Drones have become increasingly po>&'pular in recent years as™€£< professional tools, ente$≠φrtainment and air sports competi♣<tions. Unmanned aerial vehicleδ s (UAVS) are the generic term for¶©$€ unmanned aerial vehic<>les (UAVS). They include many types o★♦​©f unmanned remotely controlled aiγ‌ rcraft, including fixed-wing aircraγ€∏ft, helicopters and multi-rotor ≥₹"aircraft.

Professional drones are becoming£©'σ more widely used, aerial photograph ✔y during sporting events₽δ♠ does not have to rely on expens✔£φ£ive full-size helicopters, a✔∞nd estate agents often use dγα∑→rones to record. Drones can also ‍'"↑spot missing people andφφ can monitor habitats at risk of p€≥ollution. Power companies are using dr∑↓ones to inspect high↔& -voltage lines, avoidingφ≠ costly blackouts and dangerou>©‌s manual climbs. Even conservativ∏≠e industries like rail✔♥π✔ companies are considering usi→£↕€ng drones to check track conditi ©ons in areas with restricted acce♣↓ε>ss. There are also delivery companies§← planning to deliver smallδ±±' packages by drone

1.UAV operation technology

Drones can be piloted iε>πλn two different ways; One is →φto visually observe the♠∞ drone's line of sight, and the o→↔ther is through a first-pβ©λ↔erson perspective (FPV). In the FPV ≥γsystem,     &n♠←bsp; video images from an o‌€↑•nboard camera are trans≥₽mitted via radio to ♦↔a personal video display on the groδπδλund in the form of a'®©  screen or video goggles.

2.video transmission wire♦±★∞less technology

Wi-Fi can be used to transmit signa∞↕♦ls over fairly short distancesδ•. Wi-Fi signals can range from 30→σ≤γ0 meters to 2,000 meters, depending₹•σ on the device and conditioΩ  ns. Transmission range can v★±∞ary due to a number of factors:

Transmitter power, the ✔• larger the antenna, the faσ rther the signal radiation, the s∞₩maller the attenuation;

Antennas, arranged in ascendi©≥♠ng order of power Whip(or wireββ), Chip, PCB or external (viδ£×a U.F.L or RPSMA connector);

Frequency is used, usually the lower t$↑he frequency, the further the sig™←↑nal can travel.

The environment, surrounding∞♠• trees, buildings, di÷φγ&rect line of sight, atmospher≠<♠ic conditions, etc. can negaπ≈±&tively affect Wi-Fi signal range$₽.

Frequency band, 5GHz Wifi network is pγ£λ×referred, which has less interference i®≈λn urban areas. Other frequency ≈‍≤band features are as follows:

2.1 Less than 1GHz band

Common solutions come from thσ←δ•ose who fly FPVS (first per§®₩εson views) using simple anδ®♣alog cameras connected to 900 MHz.₹  Using a 1W 900MHz t♣☆±ransmitter with alfalfa leaf &nb÷&sp;     anten★↓φna (a common antenna type) and ‌♥an 18dB gain patch antenna poin♦$ted at your aircraft, a site line of €¶over 5 miles can be eas ∞≥₽ily obtained. It depends o±≠✔n the area one wants to operate i∞§n and the availability of ♣★frequency bands to use such applicatiλ ♥↓ons.

2.2 3G/4G band

You can use the 3G/4G donglβ≈e that comes with the drone for wire​≠₽less transmission at hig→'∏h data rates. The solution'​→ can be used based on 3G/4G netw✔↔ork availability in the ÷≈£ operating area.

2.3 Customize the solutioδ✔♣®n.

Integrated RF transceivers are widely u©"sed not only in Softw®↕€σare Defined radio (SDR)1 £™αarchitectures in cel≥≈lular telephone base stations, ∏←™such as Multi-service Distributed Aπ♠ccess Systems (MDAS) and small  ↑ αcells, but also for wi≤←reless high-definition video transmissi∑≠on in industrial, commercial an ™♦d small cells. Military appliφ↑¥cations such as unmanned aer¶₹×ial  vehicles (UAVs). You can use ♠★the RF transceiver fami≠→ly AD9361/AD9363 and manufacture↔& suitable hardware based on t≥∑¥heir spectrum availability, as these tr& ansceivers have bandwidth up to 6GHz. ™€₹A suitable baseband-side FPGA can Ω be used for digital processing.

3. Wireless video transmiδ∞$<ssion challenges

The range of wireless video ©ε∞links is limited by a number of factors÷'. Path loss itself weakensε© the signal as distance increas₹​es, and obstructionsπ∏ε in the line of sight produε×ce additional attenuation. The‌γre are some uncertain challenges of wir∞™eless link in natural environme★±₹↕nt, and effective solutions need to$₽™' be given. The follow×€ing two aspects are the main ↕ ↓       problφ♦ems:

3.1 interference

Other wireless transmis€€sion sources in natural environments ♥♦may interfere with drone vidσ↔♠eo transmission sign÷♠§αals. If the jamming signal ↔♣ occurs in the same frequency €≠♣band as the wireless video link, ±‍it will act as in-band no↕♥©ise. This will reduce th™'<✔e signal-to-noise ratio, resultinγ ★¶g in noisy video imag‌γ☆≤es and limited link rangφ£e. A typical source of interference m<δ₩ight be the video transmitt↔₽>er of another drone in the ar★Ω ₽ea, a nearby WiFi hotspot, or a ∑↓cell phone. Problems can be minimiz∑λed by choosing a channel with a™∞¥ frequency as far awa✘ ✔y from the source of interference as p>‍≠ossible or by moving the 'εΩvideo receiver and antenna. If thλ×e interference source is stron✔®≤g but outside the frequδ☆ ency band of the wirele​φss link, it  is calle∑∏←d a blocker. Blockin←₹£→g signals can penetrate iβ£nadequate front-end channel filter£←ing and reduce the dynamics of a φ low noise amplifier (LNA).

3.2 Reflection induced mult‌ ipath fading

Even with a strong, noiseless signal÷&, wireless links can suddenly go±‌©→ down, especially in cluttered or ☆™≈urban environments. This may &Ωbe due to reflection propag™σation paths cancelling out dπ÷§irect propagation paths.∑δ Cancellation occurs due to phase ∑‍¶‍shifts associated with differen☆₽<γt propagation delays. This occurs at ®αspecific points in the receiving ¶>±λspace and simply moves the an​>₽σtenna by less than one wa©✘velength to disappearφ<∑ . In addition to signal ca±★÷σncellation,multipath p∞÷ropagation also causes symbol del×€>≤ay extension. Symbols from₽✘&® different paths arrive at different ↓↑$™times, resulting in bit error if ‌©§÷the delay is large.

4. Overcome challenges

4.1 RF Frequency Switching

The 2.4GHz frequency is widely↓∑ used for Wi-Fi, Blueto♣®≥oth, and IoT short distance communicφ≥↔★ations, making it increasingly   "↕crowded. Its use for wir≈♥₩↔eless video transmissio→♦πn and control signals increases the ε←ε$chance of signal interference and in★↑™stability. This creates undesirable ‌¶ and often dangerous conditi≠ $ons for drones. Using f‌≈¶←requency switching to maintain a clλ≈☆φean frequency will make data and contro→✘l connections more reliabl¥₹∏¶e. When the transmit<♠ter senses a crowded frequency, i×λt automatically switchγ≠es to another band. For example, ÷®←βtwo drones operating®™ ♣ nearby using the frequency wou≥$ld interfere with eac™Ωβh other's communications. Automatic•÷ ☆ally switching LO frequencies a&₹λnd re-selecting bands €→₽will help maintain a sta→¥ble wireless link. Adaptive selecti☆★on of carrier frequen₹α§cy or channel during power-on is o&✔εne of the excellent features of h‌↑igh-end UAVs.

4.2 Frequency Hopping

Fast frequency hopping, widel®δ₽y used in electronic countermeasures ♣★(ECM), also helps avoid interference.±≈≤♠ Usually if we want frequency hopping, ‍₩✘∞the PLL needs to be relocked at the e‍☆nd of the program. This involves wrα↓iting to the frequency registe∑Ωr and, after VCO calibration time an€♠¶≠d PLL locking time, maki₽λng the jump frequency in>≈£φterval close to tens of  micr& oseconds.

Figure 3. Schematic diag σσram of frequency hopping scheme

4.3 OFDM modulation at the PHY l‌₩εayer

Orthogonal frequency division m↑→<ultiplexing (OFDM) is a form of sig•↕§'nal modulation that divides a high data✔​Ω rate modulated stream into a number ¥®€₹of slowly modulated narrow band ©®near-range ion carriers. T∑λ®₹his makes it less sensitive t÷φγo selective frequency fa£ "λding. Disadvantages a ₽♣re high peak-to-average pow∞£"↓er ratio and sensitivity to carrier mi"₹gration and     drif×♠→✘t. OFDM is widely us≤π₽₽ed in PHY layer of bro ♥✘adband wireless communica≤βφtion.

4.4 5G and WIFI technology

Wireless video for FPV UAVs i γ€σs still an immature technology anλ¥d we will see compact and low cos★‌×★t HD FPV systems in tγ←≥♣he near future. The key to cost r™'ε↕eduction is to improve the integ↔↕ ration of the system σ↓‌on chip and the resulting h§§↑εigh yield. A paradigm shift occurs when"∏σ an entirely new radio, camera, o✔©©r display concept appears. The next g™€←eneration of  cellu♥↓lar and WiFi technology, &∏Ωσcalled 5G, will utilize dynamic ε≠beamforming to increa₹€✘se system gain and keep interference l&•Ω♠ow. Together with mor∏™ ♣e complex MIMO, this will further ↕™  improve performance and t≈£ransmission bandwidthφ δ . These concepts are likely ₹>↑÷to be applied to future₩★ FPV systems as the tech®α ✘nology matures. This results↓✔☆ in higher performance,   greater¥± range, higher image qual♣σ♦Ωity, and better reliability. It wil↔≈¥l enable drones to deal with≈γλ more of the challenges we faε✘γ"ce today, as well as challenges we h•∞aven't yet thought of.