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Small UAV Command, Control and Communication …

Small UAV Command, Control and Communication Issues Dr Joseph Barnardjoseph.barnard@barnardmicrosystems.com Managing Director, Barnard Microsystems Limited, UK




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Small UAV Command, Control and Communication IssuesDr Joseph Director, Barnard Microsystems Limited, UKAbove: the EADS DRAC UAV developed for the French military servicesTalk outline Aircraft categories Command issues: the downlink Command issues: the uplink STANAG 4586 UA communications Wireless LAN COFDM video transmission Potential frequencies Air Traffic Control voice relay Satellite Comms frequencies Frequencies used by some UAVs Mini UAV data link Predator UAV data link Global Hawk communications links Ground Control Stations ConclusionRight: EADS DRAC UAV Ground Control Station 2Barnard Microsystems Limited 2007Model aircraft categoriesfrom Graham Lynn s presentation: UAS s are not model aircraft at UAV 2007 Conference in Microsystems Limited 2007UAV command issuesFOBLocal Support BaseInternet access viaSAT COMMS LINKWLAN DUPLEX LINKQUAD-RWLAN DUPLEX LINKQUAD-RWLAN DUPLEX LINKDELTA wing RECCE plane called up in bad weatherWLAN DUPLEX LINKC3 air vehicle hovers over centre of area of interest, providing communications and surveillance WIRELESS ETHERNET LINKWLAN DUPLEX LINKSecond C3 air vehicle acts as a communications relay in addition to providing local surveillance4Barnard Microsystems Limited 2007BEGIN HEADERtime 16:35 20071114ua_id GB_123_ABCmsg_num 133msg_version HEADERBEGIN IMUgyro_x IMUBEGIN FCUBEGIN engineid 1set_speed 13000actual_speed 14321carb_setting engineBEGIN engineid 2set_speed 13000actual_speed 11321carb_setting command issues: downlinkOn one mission, might have, for example: 1 command and control UA (helicopter) 1 investigator UA (helicopter) 9 survey UA (delta wing)Each Unmanned Aircraft has around 80 parameters to report on (see right hand side) depending on the number of engines and control surfaces (flaps) and other things to be typical UA status message size is 3,569 characters (bytes): Header Inertial Measurement Unit Flight Control Unit power warnings communications payload GPS sense (as in sense and avoid )5Barnard Microsystems Limited 2007UA command issues: downlinkStatus message frequency: During possible collision, system problems4 mini messages per second On take off and landing:1 message per second (GPS synchronised) during mission 1 message every 10 secondsPeak bandwidth required: downlink Message size = 3,569 Bytes Message format: ASCII text (not in reduced size binary format) Message rate = 1 full length message per second Message bit rate prior to coding = 3,569 x 8 = 28,552 bits / second 128 bit AES encryption is optional: no increase in bits per message With Reed Solomon (255,223) coding to enable the detection and correction of transmission errors, the message size increases to 32,650 bitsA typical GPRS modem capable of operating at 900 MHz or at 1,800 MHz can support a data rate of up to 56 kbps and can thus adequately support the downlink satellite communications modem can also readily support a bit rate of 56 Microsystems Limited 2007BEGIN MISSIONBEGIN SETUPMobileTelemetry 442083410566TEST MT_LINKWLAN CH6TEST WLANTEST FUELTEST FLAPSTEST BATTERYEND SETUPBEGIN WAYPOINT 0GPS 100AGL 120END WAYPOINT 0BEGIN LEG 0_1duration cameratype SONY_W200_1compass 90angle 270MultiShot 100END cameraEND LEG 0_1BEGIN WAYPOINT 1GPS 100ALTIMETER 150SEND TELEMETRYEND WAYPOINT 1BEGIN LEG 1_2duration 00 Cameratype Nikon_D40X_2zoom 100compass 90angle 270SingleShotEND CameraEND LEG 1_2UA command issues: uplinkThe uplink is used to change the flight plan, and needs to be protected from unauthorised flight plan is usually more than 1,000 Bytes in size, and varies greatly with mission is no regular flight plan update message rate, although there are often small GPS correction update messages broadcast from once a second to every ten to the sensitivity of the uplink messages, they are typically : Encrypted using 128 bit AES encryption Forward Error Correction coded using Reed Solomon (255,223) coding, or similar, to both detect errors and increase decryption complexity transmitted using a Spread Spectrum transmitter where the bandwidth is increased at least ten fold (from 10 to 50 times bandwidth increase)7Barnard Microsystems Limited 2007The Nato Standard Agreement ( STANAG ) 4586 defines many of the command and control protocols used in military but the document is very hard to get hold of!8Barnard Microsystems Limited 2007Barnard Microsystems Limited 20079Example of message definition in STANAG 4586 Barnard Microsystems Limited 200710STANAG 4586Unmanned Aircraft control and status messages fall into three general categories: Initialization, configuration, and mission upload messages exchanged pre flight or infrequently during flight as necessary if the operating mode or configuration of the aircraft is changed. Control messages sent to control the aircraft and its engines at a frequency highly related to the level of autonomy characterizing the aircraft. Status messages sent by the aircraft These report dynamic changes in aircraft movements, direction, orientation, engine operation, etc. These messages can be sent very frequently. Typical update rates range from 1 to 20 times per second for critical parameters according to UAS manufacturers, where 1/sec. would be appropriate for a fully autonomous aircraft, and 20/sec. would apply to a hand flown UA. These updates rates are the major drivers in determination of aggregate aircraft to ground data rate, and hence Aircraft communicationsTelemetry and command bandwidth is considered separate from payload (such as video camera and photography) and command bandwidth can be accommodated by a 56 kbit/sec link: GPRS modem satellite communications linkPayload bandwidth is usually much larger: up to 8 Mbit/sec for a high quality video link using COFDM modulation technique. Finding and using this bandwidth is considered a commercial issue: Wireless Local Area Network (WLAN) based around GHz band Coded Orthogonal Frequency Division Multiplexing ( COFDM ) based from 5 to 24 GHz. However, this system is degraded by Doppler frequency shift effects associated with UAV motion, so there is a limit on the UAV speed. Othogonal QPSK if COFDM cannot be used due to the Doppler shift problem11Barnard Microsystems Limited 2007Barnard Microsystems Limited 200712Wireless LAN channel deployment schemefrom Cisco Aironet 1200 SeriesChannel Deployment Issues for GHz WLANsThe highest bandwidth variant of the WLAN family is the new (DRAFT) variant. Switches supporting this draft standard are commercially available. For small Unmanned Aircraft, the use of WLAN is popular for short range (less than 1 km) payload data Microsystems Limited 200713COFDM transmission of video information from a beyond line of sight UAV Coded Orthogonal Frequency Division Multiplexing (COFDM) techniques are increasingly being used to transmit video payload data from a UAV to a receiving antenna on the ground, or to a relay UAV. The attributes of these links are as follows: tolerant of multi path interference efficient modulation schemes: QPSK, 16 QAM or 64 QAM the Digital Video Broadcast Terrestrial (DVB T) standard suggests the use of 2,000 orthogonal sub carriers in an 8 MHz bandwidth, with the frequencies of the sub carriers carefully selected to ensure orthogonality Bandwidth of 6 and 7 MHz are realised by scaling the frequencies of all the sub carriers. Forward Error Correction is applied (the Coded or C part of OFDM) to enable the measurement of the bit error ratio for each sub carrier signal AES encryption, typically 64 bit or 128 bit, can optionally be appliedBarnard Microsystems Limited 200714Bandwidth specifically for UAV telemetry and command usesThis and next two slides from presentation by Axel Klaeyle at UAV 2007 Conference in ParisBarnard Microsystems Limited 200715Barnard Microsystems Limited 200716Barnard Microsystems Limited 200717List of potential frequency bandsfrom EUROCAE WG 73 UAS spectrum vers by Christian Pelmoine 108 112MHz ILS LOC 112 118MHz. VOR, GBAS 118 137 MHz AM(R)S 138 144 MHz 960 1164 MHz DME / TACAN / Transponders GHz GHz GHz Radio location, Radio navigation GHz Radio navigation, mobile, .Barnard Microsystems Limited 200718Air Traffic Control voice relayUAV manufacturers and operators hope this requirement will somehow just go away ...Air Traffic Controllers are adamant this requirement is cast in need to be treated no differently from manned aircraft, from an Air Traffic UAV must respond to a voice command from an Air Traffic Control station, such as an Airport Control Tower, and acknowledge the command, from the ATC station, such as: Flight UAV123 descend to Flight Level 130 with: Flight UAV123 descending to Flight Level 130 One solution for the situation in which the UAV Ground Control Station is remote from the UAV and the Air Traffic Control station is to relay the digitised voice via satellite. The problem is the latency in satellite communications, which in tests using the Intelsat system have been found to be as much as 25 seconds. One suggestion is to use voice recognition secBarnard Microsystems Limited 200719 Satellite communications frequenciesfrom EUROCAE WG 73 UAS spectrum vers by Christian PelmoineFrequencies used by some current Unmanned Aircraftfrom UAV Frequency Management Concerns presentation by Mikel Ryan at UAV 200720Barnard Microsystems Limited 2007Barnard Microsystems Limited 200721from above link for small UAVs from L3 operates from 1,755 MHz to 1,850 MHz with a power output up to 10 Watts and a data rate up to Mbps. There is a general trend for the smaller UAVs to operate their beyond line of sight communications links at the lower frequencies, typically from 900 MHz (GSM modem) to the ISM band at Microsystems Limited 200722By contrast, the communications link for the relatively large Predator Unmanned Air Vehicle consists of:an on-board receiver operating in the frequency range from GHz to GHzand a 50 Watt transmitter operating in the frequency range from GHz to : Global Hawk communications requirements in 2007from UAV Frequency Management Concerns presentation by Mikel Ryan at UAV 200723Barnard Microsystems Limited 2007Global Hawk spectrum systemsfrom UAV Frequency Management Concerns presentation by Mikel Ryan at UAV 200724Barnard Microsystems Limited 2007Global Hawk frequency bands usedfrom UAV Frequency Management Concerns presentation by Mikel Ryan at UAV 200725Barnard Microsystems Limited 200726Barnard Microsystems Limited 2007Example of a complex Ground Control Station, here for the RUAG Ranger UAV27Barnard Microsystems Limited 2007Example of a complex Ground Control Station, here for the Predator UAVBarnard Microsystems Limited 200728Conclusion The telemetry and command link must be considered separately to the payload link. The command downlink of UA status information is relatively simple, and can be managed using a 56 kbps GPRS modem or a satellite communications link. The command and control uplink to the Unmanned Aircraft needs to take into account the need to prevent unauthorised use of the uplink, so this data path must be robust and encrypted. Although the actual information bit rate is relatively low, the transmission bandwidth used in the uplink can be comparable to the downlink bandwidth due to the use of Spread Spectrum modulation. The World Radio Conference may assign a bandwidth specifically for UAS command and telemetry by 2015. The payload link typically requires a much higher bandwidth than the telemetry and command link, typical values being 8 MHz for a COFDM video link. This bandwidth is not readily available for UAV use, so use is often made of the Industrial, Scientific and Medical (ISM) bands at GHz (WLAN ), GHz, 20 GHz and so on. Air Traffic Control voice relay must be supported: the problem at present concerns the latency often experienced with satellite communications: a case for voice recognition software?

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