Software tools for interference analysis and mitigation were developed in the Communications Link Analysis and Simulation System (CLASS) environment for: communications performance evaluation; and mission planning. Potential applications are seen in analysis, evaluation, and optimization of user schedules. Tools producing required separation angles and potential interference intervals can be used as an aid to mutual interference mitigation within a scheduling system

Rash, James L.

Wong, Yen F.

English

NASA Technical Reports Server

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An RF Interference Mitigation Methodology
with Potential Applications in Scheduling
V92-]104
GSFC
Code 531.1
Yen F. Wong
James L. Rash
December 12, 1990
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An RF Interference Mitigation Methodology
with Potential Applications in Scheduling
_Ct ,*
Agenda
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https://ntrs.nasa.gov/search.jsp?R=19920001826 2020-03-19T16:28:47+00:00Z
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An RF Interference Mitigation Methodology
with Potential Applications in Scheduling
GS F C t
• Communications Link Analysis and Simulation
System (CLASS)
• Space Network RF Mutual Interference and
Scheduling
• RF Interference Mitigation Methodology
• Interference Mitigation Aid for Scheduling
• Numerical Examples
• Conclusions and Future Work
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An RF Interference Mitigation Methodology
with Potential Applications in Scheduling
GS F C
CLASS
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Communications Link Analysis &
Simulation System (CLASS)
GS F C
• Unique software tool for the prediction and evaluation of
TDRSS/user spacecraft communications link performance.
• End-to-end modeling of Space and Ground Networks,
channel environment, and user spacecraft communications
systems.
• All communications channel parameters that affect link
performance, including interference, are maintained in
CLASS data bases.
• Developed by NASA Goddard Space Flight Center
(GSFC) Code 531.
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CLASS Interference Analysis and
Mitigation Tools
• Interference analysis and mitigation tools have been
developed in the CLASS environment for use in:
-- communications performance evaluation
-- mission planning
Potential applications in"
-- analysis, evaluation, and optimization of user
schedules
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An RF Interference Mitigation Methodology
with Potential Applications in Scheduling
Space Network RF Mutual
Interference and Scheduling
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Space Network RF Mutual
Interference and Scheduling
• Increasingly competitive climate for
scheduling of Space Network resources in the
Space Station era.
• Potential RF mutual interference warrants
increasing concern in terms of efficiency in
network resource allocation and scheduling.
• Scheduling efficiency of current network
operations system could be enhanced through
consideration of communications performance
in mutual interference mitigation.
• CLASS interference analysis tools can be
used in efforts to enhance network scheduling
efficiency.
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An RF Interference Mitigation Methodology
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Interference Mitigation Methodology
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Interference Mitigation Methodology
• STEP1
For every given pair of desired and interfering signals,
determine the discrimination required to guarantee
nonnegative BER link margin.
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Interference Mitigation Methodology
6S F C
Required discrimination
S S
"Required sir' is the value of S/I such that the degradation of the desired user's signal
equals its worst case channel margin. The worst case channel margin is a parameter
that characterizes the desired user's link performance.
'_Norst sir' is determined by formulating S/I as a function of the separation angle
between interferer and desired user. "Worst s/r' designates the global minimum of
this function.
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Interference Mitigation Methodology 6S FC t
• The signal to interference level ratio S/I in dB at TDRS is defined
as a function of the separation angle a between the desired user
and the interferer as seen from TDRS:
S(a) = (Pd+ C,(o))-(P, + G(a) + I_a)) + G,,+ Ap + Lj,
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Interference Mitigation Methodology
GS FC
Pd = the worst case (maximum range) TDRS received
power at unity antenna gain for the desired user (dB)
including the loss due to the nonperfect polarization match
between the TDRS and desired user antennas. It is
assumed that the desired user is on the TDRS antenna
boresight and that the desired user antenna is pointing
toward TDRS. Pd includes contributions from stochastic
sources such as multipath (vehicle, earth, and atmospheric)
and RFh
Pi = the best case (minimum range) TDRS received power
at unity antenna gain for the interferer (dB).
G = the TDRS antenna gain (dB) as a function of the angle
alpha.
R = the polarization rejection of the interferer signal at the
oppositely polarized TDRS antenna (dB) as a function of the
angle alpha. The value of R is always negative when
rejection is present.
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Interference Mitigation Methodology
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Gp = 10 * ALOG10 (Desired user PN chip rate/Desired
channel symbol rate) is the processing gain (in dB) of
the PN spread signal
Ap = 10 * ALOG10 (Interferer channel PN chip
rate/Desired channel symbol rate) is the reduction
factor (in dB) if the interferer is PN spread when the
desired channel is not PN spread.
Lfs = reduction of interferer power due to frequency
separation.
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Interference Mitigation Methodology
• Step 2
For every given pair of desired and interfering signals,
calculate the re(luired separation angle (the largest
separation angk,_ between the desired user and interferer
that provides the required discrimination as determined in
Step 1).
This calculation utilizes the TDRS antenna gain pattern,
adjusted as necessary to reflect polarization rejection of
the interferer signal.
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Adjusted Antenna Gain Pattern
(Example)
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Gain (dB)
Gain (dB)
65
S0i
'IS
t0
35
30
TDRS SA Antennl Pattern (G)
65
50
45
'10
35
30
0.E 1 15
Angle off boreslght, degrees
Adjusted TDRS SA
0.6 1 1.5 2
Angle 011 boflslOht, degrlms
-2,
LOSS (dB)
-6
-8
-10
-12
-14,
I 0/G i ,:s
J Polarlz=tlon Rejection (R)
/
_/
Poledzatlon rejection modeled is • function
ol Ingle Off borealght lit the TDR$ $k lUttennl
when the transndttlng Inteqma Is that of the
Space Stlltlon Manned Base.
required discrimination _ = - A(G + R)
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Interference Mitigation Methodology
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_ ,lift R,
• Step 3
Based on the separation angles obtained in step (2),
find all potential interference intervals.
A potential interference interval is defined as any time
interval during which the separation angle between the
two spacecraft is less than the required separation
angle.
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An RF Interference Mitigation Methodology
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Interference Mitigation Aid for
Scheduling
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An Approach to Interference
Mitigation Scheduling
Block Diagram
[ lmll_b Sl_l_'a I
Compe= _,- D=c=_mt_em
(M) _¢1,_=1 - (t=/1)
J
I
]
(Shaded blocks have
been implemented.)
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An RF Interference Mitigation Methodology
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Numerical Example
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• These missions operate at Ku band with carrier
frequency equal to 15.0034 GHz, unspread.
- Space Station Manned Base (SSMB) versus
Space Shuttle Orbiter (SSO)
- Earth Observing System (EOS) versus Space
Shuttle Orbiter (SSO)
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Numerical Example (continued)
-- SSO Link Characteristics
SSO operates with Right Circular Polarization (RCP). Link
characteristics are as follows:
CHANNEL DATA RATE EIRP LINK MARGIN
(kbps) (dBW) (dB)
Channel 1 : Subcarrler Q 192 39.4
Channel 2: Subcarrler I 2,000 43.6
Channel 3: Baseband 50,000 51.0
19.0
13.5
1.5
Channels 1 and 2 are rate 1/2 convolutional coded.
Channel 3 is uncoded.
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Numerical Example (continued)
-- SSMB Link Characteristics
GS F C
SSMB operates with Left Circular Polarization (LCP) at data
rates of 300 Mbps and 50 Mbps.
CHANNEL DATA RATE EIRP LINK MARGIN
(Mbps) (dBW) (dB)
I 150 57.1 3.0
Q 150 57.1 3.0
I 25 57.1 10.8
Q 25 57.1 10.8
The parameters given above for SSMB are preliminary and
subject to chaRge.
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Numerical Example (continued)
-- EOS Link Characteristics
EOS operates with RCP at a data rate of 300 Mbps.
CHANNEL DATA RATE EIRP LINK MARGIN
(Mbps) (dBW) (dB)
I 150 57.6 3.6
Q 15O 57.6 3.6
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Numerical Example (continued)
--Interference Analysis Results
There Is no unacceptable interference between the EOS 300
Mbps link and the SSO channels I and 2.
There is no unacceptable Interference between the SSMB 300
Mbps link and the SSO channels 1, 2, and 3.
Case I Case 2
Desired User User ID SSO
Channel 3
Polarization RHC
Worst Case Margin (dB) 1.5
Interferer User ID EOS
Polarization RHC
Axial Ratio (riB) 1.5
S/I Required (dB) 6.2 **
Boreslght (dB) -11.6
Worst Case (dB) -11.6
Required Discrimination (dB) 17.8
Required Separation Angle (dell) 0.74
SaD
3
RHC
1.5
SSMB
LHC
2.1
9.0""
4.0
4.0
5.0
0.92
"* Note: CLASS simulation result.
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Numerical Example (continued)
--Potential Interference Intervals
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_ I_ me _e m _
m
["' o
''''l''''l''''l''''l''''l''''l''''l''''l''''l
tH*e |eeee :_eeee m*oao s•e*e 4eeee _eeie ieeeo tmQme
Ground Elapsed Time Offset (Seconds)
Assumes the users (SSO and SSMB) have identical orbits
except for a 20 degree difference in orbital phasing.
During the 24 hour period, potential Interference exists for
a tota/of approximately 20 minutes for each TDRS.
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An RF Interference Mitigation Methodology
with Potential Applications in Scheduling
Conclusions and Future Work
G-Z7
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Conclusions and Future Work
• Tools for interference analysis and mitigation have been
developed in the CLASS environment for:
- communications performance evaluation
- mission planning
• Potential applications are seen In:
- analysis, evaluation, and optimization of user
schedules
• Tools producing "required separation angles" and
"potential interference intervals" can be used as an aid to
mutual interference mitigation within a scheduling system.
• Possible future consideration of multiple interferers.
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An RF interference mitigation methodology with potential applications in scheduling

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