Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio...
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![Page 1: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data.](https://reader035.fdocuments.in/reader035/viewer/2022062421/56649d9f5503460f94a8983b/html5/thumbnails/1.jpg)
Third Generation (3G) Systems
• Universal cell phones
• Mobile multimedia- Net phones
• Satellite radio
• Wireless internet
• Wireless local loops - Local data links- Bluetooth- Last-mile applications
• Automotive multimedia
3G “broadband, wireless communication systems”
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Some Needs for 3G Wireless
Average Power(W)Frequency Now Needed Backoff Application
Cellular0.8 GHz 100 600 MCPA cellular1.9 GHz 40 ≥200 8-10 dB IMT-2000 PCS2.1 GHz 40 100-200 8-10 dB IMT-2000
Satellite2.3 GHz 125 4000 0 Satellite Radio12 GHz 125 200-400 0 DirecTV
Mobile2.3 GHz 200 650 6 dB SatRad repeaters2.6 GHz 20 200 10 dB MMDS
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More Power….why?
• Higher data rates
- higher bit transfer rates
- increase symbol transfer rate with complex encription (16QAM, etc)
- broadband modulation schemes (CDMA, OFDM) require high peak power
• Improved amplifier linearity
- lower adjacent channel power
- increased backoff off from peak power capability
(more linearity and higher peak-to-average ratio for CDMA &OFDM)
- feed forward linearization (make up for increased losses)
• Improved availability and reliability
- ability to compensate for weather (rain)
- ability to handle partial component failure (and still broadcast)
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Higher Data Rates
Bit Error Rate for several modulation types
• For fixed error rate, the energy per bit is fixed
• Higher data rates (more bits per second) require higher power
• Higher symbol rate requires higher energy per bit, which corresponds to higher power
6 8 10 12 14 16 18 20
Energy-per-bit/Noise-density (E /N in dB)
10-1
-2
-3
-4
-5
-6
10
10
10
10
10
10
10
10
10
-7
-8
-9
-10
b o
Bit Error Rate (BER)
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Crest Factors for Spread-Spectrum Signals
Broadband, spread-spectrum signals have high peak to average ratios (high “crest-factors”)
• Advanced modulation techniques cause higher peak to average ratios due to “phase add up”
• For a given average power, these waveforms require higher peak power
0.01
0.1
1
10
100
-15 -10 -5 0 5 10 15
Time (%)
Output Power (dB relative to average)
AWGN waveform
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Adjacent Channel Power Intermodulation Distortion
Carriers
3rd-orderdistortion
C/3IM (dBc)
(2f -f ) f f1 2 1 2 (2f -f )12
2 MHz/div
3rd-orderIMD
5th-orderIMD
Carriers
1.9 GHz
Video Ave.50 sweeps
8-Tones
2-Tones
• Multi-tone operation produces intermodulation distortion (IMD)
• Intermodulation products cause adjacent channel power problems
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Adjacent Channel Power Reduction
Running amplifiers backed off from saturation for linearity (lower adjacent channel power) requires higher peak power
Backoff from non-linear region
20
25
30
35
40
45
50
456789101112
2-Tone C/3IM (dBc)
Backoff from Saturation (dB)
Improve IMD
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Adjacent Channel Power Reduction
Multi-Channel Power Amplifier(with feed-forward circuit)
InputSignal
Output
PowerAmp
CorrectionAmp
Delayline
Delayline
Pre-distorter
-10 to -20 dBc ≈ -30 dBc -30 dBc
TWT TWT with feedforward
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Solid State rf Devices
• Solid state device frequency and power
• New developments driven by communications needs
• Single device power level still insufficient (6 dB backoff from 50 W is only about 10 W per transistor)
• How do we get more power?
3 MHz 30 MHz 300 MHz 3 GHz 30 GHz 300 GHz
HF VHF UHF µwave mm-wave
Si MOSFETs, JFETs
Bipolar transistors
GaAs, GaN FETs
from "RF Power Design Techniques"by I.M. Gottlieb
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Power Combining
Gain Power
Input Output
Power combined arrays are required
• Solid state devices have limited gain and power capability per device
• Use series and parallel arrays to produce gain and power
1
2
3
4
5
6
7
8
5 10 15 20 25 30 35
Peak RMS Electric Field
Number of Tones
Coherent Phase
Random Phase
• Broadband produces high peak electric fields
• Many devices needed to avoid breakdown damage
(≈10 dB per device)
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Solid-State Arrays - Issues
• Combiner losses are significant for large numbers of devices - ultimately adding more devices doesn’t give more power
• Reliability of an array (many-components)- failures from transients, junction avalanche, overdrive, high VSWR, etc.
• Aging of solid state devices- metal migration at high current density and high junction temperature- corrosion of intermetal contacts- thermal fatigue
“Aging” produces:- transconductance decrease- threshold voltage changes- resistance changes- operating point changes (impedance change)- power and gain degradation
Example: two devices in a Wilkinson power combinerpower output decreases directly with impedance change
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The Solution - VED
• Traveling wave tubes and klystrons are used in ≥90% of the satellite communcation applications with demonstrated life and reliability well in excess of solid state amplifiers!
Tubes work everywhere within this box
Vacuum Electronic Devices
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Amplifier Efficiency
TWTs are much more efficient than solid state amplifiers
All data points are for multi-channel PCS amplifiers with feedforward linearization and -70 dBc IMD
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Highest Power LDMOS PCS Solid State Devices
Amplifier Linearity
Solid state devices and tubes have similar linearity, but tubes have significantly higher power capabilities!
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Satellite Radio Systems
Power combined array of 48 TWTs produces ≥4 kW of radiated power
Estimated link budget
Input Output
x 48TWTs
Satellite Transmitter
entered values
frequency (GHz) 2.34wavelength (m) 0.1281amplifier power (Watts) 4000power (dBm) 66.00
3.94.8
antenna efficiency (%) 70transmitter antenna gain (dB) 38.96EIRP 104.99distance (km) 35,784propagation loss (dB) -190.91atmosperic loss 2 -2.00
0.050.05
antenna efficiency (%) 55receiver antenna gain (dB) -0.83receiver noise figure (dB) 13background sky temperature (K) 25equivalent temperature (K) 5,521No, noise level (dBm/Hz) -161.18
received C/No (dB/Hz)data rate (bps) 7,000,000 -68.45
Eb/No (dB) 3.99
transmitter elliptic antennadimensions (m)
receiver elliptic antennadimensions (m)
calculated valuesParameters
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Power combining of TWTs
Power combining of two TWTs
Amplitude
Phase
P = 0.5[P1 + P2 + 2(P1 P2 )1/2 cos
Depends on power and phase balance(10 deg of phase or 2 dB in power exceeds Magic-T losses)
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Phase versus input drive measured for 35 TWTs
Phase Variability of TWT array
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
5
Phase change (degrees)
Input Power (dBm relative to sat)-35 -30 -25 -20 -15 -10 -5 0
(a)
0
2
4
6
8
10
-10 -5 0 5 10
Count
Phase relative to the mean at sat (deg)
σ=2.6˚
( )b
• The power loss in the array of TWTs is proportional to cos
• Using the phase deviation from the mean, the total power loss at saturation is about 0.1%
• Measured phase distribution creates negligible power loss
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Gain versus input drive measured for 35 TWTs
Gain Variability of TWT array
Gain distribution ±0.5 dB at saturation
Produces very small power variation
Gain is stable after sufficient burn-in time
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
-15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0
Input power (dBm relative to saturation)
Gain Change (dB relative to gain at P )
ave
48
50
52
54
56
58
-500 0 500 1000 1500 2000 2500 3000 3500
Ka-band (-15 dB)Ku-band (-1 dB)C-band
theoryS-band (-1 dB)
Saturated Gain (dB)
Time (hours)
τ=1000hrs
τ=400hrs
τ=330hrs
-pre burn
τ=2400hrs
G f = αIbσ hκ fτPoΓολ 1-e- /w λ
( )2 e kT A w2 1-e- /t τ +
PbtPoτ
⎡
⎣⎢⎤
⎦⎥+ Go
D.M.Goebel, “Theory of Long Term Gain Growth in Traveling Wave Tubes, IEEE Transactions on Electron Devices, 42 (2000) p.1286.
Gain change with time for different types of TWTs
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Power Combining Results
• 3G telecommunications applications require operation 6 to 10 dB backed off from saturation for linearity, but spread spectrum signals still sample saturation due to high “crest factor”
• Phase and gain variations were measured for 35 Model 5525H TWTs operated 6 dB backed off from saturation
• Arrays of these TWTs with ≤5˚ phase variation and ≤1 dB gain variation at saturation produce negligible power combining losses (≤0.2%)
• Primary losses at low power are in the combiners (Wilkenson, hybrids), and the primary cost at high power is in the waveguide combiners
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Conclusion
Many 3G applications need higher transmit power at higher frequency, in addition to other features like linearity, high efficiency, low cost, etc.
“The requirements for a high power and higher frequency technology continue to point obstinately in the direction of the vacuum device.”
S.C. Cripps, RF Power Amplifiers for Wireless Communication, Artech (1999)