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

typical multiplier source

receiver performance

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/m 2 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

Clear air margin as a function of link length

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

SATCOM above 100GHz satellite transmitter power and rain fading are major problems

Aeronautical satellite system

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

Gigabit/s indoor communications Access point in corner of the room (ceiling height) with ~15 dB gain (~ 90 0 sector) 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

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 m 2 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

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)

Millimetre wave system limiting performance

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