1.2 band
1.2G 2.4G is generally used for coverage, which needs to be transmitted closer and has many devices working in this frequency band, so there will be a lot of interference; 5.8G is generally used forbridgingFor example, the frequency band is relatively pure, which is farther than 2.4G transmission and stronger penetration ability of 5.8G; 1.2G and 2.4G are longer than 5.8G wavelengths, so the diffraction ability is better than 5.8G; and usually, 5.8G devices are directional devices with long transmission distances, such as Motorola's Canapy, Nanostation, etc.
1.2.2 Data Link
(1) U.S. militaryDroneTypical products of the system's general data link include CDL, TCDL, MP-CDL, and the working frequency bands include UHF, X, Ku and other frequency bands. The downlink transmission rate has multiple levels such as 10.71Mbit/s, 45Mbit/s, 137Mbit/s, 274Mbit/s, etc. It adopts a variety of modulation systems such as FSK, BPSK, QPSK, OQPSK, etc., which can realize high-speed point-to-point data transmission and low-rate network distribution and transmission functions below 10.71Mbit/s. The direct sequence spread spectrum (DSS) anti-interference transmission system is adopted in the uplink, and a hybrid spread spectrum anti-interference transmission system combined with expansion hopping is also adopted in its monitoring and control data link (SCDL).
(2) Link16 data linkbased on TDMA protocol, the tactical data link composed of the Joint Tactical Information Distribution System Waveform (JTIDS) and J-sequence message standards, and the working frequency band is in960-1215MHz between. AdoptedFrequency hopping, direct sequence spreadingAnti-interference technology is a large capacity, high confidentiality, strong anti-interference technology used by the United States' various military services, including land, sea and air.Time division multiple accessThe tactical information distribution system has powerful functions such as relative navigation, identification, mission management, air control, surveillance, weapon collaboration, confidential voice and electronic warfare. It can connect the terminal equipment of various military units to form a unified communication network to achieve battlefield situation sharing, unified command and coordinated combat. (Sun Yu)
（3) Tactical targeting network technology (TTNT)It is a high-speed, confidential, IP-basedWeapons Cooperation Data Link, mainly used to achieve timely sharing of various combat information in the process of target detection, active identification, aiming, strike and damage assessment. The UAV Roadmap released by the United States in 2005 determined that future development of tactical data links will revolve around IP To develop to meet the versatility needs of low-surface platforms.
（4) Task data link hardware: Data transmission equipment based on COFDM technology, generally mainly uses graph transmission, with a data transmission rate above 2Mb/s, and will be equipped with a GPS channel and a serial transmission channel to meet the downlink transmission of other small-capacity data. COFDM-based IP Bridge equipment, a network interface is configured on it, including a video interface, which meets the needs of images and other types of large data volumes, and is a better choice for task chain equipment.
（5) Task Data Link Protocol:The task data link is generally downlink application information, such as image, video or other remote sensing data. It is proposed according to the needs of various drone applications. The data volume is generally very large, and it generally needs to reach a data transmission rate of 1Mbps. We mentioned abovehardwareTwo options for task data links,First, use video transmission data links mainly based on image transmission equipment, the above will be supplemented by a simple serial port low-speed downlink channel. In this case, the data link protocol is generally customized by the equipment supplier, and we can obtain processed image and image data. in additionOne option is to use a wireless bridgeMany equipment suppliers can now supply equipment with power less than 1w but data transmission is 1Mb/s using microwave technology. For this type of device,TCPThe /IP protocol can perform data transmission. You can have your own richer choices for the types of information transmitted, and can realize the organizational transmission of various types of remote sensing data. In the data content encoding, the same encoding method as the control data link can be adopted, but the underlying transmission protocol and interface are different. However, for image and video transmission, code streaming technology based on udp and other means, and corresponding digital processing is performed before the aircraft is downstreamed.
1.2.3 Antenna
The basic concept of antenna:
（1）bandwidth: The resonant frequency is a frequency point, but within a certain range near this frequency point, the antenna'sperformanceThey are all the same, and this range is bandwidth. High gain is often accompanied by narrow bandwidth.
（2）Gain: refers to the relative gain, which refers to the logarithm of the intensity of the antenna's strongest radiation direction and the intensity of the reference antenna. If the reference antenna is an omnidirectional antenna, the unit of gain is dBi. If the antenna gains positive in some directions, its gain in other directions is negative due to the conservation of energy of the antenna.Omnidirectional antennaBecause it has no direction, it is mostly used in the center station of point-to-multipoint communication.Directional antennaBecause it has the maximum radiation or reception direction, the energy is concentrated and the gain is higher than that of the omnidirectional antenna, which is suitable for long-distance point-to-point communication. At the same time, it has a strong anti-interference ability due to its directionality.
（3) Antenna radio wave polarizationWhen radio waves propagate in space, their electric field direction varies according to certain rules. This phenomenon is called the polarization of radio waves. The electric field direction of the radio wave is called the polarization direction of the radio wave. If the electric field direction of the radio wave is perpendicular to the ground, we call it a vertical polarized wave. If the electric field direction of the radio wave is parallel to the ground, it is called a horizontal polarized wave. Due to the characteristics of the radio wave, the signal that determines that horizontal polarization propagates will generate polarization current on the ground when it is close to the ground. The polarization current generates heat energy due to the influence of the earth's impedance, which causes the electric field signal to rapidly attenuate. However, in the vertical polarization method, polarization current is not easy to generate, thereby avoiding a large attenuation of energy and ensuring the effective propagation of the signal.
- Input impedanceIt is the ratio of input voltage to input current at the antenna feed end.
- Standing wave ratio:It is the inverse of the traveling wave coefficient, with a value between 1 and infinity.
（6）Return loss: It is the inverse of the absolute value of the reflection coefficient, expressed as a decibel value.
1.2.4 Multi-computer communication relay planning
Multi-relay UAV relay planning [Sun Yu]: There is generally at least one ground station in a multi-drone system to manage multi-air mission flights. If the multi-drone location planning is made byUnified planning of ground stationsThen thinkOnline planning algorithm, if each drone nodeIndependent planningThis strategy is calledLocal planningAlgorithm orOffline algorithm。