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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”

Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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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

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”

Page 2: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 3: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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)

Page 4: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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)

Page 5: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 6: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 7: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 8: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 9: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 10: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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)

Page 11: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 12: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 13: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 14: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

Highest Power LDMOS PCS Solid State Devices

Amplifier Linearity

Solid state devices and tubes have similar linearity, but tubes have significantly higher power capabilities!

Page 15: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 16: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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)

Page 17: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 18: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 19: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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

Page 20: Third Generation (3G) Systems Universal cell phones Mobile multimedia - Net phones Satellite radio Wireless internet Wireless local loops - Local data

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)