Drones have become increasing♣♠ly popular in recent years as professδδional tools, entertainment and air s ∑ports competitions. Un★₽×★manned aerial vehicle Ω•s (UAVS) are the generic term fδδor unmanned aerial vehicles (UAΩ₩↑VS). They include many type$™>λs of unmanned remotely controlled aircr±↑aft, including fixed-wing airβ'↕craft, helicopters and multi-roto₩βr aircraft.
Professional drones are becom ←♣£ing more widely used, aerial photogra≠•phy during sporting events ←∞ does not have to rely on expen£↔♠>sive full-size helicopters, and estate₹∏✔ agents often use drones to record. Dro'nes can also spot missing people and ca♣¶n monitor habitats at risk of pβ¶↔ollution. Power companies are using d∑≥rones to inspect high-voltage lines, av✘₽oiding costly blackout<"≈s and dangerous manual climb↓ £≠s. Even conservative industries like r₽★ail companies are consideri↓₩∏αng using drones to check track condi↕ε©tions in areas with restricte¥φ←βd access. There are al☆γ♥so delivery companiesαδ♠ planning to deliver small pa ♥σ¶ckages by drone
1.UAV operation technology
Drones can be piloted in two diffeεrent ways; One is to visually obse★€rve the drone's line ♥¶of sight, and the other is tεπ£≠hrough a first-person pδ ↕erspective (FPV). In the FPV system,£σ≈λ video images from an onboa÷™rd camera are transmittedπ♣→φ via radio to a personal video d>γ←↑isplay on the ground ±¶in the form of a screen or v ≠♣™ideo goggles.
2.video transmission wireless♣©σ≈ technology
Wi-Fi can be used to transmit sigφ≠πnals over fairly short distances. Wi-Fi✔€ε signals can range from 300 meters to 2♠ ,000 meters, dependingλ' on the device and conditions. T↓®♦¶ransmission range can £&↔γvary due to a number of factors:
Transmitter power, the la©δλλrger the antenna, the farther t•<πhe signal radiation, the smaller the ♥♥™ attenuation;
Antennas, arranged in ascending oδ✔rder of power Whip(or wireγΩ), Chip, PCB or extern♠↑₽al (via U.F.L or RPSMA c♠α onnector);
Frequency is used, usually th≠ ×e lower the frequency, the fuφ rther the signal can tr§ ♦×avel.
The environment, surrounding'&♠ trees, buildings, direct line of↕≥ sight, atmospheric conditions, εetc. can negatively affect Wi-Fi sβ÷ignal range.
Frequency band, 5GHz ₽≈Wifi network is preferr∏★¶ed, which has less inte §rference in urban areas. Other freque→εncy band features are as follπ<εows:
2.1 Less than 1GHz band☆≈
Common solutions come from those who f÷±βly FPVS (first person views) using sδ&®imple analog cameras connected to 900 £ε>MHz. Using a 1W 900MHz transm₩₩itter with alfalfa leaf♦™≤ >≥≠ antenna (a common antenna∏'♥γ type) and an 18dB gain patch ante≈₽nna pointed at your aircraft, a sit≈e line of over 5 miles can be easily >>♥obtained. It depends on the area one φε→♠wants to operate in and t ↓±€he availability of frequλ♦☆ency bands to use such ap$ε♥✘plications.
2.2 3G/4G band
You can use the 3G/4G dongle that c↑↓ <omes with the drone for wi←reless transmission at high daπ×ta rates. The solutiεΩφon can be used based on 3G/4G network a★δβvailability in the operating area.
2.3 Customize the sol ↓≈★ution.
Integrated RF transceivers are widelyΩ ↔ used not only in Softwar↑©♣e Defined radio (SDR)1 architectures i★®n cellular telephone base stations, ✔&™>such as Multi-servicΩ♥☆λe Distributed Access Sy'₽stems (MDAS) and small cells, but a↑ ±∏lso for wireless high-definition vid÷✔ ✘eo transmission in induσ÷♣♣strial, commercial and small cells. Miλ≈εlitary applications such as unmanned₽♦δ aerial vehicles (UAVs).£&φ• You can use the RF tran↔↕sceiver family AD9361/AD9363 and manuf≥ acture suitable hardware based on thλ☆eir spectrum availabiliφ £ty, as these transceivers have ★λbandwidth up to 6GHz. A sui∏∞table baseband-side 'φ✔€FPGA can be used for digital procesφsing.
3. Wireless video transmis♣≥&δsion challenges
The range of wireless↔ video links is limited by a nu± mber of factors. Path loss itself weakφ$↔ens the signal as distance increa'∑•ses, and obstruction÷¶s in the line of sight produce ∞☆αadditional attenuati$₹ε→on. There are some uncertai±γn challenges of wireless link×®Ω in natural environm→♥§←ent, and effective solution&≤¶s need to be given. The following two ↕™↔aspects are the main ∏♣; •♥¥;problems:
3.1 interference
Other wireless transmis££∏sion sources in natural environβ✔ments may interfere with d<ε® rone video transmission signals>¶π≤. If the jamming sig♣nal occurs in the same freq•™↔uency band as the wireless video linπ→¶©k, it will act as in-band nois∏≤☆e. This will reduce the signal-to←<∏-noise ratio, resulti®✘ng in noisy video images and lim≤>©↑ited link range. A typical★α©π source of interference mig₹×♣δht be the video transmitter of another×♠≤ drone in the area, a nearby WiFi hots$↕↓pot, or a cell phone. Prob™♠lems can be minimize•♣∏d by choosing a chann ₩↕el with a frequency as far away from✔∏€ the source of interference as $£≠possible or by moving the vi →×λdeo receiver and antenna. If the inter↑↕∑ference source is stro∏屶ng but outside the frequenc÷₩"y band of the wireless link, it &βγnbsp;is called a blocker. Bδ∏σlocking signals can penetrate i¥÷βnadequate front-end channel filte≥ring and reduce the dynamics of♦ α© a low noise amplifiλ₽er (LNA).
3.2 Reflection induced multipath fadin£×g
Even with a strong, noiseless s>∏ ✔ignal, wireless links ∑ can suddenly go down, especially i ₩♠n cluttered or urban environments. T±his may be due to reflectioβπ↓n propagation paths cancel ↔ling out direct propagation p&•©₽aths. Cancellation occur£✘✔≠s due to phase shifts ε '★associated with diff♣erent propagation del® ays. This occurs at spε∞ecific points in the receiving∑✘λ space and simply moves t₩σ¶he antenna by less than one wavelength ₽₹♣to disappear. In additio♣∞∑₽n to signal cancellation,α ☆σmultipath propagation$★¶π also causes symbol delay ☆ extension. Symbols fr♣∞≤om different paths arriv♥λe at different times, resulting ¶♦¥£in bit error if the dela™≥← y is large.
4. Overcome challenges
4.1 RF Frequency Switching
The 2.4GHz frequency is widel≤ φy used for Wi-Fi, Bluetooth, and $<IoT short distance communications, maki±∏<★ng it increasingly cγ₩>rowded. Its use for wireless video tra♥≥♠σnsmission and control si€>≈gnals increases the cha'&βnce of signal interference and insta™∑bility. This creates undesira&↓ble and often dangerous conditions for♣ ≈ drones. Using frequency switchin•'₽g to maintain a clean frequency≥α★ will make data and control connectiεα♠•ons more reliable. When t♠✘he transmitter senses a cr←owded frequency, it automaticallyε★$ switches to another band. For eΩ♦xample, two drones o∏€®perating nearby using₽•© the frequency would intααerfere with each other's÷↕ communications. Automatically$• switching LO frequencies and r★£✔λe-selecting bands will help maint®←ain a stable wireless link. Adaptive seγ"¥Ωlection of carrier fre±≠quency or channel duri£♥ng power-on is one of the excellent fea¥φφ☆tures of high-end UAVs.
4.2 Frequency Hopping
Fast frequency hopping, widely us"β₽γed in electronic counterγ♠♦↑measures (ECM), also helps♣£β← avoid interference. Usually i←φ>f we want frequency hopping, th☆₹<e PLL needs to be relocked at₹•Ω¶ the end of the program♦↑×₩. This involves writing to the freqδ &γuency register and, after VCO cal✘♥ibration time and PLL ₹ locking time, making theπ≈ ≈ jump frequency interval cl✔ose to tens of microseconλ§↑'ds.
Figure 3. Schematic d§δiagram of frequency hopping scheme
4.3 OFDM modulation a∑δ t the PHY layer
Orthogonal frequency division§λ↑☆ multiplexing (OFDM) is a f≈₽orm of signal modulation that divides ←±a high data rate modulated stream int ♠≥o a number of slowly modulated∏<' narrow band near-range ion cγ♥☆arriers. This makes it less s™"ensitive to selective frequency fad₽<ing. Disadvantages are♦ high peak-to-average power ratio and ©§× sensitivity to carrier ₹σmigration and drift.€✘β" OFDM is widely used in PHY la∏↑yer of broadband wirel♠↕☆ess communication.
4.4 5G and WIFI technology
Wireless video for FPV UAVs is sti¶πll an immature technologyπα and we will see compact a¶$✘≤nd low cost HD FPV systems in the n↓∞₩ear future. The key to cost reduct₽¥≠♣ion is to improve the integration✘$γ of the system on chip and the←π resulting high yield. A para &₽≈digm shift occurs when an enti₹ rely new radio, camera, or ↕®€<display concept appears. ≤σThe next generation of cellul✔↕Ωar and WiFi technology, called 5☆₩→G, will utilize dynamic beβ'>λamforming to increase syst™★ em gain and keep interference low.§© Together with more c≥∑±omplex MIMO, this will furtε>§her improve per¶ε☆formance and transmission bandwδ✔₩¶idth. These concepts are likely ∞↔to be applied to future FPV syste←←ms as the technologyβ∏ matures. This results in higher pe>¥®•rformance, greater range, highe♠>r image quality, and better reliabilitπ≠¥♦y. It will enable drones to deal↕★ with more of the challenge<→εs we face today, as well as•♦ challenges we haven't yet thoug♠₹©ht of.
