Satellite Communication Network Fault Analysis and Solutions Satellite Communication Network Fault Analysis and Solutions

Satellite communication refers to the information communication between two or more earth station antennas using artificial earth satellites as relay stations to forward radio signals. It includes the relay station-communication satellite part, and the terminal station-earth station antenna part. Communication satellites can be divided into low orbit (LEO) communication satellites, medium orbit (MEO) communication satellites, high elliptical orbit (HEO) communication satellites and geostationary orbit (GEO) communication satellites according to their orbits. For more information about satellite orbits, please click below article.

Satellite communication earth station antenna is equivalent to the terminal station of terrestrial microwave communication, including baseband equipment, radio frequency equipment, antenna feeder equipment, monitoring equipment, etc. In order to ensure the alignment of earth station antenna antenna and satellite antenna, servo tracking equipment is added. The outstanding features of satellite communication earth station antenna are low noise reception and high power output.

At the same time, with the development of science and technology, satellite communication applications are becoming more and more widespread. However, in the process of satellite communication networks, some problems may be encountered. Below we will introduce the analysis process of typical faults in satellite communication networks and provide certain solutions.

1. General principles for analyzing typical faults of Satellite communication network

The principles that communications engineers at earth station antennas generally follow when troubleshooting are as follows.

1.1 From easy to difficult

The search for faulty equipment among the earth station antenna is a process of gradual elimination and final determination. A fault phenomenon may be caused by many reasons. The process of determining the cause of the fault should follow the general principle of from easy to difficult, gradually narrow the scope of search, finally determine the cause of the fault, and further repair and verify.

The so-called principle of from easy to difficult means that in the process of troubleshooting, first eliminate those possible factors that are easy to implement, easy to verify, easy to control, and have little impact on external objective conditions and little impact on others. For example: the receiving and transmitting lines are blocked, the Modem cannot be locked, etc. We usually first check the strength of the received signal through the front panel, and then observe the carrier-to-noise ratio of the received signal through the spectrum analyzer of the intermediate frequency monitoring, and gradually check the possible causes by comparing with other channels and checking the connecting cables.

1.2 From indoor equipment to outdoor equipment

The monitoring spectrum analyzer is usually connected to the splitter at the front end of the modem, and the monitoring computer is usually near the workbench. It is more convenient to observe the status of the earth station antenna from indoors, so when observing the fault of the earth station antenna, especially the local fault, we should start from indoors. Comparing the status of different modems is also done indoors. The status of different modems can often indicate whether the fault is common. Generally, only common problems may involve the outdoors, so from indoors to outdoors is a principle of troubleshooting. By adjusting the level indoors, checking the connecting cable, replacing the terminal equipment, adjusting the modem transceiver parameters, etc., some common faults can be determined and eliminated.

1.3 Check receive port first, then transmit port

The general principle of checking communication link faults is to check receive port first, then transmit port. The broadcasting characteristics of satellite communication make it easier to observe the signals from the other end, the onboard beacon and the outbound signals of the central station. The level of the received signal is relatively low, which is more suitable for observation by standing instruments. By checking the received signal, not only can the quality of the receiving branch of the station be determined, but also the fault of the transmitting branch of the other end can be found. In addition, the transmission signal of the local end is also checked by observing the onboard forwarding signal through the spectrum analyzer.

1.4 From software failure to hardware failure

Software failure of earth station antennas refers to failures caused by improper equipment parameter settings, poor contact, unstable power supply voltage, etc. Typical hardware failures refer to equipment damage. The general fault inspection and judgment of earth station antennas should start with software failures, and then the performance indicators of hardware equipment; first check the monitoring menu, working status, and panel indication of the equipment, and then check the receiving and transmitting level status of the link. Software failures can generally be solved on site.

1.5 Start with monitoring software

Nowadays, earth station antennas are generally equipped with station control computers. If a part turns red, it means that this part has a fault. You can determine the cause of the fault and the faulty device by checking the monitoring menu, status menu, fault indication and historical fault storage menu.

1.6 Start with the most likely cause

It is impossible for each fault diagnosis to be the same process, and it is even more impossible to repeat all the steps. This requires us to have a practical analysis of the fault phenomenon and possible causes, compare with our experience, and start from the most likely angle. Of course, the usual observation and recording of the earth station antenna status can also help us judge the cause of the fault.

2. General methods for earth station antennafault diagnosis

We generally perform fault diagnosis and repair on earth station antennas according to the following methods.

2.1 Observation method

The observation method includes observing the indicator lights and panel displays of the equipment, observing the connection relationship between the equipment, observing the operation of the equipment exhaust fan, observing the sealing condition of the outdoor cable joints, etc.

The observation method is the most basic and intuitive method. To check the status of an earth station antenna, we must first start with surface observation. Some intuitive alarms and fault displays are often the starting point for fault diagnosis.

2.2 Inquiry method

The inquiry method refers to the on-site engineer asking the on-duty personnel on the station about the recent working conditions of the earth station antenna, checking the previous fault records, and asking about the communication status of the opposite station. The inquiry method is the beginning of an engineer’s understanding of the fault and analyzing the cause of the fault. When the on-duty personnel report that the earth station antenna has a fault, the engineer must first understand the situation, reproduce the fault phenomenon, and then observe and analyze.

2.3 Elimination method

The elimination method is to eliminate the causes of the fault one by one. The method of finally determining the faulty equipment (part) generally follows the principle of from easy to difficult and from general to special mentioned above.

2.4 Replacement method

The replacement method is often used in fault inspection, which is to replace the possible faulty equipment with normal equipment locally. If the communication is normal after the replacement, it can generally be judged that the repaired equipment is faulty or has a problem with the settings. When there is a lack of detection means or equipment, the replacement method is often very convincing. In the detection of universal modems and CU boards, the replacement method is often used. In system joint debugging, when each manufacturer “confirms” that there is no problem with their equipment, the replacement method can also be used.

2.5 Comparison method

The comparison method is to compare the existing equipment parameters and technical status with previous records to confirm which equipment’s working status has changed and caused the fault:

2.6 Detection method

The detection method is to use instruments to measure the level of the detection point and test the technical indicators of the equipment. Common detection equipment used in earth station antennas include spectrum analyzers, bit error meters, multimeters, oscilloscopes, etc.

3. Routine inspection and maintenance of earth station antennas

After an earth station antenna has been in operation for a period of time, or before it is decommissioned and reactivated, it should undergo routine inspection and maintenance. Routine inspection and maintenance of earth station antennas should be organized in accordance with regulations, and should include daily inspection, weekly inspection, monthly inspection, and annual inspection. Large-scale maintenance work of earth station antennas should be organized every six months or one year.

The work procedure of the on-site engineer is as follows:

3.1 Antenna inspection

First check whether the fasteners are loose, then perform an appearance inspection to see if the antenna panel is peeling, whether the PTFE film at the feed horn is cracked, and whether the antenna azimuth and elevation axes are rusted. If the fasteners are loose, they should be tightened in time, and if the PTFE film is cracked, it should be replaced in time (for instructions on how to replace the feed film, please click this article). If the antenna is peeling, it should be repainted, and if the azimuth and elevation axes are rusted, spray a loosening agent first, and then unscrew it and apply lubricating oil for rust prevention after the rust is removed.

3.2 Alignment check

Before aligning the antenna, first loosen the azimuth and elevation locking device of the antenna, power the low noise amplifier, and then connect the spectrum analyzer under the low noise amplifier to receive the satellite beacon for precise alignment. Manual alignment must first preset the antenna elevation, azimuth, and polarization to the theoretical calculated values and verify them through the compass. If the beacon is not seen, use the compass again to check whether the elevation is set correctly and fan the azimuth. After receiving the beacon, adjust the antenna elevation and azimuth alternately to maximize the signal. Also adjust the polarization through the satellite’s reverse polarization beacon. If the satellite does not have a reverse polarization beacon, send a single carrier and adjust it with the assistance of the satellite company’s monitoring station. After the alignment is completed, first lock the polarization device, then the azimuth and elevation axes. The locking nuts of the manual antenna should be locked alternately. At the same time, during the above operations, observe the beacon received by the spectrum analyzer to prevent deviation. Finally, lock the azimuth and elevation locking device.

3.3 Device status check

(1) Infrequently used earth station antennas

earth station antennas that are not frequently used also need to be powered on and checked regularly. Before powering on the equipment, first check the grounding, power supply, and connecting cables between the equipment. After the equipment power supply voltage is normal, the grounding is good, and the connection relationship and connecting cables are correct, then power on in sequence. After powering on, first check whether the cooling fan of the equipment is running normally. After the equipment self-check is completed, observe whether the indicator lights are normal and whether the fault light is on. Then check the status indicators, working parameters, fault storage, etc. of the power amplifier, low noise amplifier, up and down converter, modem and other equipment one by one. After everything is normal, further adjust the system parameters and working level.

（2） For Operating earth station antenna

For the earth station antenna in operation, the power-on step can be omitted and the equipment status and parameter check can be performed directly.

After the equipment status check is normal, the link level adjustment is performed. First, the level of the received signal should be adjusted step by step from the low noise amplifier outlet to the modem entrance. Generally, the attenuation of the downconverter and the intermediate frequency branch unit should be set to an intermediate value so that it can be adjusted up and down later. When the entire link receiving level is to be adjusted later, the attenuation value of the downconverter can be changed; when adjusting a single channel individually, the attenuation value of the intermediate frequency branch unit can be changed. The basis for adjusting the receiving level is to make the carrier entering the modem at a suitable level value. For example, the receiving range of SCMM 2000 is -30~- 55 dBm, and a value close to the middle value of -2 dBm can be taken.

The adjustment of the transmission level should be based on the receiving level and the carrier-to-noise ratio of the receiving signal of the other party. When the other party does not have a spectrum analyzer, it can be carried out with the cooperation of the master station, or it can be transmitted and received by itself, and compared and adjusted with the signal received from the master station. Since the antenna of the master station is generally larger, the self-transmitted and self-received signals should be appropriately lower than those of the other party when communicating with the master station. When communicating with similar stations, it is generally sufficient to be flush with the received signal of the master station. After the adjustment is completed, the master station should be asked to confirm. The different satellite coverage parameters in different places have a certain impact on the signal size. As with the downlink, the attenuation value of the upconverter, high power amplifier, and intermediate frequency combiner, and the transmission level value of the Modem should generally be set at an intermediate value to ensure that the level change can be adjusted up and down in the future. The transmission level adjustment of the entire link can change the attenuation value of the upconverter; when adjusting a single channel individually, the attenuation value of the intermediate frequency combiner unit can be changed.

4. Common fault diagnosis of earth station antenna

earth station antenna faults can be divided into network-wide faults and single-station faults. We mainly analyze the faults of a single earth station antenna and its recovery. Single earth station antenna faults include communication quality degradation and communication interruption. After an earth station antenna fault occurs, the earth station antenna antenna should generally be fully inspected. The general order of inspection is to check the receiving first, then the transmitting ; check the indoor equipment first, then the outdoor antenna. Below we analyze the two situations of communication quality degradation and communication interruption respectively.

4.1 Degraded communication quality

Degraded communication quality means that the error rate of communication exceeds the design index, including single-channel, single-direction and the entire station. If the quality of single-channel communication is degraded, first check whether the transmit and receive level of the Modem is appropriate. If it is not appropriate, it can be adjusted through the intermediate frequency splitter and combiner unit; if the level is appropriate but the fault still exists, check whether there is interference in the frequency band. When checking the interference, turn off the Modem transmission and observe it with a spectrum analyzer at the intermediate frequency entrance. If there is interference, find the interference source, analyze the way of stringing in, and coordinate to solve it; of course, it may also be that the hardware of the Modem itself has a fault. The simplest way to determine the fault of a single Modem is to replace it for inspection. A single-direction fault means that the error characteristics of all communication Modems in the direction of a certain earth station antenna are poor. This situation is generally caused by the fault of the opposite station, especially the public communication part of the opposite station, which can be eliminated in cooperation with the opposite station.

The degradation of the communication quality of the entire earth station antenna may be caused by the following situations:

4.1.1 Antenna deviation

Antenna deviation can be divided into misalignment, alignment on the side lobe and poor polarization adjustment. The solution is to use a compass, spectrum analyzer and other equipment to re-align the star. Bad weather such as strong winds is an important cause of antenna deviation. After the vehicle-mounted station changes its location, the polarization needs to be readjusted.

4.1.2 Water in the feed source

Damage to the polytetrafluoroethylene film at the feed source horn will cause water to enter the feed source, duplexer, and transmitting waveguide, affecting the communication quality and even causing communication interruption. If it rained before the earth fault, the probability of water in the feed source will be greatly increased. After the antenna feed source is flooded, the duplexer needs to be removed, dried and then installed. And replace the polytetrafluoroethylene film.

4.1.3 Cable damage

Damage to the outer sheath and inner conductor of the outdoor cable will lead to a decrease in communication quality. Pay special attention to whether the semi-rigid cable has a dead bend. You can use a multimeter to measure the shortness of the electrical group. For RF cables, you also need to detect its attenuation.

4.1.4 Equipment index reduction

The decrease in gain, increase in phase noise, frequency drift and other equipment indexes of RF equipment will lead to a decrease in the communication quality of the earth station antenna. If the spectrum analyzer observes low carrier level and low carrier-to-noise ratio, it is likely that the equipment gain has decreased; if there is spectrum instability or frequency drift, it may be a frequency source or synthesizer failure; if the spectrum is distorted and the envelope is deformed, it may be phase noise or amplitude-frequency characteristics deterioration. However, when the earth station antenna detection equipment is limited, it is not important to repair and accurately test the indicators, but to locate the fault, that is, to confirm the faulty equipment. The order of equipment detection is to receive first and then transmit, that is, start from the low noise amplifier, to the downconverter, and the intermediate frequency splitter unit, and perform level tests and spectrum analysis step by step, and then start from the modem uplink outlet, to the intermediate frequency combiner unit, upconverter, and high power amplifier coupling port.

During the detection, you can first observe the carrier in the working state, then interrupt the communication, and use the signal source as input for further inspection. In the absence of a signal source, the downlink can receive a beacon as a signal reference source; the uplink can be transmitted by the modem as a single carrier as a signal reference source. Note that in the case of a high power amplifier without a coupling port, be sure not to connect a signal exceeding 30 dBm directly to the spectrum analyzer.

When checking the low noise amplifier, if no signal is received, the DC power supply of the low noise amplifier should be checked first. After the low noise amplifier is powered, the noise floor of the spectrum analyzer will rise.

4.1.5 Interference exists

Interference is usually periodic and can only be detected when the earth station antenna fails. First, it is necessary to distinguish whether it is from the satellite, the ground or the intermediate frequency. If other earth station antennas can also see it, it may be from the satellite. You can contact the central station and ask it to assist in the investigation and solution; if it can be received from the low noise but not from other stations, it is ground radio frequency interference. Contact the local Radio Management Committee Office to solve it; if there is no interference after the low noise, and the intermediate frequency interference can be seen at the Modem entrance, it is likely from other equipment in the station. First, investigate the same frequency equipment in the station.

4.2 Communication interruption

When the communication quality decreases, the Modem can sometimes lock. When the communication is interrupted, the Modem of this station or the other station will lose lock. If the Modem of this station loses lock, it may be that the transmission of the other station or the reception of this station has a fault; conversely, if the Modem of the other station loses lock, it may be that the reception of the other station or the transmission of this station has a fault. If both bidirectional Modems lose lock, it may be that the public communication part of this station or the other station has a fault. When the Modem of this station loses lock, you can use a spectrum analyzer to observe the receiving level and spectrum characteristics from the low noise amplifier outlet, RF splitter inlet/outlet, down converter inlet/outlet, intermediate frequency splitter inlet/outlet, and Modem inlet in turn to determine the fault location. If each device of the receiving branch is normal, ask whether the transmitting branch of the opposite station has a fault. When the Modem of the opposite station loses lock, first observe whether the loopback signal on the satellite is normal from the receiving end. If it is normal, it is a problem with the receiving branch of the opposite station. If it is not normal, you can check the level and spectrum from the modem output port, the intermediate frequency combiner unit inlet/outlet, the inverter inlet/outlet, the high power amplifier inlet, and the combiner output port in turn to confirm the fault location. When the modems of this station and the opposite station are both unlocked, and the opposite station communicates normally with other stations, it means that there are problems with the receiving and transmitting branches of this station. At this time, first check whether the power supply of the upstream and downstream public equipment is normal, including the RF cabinet, the integrated ODU for receiving and transmitting, the intermediate frequency splitter and combiner unit, etc., and then receive the beacon from the low noise amplifier outlet to confirm whether the antenna is deflected. If the equipment is powered normally and the antenna is aligned, you should check the receiving and transmitting branches in turn according to the steps in the above two paragraphs to confirm the faulty equipment. When the modems of this station and the opposite station are both unlocked, and the communication with other stations is normal, it is generally the fault of the opposite station. For faulty equipment, generally do not open the cover for inspection, but contact the equipment supplier and return it to the factory for repair.

The above are the common fault analysis principles and diagnostic solutions for satellite communication networks. We hope that this will be helpful to all users who encounter such problems in future operations. If you have any related questions, please feel free to consult us. Antesky is professional antenna suppliers in China for years. If you are looking for satellite communication antennas and accessories, please contact by sales@antesky.com. or you can WhatsApp us directly. we will offer you high quality antenna with the best price.