Transcript Document

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
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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
Available Output Power
100
Fundametal power
x2
Milliwatts
10
Gunns, (amplif iers)
x3
BWO tubes
1
Upconverted power
x4, or x5
0.1
Diode multipliers
Downconverted power
cascaded multipliers
Photonic mixers
.01
500 GHz
1,000 GHz
1,500 GHz
typical multiplier source
Fundamental Oscillator
Frequency Multiplier
Waveguide Coupler
xN
P hase Lock
Harmonic Mixer
Output
P ower
receiver performance
Available Receiver Performance
15
Noise Figure
12
Receiver Nooise Figure
Amplifier technology
9
FP diode mixer
SHPdiode mixer
6
Superconducting mixer
3
500 GHz
1,000 GHz
1,500 GHz
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
50.0
clear air
margin
dB
40.0
30.0
0.1% ITU-R
rain
20.0
0.01% ITU-R
rain
10.0
0.01% rain
LOWTRAN
0.0
100
-10.0
200
300
400
frequency (GHz)
500
fog 200m
visibility
0.01%
scintillations
Clear air margin as a function
of link length
clear air margin as a function of link length
50
40
30
margin (dB)
20
1 km
10
2 km
0
100
-10
5 km
200
300
400
500
600
700
-20
-30
-40
-50
frequency (GHz)
800
900 1000
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
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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 a
MESH system with ~ 1 km path length
50.0
clear air
margin
dB
40.0
30.0
0.1% ITU-R
rain
20.0
0.01% ITU-R
rain
10.0
0.01% rain
LOWTRAN
0.0
100
-10.0
200
300
400
frequency (GHz)
500
fog 200m
visibility
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
20.0
Margin (dB)
dB
10.0
0.0
100
200
300
400
-10.0
frequency GHz
500
600
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
50
clear air margin
40
0.1% ITU-R rain
dB
30
0.01% ITU-R rain
20
10
0
100
200
300
400
-10
frequency (GH z )
500
fog 200 m
visibility
0.01%
scintillations
0.01% rain
(LOW TRA N)
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
20
dB
10
Margin (dB)
0
100 200 300 400 500 600 700
-10
frequency (GHz)
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
margin for
spherical
target with
averaging
50.0
40.0
margin for
specular
reflection
(no
averaging)
200 mm/hr
dB
30.0
20.0
10.0
0.0
-10.0100 300 500 700 900
fog 5 m
visibility
-20.0
frequency (GHz)
scintillation
s 0.01%
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
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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
rain
attenuation
(0.01%
time)
fog 200 m
path
100
dB
80
60
typical FSO
fade margin
40
20
scintillation
0.01%
0
0.0
1.0
2.0
3.0
link length (km)
4.0
Millimetre wave system
limiting performance
margin for P-P at 100, 200, 300 & 400 GHz
compared with rain and fog
50
40
100 GHz
30
dB
200 GHz
20
300 GHz
10
400 GHz
0.01% rain
0
-10
0
2
4
6
-20
link lenght km
8
10
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