NLOS Wireless
Acronyms
Term
C2 Link
Fresnel Zone
BLOS
Ground Plane
Wavelength
NLOS
SWaP
TX or Tx
RX or Rx
db
dbc
dbm
RF
impedance
RF
RF Band
RF Bands
Definition
Command/Control link often using short burst of data to remote control UAV
If unobstructed, radio waves will travel in a straight line from the transmitter to the
receiver. If there are obstacles near the path, the radio waves reflecting off those
objects may arrive out of phase with the signals that travel direct and reduce the power
of the received signal. Fresnel provided a means to calculate where the zones are,
where a given obstacle will cause mostly in phase or mostly out of phase reflections
between the transmitter and the receiver. See
http://en.wikipedia.org/wiki/Fresnel_zone
Beyond Line-of-site…often refers to Satcom communications
Metallic surface (disk) at base of antenna with 3 times wave (or more) wavelength
diameter of operating frequency
Length of one wavelength of RF in free space (300/Frequency Mhz) = length in meters
299,792,458 = meters per second in vacuum
Non Line-of-site, TX cannot see RX in a direct path or there is partial obstruction in the
direct path.
Size Weight and Power requirements
Generic transmitter any type
Generic receiver any type
Decibels…smallest unit of level change that a human can sense named after Alexander
Graham Bell see: http://en.wikipedia.org/wiki/Alexander_Graham_Bell
db see: http://en.wikipedia.org/wiki/Decibel
decibels relative to carrier, a common measurement in RF engineering to specify the
power of a sideband in a modulated signal relative to the carrier in decibels or show
relative change in RF level
db relative to one milliwatt for a specified impedance see:
http://en.wikipedia.org/wiki/DBm
AC resistance of component for a specified frequency, voltage and current see:
http://en.wikipedia.org/wiki/Impedance_(electrical)
Radio frequency through the atmosphere or conducted via cable or metallic circuit
typically from 10 Khz to 300 Ghz (or higher)
A specific range of frequency defined by the Lowest and Highest frequency that can be
defined see: http://en.wikipedia.org/wiki/Frequency_spectrum#Radio
http://en.wikipedia.org/wiki/RF_spectrum#Radio_communication
(defined by FCC)
Path Loss
RF Power
Frequency
Mixer
RF level drop through the atmosphere line-of-site expressed in relative db
Calibrated RF measurement in Watts or dbm of the total RF energy measured either
peak or average with a specific load impedance
A nonlinear electrical circuit that creates new frequencies from two signals applied to it.
In its most common application, two signals at frequencies f1 and f2 are applied to a
mixer, it produces new signals at the sum f1 + f2 and difference f1 - f2 of the original
frequencies. The output will include all 4 frequencies at the same instant.
RF Detector
BW
Bandwidth
OBW
Occupied
Bandwidth
AM
Modulation
FM
Modulation
PSK
Phase Shift
Modulation
COFDM
Modulation
RX Diversity
TX Diversity
NF
See: http://en.wikipedia.org/wiki/Frequency_mixer
For AM modulation a simple diode for complex modulation DSP decoder sensing
amplitude and phase changes see: http://en.wikipedia.org/wiki/RF_detector
The -3 db upper/lower limit of a circuits RF frequency response. Example a simple
dipole antenna might have a bandwidth of 5% of its center frequency at 2.3 Ghz in this
0.115 Ghz BW
See: http://en.wikipedia.org/wiki/Bandwidth_(signal_processing)#X-dB_bandwidth
Similar to BW the total occupied bandwidth using spectral averaging/smooth to identify
the -1db upper/lower frequency roll off of the modulation envelope of a complex digital
waveform to capture 99% of the total RF power see spectrum plot at:
http://en.wikipedia.org/wiki/DVB-T
Amplitude modulation of an RF carrier see:
http://en.wikipedia.org/wiki/Amplitude_modulation
Frequency modulation of an RF carrier see:
http://en.wikipedia.org/wiki/Frequency_modulation
Phase shift modulation of an RF carrier see:
http://en.wikipedia.org/wiki/Phase_modulation
OFDM is coded OFDM (COFDM) and discrete multi-tone modulation (DMT), and is a
frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation
method. The word "coded" comes from the use of forward error correction (FEC). See:
http://en.wikipedia.org/wiki/COFDM
A receiver with two or more RF inputs that can compensate for the amplitude and
phase of two or more RF inputs to “sum” data for additional signal gain and have major
improvement over data drop versus a single antenna. This assumes the antennas
connected to the inputs are separated by several wavelengths, pointed at the same RF
signal source with identical gain and RF patterns.
RF TX power split to two antennas using OFDM or other modulation that is tolerant of
signal delay. Often done on a UAV to compensate for the UAV body blocking of the RF
signal.
Noise figure (NF) is measures of degradation of the signal-to-noise ratio (SNR), caused
by components in a radio frequency (RF) signal chain.
RX Threshold
RX Sensitivity
+ 1 dbm level higher than RF level that causes some intermittent video. In other
words…minimum RF level at the RX for solid, no break-up, video display. In data
links RF level in dbm for a specified BER often 1 part 10-4th or 1 part 10-6th
Multipath
RF signal arriving at receive antenna from 2 or more different possibly cancelling the
direct path. Multipath may come from ground bounce, water reflection, buildings,
atmospheric thermal layers, mountains etc. Result is lost data, drops outs in video
Total delay in a communications system often measured in milliseconds. Delay
noticeable around 33 ms and irritating to UAV operations as it approaches 200 ms.
Transport Stream, total data stream including all overhead as headers and FEC to move
data through a comm link often expressed in kbps or Mbps.
Parts per Million, e.g.: 3 PPM of 2.3 Ghz (2300 Mhz) = 6,900 Hz (+/-)
Latency
TS
PPM