CN-121984602-A - Photon terahertz communication system based on differential Delta-Sigma modulation and independent double single sidebands

CN121984602ACN 121984602 ACN121984602 ACN 121984602ACN-121984602-A

Abstract

The invention discloses a photon terahertz communication system based on differential Delta-Sigma modulation and independent double single sidebands, and belongs to the field of terahertz communication. The method specifically comprises a transmitting end and a receiving end, wherein a TX-DSP module of the transmitting end generates two paths of independent high-order baseband signals by applying differential DSM and independent double single sideband technology, an IQ modulator is driven to modulate an input optical carrier wave, a terahertz signal is obtained by using an optical beat frequency method, the terahertz signal is transmitted to an RX-DSP module of the receiving end through a single mode fiber, resampling and digital down-conversion are carried out to obtain two QPSK signals, matching filtering, QPSK digital signal processing, hard decision, differential DSM demodulation and low-pass filtering are respectively carried out to obtain two DMT signals, DMT demodulation is carried out again, a cyclic prefix is removed for FFT, a time domain signal is converted back to a frequency domain to obtain an original QAM sequence, and demapping is carried out on the QAM sequence to recover the original binary information sequence. The invention realizes high-order modulation and has excellent error rate performance.

Inventors

YU JIANGUO
Song Cunqiang
LIN XIANDE
WANG ZHANJIANG
ZHANG FEIXIANG
ZHOU SHUHUI
ZHANG ZUYU
CHEN JUN
WU ZHIHE

Assignees

北京邮电大学

Dates

Publication Date: 20260505
Application Date: 20260206

Claims (4)

1. A photon terahertz communication system based on differential DSM and independent double single-sideband modulation comprises a transmitting end and a receiving end, and is characterized in that the transmitting end introduces differential DSM and independent double single-sideband modulation technology, a terahertz signal is generated by using a photon beat frequency method, the terahertz signal is transmitted to the receiving end through a single-mode fiber, and an original signal is recovered by adopting methods such as digital signal processing, inverse mapping and the like.
2. The photonic terahertz communication system of claim 1, wherein the transmitting end includes two external cavity lasers ECL1 and ECL2, a TX-DSP module, an optical coupler, a single-mode fiber, an erbium-doped fiber amplifier, a single-row carrier photodetector, and a pair of horn antennas; The IQ modulator is simultaneously connected to the TX-DSP module, the module applies differential DSM and independent double single sideband technology to generate two paths of independent high-order baseband signals, the IQ modulator is driven to modulate the input optical carrier, the modulated optical carrier and continuous light waves output by the ECL2 of the external cavity laser are coupled through an optical coupler, the coupled optical signals are transmitted to an erbium-doped optical fiber amplifier through a single mode fiber to be amplified, and finally the coupled optical signals are input to a single-row carrier photoelectric detector to be beat frequency to obtain terahertz signals; the receiving end comprises a mixer, a local oscillator and an RX-DSP module; The method comprises the steps of receiving terahertz signals received by a second horn antenna, inputting the terahertz signals into a mixer to be mixed with local oscillation signals generated by a local oscillator, realizing down conversion of the signals to obtain baseband independent double single sideband signals, then inputting the baseband independent double single sideband signals into an RX-DSP module, carrying out resampling and digital down conversion to obtain two QPSK signals, respectively carrying out matched filtering, QPSK digital signal processing, hard decision, differential DSM demodulation and low pass filtering on the two QPSK signals obtained by demodulation recovery to obtain two DMT signals, carrying out DMT demodulation again, carrying out fast Fourier transform FFT (FFT) by removing cyclic prefix), converting the time domain signals back to the frequency domain to obtain an original QAM sequence, carrying out demapping on the QAM sequence to recover the original binary information sequence, and finally comparing the binary information sequence with the generated PRBS1 and PRBS2, and calculating the error rate.
3. The photonic terahertz communication system of claim 2, wherein the TX-DSP module generates two independent high order baseband signals using differential DSM and independent double single sideband techniques as follows: Step one, a TX-DSP module generates two independent pseudo-random binary sequences to be transmitted, respectively carries out high-order Quadrature Amplitude Modulation (QAM) mapping, generates two independent high-order QAM symbol sequences with the same or different orders, and respectively marks the two independent high-order QAM symbol sequences as And ; Step two, for high-order QAM symbol sequence And DMT modulation is performed respectively to convert the QAM symbols of the frequency domain into DMT waveform signals of the time domain And ; Step three, DMT waveform signals And Differential Delta-Sigma modulation is respectively carried out to obtain two paths of QPSK signals And ; Step four, for two QPSK signals And Respectively up-sampling and root-raised cosine filtering, digital mixing by digital local oscillation frequency, and mixing Moving to positive frequency domain as upper sideband, and Moving to a negative frequency domain as a lower sideband to generate two paths of independent high-order baseband signals; step five, synthesizing two paths of independent high-order baseband signals to obtain independent double single sideband broadband digital signals Sending the data to an IQ modulator; The expression is: fs is the sampling frequency.
4. The photonic terahertz communication system of claim 3, wherein the differential Delta-Sigma modulation adopts a differential DSM architecture, and uses in-phase (I) and quadrature (Q) components of QPSK to transmit a "DSM signal" and "quantization noise", respectively, and the two DMT waveform signals have the same implementation procedures, and take one DMT waveform signal as an example, the specific procedures are as follows: Firstly, inputting an original DMT waveform signal into a first-stage DSM modulator, and outputting a 1-bit OOK signal by utilizing oversampling and noise shaping; Filtering out-band high-frequency noise from the OOK signal through a digital low-pass filter LPF, reconstructing a baseband digital signal containing an original signal and in-band noise, performing differential operation on the reconstructed signal and an original DMT waveform signal, extracting an in-band quantization noise error signal generated by first-stage modulation, and performing gain adaptive amplification on the error signal through an amplifier; Then, the amplified in-band quantization noise error signal is input into a second-stage DSM modulator, the same oversampling and noise shaping processing are carried out, and a 1-bit OOK signal carrying only quantization noise information is output as a quadrature component Q-path signal of a QPSK signal; And finally, combining the I path and the Q path signals to form a path of complex QPSK signals, wherein the I path carries a main signal containing quantization noise, and the Q path carries a quantization error signal for noise cancellation at a receiving end.

Description

Photon terahertz communication system based on differential Delta-Sigma modulation and independent double single sidebands Technical Field The invention relates to a photon terahertz communication system based on differential Delta-Sigma modulation and independent double single sidebands, and belongs to the field of terahertz communication. Background With the commercialization and popularization of 5G networks and the evolution of 6G technologies, the emerging applications of Internet of vehicles, big data Internet of things and the like promote the exponential increase of network traffic. In order to meet the goals of wide coverage and broadband connection, the terahertz frequency band (0.1-10 THz) becomes a key technology for solving the bottleneck of future communication capacity by virtue of abundant frequency spectrum resources. In photonic terahertz communications, delta-Sigma modulation (DSM) has been attracting attention because of the good tradeoff between system simplicity and spectral efficiency. The DSM pushes quantization noise out of the high frequency band using oversampling and noise shaping to achieve a higher signal-to-noise ratio (SNR) within the signal bandwidth while maintaining a lower number of quantization bits. The low-bit quantization characteristic of the method has strong tolerance to nonlinear damage of the photoelectric device, and the complex equalization problem faced by high-order QAM modulation is avoided. In order to further improve the performance, a differential DSM technology is provided, wherein the technology adopts a two-stage cascade architecture, extracts a first-stage quantization error, amplifies the first-stage quantization error for secondary quantization, and obviously reduces in-band noise power (IBN) through differential cancellation at a receiving end so as to obtain higher signal-to-noise ratio gain. Conventional Double Sideband (DSB) modulation results in wasted spectral resources, while conventional Single Sideband (SSB) modulation, while saving bandwidth, often fails to fully exploit channel capacity. In this context, the independent double single sideband modulation technique is particularly important. The advantage of independent double single sideband modulation is that it allows two different signals to be independently transmitted on the Upper Sideband (USB) and the Lower Sideband (LSB) of the same optical carrier, and also reduces the nonlinear effects of fiber dispersion. Not only the spectrum efficiency is doubled, but also the transmission capacity of a single physical channel is doubled. Disclosure of Invention The invention provides a photon terahertz communication system based on differential DSM and independent double single sideband modulation, which can realize high-order modulation by introducing the differential DSM and the independent double single sideband modulation at the same time, and can improve the frequency spectrum efficiency to improve the transmission capacity of the system, reduce the influence of optical fiber dispersion and have excellent bit error rate performance. The photon terahertz communication system comprises a transmitting end and a receiving end, wherein the transmitting end introduces a differential DSM and independent double single sideband modulation technology, a terahertz signal is generated by using a photon beat frequency method, the terahertz signal is transmitted to the receiving end through a single-mode fiber, and an original signal is recovered by adopting methods such as digital signal processing, inverse mapping and the like. The transmitting end comprises two external cavity lasers ECL1 and ECL2, a TX-DSP module, an optical coupler, a single-mode fiber, an erbium-doped fiber amplifier, a single-row carrier photoelectric detector and a pair of horn antennas; The IQ modulator is connected to the TX-DSP module, the module applies differential DSM and independent double single sideband technology to generate two paths of independent high-order baseband signals, the IQ modulator is driven to modulate the input optical carrier, the modulated optical carrier is coupled with continuous light waves output by the external cavity laser ECL2 through an optical coupler, the coupled optical signals are transmitted to the erbium-doped fiber amplifier through a single mode fiber to be amplified, and finally the single-row carrier photoelectric detector is input to beat frequency to obtain terahertz signals. The terahertz signal is transmitted through a wireless link by the first horn antenna and then received by the second horn antenna. The receiving end comprises a mixer, a local oscillator and an RX-DSP module; The method comprises the steps of receiving terahertz signals received by a second horn antenna, inputting the terahertz signals into a mixer to be mixed with local oscillation signals generated by a local oscillator, realizing down conversion of the signals to obtain baseband independent double single