35 results about "Quaternary phase shift keying" patented technology

Disclosed is a unique system and method for recognizing the type of modulation embedded in an unknown complex baseband signal, comprising a receiver section for extracting the complex baseband signal from a modulated signal having a carrier frequency, and comprising an orderly series of signal processing functions for (a) estimating the bandwidth of the unknown signal, (b) removing the out-of-band noise and correcting gross carrier frequency errors, (c) discriminating between constant envelope and irregular envelope signals, (d) estimating and correcting residual carrier frequency errors, (e) classifying a constant envelope signal into one of the following modulation formats: {Continuous Wave (CW), Frequency Modulation (FM), Frequency Shift Keying (FSK)}, and (f) classifying an irregular envelope signal into one of the following modulation formats: {Amplitude Modulation (AM), Double Sideband Suppressed Carrier (DSB-SC), Binary Shift Keying (BPSK), Quaternary Phase Shift Keying (QPSK), π / 4-shifted QPSK, M-ary PSK (MPSK), and OTHER classes}.

The invention relates to a method and a system for transmitting and receiving by orthogonally dual-polarized differential quaternary phase shift keying. The system comprises a transmitting device and a receiving device, wherein the transmitting device comprises a continuous laser; the continuous laser is connected with a polarization beam splitter which is connected with a DQPSK modulator; the DQPSK modulator is connected with a precoder of which the output end is connected with a tunable optical attenuator or a polarization controller; and the polarization controller is connected with a polarization beam combiner; and the receiving device comprises a DQPSK demodulator, and the DQPSK demodulator is connected with a balanced detector which is connected with a decision circuit. In the method, four paths of electrical signals can be multiplexed, and only one demodulator and two balanced detectors are used at a receiving end to demodulate two orthogonally polarized DQPSK signals at the same time; therefore, compared with D8PSK and x-QAM systems, the system has the advantages of greatly reducing the complexity and remarkably enhancing the stability of components.

The invention provides a remote underwater acoustic communication method based on soft-demodulation soft-decoding joint iteration. The method comprises the following steps that: a transmitting end performs low density parity check (LDPC) coding on a binary information sequence which is sent by a signal source, performs quaternary phase shift keying (QPSK) modulation and Gray mapping, maps code elements to one of four positions in a constellation diagram by taking two code elements as a group, performs Walsh-m composite sequence spectrum spreading to obtain a signal to be transmitted, and converts a digital signal to be transmitted into an underwater acoustic signal; and an underwater acoustic transducer at a receiving end converts the received underwater acoustic signal, de-spreads by using a composite sequence which is the same as that of the transmitting end to obtain a receiving signal, performs self-adaptation decision feedback equalization to obtain an amplitude fading complex signal, performs soft-demodulation soft-decoding joint iteration on the signal, stops joint iteration after set iteration frequency is reached, performs belief propagation (BP) decoding on an LDPC decoder and outputs a bit value to a sink. By the method provided by the invention, the reliability of remote underwater acoustic communication is improved. The method is applicable to the remote underwater acoustic communication.

A method and apparatus for providing an asymmetrical backwards compatible communications signal that is capable of being decoded by QPSK and OQPSK receivers as well as PSK and QAM receivers is provided. The invention comprises a timing error accumulator coupled to a first bit stream. The first bit stream includes content that is common to the QPSK / OQPSK receiver and to the PSK / QAM receiver. A phase error accumulator is coupled to a second bit stream and adjusts the phase of symbols in the second bit stream. A phase and timing error compensator is coupled to the phase error accumulator and the timing error accumulator and adjusts the first and second bit streams received from the phase error accumulator and the timing error accumulator in order to reduce timing and phase errors. A higher order modulator coupled to the phase- and timing error compensator is also provided. The higher order modulator processes the first and second bit streams to provide the asymmetrical backwards compatible signal.

The invention discloses a method for recognizing a satellite communication signal modulation way. According to the scheme, the method comprises the following steps: 1, filtering a received signal to obtain a signal to be recognized; performing power spectrum smoothening, carrier frequency estimation and coherent demodulation on the signal to be recognized to obtain a demodulated signal; 3, estimating the code element rate of the demodulated signal; 4, determining whether the received signal is a binary phase shift keying signal or not by using a square spectrum; 5, determining whether the received signal is a quaternary phase shift keying signal or a hexadecimal quadrature amplitude modulation signal by using a signal quartic spectrum, carrier frequency and the code element rate; 6, determining whether the received signal is an octonary phase shift keying signal or not by using a signal eightfold spectrum; and 7, determining whether the received signal is a hexadecimal amplitude phase shift keying signal or not by using a signal duodenary spectrum, the carrier frequency and the code element rate. The method has high recognition accuracy, and can be applied to real-time monitoring of satellite communication signals. Through adoption of the method, totally-blind real-time recognition of the satellite communication signal modulation way can be realized.

A method and apparatus for providing an asymmetrical backwards compatible communications signal that is capable of being decoded by QPSK and OQPSK receivers as well as PSK and QAM receivers is provided. The invention comprises a timing error accumulator coupled to a first bit stream. The first bit stream includes content that is common to the QPSK / OQPSK receiver and to the PSK / QAM receiver. A phase error accumulator is coupled to a second bit stream and adjusts the phase of symbols in the second bit stream. A phase and timing error compensator is coupled to the phase error accumulator and the timing error accumulator and adjusts the first and second bit streams received from the phase error accumulator and the timing error accumulator in order to reduce timing and phase errors. A higher order modulator coupled to the phase and timing error compensator is also provided. The higher order modulator processes the first and second bit streams to provide the asymmetrical backwards compatible signal.

In the invention, clock recovery and optical transmission signal performance monitoring are combined, and the timing information of an optical transmission signal is extracted while the monitoring of signal accumulation dispersion and optical signal-to-noise ratio is realized. The method comprises the following steps of: performing optical domain frequency conversion to the timing information (clock) of the optical transmission signal by using an electrooptical modulator, and reducing the frequency of the clock to a lower frequency; and extracting the timing information by using a phase locked loop in the low frequency range, outputting a phase error signal in the phase locked loop by using an orthogonal phase discriminator and simultaneously outputting a direct-current level for representing the intensity of the timing information, wherein the variation rule of the level is used for monitoring the accumulation dispersion and the optical signal-to-noise ratio of the transmission signal. The invention also provides a clock extraction and performance monitoring system of a differential quaternary phase shift keying (DQPSK) system for implementing the method.

Said invention is based on a transmitter of M-ary parallel communication mode, which is characterized by combining M-ary modulation mode with traditional binary phase shift keying, quaternary phase shift keying and quadrature amplitude modulation, dividing data stream into multiplex parallel modulation, in each path, part of data is modulated by M-ary mode and part of data is modulated by traditional modulation mode, using quasi-orthogonal code character to construct as more as possible quasi-orthogonal code character, making optimal grouping, to raise demodulation property.

The present invention provides a quaternary phase shift keying signal spectrum estimation method for estimating the spectral parameter of the phase modulation signal of the quaternary phase shift keying of a complex electromagnetic space based on the mode of fast Fourier transform spectral fitting. The method comprises a step of carrying out dephasing modulation processing on a quaternary phase shift keying signal, a step of carrying out spectral line fitting weakening barrier effect on the quaternary phase shift keying signal which is subjected to the dephasing modulation processing, a step of accurately estimating the spectrum combined with the mode of spectrum complex coefficient decoherence so as to obtain a spectrum estimation result, and a step of using a threshold sliding iterative mode to optimize the spectrum estimation result, and thus ensuring the obtainment of a most effective spectrum estimation result. Accordingly, by employing the present invention, the center frequency of the QPSK signal can be accurately estimated, in a low SNR condition, and a result shows that the spectral estimation accuracy still can reach about 0.5KHz even when a signal power level is low as -110dBm.

The invention discloses a phase judgment method used for differential quaternary phase shift keying (DQPSK) demodulation. The method comprises the following steps: a) determining a fixed value n according to a signal frequency Fz and an AD sampling frequency Fs of a DQPSK modulation signal; b) judging a phase area in which a phase difference (DP) of each of AD sampling points and a corresponding adjacent sampling point is positioned, wherein (n-1) sampling points are between each of the AD sampling points and the corresponding adjacent sampling point; c) counting the number of continuous AD sampling points positioned in the same phase area as the DP between the AD sampling points and the corresponding adjacent sampling points; and d) judging a signal phase change corresponding to the counting according to the number of the AD sampling points counted each time and performing modification on the next phase. The phase judgment method used for the DQPSK demodulation provided by the invention has a very good effect in near instantaneous companded audio multiplex modulation, greatly reduces bit error rate, highly effectively restores the phase shift information before demodulating and ensures the fluency of near instantaneous companded audio multiplex decoding.

A 2n-QAM (e.g. 16-QAM) optical modulator 10 comprising cascaded I-Q modulators (22, 38). The first I-Q modulator 22 applies 2n-2 (e.g. 4) QAM to an optical signal, having a constellation diagram with the 2n-2 constellation points located in quadrant I. The second I-Q modulator (38) subsequently applies a quaternary phase-shift keying (QPSK) modulation scheme to the optical signal, thereby rotating the constellation points of the 2n-2-QAM modulation scheme to quadrants II, III and IV, to produce a 2n-QAM modulation constellation diagram. The rotation causes the 2n-QAM modulator to inherently apply four quadrant differential encoding to the optical signal. A method of 2n-QAM optical modulation is also provided and optical signal transmission apparatus comprising the 2n-QAM optical modulator.

The invention relates to a quaternary phase-shift keying signal tracking method and device, which are applied to a GNSS (Global Navigation Satellite System) receiver. Under the combined tracking mode of in-phase and orthogonal dicode channels, the method comprises the following steps of: carrying out correlation operation respectively with corresponding local PRN (Pseudo-Random Noise) codes on an in-phase (I) code channel signal and an orthogonal (Q) code channel signal after down-conversion, and outputting the integral results of the I code channel signal and the Q code channel signal; respectively carrying out identification on the integral results of the I code channel signal and the Q code channel signal in at least one tracking loop so as to obtain identification results; and carrying out mathematic operation on the identification results of the I code channel signal and the Q code channel signal in the same tracking loop so as to obtain a synthesized identification result. In the tracking loop, the corresponding devices comprise an I code channel identifier, a Q code channel identifier and a synthetic identifier. According to the quaternary phase-shift keying signal tracking method and device, the noise intensity of the tracking loops such as DLL (Dynamic Link Library), PLL (Phase Locked Loop) and FLL (Fixed Loss Loop) is obviously reduced.

A 2n-QAM (e.g. 16-QAM) optical modulator comprising cascaded I-Q modulators. The first I-Q modulator applies 2n-2 (e.g. 4) QAM to an optical signal, having a constellation diagram with the 2n-2 (e.g., 4) constellation points located in quadrant I. The second I-Q modulator subsequently applies a quaternary phase-shift keying (QPSK) modulation scheme to the optical signal, thereby rotating the constellation points of the 2n-2-QAM modulation scheme to quadrants II, III and IV, to produce a 2n-QAM modulation constellation diagram. The rotation causes the 2n-QAM modulator to inherently apply four quadrant differential encoding to the optical signal. A method of 2n-QAM optical modulation is also provided and optical signal transmission apparatus comprising the 2n-QAM optical modulator.

N (integer equal to or above 3) quaternary phase shift keying (QPSK) outputs having different amplitude levels, i.e., r2=r1×2−(i−1), i=2 . . . N with respect to a maximum amplitude level r1 are superposed after power amplification to form M(=22N)-valued / quadrature amplitude modulation (QAM), and N-1 outputs si except the quaternary phase shift keying QPSK-1 having the maximum amplitude r1 are subjected to power amplification in this formation, then the outputs are combined by a directional coupler to obtain a combined signal, and an output of the quaternary phase shift keying QPSK-1 and the combined signal are transmitted from two systems of antennas to be vectorially superposed and combined in a space.

The invention discloses a digital modulation method, a digital transmission device and equipment. The digital modulation method comprises the following steps: implementing symbol mapping on the source data of each sub-channel to obtain quaternary phase shift keying (QPSK) symbols; grouping the QPSK symbols and performing discrete Fourier transform (DFT) to obtain frequency domain signals; implementing low-pass filtering and frequency reuse processing on the frequency domain signals of each sub-channel; implementing inverse Fourier transform on the frequency domain signals that are subjected to frequency reuse to obtain an OFDM symbol, and then transmitting the OFDM symbol after adding the OFDM symbol into a cyclic prefix (CP). According to the digital modulation method, the digital transmission device and equipment disclosed by the invention, the frequency domain signals obtained by implementing DFT on each sub-channel are separately subjected to low-pass filtering, and thus the bandwidth of modulation signals subjected to frequency domain reuse becomes narrower, the crosstalk damages caused by multiplexing multiple sub-bands can also be reduced, and the spectrum efficiency can be increased.

The invention discloses a method for recognizing a satellite communication signal modulation way. According to the scheme, the method comprises the following steps: 1, filtering a received signal to obtain a signal to be recognized; performing power spectrum smoothening, carrier frequency estimation and coherent demodulation on the signal to be recognized to obtain a demodulated signal; 3, estimating the code element rate of the demodulated signal; 4, determining whether the received signal is a binary phase shift keying signal or not by using a square spectrum; 5, determining whether the received signal is a quaternary phase shift keying signal or a hexadecimal quadrature amplitude modulation signal by using a signal quartic spectrum, carrier frequency and the code element rate; 6, determining whether the received signal is an octonary phase shift keying signal or not by using a signal eightfold spectrum; and 7, determining whether the received signal is a hexadecimal amplitude phase shift keying signal or not by using a signal duodenary spectrum, the carrier frequency and the code element rate. The method has high recognition accuracy, and can be applied to real-time monitoring of satellite communication signals. Through adoption of the method, totally-blind real-time recognition of the satellite communication signal modulation way can be realized.

A modulation and demodulation method of a wave form synergy signal based on a frequency domain and a fractional Fourier domain orthogonal basis function relates to a signal modulation and demodulation method, and aims at solving the problem that a modulation and demodulation method of an existing quaternary phase shift keying (QPSK) signal is low in efficiency. Modulation and demodulation are achieved by a way of wave form synergy of a chirp signal and a sine and cosine signal, and therefore the modulation and demodulation method of the wave form synergy signal based on the frequency domain and the fractional Fourier domain orthogonal basis function is a novel modulation and demodulation method. In addition, two branches of chirp signals are respectively added to an I branch and a Q branch modulated by the existing QPSK signal and are used as carrier waves to respectively modulate one branch of baseband signal, so that existing two-way modulation is added up to four-way modulation, and at the demodulation end, filter waves are combined and matched by using a frequency domain template and a fraction domain template, and eight integrators are designed, and finally filtering results are combined so as to judge the information bit. The modulation and demodulation method is appropriate for the wireless communication field.

The invention provides a signal generation device and method applied to the technical field of communication, and the device comprises a light source which is used for generating optical carriers, two microwave sources which are used for outputting continuous single-frequency microwave signals, two pulse signal generators which are used for generating electrical coding pulse signals, and two channel DC voltage sources. Each channel outputs stable direct-current voltage and is used for providing bias voltage for the dual-drive dual-polarization Mach-Zehnder modulator, and the dual-polarization dual-drive Mach-Zehnder modulator is used for modulating an optical carrier by using a continuous single-frequency microwave signal, an electrical coding pulse signal and the bias voltage to obtain an optical signal; the optical signal comprises at least one of a radio frequency-amplitude shift keying signal, a radio frequency-frequency shift keying signal, a radio frequency-fourth order amplitude modulation signal, a radio frequency-binary phase shift keying signal, a radio frequency-binary phase shift keying pulse signal, a radio frequency-quaternary phase shift keying signal and a radio frequency-multicarrier phase shift keying signal.

A method implemented in a transmission apparatus used in an optical fiber communications system for a polarization switched differential quaternary phase-shift keying (DQPSK) signal is disclosed. The method comprises splitting data into two or more data streams, inputting said two or more data streams to 1-bit DQPSK precoders to perform 1-bit DQPSK precoding, and multiplexing inphase outputs of the 1-bit DQPSK precoders to generate a first output; and multiplexing quadrature outputs of the 1-bit DQPSK precoders to generate a second output. Other methods, apparatuses, and systems also are disclosed.

The invention relates to a method and an apparatus for modulating double UQPSK (Unbalance Quaternary Phase Shift Keying) signals. The modulation method comprises the steps of: firstly, calculating signal component coefficients c1, c2, c3 and c4 according to a branch power ratio of UQPSK service signals; next, calculating intermodulation coefficients b1, b2, b3 and b4 according to the branch power ratio of the UQPSK service signals; then generating a constant-envelope baseband signal; and finally, carrying out quadrature modulation on the constant-envelope baseband signal to a carrier. The modulation apparatus comprises a baseband signal generator and a quadrature modulator; the baseband signal generator synthesizes two paths of UQPSK service signals into one path of constant-envelope baseband signal, and outputs a real part signal and an imaginary part signal of the constant-envelope baseband signal to the quadrature modulator; and the quadrature modulator outputs signals after carrying out quadrature modulation on the input signals. According to the method and the apparatus which are disclosed by the invention, two UQPSK service signals are modulated to the same carrier, constant signal envelope and high multiplexing efficiency are achieved, and signal transmission quality and power efficiency are improved.

In the invention, clock recovery and optical transmission signal performance monitoring are combined, and the timing information of an optical transmission signal is extracted while the monitoring of signal accumulation dispersion and optical signal-to-noise ratio is realized. The method comprises the following steps of: performing optical domain frequency conversion to the timing information (clock) of the optical transmission signal by using an electrooptical modulator, and reducing the frequency of the clock to a lower frequency; and extracting the timing information by using a phase locked loop in the low frequency range, outputting a phase error signal in the phase locked loop by using an orthogonal phase discriminator and simultaneously outputting a direct-current level for representing the intensity of the timing information, wherein the variation rule of the level is used for monitoring the accumulation dispersion and the optical signal-to-noise ratio of the transmission signal. The invention also provides a clock extraction and performance monitoring system of a differential quaternary phase shift keying (DQPSK) system for implementing the method.

The invention relates to a quaternary phase-shift keying signal tracking method and device, which are applied to a GNSS (Global Navigation Satellite System) receiver. Under the combined tracking mode of in-phase and orthogonal dicode channels, the method comprises the following steps of: carrying out correlation operation respectively with corresponding local PRN (Pseudo-Random Noise) codes on an in-phase (I) code channel signal and an orthogonal (Q) code channel signal after down-conversion, and outputting the integral results of the I code channel signal and the Q code channel signal; respectively carrying out identification on the integral results of the I code channel signal and the Q code channel signal in at least one tracking loop so as to obtain identification results; and carrying out mathematic operation on the identification results of the I code channel signal and the Q code channel signal in the same tracking loop so as to obtain a synthesized identification result. In the tracking loop, the corresponding devices comprise an I code channel identifier, a Q code channel identifier and a synthetic identifier. According to the quaternary phase-shift keying signal tracking method and device, the noise intensity of the tracking loops such as DLL (Dynamic Link Library), PLL (Phase Locked Loop) and FLL (Fixed Loss Loop) is obviously reduced.

The invention discloses a blind separation device based on BPSK / QPSK / 8QAM (binary phase shift keying / quaternary phase shift keying / 8-quadrature amplitude modulation) modulation signals, wherein a radio frequency front-end processing unit 1 of the blind separation device is connected with a digital signal processor 3 via an input buffer 2; the digital signal processor 3 is connected with a field programmable gate array FPGA unit 5 and a signal output unit 6 via an output buffer 4 respectively; the field programmable gate array FPGA unit 5 is connected with a video output unit 7; the video output unit 7 is connected with an LCD liquid crystal display 8; and a timing and control unit 12 is connected with the radio frequency front-end processing unit 1, the input buffer 2, a first off-chip data memory 9a, a second off-chip data memory 9b, a FLASH memory 10, the output buffer 4, the field programmable gate array FPGA unit 5, the video output unit 7 and the digital signal processor 3 respectively. The device can eliminate interference signals, improve communication quality, and separate two paths of hybrid communication signals.

The present invention is applicable to the field of optical communication, and provides a method and a device for locking a differential quadrature-phase shift keying demodulator, the method comprising: acquiring an optical differential quadrature-phase shift keying signal, and acquiring the optical differential quadrature the frequency of the shift keying signal when there is no perturbation signal; according to the frequency of the optical differential quadrature shift keying signal when there is no perturbation signal, determine whether the optical differential quadrature shift keying signal contains a polarization interference signal; if it contains , then obtain the frequency of the polarization interference signal; set the frequency of the disturbance signal to a frequency different from the frequency of the polarization interference signal; load the set disturbance signal into the optical differential four-phase shift key control signal. In the embodiment of the present invention, the frequency of the optical DPQSK when there is no disturbance signal is obtained, and the frequency of the disturbance signal is set to be different from the frequency of the polarization disturbance signal, so that the frequency of the disturbance signal avoids the frequency of the polarization disturbance signal, and the locking of the wavelength of the optical DPQSK is realized. .

The invention discloses a phase judgment method used for differential quaternary phase shift keying (DQPSK) demodulation. The method comprises the following steps: a) determining a fixed value n according to a signal frequency Fz and an AD sampling frequency Fs of a DQPSK modulation signal; b) judging a phase area in which a phase difference (DP) of each of AD sampling points and a corresponding adjacent sampling point is positioned, wherein (n-1) sampling points are between each of the AD sampling points and the corresponding adjacent sampling point; c) counting the number of continuous AD sampling points positioned in the same phase area as the DP between the AD sampling points and the corresponding adjacent sampling points; and d) judging a signal phase change corresponding to the counting according to the number of the AD sampling points counted each time and performing modification on the next phase. The phase judgment method used for the DQPSK demodulation provided by the invention has a very good effect in near instantaneous companded audio multiplex modulation, greatly reduces bit error rate, highly effectively restores the phase shift information before demodulating and ensures the fluency of near instantaneous companded audio multiplex decoding.

The invention provides a remote underwater acoustic communication method based on soft-demodulation soft-decoding joint iteration. The method comprises the following steps that: a transmitting end performs low density parity check (LDPC) coding on a binary information sequence which is sent by a signal source, performs quaternary phase shift keying (QPSK) modulation and Gray mapping, maps code elements to one of four positions in a constellation diagram by taking two code elements as a group, performs Walsh-m composite sequence spectrum spreading to obtain a signal to be transmitted, and converts a digital signal to be transmitted into an underwater acoustic signal; and an underwater acoustic transducer at a receiving end converts the received underwater acoustic signal, de-spreads by using a composite sequence which is the same as that of the transmitting end to obtain a receiving signal, performs self-adaptation decision feedback equalization to obtain an amplitude fading complex signal, performs soft-demodulation soft-decoding joint iteration on the signal, stops joint iteration after set iteration frequency is reached, performs belief propagation (BP) decoding on an LDPC decoder and outputs a bit value to a sink. By the method provided by the invention, the reliability of remote underwater acoustic communication is improved. The method is applicable to the remote underwater acoustic communication.

The present invention provides a quaternary phase shift keying signal spectrum estimation method for estimating the spectral parameter of the phase modulation signal of the quaternary phase shift keying of a complex electromagnetic space based on the mode of fast Fourier transform spectral fitting. The method comprises a step of carrying out dephasing modulation processing on a quaternary phase shift keying signal, a step of carrying out spectral line fitting weakening barrier effect on the quaternary phase shift keying signal which is subjected to the dephasing modulation processing, a step of accurately estimating the spectrum combined with the mode of spectrum complex coefficient decoherence so as to obtain a spectrum estimation result, and a step of using a threshold sliding iterative mode to optimize the spectrum estimation result, and thus ensuring the obtainment of a most effective spectrum estimation result. Accordingly, by employing the present invention, the center frequency of the QPSK signal can be accurately estimated, in a low SNR condition, and a result shows that the spectral estimation accuracy still can reach about 0.5KHz even when a signal power level is low as -110dBm.

The application discloses a kind of distributed security transmission methods and communication systems based on intelligent reflecting surface, the method includes: transmitter carries out series-parallel conversion to binary data to be transmitted, obtains odd bit bit string and even bit bit string, and selects one bit string to carry out binary phase shift keying BPSK modulation, obtains BPSKI signal and sends.The BPSKI signal sent by transmitter reaches intelligent reflecting surface, IRS calculates phase offset coefficient, and the incident BPSKI signal is phase-shifted and reflected to obtain BPSKII signal, and BPSKII signal is reflected to receiver.The receiver superimposes the BPSKI signal directly from transmitter and the BPSKII signal reflected by IRS, and the signal obtained is the quaternary phase shift keying modulation QPSK signal carrying expected data, and the receiver recovers expected data using QPSK demodulation method.The application makes transmitter only send part data information, and signal is transmitted in two ways, which can effectively prevent the leakage of expected data information, thereby improving the security of communication system.

The invention relates to a method and a system for transmitting and receiving by orthogonally dual-polarized differential quaternary phase shift keying. The system comprises a transmitting device and a receiving device, wherein the transmitting device comprises a continuous laser; the continuous laser is connected with a polarization beam splitter which is connected with a DQPSK modulator; the DQPSK modulator is connected with a precoder of which the output end is connected with a tunable optical attenuator or a polarization controller; and the polarization controller is connected with a polarization beam combiner; and the receiving device comprises a DQPSK demodulator, and the DQPSK demodulator is connected with a balanced detector which is connected with a decision circuit. In the method, four paths of electrical signals can be multiplexed, and only one demodulator and two balanced detectors are used at a receiving end to demodulate two orthogonally polarized DQPSK signals at the same time; therefore, compared with D8PSK and x-QAM systems, the system has the advantages of greatly reducing the complexity and remarkably enhancing the stability of components.