CN112600587A

CN112600587A - Real-time adaptive optical self-interference elimination system and method based on FPGA and STM32

Info

Publication number: CN112600587A
Application number: CN202110010793.5A
Authority: CN
Inventors: 张之仪; 肖石林; 郑立卓; 刘智洋
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2021-01-06
Filing date: 2021-01-06
Publication date: 2021-04-02
Anticipated expiration: 2041-01-06
Also published as: CN112600587B

Abstract

The invention provides a real-time self-adaptive optical self-interference elimination system and method based on FPGA and STM32, comprising the following steps: the baseband real-time transceiving module completes the real-time transmission of baseband OFDM signals; the up-down frequency conversion module completes the conversion between the baseband of the signal and the working frequency band of the antenna to obtain a radio frequency signal of local communication information; after the radio frequency signal of the local communication signal is copied into a reference signal, the reference signal is transmitted out through a radio frequency antenna module; the radio frequency antenna module receives a radio frequency useful signal from another communication unit and a time-varying radio frequency self-interference signal of a transmitting antenna close to a receiving antenna; after the optical self-interference elimination module receives the useful signal and the self-interference signal, the self-adaptive control module adjusts the amplitude and the phase of the reference signal, the balance photoelectric detector in the optical self-interference elimination module cancels the reference signal and the self-interference signal to obtain the useful signal after the self-interference elimination, and the useful signal after the self-interference elimination is converted into a baseband and sent to a receiving end.

Description

Real-time adaptive optical self-interference elimination system and method based on FPGA and STM32

Technical Field

The invention relates to the technical field of microwave photonics and wireless communication, in particular to a real-time adaptive optical self-interference elimination system and a method based on FPGA and STM32, and more particularly to a real-time adaptive optical self-interference elimination system based on FPGA and STM32 and applied to an in-band full-duplex wireless communication system.

Background

With the rapid development of mobile communication technology, the 5G era of everything interconnection has come. The explosive information interaction puts higher demands on the transmission rate and the transmission capacity of the wireless communication system. Because the spectrum resources are limited, developing higher frequency bands and larger bandwidths can significantly increase the system cost, so how to fully utilize the existing spectrum resources and improve the spectrum utilization rate becomes a problem to be solved urgently by the current wireless communication system. The In-Band Full-Duplex (IBFD) technology performs transmission of wireless services at the same Time and Frequency, doubles the spectrum resource utilization rate compared with a Frequency-Division Duplex (FDD) technology, and increases the information transmission rate and reduces the delay compared with a Time-Division Duplex (TDD) technology, thereby becoming an alternative In the field of wireless communication.

Because the receiving antenna and the transmitting antenna of the same communication unit of the IBFD wireless communication system simultaneously work at the same frequency and are closely spaced, the transmitting antenna inevitably causes the same-frequency self-interference to the receiving antenna, which affects the reception of useful signals. This same-frequency self-interference is higher in power than the useful signal from another communication unit and cannot be filtered out by a simple filter, which greatly affects the development of the IBFD wireless communication system. Currently, self-interference cancellation systems based on electricity are greatly affected by electronic component performance, and perform poorly under conditions of high frequency band and wide bandwidth. The self-interference elimination system based on microwave photonics can convert electrical signals with high frequency band and wide bandwidth into optical domain for processing, and can obtain better self-interference elimination effect by means of high-precision optical devices.

Under actual communication environment, a wireless channel has strong time-varying property, channel response can change along with time, and then self-interference signals in the IBFD wireless communication system are dynamically changed and influenced, difficulty is increased for matching of reference signals, and the traditional static self-interference elimination system cannot meet the requirements of actual communication scenes. Therefore, the optical self-interference cancellation system is adaptively controlled, and the reference signal is dynamically adjusted to match the time-varying self-interference signal, which is a precondition for the optical self-interference cancellation scheme to be applied to the IBFD wireless communication system. Further, in order for different communication units to achieve low-latency bidirectional communication, the adaptive control process in the self-interference cancellation system needs to dynamically adjust the reference signal according to the time-varying characteristics of the self-interference signal as quickly as possible. Therefore, whether the system can perform high-speed data transmission and provide an evaluation index for measuring the quality of the received signal at the current time, and whether the system can perform fast and accurate adaptive control according to the evaluation index at the current time to enable the quality of the received signal to be optimal becomes a problem to be solved urgently by the IBFD wireless communication system.

The present document search shows that Matthew P.Chang et al published an article entitled "Integrated MICROWAVE Photonic Circuit for Self-Interference Cancellation" in IEEE TRANSACTIONS ON MICROWAVE THEOKE AND TECHNIQUES (Vol.65, No.11, NOVEMBER 2017) in 2017, AND proposed an optical Self-Interference Cancellation scheme. In the scheme, an upper branch adopts a Semiconductor Optical Amplifier (SOA) to amplify a mixed signal of a single-frequency signal and Gaussian white noise, and then enters a positive port of a balanced photoelectric detector; the lower branch enters a negative port of the balanced photoelectric detector after the amplitude and the phase of Gaussian white noise are adjusted through the two SOAs; and finally, the balanced photoelectric detector outputs a single-frequency signal after Gaussian white noise is eliminated. Adaptive control of the SOA is achieved by running the Nelder-Mead Simplex algorithm on a computer to reduce the signal power to a minimum. After 60-70 iterations, the system obtains-30 dB of elimination depth in the range of 400 MHz-6 GHz. The scheme has too many required iteration times and longer time, useful signals are single-frequency signals, self-interference signals are Gaussian white noise, and the two paths of signals are too simple and do not meet the IBFD wireless communication in the real environment.

An article entitled "Real-time adaptive optical self-interference system for in-band full-duplex transmission" was published by Lin Huang et al in 2019 in Optics Communications (437(2019) 259-263), and an optical self-interference cancellation scheme for running a control algorithm on an STM32 singlechip was proposed. In the scheme, an upper branch adopts SOA to amplify an interference signal and then enters a positive port of a balanced photoelectric detector, and a lower branch adopts a singlechip to control a variable optical delay line and a variable optical attenuator to adjust a reference signal and then enters a negative port of the balanced photoelectric detector. And on the premise that no useful signal exists, when the signal power of the receiving end approaches the bottom noise power or the algorithm stepping value meets the ending condition, the system stops working. The system control algorithm is an improved Hooke-Jeeves algorithm, and after 15-25 sampling points are searched, the system achieves the elimination depth of-22 dB in the range of 0-700 MHz. The iteration times of the scheme are obviously improved, but when the residual noise power is used as an evaluation index, the calculation speed is low by combining oscilloscope sampling and MATLAB. Meanwhile, the system cannot fully guarantee the actual receiving condition of the signals at the receiving end in the communication process because the receiving and processing of useful signals are not involved.

Lizhuo Zheng et al published an article on Optics Letters (Vol.45, No.5/1March2020) in 2020 entitled "Adaptive over-the-air RF self-interference using a signal-of-interest driven regular triangle algorithm" which was first published on Optics Cs EXPRESS (Vol.27, No.4|18Feb 2019) by Lizhuo Zheng et al in 2019 entitled "Adaptive chosen-interference for in-bag complex-using filtered triangle algorithm". The scheme is based on an electric absorption modulator and a balanced photoelectric detector to realize photoelectric conversion, an Arbitrary Waveform Generator (AWG) is utilized to generate a useful signal and a self-interference signal, and an oscilloscope is utilized to receive the signal. Through iterative optimization of a regular triangle algorithm, the system finally realizes the elimination depth of-22 dB in the frequency band of 18.35GHz and the bandwidth range of 300 MHz. The scheme introduces a useful signal and a radio frequency antenna, utilizes the error rate as an evaluation index, and has stronger practical significance. However, the MATLAB is slow in algorithm execution speed and poor in adaptability, and still does not involve real-time bidirectional communication between different communication units, so that the MATLAB cannot be really applied to the IBFD wireless communication system.

In order to enable the optical self-interference elimination system to meet the requirements of real-time performance and self-adaptability, information transmission and receiving between different communication units are carried out more completely, the optimal elimination effect is achieved more quickly, and the optical self-interference elimination system is really applied to an IBFD wireless communication system. The real-time modulation and transmission, the real-time demodulation and the real-time reception of signals are perfected on the basis of the existing research scheme, and a real-time evaluation index for measuring the quality of the received signals at the current moment is given; meanwhile, an optimization algorithm needs to be quickly executed on a high-speed platform, real-time evaluation indexes are received, adaptive accurate control is carried out, and a receiving end can achieve optimal receiving. The invention utilizes the FPGA to carry out real-time high-speed data transmission and utilizes the STM32 single chip microcomputer to carry out self-adaptive precise control, thereby constructing a real-time self-adaptive optical self-interference system based on the FPGA and the STM32 and applied to the IBFD wireless communication system. The system can accurately and quickly eliminate the self-interference of the transmitting antenna to the receiving antenna under the wireless channels at different moments, so that the real-time full-duplex wireless communication is realized among different communication units.

Patent document CN106788579A (application number: 201611179418.9) discloses an in-band full-duplex wireless communication system and a broadband optical self-interference cancellation system thereof, which includes: the first communication unit and the second communication unit respectively comprise a transmitting antenna and a receiving antenna, and are used for realizing real-time two-way communication, and the first communication unit and the second communication unit are provided with a broadband-based optical self-interference elimination system, comprising: the device comprises an electro-absorption modulator, a variable optical attenuator, a variable optical delay line, a balanced receiver and a predistortion filter; for canceling the generated self-interference signal. The invention mainly solves the problem of serious reduction of suppression bandwidth caused by unevenness of a wireless channel, adds a predistortion filter in an optical self-interference elimination system to compensate the unevenness of channel amplitude response, and realizes that a better self-interference suppression ratio is obtained in the whole passband occupied by transmission signals.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a real-time adaptive optical self-interference elimination method and system based on FPGA and STM 32.

The invention provides a real-time adaptive optical self-interference elimination method based on an FPGA and an STM32, which comprises the following steps:

step M1: the baseband real-time transceiving module completes real-time transmission of baseband OFDM signals by using the FPGA;

step M2: the up-down frequency conversion module receives a baseband OFDM signal, and completes the conversion between the baseband of the signal and the working frequency band of the antenna to obtain a radio frequency signal of local communication information;

step M3: after the radio frequency signal of the local communication signal is copied into a reference signal, the local communication signal is transmitted out through a transmitting antenna in a radio frequency antenna module;

step M4: a receiving antenna in the radio frequency antenna module receives a radio frequency useful signal from another communication unit and a time-varying radio frequency self-interference signal of a nearby transmitting antenna which belongs to the same communication unit with the current receiving antenna, and sends the time-varying radio frequency self-interference signal to the optical self-interference elimination module;

step M5: after the optical self-interference elimination module receives the useful signal and the self-interference signal, the amplitude and the phase of the reference signal are adjusted through the self-adaptive control module, so that the reference signal and the self-interference signal are accurately matched, the reference signal and the self-interference signal are mutually offset through a balance photoelectric detector in the optical self-interference elimination module, the useful signal with the self-interference eliminated is obtained, the useful signal with the self-interference eliminated is converted between an antenna working frequency band and a baseband through the up-down frequency conversion module, and is sent to a receiving end of the baseband real-time transceiving module;

the baseband real-time transceiving module utilizes the FPGA to complete the real-time transmission and reception of baseband OFDM signals;

the up-down frequency conversion module completes the conversion of signals between a baseband and an antenna working frequency band;

the radio frequency antenna module completes the transmission and the reception of radio frequency signals among different communication units;

the self-adaptive control module controls the adjustable light delay line and the variable optical attenuator, and adaptively adjusts the amplitude and the phase of the reference signal according to the evaluation index for measuring the quality of the received signal returned by the FPGA, so as to realize the matching and elimination of the reference signal and the self-interference signal;

the optical self-interference elimination module carries out self-interference elimination on signals from a receiving antenna in the radio frequency antenna module, so that useful signals can be received by the baseband real-time transceiving module after being converted from an antenna working frequency band to a baseband through the up-down frequency conversion module.

Preferably, the baseband real-time transceiver module includes: the FPGA, the digital-to-analog converter, the analog-to-digital converter and the low-pass filter;

the transmitting terminal utilizes the FPGA to carry out real-time OFDM modulation on the baseband digital signal to be transmitted by the FPGA to generate a modulated baseband digital signal, and sends the modulated baseband digital signal to a digital-to-analog converter to generate a baseband analog signal;

the receiving end carries out low-pass filtering on the useful signal without the self-interference signal through a low-pass filter and converts the useful signal into a digital signal through an analog-digital converter;

the FPGA carries out real-time OFDM receiving, demodulation and calculation on the digital signal of the receiving end to obtain an evaluation index for measuring the signal quality;

the evaluation index is given by the number of error bits counted by the FPGA receiving the fixed frame number signal, equivalently measures the size of the error rate of the received signal, and is a direct measure for judging whether the useful signal is correctly recovered and received at the current moment.

Preferably, the up-down conversion module comprises a mixer 1 and a mixer 2;

performing up-conversion on a transmitting end through a mixer 1, and converting a baseband analog signal into an antenna working frequency band;

and performing down-conversion at a receiving end through the mixer 2, and converting the useful signal which is positioned at the working frequency band of the antenna and is subjected to self-interference elimination into a baseband working frequency band.

Preferably, the optical self-interference cancellation module comprises: the optical fiber amplifier comprises an electric absorption modulator 1, an electric absorption modulator 2, a tunable light delay line, an erbium-doped optical fiber amplifier 1, an erbium-doped optical fiber amplifier 2, a variable optical attenuator and a balanced photoelectric detector;

converting a received mixed signal of a radio frequency useful signal and a self-interference signal into an optical signal through an electro-absorption modulator 1, and amplifying the optical signal through an erbium-doped fiber amplifier 1 and then entering a balanced photoelectric detector;

converting the reference signal into an optical signal through an electric absorption modulator 2, sequentially controlling time delay through an adjustable optical time delay line, amplifying through an erbium-doped optical fiber amplifier 2 and controlling attenuation through a variable optical attenuator to obtain a processed reference signal, and processing the processed reference signal through a balanced photoelectric detector;

and the balance photoelectric detector realizes the conversion from an optical signal to an electric signal, and subtracts the processed reference signal from a mixed signal of the useful signal and the self-interference signal to obtain the useful signal without the self-interference.

Preferably, the adaptive control module comprises an STM32 singlechip;

an STM32 single chip microcomputer is adopted to execute an unconstrained optimization regular triangle algorithm, a request instruction is sent to the FPGA under a real-time communication environment, then a real-time signal evaluation index from the FPGA is received, the evaluation index is used as an objective function value in the optimization process, the self-interference signal passing through the reference signal is cancelled out through repeated iteration and self-adaptive control of the adjustable optical delay line and the variable optical attenuator, and the evaluation index of the useful signal received by the FPGA is gradually reduced until a preset end condition is met.

Preferably, the regular triangle algorithm includes:

establishing an optimization model by taking the evaluation index of the received signal as a target function and taking the delay of a variable optical delay line and the attenuation of a variable optical attenuator as decision variables to search for a global minimum point; constructing a regular triangle on a two-dimensional plane taking delay and attenuation as coordinates by taking a starting point as a center, determining an optimal point by sampling and comparing function values of three vertexes, constructing the regular triangle again by taking the optimal point as the center, repeating iteration until the constructed vertex function value of the regular triangle is larger than the function value of the center, reducing the side length of the regular triangle, and restarting exploration by taking the current central point as the starting point until a preset optimization stop condition is met;

the preset optimization stopping condition comprises that the evaluation index of the received signal is reduced to 0 or the searching step length is smaller than a preset value.

The invention provides a real-time adaptive optical self-interference elimination system based on an FPGA and an STM32, which comprises:

module M1: the baseband real-time transceiving module completes real-time transmission of baseband OFDM signals by using the FPGA;

module M2: the up-down frequency conversion module receives a baseband OFDM signal, and completes the conversion between the baseband of the signal and the working frequency band of the antenna to obtain a radio frequency signal of local communication information;

module M3: after the radio frequency signal of the local communication signal is copied into a reference signal, the local communication signal is transmitted out through a transmitting antenna in a radio frequency antenna module;

module M4: a receiving antenna in the radio frequency antenna module receives a radio frequency useful signal from another communication unit and a time-varying radio frequency self-interference signal of a nearby transmitting antenna which belongs to the same communication unit with the current receiving antenna, and sends the time-varying radio frequency self-interference signal to the optical self-interference elimination module;

module M5: after the optical self-interference elimination module receives the useful signal and the self-interference signal, the amplitude and the phase of the reference signal are adjusted through the self-adaptive control module, so that the reference signal and the self-interference signal are accurately matched, the reference signal and the self-interference signal are mutually offset through a balance photoelectric detector in the optical self-interference elimination module, the useful signal with the self-interference eliminated is obtained, the useful signal with the self-interference eliminated is converted between an antenna working frequency band and a baseband through the up-down frequency conversion module, and is sent to a receiving end of the baseband real-time transceiving module;

the evaluation index is given by the bit error number counted by the FPGA receiving the fixed frame number signal, equivalently measures the size of the bit error rate of the received signal, and is a direct measure for judging whether the useful signal is correctly recovered and received at the current moment;

the up-down frequency conversion module comprises a frequency mixer 1 and a frequency mixer 2;

Preferably, the adaptive control module comprises an STM32 singlechip;

an STM32 single chip microcomputer is adopted to execute an unconstrained optimization regular triangle algorithm, a request instruction is sent to an FPGA under a real-time communication environment, then a real-time signal evaluation index from the FPGA is received, the evaluation index is used as an objective function value in the optimization process, an adjustable optical delay line and a variable optical attenuator are controlled in a self-adaptive mode through repeated iteration, so that a reference signal is cancelled through self-interference signals, and the evaluation index of a useful signal received by the FPGA is gradually reduced until a preset end condition is met;

the regular triangle algorithm comprises:

Compared with the prior art, the invention has the following beneficial effects:

1. the real-time self-adaptive optical self-interference elimination system based on the FPGA and the STM32, which is applied to the IBFD wireless communication system, improves the real-time performance of the optical self-interference elimination system based on the FPGA for the first time. By utilizing the characteristic that the FPGA can carry out real-time high-speed data transmission, the system can be used as a complete communication unit to carry out real-time bidirectional communication with other communication units, can receive a useful signal from another communication unit while transmitting the signal and can obtain an evaluation index for measuring the quality of the received signal at the current moment. The evaluation index has real-time performance, can provide more accurate and faster algorithm execution basis for the self-adaptive control module, solves the problem that the current optical self-interference elimination system lacks real-time data transceiving and real-time signal evaluation indexes, and enables the integral optical self-interference elimination system to better meet the requirements of actual communication and commerce;

2. the invention provides a real-time self-adaptive optical self-interference elimination system based on FPGA and STM32 and applied to an IBFD wireless communication system, which utilizes an STM32 single chip microcomputer to receive real-time signal evaluation indexes, execute an unconstrained optimization regular triangle algorithm, adaptively and precisely control an adjustable optical delay line and a variable optical attenuator. The phase and the amplitude of the reference signal can be adjusted rapidly and adaptively, so that the reference signal can be matched and offset with the self-interference signal under the time-varying wireless channel rapidly in time. Compared with the prior art, the execution efficiency of a system hardware platform and an algorithm is remarkably improved, and the problems of low optimization speed and multiple algorithm iteration times of the current optical self-interference elimination system in adaptivity are solved;

3. the real-time self-adaptive optical self-interference elimination system based on the FPGA and the STM32, which is applied to the IBFD wireless communication system, adopts the bit error number of the fixed frame number receiving signal of the FPGA receiving end as an optimized evaluation index, and equivalently measures the bit error rate of the receiving signal at the current moment. Compared with the error rate, the decision index avoids floating point operation and division operation at the FPGA serial port part, saves hardware resources and improves the serial port communication speed. Compared with the existing evaluation index of the residual signal power, the evaluation index is based on the receiving and calculation of the useful signal of the receiving end, the receiving quality of the signal is ensured when an optimization algorithm is executed, the actual communication scene and the communication requirement are better met, and the practical significance and the practical value are better realized;

4. the invention is applied to an in-band full-duplex wireless communication system, is transparent to bandwidth, can work in a high frequency band, and mainly solves the real-time problem and the self-adaptability problem of an optical self-interference elimination system in the in-band full-duplex wireless communication system. Through the real-time high-speed data processing of the FPGA, the self-adaptive accurate control of the STM32 and the cooperation between the two platforms, the system can accurately and quickly eliminate the self-interference of the transmitting antenna of the same communication unit to the receiving antenna under different wireless channels, so that the full-duplex wireless communication is realized between different communication units.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a real-time adaptive optical self-interference cancellation system based on FPGA and STM32 and applied to an IBFD wireless communication system;

FIG. 2 is a block diagram of the modulation and demodulation function of the baseband OFDM signal inside the FPGA according to the present invention;

fig. 3 is a serial port work flow chart of the FPGA and the STM32 provided by the present invention.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.

Example 1

The optical self-interference elimination in the invention is to copy the transmitting signal into a path of reference signal before the transmitting antenna, and then adjust the phase and amplitude of the reference signal to make the reference signal matched with the self-interference signal of the transmitting antenna to the receiving antenna as much as possible. Thus, the balanced photodetector can smoothly subtract the self-interference signal by the reference signal, and only the useful signal is left, thereby completing the reception of information.

Based on this, the precise matching of the reference signal and the self-interference signal is a key factor for determining the cancellation effect of the system. Since the wireless channel has time-varying characteristics, the self-interference signal varies from time to time, and therefore, a system is required to be able to quickly adjust the phase and amplitude of the reference signal in real time. The invention utilizes the STM32 singlechip to control the adjustable delay line and the variable optical attenuator of the branch where the reference signal is located in the system, thereby changing the phase and amplitude of the reference signal. The algorithm operated by the STM32 single chip microcomputer is an unconstrained optimization algorithm, and the optimization objective function is the bit error number of a signal receiving end. Through continuous iteration, the STM32 single chip microcomputer searches for an optimal delay value and an optimal attenuation value, so that the number of signal bit errors at the receiving end reaches the minimum or meets the algorithm stop condition. The size of the index of the bit error number is obtained by receiving and counting the useful signals through the FPGA at high speed in real time, and compared with the prior art that the signal power of a receiving end is used as an objective function, the index of the bit error number guarantees the actual communication quality and the accuracy. Meanwhile, the high-speed real-time characteristic of the FPGA enables the self-interference elimination system to rapidly and timely obtain the bit error number reflecting the signal quality of the receiving end at the current moment, reduces the delay in the process of obtaining the evaluation index from signal receiving, and improves the self-interference elimination efficiency and precision.

According to the real-time adaptive optical self-interference elimination method based on the FPGA and the STM32, as shown in FIGS. 1 to 3, the method comprises the following steps:

the up-down frequency conversion module is used for completing the conversion of signals between the baseband and the antenna working frequency band through the up-down frequency conversion module because the antennas have corresponding working frequency bands and baseband signals cannot be directly transmitted and received through the antennas in the radio frequency antenna module;

the radio frequency antenna module completes the transmission and the reception of radio frequency signals among different communication units; the radio frequency antenna module includes: a transmitting antenna Tx, a receiving antenna Rx; the transmitting antenna Tx transmits a radio frequency signal containing local communication information, and the receiving antenna Rx receives a radio frequency useful signal from another communication unit and a time-varying radio frequency self-interference signal of the same communication unit adjacent to the transmitting antenna.

Specifically, the baseband real-time transceiver module includes: the FPGA, the digital-to-analog converter, the analog-to-digital converter and the low-pass filter;

the FPGA carries out real-time OFDM receiving, demodulation and calculation on the digital signal of the receiving end to obtain an evaluation index for measuring the signal quality; after receiving a request instruction of the STM32, sending a signal evaluation index at the current moment to an STM32 single chip microcomputer through a serial peripheral interface;

the FPGA-based OFDM modulation comprises: data caching, serial-to-parallel conversion, 16-ary Quadrature Amplitude Modulation (16 QAM), conjugate symmetry, training, Inverse Fast Fourier Transform (IFFT), cyclic prefix insertion, pilot sequence addition, and digital-to-analog conversion; the FPGA-based OFDM demodulation comprises: analog-to-digital conversion, signal synchronization, cyclic prefix removal, Fast Fourier Transform (FFT), channel equalization, conjugation release, 16QAM demodulation, parallel-to-serial conversion, and received signal evaluation;

the signal adopts OFDM modulation and demodulation mode, fully utilizes the channel bandwidth, and improves the anti-fading capability and the anti-narrow-band interference capability.

The evaluation index is given by the number of error bits counted by the FPGA receiving the fixed frame number signal, equivalently measures the size of the error rate of the received signal, and is a direct measure for judging whether the useful signal is correctly recovered and received at the current moment. After the STM32 singlechip sends a request instruction to the FPGA, the FPGA returns the evaluation index of the current received signal to the STM32 singlechip for the singlechip to execute self-adaptive accurate control according to a regular triangle algorithm.

Specifically, the up-down conversion module comprises a mixer 1 and a mixer 2;

Specifically, the optical self-interference cancellation module includes: the optical fiber amplifier comprises an electric absorption modulator 1, an electric absorption modulator 2, a tunable light delay line, an erbium-doped optical fiber amplifier 1, an erbium-doped optical fiber amplifier 2, a variable optical attenuator and a balanced photoelectric detector;

Specifically, the adaptive control module comprises an STM32 singlechip;

Specifically, the regular triangle algorithm includes:

Specifically, the up-down conversion module comprises a mixer 1 and a mixer 2;

Specifically, the adaptive control module comprises an STM32 singlechip;

Specifically, the regular triangle algorithm includes:

Example 2

Example 2 is a modification of example 1

The real-time adaptive optical self-interference elimination system based on the FPGA and the STM32 and applied to the IBFD wireless communication system provided by the invention comprises the following components: the system comprises a baseband real-time transceiving module, an up-down frequency conversion module, a radio frequency antenna module, a self-adaptive control module and an optical self-interference elimination module;

wherein: the baseband real-time transceiving module generates an OFDM signal in real time by using the FPGA at a transmitting end, demodulates and receives the OFDM signal from another communication unit in real time at a receiving end to obtain a real-time evaluation index, namely the bit error number (BEC) of a receiving signal with a fixed frame number; after the STM32 singlechip sends a request instruction to the FPGA, the FPGA sends a signal BEC at the current moment to the STM32 singlechip;

the up-down frequency conversion module realizes the conversion between the baseband and the antenna working frequency band by using a frequency mixer;

the radio frequency antenna module is used for completing the transmission and the reception of radio frequency signals by using a radio frequency antenna;

the self-adaptive control module executes an unconstrained optimized regular triangle algorithm by using the STM32 singlechip, sends a request instruction to the FPGA, receives a real-time evaluation index from the FPGA, and self-adaptively controls the adjustable optical delay line and the variable optical attenuator according to the real-time evaluation index;

the optical self-interference elimination module copies a reference signal from the local transmitting terminal and adjusts the phase and amplitude of the reference signal after receiving a useful signal from another communication unit and a co-frequency time-varying self-interference signal caused by the local transmitting antenna at the receiving antenna Rx post-stage, so that the reference signal and the self-interference signal are accurately matched and mutually offset, and the receiving terminal recovers and receives the useful signal.

The baseband real-time transceiving module comprises: the FPGA, the digital-to-analog converter, the analog-to-digital converter and the low-pass filter; specifically, real-time OFDM modulation is carried out by using an FPGA at a transmitting end, a baseband digital signal is generated and sent to a digital-to-analog converter to be converted into an analog signal; and after the low-pass filtering is carried out on the useful signal subjected to the self-interference signal elimination at the receiving end, the useful signal is converted into a digital signal through an analog-to-digital converter. The FPGA carries out real-time OFDM demodulation and receiving on the digital signal to obtain a judgment index for measuring the quality of the received signal at the current moment. And after receiving the request instruction of the STM32, the FPGA sends the real-time evaluation index to the STM32 single chip microcomputer through the SPI.

Specifically, the OFDM modulation includes: data caching, serial-to-parallel conversion, 16-system orthogonal amplitude modulation, conjugate symmetry, training, inverse fast Fourier transform, cyclic prefix insertion, pilot frequency sequence addition and digital-to-analog conversion; the OFDM demodulation includes: analog-to-digital conversion, signal synchronization, cyclic prefix removal, fast Fourier transform, channel equalization, conjugate removal, 16QAM demodulation, parallel-to-serial conversion and received signal evaluation; the signal adopts OFDM modulation and demodulation mode, fully utilizes the channel bandwidth, and improves the anti-fading capability and the anti-narrow-band interference capability.

Specifically, the decision index is given by the number of error bits counted by the fixed frame number signal received by the FPGA, and equivalently measures the size of the error rate of the received signal. After the STM32 singlechip sends a request instruction to the FPGA, the FPGA returns the real-time BEC of the current received signal to the STM32 singlechip. Compared with the error rate, the decision index avoids floating point operation and division operation at the FPGA serial port part, saves FPGA hardware resources and improves the serial port communication speed.

The up-down frequency conversion module comprises: a mixer 1, a mixer 2; specifically, the mixer 1 up-converts a baseband signal to an antenna operating frequency band at a signal transmitting end, and the mixer 2 down-converts the antenna operating frequency band signal to a baseband at a signal receiving end.

The radio frequency antenna module includes: a transmitting antenna Tx, a receiving antenna Rx; specifically, the transmitting antenna Tx transmits a radio frequency signal containing local communication information, and the receiving antenna Rx receives a radio frequency useful signal from another communication unit and a time-varying radio frequency self-interference signal of the same communication unit adjacent to the transmitting antenna. Since the radio channel between the transmit antenna Tx and the receive antenna Rx has a time-varying characteristic, the self-interference signal also varies over time.

The adaptive control module comprises: STM32 singlechip. Specifically, the STM32 single chip microcomputer executes a control process according to a regular triangle algorithm, and after the STM32 single chip microcomputer sends a request instruction to the FPGA, the FPGA sends real-time BEC for measuring the error rate of received signals to the STM32 single chip microcomputer, namely the number of error bits counted according to the received signals with fixed frame number. And the STM32 singlechip judges the self-interference elimination condition at the current moment according to the size of the BEC and continuously executes an algorithm to iterate, adaptively controls the adjustable light delay line and the variable optical attenuator and gradually reduces the BEC of the received useful signal to meet the end condition.

Further, the regular triangle algorithm uses the BEC of the received signal at the current moment as an objective function, and uses the delay of the variable optical delay line and the attenuation of the variable optical attenuator as decision variables to establish an optimized model to search for a global minimum point; specifically, on a two-dimensional plane formed by taking delay and attenuation as coordinates, a regular triangle is constructed by taking a starting point as a center, and the optimal point is determined by sampling and comparing the BEC values corresponding to three vertexes. And (5) constructing the regular triangle again by taking the optimal point as a center, and repeating iteration. And reducing the side length of the regular triangle until the BEC value of the constructed vertex of the regular triangle is larger than the BEC value of the center. And restarting the exploration by taking the current central point as a starting point until the optimization stop condition is met, namely the BEC of the received signal at the current moment is reduced to 0 or the exploration step length is smaller than a set value.

Further, the serial port work flow of the FPGA and the STM32 is as follows: and the STM32 singlechip sends an instruction for requesting the BEC to the FPGA when needing to acquire the receiving signal BEC at the current moment, and the FPGA sends the BEC value of the receiving signal at the current moment to the STM32 singlechip after receiving the instruction. And after receiving the BEC value, the STM32 singlechip continues to execute the algorithm until an optimization stop condition is met, and sends an end instruction to the FPGA, and the FPGA finishes the work of the serial port part after receiving the end instruction and is in a waiting state.

The optical self-interference cancellation module comprises: the optical fiber modulator comprises an electric absorption modulator 1, an electric absorption modulator 2, a light-adjustable delay line, an erbium-doped optical fiber amplifier 1, an erbium-doped optical fiber amplifier 2, a variable optical attenuator and a balanced photoelectric detector; specifically, the branch in which the electro-absorption modulator 1 is located is referred to as an upper branch, and the branch in which the electro-absorption modulator 2 is located is referred to as a lower branch.

Further, the upper branch comprises: an electroabsorption modulator 1, an erbium-doped fiber amplifier 1; after a receiving antenna Rx receives a useful signal from another communication unit and a same-frequency self-interference signal close to a transmitting antenna Tx, an electro-absorption modulator 1 converts a mixed signal of the useful signal and the self-interference signal into an optical signal, and an erbium-doped optical fiber amplifier 1 further amplifies the optical signal of an upper branch and then transmits the optical signal to a positive port of a balanced photoelectric detector through an optical fiber.

Further, the lower branch comprises: the optical fiber amplifier comprises an electric absorption modulator 2, a light adjustable delay line, an erbium-doped optical fiber amplifier 2 and a variable optical attenuator; the signal output by the mixer 1 is copied as a reference signal before reaching the transmitting antenna Tx, and the electric absorption modulator 2 converts the reference signal into an optical signal and inputs the optical signal into the adjustable optical delay line to control the optical path delay. And then the erbium-doped optical fiber amplifier 2 amplifies the optical signal, the variable optical attenuator attenuates the optical signal, and dynamic adjustment of the phase and amplitude of the reference signal is completed, so that the reference signal is matched with a time-varying self-interference signal transmitted through a time-varying wireless channel, and the adjusted reference signal is transmitted to a negative port of the balanced photoelectric detector through an optical fiber.

Furthermore, signals of the upper branch and the lower branch enter a positive port and a negative port of the balanced photoelectric detector respectively after passing through each device, so that the subtraction of a mixed signal of a useful signal and a time-varying self-interference signal from a dynamically adjusted reference signal is realized while the conversion from an optical signal to an electric signal is completed. The signal output by the balanced photoelectric detector is a useful signal after the self-interference signal is eliminated, the signal is an electric signal in a working frequency band, and the signal enters a receiving end of the baseband real-time transceiving module after down-conversion.

In the optical self-interference cancellation module based on the electro-absorption modulator under study, the two optical powers P1 and P2 entering the positive port and the negative port of the balanced photodetector can be respectively expressed as:

P₁＝kβU_SI(t-τ')+kU₀+kU_SOI(1)

P₂＝kαU_Ref(t-τ)+kαU₀(2)

the expression for balancing the residual signal voltage output by the photodetector is:

U_r＝γ(P₁-P₂)(3)

＝γk[βU_SI(t-τ')-αU_Ref(t-τ)]+γkU_SOI+γkU₀(1-α)(4)

where k denotes the slope of the modulation curves of the two electroabsorption modulators, U_rRepresenting the residual signal voltage, U, of the output of the balanced photodetector_SOIVoltage, U, representing useful signal_SIVoltage, U, representing a self-interference signal_RefVoltage, U, representing a reference signal₀The bias voltages of the two electroabsorption modulators are shown, gamma represents the response slope of the balanced photodetector, beta represents the attenuation of the wireless channel, tau' represents the delay of the wireless channel, alpha represents the amplitude modulation of the variable optical attenuator, tau represents the delay of the variable optical delay line, and t represents time.

The cancellation depth may be defined as the ratio of the energy after cancellation from the interference signal to the energy before cancellation:

in the formula, E₂Representing the energy after removal from the interference signal, E₁Representing the energy before cancellation from the interference signal,

denotes the relative amplitude deviation,. DELTA.tau. -. tau. -. tau.denotes the relative delay deviation,. B denotes the bandwidth,. f₀Representing the center frequency of the self-interference signal.

The formula (4) and the formula (6) show that when the relative amplitude deviation and the relative delay deviation of the time-varying self-interference signal passing through the wireless channel and the reference signal after the optical path dynamic adjustment are reduced to 0, the output signal power of the balanced photodetector is minimum, and the optical self-interference elimination depth is optimal. In the self-adaptive control process of the system, the reduction of the relative amplitude deviation and the relative delay deviation is realized by controlling a variable optical delay line and a variable optical attenuator through an STM32 singlechip according to a real-time BEC evaluation index sent by an FPGA.

The working principle of the system can be summarized as follows: when the receiving antenna Rx receives a useful signal from another communication unit in real time, it suffers from co-channel self-interference from the adjacent transmitting antenna Tx. Therefore, the transmission signal needs to be copied to be the reference signal, and the self-interference signal is cancelled by using the reference signal, so as to ensure the successful reception of the useful signal. The transmission signal of the transmitting antenna Tx may have amplitude and phase changes after passing through the wireless channel between the transmitting antenna Tx and the receiving antenna Rx, and the amplitude and phase changes with time. Therefore, the key of self-interference cancellation is to adaptively and accurately control the amplitude and phase of the reference signal in real time so as to match the reference signal with the self-interference signal, and the basis of adaptive control is an evaluation index, namely BEC, for measuring the quality of the received signal. The size of the BEC is given by demodulating the useful signal after the self-interference signal is eliminated by the FPGA receiving end and according to the bit error number of the received signal with the fixed frame number. In the system, the real-time high-speed communication among different communication units is realized based on the FPGA, and a real-time signal BEC is calculated; and the accurate control of self-adaptation is realized by STM32 singlechip. When the STM32 executes an algorithm and the BEC of a point corresponding to the current delay and attenuation needs to be acquired, a request instruction is sent to the FPGA, and the FPGA receives the instruction and returns the instruction to the STM32 singlechip according to the size of the BEC at the current moment. The regular triangle algorithm executed in the STM32 single chip microcomputer continuously constructs a regular triangle from an initial point according to the size of a decision index BEC, and completes exploration and iteration. When the BEC is reduced to meet the optimization stop condition, the horizontal and vertical coordinates of the corresponding point are the optimal delay value and the attenuation value of the reference signal. The working principle of the real-time adaptive optical self-interference elimination system based on the FPGA and the STM32 and applied to the IBFD wireless communication system is shown in the specification.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. In the case of no conflict, the embodiments and features of the embodiments of the present application may be arbitrarily combined with each other.

Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the device and the modules thereof provided by the present invention can be considered as a hardware component, and the modules included in the system, the device and the modules thereof for implementing various programs can also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims

1. A real-time adaptive optical self-interference elimination method based on FPGA and STM32 is characterized by comprising the following steps:

2. The method for real-time adaptive optical self-interference cancellation based on FPGA and STM32 as claimed in claim 1, wherein the baseband real-time transceiver module comprises: the FPGA, the digital-to-analog converter, the analog-to-digital converter and the low-pass filter;

3. The FPGA and STM32 based real-time adaptive optical self-interference cancellation method according to claim 1, wherein the up-down conversion module comprises a mixer 1 and a mixer 2;

4. The method of real-time adaptive optical self-interference cancellation based on FPGA and STM32 as claimed in claim 1, wherein the optical self-interference cancellation module comprises: the optical fiber amplifier comprises an electric absorption modulator 1, an electric absorption modulator 2, a tunable light delay line, an erbium-doped optical fiber amplifier 1, an erbium-doped optical fiber amplifier 2, a variable optical attenuator and a balanced photoelectric detector;

5. The real-time adaptive optical self-interference elimination method based on the FPGA and the STM32 as claimed in claim 4, wherein the adaptive control module comprises an STM32 single chip microcomputer;

6. The method for real-time adaptive optical self-interference cancellation based on FPGA and STM32 as claimed in claim 5, wherein the regular triangle algorithm comprises:

7. A real-time adaptive optical self-interference cancellation system based on FPGA and STM32 is characterized by comprising:

8. The FPGA and STM32 based real-time adaptive optical self-interference cancellation system of claim 7, wherein the baseband real-time transceiver module comprises: the FPGA, the digital-to-analog converter, the analog-to-digital converter and the low-pass filter;

9. The FPGA and STM32 based real-time adaptive optical self-interference cancellation system of claim 7, wherein the optical self-interference cancellation module comprises: the optical fiber amplifier comprises an electric absorption modulator 1, an electric absorption modulator 2, a tunable light delay line, an erbium-doped optical fiber amplifier 1, an erbium-doped optical fiber amplifier 2, a variable optical attenuator and a balanced photoelectric detector;

10. The real-time adaptive optical self-interference cancellation system based on the FPGA and the STM32, according to claim 9, wherein the adaptive control module comprises an STM32 single chip microcomputer;

the regular triangle algorithm comprises: