CN107508642B - Nonlinear evaluation system and method of high-order modulation communication system - Google Patents
Nonlinear evaluation system and method of high-order modulation communication system Download PDFInfo
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Abstract
The invention discloses a nonlinear evaluation system and a nonlinear evaluation method of a high-order modulation communication system, which are used for evaluating the nonlinear strength of the communication system. The radio frequency signal which is transmitted by the high-order modulation communication system and undergoes nonlinear distortion is converted to a baseband, matched filtering is carried out to obtain a constellation diagram, and the nonlinear intensity of the system is evaluated by calculating the specific change degree of constellation points. The invention counts the nonlinear intensity into an accurate numerical value, numerically expresses the influence of the nonlinearity of the communication system on the high-order modulation signal, and is convenient for comparing the nonlinear intensities of different communication systems. The invention solves the problem of nonlinear intensity evaluation in a high-order modulation communication system and has advantages in the aspects of accuracy, universality and the like.
Description
Technical Field
The invention relates to the technical field of communication, in particular to a nonlinear evaluation system and a nonlinear evaluation method of a high-order modulation communication system.
Background
With the rapid development of the information-based society, communication services with high speed, excellent quality and low charge are popularized comprehensively, and the data volume to be transmitted by a communication system is exponentially increased. Modern communication systems generally adopt a high-order modulation technology to improve the spectrum efficiency and improve the data transmission bit rate under limited spectrum resources. For example, an M-order QAM (quadrature amplitude Modulation) signal carries a number of bits log2(M) are provided. However, active devices in communication devices, such as modulators, radio frequency power amplifiers, up-down converters, and the like, all have non-linearities. High order modulation signals are highly susceptible to non-linearity: the non-linearity will cause severe in-band distortion and out-of-band interference, degrading signal quality and causing loss of performance of the communication system. Therefore, the evaluation of the nonlinear characteristics is one of the important means for evaluating the performance of the communication system.
Means for evaluating non-linear characteristics in a communication system include Total Harmonic Distortion (THD), Intermodulation Distortion (IMD), Amplitude-to-Amplitude (AM/AM) and Amplitude-Phase (AM/PM) response curves, and various non-linear mathematical models, such as: a Saleh model, a memoryless polynomial model, a Volterra model, and the like.
With the spread of digital processing units in communication systems, it has become mainstream to use various mathematical models to describe nonlinear distortion in the system. The core of the chinese invention patent CN201310339185.4, a weak nonlinear distortion calculation method for amplifiers, is to calculate the distortion of the series of Volterra functional series. The chinese patent of invention with patent number CN201210083937.0, "predistortion apparatus and method based on precise inverse solution memory polynomial model equation" also describes nonlinearity by using the memory polynomial model equation.
However, these non-linear evaluation methods have two problems:
1. the accuracy is not good, and the nonlinear characteristics of the performance of the high-order modulation communication system cannot be accurately mapped: for example, the THD and IMD values are only of a magnitude that characterizes the non-linear behavior of the excitation signal when it is a dot frequency signal; the accuracy with which AM/AM and AM/PM curves describe non-linearities also strongly depends on the measurement conditions; a small amount of nonlinear mathematical model parameters cannot clearly reflect the nonlinear embodiment of the system, a large amount of parameters can approximate the nonlinearity of the expression system, and the parameter solving process is too complex and is not easy to realize.
2. The generality is not strong, the nonlinear evaluation value is missing or ambiguous, and different nonlinearities cannot be effectively compared: the magnitude of the THD and IMD values are not suitable for assessing the non-linearity of the broadband signal; clear numerical values cannot be extracted from AM/AM and AM/PM curves to evaluate the nonlinearity of the system; there is no direct comparison between two different sets of non-linear mathematical model parameters.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention is directed to a system and a method for non-linear evaluation of a high-order modulation communication system, which solve the problem of non-linear evaluation in the high-order modulation communication system and can accurately express the non-linear characteristics of the communication system in a numerical form. Based on the nonlinear evaluation system and method, the system nonlinearity can be simply and effectively compared. The nonlinear evaluation system and method provided by the invention have the characteristics of clear calculation rule, high accuracy, strong universality and the like.
In order to achieve the purpose, the invention adopts the technical scheme that: a non-linear evaluation system of a high-order modulation communication system is used for receiving a radio frequency signal and calculating a non-linear evaluation value contained in the radio frequency signal, and the non-linear evaluation system comprises: radio frequency signal receiver, down converter, wave filter, adc, digital signal processor, its characterized in that:
the radio frequency signal receiver is used for receiving a radio frequency signal xRF(t) amplifying or attenuating the radio frequency signal to a suitable power range by using a low noise amplifier or an attenuator;
the down converter comprises a local oscillator signal generator and a down conversion link, wherein the down conversion link mixes a local oscillator signal generated by the local oscillator signal generator with a radio frequency signal received by a radio frequency signal receiver to obtain an analog signal x after down conversionD(t)；
The filter is used for filtering the analog signal after down conversion to obtain the analog signal x after filteringF(t)；
The analog-to-digital converter is used for converting the analog signal after filtering into a digital signal xF(n)；
The digital signal processor comprises a low-pass filter, a matched filter, an ideal constellation point judgment module and a nonlinear evaluation algorithm module, wherein:
the low-pass filter is used for the digital signal xF(n) low-pass filtering to obtain digital signal xL(n)；
The matched filter is used for the digital signal xL(n) performing matched filtering to obtain a digital signal xM(m)；
The ideal constellation point decision module is used for judging the digital signal xM(m) making an ideal constellation point decision,obtaining a digital signal xREF(m)；
The nonlinear evaluation algorithm module is used for realizing a nonlinear evaluation method of a high-order modulation communication system, and is used for carrying out nonlinear evaluation on a digital signal xM(m) and xREF(m) comparing, calculating and giving a nonlinear evaluation value.
Further, the nonlinear evaluation algorithm module specifically implements a process including: and (3) carrying out regional division on the signals processed by the ideal constellation point judgment module, then calculating a regional nonlinear evaluation value, and further calculating to obtain a system overall nonlinear evaluation value.
Further, the carrier frequency of the radio frequency signal is fRFWherein the frequency f of the local oscillator signal generated by the local oscillator signal generatorLOLess than or equal to the carrier frequency f of the received radio frequency signalRFI.e. fLO≤fRF。
Furthermore, the high-order modulation communication system further comprises a signal source, an M-order modulation, a shaping filter, a digital-to-analog converter, an up-converter, a linear radio frequency transmitter or a nonlinear radio frequency transmitter, and an additive white gaussian noise generator at the front end of the radio frequency signal receiver.
The invention also provides a nonlinear evaluation method of the high-order modulation communication system, which is used for evaluating the nonlinear intensity of the high-order modulation communication system and is characterized in that the method transforms the radio-frequency signal which is transmitted by the high-order modulation communication system and undergoes nonlinear distortion to a baseband, performs matched filtering, performs ideal constellation point judgment to obtain a constellation diagram, and evaluates the nonlinear intensity of the system by calculating the specific change degree of the constellation point.
The invention provides a nonlinear evaluation method of a high-order modulation communication system, which adopts the nonlinear evaluation system of the high-order modulation communication system and is characterized in that the nonlinear evaluation method comprises the following steps:
signal x processed by ideal constellation point decision moduleREFThe number of values of (M) is limited, for an M-order modulation system, xREFThe number of values of (m) is 2MThe complex coordinate plane is divided into 2 according to the principle of ideal constellation point judgmentMA decision region; thus, all data points x may be mappedREF(M), M1, 2, …, M, is divided into 2MGroup data xREF(mi) Where M is the total length of the data, i ═ 1,2, …,2MThe values of each set of data being equal, i.e. for all mi，xREF(mi)＝xREF(i) And is a constant; according to xM(m) and xREF(m) mapping of all data points xM(M), M1, 2, …, M divided into 2MGroup data xM(mi)；
And step 2, calculating a region nonlinear evaluation value:
for the ith area of the division, the value range is i-1, 2, …,2MFirst, for data set xM(mi) Taking the average to obtain the average value xMavg(i) (ii) a Then, the non-linear evaluation values P (i) and their logarithm values P in the region are calculated respectivelydB(i)：
PdB(i)＝10·log10(P(i))，
Wherein M isiIs miThe number of values of (a);
and 3, calculating the overall nonlinear evaluation value:
weighting the nonlinear evaluation values of all the regions to calculate the nonlinear evaluation value P of the wholeallAnd its logarithmic value Pall_dB：
Pall_dB＝10·log10(Pall)。
Further, in step 1, the method for dividing the region includes the specific steps of:
s1, area division starts;
s2, obtaining modulation order M, and resetting counter i to 0;
s3, the counter starts counting i ═ i + 1;
s4, for the ith value xREF(i) At all data points xREF(M), where M is 1,2, …, M, finding a data point x that satisfies the conditionREF(mi)＝xREF(i) M ofiA value;
s5, store miA value;
s6, according to miDividing the ith group of ideal decision signals xREF(mi)＝xREF(i)；
S7, according to miDividing the signal x before the i-th decisionM(mi)；
S8, judging whether 2 is traversed or notMA decision region, i.e. i-2M(ii) a If so, completing the area division; if not, the process loops to step S3 until the traversal condition is satisfied.
Further, in step 2, the specific steps of the region nonlinear evaluation value calculation method include:
s1, the calculation of the area nonlinear evaluation value is started;
s2, acquiring packet data, resetting counter i to 0;
s3, the counter starts counting i ═ i + 1;
s4, calculating m of the ith packetiNumber of values Mi；
S5, signal x before decision of ith packetM(mi) Averaging to obtain the average value x of the signals before the decision of the ith groupMavg(i)；
S6, based on the nonlinear evaluation value calculation formula in the region, finds the nonlinear evaluation value p (i) of the i-th region:
wherein,Miis miThe number of values of (a);
s7, calculating the logarithm value P of the non-linear evaluation value P (i) of the ith areadB(i)：
PdB(i)＝10·log10(P(i))；
S8, judging whether 2 is traversed or notMA decision region, i.e. i-2M(ii) a If so, completing the calculation of the nonlinear evaluation value of the area; if not, the process loops to step S3 until the traversal condition is satisfied.
Compared with the prior art, the nonlinear evaluation system and method of the high-order modulation communication system have the following beneficial effects:
(1) counting the influence of the nonlinearity into an accurate numerical value by calculating the change degree of the constellation points caused by the nonlinearity;
(2) the influence caused by the nonlinearity can be reasonably evaluated, so that system-level comparison of different nonlinearities is facilitated;
(3) the invention solves the problem of nonlinear evaluation in a high-order modulation communication system and has advantages in the aspects of universality, accuracy and the like.
Drawings
FIG. 1 is a block diagram of a non-linearity evaluation system for a high order modulation communication system;
FIG. 2 is a flow chart of a method for non-linear estimation of a high order modulation communication system implemented in a digital signal processor according to the present invention;
FIG. 3 is a flowchart of a region allocation method in a non-linear estimation calculation method of a high-order modulation communication system according to the present invention;
fig. 4 is a flowchart illustrating a method for calculating a non-linear evaluation value of a region in a method for calculating a non-linear evaluation value of a high-order modulation communication system according to the present invention;
FIG. 5 is a system flow diagram of a comparative experiment in an embodiment of the present invention, in which a "DSP" module implements the non-linearity evaluation method shown in FIG. 2;
fig. 6 shows a constellation diagram of a signal after matched filtering and a region division relationship thereof in embodiment #1 (comparison experiment) of the present invention;
fig. 7 is a flowchart of an experimental system for evaluating nonlinearity according to embodiments # 2 and #3 of the present invention, in which a "dsp" module implements the nonlinearity evaluation method shown in fig. 2.
Fig. 8 shows the non-linear characteristic # 1 to be evaluated in embodiment # 2 of the present invention, which is described by an amplitude-amplitude (AM-AM) curve.
Fig. 9 shows a constellation diagram of a signal after matched filtering and a region division relationship thereof in embodiment #2 (non-linear evaluation experiment #1) of the present invention;
fig. 10 shows the non-linear characteristic # 2 to be evaluated in embodiment # 3 of the present invention, which is described by an amplitude-amplitude (AM-AM) curve.
Fig. 11 shows a constellation diagram of a signal after matched filtering and a region division relationship thereof in embodiment #3 (non-linear evaluation experiment #2) of the present invention.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
The core technical idea of the nonlinear evaluation method of the high-order modulation communication system is to realize a novel calculation method of the nonlinear evaluation value. In order to make the technical scheme of the invention clearer, the invention is further described in detail with reference to the accompanying drawings.
Fig. 1 is a block diagram of a non-linear evaluation system of a high-order modulation communication system according to the present invention, which is used for receiving a radio frequency signal and finally calculating a non-linear evaluation value included in the radio frequency signal. Specifically, the nonlinear evaluation system includes: the device comprises a radio frequency signal receiver, a down converter, a filter, an analog-to-digital converter, a digital signal processor and the like.
Fig. 2 is a flow chart of a non-linear evaluation method of a high-order modulation communication system implemented in a digital signal processor according to the present invention, which implements the functions of the digital signal processor in the non-linear evaluation system shown in fig. 1. Specifically, the processing flow includes: low-pass filter, matched filter, ideal constellation point judgment, nonlinear evaluation algorithm and the like.
Fig. 3 is a flowchart of a region allocation method in a nonlinear evaluation calculation method of a high-order modulation communication system according to the present invention, which implements the region allocation method in a nonlinear evaluation algorithm. Signal x after decision according to ideal constellation pointREFThe number of values of (M) is limited, for an M-order modulation system, xREFThe number of values of (m) is 2MThe complex coordinate plane is divided into 2 according to the principle of ideal constellation point judgmentMA decision region. Specifically, the region allocation method comprises the following steps:
s1, area division starts;
s2, obtaining modulation order M, and resetting counter i to 0;
s3, the counter starts counting i ═ i + 1;
s4, for the ith value xREF(i) At all data points xREF(M), where M is 1,2, …, M (where M is the total length of the data), a data point x is found that satisfies the conditionREF(mi)＝xREF(i) M ofiA value;
s5, store miA value;
s6, according to miDividing the ith group of ideal decision signals xREF(mi)＝xREF(i)；
S7, according to miDividing the signal x before the i-th decisionM(mi)；
S8, judging whether 2 is traversed or notMA decision region, i.e. i-2M(ii) a If so, completing the area division; if not, the process loops to step S3 until the traversal condition is satisfied.
Fig. 4 is a flowchart of a region nonlinear evaluation value calculation method in the nonlinear evaluation calculation method of the high-order modulation communication system in the present invention, which realizes calculation of nonlinear evaluation values of each decision region. The nonlinear evaluation values in the respective areas are settled based on the area division result. Specifically, the step of calculating the nonlinear evaluation value of the region is as follows:
s1, the calculation of the area nonlinear evaluation value is started;
s2, acquiring packet data, resetting counter i to 0;
s3, the counter starts counting i ═ i + 1;
s4, calculating m of the ith packetiNumber of values Mi；
S5, signal x before decision of ith packetM(mi) Averaging to obtain the average value x of the signals before the decision of the ith groupMavg(i)；
S6, based on the nonlinear evaluation value calculation formula in the region, finds the nonlinear evaluation value p (i) of the i-th region:
s7, calculating the logarithm value P of the non-linear evaluation value P (i) of the ith areadB(i)：
PdB(i)＝10·log10(P(i))；
S8, judging whether 2 is traversed or notMA decision region, i.e. i-2M(ii) a If so, completing the calculation of the nonlinear evaluation value of the area; if not, the process loops to step S3 until the traversal condition is satisfied.
FIG. 5 is a system flow diagram of a comparative experiment in an embodiment of the present invention, in which a "DSP" module implements the non-linear evaluation method shown in FIG. 2. Specifically, the comparative example includes: the system comprises a signal source, an M-order modulation, a shaping filter, a digital-to-analog converter, an up-converter, a radio frequency transmitter (linear), an additive white Gaussian noise generator, a radio frequency receiver (linear), a down-converter, a filter, an analog-to-digital converter, a digital signal processor and the like.
The following describes a calculation method for non-linearity evaluation of a high-order modulation communication system according to the present invention, with reference to a specific example #1 (comparative example).
In this embodiment #1 (comparative example), the nonlinear estimation calculation method of the present invention will be verified by comparison with simplified experimental cases, the signal generated by the source is a pseudo-random binary sequence, the sequence length is 30000, the Modulation order of the M-order Modulation module is M16, i.e., the Modulation mode is Quadrature Amplitude Modulation (QAM), the shaping filter is a Root-Raised Cosine filter (SRRC), the Roll-off coefficient (Roll-off) α is 0.5, the sampling rate of the analog-to-digital converter is fsDAC10 MSps. The up-converter up-converts the signal to a carrier frequency fc2.4 GHz. The radio frequency transmitter (linear) has a linear gain G-10. An additive white gaussian Noise generator adds white Noise To the output Signal with a Signal-To-Noise Ratio (SNR) of 20 dB. Radio frequency receiver (linear) is a linear attenuation Att0.1. A down converter down converts the radio frequency signal to baseband. The filter low-pass filters the baseband signal. The sampling rate of the analog-to-digital converter is fsADC10 MSps. The digital signal processor implements the nonlinear evaluation method shown in fig. 2 and obtains a nonlinear evaluation value.
Fig. 6 is a constellation diagram and a region division relationship thereof after a signal received in a comparison experiment in an embodiment of the present invention passes through a matched filter. The red line in fig. 6 is to divide the whole constellation diagram into 16 regions from left to right and from top to bottom, and the region numbers are #1, #2, #16 in sequence. The quincunx point at the center of each region is an ideal decision point of the region, namely xREF(i) In that respect According to the nonlinear evaluation method, the nonlinear evaluation values of each region are respectively:
the logarithmic value of the nonlinear evaluation value for each area is:
PdB(1)＝-36.50dB，PdB(2)＝-35.25dB，PdB(3)＝-37.74dB，PdB(4)＝-45.05dB，
PdB(5)＝-36.67dB，PdB(6)＝-40.79dB，PdB(7)＝-34.79dB，PdB(8)＝-29.89dB，
PdB(9)＝-43.88dB，PdB(10)＝-34.47dB，PdB(11)＝-39.92dB，PdB(12)＝-41.09dB，
PdB(13)＝-47.78dB，PdB(14)＝-39.11dB，PdB(15)＝-29.46dB，PdB(16)＝-36.00dB。
overall nonlinear estimate of Pall0.0026, logarithmic value Pall_dB＝-25.81dB。
As can be seen from the nonlinear evaluation values obtained above, the communication system in this embodiment # 1 has very small nonlinear strength and excellent linearity. This evaluation result was in accordance with the setup of example # 1, thereby demonstrating the feasibility and accuracy of this nonlinear evaluation method.
Fig. 7 is a flowchart of an experimental system for evaluating nonlinearity according to an embodiment of the present invention, in which a "dsp" module implements the nonlinear evaluation method shown in fig. 2. Specifically, the embodiment includes: information source, M order modulation, shaping filter, digital-to-analog converter, up-converter, radio frequency transmitter (non-linear), additive white Gaussian noise generator, radio frequency receiver (linear), down-converter, filter, analog-to-digital converter, digital signal processor, etc.
The following describes a method for calculating the non-linearity evaluation of the high-order modulation communication system according to the present invention, with reference to specific embodiment # 2.
In this embodiment # 2, simplified experimental cases will be used to comparatively verify the non-linear estimation calculation method of the present invention, the signal generated by the source is a pseudo-random binary sequence, the sequence length is 30000, the Modulation order of the M-th order Modulation module is M16, that is, the Modulation mode is Quadrature Amplitude Modulation (QAM), the shaping filter is a Root-Raised Cosine filter (SRRC), the Roll-off coefficient (Roll-off Factor) α is 0.5, and the sampling rate of the analog-to-digital converter is fsDAC10 MSps. The up-converter up-converts the signal to a carrier frequency fc2.4 GHz. Radio frequency transmitter (non-linear) comprising a linear gain G-10 and a non-linear mathematical model
Is cascaded. The AM-AM curve of the nonlinear mathematical model is shown in fig. 8. An additive white gaussian Noise generator adds white Noise To the output Signal with a Signal-To-Noise Ratio (SNR) of 20 dB. Radio frequency receiver (linear) is a linear attenuation Att0.1. A down converter down converts the radio frequency signal to baseband. The filter low-pass filters the baseband signal. The sampling rate of the analog-to-digital converter is fsADC10 MSps. The digital signal processor implements the nonlinear evaluation method shown in fig. 2 and obtains a nonlinear evaluation value.
Fig. 9 is a constellation diagram and its region division relationship after the signal received in embodiment # 2 passes through the matched filter. The red line in fig. 9 is to divide the whole constellation diagram into 16 regions from left to right and from top to bottom, and the region numbers are #1, #2, #16 in sequence. The quincunx point at the center of each region is an ideal decision point of the region, namely xREF(i) In that respect According to the nonlinear evaluation method, the nonlinear evaluation values of each region are respectively:
the logarithmic value of the nonlinear evaluation value for each area is:
PdB(1)＝-2.72dB，PdB(2)＝-8.38dB，PdB(3)＝-9.15dB，PdB(4)＝-3.25dB，
PdB(5)＝-8.76dB，PdB(6)＝-7.28dB，PdB(7)＝-7.51dB，PdB(8)＝-8.86dB，
PdB(9)＝-8.94dB，PdB(10)＝-7.49dB，PdB(11)＝-7.76dB，PdB(12)＝-8.43dB，
PdB(13)＝-2.89dB，PdB(14)＝-9.04dB，PdB(15)＝-8.50dB，PdB(16)＝-3.05dB。
overall nonlinear estimate of Pall3.02, its logarithm Pall_dB＝4.80dB。
As can be seen from the nonlinear evaluation values obtained above, the communication system in this embodiment # 2 has a certain nonlinearity, and the strength of the nonlinearity is stronger than that in embodiment # 1. The evaluation result is in accordance with the setting of example # 2, and the validity of the nonlinear evaluation method can be proved by comparison.
Example # 3: the modules and parameters were substantially the same as those of example # 2, except that the rf transmitter (non-linear) settings were different. The radio frequency transmitter (non-linear) in this embodiment # 3 includes a linear gain G-10 and a non-linear mathematical model
Is cascaded. Wherein the non-linear mathematical modelThe AM-AM curve of (a) is shown in FIG. 10. The digital signal processor implements the nonlinear evaluation method shown in fig. 2 and obtains a nonlinear evaluation value.
Fig. 11 is a constellation diagram and its region division relationship after the signal received in embodiment # 3 passes through the matched filter. The red line in fig. 11 is to divide the whole constellation diagram into 16 regions from left to right and from top to bottom, and the region numbers are #1, #2, #16 in sequence. The quincunx point at the center of each region is an ideal decision point of the region, namely xREF(i) In that respect According to the nonlinear evaluation method, the nonlinear evaluation values of each region are respectively:
the logarithmic value of the nonlinear evaluation value for each area is:
PdB(1)＝2.67dB，PdB(2)＝-5.06dB，PdB(3)＝-4.94dB，PdB(4)＝2.53dB，
PdB(5)＝-4.99dB，PdB(6)＝2.04dB，PdB(7)＝1.78dB，PdB(8)＝-5.64dB，
PdB(9)＝-5.21dB，PdB(10)＝1.74dB，PdB(11)＝2.04dB，PdB(12)＝-5.63dB，
PdB(13)＝2.51dB，PdB(14)＝-4.91dB，PdB(15)＝-4.83dB，PdB(16)＝2.67dB。
overall nonlinear estimate of Pall＝10.49Logarithmic value P ofall_dB＝10.21dB。
As can be seen from the nonlinear evaluation values obtained above, the communication system in this embodiment # 3 has strong nonlinearity, and the strength of the nonlinearity is stronger than in both embodiments # 1 and # 2. The evaluation result conforms to the settings of the three embodiments, and the effectiveness and the accuracy of the nonlinear evaluation method are verified through comparison.
In summary, the nonlinear evaluation system and the calculation method of the high-order modulation communication system of the present invention calculate the degree of change of the constellation point caused by the nonlinearity to make statistics of the nonlinear influence as an accurate value, thereby effectively solving the problem of nonlinear evaluation in the high-order modulation communication system. The system and the method can reasonably evaluate the influence caused by the nonlinearity, are convenient for carrying out system-level comparison on different nonlinearities, and have advantages in the aspects of universality, accuracy and the like. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (6)
1. A nonlinear evaluation method of a high-order modulation communication system is used for evaluating the nonlinear intensity of the high-order modulation communication system and is characterized in that a radio frequency signal which is transmitted by the high-order modulation communication system and undergoes nonlinear distortion is converted to a baseband, matched filtering is carried out, ideal constellation point judgment is carried out, a constellation diagram is obtained, and the nonlinear intensity of the system is evaluated by calculating the specific change degree of the constellation points; the method adopts a nonlinear evaluation system of a high-order modulation communication system, is used for receiving a radio frequency signal and calculates to obtain a nonlinear evaluation value contained in the radio frequency signal, and the nonlinear evaluation system comprises the following steps: radio frequency signal receiver, down converter, filter, adc, digital signal processor:
the radio frequency signal receiver is used for receiving a radio frequency signal xRF(t) amplifying or attenuating the radio frequency signal to a suitable power range by using a low noise amplifier or an attenuator;
the down converter comprises a local oscillator signal generator and a down conversion link, wherein the down conversion link mixes a local oscillator signal generated by the local oscillator signal generator with a radio frequency signal received by a radio frequency signal receiver to obtain an analog signal x after down conversionD(t)；
The filter is used for filtering the analog signal after down conversion to obtain the analog signal x after filteringF(t)；
The analog-to-digital converter is used for converting the analog signal after filtering into a digital signal xF(n)；
The digital signal processor comprises a low-pass filter, a matched filter, an ideal constellation point judgment module and a nonlinear evaluation algorithm module, wherein:
the low-pass filter is used for the digital signal xF(n) low-pass filtering to obtain digital signal xL(n)；
The matched filter is used for the digital signal xL(n) performing matched filtering to obtain a digital signal xM(m)；
The ideal constellation point decision module is used for judging the digital signal xM(m) making ideal constellation point judgment to obtain digital signal xREF(m)；
The nonlinear evaluation algorithm module is used for realizing a nonlinear evaluation method of a high-order modulation communication system, and is used for carrying out nonlinear evaluation on a digital signal xM(m) and xREF(m) comparing, calculating and giving a nonlinear evaluation value; the nonlinear evaluation method comprises the following steps:
step 1, area division:
signal x processed by ideal constellation point decision moduleREFThe number of values of (m) isLimited, for M-order modulation systems, xREFThe number of values of (m) is 2MThe complex coordinate plane is divided into 2 according to the principle of ideal constellation point judgmentMA decision region; thus, all data points x may be mappedREF(M), M1, 2, …, M, is divided into 2MGroup data xREF(mi) Where M is the total length of the data, i ═ 1,2, …,2MThe values of each set of data being equal, i.e. for all mi，xREF(mi)＝xREF(i) And is a constant; according to xM(m) and xREF(m) mapping of all data points xM(M), M1, 2, …, M divided into 2MGroup data xM(mi)；
And step 2, calculating a region nonlinear evaluation value:
for the ith area of the division, the value range is i-1, 2, …,2MFirst, for data set xM(mi) Taking the average to obtain the average value xMavg(i) (ii) a Then, the non-linear evaluation values P (i) and their logarithm values P in the region are calculated respectivelydB(i)：
PdB(i)＝10·log10(P(i))，
Wherein M isiIs miThe number of values of (a);
and 3, calculating the overall nonlinear evaluation value:
weighting the nonlinear evaluation values of all the regions to calculate the nonlinear evaluation value P of the wholeallAnd its logarithmic value Pall_dB：
Pall_dB＝10·log10(Pall)。
2. The method for nonlinear estimation in a higher order modulation communication system as claimed in claim 1, wherein in step 1, the specific steps of the region partition method include:
s1, area division starts;
s2, obtaining modulation order M, and resetting counter i to 0;
s3, the counter starts counting i ═ i + 1;
s4, for the ith value xREF(i) At all data points xREF(M), where M is 1,2, …, M, finding a data point x that satisfies the conditionREF(mi)＝xREF(i) M ofiA value;
s5, store miA value;
s6, according to miDividing the ith group of ideal decision signals xREF(mi)＝xREF(i)；
S7, according to miDividing the signal x before the i-th decisionM(mi)；
S8, judging whether 2 is traversed or notMA decision region, i.e. i-2M(ii) a If so, completing the area division; if not, the process loops to step S3 until the traversal condition is satisfied.
3. The nonlinear estimation method of a higher order modulation communication system as claimed in claim 1, wherein in the step 2, the specific steps of the region nonlinear estimation value calculation method include:
s1, the calculation of the area nonlinear evaluation value is started;
s2, acquiring packet data, resetting counter i to 0;
s3, the counter starts counting i ═ i + 1;
s4, calculating m of the ith packetiNumber of values Mi；
S5, signal x before decision of ith packetM(mi) Averaging to obtain the average value x of the signals before the decision of the ith groupMavg(i)；
S6, based on the nonlinear evaluation value calculation formula in the region, finds the nonlinear evaluation value p (i) of the i-th region:
wherein M isiIs miThe number of values of (a);
s7, calculating the logarithm value P of the non-linear evaluation value P (i) of the ith areadB(i)：
PdB(i)＝10·log10(P(i))；
S8, judging whether 2 is traversed or notMA decision region, i.e. i-2M(ii) a If so, completing the calculation of the nonlinear evaluation value of the area; if not, the process loops to step S3 until the traversal condition is satisfied.
4. The nonlinear evaluation method of the higher order modulation communication system according to claim 1, wherein the nonlinear evaluation algorithm module is implemented in a specific process comprising: and (3) carrying out regional division on the signals processed by the ideal constellation point judgment module, then calculating a regional nonlinear evaluation value, and further calculating to obtain a system overall nonlinear evaluation value.
5. The method of claim 1 wherein the carrier frequency of the rf signal is fRFWherein the frequency f of the local oscillator signal generated by the local oscillator signal generatorLOLess than or equal to the carrier frequency f of the received radio frequency signalRFI.e. fLO≤fRF。
6. The method as claimed in claim 1, wherein the higher order modulation communication system further comprises a source, an M-order modulation, a shaping filter, a digital-to-analog converter, an up-converter, a linear or non-linear rf transmitter, an additive white gaussian noise generator at the rf receiver front end.
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