1. Title of the invention
[001] A Method for simulating the L-Band Free space channel.
2. Field of invention
5 [002] The field of invention is related to a method for simulating the
free space Channel effects on L-Band Avionic systems.
3. Background of invention
[003] The L-Band avionics systems designed and developed by
10 SLRDC (Strategic Electronics Research and Design Centre) are used as
navigation equipment in Military aircrafts and Helicopters. These Military
alrcrafts and Helicopters are used by Indian Defense services shall undergo
various phases of evaluations; flight testing is one among them and it is
considered as the final stage of evaluation Flight evaluation involves
15 integration of avionics equipment to aircraft and testing the performance in
airborne condition. During flight testing, loss of RF (Radio Frequency) signal
communication is envisaged due to high maneuverability of airborne
platform (Aircraft or Helicopter). _
[004] During flight evaluation it was observed that L-band Avionic
20 equipment lost signals and performance was degrading. On analysis it was
found that one of the reasons for degraded performance is due to free space
channel effects like, atmospheric refractivity. surface reflectivity, aircraft
maneuvering, polarization, fading, multi path reception etc.
[005] The qualification and flight evaluation of these L-Band 25 avionics system involves many test points and test conditions. Sometimes
the degraded performance of the avionics systems observed during flight
evaluation is not replicated after flight testing. It becomes difficult to simulate
the degraded performance of L—Band avionics equipment on bench level or
in the Aircraft on ground scenario.
30 [006] As simulation of the problem conditions was difficult,
Debugging or troubleshooting the flight evaluation issues becomes tough.
Sometimes it takes months to identify the root cause and during this time it
consumes huge manpower, more facility utilization and financial implication
like fuel consumption etc. To simulate this scenario there is need for a Free
space channel simulator.
3.1. Prior Art
The search for the similar patents shows up the patent no.
US7508868BZ dated Mar 24‘2009. However, there are differences between
the mentioned US patent and the invention proposed in the patent.
The differences are the proposed patent is for L-Band avionics system
and the similar invention can be carried out for other frequency bands with
the appropriate components. Whereas the US patent is for mobile
communication systems. The power levels are high in the proposed
.
invention and the addition of noise and interference signals simulates the
avionics environment compared to the Mobile environment in the US Patent.
4. Brief Summary of Invention
[007] In order to address the issue of signal variations due to
Free space channel effects on L-Band avionics systems and to reduce
the flight evaluation time and cost involved. a novel method called L Band
Free space channel simulator is invented.
[008] The present embodiment consists of relevant test equipment
(1) to initiate Test signal (2) and this signal is passed via High-power
Handling circuit (3) and a Test signal without Free space channel
simulator effects (2.1) is given to Unit under Test (UUT) (14) and the
Response signal (13) sent by UUT(14) is sent to Test signal equipment
(1) via High-power Handling circuit (3) to confirm UUT (14) normal
operation.
[009] As per Graphical User Interface .(GUI) (20) selections, the
Control logic generator(15) generates corresponding Simulator control
signals (18) to signal path selection & Signal combining circuit (5), signal
strength variation simulator (7), Noise signal generator &Noise level
controller (9) and Multipath signal generator & signal amplitude
controller (11)
[010] For simulating the Free space channel conditions on test
signal (2) to UUT (14). The test signal (2) is passed via High—power
Handling circuit (3) to signal path selection & Signal combining circuit
(5) which passes the test signal (2) to signal strength variation simulator
(7) and Multipath signal generator & signal amplitude
controller(11).Based on the selection from Graphical user interface
(20)the signal path selection & Signal combining circuit (5) selects the
test signal with signal strength variation signal (8) or Amplitude variable
noise signal (16) or Random Pulse fed from external source (17) or
Multi path simulated version of test signal (12.1) or any combination of
these four signals (8,16,17,121). After appropriate selection, free space
channel simulated signal (4.1) is fed back to the High—power Handling
circuit (3). Now the free space channel fading simulated version of test
signal (2.1) is fed to the Unit under test (14) and the response from the
unit can be checked at Test equipment (1)
[011] Similarly, to simulate the free space effects on
response signal, the response signal from UUT (13),is fed to signal path
selection & Signal combining circuit (5) via High-power Handling circuit
.(3). Based on the selection from GUI (20),the signal path selection &
Signal combining circuit (5) selects the Response signal, with or without
amplitude variations (8) or Amplitude variable noise signal (16)or
Random Pulse feed from external source (17) or Response signal, with
or without Multi path effects(12.1) or any combination of these four,
signals (8,16.17,12.1) which is a Response signal, with or without Free
space channel simulator effects(4.1) is fed back to the High—power
Handling circuit (3). Now the free space channel fading simulated
version of response signal (13.1) is received by the test equipment (1)
for declaring the performance of UUT (14).
[012] Thus, the free space channel effects Might-testing
effects during flight trials like. atmospheric refractivity, surface
reflectivity, aircraft maneuvering, polarization, fading. multipath
reception etc.. can be simulated in lab.
[013] The free space channel effects simulated results of the
airborne L-Band avionic equipment in lab environment (and) the
degraded performance of the airborne L—Band equipment during flight
test results can be compared. Based on the comparison. rectification
measures can be taken and this results in reducing the manpower utilization, fuel consumption, time taken for flight evaluation of L-band
airborne equipment.
5 Detailed Description of Invention;
[014] The L-Band. Free space channel simulator operates in
the frequency range of 960MHz to 1215MHz and can handle the peak
power up to 1KW.
[015] The front-end High-power handling circuit (3) provides
better RF signal isolation between input and oUtput paths. It shall
provide low insertion loss in interested signal path and provides high
isolation in unintended signal path. At the same time, it can handle
signal levels of wide dynamic range.
[016] The major block of this embodiment is Signal path selection
&Signal combining circuit (5) The received Test signal, (or) Response
signal(4) from the high-power handling circuit (3) is provisioned to
undergo amplitude variation effects and multi path effects by using
signal strength variation simulator (7) and Multi path signal generator &
Signal amplitude controller (11) circuits respectively. As per the control
signals from Control logic generator (18), this block selects various
combinations of four inputs,
(i) The amplitude-controlled noise signal (16), from Noisé signal
generator &Noise level controller (9)
(ii) Random pulse signal (17),
(iii) Test signal, with or without fading effects (or) Response signal, with
or without fading effects (6)
(iv) Test signaI, with or without Multipath effects (or) Response signal,
With or without Multipath effects (12).
The selection of four type input signals of this section can be done in
16combinations. Based on the selection, the Test signal, (or) Response
signal. with or without free space channel simulator effects (4.1) shall
be fed to High power handling circuit (3).
[017] The Signal strength variation effects on input RF signal
can be simulated by using signal strength variation simulator (7).Based
on the selection in GUI (20)Control logic generator (15) shall generate
required Simulator control signals(18) to Signal strength variation
simulator (7).
'
Different attenuation levels and different durations (duty cycle) for the
attenuation level can be selected on GUI (20). The random selection of
Attenuations duration and attenuation levels shall simulate required
amplitude variation effects on input RF signal. Output of the Signal
strength variation simulator (7) shall be called as Test signal, with or
without Fading effects (or) Response signal. with or without-fading
effects (8).
[018] The Noise signal generator &Noise level controller (9)
is intended to generate random noise. The generated noise amplitude
can be varied as per the Simulator control signals (18). Based on the
Noise level section on GUI (20) the Noise signal (16) with different
amplitudes can be fed to the Signal path selection & Signal combining
circuit (5). combinations of Noise amplitudes can be selected with this circuit.
[019] This embodiment has a provision to input external
pulsed signal from external source.
[020] The Input Test signal. without Multi path effects (or)
Response signal. without Multi path effects (12) form Signal path
selection & Signal combining circuit (5) can be simulated for Multi path
reception signal using Multi path signal generator & Signal level
*controller (11). The output of the Multi path signal generator & Signal
level controller (1 1), Le, test signal, with or without Multi path effects (or)
Response signal, with or without Multi path effects (12.1) is fed back to
Signal path selection & Signal combining circuit (5). The simulated
Multi path signal level can be varied as per selections in Graphical User
Interface (20). The Control logic generator (15) generates
corresponding Simulator control signals (18).
[021] GUI (20), is having provision to select various
combination of
i) Variable signal strength selection,
ii) Multi path signal level selection,
iii) Noise signal amplitude selection and
iv) Signal, path selection & Signal combining circuit also.
The Control logic generator (15) generates corresponding Simulator
control signals (18) to various circuits to simulate Free space channel
effects on the test signal (2) and Response signal (13).
6. Claims:
Title: A Method for simulating the L-Band Free space channel
We claim,
1) A method for simulating L-Band, Free space channel is the
test simulator to work in the frequency range of 960 MHz to 1215 MHz
range to handle the peak power up to 1KW and its applications
comprising:
The front-end High-powei handling circuit (3) shall allow wide
dynamic range of signal levels. It shall provide low insertion loss in
interested signal path and provides high isolation in unintended
signal path.
The Signal path selection & Signal combining circuit (5) shall select
and combine various combinations of free space simulated
versions of receive plain test signal(2) or response signal (13) and
generates Test signal with or without Free space channel simulator
effects (2.1) or Response signal with or without Free spape channel
| simulator effects.
The signal strength variation simulator (7) shall simulate selected
signal strengths variation effects on input RF signal.
The Noise signal generator &Noise level controller (9) is intended
to generate random noise with different amplitude levels.
The pulsed Input provision allows different signals from external
signal generators.
The Multi path signal generator & Signal level controller (11) is to
generate multi path simulated versions of input RF signal at
different amplitude levels.
The Control logic generator (15) shall generate various Simulator
control signals (18) based on Graphical User Interface (20) selections.
The Graphical User Interface (20) is to select the different
combinations to generated free space simulated version of Input L Band
RF Signal.
- Test equipment (1) is to generate the required test signal for the LBand
airborne Avionics equipment, Unit Under Test (14)
- The Unit Under Test (14) is test specimen which shall undergo
flight trials.
2) A High-power handling circuit (3) block, as per claim 1, It can
handle wide dynamic range of -90 dBm to +60 dBm. It shall provide the
high isolation between input and out paths; Minimum isolation is 75:18.
3) Signal path selection & Signal combining circuit (5) shall select
the required. free space simulated version of the Input RF signal and
sends it in the intended direction to test equipment (1) side or Unit
Under Test (14) side. The output of this Block is the intended Free
space simulated version of the Input L-Band RF signal.
4) Signal strength variation simulator (7) is capable of imposing
Signal amplitude variation effects on Input RF signal. The input signal
amplitude variations can be simulated with synchronous and
asynchronous on-off timings. The amplitude variation timings, duration
and combination of both can be selected.
5) The Noise signal generator &Noise level controller (9) is
palpable of generating 32 combinations noise amplitudes.
6) Multi bath signal generator & Signal level controller (11) is
capable of generating the duplicate of the input RF signal vying different
amplitudes to simulate multi path effect in free space.