Does NB iot module need a sim card? The simple answer is needed. (More wireless communication knowledge; IoT knowledge, antenna cable https://www.whwireless.com ) NB iot is deployed under the signal coverage of the existing cellular network and uses the licensed frequency band, so it can only be used through the network provided by the operator. Someone may ask why lora, which is also a low-power wide area network, can not use a sim card, while nbiot has to use a sim card? This is still related to the network frequency bands used by the two networks. NB iot devices do not need a gateway, and they rely on 4G coverage and use the spectrum in LTE, so NB-IoT is not easy to work in remote areas without 4G signals. Lora uses an unlicensed frequency band, which means that there is no frequency band operated by an operator. Therefore, Lora needs to pass through a gateway during use. NB-IoT network The NB-IoT network is shown in the figure. It can be seen that it consists of 5 parts: NB-IoT terminal. As long as the corresponding SIM card is installed, IoT devices in all industries can access the NB-IoT network; NB-IoT base station. It mainly refers to base stations that have been deployed by operators, and it supports all three deployment modes mentioned earlier; NB-IoT core network. Through the NB-IoT core network, the NB-IoT base station can be connected to the NB-IoT cloud; NB-IoT cloud platform. The NB-IoT cloud platform can process various services and forward the results to the vertical business center or NB-IoT terminal; Vertical business center. It can obtain NB-IoT service data and control NB-IoT terminals in its own center. Compared with the transport layer in the traditional IoT, NB-IoT changes the complex network deployment, in which the relay gateway collects information and feeds it back to the base station. Therefore, many problems such as multi-network networking, high cost and high-capacity batteries are solved. A network throughout the city can bring convenience to maintenance and management, and can easily solve and install advantages by separating it from property services. However, there are new security threats: Access to high-capacity NB-IoT terminals One sector of NB-IoT can support connections with approximately 100,000 terminals. The main challenge is to perform effective authentication and access control on these large-scale real-time high-volume connections to avoid malicious nodes from injecting false information. Open network environment The communication between the perception and transport layer of NB-IoT is completely through the wireless channel. The inherent vulnerabilities of the wireless network bring potential risks to the system. That is, an attacker can transmit interference signals to cause communication interruption. In addition, because there are a large number of nodes in a single sector, an attacker can use nodes controlled by him to sponsor a denial of service (DoS) attack, so he can affect network performance...

The difference between RTK and PPK UAVs are widely used, with low cost, multi-tasking, good maneuverability, high efficiency, and low radiation. They are widely used in all aspects of military and civilian production. Because GPS has the characteristics of all-weather, high-precision and automatic measurement, the UAVs currently used for surveying and mapping basically use GPS for positioning and navigation. The GPS single-point positioning accuracy of UAV flight control is too poor. Previously, a large number of image control points were used to correct image distortion. However, in some special terrains (such as mountains, valleys, rivers, etc.), it is difficult for field personnel to deploy image control points. In order to reduce the workload, most image control points are not even needed, and it is necessary to improve the positioning accuracy of the aircraft, RTK technology and PPK technology can achieve centimeter-level accuracy. Below we start from the two technical principles of RTK and PPK, and conduct a comparative analysis to find a more suitable method for GPS air positioning. 1. The working principle of RTK   RTK (real-time motion) measurement system usually includes three parts: GPS receiving equipment, data transmission system and software system for dynamic measurement. The RTK measurement technology is based on the carrier phase observation and has a fast and high-precision positioning function. The carrier phase differential measurement technology can obtain real-time three-dimensional positioning results of the measuring station in the specified coordinate system, and has centimeter-level positioning accuracy. The working principle of RTK measurement is: put one receiver on the base station and put the other receiver on the carrier (called the mobile station). The base station and the mobile station simultaneously receive signals sent by the same GPS satellite. The obtained observation value is compared with the known position information to obtain the GPS differential correction value. Then, the correction value is sent to the mobile station of the public satellite via the radio data link station in time to refine its GPS observation value so as to obtain a more accurate real-time position of the mobile station after the differential correction. At present, the positioning plane accuracy of the mainstream manufacturer RTK can reach 8mm + 1ppm, and the elevation accuracy can reach 15mm + 1ppm. There are two main communication methods between base station and mobile station: radio station and network. The radio station signal is stable, and the network signal transmission distance is long, and each has its own advantages. Second, the working principle of PPK   The working principle of PPK (post-processing kinematics, GPS dynamic post-processing differential) technology is to use base station receivers for simultaneous observation, and at least one mobile receiver for simultaneous observation of GPS sate...

In which conventional civil frequency bands are the control signals used by drones mostly? The device consists of a handheld host and a battery pack. The handheld host is a three-band transmitter antenna integrated design, which can simultaneously generate 2.4GHz/5.8GHz frequency UAV flight control jamming signals and satellite positioning jamming signals, through the UAV's uplink flight control channel and satellite positioning channel Blocking interference causes it to lose flight control commands and satellite positioning information, making it unable to fly normally. Depending on the design of the UAV, it will have the control effect of returning, landing and falling.  In the offensive and defensive situation, there is usually a certain distance between the drone operator and the sensitive area that needs to be fortified. The drone took off from the vicinity of the manipulator, and then gradually approached the fortified area. When the drone arrives near the fortified area and can carry out effective reconnaissance or sabotage activities, the distance from the drone to the fortified area is usually much closer than the distance between it and the operator.  In the above situation, all uplink signals sent by the operator (sent from the ground to the drone) will be relatively weak due to the long distance. With the same power, because the defender is closer to the drone, the signal will be stronger than the manipulator. The downlink signal received by the defender will also be stronger than the manipulator. But the goal of defense against the downlink signal is to prevent the operator from receiving it, and the distance from the drone to the operator at this time is about the same as the distance from the defender to the operator. Therefore, the blocking of the downward signal does not have a topographical advantage.  It can be seen from the above analysis that interference with uplink signals is more beneficial. It just so happens that the uplink signal is usually a remote control signal, which is directly related to the control of the drone. If the uplink signal is interfered, the drone will lose immediate control and can only operate according to the steps preset by the program (usually landing or hovering). The downlink signals are mainly telemetry and images. Although there may be sensitive information, it is not as important as the control signal. In addition, the defender is not dominant in the situation and usually takes a laissez-faire attitude to the downlink signal.  GPS relies on medium orbit satellites. Generally speaking, the signal reaches the surface of the earth after tens of thousands of kilometers, which is already very weak. Therefore, it is easier to interfere with GPS signals when the UAV is very close to the defender. If you want to deceive it, you need to use more complicated methods to simulate GPS satellites, which is much more difficult.  At present, the control of UAVs mostly uses radio commu...

Industrial wireless network is unreliable? Not dare to use it? That is because the design and implementation work has not been done well! Expected to finish reading in 10 minutes Industrial environments have many common attributes: they are dirty, no isy, and cause many obstacles or interferences to radio frequency propagation. In the long run, it will be difficult for consumer wireless devices to work normally in this harsh environment. The equipment must be tailored to the operating environment-industrial installations do not follow standard design rules. On-site investigations are useful, but the presence of electrical noise and mobile equipment, large metal structures, and even the presence of factories in the industrial process may have a significant impact on signal propagation. Industrial wireless access point Compared with office installations, industrial installations require more wireless access points due to the large number of signal interruptions. Due to the topology of industrial facilities, it may be necessary to use directional antennas. For example, a warehouse requires the use of directional antennas to guide radio frequency down to narrow aisles between metal racks. These metal racks may be filled with metal or some material that absorbs radio frequency. There may be electric motors and moving objects everywhere in the factory floor, such as forklifts and overhead cranes. Certain manufacturing requires liquid coolants. These liquid coolants can generate vapor, spray, or splash, which can disrupt transmission or cause wireless devices to get grease or water. Some processes require the use of electric arc welding, which will generate a powerful broad-spectrum noise signal, which will interfere with many radio frequency signals. The first parameter to consider is the working environment. Considering the above situation, the most obvious problem is the device casing. Choosing the right casing is the most basic technical indicator, which can protect the access point from environmental factors. Industrial cabinets using NEMA definition or IP classification system can simplify the design specifications, but the equipment engineering department is required to classify the specific area where the equipment is installed. It is not the correct method to imagine which cabinets are suitable, and it will lead to premature and unexpected system failures. . All industrial environments are different and need to be assessed on a case-by-case basis. Another option is to place the wireless device outside the harsh environment and install a distributed antenna system (DAS) to provide radio frequency to the required area; however, this is usually impractical and will greatly increase the installation cost. A thorough understanding of the signal propagation through the distributed antenna system is required, and the operation through the cable and directional signal splitter or coupler system is required. The design of this system may be difficult. A...