A Study into the Theoretical Appraisal of the Highest

Usable Frequencies

RA Contract AY 4329

Contributors

• The study concentrated on the millimetric and Infra red bands

– Propagation Chris Gibbins (RAL)

– Technology Dave Matheson (RAL)

– Systems Applications John Norbury (Satconsult)

Systems Applications to be evaluated

• Point to point fixed services 1 to 10 km• broadband fixed wireless access (P-MP & Mesh)• satellite communications• HAPS• Mobile systems• Personal area networks• home communications• very high data rate indoor communications• short range anti-collision vehicle radar• comparison of free space optical (FSO) systems with

millimetre wave systems

Specific gaseous attenuation at sea level

Specific rain attenuation

Power levels for oscillators

500 GHz 1,000 GHz 1,500 GHz

.01

0.1

1

10

Mill

iwatt

s

x2

x3

x4, or x5

cascaded multipliers

100

Upconverted power

Fundametal power

BWO tubes

Available Output Power

Diode multipliers

Downconverted power

Photonic mixers

Gunns, (amplifiers)

typical multiplier source

Phase Lock

Harmonic Mixer

x N

Waveguide Coupler

Fundamental Oscillator

Frequency Multiplier

Output Power

receiver performance

500 GHz 1,000 GHz 1,500 GHz

3

6

9

12

No

ise

Fig

ure

15

Available Receiver Performance

FP diode mixer

Receiver Nooise Figure

Amplifier technology

SHPdiode mixer

Superconducting mixer

Schottky diode mixer at 200 GHz

Important systems features

• Frequency range 100 to 1000 GHz and near infrared; bandwidth galore!

• high gain but compact antennas ( G ~ 50 dB; D=0.2m at 200 GHz)

• near field can be large; 266m at 1000 GHz for D=0.2m

• Restricted power levels; < 100 mw

• All scenarios are line of sight links or reflected paths

• RF safety level 100W/m2 in this frequency range could cause problems for very small antennas due to high flux density

• best performances on short paths with high gain antennas

System evaluation methodology

• RF powers and noise figures were shown in previous slides

• antenna sizes were chosen to be small and practical for low cost production

• C/N ~11 dB (Eb/No =8 dB using QPSK modulation, achieves a BER of 1 in 10^4 allows error free channel with coding)

• clear air margins include gaseous absorption

• additional margins for rain, fog and scintillation were calculated to determine systems availabilities

Typical performance for a LoS link with data rate ~ 600 Mbps

margin and fade levels for a 2 km path length

-10.0

0.0

10.0

20.0

30.0

40.0

50.0

100 200 300 400 500

frequency (GHz)

dB

clear airmargin

0.1% ITU-Rrain

0.01% ITU-Rrain

0.01% rainLOWTRAN

fog 200mvisibility

0.01%scintillations

Clear air margin as a function of link length

clear air margin as a function of link length

-50

-40

-30

-20

-10

0

10

20

30

40

50

100 200 300 400 500 600 700 800 900 1000

frequency (GHz)

marg

in (

dB

)

1 km

2 km

5 km

10 km

Fixed wireless access

• Data rates to users are between 2 and 10 Mbps each way; implies a base station down link rate of ~100 Mbps

• BFWA operating above 100 GHz as a fill-in to enhance capacity of a lower frequency P-MP system with

– narrow sector base station antenna ~25 dB gain

– user terminals ~15 cm diameter (similar to 40 GHz BFWA)

– maximum range ~ 2 km

– availabilities from 99.9% to 99.99%

– Or MESH system with smaller antennas ~ 10 cm

margin and fade levels for aMESH system with ~ 1 km path length

-10.0

0.0

10.0

20.0

30.0

40.0

50.0

100 200 300 400 500

frequency (GHz)

dB

clear airmargin

0.1% ITU-Rrain

0.01% ITU-Rrain

0.01% rainLOWTRAN

fog 200mvisibility

0.01%scintillations

SATCOM above 100GHz

satellite transmitter power and rain fading are major problems

Aeronautical satellite system

Margin from satellite to aircraft at 5 km height

-10.0

0.0

10.0

20.0

100 200 300 400 500 600

frequency GHz

dB

Margin (dB)

Mobile and nomadic systems

• access point is mounted at lamp post height (America traffic light position) with a high gain antenna( 40 gain dB) which illuminates the road for 0.5 to 1 km

• the mobile has a steerable patch antenna (5 cm diameter)

• range is up to 1 km• data rate ~100 Mbps • path with line of sight path or limited number of

reflections• system applicable to urban streets, motorways and

railways• weather has minimal effect

Mobile systems

margin and fade levels for a mobile/nomadic system at a range of 0.5 km

-10

0

10

20

30

40

50

100 200 300 400 500

frequency (GH z )

dB

clear air margin

0.1% ITU-R rain

0.01% ITU-R rain

fog 200 mvisibility0.01%scintillations0.01% rain(LOW TRAN)

Gigabit/s indoor communications

• Access point in corner of the room (ceiling height) with ~15 dB gain (~ 900sector)

• user antenna is ~3 cm diameter, which needs to be pointed to acquire best signal

• range 100m (I.e. large exhibition hall)• inverse square law assumed; i.e. l-o-s or good reflected

path• raw data rate ~1 Gbps• user transmitter RF power flux density near the allowed

safety limit at the lower frequencies• ample margin up to 400 GHz

Gigabit/s WiFi

Margins (dB) for Gbit ETHERNET

-10

0

10

20

100 200 300 400 500 600 700

frequency (GHz)

dB Margin (dB)

Anti collision radar

• Antenna size ~7 cm (size of license disc)• range 5 to 100 m• must operate in worst conditions 200mmh-1 and 5 m

visibility fog• target cross section assumptions

– either spherical target with 0.5 m2 area (low return signal)

– or specular reflection from number plate with 10 dB loss (high return signal)

– integration time 1 ms (target remains quasi stationary)

• pulse length ~20 ns requires 50 MHz bandwidth• operates up to at least 500 GHz

Anti collision radar

anti collision radar margins

-20.0

-10.0

0.0

10.0

20.0

30.0

40.0

50.0

100 300 500 700 900

frequency (GHz)

dB

margin forsphericaltarget withaveraging

margin forspecularreflection(noaveraging)200 mm/hr

fog 5 mvisibility

scintillations 0.01%

Series6

Series7

Series8

Attenuation in Fog

Free space optical systems (FSO)

• Available as commercial devices – operating on ranges from 100 m to several km

– data rates from 10 Mbps to 1 Gbps

• Operate in near infra red window (0.7 to 1 microns)• transmitter devices: lasers or LED• power limited by eye safety requirement• main operational problems

– beam wander due to turbulence

– cannot penetrate thick fog

– typical availabilities ~99%

Free space optical systems (FSO)

FSO margin with fade levels in rain, fog and turbulent conditions

0

20

40

60

80

100

0.0 1.0 2.0 3.0 4.0

link length (km)

dB

rainattenuation(0.01%time)fog 200 mpath

typical FSOfade margin

scintillation0.01%

Millimetre wave system limiting performance

margin for P-P at 100, 200, 300 & 400 GHz compared with rain and fog

-20

-10

0

10

20

30

40

50

0 2 4 6 8 10

link lenght km

dB

100 GHz

200 GHz

300 GHz

400 GHz

0.01% rain

fog at 300 GHz

Conclusions

• best performance obtained for short range systems with high gain antennas ; e.g. radar, MESH & short range devices up to 700 GHz (IR systems also)

• acceptable performance from LoS applications >1 km up to 5 km (up to 440 GHz) also useful for MESH applications

• gigabit distribution possible up to 300 GHz with personal networks and home networks limited to below 260 GHz

• poor performance with fixed satellite but could be used for niche market aeronautical satellites

• FSO systems have poorer performance in fog than millimetre wave systems in rain