CN109067468B - KK transmission method applied to direct detection optical communication system and direct detection optical communication system - Google Patents
KK transmission method applied to direct detection optical communication system and direct detection optical communication system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/5165—Carrier suppressed; Single sideband; Double sideband or vestigial
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/616—Details of the electronic signal processing in coherent optical receivers
- H04B10/6162—Compensation of polarization related effects, e.g., PMD, PDL
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/616—Details of the electronic signal processing in coherent optical receivers
- H04B10/6164—Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/616—Details of the electronic signal processing in coherent optical receivers
- H04B10/6165—Estimation of the phase of the received optical signal, phase error estimation or phase error correction
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/66—Non-coherent receivers, e.g. using direct detection
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- H04B10/691—Arrangements for optimizing the photodetector in the receiver
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Abstract
The invention discloses a KK transmission method applied to a direct detection optical communication system and the direct detection optical communication system, and relates to the field of direct detection optical communication systems. The method comprises the following steps: at a transmitting end, performing single-sideband modulation on an original data stream, performing Alamouti coding, digital-to-analog conversion, IQ modulation and polarization beam combination to obtain a polarization multiplexing optical signal, and transmitting the polarization multiplexing optical signal to an optical fiber; at a receiving end, coupling a received optical signal with a local oscillator light source, wherein the power of the local oscillator light source is far greater than that of the received optical signal; performing photoelectric conversion and analog-to-digital conversion on the coupled optical signal to obtain a digital signal; KK receiving is carried out on the digital signal, and amplitude and phase information of the single-sideband Alamouti coded signal are recovered; performing Alamouti decoding and single sideband demodulation to recover the original data stream. The invention simplifies the structure of the sending end and the receiving end, improves the bandwidth and the performance of the system and enhances the stability.
Description
Technical Field
The invention relates to the field of direct detection optical communication systems, in particular to a KK transmission method applied to a direct detection optical communication system and the direct detection optical communication system.
Background
In optical communication networks such as short distance, access, metropolitan area and the like, due to the limitation of cost, a scheme of direct modulation and direct detection is mostly adopted for a transmission structure, and the scheme is widely applied due to low cost and simple structure. However, such a structure cannot detect a phase, and thus, modulation efficiency is low, and it is difficult to implement a modulation coding scheme with high spectral efficiency. Meanwhile, when long-distance transmission is performed, the original phase information of the signal cannot be recovered during direct detection, so that the dispersion accumulated during long-distance transmission cannot be compensated.
In order to solve the above problems, researchers have proposed many methods, such as: the method adopts a DMT (Discrete Multi-Tone) modulation mode with higher modulation efficiency or a mode of carrying out dispersion pre-compensation through a transmitting end to solve the problems of low spectral efficiency and accumulated dispersion. The methods not only increase the complexity of the sending end and the receiving end of the system, but also consume the bandwidth of the system, so that the application of the technologies in practice is limited.
Disclosure of Invention
The present invention is directed to overcome the above-mentioned drawbacks of the prior art, and provides a KK transmission method applied to a direct detection optical communication system and a direct detection optical communication system, which not only simplifies the structures of a transmitting end and a receiving end, improves the bandwidth and performance of the system, but also enhances the stability thereof, so that the method can become a practical technical means.
The invention provides a KK transmission method applied to a direct-detection optical communication system, which comprises the following steps:
at a sending end, carrying out single-side band modulation on an original data stream to obtain an original single-side band sending signal; performing Alamouti coding to obtain two single-sideband Alamouti coding signals; performing digital-to-analog conversion and IQ modulation on the two single-sideband Alamouti coded signals to form two orthogonal single-sideband optical signals; carrying out polarization beam combination on the two paths of orthogonal single-sideband optical signals to obtain polarization multiplexing optical signals, and sending the polarization multiplexing optical signals to an optical fiber;
at a receiving end, coupling a received optical signal with a local oscillator light source, wherein the power of the local oscillator light source is far greater than that of the received optical signal; performing photoelectric conversion on the coupled optical signal to obtain an analog electric signal; performing analog-to-digital conversion to obtain a digital signal; KK receiving is carried out on the digital signal, and amplitude and phase information of the single-sideband Alamouti coded signal are recovered; performing Alamouti decoding to recover the original single-sideband transmission signal; and carrying out single sideband demodulation to recover the original data stream.
On the basis of the above technical solution, the expression of the original single-sideband transmission signal is as follows:
where x (t) is the input signal, i is the unit of an imaginary number,for Hilbert transform of the input signal, yUSB(t) is the upper sideband signal, yLSB(t) is the lower sideband signal;
when carrying out the doubleFor transmission, the uplink channel adopts yUSB(t) modulation for upper sideband transmission and downlink channel using yLSBAnd (t) modulating to carry out lower sideband transmission, and simultaneously realizing a modulation light source at a transmitting end and a local oscillation light source at a receiving end by adopting a single light source structure.
On the basis of the technical scheme, the specific process for Alamouti coding is as follows:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1T is any time, T is code element time interval, two Alamouti coded signals are obtained after Alamouti coding, and the two Alamouti coded signals are respectively expressed as T and T + T timeAnd
the channel responses corresponding to the two Alamouti coded signals are h respectively0And h1At times T and T + T, the same receiver receives signal r0And r1Respectively as follows:
r0＝r(t)＝h0s0+h1s1+n0；
n0and n1Respectively representing the noise signals of the two channels.
On the basis of the technical scheme, KK reception is carried out on the digital signal, amplitude and phase information of the single-sideband Alamouti coded signal are recovered, and the specific process is as follows:
the digital signal is expressed as ss (t), and after KK reception is carried out on ss (t), the amplitude of the single-side-band optical signal is obtainedPhase positionWherein H (-) is Hilbert transform to recover single-sideband optical signal
On the basis of the technical scheme, Alamouti decoding is carried out to recover the original single-sideband transmitting signal, and the specific process is as follows:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1Part s of the original single sideband transmitted signal for channel estimation0And s1As is known, the Alamouti decoding is performed on the recovered single-sideband optical signal to obtain the channel response h0And h1Respectively as follows:
estimating other transmitted data not used for channel estimation:
wherein the content of the first and second substances,andeach is an estimate of the original single sideband transmitted signal.
The invention also provides a direct detection optical communication system based on KK transmission, which comprises a sending end and a receiving end, wherein the sending end comprises a single sideband modulation unit, an Alamouti coding unit, a first digital-to-analog converter, a second digital-to-analog converter, a modulation light source, a first optical IQ modulator, a second optical IQ modulator and a polarization beam combiner, and the single sideband modulation unit carries out single sideband modulation on the original data stream to obtain an original single sideband sending signal; the Alamouti coding unit carries out Alamouti coding to obtain two paths of Alamouti coding signals; the first digital-to-analog converter and the second digital-to-analog converter respectively perform digital-to-analog conversion on the two paths of Alamouti coded signals; carrying out IQ modulation on a modulation light source, a first optical IQ modulator and a second optical IQ modulator to form two paths of orthogonal single-sideband optical signals; the polarization beam combiner performs polarization beam combination on the two paths of orthogonal single-sideband optical signals to obtain polarization multiplexed optical signals, and the polarization multiplexed optical signals are sent to the optical fiber;
the receiving end comprises a local oscillator light source, a photoelectric detector, an analog-to-digital converter, a KK receiving unit, an Alamouti decoding unit and a single-sideband demodulation unit, the receiving end couples a received optical signal with the local oscillator light source, and the power of the local oscillator light source is far greater than that of the optical signal received by the receiving end; the photoelectric detector performs photoelectric conversion on the coupled optical signal to obtain an analog electric signal; the analog-to-digital converter performs analog-to-digital conversion on the analog electric signal to obtain a digital signal; the KK receiving unit is used for KK receiving the digital signal and recovering amplitude and phase information of the single-sideband Alamouti coded signal; the Alamouti decoding unit carries out Alamouti decoding and restores the original single-sideband transmitting signal; the single side band demodulation unit carries out single side band demodulation to recover the original data stream.
On the basis of the above technical solution, the expression of the original single-sideband transmission signal is as follows:
where x (t) is the input signal, i is the unit of an imaginary number,for Hilbert transform of the input signal, yUSB(t) is the upper sideband signal, yLSB(t) is the lower sideband signal;
when bidirectional transmission is performed, the uplink channel adopts yUSB(t) modulation for upper sideband transmission and downlink channel using yLSB(t) modulation for lower sideband transmission using single carrierThe light source structure simultaneously realizes a modulation light source at a transmitting end and a local oscillation light source at a receiving end.
On the basis of the technical scheme, the specific process of Alamouti coding by the Alamouti coding unit is as follows:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1T is any time, T is code element time interval, two Alamouti coded signals are obtained after Alamouti coding, and the two Alamouti coded signals are respectively expressed as T and T + T timeAnd
the channel responses corresponding to the two Alamouti coded signals are h respectively0And h1At times T and T + T, the same receiver receives signal r0And r1Respectively as follows:
r0＝r(t)＝h0s0+h1s1+n0；
n0and n1Respectively representing the noise signals of the two channels.
On the basis of the technical scheme, the KK receiving unit KK receives the digital signal and recovers the amplitude and phase information of the single-sideband Alamouti coded signal, and the specific process is as follows:
the digital signal is expressed as ss (t), and after KK reception is carried out on ss (t), the amplitude of the single-side-band optical signal is obtainedPhase positionWherein H (-) is Hilbert transform to recover single-sideband optical signal
On the basis of the technical scheme, the Alamouti decoding unit performs Alamouti decoding to recover the original single-sideband transmitting signal, and the specific process is as follows:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1Part s of the original single sideband transmitted signal for channel estimation0And s1As is known, the Alamouti decoding is performed on the recovered single-sideband optical signal to obtain the channel response h0And h1Respectively as follows:
estimating other transmitted data not used for channel estimation:
wherein the content of the first and second substances,andeach is an estimate of the original single sideband transmitted signal.
Compared with the prior art, the invention has the following advantages:
(1) the invention fully utilizes the technical characteristics of KK transmission, after the strength of a signal is detected, the amplitude and phase information of the original signal is recovered through a KK algorithm, so that the signal can be subjected to high-spectrum-efficiency coding transmission, such as QAM, OFDM and the like, meanwhile, Alamouti decoding polarization multiplexing signals are adopted, the influence of polarization state change when a single photoelectric detector at a receiving end receives the signal can be compensated, polarization-independent receiving is realized, and meanwhile, the diversity effect generated by two paths of signals can effectively improve the transmission capability of the signal in a fading channel, so that the structure of a transmitting end and the receiving end is simplified, the bandwidth and the performance of a system are improved, the stability of the system is also enhanced, and the system can become a practical technical means.
(2) According to the invention, two paths of signals obtained by Alamouti coding have a certain coding symmetry relation, so that the original transmission signals can be recovered even if the two paths of signals are mixed together. Meanwhile, the two-transmitting one-receiving system structure forms diversity gain, and can effectively compensate fading of a channel.
(3) The invention adopts a polarization multiplexing structure based on Alamouti coding at a transmitting end, and uses one local oscillator light source at a receiving end, wherein the power of the local oscillator light source is far greater than that of an optical signal received by the receiving end; still, a single PD (Photo Detector) is used for direct detection. Through Alamouti coding technique and KK transmission technique, realized carrying out phase detection in directly examining optical communication system for the modulation mode of high spectral efficiency can be realized to the signal, also can carry out the compensation of phase place at the receiving terminal simultaneously, when improving the system bandwidth, has also promoted the transmission performance of system. Meanwhile, the system adopting the Alamouti coding structure ensures that the quality of the recovered signals after receiving is irrelevant to the polarization state of the signals, and enhances the stability and the practicability of the direct detection optical communication system in the application of the real environment.
Drawings
Fig. 1 is a schematic structural diagram of a transmitting end of a direct detection optical communication system based on KK transmission in an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a receiving end of a direct detection optical communication system based on KK transmission in the embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments.
The embodiment of the invention provides a KK (Kramers-Kronig, Kramerol-Crannixi) transmission method applied to a direct-detection optical communication system, which comprises the following steps:
referring to fig. 1, at a transmitting end, single-sideband modulation is performed on an original data stream to obtain an original single-sideband transmitting signal; performing Alamouti (Allamouti) coding on an original single-sideband transmitting signal to obtain two single-sideband Alamouti coding signals; performing digital-to-analog conversion and IQ modulation on the two single-sideband Alamouti coded signals to form two orthogonal single-sideband optical signals; and carrying out polarization beam combination on the two paths of orthogonal single-sideband optical signals to obtain polarization multiplexing optical signals, and sending the polarization multiplexing optical signals to the optical fiber to finish the signal sending process.
Referring to fig. 2, at a receiving end, a received optical signal is coupled to a local oscillator light source with power much greater than that of the optical signal, and a single photodetector is used to perform photoelectric conversion on the coupled optical signal to obtain an analog electrical signal; performing analog-to-digital conversion on the analog electric signal to obtain a digital signal; KK receiving is carried out on the digital signal, and amplitude and phase information of the single-sideband Alamouti coded signal are recovered; performing Alamouti decoding (channel estimation) to recover the original single sideband transmission signal; the original single sideband transmission signal is subjected to single sideband demodulation to recover the original data stream.
The embodiment of the invention also provides a direct detection optical communication system based on KK transmission, which comprises a sending end and a receiving end.
Referring to fig. 1, the transmitting end includes a first digital signal processor 101, a first digital-to-analog converter 105, a second digital-to-analog converter 106, a modulated light source 107, a first optical IQ modulator 108, a second optical IQ modulator 109, and a polarization beam combiner 110, where the first digital signal processor 101 includes a single-sideband modulation unit 103 and an Alamouti coding unit 104, and the single-sideband modulation unit 103 performs single-sideband modulation on an original data stream 102 to obtain an original single-sideband transmission signal; the Alamouti coding unit 104 performs Alamouti coding on the original single-sideband transmitting signals to obtain two single-sideband Alamouti coding signals; the first digital-to-analog converter 105 and the second digital-to-analog converter 106 respectively perform digital-to-analog conversion on the two single-sideband Alamouti coded signals; the modulation light source 107, the first optical IQ modulator 108 and the second optical IQ modulator 109 perform IQ modulation to form two paths of orthogonal single-sideband optical signals; the polarization beam combiner 110 performs polarization beam combination on the two orthogonal single-sideband optical signals to obtain polarization multiplexed optical signals, and sends the polarization multiplexed optical signals to an optical fiber.
Referring to fig. 2, the receiving end includes a local oscillator light source 201, a PD (Photo Detector) 203, an analog-to-digital converter 204, and a second digital signal processor 208, where the second digital signal processor 208 includes a KK receiving unit 205, an Alamouti decoding unit 206, and a single-sideband demodulation unit 207, the receiving end couples the received optical signal 202 with the local oscillator light source 201, and the power of the local oscillator light source 201 is much greater than that of the optical signal received by the receiving end; the photoelectric detector 203 performs photoelectric conversion on the coupled optical signal to obtain an analog electrical signal; the analog-to-digital converter 204 performs analog-to-digital conversion on the analog electrical signal to obtain a digital signal; the KK receiving unit 205 performs KK receiving on the digital signal to recover amplitude and phase information of the single-sideband Alamouti coded signal; alamouti decoding unit 206 performs Alamouti decoding to restore the original single sideband transmission signal; the single-sideband demodulation unit 207 performs single-sideband demodulation on the restored original single-sideband transmission signal to restore the original data stream.
At a transmitting end, the single-sideband modulation unit 103 performs single-sideband modulation on an original data stream to obtain an original single-sideband transmission signal, where the original single-sideband transmission signal may be: an OFDM (Orthogonal Frequency division multiplexing) signal, a QAM (Quadrature Amplitude Modulation) signal, or a PAM (Pulse Amplitude Modulation) signal.
The two single-sideband Alamouti coded signals have a certain coding symmetry relation, so that the original transmitted signals can be recovered even if the two signals are mixed together. Meanwhile, the two-transmitting one-receiving system structure forms diversity gain, and can effectively compensate fading of a channel.
The embodiment of the invention fully utilizes the technical characteristics of KK reception, after the strength of the signal is detected, the amplitude and phase information of the original signal are recovered through a KK algorithm, so that the signal can be subjected to high-frequency spectrum efficiency coding transmission, such as QAM, OFDM and the like, meanwhile, the polarization multiplexing signal decoded by Alamouti can compensate the influence of polarization state change when a single photoelectric detector at a receiving end receives the signal, polarization-independent reception is realized, meanwhile, the diversity effect generated by two paths of signals can effectively improve the transmission capability of the signal in a fading channel, the diversity effect can not only improve the performance of the system, but also enhance the stability of the system, and the method can become a practical technical means.
The following is a detailed description by means of specific formulas.
Referring to fig. 1, at a transmitting end, first, a single-sideband modulation is performed on data to be transmitted by a first digital signal processor 101, which includes the following steps:
a single-sideband modulation unit 103 in the first digital signal processor 101 performs single-sideband modulation on an original data stream 102 to be transmitted, so as to obtain an original single-sideband transmission signal:
where x (t) is the input signal, i is the unit of an imaginary number,for Hilbert transform of the input signal, yUSB(t) is the upper sideband signal, yLSB(t) is the lower sideband signal.
When bidirectional transmission is performed, the uplink channel adopts yUSB(t) modulation for upper sideband transmission and downlink channel using yLSBAnd (t) modulating to carry out lower sideband transmission, so that the optical fiber can be used as a modulation light source of a sending end and can also be used as a local oscillator light source of a receiving end only by adopting a single light source structure, and meanwhile, signals for bidirectional transmission are respectively positioned in different bandwidth ranges, so that mutual interference is avoided, and a modulation coding mode with low cost and high spectral efficiency is realized.
At the receiving end, because the received optical signal is coupled to the local oscillator light source and then received by the photodetector, and the size of the beat signal is affected by the change of the polarization state of the signal, the Alamouti encoding unit 104 in the first digital signal processor 101 performs Alamouti encoding on the original single-sideband transmission signal, which specifically includes the following steps:
setting the original single sideband transmit signal without Alamouti coding as s at times T and T + T, respectively0And s1T is an arbitrary time, and T is a symbol time interval.
The Alamouti encoding unit 104 in the first digital signal processor 101 performs Alamouti encoding on the original single sideband transmission signal to obtain two single sideband Alamouti encoded signals, which are denoted as T and T + T times respectivelyAnd
when the channel responses corresponding to the two single-sideband Alamouti coded signals are h respectively0And h1At times T and T + T, the same receiver receives signal r0And r1Respectively as follows:
r0＝r(t)＝h0s0+h1s1+n0 (3)
n0and n1Representing the noise signals of the two channels, so far the signal processing flow in the digital signal processing 101 is completed.
The digital signal output from the digital signal processing 101 is converted into two analog signals by digital-to-analog conversion of the first digital-to-analog converter 105 and the second digital-to-analog converter 106, the two analog signals are output to the first optical IQ modulator 108 and the second optical IQ modulator 109, respectively, and the wavelength of the modulated light source 107 is λ0Under the coordination of the modulation light source 107, the two paths of analog signals of the first optical IQ modulator 108 and the second optical IQ modulator 109 are respectively subjected to IQ modulation to form two paths of orthogonal single-sideband optical signals; the polarization beam combiner 110 feeds two paths of orthogonal single-sideband optical signalsAnd performing polarization beam combination to obtain a polarization multiplexing optical signal, and sending the polarization multiplexing optical signal to an optical fiber to finish the signal processing flow of a sending end.
Referring to fig. 2, at the receiving end, the received polarization-multiplexed optical signal 202 is coupled with the local oscillator light source 201, and the power of the local oscillator light source 201 is much greater than that of the polarization-multiplexed optical signal 202 received by the receiving end, and is at least greater than 7-8 dB; then the photoelectric detector 203 performs photoelectric conversion on the coupled optical signal to obtain an analog electrical signal; the analog electrical signal enters the analog-to-digital converter 204, and the analog-to-digital converter 204 performs analog-to-digital conversion on the analog electrical signal to obtain a digital signal, and then the digital signal is sent to the second digital signal processor 208 for processing.
According to the principle of KK reception, when a signal is composed of a single-side signal and a larger direct current, a synthesized signal satisfies the KK relation, that is, the amplitude and the phase satisfy the relation of Hilbert transform. The second digital signal processor 208 therefore performs the following processing on the received digital signal:
a KK receiving unit 205 in the second digital signal processor 208 performs KK receiving on the digital signal to recover amplitude and phase information of the single-sideband Alamouti coded signal; the Alamouti decoding unit 206 in the second digital signal processor 208 performs Alamouti decoding to restore the original single sideband transmission signal; the single sideband demodulation unit 207 in the second digital signal processor 208 performs single sideband demodulation on the recovered original single sideband transmission signal to recover the original data stream.
KK receiving section 205 in second digital signal processor 208 performs KK receiving on the digital signal to recover the amplitude and phase information of the single sideband Alamouti encoded signal, and the specific steps are as follows:
the digital signal received by the KK receiving unit 205 is set to ss (t), and the amplitude of the single-sideband optical signal is recovered through KK reception:
and (3) recovering the phase of the single-sideband optical signal:
wherein H (·) is a Hilbert transform.
Recovering the single sideband Alamouti encoded signal:
after the KK receiving unit 205 in the second digital signal processor 208 recovers the amplitude and phase information of the single sideband optical signal by KK reception, the Alamouti decoding unit 206 in the second digital signal processor 208 decodes the recovered single sideband Alamouti encoded signal (7) row Alamouti:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1The section s is set when part of the original single sideband transmission signal is used for channel estimation0And s1As known, Alamouti decoding is performed on the recovered single-sideband optical signal, and according to the formulas (3) and (4), the channel response h is obtained0And h1Respectively as follows:
according to the formulas (8) and (9), the other data which is not used for channel estimation can be estimated, and the estimation method is as follows:
wherein the content of the first and second substances,andeach is an estimate of the original single sideband transmitted signal.
Finally, the single-sideband demodulation unit 207 in the second digital signal processor 208 performs single-sideband demodulation on the recovered original single-sideband transmission signal to recover the original data stream, thereby completing the entire reception process.
The whole system of the embodiment of the invention adopts a polarization multiplexing structure based on Alamouti coding at the transmitting end, uses one local oscillator light source at the receiving end and still adopts single PD direct detection for receiving. Through Alamouti coding technique and KK transmission technique, realized carrying out phase detection in directly examining optical communication system for the modulation mode of high spectral efficiency can be realized to the signal, also can carry out the compensation of phase place at the receiving terminal simultaneously, when improving system capacity, has also promoted the transmission performance of system. Meanwhile, the system adopting the Alamouti coding structure ensures that the quality of the recovered signals after receiving is irrelevant to the polarization state of the signals, and enhances the stability and the practicability of the direct detection optical communication system in the application of the real environment.
Various modifications and variations of the embodiments of the present invention may be made by those skilled in the art, and they are also within the scope of the present invention, provided they are within the scope of the claims of the present invention and their equivalents.
What is not described in detail in the specification is prior art that is well known to those skilled in the art.
Claims (10)
1. A KK transmission method applied to a direct-detection optical communication system is characterized by comprising the following steps:
at a sending end, carrying out single-side band modulation on an original data stream to obtain an original single-side band sending signal; performing Alamouti coding to obtain two single-sideband Alamouti coding signals; performing digital-to-analog conversion and IQ modulation on the two single-sideband Alamouti coded signals to form two orthogonal single-sideband optical signals; carrying out polarization beam combination on the two paths of orthogonal single-sideband optical signals to obtain polarization multiplexing optical signals, and sending the polarization multiplexing optical signals to an optical fiber;
at a receiving end, coupling a received optical signal with a local oscillator light source, wherein the power of the local oscillator light source is far greater than that of the received optical signal; performing photoelectric conversion on the coupled optical signal to obtain an analog electric signal; performing analog-to-digital conversion to obtain a digital signal; KK receiving is carried out on the digital signal, and amplitude and phase information of the single-sideband Alamouti coded signal are recovered; performing Alamouti decoding to recover the original single-sideband transmission signal; and carrying out single sideband demodulation to recover the original data stream.
2. The KK transmission method applied to the direct-check optical communication system according to claim 1, wherein: the expression of the original single sideband transmission signal is as follows:
where x (t) is the input signal, i is the unit of an imaginary number,for Hilbert transform of the input signal, yUSB(t) is the upper sideband signal, yLSB(t) is the lower sideband signal;
when bidirectional transmission is performed, the uplink channel adopts yUSB(t) modulation for upper sideband transmission and downlink channel using yLSBAnd (t) modulating to carry out lower sideband transmission, adopting a single light source structure, and simultaneously serving as a modulation light source of a sending end and a local oscillation light source of a receiving end.
3. The KK transmission method applied to the direct-check optical communication system according to claim 2, wherein: the specific process for Alamouti coding is as follows:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1T is any time, T is code element time interval, two Alamouti coded signals are obtained after Alamouti coding, and are respectively expressed as s at T and T + T0，And s1，
The channel responses corresponding to the two Alamouti coded signals are h respectively0And h1At times T and T + T, the same receiver receives signal r0And r1Respectively as follows:
r0＝r(t)＝h0s0+h1s1+n0；
n0and n1Respectively representing the noise signals of the two channels.
4. The KK transmission method applied to the direct-check optical communication system according to claim 3, wherein: KK receiving is carried out on the digital signal, amplitude and phase information of the single-sideband Alamouti coded signal are recovered, and the specific process is as follows:
the digital signal received by the KK receiving unit is represented as ss (t), and after KK receiving is carried out on ss (t), the amplitude of the single-sideband optical signal is obtained and represented asThe phase of the single-sideband optical signal is obtained and is expressed asWhere H (-) is the Hilbert transform, recovering the single sideband optical signal, denoted as
5. The KK transmission method applied to the direct-check optical communication system according to claim 4, wherein: performing Alamouti decoding to recover the original single-sideband transmission signal, which comprises the following specific processes:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1Part s of the original single sideband transmitted signal for channel estimation0And s1As is known, the Alamouti decoding is performed on the recovered single-sideband optical signal to obtain the channel response h0And h1Respectively as follows:
estimating other transmitted data not used for channel estimation:
wherein the content of the first and second substances,andeach is an estimate of the original single sideband transmitted signal.
6. The utility model provides a directly examine optical communication system based on KK transmission, includes sending end and receiving terminal, its characterized in that:
the transmitting end comprises a single-sideband modulation unit, an Alamouti coding unit, a first digital-to-analog converter, a second digital-to-analog converter, a modulation light source, a first optical IQ modulator, a second optical IQ modulator and a polarization beam combiner, wherein the single-sideband modulation unit performs single-sideband modulation on original data flow to obtain an original single-sideband transmitting signal; the Alamouti coding unit carries out Alamouti coding to obtain two paths of Alamouti coding signals; the first digital-to-analog converter and the second digital-to-analog converter respectively perform digital-to-analog conversion on the two paths of Alamouti coded signals; carrying out IQ modulation on a modulation light source, a first optical IQ modulator and a second optical IQ modulator to form two paths of orthogonal single-sideband optical signals; the polarization beam combiner performs polarization beam combination on the two paths of orthogonal single-sideband optical signals to obtain polarization multiplexed optical signals, and the polarization multiplexed optical signals are sent to the optical fiber;
the receiving end comprises a local oscillator light source, a photoelectric detector, an analog-to-digital converter, a KK receiving unit, an Alamouti decoding unit and a single-sideband demodulation unit, the receiving end couples a received optical signal with the local oscillator light source, and the power of the local oscillator light source is far greater than that of the optical signal received by the receiving end; the photoelectric detector performs photoelectric conversion on the coupled optical signal to obtain an analog electric signal; the analog-to-digital converter performs analog-to-digital conversion on the analog electric signal to obtain a digital signal; the KK receiving unit is used for KK receiving the digital signal and recovering amplitude and phase information of the single-sideband Alamouti coded signal; the Alamouti decoding unit carries out Alamouti decoding and restores the original single-sideband transmitting signal; the single side band demodulation unit carries out single side band demodulation to recover the original data stream.
7. Direct detection optical communication system based on KK transmission according to claim 6, characterized in that: the expression of the original single sideband transmission signal is as follows:
where x (t) is the input signal, i is the unit of an imaginary number,for Hilbert transform of the input signal, yUSB(t) is the upper sideband signal, yLSB(t) is the lower sideband signal;
when bidirectional transmission is performed, the uplink channel adopts yUSB(t) modulation for upper sideband transmission and downlink channel using yLSBAnd (t) modulating to carry out lower sideband transmission, adopting a single light source structure, and simultaneously serving as a modulation light source of a sending end and a local oscillation light source of a receiving end.
8. Direct detection optical communication system based on KK transmission according to claim 7, characterized in that: the specific process of Alamouti coding by the Alamouti coding unit is as follows:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1T is any time, T is code element time interval, two Alamouti coded signals are obtained after Alamouti coding, and are respectively expressed as s at T and T + T0，And s1，
The channel responses corresponding to the two Alamouti coded signals are h respectively0And h1At times T and T + T, the same receiver receives signal r0And r1Respectively as follows:
r0＝r(t)＝h0s0+h1s1+n0；
n0and n1Respectively representing the noise signals of the two channels.
9. Direct detection optical communication system based on KK transmission according to claim 8, characterized in that: the KK receiving unit KK receives the digital signal and recovers the amplitude and phase information of the single-sideband Alamouti coded signal, and the specific process is as follows:
the digital signal received by the KK receiving unit is represented as ss (t), and after KK receiving is carried out on ss (t), the amplitude of the single-sideband optical signal is obtained and represented asThe phase of the single-sideband optical signal is obtained and is expressed asWhere H (-) is the Hilbert transform, recovering the single sideband optical signal, denoted as
10. Direct detection optical communication system based on KK transmission according to claim 9, characterized in that: the Alamouti decoding unit performs Alamouti decoding to recover the original single sideband transmitting signal, and the specific process is as follows:
the original single sideband transmitted signal is denoted s at times T and T + T, respectively0And s1Part s of the original single sideband transmitted signal for channel estimation0And s1As is known, the Alamouti decoding is performed on the recovered single-sideband optical signal to obtain the channel response h0And h1Respectively as follows:
estimating other transmitted data not used for channel estimation:
wherein the content of the first and second substances,andeach is an estimate of the original single sideband transmitted signal.
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