High-latitude mountainous area emergency satellite communication method and system based on multi-band adaptive selection

Abstract

The invention discloses a high-latitude mountainous area emergency satellite communication method and system based on multi-band adaptive selection. The high-latitude mountainous area emergency satellite communication method comprises the steps that S1, the system receives a data transmission request; s2, judging the size and the type of the data packet; s3, acquiring related information of the overhead satellite; s4, adjusting the broadband / narrowband phased array antenna; s5, satellite signal quality index extraction; s6, signal quality evaluation; s7, selecting an optimal transmission network; s8, dynamically allocating the bandwidth; s9, data transmission; s10, current network signal quality judgment is carried out to carry out network switching selection; s11, not switching the network so as to avoid data transmission congestion caused by frequent switching of the network; and S12, completing a data transmission task. According to the invention, the communication problem of the existing satellite communication technology in the emergency disaster relief scene in the high-latitude mountainous area is solved.

Description

Technical Field

[0001] This application belongs to the field of satellite communication technology, and particularly relates to a high-latitude mountain emergency satellite communication method and system based on multi-band adaptive selection. Background Art

[0002] In high-latitude mountainous areas, due to complex terrain and satellite signal occlusion, satellite communication is easily affected by the "South Mountain Effect", resulting in problems such as signal quality degradation and communication interruption. In emergency rescue scenarios, such communication problems will seriously affect the progress of rescue work and the timely transmission of information.

[0003] Although existing satellite communication technologies can solve the signal occlusion problem to a certain extent, in the complex environment of high-latitude mountainous areas, there are still problems such as inaccurate signal quality assessment, unreasonable frequency band selection, and inflexible bandwidth allocation. In addition, existing satellite communication systems usually use a single frequency band for communication and cannot dynamically switch frequency bands according to signal quality, resulting in poor communication stability in complex environments. Summary of the Invention

[0004] The purpose of this application is to disclose a high-latitude mountain emergency satellite communication method and system based on multi-band adaptive selection in order to overcome the problems of existing technologies, aiming to solve the problems of inaccurate signal quality assessment, unreasonable frequency band selection, and inflexible bandwidth allocation existing in existing satellite communication technologies in high-latitude mountain emergency rescue scenarios, so as to improve the stability and efficiency of communication.

[0005] On the one hand, the purpose of this application is achieved through the following technical solutions:

[0006] A high-latitude mountain emergency satellite communication method based on multi-band adaptive selection, the high-latitude mountain emergency satellite communication method includes:

[0007] S1: The system receives a data transmission request and starts processing the data transmission task;

[0008] S2: Judge the size and type of the data packet;

[0009] S3: Obtain relevant information of the over-the-horizon satellite, including: obtaining ephemeris data and predicting the over-the-horizon satellite;

[0010] S4: Adjust the broadband / narrowband phased array antenna to complete the tracking of low-earth-orbit broadband satellite signals, geostationary-orbit broadband satellite signals, and low-earth-orbit narrowband satellite signals;

[0011] S5: Extract satellite signal quality indicators to complete the signal quality extraction of low-earth-orbit broadband satellite signals, geostationary-orbit broadband satellite signals, and low-earth-orbit narrowband satellite signals;

[0012] S6: Signal quality assessment, by comparing the comprehensive quality scores of each signal, to determine the satellite signal with the best quality at the moment;

[0013] S7: Select the best transmission network. When communication starts, select the low-orbit Ka band for communication, and automatically select the communication frequency band for communication based on the signal quality evaluation result of S6;

[0014] S8: Dynamic bandwidth allocation. According to the result of S2, the size and type of the data packet are judged, the size and priority of the transmitted data are obtained, bandwidth resources are dynamically allocated, and bandwidth allocation is adjusted according to the network load and signal quality.

[0015] S9: Data transmission: data transmission is performed through the selected optimal network and bandwidth allocation, and the data is sent to the Ka / L band communication module of the corresponding network for data modulation, DA digital-to-analog conversion, filtering, and amplification. Then, the data is transmitted to free space for transmission using a phased array antenna.

[0016] S10: judging the quality of the current network signal. During data transmission, the signal quality of the current network is continuously monitored to judge whether the quality of the current network signal is gradually deteriorating to the point of being unusable, until the data transmission is completed.

[0017] If the signal quality gradually deteriorates to the point of being unusable, the process returns to steps S4 to S6 to re-evaluate the signal quality and select a network;

[0018] If the signal quality is acceptable, then enter S11;

[0019] S11: Do not switch networks to avoid data transmission congestion caused by frequent network switching;

[0020] S12: Complete the data transmission task.

[0021] According to a preferred embodiment, step S2 includes: evaluating the size of the data by file size or data packet size; identifying the data type by file extension, data header information or content analysis.

[0022] According to a preferred embodiment, in step S3, ephemeris data is obtained from a satellite navigation system or a satellite operator, wherein the ephemeris data includes the position, orbital parameters, and overpass time information of the satellite;

[0023] Overhead satellite estimation is: based on the ephemeris data and the position of the base station, the satellites that will pass over the set base station within a preset time period are estimated.

[0024] According to a preferred embodiment, in step S4,

[0025] The tracking process of low-earth-orbit broadband satellite signals includes: first, adjusting the broadband phased array antenna to scan and track the low-earth-orbit satellite signals. After tracking and locking, the Ka-band communication module processes the signals and then transmits the signal quality to the base station CPU processor for extracting the signal quality indicators of S5.

[0026] The tracking process of geostationary-orbit broadband satellite signals includes: after the signal quality indicators of the low-earth-orbit satellite are extracted, adjusting the broadband phased array antenna to scan and track the geostationary-orbit satellite signals. After tracking and locking, the Ka-band communication module processes the signals and then transmits the signal quality to the base station CPU processor for extracting the signal quality indicators of S5.

[0027] The tracking process of low-earth-orbit narrowband satellite signals includes: after tracking and locking the L narrowband satellite signals, the L-band communication module processes the signals and then transmits the signal quality to the base station CPU processor for extracting the signal quality indicators of S5.

[0028] According to a preferred embodiment, the Ka-band communication module performs amplification, filtering, AD / DA analog-to-digital conversion, modulation and demodulation preprocessing operations on the received low-earth-orbit / geostationary-orbit broadband satellite signals, and then obtains digital signals.

[0029] The L-band communication module performs amplification, filtering, AD / DA analog-to-digital conversion, modulation and demodulation and other preprocessing operations on the received low-earth-orbit narrowband satellite signals, and then obtains digital signals.

[0030] According to a preferred embodiment, step S5 includes: transmitting the digital signals to the base station CPU processor through the wide / narrowband communication module serial port, and the base station CPU processor extracts the signal-to-noise ratio SNR, bit error rate BER and carrier-to-noise ratio CNR data information of the low-earth-orbit broadband signals, geostationary-orbit broadband signals and low-earth-orbit narrowband signals from the data transmitted by the module.

[0031] According to a preferred embodiment, step S6 includes:

[0032] Real-time monitoring of signal quality indicators, analyzing in combination with historical data, establishing a mapping relationship between signal quality indicators and weights, and transmitting the analyzed results to the weight dynamic adjustment algorithm to obtain weight values.

[0033] Using the adjusted weights, comprehensively evaluating the quality of low-earth-orbit broadband signals, geostationary-orbit broadband signals and low-earth-orbit narrowband signals, and calculating their respective comprehensive quality scores. The comprehensive quality score is:

[0034] Q = α * SNR + β * BER + γ * CNR

[0035] Among them, α, β and γ are weight coefficients, which are adjusted according to actual needs.

[0036] According to a preferred embodiment, in step S8, bandwidth resource B is dynamically allocated,

[0037] B = P * S

[0038] where P is the priority of the data and S is the size of the data;

[0039] Adjust the bandwidth allocation B adjusted ,

[0040] B adjusted = B * (1 + L / Q)

[0041] where L is the network load and Q is the signal quality.

[0042] According to a preferred embodiment, step S9 further includes adjusting the antenna angle during data transmission to maintain signal tracking, including: based on the smart antenna system and beamforming method, automatically adjusting the direction and gain of the antenna according to the direction and intensity of the satellite signal, and concentrating the signal in a set direction to ensure that the satellite signal quality used during data transmission is always in the best state.

[0043] On the other hand, the present application also discloses:

[0044] A high-latitude mountain emergency satellite communication system based on multi-band adaptive selection, and the high-latitude mountain emergency satellite communication system is configured to perform data transmission according to the foregoing high-latitude mountain emergency satellite communication method.

[0045] The foregoing main solution of the present application and its various further selection solutions can be freely combined to form multiple solutions, all of which are solutions that can be adopted and claimed by the present application. Those skilled in the art can understand that there are various combinations according to the prior art and common general knowledge after understanding the solution of the present application, all of which are the technical solutions to be protected by the present application and will not be enumerated herein.

[0046] Advantages of the present application:

[0047] 1. Improve communication stability: By multi-dimensional signal quality evaluation and intelligent frequency band selection, improve the stability of satellite communication and reduce the influence of signal occlusion and attenuation.

[0048] 2. Optimize resource utilization: By dynamic bandwidth allocation and phased array antenna control, optimize the utilization of bandwidth resources and improve communication efficiency.

[0049] 3. Enhance system flexibility: By integrating multiple communication technologies, enhance the flexibility and adaptability of the system and ensure communication continuity in complex environments.

[0050] 4. Improve rescue efficiency: By real-time data transmission and efficient communication, improve the efficiency and effect of emergency disaster relief and ensure the smooth progress of rescue work.

[0051] 5. Facilitate portability and deployment: This method is particularly applicable to portable ground base stations, enabling rapid deployment and use in high-latitude mountainous areas to meet the rapid response requirements in emergency rescue scenarios. Description of the Drawings

[0052] Figure 1 is the data signal transmission flowchart of this application;

[0053] Figure 2 is the multi-dimensional signal quality assessment flowchart of this application. Detailed Implementation Modes

[0054] The following uses specific specific examples to illustrate the implementation modes of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific implementation modes. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0055] Embodiment 1

[0056] Refer to Figure 1 and Figure 2 As shown, this application discloses a high-latitude mountainous area emergency satellite communication method based on multi-band adaptive selection. The high-latitude mountainous area emergency satellite communication method includes the following steps.

[0057] Step S1: The system receives a data transmission request and starts to process the data transmission task.

[0058] Step S2: Determine the size and type of the data packet. After determining the size and type of the data packet, it provides a basis for subsequent processing methods.

[0059] Preferably, step S2 includes: evaluating the size of the data by the file size or the data packet size; identifying the data type by the file extension, data header information, or content analysis.

[0060] Step S3: Obtain relevant information about the over-the-top satellite, including: obtaining ephemeris data and predicting the over-the-top satellite.

[0061] Preferably, in step S3, the ephemeris data is obtained from a satellite navigation system (such as GPS, Beidou) or a satellite operator. Among them, the ephemeris data includes the position, orbital parameters, and over-the-top time information of the satellite.

[0062] Overhead satellite prediction: Based on ephemeris data and the location of the base station, predict the satellites passing over the set base station within a preset time period. For example, use a satellite orbit calculation tool to predict the satellites passing over the base station within the next 24 hours.

[0063] Preferably, steps S2 and S3 can be carried out synchronously.

[0064] Step S4: Adjust the broadband / narrowband phased array antenna to complete the tracking of low-earth-orbit broadband satellite signals, geostationary-orbit broadband satellite signals, and low-earth-orbit narrowband satellite signals.

[0065] Preferably, the process of tracking low-earth-orbit broadband satellite signals includes: first, adjust the Ka broadband phased array antenna to scan and track the low-earth-orbit satellite signals. After tracking and locking, use the Ka-band communication module to process the signals, and then transmit the signal quality to the base station CPU processor for signal quality index extraction in S5.

[0066] Preferably, the process of tracking geostationary-orbit broadband satellite signals includes: after the signal quality index extraction of low-earth-orbit satellite signals is completed, adjust the Ka broadband phased array antenna to scan and track the geostationary-orbit satellite signals. After tracking and locking, use the Ka-band communication module to process the signals, and then transmit the signal quality to the base station CPU processor for signal quality index extraction in S5.

[0067] Furthermore, the Ka-band communication module performs preprocessing operations such as amplification, filtering, AD / DA analog-to-digital conversion, and modulation and demodulation on the received low-earth-orbit / geostationary-orbit broadband satellite signals, and then obtains digital signals.

[0068] Preferably, the process of tracking low-earth-orbit narrowband satellite signals includes: after tracking and locking the L narrowband satellite signals, use the L-band communication module to process the signals, and then transmit the signal quality to the base station CPU processor for signal quality index extraction in S5.

[0069] Furthermore, the L-band communication module performs preprocessing operations such as amplification, filtering, AD / DA analog-to-digital conversion, and modulation and demodulation on the received low-earth-orbit narrowband satellite signals, and then obtains digital signals.

[0070] Step S5: Extract satellite signal quality indicators to complete the signal quality extraction of low-earth-orbit broadband satellite signals, geostationary-orbit broadband satellite signals, and low-earth-orbit narrowband satellite signals.

[0071] Preferably, step S5 includes: transmit the digital signals to the base station CPU processor through the serial port of the wide / narrowband communication module, and use the base station CPU processor to extract the signal-to-noise ratio SNR, bit error rate BER, and carrier-to-noise ratio CNR data information of the low-earth-orbit broadband signals, geostationary-orbit broadband signals, and low-earth-orbit narrowband signals from the data transmitted by the module.

[0072] Step S6: Signal quality assessment. By comparing the comprehensive quality scores of each signal, determine the satellite signal with the best current quality.

[0073] Preferably, step S6 includes: real-time monitoring of signal quality indicators, analyzing in combination with historical data, establishing a mapping relationship between signal quality indicators and weights, and transmitting the analysis results to the weight dynamic adjustment algorithm to obtain weight values;

[0074] Using the adjusted weights, comprehensively evaluate the quality of low-earth orbit broadband signals, high-earth orbit broadband signals, and low-earth orbit narrowband signals, and calculate their respective comprehensive quality scores. The comprehensive quality score is:

[0075] Q = α * SNR + β * BER + γ * CNR

[0076] Where α, β, and γ are weight coefficients, which are adjusted according to actual requirements.

[0077] Specifically, the weight dynamic adjustment process is to dynamically adjust the weights of each signal quality indicator according to real-time data and historical data. This step is to adapt to different signal environments and improve the accuracy of evaluation. For example, by analyzing the influence degree of each signal quality indicator on the communication effect under different environmental conditions, determine the initial weight values. Then, use machine learning algorithms or adaptive algorithms to dynamically adjust the weights of each signal quality indicator according to the change trend of the signal quality indicators and the actual application scenarios. For example, in an environment with strong signal interference, adjust the algorithm to increase the weight of the signal-to-noise ratio, so that the signal-to-noise ratio occupies a more important position in the comprehensive evaluation of signal quality. Thus, incorporate the weight values and signal quality indicators into the S6 signal quality comprehensive evaluation.

[0078] This application uses indicators such as signal-to-noise ratio SNR, bit error rate BER, and carrier-to-noise ratio CNR to comprehensively evaluate the satellite signal quality of low-earth orbit Ka, high-earth orbit Ka, and low-earth orbit L bands, improving the evaluation accuracy.

[0079] Step S7: Select the best transmission network. At the beginning of communication, select the low-earth orbit Ka band for communication, and automatically select the communication band for communication according to the signal quality assessment result of S6.

[0080] According to the signal quality assessment result, automatically select the band with better signal quality for communication. Since low-earth orbit broadband, high-earth orbit broadband, and low-earth orbit narrowband satellites are all managed by the same operator, it can be ensured that the communication will not be interrupted due to authentication failure when switching communication links.

[0081] Alternatively, during the communication process, when the signal quality of the low-earth orbit Ka-band gradually deteriorates, the system automatically determines whether the high-earth orbit Ka-band is available. If the high-earth orbit Ka-band is available, it switches to the high-earth orbit Ka-band; if the high-earth orbit Ka-band is not available, it switches to the low-earth orbit L-band. The method of this application preferentially selects the low-earth orbit Ka-band and automatically switches to the high-earth orbit Ka-band or the low-earth orbit L-band when the signal quality deteriorates, ensuring communication continuity and stability.

[0082] Step S8: Bandwidth dynamic allocation. According to the result of judging the size and type of the data packet in S2, obtain the size and priority of the transmitted data, and dynamically allocate bandwidth resources. For example, for data with high real-time requirements (such as video surveillance and remote command), preferentially allocate a wider bandwidth; for non-real-time data (such as disaster reports and material requirements), allocate a narrower bandwidth. And adjust the bandwidth allocation according to the network load and signal quality, thereby optimizing the resource utilization rate.

[0083] Preferably, in step S8, dynamically allocate the bandwidth resource B,

[0084] B = P * S

[0085] where P is the priority of the data and S is the size of the data;

[0086] Adjust the bandwidth allocation B adjusted ,

[0087] B adjusted = B * (1 + L / Q)

[0088] where L is the network load and Q is the signal quality.

[0089] Step S9: Data transmission. Perform data transmission through the selected optimal network and bandwidth allocation, send the data into the Ka / L-band communication module of the corresponding network, perform data modulation, DA digital-to-analog conversion, filtering, and amplification, and then use the phased array antenna to transmit the data into free space for transmission.

[0090] Preferably, step S9 further includes adjusting the antenna angle during the data transmission process to maintain signal tracking, including: based on the intelligent antenna system and beamforming method, automatically adjusting the direction and gain of the antenna according to the direction and intensity of the satellite signal, concentrating the signal in a set direction to ensure that the satellite signal quality used during the data transmission process is always in the best state. By automatically adjusting the antenna direction and gain, using beamforming technology to reduce signal occlusion and improve the signal reception quality.

[0091] Step S10: Judgment of the current network signal quality. During the data transmission, continuously monitor the signal quality of the current network to judge whether the current network signal quality gradually deteriorates to unavailable until the data transmission ends;

[0092] If the signal quality gradually deteriorates to an unusable state, return to steps S4 to S6 to re-evaluate the signal quality and select a network again;

[0093] If the signal quality is available, proceed to S11.

[0094] Step S11: Do not switch the network to avoid data transmission blockage caused by frequent network switching.

[0095] Step S12: Complete the data transmission task.

[0096] Embodiment 2

[0097] This embodiment also discloses a high-latitude mountain emergency satellite communication system based on multi-band adaptive selection. The high-latitude mountain emergency satellite communication system is configured to perform data transmission according to the high-latitude mountain emergency satellite communication method described in Embodiment 1.

[0098] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included within the protection scope of the present application.

Claims

1. A high-latitude mountain emergency satellite communication method based on multi-band adaptive selection, characterized in that The emergency satellite communication method for high-latitude mountainous areas includes: S1: When the system receives a data transmission request, it starts to process the data transmission task; S2: Judge the size and type of the data packet; S3: Obtain relevant information of the overpass satellite, including: obtaining ephemeris data and predicting the overpass satellite; S4: Adjust the broadband / narrowband phased array antenna to complete the tracking of low-earth-orbit broadband satellite signals, high-earth-orbit broadband satellite signals, and low-earth-orbit narrowband satellite signals; S5: Extract the satellite signal quality indicators to complete the signal quality extraction of low-earth-orbit broadband satellite signals, high-earth-orbit broadband satellite signals, and low-earth-orbit narrowband satellite signals; S6: Evaluate the signal quality. By comparing the comprehensive quality scores of each signal, determine the satellite signal with the best current quality; S7: Select the best transmission network. At the beginning of communication, select the low-earth-orbit Ka band for communication, and automatically select the communication band for communication according to the signal quality evaluation result of S6; S8: Dynamically allocate bandwidth. According to the result of judging the size and type of the data packet in S2, obtain the size and priority of the transmitted data, dynamically allocate bandwidth resources, and adjust the bandwidth allocation according to the network load and signal quality; S9: Transmit data. Transmit data through the selected best network and bandwidth allocation, send the data into the Ka / L band communication module of the corresponding network, perform data modulation, DA digital-to-analog conversion, filtering, amplification, and then use the phased array antenna to transmit the data into free space for transmission; S10: Judge the signal quality of the current network. During data transmission, continuously monitor the signal quality of the current network to judge whether the signal quality of the current network gradually deteriorates to unusable until the data transmission ends; If the signal quality gradually deteriorates to unusable, return to steps S4 - S6 to re-evaluate the signal quality and select the network; If the signal quality is available, enter S11; S11: Do not switch the network to avoid data transmission blockage caused by frequent network switching; S12: Complete the data transmission task.

2. The high-latitude mountain area emergency satellite communication method according to claim 1, characterized in that Step S2 includes: evaluating the size of the data by the file size or data packet size; identifying the data type by analyzing the file extension, data header information, or content.

3. The high-latitude mountain area emergency satellite communication method according to claim 1, characterized in that, In step S3, the ephemeris data is obtained from a satellite navigation system or a satellite operator. Among them, the ephemeris data includes the position, orbital parameters, and overpass time information of the satellite; The prediction of the overpass satellite is: according to the ephemeris data and the position of the base station, predict the satellite passing over the set base station within a preset time period.

4. The high-latitude mountain area emergency satellite communication method according to claim 1, wherein In step S4, The process of tracking low-earth-orbit broadband satellite signals includes: first, adjust the broadband phased array antenna to scan and track low-earth-orbit satellite signals. After tracking and locking, use the Ka band communication module to process the signal, and then transmit the signal quality to the base station CPU processor for signal quality indicator extraction in S5; The process of tracking high-earth-orbit broadband satellite signals includes: after the signal quality indicators of low-earth-orbit satellite signals are extracted, adjust the broadband phased array antenna to scan and track high-earth-orbit satellite signals. After tracking and locking, use the Ka band communication module to process the signal, and then transmit the signal quality to the base station CPU processor for signal quality indicator extraction in S5; The tracking process of low-earth orbit narrowband satellite signals includes: after tracking and locking the L narrowband satellite signals, the L-band communication module processes the signals and then transmits the signal quality to the base station CPU processor for signal quality index extraction in S5.

5. The high-latitude mountain area emergency satellite communication method according to claim 4, characterized in that The Ka-band communication module performs amplification, filtering, AD / DA analog-to-digital conversion, modulation and demodulation preprocessing operations on the received low-earth orbit / high-earth orbit broadband satellite signals, and then obtains digital signals. The L-band communication module performs amplification, filtering, AD / DA analog-to-digital conversion, modulation and demodulation preprocessing operations on the received low-earth orbit narrowband satellite signals, and then obtains digital signals.

6. The high-latitude mountain area emergency satellite communication method according to claim 5, wherein Step S5 includes: transmitting the digital signals to the base station CPU processor through the wide / narrowband communication module serial port, and the base station CPU processor extracts the signal-to-noise ratio SNR, bit error rate BER, and carrier-to-noise ratio CNR data information of the low-earth orbit broadband signal, high-earth orbit broadband signal, and low-earth orbit narrowband signal from the data transmitted by the module.

7. The high-latitude mountain area emergency satellite communication method according to claim 6, characterized in that Step S6 includes: Real-time monitoring of signal quality indicators, analyzing in combination with historical data, establishing a mapping relationship between signal quality indicators and weights, and transmitting the analyzed results to the weight dynamic adjustment algorithm to obtain weight values. Using the adjusted weights, comprehensively evaluate the quality of the low-earth orbit broadband signal, high-earth orbit broadband signal, and low-earth orbit narrowband signal, and calculate their respective comprehensive quality scores. The comprehensive quality score is: Q = α * SNR + β * BER + γ * CNR where α, β, and γ are weight coefficients, which are adjusted according to actual requirements.

8. The high-latitude mountain area emergency satellite communication method according to claim 1, characterized in that, In step S8, dynamically allocate the bandwidth resource B, B = P * S where P is the priority of the data and S is the size of the data; Adjust the bandwidth allocation B adjusted , B adjusted = B * (1 + L / Q) where L is the network load and Q is the signal quality.

9. The high-latitude mountain area emergency satellite communication method according to claim 1, characterized in that, Step S9 also includes adjusting the antenna angle during data transmission to maintain signal tracking, including: based on the intelligent antenna system and beamforming method, automatically adjusting the direction and gain of the antenna according to the direction and intensity of the satellite signal, and concentrating the signal in a set direction.

10. A high-latitude mountain emergency satellite communication system based on multi-band adaptive selection, characterized in that, The high-latitude mountain emergency satellite communication system is configured to perform data transmission according to the high-latitude mountain emergency satellite communication method according to any one of claims 1 to 9.

Images