CN110868281A - Anti-blackout communication method based on carrier aggregation and frequency diversity - Google Patents
Anti-blackout communication method based on carrier aggregation and frequency diversity Download PDFInfo
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- CN110868281A CN110868281A CN201911079289.XA CN201911079289A CN110868281A CN 110868281 A CN110868281 A CN 110868281A CN 201911079289 A CN201911079289 A CN 201911079289A CN 110868281 A CN110868281 A CN 110868281A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0003—Two-dimensional division
- H04L5/0005—Time-frequency
- H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
- H04L5/001—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT the frequencies being arranged in component carriers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0053—Allocation of signaling, i.e. of overhead other than pilot signals
- H04L5/0055—Physical resource allocation for ACK/NACK
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0091—Signaling for the administration of the divided path
- H04L5/0096—Indication of changes in allocation
- H04L5/0098—Signalling of the activation or deactivation of component carriers, subcarriers or frequency bands
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Abstract
The invention provides an anti-blackout communication method based on carrier aggregation and frequency diversity.A ground distance and a shell temperature of an aircraft are detected after the aircraft enters an atmosphere, and communication link interruption state detection is carried out after the ground distance and the shell temperature reach set parameter ranges; after a communication link is interrupted, communication information is respectively modulated to subcarriers of different frequency bands through an OFDM carrier aggregation technology, and the same transmission information is modulated on each subcarrier; the receiving end demodulates the data on the corresponding sub-carrier to obtain the backup of a plurality of transmitted information, and combines and judges each information through frequency diversity to finally recover the transmitted information.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to an anti-black-obstacle communication method.
Background
The black barrier is formed by the fact that when the aircraft returns to the earth, the aircraft passes through the atmosphere at a high speed, the aircraft rubs with air to form high temperature, the air is ionized at the high temperature and comes out of free electrons, a plasma sheath is formed around the aircraft as a result of interaction of the air and the free electrons, and communication electromagnetic waves cannot propagate in the plasma sheath. The black barrier can seriously affect the measurement and control and information transmission of the aircraft.
The prior art can resist black-barrier communication by changing the magnetic field strength. This Method is described in The document A New Method for Removing The Blackout Problem on Reentry Vehicles, R.L. Stenzel and J.M. Urrutia et al: the pulse current is immersed in an insulated conductor of the plasma to generate a rising magnetic field, so that electrons are magnetized and are driven out of the magnetic field to form a Hall electric field to drive out ions, and the purpose of consuming the ions to form a communication window is achieved. Patent No. 2015106398892 of harbin industrial university also discloses a method for mitigating black barrier communication by changing the magnetic field strength, wherein a pulsed magnet is controlled to generate a magnetic field of more than 1T in the order of milliseconds, and the magnetic field magnetizes electrons near the antenna of the spacecraft to generate a magnetic freezing effect, so as to form a window through which electromagnetic waves pass through the plasma sheath, thereby mitigating the black barrier communication of the spacecraft. The method needs a large-scale discharge device, and if the method is applied to practice, a specific discharge device needs to be installed on the aircraft, so that the design cost of the aircraft is increased, and the weight of the aircraft is increased. This approach is expensive and not very effective.
The prior art can adopt a method of changing communication frequency to resist black-out communication. The inventor's anky application patent "reentry vehicle communication system for black barrier breaching" (patent No. 201610056782X) discloses a method for black barrier communication breaching by means of a laser communication transmitter, where the reentry vehicle can transmit information outwards in the form of laser light, and thus can still transmit information outwards in the black barrier area. The patent application No. 2018113995548 of the institute of electronic engineering of China institute of engineering and physics, application number is a terahertz wireless transmitter for high-speed wireless communication in black areas discloses a terahertz wireless transmitter for high-speed wireless communication in black areas, the working terahertz frequency band is higher than 300GHz, penetration of plasma sheath can be realized, directional and adjustable directional beams with beam directions can be generated, and transmission of wireless communication signals can be realized. The patent application No. 2017100491401 of Nanjing aerospace university discloses a method suitable for black-mask-area X-ray communication in the reentry process of an aircraft, and the method utilizes controllable X-rays with different energies to perform reliable uplink data communication process, thereby effectively solving the problem of black-mask-area communication. The wireless transmission mode using laser, terahertz wave or X-ray as a communication carrier has very high carrier frequency, and has the problems of short communication distance, large transmitting power, high orientation requirement, easy shielding by cloud layers and the like.
The prior art can also alleviate the blackout problem by physically cooling or changing the profile of the aircraft. PriyankaGarg, Abhishek Kumar Dodiyal et al, in the document reduction RF Blackout Reducing Re-Entry Reusable Launch Vehicle, teaches the use of quenchers to cool the plasma, requiring manipulation of plasma conditions and electron density in a localized region around the communications antenna to facilitate radio frequency transmission; or the influence of plasma on communication signals is reduced as much as possible by an aerodynamic forming design, and the cost is low. Both of these methods, however, require changes in the profile of the aircraft and are not easily implemented.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides an anti-black-barrier communication method based on carrier aggregation and frequency diversity, which is used for anti-black-barrier communication on the premise of not changing the appearance of an aircraft and not increasing additional devices, increases the high-frequency-band communication distance, reduces the transmission power and the orientation requirement and is not easy to be shielded.
The technical scheme adopted by the invention for solving the technical problem comprises the following steps: after the aircraft enters the atmosphere, detecting the ground distance and the shell temperature of the aircraft, and detecting the interruption state of a communication link when the ground distance and the shell temperature reach the set parameter range; after a communication link is interrupted, communication information is respectively modulated to subcarriers of different frequency bands through an OFDM carrier aggregation technology, and the same transmission information is modulated on each subcarrier; the receiving end demodulates the data on the corresponding sub-carrier to obtain the backup of a plurality of transmitted information, and combines and judges each information through frequency diversity to finally recover the transmitted information.
And when the ground distance of the aircraft reaches 35-80Km and the shell temperature reaches above 2000 ℃, the communication link interruption state is detected.
When the communication link interruption state is detected, the aircraft and the ground station send out handshake signals to wait for feedback signals of the handshake signals; when the aircraft and the ground station receive the feedback signal within a set time interval, the aircraft and the ground station do not reach a blackout area, request to establish communication connection, keep the original communication state and repeat the operation; otherwise, sending out handshake signals again, waiting for feedback signals of the handshake signals, confirming that the feedback signals are not received, and judging that the communication link is interrupted.
The invention has the beneficial effects that: the bandwidth span is increased by carrier aggregation, and meanwhile, the plurality of subcarriers are used for up-and-down transmission, so that the problem of communication interruption caused by the blockage of all carriers in a communication frequency band by a black barrier is avoided; compared with the prior art, the appearance of the aircraft is not required to be changed, and an additional device is not required to be added; by adopting the carrier aggregation technology combining low frequency, intermediate frequency and high frequency, better transmission carrier waveform is obtained, and the problems of short communication distance, large transmitting power, high orientation requirement, easy shielding and the like are solved.
Drawings
Fig. 1 is a schematic diagram of the technical solution of the present invention, wherein (a) is a schematic diagram of a carrier aggregation principle, and (b) is a schematic diagram of an OFDM principle.
Fig. 2 is a schematic diagram of a carrier aggregation-based anti-blackout communication mechanism.
Fig. 3 is a schematic block diagram of a communication transceiver based on carrier aggregation and frequency diversity.
Fig. 4 is a graph showing the attenuation characteristics of the plasma sheath for the communication signal in different frequency bands.
Fig. 5 is a schematic diagram of a bit error rate curve when the method of the present invention is applied to a black-fault communication scenario.
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.
After the aircraft enters the atmosphere, the invention assists in detecting the state of the interruption of the communication link by detecting the state information such as the ground distance, the shell temperature and the like. After the conventional communication link is interrupted, the communication system is switched to the anti-black-obstacle communication system, that is, the communication information is respectively modulated to the subcarriers of different frequency bands through the OFDM carrier aggregation technology, the subcarriers are positioned at different frequency bands of low frequency, medium frequency, high frequency and the like, and the same transmission information is modulated on each subcarrier. The receiving end demodulates the data on the corresponding sub-carrier to obtain the backup of a plurality of transmitted information, and combines and judges each information through frequency diversity to finally recover the transmitted information.
The invention comprises the following steps:
step 1: and detecting the distance between the aircraft and the ground.
The aircraft judges the real-time distance between the aircraft and the ground in the process of returning to the earth when the aircraft enters the atmosphere again by using a distance detector;
when the distance reaches 35-80Km (the distance range of the black barrier), the black barrier area can be reached, and the step 2 is carried out;
when the distance does not reach 35-80Km, the distance probably does not reach the black barrier area, and the step 6 is carried out;
step 2: aircraft skin temperature is detected.
The aircraft detects the temperature by using a temperature sensor outside the aircraft;
when the temperature of the shell of the aircraft reaches more than 2000 ℃ (the temperature range of the occurrence of the black barrier), the shell of the aircraft possibly reaches the black barrier area, and the step 3 is carried out;
when the temperature of the shell of the aircraft is not more than 2000 ℃, the shell of the aircraft possibly does not reach a blackout area, and the step 6 is carried out;
and step 3: a communication status of the aircraft with the ground station is detected.
The aircraft and the ground station send out handshake signals to wait for feedback signals of the handshake signals;
when the aircraft and the ground station receive the feedback signal within a certain time interval (such as set 5s), the aircraft does not reach a blackout area, requests to establish communication connection, keeps the original communication state and repeats the operation;
when the aircraft or the ground station does not receive the feedback signal within a certain time interval (for example, setting 5s), the aircraft or the ground station may reach a black-obstacle area, repeating the step 3 again to confirm that the feedback signal is not received, and turning to the step 4;
and 4, step 4: and switching the communication mechanism of the aircraft and the ground station.
The aircraft and the ground station switch communication mechanisms. The communication information is modulated to sub-carriers of different frequency bands respectively through an OFDM carrier aggregation technology, the sub-carriers are located in different frequency bands of low frequency, medium frequency, high frequency and the like, and the same transmission information is modulated on each sub-carrier.
The carrier aggregation technology is one of the key technologies of the mobile communication 4G standard LTE-Advanced. The carrier aggregation technology provides the expandability and the flexibility of the bandwidth, is beneficial to more flexibly using different bandwidths and realizes higher frequency spectrum utilization rate. There are three different combination patterns for carrier aggregation: intra-band contiguous carrier aggregation, intra-band non-contiguous carrier aggregation, and inter-band carrier aggregation. By changing the size of the IFFT (number of subcarriers) and calculating the center frequency of the carrier, intra-band contiguous carrier aggregation can be easily achieved. The intra-band non-contiguous carrier aggregation based on OFDM requires two steps: first, as with contiguous carrier aggregation in the frequency band, both non-contiguous channels are included by a larger IFFT and carrier transform. Second, subcarrier suppression (subcarrier suppression) is used to suppress the carriers of other channels. Carrier aggregation between frequency bands currently requires a separate IFFT module and a separate rf link in each frequency band. The current back-end hardware conditions are also difficult to satisfy the conditions of the shared radio frequency link. The carrier aggregation between the frequency bands needs to be completed by adding a baseband IFFT module and an additional radio frequency link.
The selection of the modulation frequency band is related to the oscillation frequency of the plasma. The plasma oscillating body frequency is a physical quantity that describes the properties of the plasma. In plasma, when positive and negative charges are separated, ions can be regarded as stationary due to large mass, and electrons can generate simple harmonic oscillation under the action of electrostatic force, which is called plasma oscillation. The oscillation frequency calculation formula is as follows:
the physical quantities under the root number are electron density, electron electric quantity, vacuum dielectric constant and electron mass, respectively. The electron density can be calculated from the atmospheric density sensor data.
Signal attenuation is most severe when the communication frequency is near the plasma oscillation frequency. The frequency band is therefore selected to avoid the plasma oscillation frequency. If the plasma oscillation frequency is f, the communication frequency band can be selected to be f-1000MHz and f +1000 MHz.
Although the fading characteristics of the plasma sheath are complex and non-linear, for OFDM subcarriers of different frequency band distributions, subcarriers in a partial frequency band always exist in non-fading or low-fading positions. Therefore, partial OFDM subcarrier information can be accurately received. The receiving end demodulates the data on the corresponding sub-carrier to obtain the backup of a plurality of transmitted information, and combines and judges each information through frequency diversity to finally recover the transmitted information. Converting the communication frequency band from the traditional C frequency band, the traditional X frequency band or the traditional Ku frequency band into the carrier aggregation communication frequency band in the aspect, and turning to the step 5;
and 5: and judging the communication state of the aircraft and the ground station.
The aircraft and the ground station send out handshake signals again to request for establishing communication connection;
when the communication connection is successful, the communication state is maintained;
and when the communication connection cannot be established, repeating the step 5 again to confirm that the communication cannot be established, and returning to the original communication mechanism.
Step 6: the aircraft sends a handshake signal to the ground station to confirm whether the communication is smooth.
The embodiment of the invention mainly comprises the stages of aircraft flight state detection, judgment of whether the aircraft is in a black barrier area, switching of a conventional communication system and the anti-black-barrier communication system, information transmission of the anti-black-barrier communication system and the like. The invention is mainly characterized in that the data transmission of the anti-black-barrier communication system based on carrier aggregation and frequency diversity is realized, and other steps belong to conventional technical means.
When the aircraft returns to the earth, the aircraft passes through the atmosphere at a high speed and rubs with air to form high temperature, the air is ionized at the high temperature and is self-generated by electrons, the interaction of the electrons and the plasma sheath can form a plasma sheath around the aircraft, and a black barrier can be formed when communication electromagnetic waves cannot propagate in the plasma sheath.
The implementation steps of the invention are as follows:
step 1: detecting the ground distance of the aircraft, judging that the real-time distance between the aircraft and the ground is 50Km by using a distance detector when the aircraft reenters the atmosphere and returns to the earth, judging that the aircraft possibly reaches a black barrier area, and turning to the step 2;
step 2: detecting the temperature of the shell of the aircraft, detecting the temperature of the aircraft by using an external temperature sensor to exceed 2000 ℃, judging that the aircraft possibly reaches a black-out area, and turning to the step 3;
and step 3: a communication status of the aircraft with the ground station is detected.
Sending handshake signals by the aircraft and the ground station, waiting for feedback signals of the handshake signals, judging that the aircraft does not receive the feedback signals after 5 seconds, judging that the aircraft reaches a black-error area, repeating the step 3 again to confirm that the feedback signals are not received, and switching to the step 4;
in order to evaluate the blocking characteristic of the plasma sheath in the blackout area on the wireless signal, the literature, "xi shui, plasma sheath ground simulation technique and radio wave propagation experimental study [ D ] is adopted]Plasma sheath attenuation model in seian electronics university, 2014 ", fig. 4 gives the plasma thickness 10cm, electron density ne＝1011cm-3The plasma sheath acts to attenuate the wireless signal. The plasma sheath attenuates radio signals at 2GHz maximally, approximately 37dB, while attenuating radio signals at 30GHz and 1MHz little. For the traditional S measurement and control frequency band of 2GHz, signals are blocked due to too large signal attenuation, and communication cannot be carried out.
And 4, step 4: as shown in fig. 1 and 2, the communication mechanism between the aircraft and the ground station is switched, and OFDM carrier aggregation and frequency diversity techniques are adopted to modulate signals to be transmitted onto OFDM subcarriers of multiple frequency bands for transmission. As can be seen from the attenuation characteristics of the plasma sheath for the signal, the information to be transmitted is modulated onto the OFDM carriers of all frequency bands, and there must be some frequency bands in which the communication signal can be transmitted. The carrier aggregation is carried out by adopting two sub-carrier frequency bands of 30GHz and 1MHz, wherein each frequency band is allocated with 0.625MHz, and the total bandwidth of the system is 1.25 MHz. A block diagram of a system architecture for observing and controlling a communication link is shown in fig. 3. After the information source is modulated by a baseband, OFDM modulation of carrier aggregation is carried out, and the same baseband information source signal is modulated to OFDM subcarriers of different frequency bands; after the signals are attenuated by the plasma, the OFDM signals of different frequency bands are demodulated, then merging diversity reception is carried out, and the error rate performance statistics calculation is carried out after the baseband demodulation. In the simulation verification system, the baseband modulation adopts a BPSK modulation mode commonly used for measurement and control communication. The OFDM carrier aggregation band selection comprises the conventional S-band 2 GHz. For black-barrier resistant communication, two frequency bands are additionally selected, namely a millimeter wave frequency band of 30GHz and a low frequency band of 1 MHz. The frequency diversity scheme employs a maximal ratio combining scheme with the best performance.
And 5: and judging the communication state of the aircraft and the ground station, sending handshake signals to the aircraft and the ground station again to request to establish communication connection, and if the communication connection is found to be successful, keeping the communication connection state.
Fig. 5 shows an error performance curve of the measurement and control communication link under OFDM carrier aggregation. When the traditional single carrier frequency, namely 2GHz frequency band communication, is carried out, because the characteristic frequency of plasma is about 2GHz, serious signal fading occurs, the communication error code is very large, communication can hardly be carried out, and communication interruption is caused. After carrier aggregation is adopted, after a traditional frequency range of 2GHz and a certain high frequency of 30GHz or a low frequency of 1MHz are aggregated, the plasma attenuation of the high frequency range and the low frequency range is very small, so that the code rate performance of a system after diversity reception is greatly improved, the communication requirement is met, and the communication connection is successful. After the three frequency bands are aggregated, the error code performance of the system can be further improved. The figure shows that the more the frequency bands adopting OFDM subcarriers for carrier aggregation, the better the link error rate performance, thereby illustrating the effectiveness of the method of the invention.
Claims (3)
1. A blackout resistant communication method based on carrier aggregation and frequency diversity is characterized by comprising the following steps: after the aircraft enters the atmosphere, detecting the ground distance and the shell temperature of the aircraft, and detecting the interruption state of a communication link when the ground distance and the shell temperature reach the set parameter range; after a communication link is interrupted, communication information is respectively modulated to subcarriers of different frequency bands through an OFDM carrier aggregation technology, and the same transmission information is modulated on each subcarrier; the receiving end demodulates the data on the corresponding sub-carrier to obtain the backup of a plurality of transmitted information, and combines and judges each information through frequency diversity to finally recover the transmitted information.
2. The carrier aggregation and frequency diversity based anti-blackout communication method according to claim 1, wherein: and when the ground distance of the aircraft reaches 35-80Km and the shell temperature reaches above 2000 ℃, the communication link interruption state is detected.
3. The carrier aggregation and frequency diversity based anti-blackout communication method according to claim 1, wherein: when the communication link interruption state is detected, the aircraft and the ground station send out handshake signals to wait for feedback signals of the handshake signals; when the aircraft and the ground station receive the feedback signal within a set time interval, the aircraft and the ground station do not reach a blackout area, request to establish communication connection, keep the original communication state and repeat the operation; otherwise, sending out handshake signals again, waiting for feedback signals of the handshake signals, confirming that the feedback signals are not received, and judging that the communication link is interrupted.
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