The document describes a satellite communication system using SC-WFMT modulation.
SC-WFMT combines SC-FDMA and wavelet modulation techniques. It offers advantages over traditional QPSK modulation used in satellite communications, including programmable spectrum and compensation for distortions. SC-WFMT provides multipath immunity like OFDM with lower peak-to-average power ratio. It can support mobile satellite communication in urban areas with significant multipath delay spreads. The system uses novel wavelet-based modulation at the transmitter and equalization at the receiver to mitigate distortions from the satellite transponder and multipath propagation.
2. PROJECT OBJECTIVE
• The Project describes a Satellite Communication System intended for connection
of the mobile devices in Urban areas.
• The proposed system uses a novel SC-WFMT modulation that was developed on
basis of synthesis two technologies : well known SC-FDMA and WFMT technology
that was proved during eight years research.
• SC-WFMT modulation has several advantages before QPSK that commonly used in
Satellite communications.
– The programmable spectrum by changing form of the wavelets.
– Compensation of phase and amplitude distortions inserted by the satellite
transponder.
– Compensation of distortions inserted by multipath propagation of the
electromagnetic waves in the urban area.
• SC-WFMT modulation has the same energy efficiency as a single carrier QPSK
modulation and the same immunity to multipath as a multicarrier OFDM
modulation.
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3. PROJECT OBJECTIVE ( continue)
• Mobile satellite communication channel has been evaluated mainly with fading
statistics of the signal. When the bandwidth of transmitting signal becomes wider,
frequency selectivity of fading becomes a significant factor of the channel. Channel
characteristics, not only signal variation but multipath delay spread were
evaluated. A multipath measurement system was proposed and developed for
mobile satellite applications. With this system and ETS-V satellite, multipath delay
profiles are measured in various environments including Tokyo metropolis and
Sapporo city at 1.5 GHz. Results show that the maximum excess delay is within 1 us
and the maximum delay spread is 0.2 us at elevation angles of 40 to 47 degrees. In
the wideband signal transmission of about 1MHz and more, designers should
consider the effect of selective fading due to the multipath of land mobile satellite
channel. For elevation angles of 5 to 20 degrees the maximum excess delay and
delay spread are significantly increased.
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4. PROJECT OBJECTIVE ( continue)
• Currently for satellite TV uses a QPSK modulation which is not able to provide
reliable communication in multipath channel.
• The bandwidth of Broadcast TV channel is 6~8 MHz, therefore direct receiving
satellite TV on a mobile device is not possible in Urban areas.
• SC-FDMA and SC-WFMT system are able to provide a communication in
multipath channel with a maximum delay spread more than 10 us. Because of the
possibility to change a spectrum form,
• SC-WFMT has lower PAPR (5.3 dB) instead of SC-FDMA (7.5 dB).
• Therefore the power of receiving signal will be at 1.8 times more than in
case of SC-FDMA.
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5. Multipath propagation in Urban area
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Common mode QPSK
Satellite signal can not
be received in the moving
car in this area.
SC-WFMT based satellite
signal can be received
without errors.
6. Typical measured values of RMS delay spread
( Satellite – Ground channel)
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Environment Freq.(MHz) RMS Delay Spread Notes
Urban 910 1300 ns avg., 3500 ns max New York
Urban 892 10-25 us worst case San Franc.
Suburban 910 200-310 ns typical case Average
Suburban 910 1960-2110 ns extreme case Average
Country 910 120 ns typical case Average
Country 910 750 ns worst case Average
Max. available RMS delay spread for different systems.
SYSTEM MODULATION Symbol
length
Max . available RMS
delay spread
Wi-MAX OFDM 102.9 us 4.5 us
Satellite QPSK 60 ns 30 ns
Satellite SC-WFMT 144 us 11 us
7. NOVEL MODULATIONS
• SC-FDMA modulation was developed for uplink of cellular LTE
system. This modulation has a low peak-to-average power
ratio (PAR) ~6.5 dB and uses multicarrier transmission and
cyclic prefix for decreasing of multipath distortions.
• SC-WFMT modulation has the same immunity to multipath
distortion like SC-FDMA but not use cyclic prefix. The
Spectrum of SC-WFMT signal has not out-of-band side lobes.
SC-WFMT transmitter may be realized
without the complex DFT and IDFT cores.
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8. Introduction to SC-FDMA
• SC-FDMA can be regarded as the discrete Fourier transform (DFT)-spread OFDMA,
where time domain data symbols are transformed into the frequency domain by
DFT before going through OFDMA modulation. The orthogonality of the users
steams from the fact that each user occupies different subcarriers in the frequency
domain, similar to the case of OFDMA. Because the overall transmit signal is a
single carrier signal, PAPR is inherently low compared to the case of OFDMA which
produces a multicarrier signal. SC-FDMA uses the cyclic prefix like OFDM.
• SC-FDMA has the same immunity to multipath distortion as OFDM and the same
spectrum of the transmitted signal. Because PAR of SC-FDMA is only ~7.5 dB and
PAR of OFDM is about 10~12.5 dB, the SC-FDMA system needs in significant lower
power of the RF transmitter.
• Unfortunately, SC-FDMA comprises DFT and IDFT cores these are high complexity
devices. For processing of N-point DFT N^2 operations are required. For N-point
FFT, only N*log2(N) operations are required. This is the reason why SC-FDMA is
used only in narrowband LTE uplink.
•
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10. Introduction to SC- WFMT
• In SC-WFMT system information symbols come to WFMT Transmitter,
which generates a single carrier signal with the spectrum and peak-to-
average ratio which depend of the defined wavelet form. This signal
comes to M-point FFT core. After a fft transform and subcarrier mapping
the signal arises to the digital filter. The filtered signal is added to a
number of pilot signals. After M-point IFFT transform in the SC-WFMT
signal inserts a cyclic prefix. Because of this cyclic prefix the SC-WFMT
signal has the same an immunity to multipath distortion as OFDM or SC-
FDMA signal .
• The PAR of SC-WFMT signal is about 5~7.5 dB, that's significantly less than
PAR of OFDM (10~12 dB) and SC-FDMA (7~8.5dB).
• Because of absence of DFT the SC-WFMT system can be used for
transmission of broadband signals like TV or broadcast satellite. Note that,
in SC-WFMT system, both FFT and IFFT transforms have the same
order(M) and may use the same physical core.
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12. 0 5 10 15
-6
-5
-4
-3
-2
-1
0
PAPR in dB
CCDF
CCDF of TX signal
CCDF in baseband
CCDF in passband
Spectrum and CCDF of PARP for
SC-WFMT signal (Wavelet filter 1)
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PAPR= 7.5 dB
PAPR=5.5 dB
0.5 0.52 0.54 0.56 0.58 0.6 0.62 0.64 0.66 0.68
-100
-90
-80
-70
-60
-50
-40
-30
Normalized Frequency (rad/sample)
Power/frequency(dB/rad/sample)
Spectrum of TXIF signal after IF filter
65 dB
13. Spectrum and CCDF of PARP for
SC-WFMT signal (Wavelet filter 2)
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0 5 10 15
-6
-5
-4
-3
-2
-1
0
PAPR in dB
CCDF
CCDF of TX signal
CCDF in baseband
CCDF in passband
PAPR=6 dB
PAPR=3.5 dB
0.54 0.56 0.58 0.6 0.62 0.64 0.66 0.68
-100
-90
-80
-70
-60
-50
-40
-30
Normalized Frequency (rad/sample)
Power/frequency(dB/rad/sample)
Spectrum of TX IF signal after IF filter
14. Spectrum and CCDF of PARP for
SC-WFMT signal (Wavelet filter 3)
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0 5 10 15
-6
-5
-4
-3
-2
-1
0
PAPR in dB
CCDF
CCDF of TX signal
CCDF in baseband
CCDF in passband
PAPR=5.3 dB
PAPR=2.5 dB
0.55 0.6 0.65 0.7 0.75
-90
-80
-70
-60
-50
-40
-30
Normalized Frequency (rad/sample)
Power/frequency(dB/rad/sample)
Spectrum of TXIF signal after IF filter
19. SC-WFMT (mod QAM256) signal spectrum after
multipath channel
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20. Constellation diagram of received SC-WFMT
signal after equalizer.
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21. Equalizer coefficients
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0 20 40 60 80 100 120 140
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
real and image components of corrector(equalizer)
real after filter
real + noise
imag+noise
imag after filter
22. Frame correlator output
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0 0.5 1 1.5 2 2.5 3 3.5 4
x 10
4
-15
-10
-5
0
5
10
15
20
frame correlator output
TRAINING
SYMBOL
DATA
SYMBOL
DATA
SYMBOL
DATA
SYMBOL
23. Frame correlator output (details)
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2000 4000 6000 8000 10000 12000
-10
-5
0
5
10
15
frame correlator output
DATA SYMBOL
Cyclic Prefix
24. Constellation diagram on output
of non-linear RF AMPLIFIER
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-1 -0.5 0 0.5 1
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Quadrature
In-Phase
RX constellation diagram
Real and Image components of SC-WFMT Signal
on the output of non-linear RF POWER AMPLIFIER :
MODEL: Hyperbolic tangent , Gain = 20 dB,
IIP3 = 40 dB, AM/PM distortion = 2◦ / dB. Peak power of signal = 1 dB point.
25. Correction of distortion of RF amplifier (peak of
signal = +1dB-point + 2 dB)
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Before correction After correction
-1 -0.5 0 0.5 1
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Quadrature
In-Phase
RX constellation diagram before NPA corrector
-1 -0.5 0 0.5 1
-1
-0.5
0
0.5
1
Quadrature In-Phase
RX constellation diagram
Rapp Model , sat. point 31 dB
26. Parameters of SC-WFMT modulation
versus QPSK and OFDM for satellite appl.
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Parameter SC-WFMT QPSK OFDM NOTES
Channel Bandwidth 8 MHz 8 MHz 8 MHz
Data Rate (QPSK mode) 16 Mbps 16 Mbps 16 Mbps
Peak-to-Average Ratio 5~6 dB 5~6 dB 12 dB
Number of subcarriers 1025 1 2048
Symbol duration 144 us 125 ns 300 us
Max. available multipath delay spread 11 us 30 ns 20 us
Cyclic prefix duration 16 us no 50 us
Satellite transponder RF power (peak) ~ 10 W ~ 10 W ~ 160 W
Complexly of Transmitter Medium Low Medium
Complexity of Receiver High Low Medium
Immunity to phase noise and carrier
frequency offset
High Medium Low
Immunity to narrowband interference High Low High
Immunity to Doppler effect High High Low
Rejection of adjacent channel High Low Medium
27. SC-WFMT in return satellite channel
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SC-WFMT system with
Wavelet form 1 can be
successfully used in
return satellite channel
because of high sensitivity
of the ground receiver.
