CN107370710B - Helicopter rotor shielding high-order modulation signal compensation method - Google Patents
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Abstract
The invention relates to the technical field of satellite communication for preventing helicopter rotor wing shielding, in particular to a method for compensating a helicopter rotor wing shielding high-order modulation signal. The method of the invention aims at a high-order modulation mode, carries out energy compensation on a high-order signal shielded by a helicopter rotor wing, and can solve the problem that in helicopter satellite communication, due to the attenuation influence of the rotor wing shielding on the signal amplitude, the error code performance can be reduced by directly utilizing the shielding signal. By using the method of the invention, the data constellation of the occlusion part can be improved; when the shielding utilization rate is the same, the signal transmission error code performance is better; when the same performance is achieved, the shielding utilization rate is higher. The method is simple to implement, and can be implemented by using simple multiplication and division operation and comparison operation. The application scenes of high-order modulation modes with different orders can be met by setting the corresponding signal-to-noise ratio threshold and the corresponding compensation peak value threshold, and the MQAM signals (M > 4) such as 16QAM, 32QAM, 64QAM and the like have a large application range effectively, and the characteristic of simple realization is achieved.
Description
Technical Field
The invention relates to the technical field of satellite communication for preventing helicopter rotor wing shielding, in particular to a method for compensating a helicopter rotor wing shielding high-order modulation signal.
Background
The satellite communication has the characteristics of long communication distance, low relative cost, large coverage area, large communication capacity, no influence of geographical conditions and natural disasters and the like; in the aircraft, the helicopter can fly at low altitude and low speed, has low requirements on take-off and landing conditions, and has a series of advantages of high flexibility and the like; based on the advantages of the helicopter and the satellite communication, the helicopter adopting the satellite communication can be widely applied to scenes such as medical rescue, disaster relief and life saving, emergency rescue, geological exploration, forest protection and fire extinguishing after the helicopter and the satellite communication are combined.
However, with the development of technology, the requirements for real-time high-quality communication in various application scenes are continuously increased, so that the satellite communication adopted by the helicopter is forced to have higher communication speed; a common method for improving the communication rate of the helicopter satellite is to use a high-order modulation mode, which can meet the real-time high-rate communication requirement in the helicopter satellite communication to a certain extent; however, the high-order modulation mode still has some problems to be solved; specifically, in helicopter satellite communication, signal transmission between the communication antenna and the satellite is easily blocked by the helicopter rotor, so that the helicopter satellite communication signal is influenced by periodic fading. Communicating with rotor blade clearance is an effective way to combat rotor blade occlusion, but in this way the signal actually occluded by the rotor blade is wasted.
The amplitude of the signal is attenuated due to the shielding of the helicopter rotor, but the polarity and the phase of the signal are not changed, so that the demodulation accuracy cannot be influenced by the amplitude attenuation after the low-order phase modulation signals such as QPSK and the like are shielded by the rotor; after the amplitude of the multi-amplitude high-order modulation signal such as 16QAM or 32QAM is affected, the constellation point may deviate from the originally correct decoding area, as shown in fig. 7a, thereby causing an error, and the direct utilization may bring about a serious error effect. Therefore, in order to realize a limited bandwidth high-speed communication scheme, when a high-order signal of a shielding part is utilized, corresponding signal amplitude compensation is performed on the high-order modulation signal, which is very necessary; in the prior art, AGC (automatic gain control) is usually used to compensate the signal, and the amplitude of the transmission signal is compensated to a target value, which is effective for phase modulation signals with equal amplitude, such as QPSK signal; however, for high-order signals with multiple amplitudes such as 16QAM, AGC not only compensates the signals of the blocked part, but also compensates the signals with originally different amplitudes to the targetAmplitude, which causes some originally correct constellation points to deviate, thereby introducing additional errors. As shown in fig. 5a and 5b, the circle Re in the constellation is the average amplitude of the 16QAM signal
Being circles of radii, AGC will make the radii be respectively
And
the constellation point on the circle of (1) takes the origin of coordinates as the center, and the compensation is carried out near the circle Re, so that the error of the constellation point is directly caused; therefore, the AGC is not suitable for compensating high-order signals in helicopter communication, and other technologies are needed to compensate for the high-order signals blocked by the rotor in helicopter communication.
Disclosure of Invention
The invention aims to solve the problem that in helicopter communication in the prior art, communication signals between a satellite communication antenna and a satellite are easily blocked by a rotating helicopter rotor, so that the utilization rate of the communication signals is not high, and provides a signal compensation method for helicopter satellite communication, which has higher communication efficiency and better communication effect.
In order to achieve the above purpose, the invention provides the following technical scheme:
a helicopter rotor shelters from high order modulation signal compensation method includes:
a: according to the received signals, combining the shielding state of the helicopter rotor, parameterizing the shielding state of the rotor to obtain a shielding curve h (t) of the helicopter rotor;
b: according to the helicopter rotor wing shielding curve h (t) obtained by processing, calculating by taking reciprocal to obtain a rotor wing shielding signal primary compensation model curve
C: according to different signal-to-noise ratios of signals, carrying out topping processing on the compensation curve function, setting the peak value of a matched compensation curve, and acquiring a final compensation function c (t); the peak value of the compensation curve is set to restrain the compensation of the signal with lower signal-to-noise ratio;
d: the received signal s (t) is multiplied by the final compensation function c (t) to obtain a compensated signal r (t). Specifically, the received signal s (t) is multiplied by the compensation function c (t) according to the corresponding time, that is, actually, the value of each time of the signal s (t) is multiplied by the value (compensation coefficient) of the compensation function c (t) at the time, so as to obtain the compensated signal r (t).
Further, in the step a, a helicopter rotor occlusion curve h (t) is obtained by using the following formula:
t is more than or equal to 0 and less than or equal to T, S is the ratio of the average value of the amplitude of the shielding signal to the original signal when the rotor wing is completely shielded, the value range is more than 0 and less than or equal to 1, T1,t2,t3,t4Respectively an occlusion start time, a complete occlusion end time, an occlusion end time, t1,t2,t3,t4T is more than or equal to 01≤t2≤t3≤t4T is less than or equal to T, and T is a helicopter rotor wing shielding period.
Further, in the step C, a signal-to-noise ratio threshold SNR is setthresholdGet 0dB, get SNR with this thresholdthresholdCompensation peak threshold value G of corresponding compensation curvethreshold，GthresholdWith the signal-to-noise ratio threshold SNRthresholdThe setting is determined according to the relationship0+20log10h(t0)＝SNRthreshold，Gthreshold＝g(t0) Wherein SNR is0The signal-to-noise ratio of the signal when the current transmission is not shielded. For the primary compensation model curve g (t), if g (t)x)＞GthresholdLet g (t)x)＝GthresholdUsing the formula
Acquiring a final compensation function c (t); this is because the occlusion process is actually the process of reducing the signal-to-noise ratio of the signal, if the signal-to-noise ratio of the signal is too low, the noise is excessively amplified by directly using the function g (t) for compensation, and in order to suppress the noise, the threshold SNR is setthreshold0dB, only for SNR > SNRthresholdIs compensated according to g (t), the signal-to-noise ratio SNR ≦ SNRthresholdAccording to SNR of partial signalthresholdAnd (6) processing.
Compared with the prior art, the invention has the beneficial effects that: the method of the invention aims at a high-order modulation mode, carries out energy compensation on a high-order signal shielded by a helicopter rotor wing, and can solve the problem that in helicopter satellite communication, due to the attenuation influence of the rotor wing shielding on the signal amplitude, the error code performance can be reduced by directly utilizing the shielding signal. By using the method of the invention, the data constellation of the occlusion part can be improved; when the shielding utilization rate is the same, the signal transmission error code performance is better; when the same performance is achieved, the shielding utilization rate is higher. The method is simple to implement, and can be implemented by using simple multiplication and division operation and comparison operation. By setting the corresponding SNRthresholdAnd GthresholdApplication scenarios of high-order modulation modes with different orders can be met, such as MQAM signals (M) of 16QAM, 32QAM, 64QAM and the like>4) The method has the characteristics of wide application range and simple realization.
Description of the drawings:
FIG. 1 is a signal trace diagram of a compensation method provided by the present invention;
FIG. 2 is a diagram of a parameterized occlusion model of the present invention;
FIG. 3 is a diagram of a compensation model calculated according to an occlusion model according to the present invention;
FIG. 4 is a diagram of a final compensation model obtained by the signal-to-noise ratio (SNR) topping process according to the present invention;
fig. 5a and 5b are specific embodiments of 16QAM signal constellation before and after AGC compensation, respectively;
FIG. 6 is a schematic block diagram of an example of pre-compensation for a high-order signal of an occlusion part;
FIG. 7a and FIG. 7b are the comparison of the constellation before and after compensation of the high-order signal of the shielding part in the case of no noise;
fig. 8a and 8b are the constellation comparison before and after compensation of the occluded part of the high-order signal when the SNR is 20dB, respectively;
fig. 9 is a block diagram of an exemplary time-diversity-free transmission system applied to 64QAM signal transmission in the present invention;
FIG. 10 is a schematic diagram illustrating data gap transmission performed by the time diversity free transmission system in FIG. 9;
FIG. 11a is a diagram illustrating the performance of the time diversity-free 64QAM transmission error bit in the time diversity-free transmission system of FIG. 9;
FIG. 11b is a bit error diagram of the time diversity free transmission system of FIG. 9;
FIG. 12 is an exemplary block diagram of a 64QAM signal transmission time diversity transmission system in accordance with the present invention;
fig. 13 is a schematic diagram of data retransmission of the time diversity transmission system of fig. 12;
fig. 14 is a graph of bit error performance for the time diversity transmission system of fig. 12.
Detailed Description
The invention is described in further detail below with reference to the figures and the embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.
The method obtains the shielding state of the helicopter rotor by using a method based on the shielding prediction of the helicopter rotor, is used for calculating a preliminary compensation model function after parameterization, then carries out topping optimization processing on the compensation function according to signal-to-noise ratio to obtain a final compensation function, and then multiplies the compensation function by a received signal correspondingly to obtain a compensated signal. This will be explained in detail below.
As shown in fig. 1, the present embodiment provides a method for compensating a helicopter rotor blocking high-order modulation signal, including:
step 100: according to the received signals, combining the shielding state of the helicopter rotor, parameterizing the shielding state of the rotor to obtain a shielding curve h (t) of the helicopter rotor; specifically, a helicopter rotor wing shielding curve h (t) is obtained by using the following formula:
t is more than or equal to 0 and less than or equal to T, S is the ratio of the average value of the amplitude of the shielding signal to the original signal when the rotor wing is completely shielded, the value range is more than 0 and less than or equal to 1, T1,t2,t3,t4Respectively an occlusion start time, a complete occlusion end time, an occlusion end time, t1,t2,t3,t4T is more than or equal to 01≤t2≤t3≤t4T, T is the helicopter rotor shading period, and the period T is typically shown in figure 2.
S200: according to the helicopter rotor wing shielding curve h (t) obtained by processing, calculating by taking reciprocal to obtain a rotor wing shielding signal primary compensation model curve
This is due to the occlusion signal s (t) x (t) h (t), where x (t) is the original transmitted signal, due to the compensation signal rc(t) s (t) g (t) in order to restore the compensated signal to the original signal, i.e. rc(t) x (t), the compensation function is obtained
As shown in particular in figure 3.
S300: setting a signal-to-noise ratio threshold SNRthresholdGet 0dB, get SNR with this thresholdthresholdCompensation peak threshold value G of corresponding compensation curvethreshold，GthresholdWith the signal-to-noise ratio threshold SNRthresholdThe setting is determined according to the relationship0+20log10h(t0)＝SNRthreshold，Gthreshold＝g(t0) Wherein SNR is0The signal-to-noise ratio of the signal when the current transmission is not shielded. For the primary compensation model curve g (t), if g (t)x)＞GthresholdLet g (t)x)＝GthresholdUsing the formula
Acquiring a final compensation function c (t); this is because the occlusion process is actually the process of reducing the signal-to-noise ratio of the signal, if the signal-to-noise ratio of the signal is too low, the noise is excessively amplified by directly using the function g (t) for compensation, and in order to suppress the noise, the threshold SNR is setthreshold0dB, only for SNR > SNRthresholdIs compensated according to g (t), the signal-to-noise ratio SNR ≦ SNRthresholdAccording to SNR of partial signalthresholdAnd (6) processing. As shown in particular in fig. 4.
S400: the received signal s (t) is multiplied by the final compensation function c (t) to obtain a compensated signal r (t). Specifically, the received signal s (t) is multiplied by the compensation function c (t) according to the corresponding time, that is, actually, the value of each time of the signal s (t) is multiplied by the value (compensation coefficient) of the compensation function c (t) at the time, so as to obtain the compensated signal r (t).
The invention will be further described with reference to a specific example.
Example one: the influence of the compensation method on the constellation points:
example one simulation platform used was MATLAB R2014a, and the occlusion model used was as shown in FIG. 2, with an occlusion rate of 20%, which is the ratio of the occlusion time to the occlusion period, i.e. (t)4-t1) And the shielding descending time and the shielding ascending time respectively account for 40 percent of the shielding time, the complete shielding time accounts for 20 percent of the shielding time, the signal energy attenuation is 20dB when the shielding is complete, the signal energy attenuation is 0dB when the shielding is not available, and the shielding descending and the shielding ascending of the shielding model curve are linear change processes.
In an example I, 64QAM modulation signals are used, shielded high-order signals are obtained through shielding model processing, and simulated receiving-end helicopter shielding high-order signals are obtained through noise adding. And calculating a compensation function c (t) according to a calculation formula, and compensating the received signal, wherein an example schematic block diagram is shown in fig. 6. The constellation diagrams before and after the compensation of the partial high-order modulation signal are shielded under the conditions of no noise and the signal-to-noise ratio SNR being 20dB, as shown in fig. 7a and fig. 7b, and fig. 8a and fig. 8 b.
As shown in fig. 7a and 7b, which are constellation diagrams before and after compensation under a noise-free condition, respectively, the amplitude of the high-order modulation signal is attenuated due to occlusion, the signal constellation point is shifted to the origin of coordinates and deviates from the original constellation point region, and an error may be caused by directly using the signal. And the shading compensation method can well compensate the signal back to the original constellation point region.
As shown in fig. 8a and 8b, the constellation diagrams before and after compensation under the condition that the SNR is 20dB, the shielded noisy high-order modulation signal constellation points are mainly concentrated in the middle area with the origin of coordinates as the center, and the same error is caused by direct utilization, and after the shielding compensation, the constellation points can be well compensated back to the original constellation point area. The comparison shows that the occlusion compensation can greatly reduce the error of the signal constellation point caused by the occlusion deviation from the original region.
Example two: effect of compensation method on the Performance of time-diversity-free Transmission systems
The simulation platform in the second example and the used shielding model are the same as the first example, the helicopter rotor shielding-resistant time-free diversity transmission system shown in fig. 9 is set up, the receiving end is respectively provided with two processing schemes of shielding signal compensation and non-compensation, and the final result is compared to verify the effect brought by the use method of the invention.
A transmitting end randomly generates 60480bits binary data, and then block LDPC coding is carried out on the binary data, wherein the LDPC coding length is 2016, and the code rate is 1/2; interleaving the LDPC coded data; carrying out 64QAM symbol mapping on the interleaved data, wherein the mapping uses a Gray coding mode; carrying out interval sending according to the shielding condition of the helicopter rotor and the shielding utilization rate, as shown in FIG. 10; the transmission signal is processed by a rotor shielding module and a Gaussian noise module in sequence, and an actual transmission channel is simulated; the receiving end receives signals and divides the signals into two paths: the first path calculates a compensation function c (t) according to a calculation formula, compensates the signals, performs corresponding 64QAM soft demodulation on the compensated signals, de-interleaves, processes LDPC decoding baseband data, directly performs the same subsequent processing as the first path without performing shielding compensation on the second path, and performs two position statistics 6 (a) and (b) in FIG. 9 respectivelyThe bit error rate after 4QAM demodulation and the bit error rate after LDPC decoding respectively correspond to FIG. 11a and FIG. 11b, and the conditions are respectively set, wherein (1) 50% of the occlusion utilization rate is compensated, (2) 50% of the occlusion utilization rate is uncompensated, (3) 20% of the occlusion utilization rate is uncompensated, and the influence of the contrast verification compensation method on the signal transmission performance is defined, wherein the occlusion utilization rate is defined as the ratio of the data length utilized by the occlusion part to the total data length of the occlusion part, as shown in FIG. 10, namely the occlusion utilization rate β is 2Td/(t4-t1)。
Fig. 11a shows a graph of the bit error performance of 64QAM signal transmission without time diversity in gaussian channel. When the SNR is less than 5.5dB, the compensation method has no great influence on the bit error performance of the signal due to large noise; when the SNR is greater than 5.5dB, comparing the curve 2, the curve 3 and the curve 4 in fig. 11a, it can be found that, when there is no shielding compensation, the performance is slightly worse than the pure gaussian noise channel condition at 20% shielding utilization rate, and the transmission performance is further decreased at 50% shielding utilization rate, that is, the higher the signal shielding utilization rate is, the greater the signal transmission error bit performance loss is; comparing the curve 1 and the curve 2 in fig. 11a, it is found that the transmission performance is obviously better than that of the uncompensated case of 50% shielding utilization rate when the compensation is available for 50% shielding utilization rate (when BER is less than 0.05, the performance differs by 1dB), which indicates that the performance loss caused by improving the signal shielding utilization rate can be compensated to a certain extent by using the shielding compensation method, that is, the transmission performance with shielding compensation is better when the shielding utilization rate is the same; comparing curve 1 and curve 3 in fig. 11a, it is found that the performance of the 50% shielding utilization rate with compensation is similar to that of the 20% shielding utilization rate without compensation, which indicates that the shielding utilization rate with shielding compensation is higher when the same transmission performance is achieved.
Fig. 11b is a diagram showing the bit error performance of the transmission system without time diversity in the gaussian channel. When there is no time diversity, after de-interleaving LDPC decoding, the curves in fig. 11b are compared, and by combining the above result analysis, the occlusion compensation method still has the following conclusions for the transmission system without time diversity: by using the shielding compensation method, the system error code performance is better when the shielding utilization rate is the same; when the same system error code performance is achieved, the shielding utilization rate is higher. Fig. 11b is further illustrated in comparison with fig. 14 in example three.
Example three: the impact of the compensation method on the performance of the time diversity transmission system:
the simulation platform in the third example and the used shielding model are the same as the first example, the helicopter rotor shielding time diversity transmission system shown in fig. 12 is set up, two processing schemes of shielding signal compensation and non-compensation are respectively arranged at the receiving end, and the final result is compared to verify the effect brought by the use method of the invention.
A transmitting end randomly generates 60480bits binary data, and then block LDPC coding is carried out on the binary data, wherein the LDPC coding length is 2016, and the code rate is 1/2; interleaving the LDPC coded data; carrying out 64QAM symbol mapping on the interleaved data, wherein the mapping uses a Gray coding mode; the mapped symbols are subjected to time diversity processing according to the rotor wing shielding condition at a repetition rate of 80%, as shown in fig. 13, so as to resist the helicopter rotor wing shielding and ensure normal communication; the transmission signal is processed by a rotor shielding module and a Gaussian noise module in sequence, and an actual transmission channel is simulated; the receiving end receives signals and divides the signals into two paths: the first path calculates a compensation function c (t) according to a calculation formula, compensates the signals, performs subsequent recombination, performs 64QAM soft demodulation, deinterleaves, performs LDPC decoding processing, and finally counts bit error rate, and the second path does not perform occlusion compensation and directly performs subsequent processing which is the same as the first path; the conditions are set separately: (1) the method comprises the following steps of (1) compensating for 50% of shielding utilization rate, (2) uncompensating for 50% of shielding utilization rate, and uncompensating for 20% of shielding utilization rate, wherein the influence of a compensation method on signal transmission performance is verified in a contrast mode.
The bit error performance diagram of the system is shown in fig. 14, and comparison shows that when the SNR is less than 5dB, the compensation method has no great influence on the bit error performance of the signal due to the large noise; when SNR is more than 5dB, the comparison curves 1 and 2 show that BER is less than 10 under the condition that the shielding utilization rate is 50 percent-3The bit error performance of the existing shielding compensation is about 0.2dB better than that of the non-shielding compensation, namely, the transmission performance of the existing shielding compensation is better when the shielding utilization rate is the same; comparing curves 1 and 3, it is found that 50% of the occlusion utilization rate has the bit error performance of occlusion compensation and 20% of the occlusion utilization rate has no bit error performance of occlusion compensationSimilarly, it can be seen that the utilization of the signal of the occluded part with occlusion compensation is higher than that of the non-occlusion compensation when the same performance is achieved, and the utilization of the signal with occlusion compensation is higher than that of the non-occlusion compensation by about 30% when the same performance is achieved in the third example. In combination with the above result analysis, the occlusion compensation method still has the following conclusions for the time diversity transmission system: by using shielding compensation, the system error code performance is better when the shielding utilization rate is the same; when the same system performance is achieved, the shielding utilization rate is higher.
Comparing curves 1 and 3 in fig. 11b and 14, it is found that the uncompensated case of 20% occlusion utilization is better than the compensated case of 50% occlusion utilization without time diversity, and that the two performances are almost identical with time diversity, due to the fact that the combining gain is larger for the case of 50% occlusion utilization than for the case of 20% occlusion utilization. Comparing fig. 11b and fig. 14, it is found by combining the comparison of the spectrum efficiency of different conditions in table one that the error code performance of the time diversity system is better than that of the time diversity-free system, and the channel spectrum efficiency of the time diversity-free system is higher, but the occlusion compensation method of the present invention has significant effect in both systems. The occlusion compensation method of the invention is not only effective for 64QAM signals, but also effective for other high-order modulation modes with multiple amplitudes.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the above embodiments, and various modifications or alterations can be made by those skilled in the art without departing from the spirit and scope of the claims of the present application.
Claims (3)
1. A helicopter rotor shielding signal compensation method is characterized by comprising the following steps: the method comprises the following steps:
step A: according to the received signals, combining the shielding state of the helicopter rotor, parameterizing the shielding state of the rotor to obtain a shielding curve h (t) of the helicopter rotor;
and B: according to the helicopter rotor wing shielding curve h (t) obtained by processing, calculating by taking reciprocal to obtain a rotor wing shielding signal primary compensation model curve
And C: according to different signal-to-noise ratios of signals, carrying out topping processing on the compensation curve function, setting the peak value of a matched compensation curve, and acquiring a final compensation function c (t);
step D: the received signal s (t) is multiplied by the final compensation function c (t) to obtain a compensated signal r (t).
2. A helicopter rotor blockage signal compensation method according to claim 1, wherein: in the step A, a helicopter rotor wing shielding curve h (t) is obtained by using the following formula:
t is more than or equal to 0 and less than or equal to T, S is the ratio of the average value of the amplitude of the shielding signal to the original signal when the rotor is completely shielded, the value range is more than 0 and less than or equal to 1, T1, T2, T3, T4 are shielding starting time, complete shielding ending time and shielding ending time respectively, T1, T2, T3 and T4 meet the conditions that T1 is more than or equal to 0 and less than or equal to T2 is more than or equal to T3 and less than or equal to T4 and less than or equal to T, and T is the shielding period of.
3. A helicopter rotor blockage signal compensation method according to claim 2 wherein: in the step C, a signal-to-noise ratio threshold SNRthreshold is set to 0dB, a compensation peak threshold gthrehold of a compensation curve corresponding to the threshold SNRthreshold is obtained, and a formula is used
A final compensation function c (t) is obtained.
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| CN104660323A (en) * | 2015-03-10 | 2015-05-27 | 中国人民解放军国防科学技术大学 | Rotor wing shielding resisting satellite communication method for helicopter |
| WO2016060816A1 (en) * | 2014-09-25 | 2016-04-21 | Sikorsky Aircraft Corporation | Steady state differential roll moment control with automated differential lateral control |
| CN105847203A (en) * | 2016-03-18 | 2016-08-10 | 熊猫电子集团有限公司 | High-precision detection and compensation method for Doppler frequency shift in airborne satellite communication |
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| CN104660323A (en) * | 2015-03-10 | 2015-05-27 | 中国人民解放军国防科学技术大学 | Rotor wing shielding resisting satellite communication method for helicopter |
| CN105847203A (en) * | 2016-03-18 | 2016-08-10 | 熊猫电子集团有限公司 | High-precision detection and compensation method for Doppler frequency shift in airborne satellite communication |
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