CN110943752A - OQPSK self-adaptive variable rate digital transceiver based on adjacent space link protocol - Google Patents
OQPSK self-adaptive variable rate digital transceiver based on adjacent space link protocol Download PDFInfo
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
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Abstract
The invention discloses an OQPSK system self-adaptive variable-rate digital transceiver based on a neighbor space link protocol. The transmitter comprises an OQPSK modulation module and a transmitter rate control module, and the receiver comprises an OQPSK demodulation module, a signal-to-noise ratio estimation module and a receiver rate control module; the transmitter adjusts the parameter configuration of the transmitter according to the feedback information of the receiver, and adjusts the transmission signal rate by controlling the clock module, interpolating multiple and extracting multiple through the transmitter rate control module. The receiver carries out signal-to-noise ratio estimation on the received signal through a signal-to-noise ratio estimation module, and a receiver rate control module controls a clock module, an interpolation multiple and an extraction multiple of the receiver according to the signal-to-noise ratio estimation value, and simultaneously provides rate feedback information for the transmitter to synchronously carry out self-adaptive rate switching. The digital transceiver can effectively face the severe environment of a deep space communication channel.
Description
The technical field is as follows:
the invention relates to a design of an adaptive digital transceiver for a neighboring link space under the background of large loss difference in a deep space environment, in particular to an OQPSK adaptive variable rate digital transceiver based on a neighboring space link protocol.
Background art:
the united states Space administration (NASA), European Space Administration (ESA) and many Space agencies created the council for Space Data Systems (CCSDS) in the last 80 centuries, and aiming at the characteristics of deep Space communication, the CCSDS standard protocol, namely the adjacent Space link protocol, was proposed to realize the close cooperation of the international deep Space exploration side. According to the CCSDS Proximaty-1 protocol standard, communication between a spacecraft and a spacecraft, between the spacecraft and the ground and between the spacecraft and a lander is specified, the standard requires that a deep space transceiver supports switching of 12-grade transmission rates in the ranges of 1kbps, 2kpbs, 4kbps, 8 kbps-1024 kbps and 2048kbps, and the condition that link margin is less than 10 degrees for an asynchronous link is met-6Error rate of.
Compared with the ground traditional communication, the deep space channel has a great amount of deterioration degree, and fig. 2 shows a deep space channel attenuation model, and a transmission signal is often influenced by not only small-scale fading such as doppler shift and multipath delay, but also large-scale fading such as path loss, cosmic noise, planetary noise and sun flicker, so that the channel capacity is changed rapidly. Therefore, communication at a fixed transmission rate cannot meet the demand of a deep space channel.
The invention content is as follows:
the purpose of the invention is as follows: in order to solve the influence of severe channel conditions of deep space communication on the effectiveness and reliability of signal transmission, the invention combines an adjacent space link protocol to provide an OQPSK adaptive variable rate digital transceiver based on the adjacent space link protocol, an adaptive rate control module of the transceiver is controlled by outputting information through a signal-to-noise ratio estimation module to obtain a code element rate required under the current bit error rate requirement, then the adaptive control module controls a transceiver clock module to change an interpolation extraction multiple and control the bandwidth of a transceiver filter at the same time, the throughput of signals is improved as much as possible on the premise of meeting the bit error rate, the requirement of the transceiver of the deep space communication on reducing the influence of channel change on the transceiver through an adaptive variable rate technology is met, and the real-time performance and the effectiveness of the signal transmission are improved.
The invention content is as follows: in order to achieve the technical effects, the invention provides an OQPSK adaptive variable rate digital transceiver based on an adjacent space link protocol, which comprises a transmitter and a receiver; wherein the content of the first and second substances,
the transmitter comprises an OQPSK modulation module and a transmitter speed control module;
the receiver comprises an OQPSK demodulation module, a signal-to-noise ratio estimation module and a receiver rate control module;
the receiver receives the signal sent by the transmitter, the signal is demodulated by the OQPSK demodulation module and then sent to the signal-to-noise ratio estimation module, the signal-to-noise ratio estimation module carries out signal-to-noise ratio estimation on the received signal and sends the estimated value to the receiver rate control module; the receiver rate control module receives the bit error rate requirement sent by the upper computer, calculates the required signal-to-noise ratio, compares the required signal-to-noise ratio with the estimated signal-to-noise ratio of the signal-to-noise ratio estimation module, utilizes the characteristics that the OQPSK signal reduces half of the symbol rate and the signal-to-noise ratio is improved by 3dB and the OQPSK signal improves one time of the symbol rate and the signal-to-noise ratio is reduced by 3dB, changes the code element rate by adjusting the clock module and the interpolation extraction multiple, and gradually adjusts the signal rate until the signal-to-noise ratio reaches the required signal-to-noise ratio requirement, and then feeds back;
the transmitter rate control module receives signal rate feedback information sent by the receiver, adjusts a clock module, an interpolation multiple and an extraction multiple of the transmitter according to the receiver rate feedback information, and changes the transmitting rate of the transmitter to a required transmitting rate; meanwhile, the new rate information of the transmitter and the related parameter information of the transmitter are written into the SPDU and are transmitted to the receiver along with the adjacent link transmission unit.
Furthermore, the OQPSK demodulation module of the receiver includes a digital down-conversion module, a gain detection module, an automatic gain control module, a carrier synchronization module, a symbol synchronization module, a frame synchronization module, a phase compensation and decision module, and a serial-to-parallel conversion module, which are sequentially cascaded; wherein the content of the first and second substances,
the digital down-conversion module converts the signals received by the receiver into low-intermediate frequency signals required by the receiver;
the gain detection module carries out energy detection on the received signal, and when the energy of the received signal is higher than a preset energy detection threshold value, the received signal is judged to belong to useful user information, and at the moment, the receiver is started; when the energy of the received signal is lower than a preset energy detection threshold value, judging that the received signal belongs to invalid noise, and closing the receiver at the moment;
the automatic gain control module performs self-adaptive adjustment on a gain coefficient when a receiver receives signals and generates large amplitude oscillation due to channel fading and cosmic noise, so that signal saturation or loss is prevented, and the received signals meet the requirement of later-stage synchronous demodulation;
the carrier synchronization module dynamically adjusts the frequency of a local carrier of the receiver by carrying out closed-loop detection on the received signal to enable the frequency to be equal to the carrier frequency of the transmitter, so that a subsequent module of the receiver can carry out coherent demodulation;
the symbol synchronization module and the frame synchronization module respectively perform symbol synchronization and frame synchronization processing on the received signals;
the phase compensation and judgment module compensates the estimation of the phase deviation and then judges to obtain user bit information;
and the serial-parallel conversion module carries out serial-parallel conversion on the signal output by the phase compensation and judgment module and then outputs user information.
Furthermore, the automatic gain control module comprises a controllable gain amplifier, a detector module, a gain coefficient control module, a comparator and an error processing module;
the input signal enters a detector after being subjected to A/D conversion and a controllable gain amplifier, the detector detects the signal energy and sends the detection result to a comparator and a gain coefficient control module respectively;
the comparator compares the received detection value with a reference value to obtain an error with the reference value, and then sends the error value to the error processing module;
the gain coefficient control module adjusts the gain coefficient in the error processing module according to the detection value; the formula is Gain (n +1) ═ Gain (n) + aVeWherein Gain (n +1) is the adjusted Gain coefficient, Gain (n) is the current Gain coefficient, a is the weighting factor, VeIs an error from a standard value;
the error processing module adjusts the gain coefficient of the controllable gain amplifier according to the received error value and the gain coefficient adjustment result: when the error value is lower than the threshold value, the gain coefficient of the controllable gain amplifier is kept unchanged, and when the error value exceeds the threshold value, the gain coefficient is changed according to the feedback information of the error processing module to obtain a new amplification coefficient of the controllable gain amplifier.
Furthermore, the carrier synchronization module is realized by adopting a modified Costas ring, and the modified Costas ring comprises a local NCO, a matched filter, a digital phase discriminator and a loop filter; signals of an I path and a Q path received by the receiver enter the digital phase discriminator after passing through the matched filter, and the obtained output signal of the phase discriminator adjusts the local NCO of the receiver after passing through the loop filter until the loop is stable after the carrier frequency of the local NCO of the receiver is consistent with that of the received signal.
Further, the symbol synchronization module adopts an early-late loop algorithm to perform symbol synchronization design, and includes: the system comprises an early gate integrator, a late gate integrator, a data error discriminator, a loop filter, a locking decision device and a clock generator; the I path signal and the Q path signal are normalized, the processed square wave signals respectively enter an early gate integrator and a late gate integrator, the early gate integration result and the late gate integration result of the I path signal and the early gate integration result and the late gate integration result of the Q path signal are sent to a data error discriminator to be judged, when a clock error exists, the data error discriminator can quickly accumulate errors and give error data, the clock generator is adjusted after the error data pass through a loop filter, the clock frequencies of the early gate clock, the late gate clock and a sampling clock are changed until the optimal sampling time is obtained, meanwhile, a locking judgment device can give a locking indication to clearly reflect the working state of a symbol synchronization module.
Further, the signal-to-noise ratio estimation module comprises a signal-to-noise ratio estimation algorithm selection module, a DF-3 estimation algorithm module, an SNV estimation algorithm module and a signal-to-noise ratio output module, wherein the DF-3 estimation algorithm module adopts a DF-3 estimation algorithm to calculate a signal-to-noise ratio estimation value from an input signal, and the SNV estimation algorithm module adopts an SNV estimation algorithm to calculate a signal-to-noise ratio estimation value from the input signal; the signal-to-noise ratio output module takes the signal-to-noise ratio estimation value at the last moment as signal-to-noise ratio feedback information to be input into the signal-to-noise ratio estimation algorithm selection module, and the signal-to-noise ratio estimation module performs selection of a post-stage estimation module by comparing the signal-to-noise ratio feedback information with a threshold value set in the module: when the signal-to-noise ratio changes and exceeds the threshold value, the signal-to-noise ratio estimation algorithm is switched at the next moment.
Has the advantages that: the invention has the following advantages:
1. the digital transceiver supports switching of 12-step transmission rates in the range of 1kbps, 2kpbs, 4kbps, 8 kbps-1024 kbps, 2048kbps, according to the requirements of the adjacent space link protocol.
2. Compared with a QPSK modulation system, the system adopts an OQPSK modulation mode, avoids 180-degree phase reversal, improves the phase compensation and judgment performance, and reduces error codes generated by phase deviation.
3. The receiver gain detection module is used for setting a working state by an upper computer and adjusting a detection threshold value to meet working requirements under different environments.
4. The automatic gain control module adopts a variable gain coefficient, reduces the stabilization time of a feedback loop and effectively solves the problem of large signal fading.
5. The signal-to-noise ratio estimation module adopts a DF-3 estimation and SNV estimation combined estimation method, combines the advantages of two estimation algorithms, achieves the effects of lower hardware complexity and small signal-to-noise ratio estimation error, and effectively solves the problem of large time-varying property of a deep space communication channel.
6. The adaptive variable rate design is adopted, the bit error rate requirement can be set according to an upper computer, the adaptive variable rate adjustment is carried out according to the current channel quality and the current data rate, the data rate of the transceiver is changed by adjusting the clock module and the interpolation extraction multiple, the information throughput is improved on the premise of meeting the signal-to-noise ratio requirement, and the deep space communication requirement under different backgrounds is met.
Description of the drawings:
FIG. 1 is a block diagram of a digital transceiver according to an embodiment;
FIG. 2 is a deep space channel fading model;
FIG. 3 is an automatic gain module design;
FIG. 4 is a modified Costas ring symbol synchronization design;
FIG. 5 is an early-late ring symbol synchronization design;
FIG. 6 is a DF-3, SNV SNR joint estimation algorithm design;
FIG. 7 is a OQPSK signal bit error rate curve;
FIG. 8 is a bit error rate requirement 10-7Initial signal-to-noise ratio of 28dB, initial data rate of 512kbps adaptive variable rate simulation plot.
Detailed Description
The invention aims to provide a digital transceiver capable of solving the influence of severe channel conditions of deep space communication on the effectiveness and reliability of signal transmission, the transceiver combines an adjacent space link protocol, and designs the digital transceiver capable of self-adapting variable-rate transmission, so that the transmission requirement of a deep space channel can be effectively met, the transmission rate is improved as far as possible on the premise of meeting the requirement of an error rate, and parameters of the transceiver are extremely easy to adjust when the transmission requirement with lower error rate is met.
The deep space channel is influenced by various factors, the signal fading variation amplitude is large, the main fading factors comprise small-scale fading including Doppler frequency shift and multipath loss and large-scale fading including path loss, solar flicker and cosmic noise, and the channel capacity variation is large. Therefore, the traditional fixed-rate communication cannot meet the requirement of a deep space channel, and the adaptive transceiver designed by the text can perform rate switching in real time according to the channel condition to meet the communication requirement.
The CCSDS Proximaty-1 protocol defines the error rate of a deep space communication transceiver, and the error rate of an OQSPK modulation and demodulation system is reduced along with the improvement of the signal-to-noise ratio, so that in a deep space communication link, the signal-to-noise ratio needs to be effectively controlled by changing the signal code element rate, and the transmission requirement of the protocol transceiver is met. When the code element rate is reduced, the signal bandwidth is correspondingly narrowed, the filter bandwidth required by the transceiver is reduced, the in-band noise received by the filter is reduced, and under the same transmitter transmitting power, the signal power is unchanged, the noise power is reduced, and the signal-to-noise ratio is increased. Conversely, when the channel condition is good, the throughput of the signal can be improved by increasing the symbol rate.
The variable rate mode can be realized by changing the code element rate, the modulation mode and the coding mode, and the self-adaptive variable rate design can be realized by adopting the mode of changing the code element rate according to the related requirements of the protocol, thereby meeting the requirements of the protocol on 12 different rate signals. The variable rate design is carried out by changing the code element rate, and because the modulation mode is not changed and the modulation and demodulation module of the adaptive digital transceiver is relatively fixed, the adaptive control module is only required to control the clock module of the transceiver and interpolate the extraction coefficient, so that the modulation and demodulation requirements of the transceiver under different rates are met.
Based on the above analysis, the present invention provides an OQPSK adaptive variable rate digital transceiver based on a neighbor space link protocol, which includes a transmitter and a receiver; wherein the content of the first and second substances,
the transmitter comprises an OQPSK modulation module and a transmitter speed control module;
the receiver comprises an OQPSK demodulation module, a signal-to-noise ratio estimation module and a receiver rate control module;
the receiver receives the signal sent by the transmitter, the signal is demodulated by the OQPSK demodulation module and then sent to the signal-to-noise ratio estimation module, the signal-to-noise ratio estimation module carries out signal-to-noise ratio estimation on the received signal and sends the estimated value to the receiver rate control module; the receiver rate control module receives the bit error rate requirement sent by the upper computer, calculates the required signal-to-noise ratio, compares the required signal-to-noise ratio with the estimated signal-to-noise ratio of the signal-to-noise ratio estimation module, utilizes the characteristics that the OQPSK signal reduces half of the symbol rate and the signal-to-noise ratio is improved by 3dB and the OQPSK signal improves one time of the symbol rate and the signal-to-noise ratio is reduced by 3dB, changes the code element rate by adjusting the clock module and the interpolation extraction multiple, and gradually adjusts the signal rate until the signal-to-noise ratio reaches the required signal-to-noise ratio requirement, and then feeds back;
the transmitter rate control module receives signal rate feedback information sent by the receiver, adjusts a clock module, an interpolation multiple and an extraction multiple of the transmitter according to the receiver rate feedback information, and changes the transmitting rate of the transmitter to a required transmitting rate; meanwhile, the new rate information of the transmitter and the related parameter information of the transmitter are written into the SPDU and are transmitted to the receiver along with the adjacent link transmission unit.
The transceiver adopts an OQPSK modulation and demodulation mode, and due to the fact that the signals of the I path and the Q path have Ts/2 time delay, the polarity inversion of the code elements of the two paths cannot happen at the same time, compared with the traditional QPSK signals, the phase error of 180 degrees cannot be generated, and phase compensation and judgment of a receiver are facilitated. And meanwhile, after OQPSK modulation passes through a band-pass filter, the envelope fluctuation is small, the performance is stable, the frequency band is wide, and the switching before different code rates is facilitated.
The technical scheme of the invention is further illustrated by the specific embodiment in the following combined with the attached drawings.
Fig. 1 shows an implementation of the transceiver according to the invention:
the system comprises a deep space communication OQPSK adaptive variable rate transmitter and a deep space communication OQPSK adaptive receiver;
the transmitter adopts an OQPSK modulation technology, half code element period delay is added to a Q path signal, so that the I path signal and the Q path signal cannot simultaneously generate polarity inversion and generate 180-degree phase inversion, the transmitted signal is firstly subjected to serial-parallel conversion to obtain an I path signal and a Q path signal, then multiplied by NCO of a local transmitter through modulation modules such as zero insertion, forming filtering, low-pass filtering and the like, added to obtain a modulated OQPSK signal, and the signal enters a deep space channel after digital up-conversion. The transmitter has a transmitter rate control module that receives rate feedback information from the receiver. The transmitting rate of the transmitter is changed through the rate feedback information of the receiver, and meanwhile, the new rate information of the transmitter and the related parameter information of the transmitter are written into the SPDU and are transmitted to the receiver along with the adjacent link transmission unit. The transmitter rate control module can control the clock module, the interpolation multiple and the extraction multiple of the transmitter, control the clock rate of each module of the whole transmitter, and control the sampling rate of the transmitter by adjusting the parameters of the interpolation multiple and the extraction multiple, so that the transmitter meets the CCSDS-211 protocol standard and supports the switching of 12-grade transmission rates in the ranges of 1kbps, 2kbps, 4kbps, 8kbps to 1024kbps and 2048 kbps.
The receiver is divided into the following modules: the device comprises a digital down-conversion module, a gain detection module, an automatic gain control module, a carrier synchronization module, a symbol synchronization module, a frame synchronization module, a phase compensation and judgment module, a serial-parallel conversion module, a signal-to-noise ratio estimation module and a receiver rate control module.
The digital down-conversion module converts the signal received by the receiver into a low intermediate frequency signal which is required by us.
The gain detection module carries out energy detection on the received signal, and when the energy of the received signal is higher than a preset energy detection threshold value, the received signal is judged to belong to useful user information, and at the moment, the receiver is started; and when the energy of the received signal is lower than a preset energy detection threshold value, judging that the received signal belongs to invalid noise, and closing the receiver at the moment. The detection threshold value can be changed through upper layer parameters, so that the receiver is switched between a low power consumption working mode and a normal working mode, and the requirements of the receiver under different conditions are met.
The automatic gain control module can effectively control the gain of the receiver, when the received signal of the receiver generates large amplitude oscillation due to channel fading and cosmic noise, the automatic gain control module can carry out self-adaptive adjustment on a gain coefficient, so that signal saturation or loss is prevented, and the received signal meets the requirement of later-stage synchronous demodulation.
The automatic gain control module of this embodiment is shown in fig. 3, and mainly includes a controllable gain amplifier, a detector module, a gain coefficient control module, a comparator, and an error processing module. The input signal enters the detector after being subjected to A/D conversion and the controllable gain amplifier, the detector can detect the signal energy, part of the output signal is compared with the reference value through the comparator to obtain an error with the reference value, when the error is small, the gain coefficient of the controllable gain amplifier is kept unchanged, and when the error exceeds the threshold value, the gain coefficient can be changed according to feedback information of the error processing module. Meanwhile, the other part of the output signal of the detector enters a Gain coefficient control module to control the Gain coefficient in the error processing module, the Gain coefficient of the error processing module is changed in a self-adaptive manner, and when the Gain coefficient control module adjusts the Gain coefficient in the error processing module according to the detection value, the adjustment formula is Gain (n +1) ═ Gain (n) + aV)eWherein Gain (n +1) is the adjusted Gain coefficient, Gain (n) is the current Gain coefficient, a is the weighting factor, VeIs an error from the standard value. Based on the design, the whole loop can recover the stable state in a short time in the face of the oscillation of larger amplitude of the input data. And the error processing module receives the data of the gain control module and the comparator module to carry out operation to obtain a new controllable gain amplifier amplification coefficient.
The carrier synchronization module is realized by adopting a digital phase-locked loop, and the frequency of a local carrier of the receiver is dynamically adjusted by carrying out closed-loop detection on a received signal so as to be equal to the carrier frequency of the transmitter, so that the subsequent module of the receiver can carry out coherent demodulation.
In this embodiment, the carrier synchronization module is implemented by using a modified Costas loop, and compared with a common Costas loop and a digital Costas loop, the modified Costas loop has stronger anti-noise performance and shorter loop settling time. The modified Costas loop is shown in fig. 4 and comprises a local NCO, a matched filter, a digital phase detector and a loop filter, wherein signals of an I path and a Q path received by a receiver enter the digital phase detector after passing through the matched filter, and an output signal of the obtained phase detector adjusts the local NCO of the receiver after passing through the loop filter until the loop is stable after the carrier frequencies of the local NCO of the receiver and a received signal are consistent.
In order to obtain the optimal sampling point, the invention adopts a delay-early loop algorithm to carry out symbol synchronization design, and can realize high-precision symbol synchronization by adjusting the sampling rate. The early-late ring symbol synchronization structure is shown in fig. 5, and mainly includes an early gate integration circuit, a late gate integration circuit, a data error discriminator, a loop filter, a lock decision device, and a clock generator. The I path signal and the Q path signal are normalized, the processed square wave signal enters an early gate integrating circuit and a late gate integrating circuit, the square wave signal is judged through a data error discriminator, when a clock error exists, the algorithm can quickly accumulate the error, the data error discriminator can give out error data, the clock generator is adjusted after the square wave signal passes through a loop filter, the clock frequency is changed until the optimal sampling moment is obtained, meanwhile, a locking judgment device can give out a locking instruction, and the working state of a symbol synchronization module is clearly reflected.
The CCSDS-211 protocol adopts an additional synchronous marker bit (ASM) as a frame header of a transmission frame, and the invention adopts a frame synchronization module to accurately locate the ASM position in data information, thereby ensuring the reliability of subsequent signal processing.
The invention has a phase compensation and judgment module, effectively eliminates the 90-degree phase error caused by the polarity inversion of the OQPSK signal in the transmission process, compensates the estimation of the phase error, and then judges to obtain the user bit information, thereby effectively reducing the system error rate and ensuring the effectiveness and the reliability of the system.
And the signal after the phase compensation and the judgment is subjected to serial-parallel conversion and then user information is output.
The invention comprises a signal-to-noise ratio estimation module, which is used for estimating the signal-to-noise ratio of the received signal and judging the current communication quality of the channel. The invention adopts a signal-to-noise ratio estimation algorithm combining DF-3 estimation and SNV estimation, combines the DF-3 estimation algorithm and the SNV estimation algorithm by using the advantages of the DF-3 estimation performance under the condition of 0-10 dB and the advantages of the SNV estimation performance above 10dB, and obtains the signal-to-noise ratio combined estimation algorithm with lower hardware complexity and smaller signal-to-noise ratio estimation error. As shown in fig. 6, the algorithm first inputs the snr estimation value at the previous time as snr feedback information into an snr estimation algorithm selection module, and selects a subsequent corresponding snr estimation algorithm by comparing the snr feedback information with a threshold set in the module, and when the snr changes and exceeds the threshold, the snr estimation algorithm will be switched at the next time, so that the input signal can be estimated by selecting the snr estimation algorithm with a smaller error under different snrs. For example: and taking 10dB as a threshold, selecting SNV estimation when the threshold is higher than 10dB, selecting DF-3 estimation when the threshold is 0-10 dB, determining a signal-to-noise ratio estimation method at the next moment by using a signal-to-noise ratio at the previous moment, and calculating the current signal-to-noise ratio by using a selected signal-to-noise ratio estimation algorithm.
The invention designs a transmitter rate control module and a receiver rate control module, and adaptively adjusts the code element rate through the bit error rate requirement of an upper computer and the output signal-to-noise ratio of a signal-to-noise ratio estimation module. The required signal-to-noise ratio is calculated according to the bit error rate requirement sent by the upper computer, and then compared with the output signal-to-noise ratio of the signal-to-noise ratio estimation module, the signal rate is adjusted step by utilizing the characteristics that the OQPSK signal reduces the signal-to-noise ratio at the half symbol rate by 3dB and improves the signal-to-noise ratio at the half symbol rate by 3dB until the signal-to-noise ratio reaches the required signal-to-noise ratio. The invention has a requirement of 10 on the error rate-7The initial signal-to-noise ratio is 28dB, and the initial data rate is 64kbps, so that the self-adaptive variable rate system is verified to be capable of adaptively adjusting the data rate through the error rate requirement of the upper computer and the signal-to-noise ratio of the current channel, the throughput is improved as much as possible on the premise that the error rate requirement is met by the transceiver, and the effectiveness and the reliability of the communication system are guaranteed.
The technical effects of the present invention are further verified by specific experimental data.
The bit error rate curve characteristics of OQPSK in Gaussian channel are shown in FIG. 7, so in this experiment, according to the bit error rate requirement 10-7And calculating to obtain the signal-to-noise ratio which meets the requirement of the current bit error rate and is 14.5dB, increasing 1dB fault tolerance and setting the threshold value of the signal-to-noise ratio to be 15.5 dB.
FIG. 8 is a bit error rate requirement 10-7Initial signal-to-noise ratio of 28dB, initial data rate of 512kbps adaptive variable rate simulation plot. When the current signal-to-noise ratio is higher than the threshold value by 3dB, the symbol rate is doubled, and the system throughput is improved; when the current signal-to-noise ratio is lower than a threshold value, reducing a half symbol rate to meet the signal-to-noise ratio requirement of a system; when the current signal-to-noise ratio is higher than the threshold value within 3dB, the symbol rate is kept unchanged, and the system achieves the optimal performance. As can be seen from the simulation diagram, the initial signal-to-noise ratio is high, the current channel environment is good, the initial rate of 64kbps is increased to 1024kbps by increasing the symbol rate step by step, the system throughput is greatly improved, meanwhile, the signal-to-noise ratio still meets the requirement of the system error rate, and the designed system has excellent performance.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.
Claims (6)
1. An OQPSK adaptive variable-rate digital transceiver based on a neighbor space link protocol, which is characterized by comprising a transmitter and a receiver; wherein the content of the first and second substances,
the transmitter comprises an OQPSK modulation module and a transmitter speed control module;
the receiver comprises an OQPSK demodulation module, a signal-to-noise ratio estimation module and a receiver rate control module;
the receiver receives the signal sent by the transmitter, the signal is demodulated by the OQPSK demodulation module and then sent to the signal-to-noise ratio estimation module, the signal-to-noise ratio estimation module carries out signal-to-noise ratio estimation on the received signal and sends the estimated value to the receiver rate control module; the receiver rate control module receives the bit error rate requirement sent by the upper computer, calculates the required signal-to-noise ratio, compares the required signal-to-noise ratio with the estimated signal-to-noise ratio of the signal-to-noise ratio estimation module, utilizes the characteristics that the OQPSK signal reduces half of the symbol rate and the signal-to-noise ratio is improved by 3dB and the OQPSK signal improves one time of the symbol rate and the signal-to-noise ratio is reduced by 3dB, changes the code element rate by adjusting the clock module and the interpolation extraction multiple, and gradually adjusts the signal rate until the signal-to-noise ratio reaches the required signal-to-noise ratio requirement, and then feeds back;
the transmitter rate control module receives signal rate feedback information sent by the receiver, adjusts a clock module, an interpolation multiple and an extraction multiple of the transmitter according to the receiver rate feedback information, and changes the transmitting rate of the transmitter to a required transmitting rate; meanwhile, the new rate information of the transmitter and the related parameter information of the transmitter are written into the SPDU and are transmitted to the receiver along with the adjacent link transmission unit.
2. The OQPSK adaptive variable-rate digital transceiver based on the adjacent space link protocol according to claim 1, wherein the OQPSK demodulation module of the receiver comprises a digital down-conversion module, a gain detection module, an automatic gain control module, a carrier synchronization module, a symbol synchronization module, a frame synchronization module, a phase compensation and decision module and a serial-to-parallel conversion module which are sequentially cascaded; wherein the content of the first and second substances,
the digital down-conversion module converts the signals received by the receiver into low-intermediate frequency signals required by the receiver;
the gain detection module carries out energy detection on the received signal, and when the energy of the received signal is higher than a preset energy detection threshold value, the received signal is judged to belong to useful user information, and at the moment, the receiver is started; when the energy of the received signal is lower than a preset energy detection threshold value, judging that the received signal belongs to invalid noise, and closing the receiver at the moment;
the automatic gain control module performs self-adaptive adjustment on a gain coefficient when a receiver receives signals and generates large amplitude oscillation due to channel fading and cosmic noise, so that signal saturation or loss is prevented, and the received signals meet the requirement of later-stage synchronous demodulation;
the carrier synchronization module dynamically adjusts the frequency of a local carrier of the receiver by carrying out closed-loop detection on the received signal to enable the frequency to be equal to the carrier frequency of the transmitter, so that a subsequent module of the receiver can carry out coherent demodulation;
the symbol synchronization module and the frame synchronization module respectively perform symbol synchronization and frame synchronization processing on the received signals;
the phase compensation and judgment module compensates the estimation of the phase deviation and then judges to obtain user bit information;
and the serial-parallel conversion module carries out serial-parallel conversion on the signal output by the phase compensation and judgment module and then outputs user information.
3. The OQPSK adaptive variable rate digital transceiver based on the adjacent space link protocol according to claim 2, wherein the automatic gain control module comprises a controllable gain amplifier, a detector module, a gain coefficient control module, a comparator, an error processing module;
the input signal enters a detector after being subjected to A/D conversion and a controllable gain amplifier, the detector detects the signal energy and sends the detection result to a comparator and a gain coefficient control module respectively;
the comparator compares the received detection value with a reference value to obtain an error with the reference value, and then sends the error value to the error processing module;
the gain coefficient control module adjusts the gain coefficient in the error processing module according to the detection value; the formula is Gain (n +1) ═ Gain (n) + aVeWherein Gain (n +1) is the adjusted Gain coefficient, Gain (n) is the current Gain coefficient, a is the weighting factor, VeIs an error from a standard value;
the error processing module adjusts the gain coefficient of the controllable gain amplifier according to the received error value and the gain coefficient adjustment result: when the error value is lower than the threshold value, the gain coefficient of the controllable gain amplifier is kept unchanged, and when the error value exceeds the threshold value, the gain coefficient is changed according to the feedback information of the error processing module, the current weighting factor and the error signal to obtain a new amplification coefficient of the controllable gain amplifier.
4. The OQPSK adaptive variable rate digital transceiver based on the adjacent space link protocol according to claim 2, wherein the carrier synchronization module is implemented by a modified Costas loop, and the modified Costas loop comprises a local NCO, a matched filter, a digital phase detector and a loop filter; signals of an I path and a Q path received by the receiver enter the digital phase discriminator after passing through the matched filter, and the obtained output signal of the phase discriminator adjusts the local NCO of the receiver after passing through the loop filter until the loop is stable after the carrier frequency of the local NCO of the receiver is consistent with that of the received signal.
5. The OQPSK adaptive variable rate digital transceiver according to claim 2, wherein the symbol synchronization module employs an early-late loop algorithm for symbol synchronization design, and comprises: the system comprises an early gate integrator, a late gate integrator, a data error discriminator, a loop filter, a locking decision device and a clock generator; the I path signal and the Q path signal are normalized, the processed square wave signals respectively enter an early gate integrator and a late gate integrator, the early gate integration result and the late gate integration result of the I path signal and the early gate integration result and the late gate integration result of the Q path signal are sent to a data error discriminator to be judged, when a clock error exists, the data error discriminator can quickly accumulate errors and give error data, the clock generator is adjusted after the error data pass through a loop filter, the clock frequencies of the early gate clock, the late gate clock and a sampling clock are changed until the optimal sampling time is obtained, meanwhile, a locking judgment device can give a locking indication to clearly reflect the working state of a symbol synchronization module.
6. The OQPSK adaptive variable rate digital transceiver based on the adjacent space link protocol according to claim 2, wherein the SNR estimation module comprises an SNR estimation algorithm selection module, a DF-3 estimation algorithm module, an SNV estimation algorithm module and an SNR output module, the DF-3 estimation algorithm module adopts DF-3 estimation algorithm to calculate the SNR estimation value from the input signal, and the SNV estimation algorithm module adopts SNV estimation algorithm to calculate the SNR estimation value from the input signal; the signal-to-noise ratio output module takes the signal-to-noise ratio estimation value at the last moment as signal-to-noise ratio feedback information to be input into the signal-to-noise ratio estimation algorithm selection module, and the signal-to-noise ratio estimation module carries out signal-to-noise ratio estimation algorithm selection by comparing the signal-to-noise ratio feedback information with a threshold value set in the module: when the feedback signal-to-noise ratio information exceeds the threshold value, the signal-to-noise ratio estimation algorithm is switched at the next moment.
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