • the baseband signal interference processing module is used to receive the CDMA baseband coded signal, eliminate adjacent channel and monotone interference signals, and obtain the processed CDMA baseband coded signal;
  • the demodulation module is used to receive the processed CDMA baseband coded signal, restore the processed CDMA baseband coded signal according to the known address spreading code number, and obtain the CDMA decoded signal.
  • the present invention provides a CDMA secure coding method. Firstly, a baseband signal is generated by receiving a digital signal, and then the baseband signal is coded to obtain a baseband coded signal, and then the baseband coded signal is CDMA coded to obtain a CDMA coded signal.
  • the CDMA secure coding method is a new CDMA secure coding and decoding method that complies with the loop line transmission module of the European train operation control system, and contributes to the realization of the interconnection and interoperability of the European railway operation control system.
  • the invention provides a CDMA safe encoding and decoding method, so that the train-ground communication air interface transmission of the railway signal equipment of the European train operation control system adopts the CDMA signal system, which has strong anti-interference and extremely low error rate compared with the traditional FSK, PSK and other signal systems. Bit rate, long transmission distance, extremely low reception sensitivity threshold and multi-path reception.
  • Fig. 1 is the overall schematic flow chart of the CDMA secure coding method of the present embodiment
  • Fig. 2 is the structural block diagram that the baseband signal of the present embodiment generates
  • Fig. 3 is the structural block diagram that the analog signal and coded digital signal of the present embodiment carry out coupling processing
  • Figure 4 shows a structural block diagram of baseband signal encoding
  • Fig. 5 is the structural block diagram of the CDMA coding of the present embodiment
  • FIG. 6 is a structural block diagram of CDMA decoding in this embodiment.
  • the general CDMA technology is a mobile communication standard, which is mainly used in the industrial module application field of data transmission. It uses code sequence correlation to realize multiple access communication, and the transmitted carrier wave is modulated by both baseband digital signal and address code. The division is realized and identified according to the different code structure, and the pseudo-random code is generally selected as the address code.
  • the general CDMA technology is a wireless spread spectrum communication technology emerging in the process of digital mobile communication. It has the characteristics of high spectrum utilization, good voice quality, strong confidentiality, low call drop rate, small electromagnetic radiation, large capacity, and wide coverage. .
  • This embodiment provides a CDMA secure coding system, and the CDMA secure coding system includes a baseband signal generating device, a baseband coding device, and a CDMA coding device.
  • the baseband signal generating device includes a digital-to-analog conversion unit, a differential biphase encoding unit, a conditioning and amplifying unit, a coupling unit, a recovery unit, a processing unit, a comparison unit, a control unit, a data monitoring unit, a display unit and an isolation sampling unit.
  • the input end of the digital-to-analog conversion module receives the first clock signal
  • the output end of the digital-to-analog conversion module communicates with the input end of the conditioning amplifier unit
  • the output terminal of the conditioning amplifier unit communicates with the input end of the coupling unit.
  • the input end of the differential biphase encoding unit receives the data signal and the second clock signal, and the output end of the differential biphase encoding unit communicates with the input end of the coupling unit.
  • the output terminal of the coupling unit is used to output the baseband signal.
  • the input end of the data monitoring unit receives the output signal of the differential biphase encoding unit, and performs short-circuit protection on the output signals of the differential biphase encoding unit and the digital-to-analog conversion unit, and the output end of the data monitoring unit sends monitoring information to the display unit.
  • the input terminal of the recovery unit receives the output signal of the differential bi-phase encoding
  • the output terminal of the recovery unit communicates with the input terminal of the processing unit
  • the output terminal of the processing unit communicates with the input terminal of the comparison unit
  • the output terminal of the comparison unit communicates with the input terminal of the control unit and the input end of the differential biphase encoding unit communicates
  • the output end of the control unit communicates with the input end of the differential biphase encoding unit.
  • the isolated sampling unit communicates with the output end of the coupling unit.
  • the isolated sampling unit includes a parallel step-down transformer and a series current transformer.
  • the parallel step-down transformer performs voltage isolation sampling on the baseband signal output by the coupling unit.
  • the baseband signal is sampled in galvanic isolation.
  • the baseband encoding device includes a scrambling unit, a data converting unit, a scrambling unit and a computing unit, the input of the scrambling unit receives the baseband signal, the output of the scrambling unit communicates with the input of the data converting unit, and the output of the data converting unit communicates with the scrambling unit.
  • the input end of the unit communicates, the output end of the scrambling unit communicates with the input end of the calculation unit, and the output end of the calculation unit is used to output the baseband coded signal.
  • the CDMA encoding device includes a decoding unit, a differential modulation unit, a spread spectrum modulation unit, a carrier modulation unit, a signal amplification and filtering unit and a phase-locked loop unit.
  • the decoding unit includes a differential biphase decoding unit and a Barker decoding unit;
  • the spread spectrum modulation unit includes a spread spectrum code trigger module and a CDMA modulation module;
  • the carrier modulation unit includes a carrier signal source and a BPSK modulation module
  • the signal amplification and filtering unit includes a power amplifier and a filter.
  • the first input end of the differential biphase decoding unit receives the baseband encoded signal
  • the output end of the differential biphase decoding unit communicates with the first input end of the Barker decoding unit
  • the output end of the Barker decoding unit communicates with the first input end of the differential modulation unit Communication
  • the output end of the differential modulation unit communicates with the first input end of the CDMA modulation module
  • the first input end of the spread spectrum code trigger module is used to set the spread spectrum code
  • the output end of the spread spectrum code trigger module communicates with the first input end of the CDMA modulation module Two-input communication.
  • the output end of the CDMA modulation module communicates with the first input end of the BPSK modulation module, the output end of the carrier signal communicates with the second input end of the BPSK modulation module, the output end of the BPSK modulation module is connected with the input end of the power amplifier, and the power amplifier The output end is connected with the input end of the filter, and the output end of the filter outputs a CDMA coded signal.
  • the input end of the phase-locked loop unit receives the baseband coded signal
  • the phase-locked loop unit has multiple output ends
  • the first output end of the phase-locked loop unit communicates with the second input end of the differential bi-phase decoding unit
  • the second input end of the phase-locked loop unit The two output terminals communicate with the second input terminal of the Barker decoding unit
  • the third output terminal of the phase-locked loop unit communicates with the second output terminal of the differential modulation unit and the second output terminal of the spreading code trigger module
  • the phase-locked loop unit communicates with the second output terminal of the differential modulation unit and the second output terminal of the spread spectrum code trigger module.
  • the fourth output terminal communicates with the third input terminal of the spreading code trigger module.
  • the S1 baseband signal generation device receives digital signals to generate baseband signals, as shown in Figure 2, specifically,
  • the digital-to-analog conversion unit receives the first clock signal, and the first clock signal is illustratively from the FPGA module.
  • the FPGA module is preferably placed in a functional module with two-comparison and safety self-test, and the digital-to-analog conversion unit converts the first clock signal to obtain Analog signals, and output analog signals, the figure shows that there are two first clock signals, the digital-to-analog conversion unit receives the two first clock signals, and the digital-to-analog conversion module generates the analog signals from the two received first clock signals through the digital counter Signal, specifically, the digital counter uses one first clock signal as the data signal, and the other first clock signal as the counting clock.
  • the digital counter performs mixed accumulation at the output end, and then generates an analog signal through op amp processing; the analog signal is conditioned and amplified
  • the op amp and push-pull of the unit undergoes a series of conditioning processes and is sent to the coupling unit.
  • the differential bi-phase encoding unit receives the data signal and the second clock signal.
  • the data signal is exemplarily from the CPU unit.
  • the CPU unit is preferably placed in a functional module with two-comparison and safety self-inspection.
  • the second clock signal also comes from the above-mentioned FPGA module , carry out differential biphase encoding on the data signal to obtain the encoded digital signal, and output the encoded digital signal.
  • the figure shows that the differential biphase encoding unit receives four data signals and performs differential biphase encoding.
  • the signal is encoded by differential biphase hardware at twice the frequency of the data rate, and the encoded digital signal is sent to the coupling unit.
  • the coupling unit receives the analog signal and the coded digital signal, performs coupling processing on the analog signal and the coded digital signal, and obtains the baseband signal. Specifically, the analog signal and the coded digital signal are mixed and superimposed through a synthetic transformer with a specific ratio.
  • the first primary coil inputs an analog signal
  • the second primary coil inputs a coded digital signal
  • the secondary coil output terminal 7 and 9 output a mixed and superimposed baseband signal
  • the turns ratio of the first primary coil and the secondary coil is 35/92
  • the turns ratio of the second primary coil and the secondary coil is 104/92 (ie 26/23)
  • the number of bits of the baseband signal is 830bits or 210bits.
  • this embodiment also adopts the data monitoring unit to receive the coded digital signal, and monitor the coded digital signal. If the monitoring result considers that the coded digital signal is a short circuit signal, then turn off the output of the analog signal and the coded digital signal, specifically :
  • the data monitoring unit detects the encoded digital signal by comparing the encoded digital signal with the set threshold. If the encoded digital signal is greater than the set threshold, it means that the encoded digital signal is a short-circuit signal.
  • the data monitoring unit converts to digital-analog
  • the unit and the differential bi-phase encoding unit send a reminder message, which is convenient for the digital-to-analog conversion unit and the differential bi-phase encoding unit to turn off the output of the analog signal and the encoded digital signal, so as to realize the output signal of the differential bi-phase encoding unit and the digital-to-analog conversion unit Protection, so as to ensure the safety of the output signal of the coupling unit.
  • the display unit receives the monitoring result of the data monitoring unit (shown in Fig. 2 is to receive 8 road detection results), if the monitoring result thinks that the coded digital signal is a short circuit signal, then the display unit displays the short circuit state; if the monitoring result thinks that the coded digital signal is a short circuit signal; If there is an open circuit signal, the display unit will display the open circuit state correspondingly, so that it is convenient for external personnel to observe the internal open and short circuit state.
  • the present embodiment also adopts the recovery unit to recover the coded digital signal, specifically the recovery unit recovers the 8-way coded digital signal, and the recovery unit sends the 8-way coded digital signal to the processing unit, and the processing unit receives and decodes the coded digital signal
  • the encoded digital signal is obtained by decoding the digital signal, and the decoded digital signal is sent to the comparison unit.
  • the comparison unit compares the decoded digital signal with the data signal. If the decoded digital signal is consistent with the data signal, it is directly output through the differential bi-phase encoding unit.
  • the coded digital signal if the decoded digital signal is inconsistent with the data signal, the coded digital signal is turned off by the control unit, specifically, the control unit sends four control signals to the differential biphase coding unit, and the differential biphase coding unit turns off after receiving the control signal.
  • the output of the coded digital signal further ensures the accuracy of the output signal of the coupling unit.
  • this embodiment also uses an isolated sampling unit to perform isolated sampling of the baseband signal, specifically, the isolated sampling unit is used to perform voltage isolated sampling of the baseband signal of the coupling module through a parallel step-down transformer, and through a series current transformer. Perform current isolation sampling, detect abnormal output of baseband data, and ensure effective output of coupling unit data.
  • the S2 baseband encoding unit encodes the baseband signal to obtain a baseband encoded signal; specifically,
  • the data conversion unit receives the scrambling data for data conversion, obtains the converted data and sends it to the scrambling unit.
  • the data is grouped by each 10bits codeword in the order of output, and then the 10bits to 11bits data conversion is performed on each 10bits codeword by using the pre-defined 10bits to 11bits conversion table.
  • the conversion method is: express the 10bits binary codeword as decimal x, and then find the xth 11bits data block from the defined conversion table, then this 11bits data block is the 11bits codeword obtained after the 10bits codeword conversion.
  • the scrambling unit receives the converted data, adds control bits and scrambling bits to the converted data, obtains scrambled data, and sends it to the computing unit.
  • the control bits are 3 bits
  • the scrambling bits are 12 bits.
  • the calculation unit receives the scrambled data, selects additional trimmed bits that meet the conditions, calculates the check digit, and then adds the extra trimmed bit and the check bit to the scrambled data to obtain a baseband encoded signal with a specific number of bits.
  • additional trimmed The bit is 10bits
  • the parity bit is 85bits
  • the number of baseband coded signal bits is 1023bits or 341bits.
  • the S3CDMA encoding device performs CDMA encoding on the baseband encoded signal to obtain the CDMA encoded signal, as shown in Figure 5, including,
  • S3-1 decodes the baseband coded signal (i.e. the user data in Figure 5) to obtain the baseband decoded signal, as follows:
  • the first input end of the differential biphase decoding unit receives the baseband coded signal, and performs differential biphase decoding on the baseband coded signal to obtain an initial decoded signal.
  • the differential biphase decoding unit performs DBPL decoding on the baseband coded signal. Obtain the initial decoded signal.
  • the first input terminal of the Barker decoding unit receives the initial decoding signal, carries out Barker decoding to the initial decoding signal, obtains the baseband decoding signal (shown as binary data in Fig. 5), exemplary, the Barker decoding unit converts the initial decoding signal into The Barker code of 11-bit chips is 11100010010, and then the Barker code of 11-bit chips 11100010010 is demodulated to logic 1, and the inverse code of the 11-bit chips of Barker code is demodulated to logic 0, and then the baseband decoded signal is obtained.
  • S3-2 modulates the baseband decoded signal, and the modulation includes differential modulation, spread spectrum modulation and carrier modulation in turn, and finally obtains the carrier frequency signal, as follows:
  • the first input terminal of the differential modulation unit receives the baseband coded signal, performs differential modulation on the baseband decoded signal, and obtains a differential modulated signal, specifically, the differential modulation unit performs DBPL modulation on the baseband decoded signal, and then obtains a differentially modulated signal (shown as differential data in Figure 5) and sent to the CDMA modulation module.
  • the spread-spectrum modulation unit performs spread-spectrum modulation on the differential modulation signal to obtain a spread-spectrum modulated signal, specifically,
  • the spread spectrum code trigger module is used to generate an address code for CDMA spread spectrum modulation, and then the address code (that is, the chip sequence in FIG. 5 ) is sent to the CDMA modulation module.
  • the number of address codes is 472 bits.
  • the first input terminal of the CDMA modulation module receives the above-mentioned differential modulation signal, and the second input terminal receives the above-mentioned address code, and performs direct sequence spread spectrum modulation on the differential modulation signal and the address code to obtain the spread spectrum modulation signal (i.e. the modulation code in Figure 5 chip), and sent to the BPSK modulation module.
  • the carrier modulation unit performs carrier modulation on the spread spectrum modulation signal to obtain a carrier frequency signal; specifically,
  • the carrier signal source generates the carrier used for carrier modulation and sends it to the BPSK modulation module.
  • the BPSK modulation module receives the carrier and the spread-spectrum modulation signal to carry out carrier modulation, so that the spread-spectrum modulation signal carries out N times of spread spectrum, and obtains the carrier frequency signal (i.e. the CDMA signal in Fig. 5), preferably the BPSK modulation module utilizes the carrier to The spread-spectrum modulated signal is subjected to 3-fold spread-spectrum, and then a carrier frequency signal of 13.545MHz is generated.
  • the S3-3 signal amplification and filtering unit amplifies and filters the carrier frequency signal, specifically,
  • the power amplifier amplifies the carrier frequency signal without power distortion, and then sends the amplified signal to the filter.
  • the filter receives the amplified signal and performs filtering processing to ensure the quality of the carrier frequency signal, that is, the bit error rate ⁇ 10 -5 , which is not expected
  • the amplitude modulation of ⁇ 7% etc. finally obtains the CDMA coded signal, that is, the CDMA coded signal that conforms to the receiving signal standard of the European train operation control system loop line transmission module (ie the loop line signal in Figure 5).
  • this embodiment also uses a phase-locked loop unit to ensure the synchronization of baseband coded signal processing, specifically, the input end of the phase-locked loop unit is used to receive the baseband coded signal.
  • the first output of the phase-locked loop unit outputs the signal to the second input of the differential biphase decoding unit
  • the second output of the phase-locked loop unit outputs the signal to the second input of the Barker decoding unit
  • the phase-locked loop unit outputs the signal to the second input of the Barker decoding unit.
  • the third output terminal outputs signals to the second output terminal of the differential modulation unit and the second output terminal of the spread spectrum code trigger module
  • the fourth output terminal of the phase-locked loop unit outputs signals to the third input terminal of the spread spectrum code trigger module
  • this embodiment also provides a CDMA decoding system and decoding method.
  • the decoded spread spectrum code is transmitted to the loop line transmission module through the air interface through the European standard transponder of the signal equipment in a signal format different from FSK, and the loop line transmits
  • the module performs CDMA decoding with the decoded spreading code.
  • the European standard transponder used in this embodiment is a reduced size European standard transponder conforming to SS-036.
  • the CDMA decoding unit includes a bandpass filter (BPF), an A/D module, a digital down-conversion module, a baseband signal interference processing module, and a demodulation module, and the digital down-conversion module includes a low-pass filter (LPF), sampling module.
  • BPF bandpass filter
  • A/D A/D
  • DPF digital down-conversion module
  • LPF low-pass filter
  • the CDMA decoding method specifically includes:
  • the band-pass filter receives the above-mentioned CDMA coded signal (that is, r(t) in Figure 6), suppresses out-of-band noise and interference signals on the CDMA coded signal, and then sends the filtered signal to the A/D module.
  • the A/D module realizes IF band-pass sampling, obtains IF digital signals and sends them to the digital down-conversion module; among them, the A/D module uses a 108.38MHz crystal for sampling, with a bit width of 14 bits, and the sampling rate is 8 times that of the CDMA carrier signal. It can adapt to signal scenarios with large DC bias and high dynamic range.
  • the digital down-conversion module receives the IF digital signal, down-converts the IF signal to the baseband signal, that is, removes the carrier frequency of the IF signal, and recovers the CDMA baseband coded signal. And in order to better suppress the burst interference signal, the IF digital signal is subjected to interference processing to reduce carrier synchronization and code capture errors.
  • the IF signal interference processing is realized in the digital down-conversion module, specifically, the IF digital signal is passed through a low-pass filter , the low-pass filter has flat passband characteristics and group delay characteristics, can pass the target signal without distortion, and has a very steep transition band, which can provide very good adjacent channel rejection. The typical range of the adjacent channel suppression ability of the low-pass filter is 30-90dB.
  • the intermediate frequency digital signal suppressed by the low-pass filter is extracted by the sampling module and restored to the CDMA baseband coded signal.
  • the present embodiment divides the intermediate frequency digital signal into two paths for interference processing, that is, the intermediate frequency signal interference processing is realized through the I path and the Q path respectively, so as to avoid that when one path breaks down, the other path can be normal.
  • the baseband signal interference processing module eliminates possible Euroloop adjacent channel interference and single-tone interference for the CDMA baseband coded signal, so as to filter out the folded frequency components after down-conversion.
  • the demodulation module restores the CDMA baseband coded signal according to the known address spreading code number, and obtains the CDMA decoded signal.
  • the figure shows that BPSK demodulation is adopted.

Abstract

本发明提供CDMA安全编码、解码方法及系统，其中，CDMA安全编码方法，包括：接收第一时钟信号，将第一时钟信号转换为模拟信号；接收数据信号和第二时钟信号，将数据信号进行差分双相位编码得到编码数字信号；对所述模拟信号进行调理放大后和所述编码数字信号进行耦合处理，得到所需的基带信号；对所述基带信号进行编码，得到基带编码信号；对所述基带编码信号进行CDMA编码，得到CDMA编码信号。本发明提供的CDMA安全编码、解码方法及系统能够满足欧洲铁路运行控制系统互联互通，并解决现有的欧洲列车运行控制系统因采用FSK、PSK等信号制式，具有抗干扰性能差、仅适合短距离传输、误码率高、接收灵敏度门槛高以及不具备多径接收等问题。

Description

CDMA安全编码、解码方法及系统 技术领域
本发明属于铁路通信技术领域，具体涉及CDMA安全编码、解码方法及系统。
背景技术
为了适应中国高速铁路、客运专线的迅速发展和保证铁路运输安全的需求，我国成功研制了中国列车控制系统，根据功能要求和配置划分应用等级，中国列车控制系统划分为0～4级。
随着中国铁路在欧洲铁路市场的日渐开拓，逐步认识到欧洲各国铁路的列车运行控制系统制式复杂，各种列车控制系统之间不完全兼容，因此，需研制满足欧洲铁路运行控制系统互联互通的相关信号传输方法以及设备。
现有的欧洲列车运行控制系统采用FSK、PSK等信号制式，具有抗干扰性能差、仅适合短距离传输、误码率高、接收灵敏度门槛高以及不具备多径接收等问题。
发明内容
为了满足现有技术的需要，本发明提供CDMA安全编码、解码方法及系统，能够满足欧洲铁路运行控制系统互联互通，并解决现有的欧洲列车运行控制系统因采用FSK、PSK等信号制式，具有抗干扰性能差、仅适合短距离传输、误码率高、接收灵敏度门槛高以及不具备多径接收等问题。
本发明通过如下技术方案实现：
本发明提供CDMA安全编码方法，包括如下步骤：
接收第一时钟信号，将第一时钟信号转换为模拟信号；
接收数据信号和第二时钟信号，将数据信号进行差分双相位编码得到编码数字信号；
对所述模拟信号进行调理放大后和所述编码数字信号进行耦合处理，得到所需的基带信号；
对所述基带信号进行编码，得到基带编码信号；
对所述基带编码信号进行CDMA编码，得到CDMA编码信号。
进一步的，还包括如下步骤：
对编码数字信号进行回采；
将回采的编码数字信号进行解码，得到解码数字信号；
将所述解码数字信号与所述数据信号进行比较，若所述解码数字信号与所述数据信 号不一致，则控制关断所述编码数字信号输出；
若所述解码数字信号与所述数据信号一致，则输出所述编码数字信号。
进一步的，在所述接收所述模拟信号和所述编码数字信号，对所述模拟信号和所述编码数字信号进行耦合处理之前，还包括如下步骤：
接收所述编码数字信号，对所述编码数字信号进行监测，若监测结果得出所述编码数字信号是短路信号，则关断模拟信号以及编码数字信号的输出。
进一步的，所述对所述基带编码信号进行CDMA编码，得到CDMA编码信号，具体包括如下步骤：
对所述基带编码信号依次进行差分双相位解码和巴克解码，得到基带解码信号；
对所述基带解码信号进行差分调制，得到差分调制信号；
生成用于扩频调制的地址码，将差分调制信号与所述地址码进行直接序列扩频调制，得到扩频调制信号；
生成用于载波调制的载波，将扩频调制信号与所述载波进行载波调制，使得扩频调制信号进行N倍扩频，得到载频信号；
将载频信号进行功率放大以及滤波处理，得到CDMA编码信号。
进一步的，还包括，
锁相环接收所述基带编码信号；
锁相环根据基带编码信号控制差分双相位解码、巴克解码、差分调制以及地址码生成过程的频率、相位与所述基带编码信号的频率、相位同步。
对应上述CDMA安全编码方法，本发明还提供CDMA安全编码系统，包括基带信号生成设备、基带编码设备以及CDMA编码设备；所述基带信号生成设备包括数模转换单元、差分双相位编码单元、调理放大单元以及耦合单元；
所述数模转换单元，用于接收所述第一时钟信号，将第一时钟信号转换得到模拟信号；
所述差分双相位编码单元，用于接收数据信号和第二时钟信号，对数据信号进行差分双相位编码得到编码数字信号；
所述调理放大单元将所述模拟信号进行调理放大，得到调理放大的模拟信号；
所述耦合单元，用于对所述调理放大的模拟信号和所述编码数字信号进行耦合处理，得到所需的基带信号；
所述基带编码设备，用于对所述基带信号进行编码，得到基带编码信号；
所述CDMA编码设备，用于对所述基带编码信号进行CDMA编码，得到CDMA编码信号。
进一步的，所述基带信号生成设备还包括回采单元、处理单元、比较单元、控制单元；
所述回采单元，用于对编码数字信号进行回采；
所述处理单元，用于将回采的编码数字信号进行解码，得到解码数字信号；
比较单元，用于将所述解码数字信号与所述数据信号进行比较，若所述解码数字信号与所述数据信号不一致，则通过控制单元控制关断所述编码数字信号输出；
若所述解码数字信号与所述数据信号一致，则通过差分双相位编码单元输出所述编码数字信号。
进一步的，所述基带信号生成设备还包括数据监测单元；在所述耦合单元对所述调理放大的模拟信号和所述编码数字信号进行耦合处理，得到基带信号之前，
所述数据监测单元接收所述编码数字信号，对所述编码数字信号进行监测，若监测结果得出所述编码数字信号是短路信号，则关断模拟信号以及编码数字信号的输出。
进一步的，所述CDMA编码设备包括差分双相位解码单元、巴克解码单元、差分调制单元、扩频调制单元、载波调制单元、信号放大滤波单元；
所述扩频调制单元包括扩频码触发模块和CDMA调制模块；
所述载波调制单元包括载波信号源和BPSK调制模块；
所述差分双相位解码单元对基带编码信号进行差分双相位解码，得到初始解码信号；
所述巴克解码单元，用于对初始解码信号进行巴克解码，得到基带解码信号；
所述差分调制单元，用于对所述基带解码信号进行差分调制，得到差分调制信号；
所述扩频码触发模块，用于生成用于扩频调制的地址码；
所述CDMA调制模块，用于将差分调制信号与所述地址码进行直接序列扩频调制，得到扩频调制信号；
所述载波信号源，用于产生用于载波调制的载波；
所述BPSK调制模块，用于将扩频调制信号与载波进行载波调制，使得扩频调制信号进行N倍扩频，得到载频信号；
所述信号放大滤波单元，用于对载频信号进行放大、滤波处理，得到CDMA编码信号。
进一步的，所述CDMA编码单元还包括锁相环单元；
所述锁相环单元，用于接收所述基带编码信号，并根据基带编码信号控制差分双相位解码、巴克解码、差分调制以及地址码生成过程的频率、相位与所述基带编码信号的频率、相位同步。
进一步的，本发明还提供与上述的CDMA安全编码方法对应的CDMA安全解码方法，包括如下步骤：
带通滤波器接收所述CDMA编码信号，对所述CDMA编码信号进行滤波处理，得到滤波信号；
A/D模块接收所述滤波信号，对滤波信号进行中频带通采样，获取中频数字信号；
数字下变频模块接收所述中频数字信号，将中频信号下变频到基带信号，并对中频信号进行干扰处理，得到CDMA基带编码信号；
基带信号干扰处理模块接收所述CDMA基带编码信号，消除CDMA基带编码信号内的邻道以及单音干扰信号，得到处理后的CDMA基带编码信号；
解调模块接收所述处理后的CDMA基带编码信号，根据已知的地址扩频码编号对处理后的CDMA基带编码信号进行还原，得到CDMA解码信号。
进一步的，本发明还提供与上述的CDMA安全编码方法对应的CDMA安全解码系统，包括带通滤波器、A/D模块、数字下变频模块、基带信号干扰处理模块、解调模块，数字下变频模块；
带通滤波器，用于接收所述CDMA编码信号，对所述CDMA编码信号中的带外噪声和干扰信号进行抑制，得到滤波信号；
A/D模块，用于接收所述滤波信号，对滤波信号进行中频带通采样，获取中频数字信号；
数字下变频模块，用于接收所述中频数字信号，将中频信号下变频到基带信号，并对中频信号进行干扰处理，得到CDMA基带编码信号；
基带信号干扰处理模块，用于接收所述CDMA基带编码信号，消除邻道以及单音干扰信号，得到处理后的CDMA基带编码信号；
解调模块，用于接收所述处理后的CDMA基带编码信号，根据已知的地址扩频码编号对处理后的CDMA基带编码信号进行还原，得到CDMA解码信号。
和最接近的现有技术比，本发明的技术方案具有如下有益效果：
本发明提供CDMA安全编码方法，首先，接收数字信号生成基带信号，然后对所述基带信号进行编码，得到基带编码信号，进而对所述基带编码信号进行CDMA编码，得 到CDMA编码信号。CDMA安全编码方法是符合欧洲列车运行控制系统环线传输模块的CDMA新型安全编解码方法，为实现欧洲铁路运行控制系统互联互通做出贡献。
本发明提供CDMA安全编解码方法，使得欧洲列车运行控制系统的铁路信号设备车地通信空口传输采用CDMA信号制式，相对于传统的FSK、PSK等信号制式，具有抗干扰性强，极低的误码率，较远的传输距离，极低的接收灵敏度门槛以及具备多径接收等优势。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其他的附图。
图1为本实施例的CDMA安全编码方法的整体流程示意图；
图2为本实施例的基带信号生成的结构框图；
图3为本实施例的模拟信号和编码数字信号进行耦合处理的结构框图；
图4所示为基带信号编码的结构框图；
图5为本实施例的CDMA编码的结构框图；
图6为本实施例的CDMA解码的结构框图。
具体实施方式
下面将结合本发明的实施例，对本发明的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
通用的CDMA技术是一个移动通讯标准，主要应用于数据传输的工业模块应用领域。它利用码序列相关性实现多址通信，发射的载波既受基带数字信号调制，又受地址码调制。划分是根据码型结构不同来实现和识别的，一般选择伪随机码作地址码。通用的CDMA技术是数字移动通信进程中出现的一种无线扩频通信技术，具有频谱利用率高、语音质量好、保密性强、掉话率低、电磁辐射小、容量大、覆盖广等特点。
本实施例提供CDMA安全编码系统，CDMA安全编码系统包括基带信号生成设备、基带编码设备以及CDMA编码设备。
其中，基带信号生成设备包括数模转换单元、差分双相位编码单元、调理放大单元、 耦合单元、回采单元、处理单元、比较单元、控制单元、数据监测单元、显示单元以及隔离采样单元。
其中，数模转换模块的输入端接收第一时钟信号，数模转换模块的输出端与调理放大单元的输入端通信，调理放大单元的输出端与耦合单元的输入端通信。
差分双相位编码单元的输入端接收数据信号以及第二时钟信号，差分双相位编码单元的输出端与耦合单元的输入端通信。
耦合单元的输出端用于输出基带信号。
数据监测单元的输入端接收差分双相位编码单元的输出信号，并对差分双相位编码单元以及数模转换单元的输出信号进行短路保护，数据监测单元的输出端向显示单元发送监测信息。
回采单元的输入端接收差分双相位编码的输出信号，回采单元的输出端与处理单元输入端通信，处理单元的输出端与比较单元的输入端通信，比较单元的输出端与控制单元的输入端以及差分双相位编码单元的输入端通信，并且控制单元的输出端与差分双相位编码单元的输入端通信。
隔离采样单元与耦合单元的输出端通信，隔离采样单元包括并联降压变压器和串联电流互感器，并联降压变压器对耦合单元输出的基带信号进行电压隔离采样，串联电流互感器对耦合单元输出的基带信号进行电流隔离采样。
基带编码设备包括扰乱单元、数据转换单元、加扰单元以及计算单元，扰乱单元的输入端接收基带信号，扰乱单元的输出端与数据转换单元的输入端通信，数据转换单元的输出端与加扰单元的输入端通信，加扰单元的输出端与计算单元的输入端通信，计算单元的输出端用于输出基带编码信号。
CDMA编码设备包括解码单元、差分调制单元、扩频调制单元、载波调制单元、信号放大滤波单元以及锁相环单元。
其中，解码单元包括差分双相位解码单元和巴克解码单元；
扩频调制单元包括扩频码触发模块和CDMA调制模块；
载波调制单元包括载波信号源和BPSK调制模块；
信号放大滤波单元包括功率放大器和滤波器。
差分双相位解码单元的第一输入端接收上述基带编码信号，差分双相位解码单元的输出端与巴克解码单元的第一输入端通信，巴克解码单元的输出端与差分调制单元的第一输入端通信，差分调制单元的输出端与CDMA调制模块的第一输入端通信，扩频码触 发模块的第一输入端用于设置扩频码，扩频码触发模块的输出端与CDMA调制模块的第二输入端通信。
CDMA调制模块的输出端与BPSK调制模块的第一输入端通信，载波信号的输出端与BPSK调制模块的第二输入端通信，BPSK调制模块的输出端与功率放大器的输入端连接，功率放大器的输出端与滤波器的输入端连接，滤波器的输出端输出CDMA编码信号。
锁相环单元的输入端接收基带编码信号，锁相环单元具有多个输出端，锁相环单元的第一输出端与差分双相位解码单元的第二输入端通信，锁相环单元的第二输出端与巴克解码单元的第二输入端通信，锁相环单元的第三输出端与差分调制单元的第二输出端以及扩频码触发模块的第二输出端通信，锁相环单元的第四输出端与扩频码触发模块的第三输入端通信。
如图1所示，为采用上述CDMA安全编码系统进行CDMA编码的方法，具体如下：
S1基带信号生成设备接收数字信号生成基带信号，如图2所示，具体的，
数模转换单元接收第一时钟信号，第一时钟信号示例性来自FPGA模块，FPGA模块优选是放置在具有取二比较、安全自检的功能模块中，数模转换单元将第一时钟信号转换得到模拟信号，并输出模拟信号，图中示意是有两路第一时钟信号，数模转换单元接收两路第一时钟信号，数模转换模块将接收的两路第一时钟信号通过数字计数器生成模拟信号，具体是数字计数器将一路第一时钟信号作为数据信号，另一路第一时钟信号作为计数时钟，数字计数器在输出端进行混合累加，再通过运放处理生成了模拟信号；模拟信号经过调理放大单元的运放、推挽一系列的调理处理，送至耦合单元。
差分双相位编码单元接收数据信号以及第二时钟信号，数据信号示例性来自CPU单元，CPU单元优选是放置在具有取二比较、安全自检的功能模块中，第二时钟信号同样来自上述FPGA模块，对数据信号进行差分双相位编码得到编码数字信号，并输出编码数字信号，图中示意是差分双相位编码单元接收四路数据信号进行差分双相位编码，具体是采用JK触发器对四路数据信号按数据速率的两倍频进行差分双相位的硬件编码，得到编码数字信号送至耦合单元。
耦合单元接收模拟信号和编码数字信号，对模拟信号和编码数字信号进行耦合处理，得到基带信号，具体是将模拟信号和编码数字信号通过特定变比的合成变压器进行二合一的混合叠加，示例性的，如图3所示，第一初级线圈(输入端为1和2)输入模拟信号，第二初级线圈(输入端为3和5)输入编码数字信号，次级线圈(输出端为7和9)输出混合叠加的基带信号，其中第一初级线圈和次级线圈的匝数比为35/92，第二初级 线圈和次级线圈的匝数比为104/92(即26/23)，进而满足信号幅值14-18V和信号幅值20-23V的混叠输出，从而生成符合欧洲标准规定的基带信号，示例性的，基带信号的位数为830bits或210bits。
作为优选实施方式，本实施例还采用数据监测单元接收编码数字信号，对编码数字信号进行监测，若监测结果认为编码数字信号是短路信号，则关断模拟信号以及编码数字信号的输出，具体是：数据监测单元将编码数字信号与设定阈值进行比较的方式对编码数字信号进行检测，若编码数字信号大于设定阈值，则说明编码数字信号为短路信号，此时数据监测单元向数模转换单元以及差分双相位编码单元发送提醒消息，便于数模转换单元以及差分双相位编码单元关断模拟信号以及编码数字信号的输出，以实现对差分双相位编码单元以及数模转换单元的输出信号的保护，从而保证耦合单元输出信号的安全性。
并且显示单元接收数据监测单元的监测结果(图2中示意是接收8路检测结果)，若监测结果认为编码数字信号是短路信号，则显示单元对应显示短路状态；若监测结果认为编码数字信号是开路信号，则显示单元对应显示开路状态，从而便于外部人员观察内部开短路状态。
进一步作为优选实施方式，本实施例还采用回采单元对编码数字信号进行回采，具体是回采单元回采8路编码数字信号，回采单元将8路编码数字信号发送给处理单元，处理单元接收并解码回采的编码数字信号，得到解码数字信号，并将解码数字信号发送给比较单元，比较单元将解码数字信号与数据信号进行比较，若解码数字信号与数据信号一致，则直接通过差分双相位编码单元输出编码数字信号，若解码数字信号与数据信号不一致，则通过控制单元控制关断编码数字信号，具体是控制单元向差分双相位编码单元发送四路控制信号，差分双相位编码单元接收控制信号后关断编码数字信号的输出，更进一步保证耦合单元输出信号的准确性。
进一步作为优选实施方式，本实施例还采用隔离采样单元对基带信号进行隔离采样，具体是采用隔离采样单元分别对耦合模块的基带信号通过并联降压变压器进行电压隔离采样，以及通过串联电流互感器进行电流的隔离采样，对基带数据的异常输出进行检测，保证耦合单元数据的有效输出。
S2基带编码单元对基带信号进行编码，得到基带编码信号；具体是，
扰乱单元接收基带信号(示例性如图4所示的830bits或210bits的用户数据)进行扰乱处理，得到扰乱数据并发送给数据转换单元；具体的，用特征多项式h(x) ＝x 32+x 31+x 30+x 29+x 27+x 25+…+1的32位线性反馈移位寄存器对830bits或210bits的用户数据进行扰乱处理，其中特征多项式的初始值S＝(2801775573·B)mod2 32，B为所选的12位扰乱位的10进制表示。
数据转换单元接收扰乱数据进行数据转换，得到转换数据并发送给加扰单元，示例性的，图4中对扰乱数据进行10bits到11bits数据转换，得到913bits或231bits的转换数据；具体的，将扰乱数据按输出的先后顺序每10bits一个码字进行分组，然后利用事先定义好的10bits到11bits的转换表对每一个10bits的码字进行10bits到11bits的数据转换。转换方法是：把10bits的二进制的码字以十进制x表示，然后从定义好的转换表中找到第x个11bits数据块，则这个11bits数据块就是10bits码字转换后得到的11bits的码字。
加扰单元接收转换数据，将转换数据增加控制位和扰乱位，得到加扰数据并发送给计算单元，示例性的，控制位为3bits，扰乱位为12bits。
计算单元接收加扰数据，选择满足条件的额外修整位，计算校验位，然后在加扰数据中添加额外修整位以及校验位，得到特定位数的基带编码信号，示例性的，额外修整位为10bits，校验位为85bits，基带编码信号位数为1023bits或341bits。
S3CDMA编码设备对基带编码信号进行CDMA编码，得到CDMA编码信号，如图5所示，包括，
S3-1对基带编码信号(即图5中的用户数据)解码，获取基带解码信号，具体如下：
差分双相位解码单元的第一输入端接收所述基带编码信号，对基带编码信号进行差分双相位解码，得到初始解码信号，示例性的，差分双相位解码单元对基带编码信号进行DBPL解码的方式获得初始解码信号。
巴克解码单元的第一输入端接收所述初始解码信号，对初始解码信号进行巴克解码，得到基带解码信号(图5中示意为二进制数据)，示例性的，巴克解码单元将初始解码信号转换为11位码片的巴克码11100010010，然后将11位码片的巴克码11100010010解调为逻辑1，将11位码片的巴克码反码解调为逻辑0，进而得到基带解码信号。
S3-2对基带解码信号进行调制，调制依次包括差分调制、扩频调制以及载波调制，最终获取载频信号，具体如下：
S3-2-1：差分调制单元的第一输入端接收基带编码信号，对基带解码信号进行差分调制，得到差分调制信号，具体是差分调制单元对基带解码信号进行DBPL调制，进而获取差分调制信号(图5中示意为差分数据)并发送给CDMA调制模块。
S3-2-2：扩频调制单元将差分调制信号进行扩频调制，得到扩频调制信号，具体是，
采用扩频码触发模块生成地址码，用于CDMA扩频调制，然后将地址码(即图5中的码片序列)发送给CDMA调制模块，示例性的，地址码的位数为472位。
CDMA调制模块的第一输入端接收上述差分调制信号，第二输入端接收上述地址码，将差分调制信号与地址码进行直接序列扩频调制，得到扩频调制信号(即图5中的调制码片)，并发送给BPSK调制模块。
S3-2-3：载波调制单元将扩频调制信号进行载波调制，得到载频信号；具体是，
载波信号源产生用于载波调制的载波，并发送给BPSK调制模块。
BPSK调制模块接收所述载波以及扩频调制信号进行载波调制，使得扩频调制信号进行N倍扩频，得到载频信号(即图5中的CDMA信号)，优选的是BPSK调制模块利用载波对扩频调制信号进行3倍扩频，进而生成13.545MHz的载频信号。
S3-3信号放大滤波单元对载频信号进行放大、滤波处理，具体是，
功率放大器对载频信号进行功率不失真的放大处理，然后将放大信号发送给滤波器，滤波器接收放大信号进行滤波处理，保证载频信号发送质量，即位误码率<10 -5，非期望的幅度调制≤7％等，最终得到CDMA编码信号，即符合欧洲列车运行控制系统环线传输模块接收信号制式的CDMA编码信号(即图5中的环线信号)。
作为优选实施方式，本实施例还采用锁相环单元保证基带编码信号处理的同步性，具体是采用锁相环单元的输入端接收基带编码信号。
然后锁相环单元的第一输出端向差分双相位解码单元的第二输入端输出信号，锁相环单元的第二输出端向巴克解码单元的第二输入端输出信号，锁相环单元的第三输出端向差分调制单元的第二输出端以及扩频码触发模块的第二输出端输出信号，锁相环单元的第四输出端向扩频码触发模块的第三输入端输出信号，从而控制差分双相位解码单元、巴克解码单元、差分调制单元以及扩频码触发模块相关信号处理过程中相位以及频率保持与输入的基带编码信号的频率、相位同步。
对应于上述CDMA编码方法，本实施例还提供了CDMA解码系统以及解码方法，解码的扩频码通过信号设备欧标应答器以不同于FSK的信号制式通过空气接口传输给环线传输模块，环线传输模块以此解码的扩频码进行CDMA解码，示例性的，本实施例采用的欧标应答器是符合ss-036的缩小尺寸的欧标应答器。
具体的，如图6所示，CDMA解码单元包括带通滤波器(BPF)、A/D模块、数字下变频模块、基带信号干扰处理模块、解调模块，数字下变频模块包括低通滤波器(LPF)、 抽样模块。
CDMA解码方法具体包括：
带通滤波器接收上述的CDMA编码信号(即图6中的r(t)),对CDMA编码信号进行带外噪声和干扰信号抑制，然后将滤波信号发送给A/D模块。
A/D模块实现中频带通采样，获取中频数字信号并发送给数字下变频模块；其中，A/D模块使用108.38MHz晶体进行采样，位宽14bits，该采样速率为CDMA载波信号的8倍，可适应大直流偏置和高动态范围的信号场景。
数字下变频模块接收中频数字信号，将中频信号下变频到基带信号，即去除中频信号的载频，恢复CDMA基带编码信号。并且为了更好的抑制突发干扰信号，将中频数字信号进行干扰处理，以减少载波同步和码捕获误差，中频信号干扰处理在数字下变频模块实现，具体是将中频数字信号通过低通滤波器，低通滤波器具有平坦的通带特性及群延迟特性，能够无失真的通过目标信号，同时具有很陡峭的过渡带，能够提供非常好的邻道抑制能力。低通滤波器典型的邻道抑制能力范围为30-90dB，经低通滤波器抑制的中频数字信号通过抽样模块进行抽取操作，恢复为CDMA基带编码信号。
并且如图所示作为备份，本实施例将中频数字信号分为两路进行干扰处理，即分别通过I路以及Q路实现中频信号干扰处理，以避免在其中一路出现故障时，另一路可以正常进行中频信号干扰处理操作。基带信号干扰处理模块对CDMA基带编码信号消除可能的欧洲环线邻道干扰及单音干扰等信号，以滤掉下变频后的折叠频率分量。
解调模块根据已知的地址扩频码编号对CDMA基带编码信号进行还原，得到CDMA解码信号，图中示意采用BPSK解调方式。
以上实施例仅用以说明本发明的技术方案而非对其限制，尽管参照上述实施例对本发明进行了详细的说明，所属领域的普通技术人员依然可以对本发明的具体实施方式进行修改或者等同替换，这些未脱离本发明精神和范围的任何修改或者等同替换，均在申请待批的本发明的权利要求保护范围之内。

Claims (12)

  1. CDMA安全编码方法，其特征在于，包括如下步骤：
    接收第一时钟信号，将第一时钟信号转换为模拟信号；
    接收数据信号和第二时钟信号，将数据信号进行差分双相位编码得到编码数字信号；
    对所述模拟信号进行调理放大后和所述编码数字信号进行耦合处理，得到所需的基带信号；
    对所述基带信号进行编码，得到基带编码信号；
    对所述基带编码信号进行CDMA编码，得到CDMA编码信号。
  2. 根据权利要求1所述的CDMA安全编码方法，其特征在于，还包括如下步骤：
    对编码数字信号进行回采；
    将回采的编码数字信号进行解码，得到解码数字信号；
    将所述解码数字信号与所述数据信号进行比较，若所述解码数字信号与所述数据信号不一致，则控制关断所述编码数字信号输出；
    若所述解码数字信号与所述数据信号一致，则输出所述编码数字信号。
  3. 根据权利要求1所述的CDMA安全编码方法，其特征在于，在接收所述模拟信号和所述编码数字信号，对所述模拟信号和所述编码数字信号进行耦合处理之前，还包括如下步骤：
    接收所述编码数字信号，对所述编码数字信号进行监测，若监测结果得出所述编码数字信号是短路信号，则关断模拟信号以及编码数字信号的输出。
  4. 根据权利要求1所述的CDMA安全编码方法，其特征在于，所述对所述基带编码信号进行CDMA编码，得到CDMA编码信号，具体包括如下步骤：
    对所述基带编码信号依次进行差分双相位解码和巴克解码，得到基带解码信号；
    对所述基带解码信号进行差分调制，得到差分调制信号；
    生成用于扩频调制的地址码，将差分调制信号与所述地址码进行直接序列扩频调制，得到扩频调制信号；
    生成用于载波调制的载波，将扩频调制信号与所述载波进行载波调制，使得扩频调制信号进行N倍扩频，得到载频信号；
    将载频信号进行功率放大以及滤波处理，得到CDMA编码信号。
  5. 根据权利要求4所述的CDMA安全编码方法，其特征在于，还包括，
    锁相环接收所述基带编码信号；
    锁相环根据基带编码信号控制差分双相位解码、巴克解码、差分调制以及地址码生成过程的频率、相位与所述基带编码信号的频率、相位同步。
  6. CDMA安全编码系统，其特征在于，包括基带信号生成设备、基带编码设备以及CDMA编码设备；所述基带信号生成设备包括数模转换单元、差分双相位编码单元、调理放大单元以及耦合单元；
    所述数模转换单元，用于接收所述第一时钟信号，将第一时钟信号转换得到模拟信号；
    所述差分双相位编码单元，用于接收数据信号和第二时钟信号，对数据信号进行差分双相位编码得到编码数字信号；
    所述调理放大单元将所述模拟信号进行调理放大，得到调理放大的模拟信号；
    所述耦合单元，用于对所述调理放大的模拟信号和所述编码数字信号进行耦合处理，得到所需的基带信号；
    所述基带编码设备，用于对所述基带信号进行编码，得到基带编码信号；
    所述CDMA编码设备，用于对所述基带编码信号进行CDMA编码，得到CDMA编码信号。
  7. 根据权利要求6所述的CDMA安全编码系统，其特征在于，所述基带信号生成设备还包括回采单元、处理单元、比较单元、控制单元；
    所述回采单元，用于对编码数字信号进行回采；
    所述处理单元，用于将回采的编码数字信号进行解码，得到解码数字信号；
    比较单元，用于将所述解码数字信号与所述数据信号进行比较，若所述解码数字信号与所述数据信号不一致，则通过控制单元控制关断所述编码数字信号输出；
    若所述解码数字信号与所述数据信号一致，则通过差分双相位编码单元输出所述编码数字信号。
  8. 根据权利要求6所述的CDMA安全编码系统，其特征在于，所述基带信号生成设备还包括数据监测单元；在所述耦合单元对所述调理放大的模拟信号和所述编码数字信号进行耦合处理，得到基带信号之前，
    所述数据监测单元接收所述编码数字信号，对所述编码数字信号进行监测，若监测结果得出所述编码数字信号是短路信号，则关断模拟信号以及编码数字信号的输出。
  9. 根据权利要求6所述的CDMA安全编码系统，其特征在于，所述CDMA编码设备包括差分双相位解码单元、巴克解码单元、差分调制单元、扩频调制单元、载波调制单 元、信号放大滤波单元；
    所述扩频调制单元包括扩频码触发模块和CDMA调制模块；
    所述载波调制单元包括载波信号源和BPSK调制模块；
    所述差分双相位解码单元对基带编码信号进行差分双相位解码，得到初始解码信号；
    所述巴克解码单元，用于对初始解码信号进行巴克解码，得到基带解码信号；
    所述差分调制单元，用于对所述基带解码信号进行差分调制，得到差分调制信号；
    所述扩频码触发模块，用于生成用于扩频调制的地址码；
    所述CDMA调制模块，用于将差分调制信号与所述地址码进行直接序列扩频调制，得到扩频调制信号；
    所述载波信号源，用于产生用于载波调制的载波；
    所述BPSK调制模块，用于将扩频调制信号与载波进行载波调制，使得扩频调制信号进行N倍扩频，得到载频信号；
    所述信号放大滤波单元，用于对载频信号进行放大、滤波处理，得到CDMA编码信号。
  10. 根据权利要求9所述的CDMA安全编码系统，其特征在于，所述CDMA编码单元还包括锁相环单元；
    所述锁相环单元，用于接收所述基带编码信号，并根据基带编码信号控制差分双相位解码、巴克解码、差分调制以及地址码生成过程的频率、相位与所述基带编码信号的频率、相位同步。
  11. 与权利要求1所述的CDMA安全编码方法对应的CDMA安全解码方法，其特征在于，包括如下步骤：
    带通滤波器接收所述CDMA编码信号，对所述CDMA编码信号进行滤波处理，得到滤波信号；
    A/D模块接收所述滤波信号，对滤波信号进行中频带通采样，获取中频数字信号；
    数字下变频模块接收所述中频数字信号，将中频信号下变频到基带信号，并对中频信号进行干扰处理，得到CDMA基带编码信号；
    基带信号干扰处理模块接收所述CDMA基带编码信号，消除CDMA基带编码信号内的邻道以及单音干扰信号，得到处理后的CDMA基带编码信号；
    解调模块接收所述处理后的CDMA基带编码信号，根据已知的地址扩频码编号对处理后的CDMA基带编码信号进行还原，得到CDMA解码信号。
  12. 与权利要求1所述的CDMA安全编码方法对应的CDMA安全解码系统，其特征在于，包括带通滤波器、A/D模块、数字下变频模块、基带信号干扰处理模块、解调模块，数字下变频模块；
    带通滤波器，用于接收所述CDMA编码信号，对所述CDMA编码信号中的带外噪声和干扰信号进行抑制，得到滤波信号；
    A/D模块，用于接收所述滤波信号，对滤波信号进行中频带通采样，获取中频数字信号；
    数字下变频模块，用于接收所述中频数字信号，将中频信号下变频到基带信号，并对中频信号进行干扰处理，得到CDMA基带编码信号；
    基带信号干扰处理模块，用于接收所述CDMA基带编码信号，消除邻道以及单音干扰信号，得到处理后的CDMA基带编码信号；
    解调模块，用于接收所述处理后的CDMA基带编码信号，根据已知的地址扩频码编号对处理后的CDMA基带编码信号进行还原，得到CDMA解码信号。
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