CN113541711B - Multi-channel combined feedback signal acquisition system and method for predistortion processing - Google Patents
Multi-channel combined feedback signal acquisition system and method for predistortion processing Download PDFInfo
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Abstract
A multi-channel combined feedback signal acquisition system for predistortion processing, comprising: the invention adopts a plurality of receiving antennas to form a far-field antenna array, which can set receiving points on a plurality of beams according to requirements, perfect the collection of all beams, avoid the condition that the whole pre-correction processing can not work when a single receiving antenna has no feedback signal by adjusting and optimizing a weighting algorithm, and enhance the quality and reliability of signals sent to the pre-correction by acquiring coupling signals from the receiving antenna array, carrying out reverse rotation phase shift, amplitude weighting and final combination on the coupling signals, thereby obtaining better pre-correction effect.
Description
Technical Field
The invention relates to a technology in the field of wireless communication, in particular to a system and a method for extracting and combining feedback signals of a phased array antenna with multi-path amplification (MXN) for predistortion of the phased array antenna.
Background
Phased arrays can maximize the radiation formation of the antenna array in a particular direction by controlling the relative phase and amplitude of a plurality of different channels in the array antenna. Generally, M baseband or intermediate frequency signals are provided in an antenna array, after up-conversion, each path of signal is divided into N paths, and M × N paths of signals are respectively subjected to respective phase control, power amplification and filtering, and finally form M beam radiation through the antenna array. During power amplification, a signal may be distorted due to non-linearity of a power amplifier, so that quality of a transmitted signal is impaired, or power back-off is required to ensure signal quality, so that power amplifier efficiency is lost.
The existing pre-distortion processing of the power amplifier is to feed back the signal of the power amplifier to a signal processing unit, and to perform advanced distortion on the signal to be amplified by the power amplifier through a pre-distortion algorithm so as to correct the change brought by amplification.
For a phased array antenna, because of the existence of M multiplied by N amplifying channels, in the traditional technology, distortion caused by each amplifying channel is independently corrected, so that the whole equipment is very large and complex and is difficult to realize in a compact phased array antenna. In a further technical improvement, the feedback signals of multiple channels are often mixed together for predistortion. Although the complexity of hardware is reduced, the correction effect is often unsatisfactory depending on the quality of the combination method of the plurality of feedback signals. For example, two methods of acquiring a combined feedback signal are common: one is to collect the signals radiated by the phased antenna array by a non-contact method, which specifically comprises the following steps: the combined signal in the air is collected by a far-field antenna, but the defects and disadvantages of the technology are as follows: the strength and quality of the feedback signal collected by a single receiving antenna, no matter where the antenna is placed, may be affected by its position and status and may not fully and effectively reflect the coverage of all beams of the entire phased array. Another method is to couple and then combine each amplified signal in the phased array, but because the amplified signals are respectively subjected to phase rotation and gain adjustment due to the requirement of coverage, if the amplified signals are directly combined together for pre-correction, the correction effect is greatly influenced due to the overlapping of phases and the difference of amplitudes.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a multi-channel combined feedback signal acquisition system and method for predistortion processing.
The invention is realized by the following technical scheme:
the invention relates to a multi-channel combined feedback signal acquisition system for predistortion processing, which comprises: the base band signal processing unit, the digital signal processing unit, the phased antenna array that are located phased array equipment, are located the transmitting terminal and are located far-field receiving antenna array, the down-converting link of received signal and the signal switching unit of phased antenna array coverage, wherein: the digital signal processing unit simultaneously receives the baseband signals and the baseband digital signals from the signal switching unit, pre-corrects the baseband digital signals, outputs the pre-corrected baseband digital signals to the phased antenna array, and forms overlay broadcast by M multiplied by N transmitting antennas; each receiving antenna in the far-field receiving antenna array receives an air signal and then sends the air signal to a receiving signal down-conversion link in the phased antenna array equipment; the receiving signal down-conversion link outputs a baseband digital combined feedback signal to the signal switching unit, the signal switching unit outputs the baseband digital combined feedback signal or a coupling signal to the digital signal processor, and the digital signal processor finally realizes closed-loop pre-correction by taking the received signal as a reference signal.
The signal switching unit includes: three signal switches, wherein: the first signal switcher is connected with the receiving signal down-conversion link and receives the baseband digital combined feedback signal D 0 ～D m The first signal switcher selects at least one path from the baseband digital combined feedback signals to output to the third signal switcher under the control of the digital signal processor; the second signal switch receives the coupling signal P from the phased antenna array 0 ～P M×N The second signal switch selects at least one path from the coupling signals to output to a third signal switch under the control of the digital signal processor, and the third signal switch outputs at least one path of baseband digital combined feedback signals or coupling signals to the digital signal processor under the control of the digital signal processor.
The far-field receiving antenna array comprises: the m receiving antennas located in the coverage area of the phased antenna array are respectively distributed in the coverage areas corresponding to different beams, and each receiving antenna faces to the corresponding transmitting beam, so that feedback signals F1, F2, … and Fm of the m beams are captured and output to a receiving signal down-conversion link located in the phased antenna array equipment through feeder connection, the quality of the received feedback signals actually in the coverage areas is optimal, and the strength of the received feedback signals is maximum, wherein: m is more than or equal to 2 and less than or equal to M.
The receiving signal down-conversion link comprises; the signal weighting combination unit, m +1 analog-to-digital converters connected in parallel and the down converters corresponding to the analog-to-digital converters are provided, wherein: the output end of the signal weighting combination unit is connected with a first down converter, and the second to the m +1 th down converters are respectively and correspondingly connected with a receiving antenna in a far-field receiving antenna array, and respectively complete down conversion and analog-to-digital conversion on the m feedback signals to form m baseband digital feedback signals D1-Dm and output the signals to the first signal switcher.
The signal weighting and combining unit comprises: m multipliers and an adder, wherein: m multipliers respectively carry out amplitude weighting or signal direct connection on m feedback signals from a far-field receiving antenna array according to a control instruction of the digital signal processor, and a combined feedback signal is obtained through an adder and is output to a first down converter to form a baseband digital combined feedback signal D 0 。
The selecting at least one path from the baseband digital combined feedback signals comprises: the first signal switch selectively outputs a baseband digital combined feedback signal D from the first down converter according to an instruction from the digital signal processor 0 Or multiple baseband digital combined feedback signals D 1 ～D m To a third signal switch in which the baseband digital combines the feedback signal D 0 Weighting and combining the m feedback signals through a multiplier and an adder; baseband digital combined feedback signal D 1 ～D m And carrying the digital feedback signal for the m-mode base which is subjected to down-conversion and analog-to-digital conversion only and is not subjected to combination.
The phased antenna array comprises: synthesize radio frequency processing module, MXN way transmission link, MXN way coupling feedback link and MXN transmitting antenna, wherein: the comprehensive radio frequency processing module receives the baseband digital signals after being pre-corrected, completes analog-to-digital conversion and up-conversion, outputs M multiplied by N radio frequency signals to M multiplied by N transmitting links and outputs the signals through M multiplied by N transmitting antennas to form coverage, and the M multiplied by N radio frequency signals form M multiplied by N radio frequency coupling signals through M multiplied by N coupling feedback links and output the signals to the comprehensive radio frequency processing module to obtain M multiplied by N +1 baseband digital coupling signals and output the signals to the second signal switcher for signal selection and switching.
Each transmission chain comprises: the phase shifter, the power amplifier and the directional coupler are connected in sequence; each path coupling feedback link comprises: a derotation phase shifter and a multiplier disposed between the directional coupler and the integrated radio frequency processing module, wherein: the derotation phase shifter performs phase shifting derotation or signal through connection on the coupling signal from the transmitting link according to a control instruction of the digital signal processor, and the multiplier performs amplitude weighting adjustment or signal through connection on the coupling signal after phase shifting according to the control instruction of the digital signal processor.
The integrated radio frequency processing module comprises: an adder, M × N +1 down converters and their analog-to-digital converters, wherein: the adder receives M × N coupling signals from M × N coupling feedback links of the phased antenna array after derotation phase shifting and amplitude weighting, forms a combined signal and outputs the combined signal to the first down converter and the analog-to-digital converter thereof to form a baseband digital combined coupling signal P 0 And outputting to a second signal switcher, receiving corresponding MXN coupled signals subjected to derotation phase shift and amplitude weighting respectively by the second to MxN +1 down converters and the analog-to-digital converters thereof, and performing down-conversion and analog-to-digital conversion respectively to form MXN coupled signals P 1 ～P M×N And output to the second signal switch.
The selecting at least one output from the coupled signals comprises: the second signal switch selectively outputs a coupling signal P according to the instruction from the digital signal processor 0 Or MXN coupled signals P 1 ～P M×N Output to a third signal switch, in which the signal P is coupled 0 Combining the M multiplied by N coupled signals for baseband digital combined coupled signals after the M multiplied by N coupled signals are combined by a derotation phase shifter and an adder; coupled signal P 1 ～P M×N The digital coupling signal is an MxN baseband digital coupling signal which is only subjected to down-conversion and analog-to-digital conversion and is not subjected to combination;
the digital signal processor is internally provided with a judgment control module which outputs a control instruction to the three signal switchers so as to select one path or m-path baseband digital combined feedback signal or one path or MxN path coupling signal, and the selection sequence is not limited to random, self-adaptive judgment or manually assigned priority according to application scenes.
The digital processor takes the received signal as a reference signal, and the reference signal is as follows:
1) when one path of baseband digital combined feedback signal D is selected 0 When the digital signal processor is controlled by the judgment control module to generate and send weighting coefficients to multipliers in a signal weighting combination unit of a down-conversion link of received signals in the phased antenna array, so that the amplitude of m paths of feedback signals from the receiving antennas is weighted and combined in an analog domain, and finally a baseband digital combination feedback signal D is realized after down-conversion and analog-to-digital conversion 0 Forming; the simultaneous determination control module controls the first signal switcher to output D 0 To the third signal switch and finally to the digital signal processor, where the reference signal received by the digital signal processor is already weighted and combined in the analog domain before entering the digital domain;
2) when m road bands are selected, the digital combined feedback signal D is provided 1 ～D m When the judgment control module controls the digital signal processor to send signal through information to the multiplier in the signal weighting combination unit of the receiving signal down-conversion link in the phased antenna array, m paths of feedback signals from the receiving antenna are directly subjected to down-conversion and analog-to-digital conversion without weighting processing to become D1-Dm, and then the signals enter a first signal switcher; the simultaneous determination control module controls the first signal switcher to output D 1 ～D m And finally, outputting the signal to a digital signal processor through a third signal switcher, wherein the reference signal received by the digital signal processor is a baseband digital signal formed by the m route original feedback signals without any weighting and combination, and the digital signal processor needs to generate weighting coefficients and weight the m baseband digital signals in a digital domain, and then combines the signals into a baseband digital combination feedback signal for subsequent pre-correction. All weighting and combining is done in the digital domain by a digital signal processor.
3) When one path of coupling signal P is selected 0 When the phase-locked loop is used, the judgment control module controls the digital signal processor to send phase information of required derotation to a derotation phase shifter of an MXN coupling feedback link in a phased antenna array at a transmitting end and generate and send a weighting coefficient to a multiplier, so that the coupled signals of the MXN paths after derotation and weighting can be weighted in the comprehensive radio frequency processing module through an adder and finally subjected to down-conversion and analog-to-digital conversion to realize a baseband digital combined coupled signal P 0 Forming; the simultaneous determination control module controls the second signal switcher to output P 0 To the third signal switch and finally to the digital signal processor, where the reference signal received by the digital signal processor has been derotated, weighted and combined in the analog domain before entering the digital domain;
4) when the MxN coupling signals P are selected 1 ～P M×N During the process, the judgment control module controls the digital signal processor to transmit a direct signal (namely, no derotation and no weighting) to the derotation phase shifter of the MXN coupling feedback link in the phased antenna array of the transmitting end and to the multiplier, so that the MXN original coupling signals can respectively realize the MXN baseband digital coupling signal P after the down conversion and the analog-to-digital conversion in the comprehensive radio frequency processing module 1 ～P M×N The simultaneous determination control module controls the second signal switch to output P 1 ～P M×N And finally outputting the reference signal to a digital signal processor, wherein the reference signal received by the digital signal processor is a baseband digital coupling signal formed by the M × N routing original coupling signal which is not subjected to any phase derotation, weighting and combination, and the digital signal processor needs to derotate the M × N baseband digital coupling signal in a digital domain, generate a weighting coefficient and weight the weighting coefficient, and then combine the weighting coefficient into a baseband digital combination coupling signal for subsequent pre-correction. All derotation, weighting and combining is done in the digital domain by a digital signal processor.
The weighting coefficient is generated by any one of the following modes:
A. the equal amplitude method: and adjusting the feedback/coupling signals of each path through the weighting coefficient to enable the amplitudes to be equal when the feedback/coupling signals are combined finally. The method is simplest and direct, the acquisition speed is fastest, and the method is suitable for the phased array antenna of which a plurality of wave beams have the same strength, so that the feedback signals also have the same amplitude; the method can be applied to all application modes including the weighted combination in the analog domain or the digital domain, and is especially suitable for the application of selecting the weighted combination in the analog domain, because the hardware complexity is relatively simple, and the implementation speed is equivalent to the weighted combination in the digital domain.
B. According to the design of the coverage area of the phased antenna array, different weights are determined for feedback signals of different paths, for example, for a coupling signal obtained by a main lobe transmitting link or a feedback signal obtained by a receiving antenna set in a main coverage area, a coupling signal of a side lobe transmitting link or a feedback signal obtained by a receiving antenna set in a side area is set, and a higher weight is given, so that more main lobes or distortion conditions of the main area are reflected in a feedback combined signal. The method can help to understand the planning design and intervene manually, has the advantages of simplicity, rapidness and low hardware complexity as the equal amplitude method, but can be more flexibly applied to the application with different partition coverage requirements than the equal amplitude method; this method is equally applicable to all applications involving weighted combining in the analog or digital domain.
C. An exhaustive algorithm: the digital signal processing unit tries each path of weighting coefficients through an exhaustion method, so that the signal quality of the final overall output is the highest (for example, the signal-to-noise ratio is the highest, the shoulder is the largest, and the like). The method specifically comprises the following steps: the digital signal processor is provided with the initial parameters, the adjustable step length, the adjustable range and other key parameters of each weighting coefficient, and then the weighting coefficient which can lead the total signal quality to be the highest is found out in the preset range by depending on the huge calculation capacity of the digital signal processor and is recorded for use. The method has the advantages that the optimal combined signal can be found through different weighting attempts within a preset range to complete pre-correction; compared with the two methods, the method has the disadvantages of increased computation amount, increased completion time and correspondingly increased hardware complexity. The whole operation process is optimized by manually setting initial parameters, step length, range and the like, and can also be carried out by a digital signal processor. This method can be applied to all applications including weighting and combining in the analog domain or the digital domain, but the weighting and combining in the digital domain will make greater use of the computing power and speed of the digital signal processor and thus speed up the whole process.
D. And (3) pre-equalization algorithm: a digital signal processing unit, which analyzes and measures the signal of each received feedback/coupling signal, and sets a pre-judgment standard for each index according to a plurality of indexes such as signal strength, signal shoulder and signal quality, if the strength and shoulder of an effective signal in the received feedback/coupling signal are lower than the lowest threshold of the pre-judgment standard (such as the signal strength is lower than-70 dbm, or the signal shoulder is lower than 30dBc, or the signal strength exceeds the pre-judgment threshold, but more interference signals are mixed, so that the actual signal MER or SNR is lower than 10dB), the feedback/coupling signal is given lower reliability or is not adopted; otherwise, the feedback/coupling signal is judged to be reliable.
Further by setting multiple thresholds, the received feedback/coupled signals are classified into multiple, different degrees of reliability, and higher weights are given to feedback/coupled signals of high reliability or high degree of effectiveness. Because each received signal needs to be subjected to quality analysis and judgment, the method is relatively more suitable for selecting the application of weighting and combining in a digital domain, so that the digital signal processor can have the original information of each path of signal before the weighting and combining of each path of signal, thereby effectively estimating the signal and correspondingly generating the weight.
The invention relates to a multi-channel combined feedback signal acquisition and generation method of the acquisition system, which can ensure that receiving antennas (M is close to M) can be erected as much as possible in the coverage range of a phased array to acquire feedback signals, and the feedback signals have reliable quality, recommends a far-field receiving antenna array to acquire the feedback signals, then sends the feedback signals back to a receiving signal down-conversion link of phased array equipment in a feeder line mode, and finally outputs the feedback signals to a digital signal processor through a first signal switcher and a third signal switcher to complete subsequent pre-correction operation.
The invention relates to a multi-path combined feedback signal acquisition and generation method of the acquisition system, which is characterized in that under the condition that a plurality of receiving antennas cannot be effectively erected or the signal quality of the receiving antennas cannot be guaranteed, coupling signals of M multiplied by N radio frequency signals to be transmitted in a phased antenna array are obtained in a coupling mode in the phased antenna array, and then the coupling signals are output to a digital signal processor through a coupling feedback link and a comprehensive radio frequency processing module and finally through a second signal switcher and a third signal switcher to complete subsequent pre-correction operation.
The coupling means that: on an MXN path transmitting link of the phased antenna array and before the final output of the phased antenna array, a coupler is arranged at the MXN path radio frequency signals to be transmitted, and coupling signals of the MXN path output signals are directly obtained from a coupling port in a feeder line mode.
The reverse rotation processing is realized by adopting any one of the following modes:
firstly, in a radio frequency stage, phase deviation preset by each channel in a feedback signal is counteracted through M multiplied by N derotation phase shifting units, then a combined feedback signal is obtained after all phase-shifted feedback signals are superposed through an adding unit, and a digital baseband combined coupling signal is obtained through single-path down-conversion and analog-to-digital conversion processing.
And secondly, the M multiplied by N feedback signals are firstly subjected to M multiplied by N down-conversion and M multiplied by N analog-to-digital conversion to obtain M multiplied by N digital baseband signals, then the M multiplied by N digital baseband signals are all sent to a digital signal processing unit for phase shifting to offset the phase shift preset by each channel in the feedback signals, and then the M multiplied by N feedback signals are weighted and combined to obtain a digital baseband combined coupling signal which is used for pre-correction subsequently.
Technical effects
The invention provides a plurality of combined feedback signal acquisition and generation methods, which integrally solves the defect that the feedback signals are acquired by a single method in the prior art. For example, the feedback signals acquired by the prior art using the single receiving antenna technology may be affected by the position (e.g., the beam) and the surrounding environment (e.g., wind, rain, passing vehicles, and reflections from tall buildings), which may cause signal damage, and the prior art does not directly add and combine the feedback signals by taking into account the phase and/or amplitude adjustment of the signals before passing through the amplifying link when acquiring and combining the feedback signals by using the coupling technology, which may result in inaccurate and unreliable combined signals to be pre-corrected, which may result in poor correction effect.
Compared with the prior art, the invention adopts a far-field antenna array consisting of a plurality of receiving antennas, can set receiving points on a plurality of beams according to requirements, perfectly collect all beams, avoid the influence of unreal and deteriorated signals on the pre-correction effect by adjusting and optimizing a weighting algorithm, and simultaneously can avoid the condition that the whole pre-correction processing cannot work when a single receiving antenna does not have a feedback signal, thereby having robustness and providing possibility for continuously providing real-time and dynamic pre-correction. Or the quality and reliability of the signals sent to the pre-correction are enhanced by the modes of acquiring the coupling signals from the receiving antenna array, performing derotation phase shift, amplitude weighting and final combination on the coupling signals, so that a better pre-correction effect is obtained.
Drawings
FIG. 1 is a schematic view of the present invention;
FIG. 2 is a diagram of a phased array antenna of the present invention;
FIG. 3 is a schematic diagram of a feedback signal processing section according to the present invention.
Detailed Description
Example 1
In this embodiment, there are 64 transmitting antennas corresponding to 8 beam radiations. In application, a far-field receiving antenna with 8 receiving antennas is arranged in each beam radiation area and faces to a corresponding transmitting beam to capture a feedback signal, and the feedback signal is output to a receiving signal down-conversion link of the phased array antenna device through a feeder line connection. Because the number of the receiving antennas is enough and the stability and the reliability of the receiving signals of the antennas can be ensured due to the reasonable planning, the feedback signals obtained by the remote receiving antenna array are combined in the embodiment.
Meanwhile, since the coverage plan of the antenna is known, in this embodiment, the weighting coefficients determine that the feedback signals of different paths have different weights according to the design of the coverage area of the phased antenna array. The weighting coefficients of the 8 feedback signals are determined by weights, and are pre-stored in the digital signal processing unit through manual setting or manually corrected according to actual conditions in practical application. For example, in the areas radiated by the beams corresponding to the 8 phased antenna arrays, the 8 th area and the seventh area belong to the main radiation area, the areas 6 to 5 are medium radiation areas, and the areas 1 to 4 are secondary radiation areas, so that the corresponding coefficients obtained according to the weights are: c8 ═ c7 ═ 0.25; c 6-c 5-0.125, c 1-c 2-c 3-c 4-0.0625.
The combined weighted feedback signal is:
0.25×D8+0.25×D7+0.125×D6+0.125×D5+0.0625×(D1+D2+D3+D4)。
the combining and weighting can be performed in either the analog or digital domain.
The specific application scenario in this embodiment is applicable to: the design of the coverage area of the phased array antenna is predicted, and the actual effect of the coverage area is closer to the design effect, or the actual coverage area is calibrated periodically. In this case, a more desirable correction effect can be obtained without excessively adjusting the correction coefficient.
The specific application steps of the embodiment include:
step 1: after passing through the digital signal processing unit, the baseband signals are transmitted to the air by 8 multiplied by 8 antennas of the phased antenna array to form 8 beam radiation;
step 2: the method comprises the following steps of (1) setting 8 receiving antennas in 8 lobes corresponding to a phased antenna array, and standing independently from coverage areas of different lobes; the principle of antenna erection is: the antenna is a directional antenna, the orientation of the antenna is the direction of a phased antenna array, and no obvious barrier is shielded; the antenna is positioned in an effective coverage area of the phased antenna array, can receive effective aerial signals, and has a signal-to-noise ratio higher than a preset threshold. When the antenna receiving effect is not ideal, the mounting position or angle of the antenna needs to be readjusted;
and 3, step 3: transmitting the signals collected by each receiving antenna back to the phased array antenna through a feeder line, and selecting the feedback signals to enter a digital signal processor through a judgment control module of the digital signal processor;
and 4, step 4: since the design plan of the phased array is known and the actual coverage is close to the plan, a weighting algorithm is chosen to determine the weighting coefficients. Therefore, the weighting coefficients c 1-cm of the feedback signals are preset, and the digital signal processing unit outputs the weighting coefficients to realize the weighting and combination of the feedback signals;
and 5: the generated baseband digital combined feedback signal is used to form a reference error signal in comparison to the baseband signal and to perform pre-correction, thereby forming a closed loop.
Through specific practical experiments, under the specific environment setting that the actual antenna coverage effect is closer to the design, the preset weighting coefficients are used for weighting the multiple feedback signals and combining the weighted multiple feedback signals into a combined feedback signal, so that the distortion condition which is very close to the distortion condition of the actual output signal caused by the power amplification units of all paths can be obtained, and the predistortion can be effectively finished. Before predistortion, the indexes that each path of power amplifier can only amplify to 27dbm (0.5w) with shoulder and signal-to-noise ratio are critical, or the indexes that the shoulder and the signal-to-noise ratio are 8-10db different from the threshold value after the power amplifier is pushed to 33dbm (2w) of rated power, so that the power amplifier cannot be used for transmitting with the rated power, and then each path of power amplifier can improve at least 10db with shoulder and the signal-to-noise ratio after predistortion, so that the power backoff can be reduced, the transmitting efficiency is improved, and the rated power transmission is ensured.
In the prior art, when a single receiving antenna is adopted, a received signal is only a signal acquired in the air at a certain position and cannot represent distortion of each path of amplification of the whole phase-controlled antenna array MXN paths of antennas caused by nonlinearity or hardware difference, so that all distortion information cannot be effectively transmitted by using the single receiving antenna as a reference signal, and the distortion effect is poor naturally. The embodiment verifies that: compared with a single antenna, the actually corrected shoulder and signal-to-noise ratio are improved by more than 3-5 db by adopting a plurality of combined receiving antennas.
Example 2
Under the condition that the design effect of a coverage area of the phased array antenna is unknown or the actual effect is not measured, and whether the design coverage result is consistent with the design coverage result or not can not be confirmed, excessive measurement and calibration are not needed, the distortion of the amplified link stroke of the phased array antenna can be effectively pre-corrected by directly measuring the quality of a feedback signal and utilizing the strong processing capacity of a digital signal processing unit.
In this embodiment, the feedback signal is obtained by installing the receiving antenna array as compared with embodiment 1, but the coupling signal in the phased antenna array is also used as the feedback. After comprehensive consideration, firstly, a pre-equalization algorithm is adopted, namely, a weighting coefficient is generated by judging the information of a feedback signal; secondly, in order to cooperate with the pre-equalization algorithm D, a judgment control module is needed to sequentially receive m paths of feedback signals D from the antenna array 1 ～D m And coupling signal P from inside phased antenna array 1 ～P M×N And outputting the signal to a digital signal processor. In digital signal processor, pair D 1 ～D m And P 1 ～P M×N Signal strength, signal quality, etc. are analyzed and respective weighting coefficients are generated according to the analysis results, and then weighting and combining are performed in the digital domain. And comparing the two groups of weighted and combined signals for pre-correction, and selecting a group with better pre-correction effect through a signal switcher to finally implement pre-correction.
In this embodiment, D is selected 1 ～D m And P 1 ～P M×N And the feedback/coupling signals of each path are sent to a digital signal processor instead of being directly weighted and combined in an analog domain, so that the complete original information of each path of signal, including signal strength, shoulder, signal quality and the like, is reserved, and the reliability of each path of signal can be judged by a pre-equalization algorithm, so that a weighting coefficient is obtained. E.g. by detecting the signal strength, finding the feedback signal D 1 ～D 6 The signal is complete, the strength is moderate, and the signal-to-noise ratio is high, so that the information has high effective value and can give high weight; feedback signal D m-3 ～D m The signal is weak, the shoulder is low, the signal quality is seriously influenced by interference and noise, and therefore, the low effective value of the information should be given a low weight. Meanwhile, detailed information of the feedback signal can further give an early warning for calibrating the coverage of the phased antenna.
In addition to the pre-equalization algorithm, due to the powerful computing power of the digital signal processing unit, the formation of the combined feedback signal can be further optimized by an exhaustive algorithm on the basis of the pre-equalization algorithm. E.g. a known feedback signal D 1 ～D 6 The weights need to be high, and their specific weighting coefficients can be manually set as in the case of a pre-equalization algorithm, or the initial parameters, the adjustable range and the adjustable step length can be selected by manual setting, then the digital signal processing unit is operated to adjust each parameter within a predetermined range according to the adjustable step length, the adjustable range is limited, and all possible combinations of the weighting coefficients are tried one by one until a combined feedback signal is found, which participates in the pre-correction completed, and the output total signal quality is highest. When there are two sets of feedback/coupled signals (e.g. D) 1 ～D m And P 1 ～P M×N ) The pre-equalization algorithm and/or the exhaustive algorithm may be performed as per the above steps, respectively.
Obtaining a weighting coefficient c 1-cm (corresponding to D) according to the feedback signal information of each path 1 ～D m ) Or c 1-cMXN (corresponding to P) 1 ～P M×N ) Thereafter, the weighting and combining are simultaneously performed in the digital signal processing unit, thereby obtaining a digital combined signal for subsequent pre-correction.
Through a specific practical experiment, assuming that m is 10 in this embodiment, as described above, feedback signals D1-D6 obtained through a far-field antenna array are complete in signal, moderate in strength, and high in signal-to-noise ratio, and are determined by multiple thresholds of a pre-equalization method, wherein the weights of D3, D5, and D6 are the highest, D1, D2, and D4 are the lowest, and the weights of D7-D10 are weak, and have a low shoulder, and the signal quality is seriously affected by interference and noise, and have the lowest weight. By combining a pre-equalization method and/or an exhaustion method, the weighting coefficient of each path is obtained as follows: d1 ═ 0.143; d2 ═ 0.128; d3 ═ 0.186; d4 ═ 0.095; d5 ═ 0.213; d6 ═ 0.205; d7 ═ 0.05; d8 ═ 0.05; d9 ═ 0.13; d10 ═ 0.07. Similarly, another set of weighting coefficients of the coupled signals MxN (10 x10 in this embodiment) is obtained, and finally a combined signal of the coupled signals is obtained. In contrast, the overall quality of the combined feedback signal of the far-field antenna array is higher than the quality of the in-antenna coupled combined signal (1-2 db), the overall correction effect is better (2-3 db), and the speed is faster because the number of samples and the number of calculations are fewer (10 versus 100), so the feedback signal of the far-field antenna is selected to be used for pre-correction in the embodiment.
The combination of the pre-equalization algorithm and/or the exhaustive method can greatly utilize the effectiveness of different feedback signals and improve the reference value of the combined feedback signal, so that the optimal correction performance in a possible range can be obtained by pre-correction. Moreover, the coverage range of the phase antenna array does not need to be predicted or calibrated in advance, the design coverage range of the phase antenna array is not depended on, misjudgment caused by the change of a received signal is avoided, and real-time and automatic pre-correction is facilitated. The correction has been found to improve shoulder and signal to noise ratio by more than 5-8db in different environments and applications.
Example 3
In some situations where the receiving antenna array cannot be erected in a far field to acquire the feedback signal, for example, where the receiving antenna cannot be conveniently inserted in a dense metropolitan area, or where the receiving quality of the antenna is unstable and is easily affected by the peripheral environment, or where the installation and maintenance costs of the receiving antenna array are high, the feedback signal acquired by coupling in the phase antenna array is more likely to be used. However, compared to the conventional design in which each path needs to be individually pre-corrected, which results in very large and complex hardware and is difficult to integrate in the conventional technology, and the common design in which all coupled signals are directly added in order to save the hardware complexity, the phase and amplitude of each path of coupled signals are adjusted and then combined into the feedback signal for pre-correction in the present embodiment.
The phase derotation and amplitude adjustment may be performed in the analog domain or in the digital domain. The phase information received by the derotation phase shifter is phase deviation preset in each transmitting link for compensating the phased array in order to form lobe coverage, so that the phase information required to be compensated for each path is known, and the phase of each path is finely adjusted by a digital signal processor to make up errors caused by the precision and the inconsistency of a hardware link; the generation of the weighting coefficient of the amplitude adjustment can use an equal amplitude method, and particularly, under the condition of carrying out the amplitude adjustment in an analog domain, the equal amplitude method can effectively improve the speed and reduce the complexity of hardware. The method can also be carried out in a digital domain in a matching way by using a pre-equalization algorithm plus an exhaustion method, so that the intensity of each path of coupled signal is detected, the inconsistency of each path of signal caused by hardware differences such as amplification link gain, coupler coupling degree and the like is further accurately compensated, and the reliability and the quality of the combined feedback signal can be further improved. Also, the phase adjustment in the digital signal processor is due to the accuracy of the analog phase shift.
In the embodiment, the feedback signals acquired by each path in the mxn transmission link are combined after derotation and amplitude adjustment, so that in-phase addition can be effectively ensured and distortion suffered when each path of signals is amplified is retained, and therefore, the pre-correction effect can be improved. Actually measuring and combining the signals after carrying out phase derotation and amplitude adjustment in an analog domain to form a feedback signal, wherein the correction effect can be directly added by 4-7dB compared with the prior art; the phase derotation and the amplitude adjustment are carried out in a digital domain and then combined to form a feedback signal, and the correction effect can be directly added by 5-8dB compared with the prior art;
the foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (16)
1. A multi-channel combined feedback signal acquisition system for predistortion processing, comprising: the base band signal processing unit, the digital signal processing unit, the phased antenna array that are located phased array equipment, are located the transmitting terminal and are located far-field receiving antenna array, the down-converting link of received signal and the signal switching unit of phased antenna array coverage, wherein: the digital signal processing unit simultaneously receives the baseband signals and the baseband digital signals from the signal switching unit, pre-corrects the baseband digital signals, outputs the pre-corrected baseband digital signals to the phased antenna array, and forms overlay broadcast by M multiplied by N transmitting antennas; each receiving antenna in the far-field receiving antenna array receives an air signal and then sends the air signal to a receiving signal down-conversion link in the phased antenna array equipment; the receiving signal down-conversion link outputs a baseband digital combined feedback signal to the signal switching unit, the signal switching unit outputs the baseband digital combined feedback signal or a coupling signal to the digital signal processor, and the digital signal processor finally realizes closed-loop pre-correction by taking the received signal as a reference signal;
the signal switching unit includes: three signal switches, wherein: the first signal switcher is connected with the receiving signal down-conversion link and receives the baseband digital combined feedback signal D 0 ～D m The first signal switch digitally combines the feedback signal D from the baseband under the control of the digital signal processor 0 ～D m At least one path is selected to be output to a third signal switcher; the second signal switch receives the coupling signal P from the phased antenna array 0 ～P M×N The second signal switch is controlled by the digital signal processor to switch from the coupling signal P from the phased antenna array 0 ～P M×N The third signal switch outputs at least one baseband digital combined feedback signal or coupling signal from the phased antenna array to the digital signal processor under the control of the digital signal processor.
2. The multi-channel combined feedback signal acquisition system for predistortion processing as set out in claim 1, wherein said far field receive antenna array comprises: the m receiving antennas located in the coverage area of the phased antenna array are distributed in the corresponding coverage areas of different beams respectively, and each receiving antenna faces to the corresponding transmitting beam, so that feedback signals F1, F2, … and Fm of the m beams are captured and are output to a receiving signal down-conversion link located in the phased antenna array equipment through feeder connection, the quality of the received feedback signals actually in the coverage area is optimal, and the strength of the received feedback signals is maximum, wherein: m is more than or equal to 2 and less than or equal to M.
3. The system of claim 1, wherein the receive signal down-conversion link comprises: the signal weighting and combining unit, m +1 analog-to-digital converters connected in parallel and the down converters corresponding to the analog-to-digital converters are provided, wherein: the output end of the signal weighting combination unit is connected with a first down converter, and second to m +1 th down converters are respectively and correspondingly connected with a receiving antenna in a far-field receiving antenna array to respectively complete down conversion and analog-to-digital conversion to form a baseband digital combined feedback signal D 0 ～D m And output to the first signal switch.
4. The multi-channel combined feedback signal acquisition system for predistortion processing as set out in claim 3, wherein said signal weighting and combining unit comprises: m multipliers and an adder, wherein: m multipliers respectively carry out amplitude weighting or signal direct connection on m feedback signals from a far-field receiving antenna array according to a control instruction of the digital signal processor, and a combined feedback signal is obtained through an adder and is output to a first down converter to form a baseband digital combined feedback signal D 0 。
5. The system of claim 1, wherein the selecting at least one of the plurality of paths from the baseband digital combined feedback signal comprises: the first signal switch selects the digital combined feedback signal D from the baseband according to the instruction from the digital signal processor 0 Or D 1 ～D m Output to a third signal switch, wherein D 0 For the signals after weighted combination of the m feedback signals by the multiplier and adder, D 1 ～D m The m signals are only subjected to frequency conversion and analog-to-digital conversion and are not subjected to combination.
6. The system of claim 1 wherein the phased antenna array comprises: synthesize radio frequency processing module, MXN way transmission link, MXN way coupling feedback link and MXN transmitting antenna, wherein: the comprehensive radio frequency processing module receives the baseband digital signals after being pre-corrected, analog-to-digital conversion and up-conversion are completed, M multiplied by N radio frequency signals are output to M multiplied by N transmitting links and are output through M multiplied by N transmitting antennas to form coverage, the M multiplied by N radio frequency signals form M multiplied by N radio frequency coupling signals through M multiplied by N coupling feedback links respectively and are output to the comprehensive radio frequency processing module to obtain M multiplied by N +1 baseband digital coupling signals, and the M multiplied by N +1 baseband digital coupling signals are output to a second signal switcher to perform signal selection and switching.
7. The system of claim 1, wherein each transmit chain comprises: the phase shifter, the power amplifier and the directional coupler are connected in sequence; each path coupling feedback link comprises: a derotation phase shifter and a multiplier disposed between the directional coupler and the integrated radio frequency processing module, wherein: the derotation phase shifter performs phase shifting derotation or signal through connection on the coupling signal from the transmitting link according to a control instruction of the digital signal processor, and the multiplier performs amplitude weighting adjustment or signal through connection on the coupling signal after phase shifting according to the control instruction of the digital signal processor.
8. The system of claim 6 or 7, wherein the integrated RF processing module comprises: an adder, M × N +1 down converters and their analog-to-digital converters, wherein: the adder receives M × N coupling signals from M × N coupling feedback links of the phased antenna array after derotation phase shifting and amplitude weighting, forms a combined signal and outputs the combined signal to the first down converter and the analog-to-digital converter thereof, and M × N coupling signals after derotation phase shifting and amplitude weighting respectively pass through the second to Mx N +1 down converters and the analog-to-digital converters thereof to complete down-conversion and analog-to-digital conversion, and jointly form M × N +1 paths of coupling signals P from the phased antenna array 0 ～P M×N And output to the second signal switch.
9. The system of claim 1, wherein the selecting at least one output from the coupled signals comprises: the second signal switch selects and outputs the coupling signal P from the phased antenna array according to the instruction from the digital signal processor 0 Or P 1 ～P M×N Output to a third signal switch, where P 0 For signals which have been combined by derotation phase shifters and adders for M N coupled signals, P 1 ～P M×N Is an mxn signal that has been down-converted and analog-to-digital converted only, without being combined.
10. The system of claim 1, wherein the dsp has a built-in decision control module, which outputs control commands to three signal switches to select one or M baseband digital combined feedback signals or one or M × N coupled signals from the phased antenna array, and the selection order is not limited to random, adaptive decision, or manually assigned priority according to application scenarios.
11. The system of claim 1, wherein the digital processor uses the received signal as a reference signal to:
1) when one path of baseband digital combined feedback signal D is selected 0 When the digital signal processor is controlled by the judgment control module to generate and send weighting coefficients to multipliers in a signal weighting combination unit of a receiving signal down-conversion link in the phased antenna array, so that m paths of feedback signals from the receiving antenna are weighted and combined in an analog domain, and finally a baseband digital combination feedback signal D is realized after down-conversion and analog-to-digital conversion 0 Forming; the simultaneous judgment control module controls the first signal switcher to output a baseband digital combined feedback signal D 0 To the third signal switch and finally to the digital signal processor, where the digital signal is processedThe reference signals received by the device are weighted and combined in an analog domain before entering a digital domain;
2) when m road bands are selected, the digital combined feedback signal D is provided 1 ～D m When the judgment control module controls the digital signal processor to send signal through information to the multiplier in the signal weighting combination unit of the down-conversion link of the received signals in the phased antenna array, the m-path feedback signals from the receiving antenna are directly converted into baseband digital combination feedback signals D through down-conversion and analog-to-digital conversion without weighting processing 1 ～D m Entering a first signal switcher; the simultaneous judgment control module controls the first signal switcher to output a baseband digital combined feedback signal D 1 ～D m To a third signal switch and finally to the digital signal processor, where the reference signal received by the digital signal processor is a baseband digital combined feedback signal D formed by m-route original feedback signals without any weighting and combination 1 ～D m The digital signal processor needs to combine the feedback signal D to the baseband digital within the digital domain 1 ～D m Generating weighting coefficients and weighting, and then combining into baseband digital combined feedback signals for subsequent pre-correction, wherein all weighting and combining are completed by a digital signal processor in a digital domain;
3) when selecting a coupling signal P from the coupling signals from the phased antenna array 0 When the phase-locked loop is in use, the judgment control module controls the digital signal processor to send phase information of required derotation to derotation phase shifters of coupled feedback links of MxN paths in phased antenna array at transmitting end, and to generate and send weighting coefficients to multipliers, so that the coupled signals of MxN paths after derotation and weighting can be weighted in the integrated radio frequency processing module through the adder, and finally the coupled signals P from the phased antenna array can be realized after down-conversion and analog-to-digital conversion 0 Forming; the simultaneous determination control module controls the second signal switch to output a coupling signal P from the phased antenna array 0 To the third signal switch and finally to the digital signal processor, when the reference signal received by the digital signal processor is already weighted and combined in the analog domain before entering the digital domain；
4) When selecting the MxN coupling signals P from the coupling signals from the phased antenna array 1 ～P M×N During the process, the judgment control module respectively outputs derotation phase shifters of M multiplied by N coupling feedback links in a phased antenna array of a transmitting end and through signals without derotation and weighting to a multiplier through a digital signal processor, so that M multiplied by N original coupling signals can be subjected to down-conversion and analog-to-digital conversion respectively in an integrated radio frequency processing module to realize M multiplied by N baseband digital coupling signals P 1 ～P M×N The simultaneous determination control module controls the second signal switch to output P 1 ～P M×N And finally outputting the reference signal to a digital signal processor, wherein the reference signal received by the digital signal processor is a baseband digital coupling signal formed by the M × N routing original coupling signal which is not subjected to any phase derotation, weighting and combination, the digital signal processor needs to derotate the M × N baseband digital coupling signal in a digital domain, generate a weighting coefficient and weight the weighting coefficient, and combine the weighting coefficient and the baseband digital coupling signal into a baseband digital combination coupling signal for subsequent pre-correction, and all derotation, weighting and combination are completed by the digital signal processor in the digital domain.
12. The system of claim 11, wherein the weighting coefficients of 1) -4) are generated by any one of the following methods:
A. the equal amplitude method: adjusting each path of feedback/coupling signal through the weighting coefficient to enable the amplitude to be equal when the feedback/coupling signals are combined finally;
B. according to the design of the coverage area of the phased antenna array, determining that feedback signals of different paths have different weights;
C. an exhaustive algorithm: the digital signal processing unit tries each path of weighting coefficient through an exhaustion method so as to ensure that the final overall output signal quality is highest;
D. and (3) pre-equalization algorithm: and the digital signal processing unit is used for carrying out signal analysis and quality measurement on each received feedback/coupling signal and judging the reliability of the acquired feedback signal according to the signal strength and the quality index, so that the high-reliability feedback signal is given high weight, and the low-reliability feedback signal is given low weight.
13. A multi-channel combined feedback signal acquisition and generation method based on the acquisition system of any one of claims 1 to 12, characterized in that, under the condition that it can be ensured that as many receiving antennas as possible can be erected in the coverage area of a phased array antenna to obtain the feedback signal, and the feedback signal quality is reliable, after the feedback signal is obtained by using a far-field receiving antenna array, the feedback signal is sent back to a receiving signal down-conversion link of a phased array antenna device by means of a feeder line, and finally, the feedback signal is output to a digital signal processor through a first signal switcher and a third signal switcher to complete the subsequent pre-correction operation.
14. The method as claimed in claim 13, wherein the coupling signals P of M x N radio frequency signals to be transmitted in the phased antenna array are obtained in the phased antenna array by coupling in the case that a plurality of receiving antennas cannot be effectively erected or the signal quality of the receiving antennas cannot be guaranteed 1 ～P M×N And then through the coupling feedback link and the comprehensive radio frequency processing module, the signals are finally output to the digital signal processor through the second signal switcher and the third signal switcher so as to complete the subsequent pre-correction operation.
15. The method of claim 13, wherein said coupling is: on an MXN path transmitting link of the phased antenna array and before the final output of the phased antenna array, a coupler is arranged at the MXN path radio frequency signals to be transmitted, and coupling signals of the MXN path output signals are directly obtained from a coupling port in a feeder line mode.
16. Method according to claim 14, characterized in that said coupling signal P of the radiofrequency signal to be transmitted is a coupling signal P 1 ～P M×N The method is realized by adopting any one of the following modes:
firstly, in a radio frequency stage, offsetting preset phase offset of each channel in a feedback signal through M multiplied by N derotation phase shift units, then superposing all phase-shifted feedback signals through an addition unit to obtain a combined feedback signal, and obtaining a digital baseband combined coupling signal through single-path down-conversion and analog-to-digital conversion processing;
and secondly, performing M × N down-conversion and M × N analog-to-digital conversion processing on the M × N feedback signals to obtain M × N digital baseband signals, then, completely sending the M × N digital baseband signals to a digital signal processing unit for phase shifting to offset phase offset preset by each channel in the feedback signals, and then, combining the M × N digital baseband signals to obtain a digital baseband combined coupling signal for subsequent pre-correction.
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