advanced modulation techniques for telemetry
TRANSCRIPT
Advanced Modulation Techniques for Telemetry
A Short Course at theInternational Telemetering Conference
Las Vegas, NV • October 24, 2011Terry Hill, Quasonix
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Evolution of Telemetry
The Good Ol’ Days1960’s to mid-1990’sNo spectrum shortageRange Commander’s Council (RCC) codifies PCM/FM in IRIG 106
Wireless Everything EraLate 1990’sCongress auctions telemetry spectrum to commercial interestsTest article complexity and telemetry data payloads balloon exponentially More data, less bandwidth…Now what?
2011 International Telemetering ConferenceTerry Hill - [email protected]
ARTM ProgramAdvanced Range Telemetry (ARTM) program, initiated in mid-1990’sFunded through OSD, CTEIP (Central Test and Evaluation Investment Program)Fostered R&D in spectrally efficient modulation techniques
Tier I (2 x the spectral efficiency of PCM/FM)Tier II (2.5 x)
Both Tier I & II adopted by the RCCFully defined and characterized in IRIG 106-04Latest version (IRIG 106-09): http://www.irig106.org/docs/106-09/
2011 International Telemetering ConferenceTerry Hill - [email protected]
ARTM DeploymentReceiving infrastructure in place today
Edwards AFBEglin AFBPatuxent River NASChina LakeWhite SandsPt. MuguVandenbergKwajalein
Numerous commercial usersBoeingHoneywellSandiaLawrence LivermoreLockheed AircraftLockheed Missiles
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
World View of Communications
Figure from "Digital Communications: Fundamentals and Applications," by Bernard Sklar, 2nd Edition, Prentice-Hall, 2001. Reprinted by permission of the author.
We’re in here
2011 International Telemetering ConferenceTerry Hill - [email protected]
Performance Metrics
Information FidelityAdditive White Gaussian Noise (AWGN) channels
Bit Error Probability (BEP) or Bit Error Rate (BER)
Bursty (dropout) channelsCumulative error count
Bandwidth EfficiencyPower spectral densityFractional Out-of-band PowerChannel spacing with adjacent channel interference (ACI)
Bandwidth-Power plane
2011 International Telemetering ConferenceTerry Hill - [email protected]
Eb = signal energy per bit (in Joules/bit or Watt-seconds/bit)= carrier power × bit time= C Tb
= carrier power / bit rate= C/Rb
N0 = noise level (in Watts/Hz)= Boltzmann’s constant × Equivalent System Temperature= k × Teq
= k × (F-1)T0 (where F = system noise figure)
Bit Error Rate - in AWGNKey Ratio =
0NEb
In terms of Carrier-to-Noise Ratio C/N:
b
b
RBW
NC
NE
=0
Figure from " Quadrature Modulation for Aeronautical Telemetry”, by Michael Rice, BYU and Robert Jefferis, Tybrin Corp, ITC 2001. Reprinted by permission of the authors.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Aeronautical Channels
From http://www.ee.byu.edu/telemetry/projects/widebandchannel/
2011 International Telemetering ConferenceTerry Hill - [email protected]
Cumulative Error Countsin Bursty Channels
Bit Error Accumulation HistoryARTM flight 78, frequency diversity, 5 m antenna, high altitude corridor, easterly, 20k ft. altitude
0.0E+00
5.0E+06
1.0E+07
1.5E+07
2.0E+07
2.5E+07
0 500 1000 1500 2000 2500
Elapsed Time - Seconds
Bit
Erro
rs
ERR NDERR DBS
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Which Bandwidth?
Fixed level-60 dBc is common-25 dBm is “standard” in IRIG-106
Fractional out-of-band power99%, 99.9%, 99.99% are all used
Minimum frequency separationAccounts for receive-side effects
Receiver IF filteringDemodulator interference toleranceRelative levels of interfering signalsDepends on application
2011 International Telemetering ConferenceTerry Hill - [email protected]
Power Spectral Density (PSD)
2011 International Telemetering ConferenceTerry Hill - [email protected]
Fractional Out-of-band Power
5 Mbps
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Channel Spacing
2011 International Telemetering ConferenceTerry Hill - [email protected]
Bandwidth-Power PlaneSimultaneous representation of
Bandwidth Efficiency (Bandwidth normalized to Bit Rate)Power Efficiency (Eb/No required to achieve 10-5 BEP)
Eb/No (dB) Required for 10-5 BEP
% B
andw
idth
in B
it R
ates
Spec
tral
Effi
cien
cy
Detection Efficiency
same BW,worse BEP
Same BW,better BEP
Sam
e B
EP,
bette
r BW
sam
e B
EP,
wor
se B
W
worse BW,worse BEP
worse BW,better BEP
better BW,worse BEP
better BW,better BEP
2011 International Telemetering ConferenceTerry Hill - [email protected]
Bandwidth-Power Tradeoffs
Figure from "Digital Communications: Fundamentals and Applications," by Bernard Sklar, 2nd Edition, Prentice-Hall, 2001. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
The Modulation Universe
Analog, DigitalAmplitude modulation Quadrature amplitude modulationAngle modulations
Frequency modulationPhase modulation
2011 International Telemetering ConferenceTerry Hill - [email protected]
Angle ModulationsIncludes both frequency modulation and phase modulationSome have an amplitude modulation component
BPSKQPSKOffset QPSK
Some are constant envelopeBinary FM
FSK, MSK, premod filtered MSK, GMSK
M-ary FSKSOQPSKMulti-h continuous phase modulationNo amplitude variation
Saturated power amplifiers are ideal for constant envelope waveforms
2011 International Telemetering ConferenceTerry Hill - [email protected]
Saturated Power Amplifiers
DC-to-RF conversion efficiency is importantMinimizes cooling requirementsMaximizes battery life
Maximizing efficiency demands nonlinear operationNon-linear operation creates AM-AM and AM-PM conversion:
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Constant Envelope ModulationsBefore ARTM (Tier 0)
PCM/FM“Legacy” waveform for telemetry
Advanced Range Telemetry (ARTM) ProgramARTM Tier 1
Proprietary Feher-patented FQPSKFQPSK-B, Revision A1FQPSK-JR
SOQPSK-TGEquivalent in performance to FQPSKNon-proprietary
ARTM Tier 2 Multi-h CPM (M=4, L=3RC, h1 = 4/16, h2 = 5/16)
PCM/FM, SOQPSK and Multi-h CPM are all continuous phase modulations
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM Notation and Parameters
Where αi represents an M-ary symbol sequenceαi derived from input bits di
h is the modulation indexg(t) is the frequency pulse shape in the interval 0 < t < LT
L = 1 is “full response” signalingL > 1 yields “partial response”
CPM is a modulation with memory due to the constraint of continuous phase. Further memory is introduced with L > 1.
-∞< t <+∞
]),(2cos[/2)( oo ttfTEts φαφπ ++=
∫ ∑∞−
+∞
−∞=
−=t
ii diTght τταπαφ )(2),(
2011 International Telemetering ConferenceTerry Hill - [email protected]
Key Parameters
M – Order of Modulation (2-ary, 4-ary, etc.)g(t) - Frequency Pulse (Rectangular, Raised Cosine, etc.)L – Length of Frequency Pulseh – Modulation IndexIncrease Spectral Efficiency by
Increasing MReducing hIncreasing LChoosing Smoother Frequency Pulse Shape
In general, increasing spectral efficiency decreases detection efficiency
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM Tradeoffs
To reduce bandwidth of a CPM signal, the phase transitions must be smoothed by:
Requiring phase to have more continuous derivativesSpreading the phase change over more intervals (i.e., L > 1)Reducing h
The shape of g(t) determines the smoothness of the information-carrying phaseAn endless variety of CPM schemes can be obtained by choosing different g(t) pulse shapes and varying the parameters h and M.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Frequency Pulse Shapes
LREC - Rectangular pulse, length LL=1, h = 0.5 gives MSK
LRC - Raised cosine, pulse length LTime domain RC pulse
LSRC - Spectral raised cosine, length LSpectral domain RC filter response
TFM - Tamed FMGMSK - Gaussian shaped MSK
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM CharacteristicsContinuous PhaseConstant envelopeSignals are described by their phase trajectories
Phase tree representation is completePSD and BER can be “traded” by
Varying h, modulation indexChanging g(t), the frequency pulse shape
Phase trellis decoder is optimum for any variant of CPM Footnote
FQPSK-B (Revision A1) is not a CPM waveform because of its AM component; i. e., requires I/Q implementationFQPSK-JR is constant envelope, so it could be described in CPM terminology, but this raises patent issues
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM Examples
Minimum Shift Keying (MSK)Gaussian MSK (GMSK)
GSM Cell phones (Europe)
SOQPSKUHF SATCOM (MIL-STD-188-181A, -181B(draft), -182A, -183A)-TG (IRIG 106-04)
FQPSK (or very similar)“CPM”
Nearly unlimited variation
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK-TG as a CPM Example
2011 International Telemetering ConferenceTerry Hill - [email protected]
Phase Tree Representation
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
2011 International Telemetering ConferenceTerry Hill - [email protected]
Modulator Designs
Angle modulatorsCombine frequency pulses and apply to frequency modulator.Combine phase pulses and apply to phase modulator.
FrequencyPulse
Generator
PhasePulse
Generator
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM as Frequency Modulation
LPF FMModulator
bipolarNRZ-L
∫∞−
=t
d dmft λλπφ )(2)(frequency is the time-derivative of the phasesince the phase is proportional to the integral of m(t), the frequency is proportional to m(t).
)(tm)(tx
( ))(2cos)( 0 ttfAtx φπ +=
time-varying phase
Figure from " Quadrature Modulation for Aeronautical Telemetry”, by Michael Rice, BYU and Robert Jefferis, Tybrin Corp, ITC 2001. Reprinted by permission of the authors.
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM as Phase Modulation
)(tφ
)(tφ
( )dtfd ∫π2LPF PhaseModulator
bipolarNRZ-L )(tm
)(tx
( ))(2cos)( 0 ttfAtx φπ +=
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM as QAM
4342143421)2sin())(sin()2cos())(cos())(sin()2sin())(cos()2cos(
))(2cos()(
00
00
0
tftAtftAttfAttfA
ttfAtxYX
πφπφφπφπ
φπ
−=−=
+=
( ) YXYXYX sinsincoscoscos −=+
Apply the trigonometric identity
to our expression for the CPM modulated carrier:
“quadrature carriers”
( )dtfd ∫π2
cos( )
sin( )
~ LO
phase shift
Σ+
−
The Equations What the Equations Tell Us to Build
)(tm )(tφ
)(cos tφ
)(sin tφ
)2cos( 0tfπ
)2sin( 0tfπ
)(tx
Figure from " Quadrature Modulation for Aeronautical Telemetry”, by Michael Rice, BYU and Robert Jefferis, Tybrin Corp, ITC 2001. Reprinted by permission of the authors.
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM Quadrature Signals
cos( )
sin( )
~ LO
phase shift
Σ+
−)(tm )(tφ
)(cos tφ
)(sin tφ
)2cos( 0tfπ
)2sin( 0tfπ
)(tx
)(tφ
)(tm
)(cos tφ
)(sin tφ
( )dtfd ∫π2
Figure from " Quadrature Modulation for Aeronautical Telemetry”, by Michael Rice, BYU and Robert Jefferis, Tybrin Corp, ITC 2001. Reprinted by permission of the authors.
2011 International Telemetering ConferenceTerry Hill - [email protected]
M=2, h=1/2, 1REC (MSK)
- 2
-1.5
- 1
-0.5
0
0 . 5
1
1 . 5
2
0 1 2 3 4
CPM Phase Tree
Mul
tiple
of π
Time in Symbols
RECShaping1/2h2M1L
-120
-100
-80
-60
-40
-20
- 2 -1.5 - 1 -0.5 0 0.5 1 1.5 2
PS
D in
dB
c/H
z
CPM PSD
Frequency (Bit Rates)
PSD vertical axis is dBc per FFT bin1 FFT bin = 1/64 * symbol rate
2011 International Telemetering ConferenceTerry Hill - [email protected]
M=4, h=1/4, 1REC
- 3
- 2
- 1
0
1
2
3
0 1 2 3 4
CPM Phase Tree
Mul
tiple
of π
Time in Symbols
RECShaping1/4h4M1L
-120
-100
-80
-60
-40
-20
- 2 -1.5 - 1 -0.5 0 0.5 1 1.5 2
PS
D in
dB
c/H
z
CPM PSD
Frequency (Bit Rates)
PSD vertical axis is dBc per FFT bin1 FFT bin = 1/64 * symbol rate
2011 International Telemetering ConferenceTerry Hill - [email protected]
M=4, h=1/4, 1RC
-120
-100
-80
-60
-40
-20
- 2 -1.5 - 1 -0.5 0 0.5 1 1.5 2
PS
D in
dB
c/H
z
CPM PSD
Frequency (Bit Rates)
- 3
- 2
- 1
0
1
2
3
0 1 2 3 4
CPM Phase Tree
Mul
tiple
of π
Time in Symbols
R CShaping1/4h4M1L
PSD vertical axis is dBc per FFT bin1 FFT bin = 1/64 * symbol rate
2011 International Telemetering ConferenceTerry Hill - [email protected]
M=4, h=1/4, 2RC
-120
-100
-80
-60
-40
-20
- 2 -1.5 - 1 -0.5 0 0.5 1 1.5 2
PS
D in
dB
c/H
z
CPM PSD
Frequency (Bit Rates)
- 3
- 2
- 1
0
1
2
3
0 1 2 3 4
CPM Phase Tree
Mul
tiple
of π
Time in Symbols
R CShaping1/4h4M2L
PSD vertical axis is dBc per FFT bin1 FFT bin = 1/64 * symbol rate
2011 International Telemetering ConferenceTerry Hill - [email protected]
M=4, h=1/4, 3RC
-120
-100
-80
-60
-40
-20
- 2 -1.5 - 1 -0.5 0 0.5 1 1.5 2
PS
D in
dB
c/H
z
CPM PSD
Frequency (Bit Rates)
- 2
- 1
0
1
2
3
0 1 2 3 4
CPM Phase Tree
Mul
tiple
of π
Time in Symbols
R CShaping1/4h4M3L
PSD vertical axis is dBc per FFT bin1 FFT bin = 1/64 * symbol rate
2011 International Telemetering ConferenceTerry Hill - [email protected]
Multi-h CPM
Cyclically rotates through multiple “sets” of FSK tonesIncreases minimum distance in trellis
Improves BER performance
Widely proposed for high-performance nonlinear channels
MIL-STD-188-181B
2011 International Telemetering ConferenceTerry Hill - [email protected]
M=2, h1=1/4, h2=1/2, 1REC
-1.5
- 1
-0.5
0
0 . 5
1
1 . 5
0 1 2 3 4
CPM Phase Tree
Mul
tiple
of π
Time in Symbols
RECShaping1/4, 1/2h
2M1L
-120
-100
-80
-60
-40
-20
- 2 -1.5 - 1 -0.5 0 0.5 1 1.5 2
PS
D in
dB
c/H
z
CPM PSD
Frequency (Bit Rates)
PSD vertical axis is dBc per FFT bin1 FFT bin = 1/64 * symbol rate
2011 International Telemetering ConferenceTerry Hill - [email protected]
M=4, h1=4/16, h2=5/16, 3RC
- 2
- 1
0
1
2
3
4
0 1 2 3 4
CPM Phase Tree
Mul
tiple
of π
Time in Symbols
R CShaping4/16, 5/16h
4M3L
-120
-100
-80
-60
-40
-20
- 2 -1.5 - 1 -0.5 0 0.5 1 1.5 2
PS
D in
dB
c/H
z
CPM PSD
Frequency (Bit Rates)
PSD vertical axis is dBc per FFT bin1 FFT bin = 1/64 * symbol rate
ARTM Tier II Waveform
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
PCM/FM (Tier 0)
LPF FMModulator
bipolarNRZ-L
∫∞−
=t
d dmft λλπφ )(2)(frequency is the time-derivative of the phasesince the phase is proportional to the integral of m(t), the frequency is proportional to m(t).
)(tm)(tx
( ))(2cos)( 0 ttfAtx φπ +=
time-varying phase
Figure from " Quadrature Modulation for Aeronautical Telemetry”, by Michael Rice, BYU and Robert Jefferis, Tybrin Corp, ITC 2001. Reprinted by permission of the authors.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier 0 in CPM Notation
M = 2 (binary)αi = 2di - 1
di = 0, 1, αi = -1, +1h = 0.7g(t) is the normalized impulse response of a high order Bessel filter with 3 dB bandwidth = 0.7 * bit rate
Normalized such that the integral over all time = 1/2
-∞< t <+∞
]),(2cos[/2)( oo ttfTEts φαφπ ++=
∫ ∑∞−
+∞
−∞=
−=t
ii diTght τταπαφ )(2),(
2011 International Telemetering ConferenceTerry Hill - [email protected]
PCM/FM as a Phase Modulation
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Power Spectral Density (PSD)
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Fractional Out-of-band Power
5 Mbps
2011 International Telemetering ConferenceTerry Hill - [email protected]
PCM/FM Summary
Legacy waveformEquipment is ubiquitous
Constant envelopeSeveral practical implementations99.9% bandwidth: 2.03 times bit rate
M αi h g(t)2 -1, +1 0.7 Normalized impulse response of a high order
Bessel filter with 3 dB bandwidth = 0.7 * bit rate
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier I OverviewShaped OQPSK (SOQPSK)
Constant envelope modulation(s) introduced by Hill (ITC 2000)Defined by 4 parameters ( ρ, B, T1, T2 )Compatible with existing efficient non-linear class C power amplifierNon-proprietary waveformComparable in performance and interoperable with FQPSK
FQPSKPatented by K. FeherDefined by I and Q componentsNon-constant envelopeDetails are proprietary, contact Digcom
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK in CPM Notation
M = 3 (ternary)
αi = -1, 0, +1
ai = 2di - 1
ai = -1, +1, di = 0, 1
h = 0.5g(t) = windowed impulse response of spectral raised cosine
Normalized such that the integral over all time = 1/2
-∞< t <+∞
]),(2cos[/2)( oo ttfTEts φαφπ ++=
∫ ∑∞−
+∞
−∞=
−=t
ii diTght τταπαφ )(2),(
α i = −1( ) i+1 ai−1(ai − ai−2)2
,
2011 International Telemetering ConferenceTerry Hill - [email protected]
Definition of SOQPSK Pulse
g(t) = n(t) * w(t), where
n(t) =Acos(πρ Bt T)1− 4(ρ Bt T )2 *
sin(π Bt T )(π Bt T )
w(t) =
1, for t T < T1
12
+12
cosπ ( t T −T1)
T2
, for T1 < t T < T1 + T2
0, for t T > T1 + T2
⎧
⎨ ⎪ ⎪
⎩ ⎪ ⎪
⎫
⎬ ⎪ ⎪
⎭ ⎪ ⎪
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Frequency Pulse Shape, g(t)
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SOQPSK Variants
99.9
9% B
andw
idth
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Optimal SOQPSK Variants99
.99%
Ban
dwid
th
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Unshaped Offset QPSK
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Slightly Shaped OQPSK
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MIL-STD SOQSPK
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SOQPSK-TG
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SOQPSK-TG Phase Tree
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
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Power Spectral Density
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SOQPSK-A Eye Pattern
-1.5
-1
-0.5
0
0.5
1
1.5
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2Time (Symbols)
I Cha
nnel
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SOQPSK & FQPSK, Linear PA
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FQPSK, Non-Linear PA
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SOQPSK-A, Non-Linear PA
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SOQPSK & FQPSK, Non-Linear
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Measured PSD (Tier 0 & 1)
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Fractional Out-of-band Power
5 Mbps
2011 International Telemetering ConferenceTerry Hill - [email protected]
Shaped Offset QPSK SummaryConstant envelope, CPM waveformAdjustable shaping factor for BW and detection efficiency trade-offImproved spectral containment over OQPSKCompatible with standard OQPSK receivers and demodulatorsAdopted as an ARTM Tier I waveform99.9% bandwidth: 0.98 times bit rateInteroperable with FQPSK
M αi h g(t)3 -1, 0, +1 0.50 Normalized windowed impulse response of a
spectral raised cosine
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier II Overview
Multi-h CPM characteristicsEasy to trade off bandwidth and detection efficiency.Constant envelope is ideal for high efficiency non-linear power amplifiers.Detection efficiency is enhanced by periodically varying the modulation index (h).
Extends the point at which competing paths remerge thereby increasing the minimum distance and decreasing the probability of symbol error.
Nearly 2.5x improvement over PCM/FM in spectral efficiency with similar detection efficiency.
2011 International Telemetering ConferenceTerry Hill - [email protected]
ARTM Tier II in CPM Notation
M = 4 (quaternary)
αi = 2 [2d1i + d0i] - 3αi = -3, -1, +1, +3di = 0, 1
h = 4/16, 5/16, alternatingg(t) = raised cosine, 3 symbols (6 bits) in duration
Normalized such that the integral over all time = 1/2
-∞< t <+∞
]),(2cos[/2)( oo ttfTEts φαφπ ++=
∫ ∑∞−
+∞
−∞=
−=t
ii diTght τταπαφ )(2),(
2011 International Telemetering ConferenceTerry Hill - [email protected]
Frequency Pulse & Phase Tree
0 0.5 1 1.5 2 2.5 30
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
TIME (SYMBOLS)
NO
RM
ALI
ZED
FR
EQ
UE
NC
Y/P
HA
SE
LENGTH 3 RC FREQUENCY PULSE AND CORRESPONDING PHASE PULSE
2011 International Telemetering ConferenceTerry Hill - [email protected]
PSD (Tier 0, I, & II)
2011 International Telemetering ConferenceTerry Hill - [email protected]
Fractional Out-of-band Power
5 Mbps
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier II Multi-h CPM Summary
Similar detection efficiency to PCM/FM.Constant envelope waveform is ideal for efficient non-linear PA’s.Enhanced performance gained by increasing demodulator complexity.99.9% bandwidth: 0.75 times bit rate
M αi h g(t)4 -3, -1, +1, +3 4/16, 5/16 Normalized raised cosine, 3 symbols
(6 bits) long
2011 International Telemetering ConferenceTerry Hill - [email protected]
Side by Side SummaryTier M αi h g(t)
0 2 -1, +1 0.7 Normalized impulse response of a high order Bessel filter with 3 dB bandwidth = 0.7 * bit rate
I 3 -1, 0, +1 0.5 Normalized windowed impulse response of a spectral raised cosine, 8 bits long
II 4 -3, -1, +1, +3 4/16, 5/16 Normalized raised cosine, 3 symbols (6 bits) long
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Demodulation
As the shop manual says, “Installation is reverse of removal.”Demodulation is intrinsically more difficult
Unknown carrier frequencyUnknown carrier phaseUnknown clock frequency and phaseSignal corruption
Noise InterferenceMultipathDoppler shift
2011 International Telemetering ConferenceTerry Hill - [email protected]
Demodulation Overview
Tier 0 Tier I Tier II
Single-Symbol Countless vendorsBER = 1e-5 @12.1 to 13.0 dB Eb/N0
Numerous vendorsBER = 1e-5 @11.7 to 12.5 dB Eb/N0
Not practical
Multi-Symbol(Trellis)
Two vendorsBER = 1e-5 @8.6 to 9.4 dB Eb/N0
One vendorBER = 1e-5 @11.2 dB Eb/N0
Two vendorsBER = 1e-5 @11.4 to 12.1 dB Eb/N0
Legacy (nearly exclusive prior to 2001)
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier 0 Single-Symbol Detection
Differentiate the phase to get frequencyLimiter-discriminatorPhase locked loopDigital processing
If the frequency in this symbol > 0, data = 1If the frequency in this symbol < 0, data = 0
]),(2cos[/2)( oo ttfTEts φαφπ ++=
∫ ∑∞−
+∞
−∞=
−=t
ii diTght τταπαφ )(2),(
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier 0 Frequency Detection
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier 0 Phase Tree
-4
-3
-2
-1
0
1
2
3
4
0 1 2 3 4 5 6 7Time in bits
Phase
in C
ycle
s
h = 0.7
2011 International Telemetering ConferenceTerry Hill - [email protected]
Phase Trajectory Never Forgets
-4
-3
-2
-1
0
1
2
3
4
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
-4
-3
-2
-1
0
1
2
3
4
0 1 2 3 4 5 6 7Time in bits
Phas
e in
Cyc
les
If this bit is different, the phase trajectory is forever shifted…
Therefore, later bits can help make decisions about earlier bits.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Multi-Symbol Detector Example
Phase1
1 1
10
0 0
000001010
100101110111
011
Correlators
ChooseLargest
Magnitude
MiddleBit
Multi-SymbolDetector Span
2011 International Telemetering ConferenceTerry Hill - [email protected]
Tier 0 BER Performance
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
2 3 4 5 6 7 8 9 10 11 12 13 14Eb/N0 (dB)
BER
Conventional Single-Symbol (1990's)
First Generation Multi-Symbol (2001)
Second Generation Multi-Symbol (2004)
MLSE (Theoretical Limit)
2011 International Telemetering ConferenceTerry Hill - [email protected]
Legacy PCM/FM Transmitters
-4
-3
-2
-1
0
1
2
3
4
0 1 2 3 4 5 6 7Time in bits
Phase
in C
ycle
s
h = 0.6
-4
-3
-2
-1
0
1
2
3
4
0 1 2 3 4 5 6 7Time in bits
Phase
in C
ycle
s
h = 0.7h = 0.8
-4
-3
-2
-1
0
1
2
3
4
0 1 2 3 4 5 6 7Time in bits
Phase
in C
ycle
s
2011 International Telemetering ConferenceTerry Hill - [email protected]
Effect of TX Deviation Error
8
9
10
11
12
13
0.60 0.65 0.70 0.75 0.80Modulation Index, h
Eb/N
0 (
dB)
for
BER =
1.0
e-5
Conventional Single-Symbol (1990's)
First Generation Multi-Symbol (2001)
Second Generation Multi-Symbol (2004)
MLSE (Theoretical Limit)
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Detection
Can be detected by conventional (non-shaped) offset QPSK demodNon-matched filtering loss of about 2 dBButterworth lowpass filter is reasonable approximation to matched filterTrellis detection is optimum, but more complex
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK-A Eye Pattern
-1.5
-1
-0.5
0
0.5
1
1.5
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2Time (Symbols)
I Cha
nnel
Single-symbol detection ignores memory inherent in waveformCan be detected by conventional (non-shaped) offset QPSK demodI&D detector endures additional loss due to waveform mismatch
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Constellations
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK-TG Phase Tree
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7 8Time in bits
Phase
in C
ycle
s
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Detection Efficiency
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK-TG
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
2 3 4 5 6 7 8 9 10 11 12 13 14Eb/N0 (dB)
BER
Tier I, QSX-DMS
Tier I, MMD-44, Temple
2011 International Telemetering ConferenceTerry Hill - [email protected]
BER Performance of FQPSK
From Gene Law’s Oct 98 paper
2011 International Telemetering ConferenceTerry Hill - [email protected]
Cumulative Error Countsin Bursty Channels
Bit Error Accumulation HistoryARTM flight 78, frequency diversity, 5 m antenna, high altitude corridor, easterly, 20k ft. altitude
0.0E+00
5.0E+06
1.0E+07
1.5E+07
2.0E+07
2.5E+07
0 500 1000 1500 2000 2500
Elapsed Time - Seconds
Bit
Erro
rs
ERR NDERR DBS
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Synchronization TestTransmit randomized ones patternMeasure time at which demod output becomes “all ones” (or mostly)
IRIG Randomizer Modulator Add Noise
Noise
Switch
Demodwith
DerandomizerTimer
OnesDetector
All ones
Controller
Start
Stop
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Synchronization, No Noise
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Synchronization, 6 dB10 Mbps, 6 dB Eb/N0
0
200
400
600
800
1000
1200
1400
1600
1800
0
100
200
300
400
500
600
700
800
900
1000
Synchronization Time (Bits)
Freq
uenc
y
0%
20%
40%
60%
80%
100%
120%
FrequencyCumulative %
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Synchronization, 3 dB10 Mbps, 3 dB Eb/N0
0
200
400
600
800
1000
1200
1400
1600
1800
0
100
200
300
400
500
600
700
800
900
1000
Synchronization Time (Bits)
Freq
uenc
y
0%
20%
40%
60%
80%
100%
120%
FrequencyCumulative %
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Synchronization, 1 dB10 Mbps, 1 dB Eb/N0
0
200
400
600
800
1000
1200
1400
1600
1800
0
100
200
300
400
500
600
700
800
900
1000
Synchronization Time (Bits)
Freq
uenc
y
0%
20%
40%
60%
80%
100%
120%
FrequencyCumulative %
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK Synchronization, -1 dB10 Mbps, -1 dB Eb/N0
0
200
400
600
800
1000
1200
1400
1600
1800
0
100
200
300
400
500
600
700
800
900
1000
Synchronization Time (Bits)
Freq
uenc
y
0%
20%
40%
60%
80%
100%
120%
FrequencyCumulative %
2011 International Telemetering ConferenceTerry Hill - [email protected]
Multi-h CPM Detection
Modulator intentionally creates severe inter-symbol interference
3-symbol RC premod filter
Symbol-by-symbol detection is essentially uselessTrellis detection is requiredEnormously complex machine
12.5 million gates
2011 International Telemetering ConferenceTerry Hill - [email protected]
Demodulator Architecture
2011 International Telemetering ConferenceTerry Hill - [email protected]
Demodulator Complexity
If signal can be represented in a finite state trellis, the Viterbi Algorithm can be used for demodulation.Modulation indices = h = 2k/p
M=4, L=3, h1 = 4/16, h2 = 5/16
Receiver implementation complexityNumber of Correlations ML = 64Number of Phase States p = 32Number of Branch Metrics pML = 2048Number of Trellis States pML-1 = 512
2011 International Telemetering ConferenceTerry Hill - [email protected]
BER Performance Comparison
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
2 3 4 5 6 7 8 9 10 11 12 13 14Eb/N0 (dB)
BER
Tier 0: Conventional Single-Symbol (1990's)
Tier 0: First Generation Multi-Symbol (2001)
Tier 0: Second Generation Multi-Symbol (2004)
Tier I (SOQPSK-TG)
Tier II (Multi-h CPM)
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
If One is Good…
Two must be betterMany telemetry systems utilize multiple antenna feeds
Spatial separationFrequency separationOrthogonal polarizations
Combining two (or more) copies of the same signalDiversity combiningCreates a third signal to be demodulatedBER performance of third signal is better than either of the individual signals
2011 International Telemetering ConferenceTerry Hill - [email protected]
Maximal Ratio Combining
Weight each signal in proportion to its SNR and addYields optimum SNR on combined channel in AWGNSNRcombined = SNRa + SNRb
2011 International Telemetering ConferenceTerry Hill - [email protected]
BER Results - Fading Signals
2011 International Telemetering ConferenceTerry Hill - [email protected]
Measured Combiner BER - Tier 0PCMFM
Ch 0 Eb/N0 = Ch 1 Eb/N0
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0 5 10 15Eb/N0 (dB)
BER
Ch 0Ch 1Ch 2 (90º)Theory
PCMFMCh 0 Eb/N0 = 6
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
-2 0 2 4 6 8 10 12 14Ch 1 Eb/N0 (dB)
BER
Ch 0Ch 1Ch 2 (90º)Theory
2011 International Telemetering ConferenceTerry Hill - [email protected]
Measured Combiner BER - Tier ISOQPSK
Ch 0 Eb/N0 = Ch 1 Eb/N0
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0 5 10 15Eb/N0 (dB)
BER
Ch 0Ch 1Ch 2 (90º)Theory
SOQPSKCh 0 Eb/N0 = 6
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
-2 0 2 4 6 8 10 12 14Ch 1 Eb/N0 (dB)
BER
Ch 0Ch 1Ch 2 (90º)Theory
2011 International Telemetering ConferenceTerry Hill - [email protected]
Measured Combiner BER - Tier IIMHCPM
Ch 0 Eb/N0 = Ch 1 Eb/N0
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
0 5 10 15Eb/N0 (dB)
BER
Ch 0Ch 1Ch 2 (90º)Theory
MHCPMCh 0 Eb/N0 = 9
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
-2 0 2 4 6 8 10 12 14Ch 1 Eb/N0 (dB)
BER
Ch 0Ch 1Ch 2 (90º)Theory
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
PSD is Half the Story
Overall spectral efficiency is determined by spacing between channelsReceiver selectivity affects channel spacingA valid comparison must account for both transmitted spectrum and “tolerable” receiver filteringNot all modulations are equally “tolerant” of IF filtering and interferenceMulti-channel testing accounts for these factors
2011 International Telemetering ConferenceTerry Hill - [email protected]
Multi-channel ACI Test Set
2011 International Telemetering ConferenceTerry Hill - [email protected]
9 Mbps Multi-h CPM, Multichannel
2011 International Telemetering ConferenceTerry Hill - [email protected]
BER as a Function of ∆F0
2011 International Telemetering ConferenceTerry Hill - [email protected]
Frequency Separation Rulewhere:
• ∆F0 = the minimum center frequency separation in MHz• Rs = bit rate of desired signal in Mb/s• Ri = bit rate of interfering signal in Mb/s
∆F0 = as*Rs + ai*Ri
Modulation Type as ai Rs = Ri
NRZ PCM/FM 1for receivers with RLC final Intermediate Frequency (IF) filters
1.2 2.2
0.7for receivers with Surface Acoustic Wave (SAW) or digital IF filters
1.2 1.9
0.5with multi-symbol detectors (or equivalent devices)
1.2 1.7
FQPSK-B, FQPSK-JR, SOQPSK-TG 0.45 0.65 1.1ARTM CPM 0.35 0.5 0.85
The NRZ PCM/FM signals are assumed to be premodulation filtered with a multi-pole filter with 3 dB point of 0.7 times the bit rate and the peak deviation is assumed to be approximately 0.35 times the bit rate.The receiver IF filter is assumed to be no wider than 1.5 times the bit rate and provides at least 6 dB of attenuation of the interfering signal.The interfering signal is assumed to be no more than 20 dB stronger than the desired signal.The receiver is assumed to be operating in linear mode; no significant intermodulation products or spurious responses are present.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Multipath Propagation
This image cannot currently be displayed.
Dry lake bed = smooth reflecting surface
Narrow beam receive antennaAirborne transmitter Line-of-sight communications link
Irregular terrain
Low elevation angle
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
AssumptionsChannel can be modeled as LTI system over “short enough” time interval
( ) ( ) ( )( )
( ) ( ) ( )( )∑
∑−
=
−
−
=
−
−Γ+=
−Γ=
1
1
1
0
)(
);(
L
kk
xjk
L
kk
xjk
xtext
xtexxth
kc
kc
τδδ
τδ
τω
τω
Line-of-sight propagation path
L-1 multipath propagation paths
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
ARTM Experiments127-PNsource LPF BPSK
modlinearPA
bipolar NRZ @10 Mbits/sec
aircraft fuselage
hemisphericallyomni-directionalantenna
tracking antenna
widebandtelemetryreceiver
70 MHz IF high speeddigital
oscilloscope
BPSKdemod
BERanalyzer
triggercircuit
AGC A/D
PC
GPS
sampling trigger
L-Band 1500 MHzS-Band 2200 MHz
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Edwards AFB Flight Paths
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Signal Processing
-8 -6 -4 -2 0 2 4 6 8123456789
10
Frequency (MHz), relative to carrier
S x(e
jΩ
) (dB
)
-8 -6 -4 -2 0 2 4 6 80
2
4
6
8
10
12
14
Sy(e
j Ω) (
dB)
Frequency (MHz), relative to carrier
-35
-30
-25
-20
-15-10
-5
0
5
10
-8 -6 -4 -2 0 2 4 6 8Frequency (MHz), relative to carrier
|H(e
jΩ)|2
(dB
)
Power spectral density of transmitted signal
Power spectral density of received signal
Estimate of channel transfer function
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Modeling Procedure
This image cannot currently be displayed.
( ) ( )( )ωωω
SRH =
) power spectral density of received signalpower spectral density of transmitted signal
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Measurement and Modeling
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Channel Transfer Function
1 (0 dB)
M
D
1
2τπ
2
2τπ
ω0
( )2ωH (dB)
(3-Ray Model)( )2ωH (dB)
(2-Ray Model)
2121 and Assumes Γ>Γ< ττ
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Frequency-Dependent Parametersmagnitude of first multipath reflection: Γ1“sweep rate” of multipath null
( )2ωH
ω
( )211 Γ+=M
(dB)
( )211 Γ−=D
1 (0 dB)
1111 Γ+=Γ∠+ θτωτω cc
1
2τπ
0
null “sweep rate” ~11 Γ+θτω &&c
Figure from Dr.Michael Rice, BYU Telemetry Laboratory, Provo, Utah. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Received Signal Strength HistoryARTM flight 78, Cords Road, westerly
1
1.5
2
2.5
3
3.5
4
0 100 200 300 400 500 600 700 800
Elapsed Time - Seconds
RSS
- Vo
lts (1
0 dB
/Vol
t)
AGC1AGC4
Measured Data
Frequency Diversity
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Received Signal Strength HistoryARTM flight 78, Cords Road, westerly
0
0.5
1
1.5
2
2.5
3
3.5
100 120 140 160 180 200 220 240 260 280 300
Elapsed Time - Seconds
RSS
- Vo
lts (1
0 dB
/Vol
t)
AGC1AGC4
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
Classic Two-Ray Multipath
2011 International Telemetering ConferenceTerry Hill - [email protected]
Bit Error Accumulation HistoryARTM flight 78, frequency diversity, FQPSK-JR, 5 Mb/s, Cords westerly
0.0E+00
5.0E+05
1.0E+06
1.5E+06
2.0E+06
2.5E+06
3.0E+06
3.5E+06
4.0E+06
4.5E+06
5.0E+06
0 100 200 300 400 500 600 700 800 900 1000
Elapsed Time - Seconds
Bit
Erro
rs
ERR NDERR DBS
Classic 2-ray Multipath
Frequency Diversity Example 1
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Frequency Diversity Example 2Bit Error Accumulation History
ARTM flight 78, frequency diversity, 5 m antenna, high altitude corridor, easterly, 20k ft. altitude
0.0E+00
5.0E+06
1.0E+07
1.5E+07
2.0E+07
2.5E+07
0 500 1000 1500 2000 2500
Elapsed Time - Seconds
Bit
Erro
rs
ERR NDERR DBS
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Spatial Diversity Example 1Bit Error Accumulation History
ARTM flight 71, spatial diversity, 1.2 m antennas, 5 Mb/s FQPSK-JR, Cords Rd., Easterly, 5k ft. altitude
0.E+00
1.E+06
2.E+06
3.E+06
4.E+06
5.E+06
6.E+06
0 200 400 600 800 1000 1200
Elapsed Time - Seconds
Bit E
rror
s
ERR DBSERR ND
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Spatial Diversity Example 2Bit Error Accumulation History
ARTM flight 71, spatial diversity, 1.2 m antennas, 5 Mb/s FQPSK-JR, Bk. Mtn., Westerly, 5k ft. altitude
0.E+00
1.E+05
2.E+05
3.E+05
4.E+05
5.E+05
6.E+05
7.E+05
8.E+05
0 100 200 300 400 500 600 700 800 900
Elapsed Time - Seconds
Bit
Erro
rs
ERR DBSERR ND
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Spatial Diversity Example 3Bit Error Accumulation History
ARTM flight 69, spatial diversity, 1.2 m antennas Bk. Mtn, westerly, 5 Mb/s FQPSK-JR, 5k ft. altitude
0.0E+00
2.0E+06
4.0E+06
6.0E+06
8.0E+06
1.0E+07
1.2E+07
1.4E+07
1.6E+07
1.8E+07
2.0E+07
0 200 400 600 800 1000 1200
Elapsed Time - seconds
Bit E
rror
s
ERR DBSERR ND
Figure from Robert Jefferis, Tybrin, Edwards AFB. Reprinted by permission of the author.
2011 International Telemetering ConferenceTerry Hill - [email protected]
Multipath Summary
Your channel may - or may not - exhibit multipath propagation effectsIf so, there will be intervals during which no useful data is recoveredLoss of bit count integrity is likely
Encrypted links will lose crypto syncWhat to do?Rewind to slide 130Use diversity!
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Adaptive Equalization
Consider the multipath channel to be a filterVaries over time
Consider building a filter which “undoes” the filtering imposed by the channel
Let it keep track of the the channel and continuously adapt itself to the channel
Presto! You have an adaptive equalizerCan repair damage done by multipathWorks with a single receiverRequires no bandwidth expansion
2011 International Telemetering ConferenceTerry Hill - [email protected]
Adaptive Equalizer
2011 International Telemetering ConferenceTerry Hill - [email protected]
PCM/FM in Multipath
2011 International Telemetering ConferenceTerry Hill - [email protected]
SOQPSK in Multipath
2011 International Telemetering ConferenceTerry Hill - [email protected]
CPM in Multipath
2011 International Telemetering ConferenceTerry Hill - [email protected]
Is Equalization Helpful?Adaptive equalizer can “undo” multipath distortionHowever, it must adaptAdaptation has limitations
Equalizer length (number of taps, and total span)Adaptation rate
Trade off accuracy for speedFast adaptation necessarily degrades BER performance (relative to no equalizer)
Within these limits, equalization helpsWhen the equalizer gets lost, re-synchronization time is increased by the time required to re-adaptIn severe multipath, equalization can do more harm than goodRapid synchronization and low acquisition threshold are always beneficial
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Polarizationreceive diversity
Space-Time Coding
Air vehicle maneuveringmasks Tx antenna andcauses polarization mismatch
Ground bouncecreates multipathinterference
Spatial transmit diversity
Ronald C. Crummett, Michael A. Jensen, Michael D. RiceDepartment of Electrical and Computer EngineeringBrigham Young University
2011 International Telemetering ConferenceTerry Hill - [email protected]
Difficulties with TX Diversity
30
210
60
240
90
270
120
300
150
330
180 0
Antenna 2
Antenna 1
Spatially Separated Antennas CreateInterference Pattern
2011 International Telemetering ConferenceTerry Hill - [email protected]
MIMO CommunicationsMIMO: Multiple-Input Multiple-Output
Exploit multiple communication modes
HSpace-TimeEncoder
Data Space-TimeDecoder
Data
Potential Benefits: • Diversity (robust communications)• Increased data throughput
2011 International Telemetering ConferenceTerry Hill - [email protected]
Alamouti Space-Time Coding
A B C D E F G H I J K L ...
space-timeencoder
A -B* C -D* E -F* G -H* I -J* K -L* ...
B A* D C* F E* H G* J I* L K* ...
traditional
1st block 2nd block
• 2 transmit antennas + 1 receive antenna version• 2 transmit antennas + 2 receive antennas version• Calderbank showed that the Alamouti schemes are special cases of more
general “orthogonal designs”
2011 International Telemetering ConferenceTerry Hill - [email protected]
Traditional TransmissionEach symbol is simultaneously sent from both antennas
Received signal energy
With the noise energy as No, the received SNR is
r =12
h1 + h2( )s + ηPower equally
divided between antennas
ET = Ε12
h1 + h2( )s[ ]*h1 + h2( )s
⎧ ⎨ ⎩
⎫ ⎬ ⎭
=12
h1 + h22Ε s2 =
12
h1 + h22 Es
SNRT =12
h1 + h22 Es
No
2011 International Telemetering ConferenceTerry Hill - [email protected]
Alamouti Space-Time CodingSignal energy over one symbol time:
Received noise energy:
Signal-to-Noise Ratio:
EA ,1 = Ε12
h12 + h2
2( )⎡ ⎣ ⎢
⎤ ⎦ ⎥
2
s1*s1
⎧ ⎨ ⎩
⎫ ⎬ ⎭
=12
h12 + h2
2( )⎡ ⎣ ⎢
⎤ ⎦ ⎥
2
Es
NA ,1 = Ε12
h1*η1 + h2η2
*( )*h1
*η1 + h2η2*( )⎧
⎨ ⎩
⎫ ⎬ ⎭
=12
h12Ε η1
2 +12
h22Ε η2
2 =12
h12 + h2
2( )No
SNRA =12
h12 + h2
2( ) Es
No
2011 International Telemetering ConferenceTerry Hill - [email protected]
Symbol Error Rate - QPSK
P E( ) = 2Q Es
No
⎛
⎝ ⎜
⎞
⎠
If the aircraft is rotated 360° in the horizontal plane
SER for QPSK in AWGN
Using two transmit antennas (traditional signaling)
P E |θ,φ( ) = 2Q Es
No
h1 θ,φ( ) + h2 θ,φ( ) 2
2
⎛
⎝
⎜ ⎜
⎞
⎠
P E |θ( ) =1
2π2Q Es
No
h1 θ,φ( ) + h2 θ,φ( ) 2
2
⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟ dφ
0
2π
∫
2011 International Telemetering ConferenceTerry Hill - [email protected]
Symbol Error Rate - QPSK
For Alamouti signaling
P E |θ( ) =1
2π2Q Es
No
h1 θ,φ( ) 2+ h2 θ,φ( ) 2
2
⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟ dφ
0
2π
∫Only magnitudes oftransfer functionsused in sum
Traditional signaling
P E |θ( ) =1
2π2Q Es
No
h1 θ,φ( ) + h2 θ,φ( ) 2
2
⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟ dφ
0
2π
∫Addition of transferfunctions leads toreduction in effectiveSNR
2011 International Telemetering ConferenceTerry Hill - [email protected]
Consider BPSK Signaling and Assume s1 = s2 = 1Time Slot 1:
Gain Pattern:
Time Slot 2:Gain Pattern:
Alamouti Scheme
⎥⎦⎤
⎢⎣⎡= φφ cos
2cos2)( 2
1kdGt
⎥⎦⎤
⎢⎣⎡= φφ cos
2sin2)( 2
2kdGt
30
210
60
240
90
270
120
300
150
330
180 0
30
210
60
240
90
270
120
300
150
330
180 0
Antenna Pattern Interpretation
2011 International Telemetering ConferenceTerry Hill - [email protected]
Symbol Error Rate
Similar expressions have been derived for:• Polarization diversity at receiver (Maximal Ratio combining)
• One multipath (ground) bounce
• BPSK and 16-QAM signal constellations
for both Traditional Signaling and Alamouti Signaling
2011 International Telemetering ConferenceTerry Hill - [email protected]
SER SimulationsAntenna Separation: 20’ Horizontal, 8’ VerticalAntenna Patterns: Isotropic
Simple AWGN
Channel
2011 International Telemetering ConferenceTerry Hill - [email protected]
SER Simulations
Results Identical to Single Receive Antenna System
CircularPolarization
Diversity Reception
2011 International Telemetering ConferenceTerry Hill - [email protected]
SER SimulationsAntenna Separation: 20’ Horizontal, 8’ VerticalAntenna Patterns: Isotropic
One Ground Bounce
(Multipath)
Prototype Testing
164
QuasonixSTC
TransmitterCombiner
Noise+
InterferenceTest Set
TelemetryReceiver
BYUSTC
DemodBERT
Laptop PC
RF1485.5 MHz
IF
70 MHz
EAFB Telemetry Lab Configuration
FastBit FB2000
AgilentStep Attenuator
8496B
Narda 4322-2
BERT
Fireberd 6000A
20 dBatten
PasternackPE7017-20
Reach TechnologiesVBERT-50S-1-R
M/A Com SMR 5550i
PasternackPE7017-20
AgilentStep Attenuator
8495B
AgilentStep Attenuator
8495B
20 dBatten
10 dBatten
10 dBatten
20 dBatten
A
(10 W)
B
(10 W)
DirectionalCoupler
SpectrumAnalyzer
−6 dB output
Agilent E4404A
Adtran 10866-6
Reference Link BER Calibration
165
RFN I/QSource
CalibratedNoise
Source
Tier-1Demod BERT
IF
70 MHz
HP 3708A
VectorGenerator
MXG Series
I
Q
RF Networks2120
HP3784ADigital Traffic Analyzer
Reference Link BER Calibration
166
10 W
10 W
Flight Tests: Airborne Configuration
167
STCTransmitter
SOQPSKTransmitter
L-bandisolator +
+÷
Channel MicrowaveL320I
3 dB
3 dB
PasternakPE 7016-3
Narda 4322-2
upper antenna
lower antenna
10 W5 W
5 W
5 W
5 W
SOQPSKTransmitter
GPS/AHRShouse keeping link antenna (separate lower antenna)
Quasonix QSX-VLT-110-105-20-6A
Quasonix
Channel MicrowaveL320I
L-bandisolator
Channel MicrowaveL320I
L-bandisolator
Channel MicrowaveL320I
L-bandisolator
Channel MicrowaveL320I
Narda 4322-2Narda 4322-2
L-bandisolator
Channel MicrowaveL120I
PasternakPE 7016-3
168
C-12 Beechcraft: Airborne Platform
Antenna Locations
169
Flight Tests: Transmit Antennas
170
Lower Telemetry Antenna(behind the antenna looking forward)
Upper Telemetry Antenna(looking across the fuselage)
fuselage station = 222.25”centerline = 10” (left)waterline = 76”
fuselage station = 302””centerline = 9” (right)waterline = 145.5”
Flight Tests: Idealized Gain Patterns
171
STC FrequencyReference Link
Frequency
spectrum display
Flight Tests: Ground Station Configuration
172
LNA
Bldg 4795: “Antenna 5”EMT Model 150
5-m parabolic reflector
RHCP
multi-coupler
MU-Dell2MDP1425
T/M Receiver
1496.5 MHz
L-3/MicrodyneRCB 2000
Antenna Tracking
TCS ACU-M1
Housekeeping data logging and display
A 20 dBatten
1:4split
MU-Dell2MDA1424D-06
MU-Dell2MDA1424D-06
unity gain input-to-each-output
PC
AGC
AM
Data
Clock
to antennaservo motors
reference link1514.5 MHz
STC link1485.5 MHz
SpectrumAnalyzer
to DVD
Clk
IF
70 MHz
Test Flights: Ground Station Configuration
173
Receiver1514.5 MHz
M/A Com SMR 5550i
Tier 1Demod.
RF NetworksModel 2120
BERT
Fireberd 6000A
Data
Receiver1485.5 MHz
Microdyne 700 MR
AGC
AM
Data Acquisition
Wideband SystemsDRS 3300 (5 Msamples/s)
Clk
IF
70 MHzReceiver
1485.5 MHz
M/A Com SMR 5550i
BYUPrototype
STC Demod.BERT
Fireberd 6000A
Data
to PC data logging
Receiver1514.5 MHz
Microdyne 700 MR
AGC
AM
to PC data logging
Laptop PCfrom
splitter
National InstrumentsDAQ (20 samples/s)
Data Acquisition
AGC
AGC
Test Flights: Ground Station Configuration
174
Test Flights: Ground Station Configuration
175
STC Video Clip
176
M1: Left-Hand Turn @ 10° bank
177
M1: Test Results
178
M2: Right-Hand Turn @ 10° bank
179
M2: Test Results
180
M3: Left-Hand Turn @ 30° bank
181
M3: Test Results
182
M4: Right-Hand Turn @ 30° bank
183
M4: Test Results
184
M3 to C2 Transition
185
M3 to C2 Transition Test Results
186
C2: Cords Road West-to-East
187
C2: Test Results
188
D2: Cords Road East-to-West
189
D2: Test Results
190
2011 International Telemetering ConferenceTerry Hill - [email protected]
STC Summary
Dual-Antenna Diversity Scheme Removes interference created by multiple transmit antennas
SNR equivalent to single antenna transmissionMulti-antenna scheme alleviates masking during maneuveringCan be used with diversity reception
Realtime hardware flight tested at Edwards AFB and showed substantial performance benefit
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Forward Error CorrectionBasic premise
Insert redundant bits into transmitted streamUse known relationships between bits to correct errors
Countless schemes have been developedConvolutional code / Viterbi decoderBlock codes
BCHReed-Solomon
Low Density Parity Check (LDPC)Concatenated codes
RS / ViterbiTurbo product codes (TPC)
2011 International Telemetering ConferenceTerry Hill - [email protected]
BER with TPC
2011 International Telemetering ConferenceTerry Hill - [email protected]
Spectral Expansion - Tier 0
2011 International Telemetering ConferenceTerry Hill - [email protected]
Spectral Expansion - Tier I
2011 International Telemetering ConferenceTerry Hill - [email protected]
Sync Time with FEC
2011 International Telemetering ConferenceTerry Hill - [email protected]
Cumulative Error Results
2011 International Telemetering ConferenceTerry Hill - [email protected]
Does FEC help?
FEC is certainly effective in the AWGN channelReduces number of errors
FEC certainly increases the sync time of the receiving system
Increases number of errors
Net effect depends on your channelIf your channel is always in sync but has isolated one-at-a-time bit errors, FEC helpsIf your link has dropouts (due to multipath, shadowing, interference, etc.), FEC may do more harm than good
2011 International Telemetering ConferenceTerry Hill - [email protected]
Course OutlineHistorical PerspectivePerformance MetricsModulation UniverseLife on the Unit Circle
ARTM Tier 0ARTM Tier IARTM Tier II
DemodulationDiversity CombiningChannel Impairments & Mitigation
Adjacent Channel InterferenceMultipath Propagation
Adaptive EqualizationSpace-Time Coding
Forward Error Correction (FEC)Performance Comparison & Summary
2011 International Telemetering ConferenceTerry Hill - [email protected]
Waveform ComparisonPCM/FM (1x) SOQPSK (2x) Multi-h CPM (2.5x)
0 20 40 60 80 100 120 140 160 180 200-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120 140 160 180 200-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04Eye Diagram of PCM/FM
0 20 40 60 80 100 120 140 160 180 200-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
2011 International Telemetering ConferenceTerry Hill - [email protected]
Power Spectral Densities
2011 International Telemetering ConferenceTerry Hill - [email protected]
Out-of-Band Power
2011 International Telemetering ConferenceTerry Hill - [email protected]
BER Performance Comparison
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
2 3 4 5 6 7 8 9 10 11 12 13 14Eb/N0 (dB)
BER
Tier 0: Conventional Single-Symbol (1990's)
Tier 0: First Generation Multi-Symbol (2001)
Tier 0: Second Generation Multi-Symbol (2004)
Tier I (SOQPSK-TG)
Tier II (Multi-h CPM)
2011 International Telemetering ConferenceTerry Hill - [email protected]
Bandwidth-Power Plane
2011 International Telemetering ConferenceTerry Hill - [email protected]
Acknowledgements
Mark Geoghegan, Nova Dr. Michael Rice, Brigham Young UniversityBob Jefferis, Tybrin, Edwards AFBDr. Bernard SklarKip Temple, ARTM, Edwards AFBGene Law, NAWCWD, Pt. Mugu Vickie Reynolds, White Sands Missile Range
2011 International Telemetering ConferenceTerry Hill - [email protected]
Questions/Comments