A photon terahertz multi-body system communication system combining envelope detection and KK principle

Abstract

The application belongs to the technical field of terahertz communication, and particularly relates to a photonic terahertz multi-system communication system combining envelope detection and KK principle, which comprises a photonic-wireless terahertz transmitter and a multi-system receiver based on the combination of envelope detection and KK principle. A digital signal of multiple adjustment formats is generated by a digital-to-analog converter (DAC) in the transmitter and is converted into an analog signal. In the receiver, a multi-system communication is realized only by relying on an intensity detector through the combination of envelope detection and KK principle. In addition, the non-coherent and KK receiving technologies are fused by using the characteristic that the direct detection mode (DD) and the KK receiving mode adopt the receiver with the same hardware, and cooperating with the photonic-wireless terahertz transmitter, the multi-system communication with both DD (non-coherent) and KK (coherent) receiving modes is realized under the premise of no additional hardware cost.

Description

Technical Field

[0001] This invention relates to the field of terahertz communication technology, specifically to a photonic terahertz multi-mode communication system that combines envelope detection and the KK principle, and can be applied to the next-generation 6G mobile communication field. Background Technology

[0002] Traditional methods for terahertz communication with multi-mode reception are based on coherent demodulation. However, coherent terahertz reception inevitably requires a local terahertz source and terahertz mixer, which undoubtedly increases the complexity and cost of the receiver. In recent years, communication schemes based on Kramers-Kronig (KK) receivers have been widely studied because they can reconstruct complex signals using only a single intensity detector. Currently, related research mainly addresses the limitations of the KK scheme principle, including reducing CSPR, reducing digital upsampling rate, reducing required bandwidth, and DSP optimization. However, current research still has two limitations and shortcomings: First, communication systems based on KK receivers mostly use QAM modulation format, and research on KK reception schemes for other modulation formats such as FSK is lacking; second, communication based on KK receivers is mostly in a single operating mode, and a fusion reception scheme combining direct detection DD and KK reception technologies needs further research. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by proposing a photonic terahertz multi-mode communication system that combines envelope detection and the KK principle to achieve multi-mode communication, i.e., compatibility with multiple information modulation formats such as PAM, PSK, FSK, and QAM. By integrating traditional DD (non-coherent) and KK (coherent) reception modes, and in conjunction with a photonic-wireless terahertz transmitter, multi-mode communication with both DD (non-coherent) and KK (coherent) reception modes is achieved without adding additional hardware, thus broadening the application scope.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A photonic terahertz multimode communication system combining envelope detection and KK principle includes: a photonic-wireless terahertz transmitter and a multimode receiver based on the combination of envelope detection and KK principle;

[0006] The photonic-wireless terahertz transmitter includes: a digital-to-analog converter (DAC), a first laser, a first optical coupler, an optoelectronic modulator, an erbium-doped fiber amplifier, a polarization controller, a second optical coupler, a third optical coupler, a second laser, a polarizer, an adjustable optical attenuator, a photodetector (PD), and a first antenna. The DAC generates digital signals in PAM, PSK, FSK, QAM, or OFDM modulation formats and converts them into analog signals for transmission to the optoelectronic modulator. The first laser transmits a first optical signal to the first optical coupler. The first optical coupler splits the first optical signal into two paths, one of which serves as the modulation light and is sequentially modulated by an electro-optic modulator. After passing through a preamplifier, erbium-doped fiber amplifier, and polarization controller, the signal is sent to a second optical coupler; another signal is sent directly to the second optical coupler; the second optical coupler couples the two first optical signals to obtain a first optically coupled signal, and sends the first optically coupled signal to a third coupler; a second laser provides a reference optical signal with a terahertz frequency interval to the third coupler; the third coupler couples the first optically coupled signal and the reference optical signal with a terahertz frequency interval; and the coupled signal is then sent to a photodetector after passing through a polarizer and an adjustable optical attenuator; the photodetector converts the optical signal into a terahertz signal; and the first antenna radiates the input terahertz signal into free space.

[0007] The multi-mode receiver based on envelope detection and the KK principle includes: a second antenna, a low-noise amplifier, an intensity detector, an ADC sampling unit, and a DSP processing unit. The second antenna receives terahertz signals in free space and sends them to the low-noise amplifier. The low-noise amplifier amplifies the received terahertz signals and sends the amplified signals to the intensity detector. The intensity detector extracts the envelope of the received terahertz signals. The ADC sampling unit samples the envelope signal and sends the sampled signal to the DSP processing unit. The DSP processing unit calculates the sampled terahertz signal envelope using either the DD or KK algorithm to obtain the reconstructed baseband signal. The DSP algorithm is divided into direct detection mode (DD) and KK reception mode. In direct detection mode (DD), it is only used to identify PAM signals. In KK reception mode, it uses the KK algorithm to identify baseband digital signals s(t) that satisfy the minimum phase, including digital signals with modulation formats such as PAM, PSK, FSK, and QAM.

[0008] Furthermore, the digital-to-analog converter (DAC) uses a built-in encoding unit to generate digital signals in single-sideband PAM, PSK, FSK, or QAM modulation formats.

[0009] Furthermore, the first coupler is a polarization-maintaining equal-power split coupler to ensure that the polarization states of the two output signals are consistent, which facilitates subsequent polarization state adjustment.

[0010] Furthermore, the electro-optic modulator is an IQ modulator, which can obtain a carrier-suppressed modulated signal when operating at the Null point.

[0011] Furthermore, the photodetector is a PIN-type structure or a single-row carrier UTC-type structure.

[0012] By adopting the above technical solution, the present invention has the following advantages:

[0013] 1. This invention achieves efficient transmission of multiple modulation formats such as PAM, PSK, FSK, QAM and OFDM signals by combining envelope detection and KK principle, relying solely on intensity detectors. This achieves the multi-mode reception capability that other technical solutions require complex and expensive coherent reception methods such as "terahertz local oscillator + terahertz mixer + IQ branch".

[0014] 2. By integrating non-coherent and KK reception technologies, this invention provides two working modes, Direct Detection (DD) and KK Reception (KK), without additional hardware overhead, which can be applied to scenarios with low latency and high information rate requirements, respectively. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the transmitter of the communication system of the present invention;

[0016] Figure 2 This is a schematic diagram of the receiver of the communication system of the present invention;

[0017] Figure 3 The following is a flowchart of the digital signal processing in the transmitter of the embodiment;

[0018] Figure 4 The following is a flowchart of the KK algorithm in the receiver of the embodiment;

[0019] Figure 5 The communication system in this embodiment shows the signal demodulation results under modulation formats such as PAM, FSK, PSK, and QAM; where a is the signal demodulation result under 4-PAM modulation format, b is the signal demodulation result under 4-FSK modulation format, c is the signal demodulation result under 12-PSK modulation format, and d is the signal demodulation result under 16-QAM format. Detailed Implementation

[0020] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Before implementation, this embodiment first analyzed the technical principle of the KK receiving mode, concluding that this mode has the characteristic of enabling multi-mode reception. Based on this, this embodiment utilizes the multi-mode reception capability of the KK receiving mode to propose a photonic terahertz multi-mode communication system combining envelope detection and the KK principle. This communication system includes a photonic-wireless terahertz transmitter and a multi-mode receiver based on the combination of envelope detection and the KK principle.

[0022] like Figure 1 As shown, the photonic-wireless terahertz transmitter includes: a digital-to-analog converter (DAC), a first laser, a first optical coupler, an electro-optic modulator, an erbium-doped fiber amplifier, a polarization controller, a second optical coupler, a third optical coupler, a second laser, a polarizer, an adjustable optical attenuator, a photodetector, and a first antenna.

[0023] The digital-to-analog converter (DAC) generates digital signals in PAM, PSK, FSK, or QAM modulation formats and converts them into analog signals for transmission to the electro-optic modulator. The digital signal is generated using a built-in encoding unit in PAM, PSK, FSK, QAM, or OFDM modulation formats; the generation process is as follows: Figure 3 As shown, the process includes steps such as encoding (Gray), mapping, pulse shaping, SSB transformation, and resampling. Each step is existing technology and will not be described in detail here.

[0024] The first laser is the first optical coupler that sends the first optical signal.

[0025] To ensure consistent polarization states of the two output signals and facilitate subsequent polarization state adjustment, the first optical coupler is a polarization-maintaining equal-power splitter coupler. The first optical coupler divides the first optical signal into two paths: one path, acting as modulated light, passes sequentially through an electro-optic modulator, an erbium-doped fiber amplifier, and a polarization controller before being sent to the second optical coupler; the other path is directly sent to the second optical coupler. In this embodiment, the electro-optic modulator is an IQ modulator, which, when operating at the Null point, can obtain a carrier-suppressed modulated optical signal.

[0026] The second optical coupler is used to couple the two first optical signals to obtain a first optical coupled signal, and send the first optical coupled signal to the third coupler; the second laser is used to provide the third coupler with a reference optical signal with a terahertz frequency interval.

[0027] The third coupler is used to couple the first optically coupled signal and the reference optical signal with a terahertz frequency interval; and the coupled signal is then sent to the photodetector after passing through a polarizer and an adjustable optical attenuator in sequence. The coupled signal can be expressed by the following mathematical model:

[0028]

[0029] Where, ω C1 With ω C2 These represent the operating frequencies of the two lasers, ω and ω'. Z The shift frequency represents the up-conversion frequency of the baseband signal, s(t) is the baseband digital signal in various desired modulation formats, and c and A are used to represent the amplitudes of the two coupled optical signals. It is worth noting that when the system operates in direct detection mode (DD) with PAM modulation format, c and ω in the above formula... Z All signals must be zeroed. If they are not zeroed, the receiver signal needs to be processed using KK receiver mode (KK) to recover the PAM signal.

[0030] The photodetector has a PIN structure or a single-row carrier structure. Based on the heterodyne beat frequency principle, it generates a terahertz signal by performing square-law detection on the received signal. The generated terahertz signal is then transmitted to a first antenna, which radiates it into free space. The generated terahertz signal can be expressed mathematically as follows:

[0031]

[0032] ω M =ω C1 -ω C2

[0033] In this embodiment, the electro-optic modulator outputs a modulated optical signal, and with the cooperation of the polarization controller PC and the polarizer Pol, the polarization state of the signal is adjusted. When the polarization controller PC is adjusted, the output power of the polarizer will change accordingly. When the output power reaches its maximum value in a certain state, it is considered that the polarization state of the input optical signal is consistent.

[0034] like Figure 2 As shown, the multi-mode receiver based on envelope detection and the KK principle includes: a second antenna, a low-noise amplifier, an intensity detector, an ADC sampling unit, and a DSP processing unit.

[0035] The second antenna is used to receive terahertz signals in free space and transmit them to a low-noise amplifier.

[0036] A low-noise amplifier amplifies the received terahertz signal and sends the amplified signal to an intensity detector. The intensity detector extracts the envelope of the received terahertz signal. The mathematical model expression for the envelope-recovered terahertz signal is as follows:

[0037]

[0038] The ADC sampling unit samples the recovered terahertz signal envelope according to requirements and sends the sampled terahertz signal envelope to the DSP processing unit. The DSP processing unit calculates the original input signal output using the DSP algorithm on the sampled terahertz signal envelope. The DSP algorithm is divided into direct detection mode (DD) and KK receiving mode. In direct detection mode (DD), it is only used to identify PAM signals. In KK receiving mode, it uses the KK algorithm to identify baseband digital signals s(t) that satisfy the minimum phase, including digital signals with modulation formats such as PAM, PSK, FSK, and QAM. Figure 4 The diagram shows the algorithm flowchart for signal reconstruction based on the KK algorithm in the proposed solution of this invention. It mainly includes steps such as upsampling, KK relation reconstruction, DC removal, frequency downconversion, and downsampling. The specific formula for reconstructing the complex signal using the KK relation is expressed as follows:

[0039]

[0040] Among them, S L ′(t) is the sampled value of the envelope signal output by the intensity detector. H[·] is the Hilbert transform of the amplitude signal, used to recover the phase information of the signal.

[0041] Example

[0042] Figure 1 The photon-wireless terahertz transmitter shown has two lasers operating at frequencies of 1550.12 nm and 1549.32 nm, respectively, with a frequency interval of 100 GHz (0.1 THz). Digital signals are generated by PRBS, then encoded with Gray code and mapped to a constellation diagram. The specific data mapping format depends on the chosen modulation format; here, 4FSK modulation is used as an example. 4FSK modulation represents the operating mode of KK reception; DD reception mode is consistent with traditional incoherent PAM reception and will not be elaborated further. The data symbol rate is set to 10 GBd, and the root-raised-cosine roll-off factor is 0.1. Due to the use of 4FSK modulation, DD mode cannot be used for reception; therefore, the 4FSK signal requires Hilbert transform or single-sideband processing after pulse shaping. Detailed processing steps can be found in [reference needed]. Figure 3 .

[0043] The digital signal is converted into a matched analog signal by a 64GSa / s DAC and then input to an IQ modulator to generate an optical carrier signal. Since the IQ modulator operates at the null point, the output power of the optical carrier signal is relatively low (-10dBm). Subsequently, it is amplified to 10dBm by an EDFA and then coupled to another source optical signal (reference carrier) via a polarization controller. This coupled optical signal is then coupled to an optical signal generated by another laser with a frequency spacing of 100GHz. After power adjustment by a VOA, the coupled optical signal is input to a PD to generate an electrical signal with a 0.1THz carrier frequency. Finally, the terahertz signal is amplified by a terahertz amplifier and an antenna and radiated into free space.

[0044] like Figure 2 As shown, at the receiver, a matched terahertz antenna is used to receive terahertz signals in free space. The terahertz signal is then amplified by a low-noise amplifier (to -10dBm) and input to an intensity detector. The intensity detector outputs the envelope of the terahertz signal, which is then sampled by an 80GSa / s ADC. Considering the digital upsampling requirements of the KK algorithm, the digital sampling rate of the sampled signal needs to be controlled above 6sps. If the actual sampling rate is insufficient, it needs to be increased through digital upsampling. In this example, each symbol of the received signal has 8 sampling points, so no additional digital upsampling is required. After the sampled signal is reconstructed using the KK algorithm, it still needs carrier removal, frequency conversion, and downsampling to finally obtain the baseband signal, i.e., the baseband digital information (4FSK) is recovered.

[0045] Figure 5 To demonstrate the signal demodulation results of the communication system proposed in this embodiment under PAM, PSK, FSK, and QAM modulation formats; where a represents the signal demodulation result under 4-PAM modulation, b represents the signal demodulation result under 4-FSK modulation, c represents the signal demodulation result under 12-PSK modulation, and d represents the signal demodulation result under 16-QAM. Figure 5 As can be seen, the technical solution in this embodiment realizes multi-system communication.

[0046] In summary, this embodiment provides a photonic terahertz multi-mode communication system that combines envelope detection and the KK principle. The transmitter uses a digital-to-analog converter (DAC) to generate digital signals with various adjustment formats and converts them into analog signals. In the receiver, by combining envelope detection and the KK principle, multi-mode communication is achieved using only an intensity detector. Furthermore, by leveraging the fact that the receivers for both Direct Detection (DD) and KK reception modes share the same hardware, the system integrates incoherent and KK reception technologies. Combined with a photonic-wireless terahertz transmitter, this achieves multi-mode communication with both DD (incoherent) and KK (coherent) reception modes without additional hardware overhead.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered as equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A photonic terahertz multi-body regime communication system incorporating envelope detection and KK principle, characterized by, include: Photonic wireless terahertz transmitter and multi-mode receiver based on envelope detection and KK principle; The photonic-wireless terahertz transmitter includes: a digital-to-analog converter (DAC), a first laser, a first optical coupler, an electro-optic modulator, an erbium-doped fiber amplifier, a polarization controller, a second optical coupler, a third optical coupler, a second laser, a polarizer, an adjustable optical attenuator, a photodetector, and a first antenna. The DAC generates digital signals in PAM, PSK, FSK, QAM, or OFDM modulation formats and converts them into analog signals for transmission to the electro-optic modulator. The first laser transmits a first optical signal to the first optical coupler. The first optical coupler splits the first optical signal into two paths, one of which serves as the modulation light, which sequentially passes through the electro-optic modulator and the erbium-doped fiber amplifier. After the amplifier and polarization controller, the signal is sent to the second optical coupler; another signal is sent directly to the second optical coupler; the second optical coupler is used to couple the two first optical signals to obtain a first optically coupled signal, and then sends the first optically coupled signal to the third coupler; the second laser is used to provide a reference optical signal with a terahertz frequency interval to the third coupler; the third coupler is used to couple the first optically coupled signal and the reference optical signal with a terahertz frequency interval; and the coupled signal is then sent to the photodetector after passing through a polarizer and an adjustable optical attenuator in sequence; the photodetector converts the optical signal into a terahertz signal and sends it to the first antenna; the first antenna radiates the input terahertz signal into free space; The multi-mode receiver based on envelope detection and the KK principle includes: a second antenna, a low-noise amplifier, an intensity detector, an ADC sampling unit, and a DSP processing unit. The second antenna receives terahertz signals in free space and sends them to the low-noise amplifier. The low-noise amplifier amplifies the received terahertz signals and sends the amplified terahertz signals to the intensity detector. The intensity detector extracts the envelope of the received terahertz signals. The ADC sampling unit samples the envelope signal and sends the sampled signal to the DSP processing unit. The DSP processing unit calculates the sampled terahertz signal envelope according to either the DD or KK DSP algorithm to obtain the reconstructed baseband signal. The DSP algorithm is divided into direct detection mode (DD) and KK reception mode. In direct detection mode (DD), it is only used to identify PAM signals. In KK reception mode, it uses the KK algorithm to identify baseband digital signals s(t) that satisfy the minimum phase, including digital signals with modulation formats such as PAM, PSK, FSK, and QAM.

2. The photonic terahertz multi-body communication system combined with envelope detection and KK principle according to claim 1, characterized in that: The digital-to-analog converter (DAC) uses a built-in encoding unit to generate digital signals in single-sideband PAM, PSK, FSK, or QAM modulation formats.

3. The photonic terahertz multi-body communication system combined with envelope detection and KK principle according to claim 1, characterized in that: The first coupler is a polarity-maintaining equal-power split coupler.

4. The photonic terahertz multi-body communication system combined with envelope detection and KK principle according to claim 1, characterized in that: The electro-optic modulator is an IQ modulator.

5. A photonic terahertz multi-body system communication system combining envelope detection and KK principle according to any one of claims 1-4, characterized in that: The photodetector is a PIN-type structure or a single-row carrier UTC-type structure.

Images