BARNARD MICROSYSTEMS LIMITED

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unmanned air ...

avionics

Line-of-Sight (LOS) Point-to-Point comms links

Ethernet Links or "Bridges" are useful to exchange duplex Local Area Network data between a Ground Control Station and an Unmanned Aircraft.

• Digital modulation efficiencies
• VHF receiver sensitivity
• Introduction to COFDM
• Introduction to the 5.8 GHz ISM band
• The Mini-Link ML WES-2500 system
• Huber + Suhner SL60-100-57/64-38-E-O SENCITY
• Canon Canobeam FSO link  

from http://www.cse.mrt.ac.lk/lecnotes/cs5424/ppt2.pdf

above and below from http://www.cse.mrt.ac.lk/lecnotes/cs5424/ppt2.pdf

QAM is a combination of ASK and PSK.

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We use the ICOM IC-R9500 receiver, shown above, to determine some receiver sensitivities. This receiver can be tuned from 5 kHz to 3,335 MHz, with a frequency stability over 50 degrees Centigrade of 0.05 ppm.

Above and next from http://www.icomuk.co.uk/categoryRender.asp?categoryID=3510&cCID=6804&tID=477

For a VHF radio used on an Unmanned Aircraft operating in the frequency range from 118 MHz to 132 MHz, we would expect an FM sensitivity of around 0.5 uV in a 15 kHz bandwidth at 12 dB SINAD. The ICOM IC-A24 shown below is a small aircraft VHF transceiver with an FM sensitivity of less than 0.22 uV at 12 dB SINAD.

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COFDM = Coded Orthogonal Frequency Division Multiplexing

Main ponts are:

• PAL video data transmission modulation scheme
• DVB-T bandwidth = 7.61 MHz, with a typical channel spacing of 8 MHz
• The bandwidth can be reduced to 6 or 7 MHz by scaling the clock rate
• "Coded" = Forward Error Correction convolution coding
• This is the modulation scheme used in Digital Video Broadcasting - Terestrial (DVB-T) ETSI EN 300 744
• modulation scheme is QPSK or 16 QAM or 64 QAM
• due to the effects of Doppler shift, the max speed difference between Tx and Rx = 53 - 185 kph

An excellent introduction to this technology can be found at:

• http://www.bbc.co.uk/rd/pubs/papers/pdffiles/ptrev_278-stott.pdf    
• http://www.digitalradiotech.co.uk/cofdm.htm, from where we have copied the following information.

Above: diagrammatic view of a COFDM transmitter

Above: another view of a COFDM transmitter, from http://en.wikipedia.org/wiki/COFDM

Above: diagrammatic view of an OFDM modulator

Above: diagrammatic view of a COFDM demodulator

Above: another view of a COFDM receiver, from http://en.wikipedia.org/wiki/COFDM

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The license free, 5.8 GHz Industrial, Scientific and Medical ("ISM") band, is a large, contiguous, 125 MHz band stretching from 5,725 MHz to 5,850 MHz. It appears that manufacturers have selected bands in the 5.8 GHz ISM band to suit their communication system technology.

Communications modulation schemes used are:

• Orthogonal Frequency Division Multiplexing (OFDM)
• Direct Sequence Spread Spectrum (DSSS)
• Quadrature Phase Shift Keying (QPSK)

Manufacturers and distributors of Wireless Ethernet Links operating in the 5.8 GHz ISM band:

• See http://www.howin.com.tw/PDF/Product_pdf/HM58-8310.pdf
• See http://www.wirelessvideocameras.net/category/230microtek_microtektechnologies_minilink/  
• See http://www.trangobroadband.com/wireless_products/atlas_5010.shtml
• See http://www.winncom.com/moreinfo/item/WWM58-GX-57710L/index.html

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- from http://www.wirelessvideocameras.net/category/230microtek_microtektechnologies_minilink/

Product Features

• Transmits up to 20 Mbps in standard mode and 50 Mbps in super mode

• 8 user selectable channels, 802.11a technology

• Switch selectable setup with LED indicators for ease of operation

• Connects with standard Ethernet devices

• Connects to DVRs, video servers, IP cameras, router/hubs, etc.

• Uses encrypted communication for secure transmission

• Transmits up to 2500 (5.3GHz) or 3900 (5.8GHz) feet

• Unique compact, rugged modular design for easy installation

• Plug and play operability

The MiniLink  Wireless Ethernet system is a dual band wireless transmission system.  It operates in the license free 5.3 and 5.8 GHz U-NII bands. The system consists of dual 802.11a RF modules.  A secure encryption method is used to prevent unauthorized access to the system. 

The MiniLink Wireless Ethernet (WES) system is designed as a plug and play CAT5/Ethernet cable replacement device.  Installing the system is as easy as mounting the RF modules, pointing them at each other and connecting the power and Ethernet/CAT5 cables.  Three LED indicators on the back of each module give power, link activity and signal level status.

The WES modules transmit bi-directional data at 20 Mbps in standard mode and 50 Mbps in super mode.  Standard operation requires no computer programming.  For advanced setup, such as WEP encryption programming, turbo mode, setting IP addresses and User ID/Password changes, the system employs an easy to use web browser interface.

WES modules operate on channels 2 - 4 in the 5.3 GHz band and channels 5 - 9 in the 5.8 GHz band.  Individual channels are selected via a rotary switch on the side of each module.

RF Section

Management

Mechanical

Power

Environmental

System Ranges

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- from http://www.hubersuhner.com/de/hs-rf-wireless-data-links

The principle drawback of this 61.0 - 61.5 GHz, millimetre wave based, Ethernet link for use on a small Unmanned Aircraft is the weight of this antenna: 3.5 kg. This information thus serves the purpose of indicating the capabilities of a millimetre wave link.

General Information

Transmitter

Receiver

Antenna

Mechanical data

Power supply

Environmental data

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- from http://www.airlinx.com/files/AIRLINX Canobeam DT-100Series Data Sheet 0606.pdf

Again, we see the weight of this system (approx 8 kg) being a serious impediment to its deployment on a small Unmanned Aircraft.

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