Measures
The basic principle of anti-interference measures is to inhibit the source of interference, cut off the interference propagation path, and improve the anti-interference performance of sensitive devices.
1, inhibit the source of interference
Inhibit the source of interference is to reduce the source of interference as much as possible, du/dt, di/dt. This is the most important principle of anti-jamming design and the most important priority, often play a multiplier effect. Reduce the du/dt of the interference source is mainly through the interference source at both ends of the parallel capacitance to realize. Reduce the di/dt of the interference source is in the interference source circuit series inductance or resistance and increase the continuity diode to realize. Common measures to suppress the source of interference are as follows:
(1) the relay coil to add a diode to eliminate the reverse electromotive force generated when the coil is disconnected interference. Adding only the continuity diode will make the relay disconnect time lag, increase the voltage regulator diode relay can be operated more times in a unit of time.
(2) in the relay contacts at both ends of the parallel spark suppression circuit (generally RC series circuit, resistance is generally selected from a few K to tens of K, capacitance selection of 0.01uF), reduce the impact of sparks.
(3) to the motor with a filter circuit, pay attention to the capacitor, inductor leads to be as short as possible.
(4) each IC on the board should be connected in parallel with a 0.01μF ~ 0.1μF high-frequency capacitors to reduce the impact of IC on the power supply. Pay attention to the wiring of the high-frequency capacitors, the wires should be close to the power supply and try to be as thick and short as possible, otherwise, it is the same as increasing the equivalent series resistance of the capacitor, which will affect the filtering effect.
(5) avoid 90-degree folding line when wiring to reduce high-frequency noise emission.
(6) parallel connection of RC suppression circuit at both ends of the SCR, to reduce the noise generated by the SCR (this noise may be serious when the SCR breakdown).
2, cut off the interference propagation path of common measures
1) fully consider the power supply on the impact of the microcontroller. Power to do a good job, the whole circuit of anti-interference on the solution of a large part. Many microcontrollers are very sensitive to power supply noise, to the microcontroller power supply filtering circuit or voltage regulator, in order to reduce the power supply noise on the microcontroller interference. For example, you can use the beads and capacitors to form a π-shaped filter circuit, of course, the conditions do not require high requirements can be used in place of 100Ω resistor beads.
(2) If the I/O port of the microcontroller is used to control noisy devices such as motors, isolation should be added between the I/O port and the noise source (adding a π-shaped filter circuit). If the I/O port of the microcontroller is used to control a noise device such as a motor, isolation should be added between the I/O port and the noise source (adding a π-shaped filter circuit).
(3) Pay attention to the crystal wiring. Crystals and microcontroller pins as close as possible, with ground wires to isolate the clock area, crystal shell grounded and fixed. This measure can solve many difficult problems.
(4) circuit board reasonable partition, such as strong and weak signals, digital and analog signals. As far as possible, the source of interference (such as motors, relays) and sensitive components (such as microcontroller) away.
(5) with the land line to isolate the digital area and analog area, digital ground and analog ground to be separated, and finally at a point connected to the power supply ground.A/D, D/A chip wiring is also the principle of the manufacturer to allocate A/D, D/A chip pin arrangement has been taken into account when this requirement.
(6) Microcontroller and high-power devices should be grounded separately to reduce mutual interference. High-power devices are placed at the edge of the board as far as possible.
(7) in the microcontroller I / O ports, power lines, circuit board connecting lines and other key places to use anti-jamming components such as magnetic beads, magnetic rings, power filters, shielding, can significantly improve the circuit's anti-interference performance.
3 Improve the anti-interference performance of sensitive devices
Improve the anti-interference performance of sensitive devices refers to the sensitive device side of the consideration to minimize the interference noise pickup, as well as from the abnormal state as soon as possible to restore the method.
The common measures to improve the anti-interference performance of sensitive devices are as follows:
(1) minimize the area of the loop ring when wiring to reduce the induced noise.
(2) When wiring, the power and ground lines should be as thick as possible. In addition to reducing the voltage drop, it is more important to reduce the coupling noise.
(3) For the idle I/O ports of the microcontroller, do not dangle, but ground or connect to the power supply. The idle end of other ICs is grounded or connected to power without changing the system logic.
(4) on the microcontroller using power monitoring and watchdog circuits, such as: IMP809, IMP706, IMP813, X25043, X25045, etc., can greatly improve the anti-interference performance of the entire circuit.
(5) in the speed can meet the requirements of the premise, try to reduce the crystal oscillator of the microcontroller and the choice of low-speed digital circuits.
(6) IC devices as far as possible directly welded to the circuit board, less IC seat.
4, software
(1) I am used to the code space will not be used to clear all the "0", because this is equivalent to the NOP, can be run in the program when the fly back to the place;
(2) in the jump instruction before the addition of a few NOP, the purpose of the same as 1;
(3) in the absence of a hardware WatchDog can be used in the software simulation of WatchDog, in order to monitor the program's operation;
(4) involves the processing of external device parameter adjustment or setting, in order to prevent the external device due to interference and error can be timed to re-send the parameters again, so that the external device as soon as possible to restore the correct; (5) communication in the anti-interference, can add data parity bit, you can take 3 to take 2 or 5 to take 3 strategy;
(6) in the case of a communication line, such as I ^ 2C, three-wire, etc., the actual We found that the Data line, CLK line, INH line constant set to high, its anti-interference effect is better than set to low.5, hardware
1) ground, power line wiring is certainly important!
(2) line decoupling;
(3) digital, analog ground separation;
(4) each digital component between the ground and the power supply are 104 capacitors;
(5) in the application of relays, especially when the high current, the anti-relay contact sparks on the circuit of the interference can be in the relay coil and a 104 and a diode, indirectly between the contact and the normally open end of the 472 capacitor, the effect is good!
(6) in order to prevent crosstalk I / O port, the I / O port can be isolated, the method of diode isolation, gate isolation, optical coupling isolation, electromagnetic isolation, etc.;
(7) of course, multi-layer board anti-jamming is certainly better than a single panel, but the cost is a few times higher.
(8) choose a strong anti-interference ability of the device than any method is effective, I think this point should be the most important. Because the device is difficult to make up for the inherent shortcomings of external methods, but often anti-jamming ability of the more expensive, anti-jamming ability of the poor on the cheap, just as Taiwan's East is cheap but the performance is greatly reduced! Mainly depends on your application!
The realization of the approach
⒈ interference phenomenon analysis Interference causes: The existing domestic satellite broadcasting and television systems are generally used transparent transponders and single-beam fugitive transceiver antennas. And, because the geostationary orbit position resources and radio frequency resources are limited, so the satellite's space position and operating frequency must be declared to the ITU and to comply with international regulations, and its parameters, including the coding of television signals are open. Anti-jamming connector In addition, the frequency band utilization of satellite broadcasting and television is usually by SCPC (single channel single carrier) and MCPC (multi-channel single carrier) two ways. SCPC way, multiple programs can be allocated through the frequency *** with the same satellite transponder, saving a large number of terrestrial program reception facilities, but due to the existence of intermodulation interference in the multicarrier uplink, the transponder power back more power utilization is not high, and because each carrier needs to be sufficient to protect the frequency band between the band utilization is not high, the satellite transponder is more susceptible to the interference of the signals of other carriers, the security of the lower. The security is lower. The MCPC mode, multiple programs **** with a complete transponder uplinked by the same uplink station, due to a single carrier uplink, satellite transponder power resources can be fully utilized, and save the frequency protection interval of the multicarrier uplink, the transponder can be working in a saturated state, the security has been maximized to protect the security, but also correspondingly increased the ground signal lead facilities.
Therefore, the existing satellite radio and television system is more vulnerable to interference by illegal signals. And the transmission system adopts SCPC is more vulnerable to illegal signal interference than MCPC.
2, the type of interference and countermeasures
From the source of interference, mainly divided into natural phenomena, equipment failure interference, ground electromagnetic environmental interference, neighboring star interference and human-caused interference, etc., some of the interference is cross each other.
Natural phenomenon interference mainly includes solarization interference, rain and snow decay. There is no effective way to avoid the sunrise interference, generally the satellite company will notify the user of the sunrise time in various places so that the user can make preparations in advance, and the earth station can shorten the duration of the sunrise interference by increasing the antenna aperture and reception sensitivity. The deterioration of received signals caused by rain (snow) fading has a gradual process, and the loss caused by rain (snow) fading can be reduced by compensating the rain (snow) fading loss of the uplink and leaving enough rain fading reserve for the downlink.
Equipment failure interference mainly includes satellite failure interference and ground equipment failure interference two categories. Satellite equipment failure interference can be resolved by timely switching backup devices, when serious, turn the star or replace the transponder to solve. The ground equipment failure interference is divided into intermediate frequency retransmission interference, ground FM broadcasting interference, cross-talk interference, spurious interference and so on. The first two belong to the interference introduced by the intermediate frequency, which can be reduced by the assistance of the satellite company to investigate the source of the interference and the electromagnetic shielding work of the corresponding system or transmission line of the earth station to minimize the possibility of interference. Spurious interference can be minimized by changing the gain setting of the affected transponder by the satellite company and increasing the uplink power of the earth station accordingly. Intermodulation interference can be solved by strictly controlling the uplink power of the earth station and ensuring that modems, upconverters, transmitters, etc., have enough reserve back margin.
The ground electromagnetic environment interference mainly includes microwave communication relay signal interference, radar signal interference, etc., which can be solved by electromagnetic detection and frequency coordination, as well as electromagnetic shielding means. Anti-jamming capacitance 3, the anti-jamming system of the earth station to realize anti-jamming earth station anti-jamming measures. Through the above analysis of the interference phenomenon, at present, the earth station can take the following anti-interference measures.
1) uplink earth station should use high-power transmitter and large diameter high-gain transmitter antenna: once the satellite is interfered with, reduce the star receiver gain, increase the uplink power to enhance the transponder input carrier-to-noise ratio, reduce the impact of interference.
(2) uplink earth station should use high-power MCPC uplink signal pushed to the transponder saturation point: transmission of television programs less or no SCPC signal, thus using the transponder saturation point of the strong signal on the weak signal suppression effect characteristics, to further reduce the impact of illegal interference.
(3) The uplink earth station should be equipped with corresponding anti-jamming system, through the real-time monitoring of all the equipment of the earth station, all kinds of interference in a timely manner to find, judge and deal with.
Satellite communication anti-jamming technology
With the development of the national economy, wireless communication has been widely used in various fields of the national economy and people's daily life, especially the rapid development of public mobile communication, the number of all kinds of wireless communication equipment used in the society has risen sharply. In modern warfare, command communications, military intelligence and arms control are increasingly dependent on electronic equipment, especially the support of radio equipment. Information warfare and electronic warfare as a brand new form of combat involves the military field, opening up the fourth-dimensional battlefield after the land, sea and air battlefield - electromagnetic battlefield ... In order to improve the reliability of information transmission of communication system and to fight against various forms of interference, people have adopted various communication anti-jamming technologies to protect the communication system to transmit information accurately, in real time and uninterruptedly under the interference environment. Therefore, a systematic introduction to the principles and techniques of communication anti-jamming is necessary. Generally speaking, the basic system, methods and measures of communication anti-jamming can be divided into three categories:
1) signal processing. Such as direct sequence spread spectrum technology (DS-SS), its key parameter is the phase as a function of time; frequency hopping technology (FH-SS) its key parameter is the carrier frequency as a function of time; and so on.
(2) spatial processing. Such as the use of adaptive antenna zeroing technology, when the receiving end of the interference, so that the zero point of its antenna direction map automatically points to the direction of the interference, in order to improve the signal-to-dry ratio of the communication receiver.
3) time processing. Such as burst transmission technology, due to the communication signal in the transmission process exposure time is very short, thus greatly reducing the probability of the interfering party reconnaissance, interception.
Communication anti-jamming technology research is known or predict the enemy's interference means, on the basis of the above technology (of course, does not exclude the future of new technology categories) to select the appropriate technical means to eliminate or mitigate the enemy's interference, so that we need to carry out the continuation of the communication of a technology. The nature of the enemy's interference, intensity, type, means, the use of the system, the clearer the understanding, the more targeted measures taken, the better the results achieved. As the enemy's countermeasures are often integrated, multi-variable, some may be completely new, so the anti-jamming means must be taken in a variety of ways in order to achieve better results.
Communication anti-jamming technology features:
(1) confrontational, technologically comprehensive, difficult, fast development, to some extent, is the enemy and our wisdom and technology struggle. The success or failure of communication is related to the victory or defeat of the war, so this technology is very strong confrontation. Communication anti-jamming with new technology, engage in confrontation will want to new countermeasures, and vice versa, so as to promote the development of technology and difficulty.
(2) the practicality of the technology and the reliability of the requirements of the high, communications anti-jamming must be in the battlefield to actually solve the problem. High indicators but unreliable or impractical is intolerable, the consequences of which are unimaginable.
Military satellite communications anti-jamming means
(1) Direct Sequence (DS) spread spectrum
The so-called Direct Sequence Spread Spectrum, that is, directly with a high code rate spreading code sequences (usually pseudo-random sequences) in the transmitting end to expand the signal's frequency spectrum, so that the power in the unit frequency band becomes smaller, that is, the signal's power spectral density becomes lower, the communication can be in the background of channel noise and thermal noise. So that the signal is drowned in noise, the enemy is very unlikely to detect the presence of a signal. At the receiving end, the same spread spectrum code to de-expansion (spectral reduction), the DS spread spectrum signal energy can be concentrated to restore the original state, but also the interference energy dispersed and suppressed. Therefore, the system is characterized by good signal concealment, the probability of being intercepted is small, anti-jamming capability with the increase in the length of the code sequence and strengthen. It is generally believed that the direct spreading signal to be covert, its code length can not be less than 32 bits. DS spread spectrum technology is used in military communications satellites such as Military Star (Milstar), Leased Satellite (LEASAT) and Fleet Communications Satellite (FLTSATCOM). (2) frequency hopping (FH)
The so-called frequency hopping, refers to the use of a certain code sequence to select the multi-frequency frequency shift keying, so that the carrier frequency is constantly jumping, this is a kind of "avoidance" way of the main anti-jamming system. In order to deal with tracking interference, countries are trying to improve the frequency hopping speed. 1980s frequency hopping speed is generally about 200 hops / sec, at present, the hopping speed of up to 300 ~ 500 hops / sec. The United States of America's military star and fleet communication satellite 7 and 8 are equipped with extremely high frequency (EHF) components, up and down the use of frequency hopping technology. Military Star-2 has a frequency hopping range of up to 2 GHz bandwidth. Anti-jammer (3) time-hopping (TH)
Time-hopping is the time-shift keying of multiple time slices selected with a certain sequence of codes, so that the transmitted signal jumps on the time axis. From the point of view of interference suppression, time-hopping benefits little, the only advantage lies in the reduction of the duty cycle, a jamming transmitter in order to achieve the effect of interference must be transmitted continuously, because the jamming machine is not easy to recognize the time-hopping pseudo-code parameters used.
(4) a variety of hybrid
In the above several kinds of basic anti-jamming way on the basis, can be combined with each other, constitute a variety of hybrid. For example, FH/DS, DS/TH, FH/TH or DS/FH/TH. The use of two-dimensional or even three-dimensional hybrid anti-jamming technology system is a trend in the development of foreign anti-jamming communications. For example, the frequency hopping signal modulated with direct expansion code frequency hopping / direct expansion (FH / DS) hybrid anti-jamming system, this system every hopping frequency point are to expand the signal in the way of the direct expansion, the direct expansion of the signal is characterized by its power spectral density is low, the enemy is difficult to detect, even if detected, as long as the detection time more than the frequency hopping time, but also can not be tracked to interfere. The U.S. military star and fleet communications satellites using frequency hopping / direct expansion hybrid system, the U.S. three armed forces joint tactical information dissemination system (JTIDS) on the use of time-hopping, frequency hopping plus direct expansion of the three-dimensional anti-jamming technology system.
(5) Expansion of frequency bands, development of microwave, millimeter wave, optical communications
The U.S. Defense Communications Satellite System (DSCS), the UK's Skynet and NATO satellites initially operated at ultra-high frequency (SHF) (about 8 GHz). In the 1990s, DSCS III added the UHF band to accommodate mobile communications. And Skynet IV (Skynet IV) and NATO IV (NATO IV) added the EHF (44 GHz) uplink channel for experimenting with improved immunity to interference, in addition to the UHF band. The UHF Follow-on Star (UFO) series of the U.S. Navy began with the fourth satellite, which added an EHF communications subsystem compatible with Military Star, and used the SHF band for its fleet broadcast uplink. The U.S. Military Star system uses a 60 GHz interstellar link, which is not subject to interception and interference by ground-based electronic warfare equipment due to the high attenuation in the upper atmosphere at that frequency, and its satellite terrestrial link is in the EHF band (44 GHz uplink, 20 GHz downlink). There is no interference problem between satellites using optical communication and electric waves, and optical communication can realize high-capacity satellite communication of more than 1Gbit/s. NASA of the United States, ESA of Europe, Japan and other countries are making great efforts to study optical communication technology.
(6) Multibeam Antenna and Interference Zeroing Technology
The multibeam antenna of the U.S. Defense Satellite Communications System (DSCS Ⅲ) (containing 19 transmitter beams and 61 receiver beams) is able to control the relative amplitude and phase of each beam through the beam-forming network according to the location of the interference source detected by the sensitizers so that the antenna gain in the direction of interference is zero. Military and fleet communications satellite EHF components have point-beam antennas, making interference in the point-beam direction difficult.
(7) transponders plus limiter anti-saturation anti-jamming transparent linear transponders that do not use the spread spectrum modulation technique and other techniques mentioned above, its anti-jamming is very weak, the use of conventional jamming styles and the Earth station's transmitting power comparable to the power of the jamming power can be pushed into the saturation zone, so that it can not work properly. A transponder with a limiter has better immunity to interference than a linear transponder. However, because it has a strong signal to suppress the role of weak signals, as long as the interference power is large enough, the interference can still work.