Drones have become increasingly popu&↕lar in recent years as professional too™✘∏ls, entertainment and ₹♠ε§air sports competitions. € ♥Unmanned aerial vehicleΩ£≈s (UAVS) are the generic t≤←π★erm for unmanned aerial vehic★←> les (UAVS). They incl€★ude many types of unmanned remotel¥ ≠y controlled aircraft, including f±¥¶ixed-wing aircraft, helicopters and mu€←↔¶lti-rotor aircraft.
Professional drones are becom÷←ing more widely used, aerial photog¥≥raphy during sportin®'g events does not have to ✔'rely on expensive full-size h≈¶&→elicopters, and estate ↑agents often use dro≥☆✔nes to record. Drones can also spot mσΩissing people and can monito¶Ω♣↔r habitats at risk of pollutφion. Power companies are using drones §♠↓ to inspect high-voltag✔≤e lines, avoiding co ↔stly blackouts and dangerous manual cli γmbs. Even conservative ε>industries like rail companies are co$"♣nsidering using drones to check tra♦π®γck conditions in areas wi♥ th restricted access. There are al♣∏so delivery companies planning to dα♥•eliver small packages by drone
1.UAV operation technology
Drones can be piloted i'®n two different ways; One is to vi÷©"sually observe the drone's line ☆≤βof sight, and the ot'☆βher is through a first-person p♦≈erspective (FPV). In the FPV sys₽♦tem, video images from an on™©>board camera are transmitted vi☆α₩σa radio to a personal video display ★♠on the ground in the form of a screen<'"£ or video goggles.
2.video transmission wireless technol $ogy
Wi-Fi can be used to ÷≠≈transmit signals over fairly ✘★βshort distances. Wi-Fi sig♣<™↑nals can range from 300 meters to★≥ 2,000 meters, depending on↑♣ the device and conditio♠σns. Transmission range can vaΩβ↔←ry due to a number of fact★$ors:
Transmitter power, the larger th<™e antenna, the farther the®< signal radiation, the s §€εmaller the attenuation;
Antennas, arranged i≈§∞n ascending order of po₽φwer Whip(or wire), Chip, PCB ₽or external (via U.F.L or RPSMA conλπ∏nector);
Frequency is used, usually ≈↑the lower the frequen★>cy, the further the siγ≤gnal can travel.
The environment, surro₽β↑unding trees, buildings±♠→, direct line of sight, atmospheric φ→÷conditions, etc. can negativδφ¶ely affect Wi-Fi sig✔ ★nal range.
Frequency band, 5GHz W™®♥ ifi network is preferr£α§↑ed, which has less interference in ₽₽ urban areas. Other frequency band f₩eatures are as follows:
2.1 Less than 1GHz band
Common solutions come from those who ε®♥fly FPVS (first person views) uφ₽ §sing simple analog cameras≠•✔δ connected to 900 MHz. Using a 1W®←α 900MHz transmitter with alfalfa leaf &δ∏ nbsp; a≤£ntenna (a common antenna type) βand an 18dB gain patch a¶ntenna pointed at your aircγ₹↓ raft, a site line of over 5 >★€αmiles can be easily obtained. ←↕It depends on the area one wants to ♥λγoperate in and the availaεδπ bility of frequency bands to ↓≤÷δuse such applications.
2.2 3G/4G band
You can use the 3G/4G dong§$le that comes with the drone for λwireless transmission at high data r©♥↑>ates. The solution can be u♠$sed based on 3G/4G network avai×↓lability in the operating area.
2.3 Customize the solution.
Integrated RF transceivers are w∑ ↕•idely used not only i±'£≤n Software Defined radio (SDR)1 ←≥≈architectures in cellular telephone ba↓φ→±se stations, such as Mult∏¶i-service Distributed A'↔₽ccess Systems (MDAS) and small ce♦←♥®lls, but also for wireless high-₹≥∞↔definition video transmission in indu<&♥∑strial, commercial and small cells. Mil♠λλ"itary applications suc£←★∞h as unmanned aerial vehicles↕®♣ (UAVs). You can use the R∑₹F transceiver family AD9361/AD9363 and manufact₽→∞§ure suitable hardware b™♠ased on their spectrum availa★☆×>bility, as these transceivers have✘φ bandwidth up to 6GHz. A suitable ♥εγbaseband-side FPGA can be used for d♣&∑₽igital processing.
3. Wireless video transmi&₹≥ssion challenges
The range of wireles¥γ✔δs video links is limited by a nu₩mber of factors. Path loss itse↑lf weakens the signal as dis≠ε↑tance increases, and obstructions in ± "∞the line of sight produce addi₹₽★'tional attenuation. There are ♥™some uncertain challenges of α wireless link in natur≤$₽≠al environment, and effective solution≤"s need to be given. The following two ←✘Ωaspects are the main ®↔; prob♣↔lems:
3.1 interference
Other wireless transmission s↑ources in natural envir≥λ∞≈onments may interfere w™σith drone video transmission si₹•€gnals. If the jamming signal ÷→§occurs in the same frequency band£€₹& as the wireless video →σlink, it will act as in-band noise. Th$φ£is will reduce the sigγ"₩nal-to-noise ratio, resulting in noisy video images andφλ¥± limited link range. A₩≠ typical source of interference ← ₽might be the video transmitter¶← of another drone in the ©∞σarea, a nearby WiFi hots↑₩pot, or a cell phone. Pr∏∏'oblems can be minimized ¶₩↕ by choosing a channel with a frequ'σ &ency as far away from the sour€≤ce of interference as≠★₹ possible or by movi♥™ng the video receiver and a→¶&ntenna. If the inter≤♥γ₹ference source is strong but outside t₽∑&he frequency band of¥σβ the wireless link, it is calle✘¶d a blocker. Blocking signals can penet↕αrate inadequate front-en✘±d channel filtering and reduce ★σthe dynamics of a low n♦ oise amplifier (LNA).
3.2 Reflection induced>' multipath fading
Even with a strong, noisele♠♠¶₩ss signal, wireless links can γ&suddenly go down, es'πδ×pecially in cluttered or urba★∏n environments. This may be due to↓ reflection propagation paths c↑βγ>ancelling out direct propagation paths¥€. Cancellation occurs du♠¶e to phase shifts associat≥★ed with different propagation delay¶•s. This occurs at specific po↓→ints in the receiving >↑✔space and simply moves th∑↕✔±e antenna by less than one wavelength t®★γ≠o disappear. In addition to s∞ ignal cancellation,multipath propa• gation also causes symbo♣₽≥¶l delay extension. Symbols from₽π different paths arrive at dif↕₹ferent times, resultiα÷ng 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-F±↓±λi, Bluetooth, and IoT sαΩhort distance communications, making £×it increasingly crowded. Its use fo"¥r wireless video transmission σ≠and control signals increases the•↑ chance of signal in•∞♦<terference and instability. ₽This creates undesirable and often₽≥€ dangerous conditions for drones. ↑₹₹♣Using frequency switching to maintain aΩ♥δφ clean frequency will ₹δ₹make data and control con¶$nections more reliable. When t★≥he transmitter senses a crowded frequ<≥ency, it automatically swit♠♦♣ches to another band.>✘λ For example, two drones operatin☆$g nearby using the frequency wo•$uld interfere with each other's co≈¥mmunications. Automatically₹& switching LO frequencieγΩ≈s and re-selecting bands will help mai₹≠≥πntain a stable wireless link. Adapti€βve selection of carrier frequency ≠÷™or channel during power-on γ↓is one of the excellent fe™♦>atures of high-end U↔→AVs.
4.2 Frequency Hopping
Fast frequency hopping,> widely used in electronic counterm∞φeasures (ECM), also €¶∑helps avoid interference. Ω✘πUsually if we want frequency hopδ©ping, the PLL needs to be reloλ♣¥×cked at the end of the progr am. This involves writing to ±± the frequency register and, after σ£VCO calibration time and PLL lock&₩ing time, making the jump frequ• ency interval close to tens of $φ₩microseconds.
Figure 3. Schematic diagram of♣™ frequency hopping schem←$®e
4.3 OFDM modulation a¥₽↕®t the PHY layer
Orthogonal frequency division multip"✘≠lexing (OFDM) is a form of sign'al modulation that divide✔s a high data rate modulated stream in¶ ✘to a number of slowly modulated narro★→♣©w band near-range ion carriers. This ×÷★★makes it less sensitive to selectivδ™≤e frequency fading. Dis$"advantages are high peak-to-average󙙥 power ratio and sen>±sitivity to carrier migration a≥σnd drift. OFD αM is widely used in PHY layer of broadb∏®δ₩and wireless communicatδ≤δion.
4.4 5G and WIFI technology
Wireless video for FPV UAVs is stillφ©<' an immature technology and wδΩ↕₩e will see compact aε nd low cost HD FPV systems in theπ$÷ near future. The key to co÷↔st reduction is to improve the integrat♣→∏ion of the system on chip and ↓♠εthe resulting high yieldγ€ α. A paradigm shift occurs when an ent§✘irely new radio, camera, or displa©₩"y concept appears. The'<÷∑ next generation of c"↑≤ellular and WiFi technol€ ogy, called 5G, will utilize dynam≥≥ic beamforming to increase sys"∑→∑tem gain and keep inte∏♠rference low. Together w∑€≥ith more complex MIMO, this ∏★will further improve performance and transmission bandwid↕"th. These concepts are likely to be ♦→∞Ωapplied to future FPV systems as t>£he technology matures. This r€₩λesults in higher performance,♠✔↑ greater range, higher image qu§ ality, and better reliability. It wil↓λl enable drones to deal with more of th✘'£e challenges we face today, as well a→λβ∏s challenges we haven't •™×yet thought of.
