CN110943752A - An OQPSK Adaptive Variable Rate Digital Transceiver Based on Proximity Space Link Protocol - Google Patents

Abstract

The invention discloses an OQPSK system adaptive variable rate digital transceiver based on the adjacent space link protocol. The transmitter includes an OQPSK modulation module and a transmitter rate control module, and the receiver includes 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, through The transmitter rate control module controls the clock module, the interpolation multiple, and the decimation multiple to adjust the transmission signal rate. The receiver estimates the signal-to-noise ratio of the received signal through the signal-to-noise ratio estimation module, and the receiver rate control module controls the receiver's clock module, interpolation multiple, and extraction multiple according to the estimated signal-to-noise ratio, and provides the transmitter with the rate. Feedback information, synchronously perform adaptive rate switching. This digital transceiver can effectively face the harsh environment of deep space communication channels.

Description

An OQPSK adaptive variable rate digital receiver based on adjacent space link protocol engine

Technical field:

The invention relates to the design of an adaptive digital transceiver for adjacent 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 the adjacent space link protocol.

Background technique:

More than space agencies such as NASA and the European Space Agency (ESA) established the Consultative Committee for Space Data Systems (CCSDS) in the 1980s. The utilization rate of space channel resources, in order to realize the close cooperation of the international deep space exploration side, proposed the CCSDS standard protocol, that is, the adjacent space link protocol. According to the CCSDS Proximity-1 protocol standard, the communication between the spacecraft and the spacecraft, the spacecraft and the ground, and the spacecraft and the lander is standardized. Switching of 12 transmission rates in the range of 2048kbps and meeting the link margin should provide a bit error rate of less than 10 ^-6 for the asynchronous link.

Compared with the traditional communication on the ground, the deterioration degree of the deep space channel is much more severe. Figure 2 shows the deep space channel attenuation model. The transmitted signal is often not only affected by small-scale fading such as Doppler frequency shift and multipath delay. In addition, it will be affected by large-scale fading such as path loss, cosmic noise, planetary noise, and solar scintillation, resulting in a sharp change in channel capacity. Therefore, fixed transmission rate communication cannot meet the needs of deep space channels.

Invention content:

Purpose of the invention: In order to solve the influence of the bad channel conditions of deep space communication on the validity and reliability of signal transmission, the present invention combines the adjacent space link protocol, and proposes an OQPSK adaptive variable rate digital transceiver based on the adjacent space link protocol. The adaptive rate control module of the transceiver is controlled by the output information of the signal-to-noise ratio estimation module to obtain the required symbol rate under the current bit error rate requirement, and then the adaptive control module controls the transceiver clock module to change the interpolation and extraction multiples, and at the same time Control the bandwidth of the transceiver filter to ensure that the signal throughput can be improved as much as possible on the premise of satisfying the bit error rate, and meet the needs of the deep space communication transceiver to reduce the impact of channel changes on the transceiver through adaptive variable rate technology. , to improve the real-time and effectiveness of signal transmission.

SUMMARY OF THE INVENTION: In order to achieve the above technical effects, the present invention proposes an OQPSK adaptive variable rate digital transceiver based on the adjacent space link protocol, including a transmitter and a receiver; wherein,

The transmitter includes an OQPSK modulation module and a transmitter rate control module;

The receiver includes 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, demodulates it through the OQPSK demodulation module, and then sends it to the SNR estimation module. The SNR estimation module estimates the SNR of the received signal, and sends the estimated value to the receiver. Control module; the receiver rate control module receives the bit error rate request sent by the host computer, calculates the required SNR, and then compares it with the estimated SNR from the SNR estimation module, and uses the OQPSK signal to reduce the symbol by half The rate signal-to-noise ratio is increased by 3dB and the OQPSK signal is doubled. The symbol rate is reduced by 3dB. The symbol rate is changed by adjusting the clock module and the interpolation and extraction multiples, so that the signal rate is adjusted step by step until the signal-to-noise ratio is adjusted. ratio to meet the required signal-to-noise ratio requirements, and then feedback the adjusted signal rate to meet the required signal-to-noise ratio requirements to the transmitter rate control module;

The transmitter rate control module receives the signal rate feedback information sent by the receiver, adjusts the transmitter's clock module, interpolation multiple and decimation multiple according to the receiver rate feedback information, and changes the transmitter's transmission rate to the desired transmission rate; at the same time, Write the transmitter's new rate information and transmitter-related parameter information into the SPDU, and send it to the receiver along with the adjacent link transmission unit.

Further, 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 judgment module, and a serial and transform the module; where,

The digital down-conversion module converts the signal received by the receiver into the required low-IF signal;

The gain detection module performs energy detection on the received signal. When the energy of the received signal is higher than the preset energy detection threshold, it is judged that the received signal belongs to useful user information, and the receiver is turned on at this time; when the energy of the received signal is lower than the preset energy detection threshold When the energy detection threshold value is higher than the energy detection threshold, it is judged that the received signal is invalid noise, and the receiver is turned off at this time;

The automatic gain control module adjusts the gain coefficient adaptively when the received signal of the receiver oscillates with a relatively large amplitude due to channel fading and cosmic noise, to prevent signal saturation or loss, and to make the received signal meet the requirements of post-stage synchronous demodulation;

The carrier synchronization module dynamically adjusts the frequency of the local carrier of the receiver to make it equal to the carrier frequency of the transmitter through closed-loop detection of the received signal, so that the subsequent modules of the receiver can perform coherent demodulation;

The symbol synchronization module and the frame synchronization module respectively perform symbol synchronization and frame synchronization processing on the received signal;

The phase compensation and judgment module compensates by estimating the phase deviation, and then judges to obtain user bit information;

The serial-to-parallel conversion module performs serial-to-parallel conversion on the signal output by the phase compensation and decision module, and then outputs the user information.

Further, the automatic gain control module 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 A/D conversion and controllable gain amplifier, the detector detects the signal energy, and sends the detection results to the comparator and the gain coefficient control module respectively;

The comparator compares the received detection value with the reference value, and sends the error value to the error processing module after obtaining the error with the reference value;

The gain coefficient control module adjusts the gain coefficient in the error processing module according to the detected value; the adjustment formula is Gain(n+1)=Gain(n)+aV _e , where Gain(n+1) is the adjusted gain coefficient, Gain(n) is the current gain coefficient, a is the weighting factor, and V _e is the error from the 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 remains unchanged, and when the error value exceeds the threshold value When , the gain coefficient is changed according to the feedback information of the error processing module to obtain a new controllable gain amplifier amplification coefficient.

Further, the carrier synchronization module is implemented by using a modified Costas loop, and the modified Costas loop includes a local NCO, a matched filter, a digital phase detector, and a loop filter; After the matched filter enters the digital phase detector, the obtained output signal of the phase detector adjusts the local NCO of the receiver after passing through the loop filter, until the local NCO of the receiver is consistent with the carrier frequency of the received signal, the loop reaches Stablize.

Further, the symbol synchronization module adopts an early and early loop algorithm to carry out symbol synchronization design, including: an early gate integrator, a late gate integrator, a data error discriminator, a loop filter, a lock decision device and a clock generator; , Q channel signals are normalized, the square wave signal obtained after processing enters the early gate integrator and the late gate integrator respectively, the early and late gate integration results of the I channel signal and the early and late gate integration results of the Q channel signal are sent to When there is a clock error, the data error discriminator will quickly accumulate the error and give the error data. After the error data passes through the loop filter, the clock generator is adjusted to change the early gate clock, late gate clock and late gate clock. The clock frequency of the gate clock and the sampling clock is determined until the optimal sampling time is obtained. At the same time, the lock decision device will give a lock indication to clearly reflect the working status of the symbol synchronization module.

Further, the signal-to-noise ratio estimation module includes 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, and the DF-3 estimation algorithm module adopts DF-3 estimation. The algorithm calculates the SNR estimate from the input signal, and the SNV estimation algorithm module uses the SNV estimation algorithm to calculate the SNR estimate from the input signal; the SNR output module feeds back the SNR estimate at the previous moment as the SNR The information is input to the signal-to-noise ratio estimation algorithm selection module, and the signal-to-noise ratio estimation module selects the subsequent estimation module by comparing the signal-to-noise ratio feedback information with the threshold value set in the module: when the signal-to-noise ratio changes beyond the threshold value , the SNR estimation algorithm will switch at the next moment.

Beneficial effects: the present invention has the following advantages:

1. According to the requirements of the adjacent space link protocol, the digital transceiver supports the switching of 12 transmission rates in the range of 1kbps, 2kpbs, 4kbps, 8kbps ~ 1024kbps, and 2048kbps.

2. Compared with the QPSK modulation system, the system adopts the OQPSK modulation method, which avoids the 180° phase inversion, improves the phase compensation and decision performance, and reduces the bit error caused by the phase deviation.

3. The receiver gain detection module is set by the host computer to set the working state and adjust the detection threshold to meet the work requirements in different environments.

4. The automatic gain control module adopts variable gain coefficient to reduce the stabilization time of the feedback loop and effectively solve the problem of large signal fading.

5. The signal-to-noise ratio estimation module adopts the joint estimation method of DF-3 estimation and SNV estimation, and combines the advantages of the two estimation algorithms to achieve the effect of low hardware complexity and small signal-to-noise ratio estimation error, effectively solving deep space communication. The problem of large time-varying channel.

6. Adopting the adaptive variable rate design, the bit error rate requirements can be set according to the host computer, and the adaptive variable rate can be adjusted according to the current channel quality and current data rate, and the transceiver can be changed by adjusting the clock module and the interpolation and extraction multiples. It can improve the information throughput under the premise of meeting the requirements of signal-to-noise ratio, and meet the requirements of deep space communication in different backgrounds.

Description of drawings:

Fig. 1 is the structure diagram of the digital transceiver according to the embodiment;

Figure 2 is a deep space channel attenuation model;

Figure 3 is the automatic gain module design;

Figure 4 is a modified Costas ring symbol synchronization design;

Fig. 5 is the early and late ring symbol synchronization design;

Figure 6 shows the design of the joint estimation algorithm of DF-3 and SNV signal-to-noise ratio;

Fig. 7 is the OQPSK signal bit error rate curve;

Fig. 8 is a simulation diagram of a bit error rate requirement of 10 ^-7 , an initial signal-to-noise ratio of 28dB, and an initial data rate of 512kbps adaptive variable rate.

Detailed ways

The present invention aims to propose a digital transceiver that can solve the effect of bad channel conditions of deep space communication on the validity and reliability of signal transmission. Digital transceivers can effectively meet the transmission requirements of deep space channels. On the premise of meeting the requirements of the bit error rate, the transmission rate should be increased as much as possible. In the face of transmission requirements with a lower bit error rate, it is also easy to transmit and receive. machine parameters to adjust.

The deep space channel is affected by many factors, and the signal fading varies greatly. The main fading factors include small-scale fading including Doppler frequency shift and multipath loss and large-scale fading including path loss, solar scintillation, and cosmic noise. Fading, the channel capacity changes greatly. Therefore, the traditional fixed rate communication cannot meet the requirements of deep space channels. The adaptive transceiver designed in this paper can perform rate switching according to the channel conditions in real time to meet the communication requirements.

The CCSDS Proximity-1 protocol specifies the bit error rate of the deep space communication transceiver, and the bit error rate of the OQSPK modulation and demodulation system will decrease with the increase of the signal-to-noise ratio, so in the deep space communication link, It is necessary to effectively control the signal-to-noise ratio by changing the signal symbol rate, so as to meet the transmission requirements of the protocol transceiver. When the symbol rate decreases, the signal bandwidth will also be narrowed accordingly, the filter bandwidth required by the transceiver will also decrease, and the in-band noise received by the filter will also decrease. Under the power, the signal power remains unchanged, the noise power decreases, and the signal-to-noise ratio increases accordingly. Conversely, when the channel conditions are good, the signal throughput can be improved by increasing the symbol rate.

The variable rate method can be realized by changing the symbol rate, the modulation method, and the coding method. According to the relevant requirements of the protocol, the adaptive variable rate design can be realized by changing the symbol rate to meet the requirements of the protocol for 12 different rate signals. Require. However, the variable rate design is carried out by changing the symbol rate. Since the modulation method is not changed, and the modulation and demodulation module of the adaptive digital transceiver is relatively fixed, only the adaptive control module is required to control the clock module of the transceiver, and the interpolation and extraction The coefficients are sufficient to meet the modulation and demodulation requirements of the transceiver at different rates.

Based on the above analysis, the present invention proposes an OQPSK adaptive variable rate digital transceiver based on the adjacent space link protocol, including a transmitter and a receiver; wherein,

The transmitter includes an OQPSK modulation module and a transmitter rate control module;

The receiver includes 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, demodulates it through the OQPSK demodulation module, and then sends it to the SNR estimation module. The SNR estimation module estimates the SNR of the received signal, and sends the estimated value to the receiver. Control module; the receiver rate control module receives the bit error rate request sent by the host computer, calculates the required SNR, and then compares it with the estimated SNR from the SNR estimation module, and uses the OQPSK signal to reduce the symbol by half The rate signal-to-noise ratio is increased by 3dB and the OQPSK signal is doubled. The symbol rate is reduced by 3dB. The symbol rate is changed by adjusting the clock module and the interpolation and extraction multiples, so that the signal rate is adjusted step by step until the signal-to-noise ratio is adjusted. ratio to meet the required signal-to-noise ratio requirements, and then feedback the adjusted signal rate to meet the required signal-to-noise ratio requirements to the transmitter rate control module;

The transmitter rate control module receives the signal rate feedback information sent by the receiver, adjusts the transmitter's clock module, interpolation multiple and decimation multiple according to the receiver rate feedback information, and changes the transmitter's transmission rate to the desired transmission rate; at the same time, Write the transmitter's new rate information and transmitter-related parameter information into the SPDU, and send it to the receiver along with the adjacent link transmission unit.

The above transceiver adopts OQPSK modulation and demodulation method. Due to the delay of Ts/2 in the I channel and Q channel signals, the polarity of the two channels will not be reversed at the same time. Compared with the traditional QPSK signal, there will be no 180° deviation. The phase error is helpful for receiver phase compensation and judgment. At the same time, the envelope fluctuation of OQPSK modulation is small after passing through the band-pass filter, the performance is relatively stable, and the frequency band is wide, which is beneficial to the switching before different code rates.

The technical solutions of the present invention are further described below with reference to the accompanying drawings through specific embodiments.

Figure 1 shows an implementation of the transceiver according to the present invention:

Including deep space communication OQPSK adaptive variable rate transmitter and deep space communication OQPSK adaptive receiver;

The transmitter adopts OQPSK modulation technology, adding a half-symbol period delay to the Q channel signal, so that the I channel and Q channel signals will not have polarity inversion at the same time, resulting in a 180° phase inversion, and the transmitted signal is first serial-parallel conversion to get The I channel and Q channel signals are then multiplied by the local transmitter NCO through modulation modules such as zero insertion, shaping filtering, and low-pass filtering to obtain the modulated OQPSK signal. The signal enters the deep space channel after digital up-conversion. . The transmitter has a transmitter rate control module, which can receive the rate feedback information sent by the receiver. The transmission rate of the transmitter is changed through the rate feedback information of the receiver, and at the same time, the new rate information of the transmitter and the relevant parameter information of the transmitter are written into the SPDU, and sent to the receiver along with the adjacent link transmission unit. The transmitter rate control module can control the clock module, interpolation multiple and decimation multiple of the transmitter, control the clock rate of each module of the entire transmitter, and control the sampling rate of the transmitter by adjusting the parameters of the interpolation multiple and decimation multiple. The transmitter complies with the CCSDS-211 protocol standard, and supports the switching of 12 transmission rates in the range of 1kbps, 2kpbs, 4kbps, 8kbps ~ 1024kbps, and 2048kbps.

The receiver is divided into the following modules: digital down-conversion module, gain detection module, automatic gain control module, carrier synchronization module, symbol synchronization module, frame synchronization module, phase compensation and decision module, serial-parallel conversion module, signal-to-noise ratio estimation module, receiver rate control module.

The digital down-conversion module converts the signal received by the receiver into the low-IF signal we need.

The gain detection module performs energy detection on the received signal. When the energy of the received signal is higher than the preset energy detection threshold, it is judged that the received signal belongs to useful user information, and the receiver is turned on at this time; when the energy of the received signal is lower than the preset energy detection threshold When it reaches the energy detection threshold value, it is judged that the received signal is invalid noise, and the receiver is turned off at this time. The detection threshold value can be changed through the upper layer parameters, so that the receiver can switch between the low power consumption working mode and the normal working mode to meet the requirements of the receiver in different situations.

The automatic gain control module can effectively control the gain of the receiver. When the received signal of the receiver oscillates with a large amplitude due to channel fading and cosmic noise, the automatic gain control module will adaptively adjust the gain coefficient to prevent signal saturation or loss. Make the received signal meet the requirements of post-stage synchronous demodulation.

As shown in FIG. 3 , the automatic gain control module of this embodiment 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 A/D conversion and controllable gain amplifier, the detector will detect the signal energy, part of the output signal is compared with the reference value through the comparator, and the error with the reference value is obtained, when the error is small , the gain coefficient of the controllable gain amplifier remains unchanged, and when the error exceeds the threshold, the gain coefficient will be changed according to the feedback information of the error processing module. At the same time, the other part of the output signal of the detector enters the gain coefficient control module, controls the gain coefficient in the error processing module, adaptively changes the gain coefficient of the error processing module, and the gain coefficient control module adjusts the gain coefficient in the error processing module according to the detected value. When adjusting, the adjustment formula is Gain(n+1)=Gain(n)+aV _e , where Gain(n+1) is the adjusted gain coefficient, Gain(n) is the current gain coefficient, and a is the weighted factor, and _Ve is the error from the standard value. Based on the above design, the entire loop can be restored to a stable state in a relatively short period of time in the face of relatively large oscillations of the input data. The error processing module receives the data of the gain control module and the comparator module and performs operations to obtain a new controllable gain amplifier amplification factor.

The carrier synchronization module is implemented by a digital phase-locked loop. Through closed-loop detection of the received signal, the frequency of the local carrier of the receiver is dynamically adjusted to make it equal to the carrier frequency of the transmitter, so that the subsequent modules of the receiver can perform coherent demodulation.

In this embodiment, the carrier synchronization module is implemented by the modified Costas loop. Compared with the ordinary Costas loop and the digital Costas loop, the modified Costas loop has stronger anti-noise performance and shorter loop stabilization time. The modified Costas loop is shown in Figure 4. It consists of a local NCO, a matched filter, a digital phase detector, and a loop filter. The I and Q signals received by the receiver enter the digital phase detector after passing through the matched filter. The obtained output signal of the phase detector adjusts the local NCO of the receiver after passing through the loop filter, until the local NCO of the receiver is consistent with the carrier frequency of the received signal, the loop becomes stable.

In order to obtain the best sampling point, the present invention adopts the sooner or later loop algorithm to design the symbol synchronization, and can realize the high-precision symbol synchronization by adjusting the sampling rate. The symbol synchronization structure of the sooner or later loop is shown in Figure 5, which mainly includes an early gate integrator circuit, a late gate integrator circuit, a data error discriminator, a loop filter, a lock decision device and a clock generator. The I channel and Q channel signals are normalized, and the square wave signal obtained after processing enters the early gate integrator circuit and the late gate integrator circuit, and is judged by the data error discriminator. When there is a clock error, the algorithm will quickly accumulate Error, the data error discriminator will give error data, adjust the clock generator after passing through the loop filter, change the clock frequency until the best sampling time is obtained, at the same time, the lock judger will give a lock indication, clear Indicates the working status of the symbol synchronization module.

The CCSDS-211 protocol adopts the additional synchronization flag (ASM) as the frame header of the transmission frame, and the present invention adopts the frame synchronization module to accurately locate the ASM position in the data information to ensure the reliability of subsequent signal processing.

The present invention has a phase compensation and judgment module, which effectively eliminates the 90° phase error caused by the polarity inversion of the OQPSK signal during the transmission process, compensates for the phase deviation estimation, and then judges to obtain user bit information, effectively Therefore, the bit error rate of the system is greatly reduced, and the effectiveness and reliability of the system are guaranteed.

The signal after phase compensation and judgment is serial-parallel converted and then output user information.

The present invention includes a signal-to-noise ratio estimation module, which estimates the signal-to-noise ratio of the received signal and judges the current communication quality of the channel. The present invention adopts the signal-to-noise ratio estimation algorithm combining DF-3 estimation and SNV estimation, utilizes the superior performance of DF-3 estimation under the condition of 0-10 dB and the superior SNV estimation performance under the condition of 10 dB or more, and combines the DF-3 estimation algorithm with SNV estimation Combining the algorithms, a SNR joint estimation algorithm with lower hardware complexity and smaller SNR estimation error is obtained. As shown in Figure 6, the algorithm first takes the estimated value of the signal-to-noise ratio at the previous moment as the feedback information of the signal-to-noise ratio into the signal-to-noise ratio estimation algorithm selection module, and compares the feedback information of the signal-to-noise ratio with the threshold value set in the module. Select the corresponding signal-to-noise ratio estimation algorithm in the later stage. When the signal-to-noise ratio changes beyond the threshold value, the signal-to-noise ratio estimation algorithm will be switched at the next moment, so that the input signal can choose the error comparison under different signal-to-noise ratio conditions. A small signal-to-noise ratio estimation algorithm is used for estimation. For example: take 10dB as the threshold, use SNV estimation when it is higher than 10dB, DF-3 estimation is used for 0~10dB, the SNR at the previous moment determines the SNR estimation method at the next moment, and the current SNR is determined by the selected SNR Calculated by the estimation algorithm.

The invention designs a transmitter rate control module and a receiver rate control module, and adjusts the symbol rate adaptively according to the bit error rate requirement of the upper computer and the output signal-to-noise ratio of the signal-to-noise ratio estimation module. Calculate the required signal-to-noise ratio through the bit error rate request sent by the host computer, and then compare it with the output signal-to-noise ratio of the signal-to-noise ratio estimation module, and use the OQPSK signal to reduce the symbol rate by half and increase the signal-to-noise ratio by 3dB and double. The signal-to-noise ratio of the symbol rate is reduced by 3dB, and the signal rate is adjusted step by step until the signal-to-noise ratio reaches the required signal-to-noise ratio requirement. The present invention simulates the bit error rate requirement of 10 ^-7 , the initial signal-to-noise ratio of 28dB, and the initial data rate of 64kbps, and verifies that the self-adaptive variable rate system can be adapted by the bit error rate requirement of the upper computer and the signal-to-noise ratio of the current channel. The data rate is adjusted so that the transceiver can improve the throughput as much as possible on the premise of meeting the bit error rate requirements, which ensures the effectiveness and reliability of the communication system.

The technical effect of the present invention is further verified below through specific experimental data.

The bit error rate curve characteristics of OQPSK under the Gaussian channel are shown in Figure 7. Therefore, in this experiment, according to the bit error rate requirement of 10 ^-7 , the SNR that meets the current bit error rate requirement is calculated to be 14.5dB. 1dB fault tolerance, set the signal-to-noise ratio threshold to 15.5dB.

Fig. 8 is a simulation diagram of a bit error rate requirement of 10 ^-7 , an initial signal-to-noise ratio of 28dB, and an initial data rate of 512kbps adaptive variable rate. When the current SNR is higher than the threshold by 3dB, the symbol rate is doubled to improve the system throughput; when the current SNR is lower than the threshold, the symbol rate is reduced by half to meet the system SNR requirements; the current SNR When the ratio is higher than the threshold value within 3dB, the symbol rate remains unchanged, and the system achieves the optimal performance. It can be seen from the simulation diagram that the initial signal-to-noise ratio is high, and the current channel environment is good. By increasing the symbol rate step by step, the initial rate of 64kbps is increased to 1024kbps, which greatly improves the system throughput. At the same time, the signal-to-noise ratio is still satisfactory. System bit error rate requirements, the designed system has superior performance.

The above is only the preferred embodiment of the present invention, it should be pointed out that: for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications are also It should be regarded as the protection scope of the present invention.

Claims (6)

1. an OQPSK adaptive variable rate digital transceiver based on adjacent space link protocol, is characterized in that, comprises transmitter and receiver; Wherein, The transmitter includes an OQPSK modulation module and a transmitter rate control module; The receiver includes 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, demodulates it through the OQPSK demodulation module, and then sends it to the SNR estimation module. The SNR estimation module estimates the SNR of the received signal, and sends the estimated value to the receiver. Control module; the receiver rate control module receives the bit error rate request sent by the host computer, calculates the required SNR, and then compares it with the estimated SNR from the SNR estimation module, and uses the OQPSK signal to reduce the symbol by half The rate signal-to-noise ratio is increased by 3dB and the OQPSK signal is doubled. The symbol rate is reduced by 3dB. The symbol rate is changed by adjusting the clock module and the interpolation and extraction multiples, so that the signal rate is adjusted step by step until the signal-to-noise ratio is adjusted. ratio to meet the required signal-to-noise ratio requirements, and then feedback the adjusted signal rate to meet the required signal-to-noise ratio requirements to the transmitter rate control module; The transmitter rate control module receives the signal rate feedback information sent by the receiver, adjusts the transmitter's clock module, interpolation multiple and decimation multiple according to the receiver rate feedback information, and changes the transmitter's transmission rate to the desired transmission rate; at the same time, Write the transmitter's new rate information and transmitter-related parameter information into the SPDU, and send it to the receiver along with the adjacent link transmission unit. 2. a kind of OQPSK adaptive variable rate digital transceiver based on adjacent space link protocol protocol according to claim 1, is characterized in that, the OQPSK demodulation module of described receiver comprises the digital down-conversion module that cascades successively , 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, and a serial-to-parallel conversion module; wherein, The digital down-conversion module converts the signal received by the receiver into the required low-IF signal; The gain detection module performs energy detection on the received signal. When the energy of the received signal is higher than the preset energy detection threshold, it is judged that the received signal belongs to useful user information, and the receiver is turned on at this time; when the energy of the received signal is lower than the preset energy detection threshold When the energy detection threshold value is higher than the energy detection threshold, it is judged that the received signal is invalid noise, and the receiver is turned off at this time; The automatic gain control module adjusts the gain coefficient adaptively when the received signal of the receiver oscillates with a relatively large amplitude due to channel fading and cosmic noise, to prevent signal saturation or loss, and to make the received signal meet the requirements of post-stage synchronous demodulation; The carrier synchronization module dynamically adjusts the frequency of the local carrier of the receiver to make it equal to the carrier frequency of the transmitter through closed-loop detection of the received signal, so that the subsequent modules of the receiver can perform coherent demodulation; The symbol synchronization module and the frame synchronization module respectively perform symbol synchronization and frame synchronization processing on the received signal; The phase compensation and judgment module compensates by estimating the phase deviation, and then judges to obtain user bit information; The serial-to-parallel conversion module performs serial-to-parallel conversion on the signal output by the phase compensation and decision module, and then outputs the user information. 3. a kind of OQPSK adaptive variable rate digital transceiver based on adjacent space link protocol according to claim 2, is characterized in that, described automatic gain control module comprises controllable gain amplifier, detector module, gain coefficient control module, comparator, error processing module; The input signal enters the detector after A/D conversion and controllable gain amplifier, the detector detects the signal energy, and sends the detection results to the comparator and the gain coefficient control module respectively; The comparator compares the received detection value with the reference value, and sends the error value to the error processing module after obtaining the error with the reference value; The gain coefficient control module adjusts the gain coefficient in the error processing module according to the detected value; the adjustment formula is Gain(n+1)=Gain(n)+aV _e , where Gain(n+1) is the adjusted gain coefficient, Gain(n) is the current gain coefficient, a is the weighting factor, and V _e is the error from the 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 remains unchanged, and when the error value exceeds the threshold value When , the gain coefficient is changed according to the feedback information of the error processing module, the current weighting factor and the error signal, and a new controllable gain amplifier amplification coefficient is obtained. 4. a kind of OQPSK adaptive variable rate digital transceiver based on adjacent space link protocol according to claim 2, is characterized in that, described carrier synchronization module adopts modified Costas loop to realize, and described modified Costas loop comprises local NCO, matched filter, digital phase detector, and loop filter; the I-channel and Q-channel signals received by the receiver enter the digital phase detector after passing through the matched filter, and the obtained phase detector output signal passes through the loop. After the filter, the local NCO of the receiver is adjusted until the local NCO of the receiver is consistent with the carrier frequency of the received signal and the loop is stable. 5. a kind of OQPSK adaptive variable rate digital transceiver based on adjacent space link protocol according to claim 2, is characterized in that, described symbol synchronization module adopts sooner or later loop algorithm to carry out symbol synchronization design, comprising: early gate integral Integrator, late gate integrator, data error discriminator, loop filter, lock judging device and clock generator; normalize the I channel and Q channel signals, and the square wave signals obtained after processing enter the early gate integrator respectively With the late gate integrator, the early and late gate integration results of the I-channel signal and the early and late gate integration results of the Q-channel signal are sent to the data error discriminator for judgment. When there is a clock error, the data error discriminator will quickly accumulate errors. And give the error data. After the error data passes through the loop filter, the clock generator is adjusted, and the clock frequencies of the early gate clock, the late gate clock and the sampling clock are changed until the best sampling time is obtained. Give lock indication, clearly reflect the working status of the symbol synchronization module. 6. a kind of OQPSK adaptive variable rate digital transceiver based on adjacent space link protocol according to claim 2, is characterized in that, described signal-to-noise ratio estimation module comprises signal-to-noise ratio estimation algorithm selection module, DF-3 The estimation algorithm module, the SNV estimation algorithm module and the signal-to-noise ratio output module, the DF-3 estimation algorithm module adopts the DF-3 estimation algorithm to calculate the signal-to-noise ratio estimated value from the input signal, and the SNV estimation algorithm module adopts the SNV estimation algorithm from the input signal. Signal calculation to obtain the estimated value of SNR; the SNR output module takes the estimated value of SNR at the previous moment as the SNR feedback information and input it to the SNR estimation algorithm selection module, and the SNR estimation module feeds back the information by comparing the SNR Select the SNR estimation algorithm with the threshold value set in the module: when the feedback SNR information exceeds the threshold value, the SNR estimation algorithm will switch at the next moment.

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