Microwave Design Considerations

Microwave design considerations ROUTE AND SITE SELECTION •

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MUST HAVE COMPLETED PRELIMINARY FACILITY PLANNING  OPERATIONAL REQUIREMENTS  TRAFFIC STUDIES (SYSTEM’S CAPACITY)  EXPANSION POTENTIAL  RELIABILITY REQUIREMENTS  COST STUDIES MAPS & AERIAL PHOTOGRAPHS ARE SOURCES OF PRELIMINARY STUDIES FINAL SITE SELECTIONS ARE MADE BASE ON FIELD SURVEYS

SITE REQUIREMENTS • • • • •

TERMINAL SITES ARE NORMALLY LOCATIONS OF EXISTING STRUCTURES TAKE INTO ACCOUNT THE FUTURE BUILDING CONSTRUCTION ALONG THE PATH SITES SHOULD BE AS LEVEL AS POSSIBLE. COST OF LEVELING MUST BE CONSIDERED PATH DISTANCE IS ABOUT 25 TO 35 mi FROM 2 TO 8 GHz BAND ACCESS ROADS, AVAILABILITY OF AC POWER & TELEPHONE FACILITIES

SITE CONSIDERATIONS § § § § § § § § §

GEOGRAPHICAL COORDINATES, POLITICAL SUBDIVISION, ACCESS ROADS & LANDMARKS THAT WILL IDENTIFY THE SITE UNUSUAL WEATHER CONDITIONS  MAX WIND VELOCITY, SNOW & ICE ACCUMULATIONS, RANGE OF TEMP PHYSICAL CHARACTERISTICS  LEVELING REQUIRED, REMOVAL OF ROCKS. TREES OR OTHER STRUCTURES CHECK IF SITE IS A POTENTIAL OBSTRUCTION TO AIR TRAFFIC MEAN SEA LEVEL ELEVATION AT THE TOWER LOCATION FULL DESCRIPTION FOR AN ACCESS ROAD FROM THE NEAREST IMPROVED ROAD BUILDING CODE RESTRICTIONS ON THE SITE NEAREST LOCATION OF COMMERCIAL ELECTRIC POWER NEAREST TELEPHONE FACILITY

§

OTHER IMPORTANT FACTS THAT CAN BE SEEN DURING THE FIELD SURVEY

LOSSES ALONG THE MICROWAVE PATH § WHEN THE SIGNAL GRAZES AN OBSTACLE IT MAY SUFFER A LOSS OF 6 TO 20 dB DEPENDING ON THE TYPE OF SURFACE  KNIFE EDGE DIFFRACTION RESULTS TO A 6 dB LOSS BASE ON EXPERIMENTS  SMOOTH SURFACE (FLAT TERRAIN OR WATER) PRODUCE THE MAXIMUM LOSS  LOSSES DUE TO TRESS IS ABOUT 6 dB DIFFRACTION VS REFRACTION

LESS DENSE MORE DENSE

§ § §

FOG CONDITIONS MAY RESULT TO TEMPERATURE INVERSION (VERY STILL AIR) ACCOMPANIED BY STRATIFICATION NEGATING CLEARANCES ABOVE 10 GHz, RAIN ATTENUATION MAY BE SEVERE. THE ATTENUATION WILL DEPEND ON THE RATE OF RAINFALL, THE SIZE OF DROPS AND LENGTH OF EXPOSURE ATMOSPHERIC ABSORPTION DUE TO OXYGEN AND WATER VAPOR IS PROPORTIONAL TO THE PATH LENGTH

FRESNEL ZONE §

FRESNEL ZONES ARE A SERIES OF CONCENTRIC ELLIPSOIDS SURROUNDING THE PATH  THE 1ST FRESNEL ZONE IS THE SURFACE CONTAINING EVERY POINT FOR WHICH THE SUM OF THE DISTANCES FROM THAT POINT TO THE TWO ENDS OF THE PATH IS EXACTLY ONE-HALF WAVELENGTH LONGER THAN THE DIRECT PATH  INFLUENCE OF OBJECTS ALONG THE PATH

EARTH PROFILE § §

TYPICAL SCALE: V - 1 INCH: 100 ft H - 1 INCH: 2 mi TO PRESERVE THE PROPER RELATIONSHIP, IF THE DISTANCE SCALE IS DOUBLED, THE HEIGHT SCALE SHOULD BE QUADRUPLED h = d1d2 / 1.50 k where: d1, d2 - in miles h - in feet k - the equivalent earth radius factor

FIELD SURVEY OBJECTIVES § § § § § § § §

VERIFY EXACT SITE LOCATION VERIFY LINE OF SIGHT CLASSIFY PATH TYPE CONFIRM SPACE IN EXISTING STATIONS CHECK PROPAGATION CONDITIONS CHECK FREQUENCY INTERFERENCE POSSIBILITIES CHECK SOIL CONDITION FOR NEW TOWERS CHECK SITE ACCESS AND INFRASTUCTURE IN THE AREA

SURVEY PROCEDURES §

PREPARATION In order to reduce the field work, a detailed map study is always a good start. Maps to scale of 1:50,000 (or more detailed) should be used. Critical obstacles must be marked and possible reflection points should be noted. Preliminary antenna heights can be determined at this stage. §

FIELD WORK - VERIFICATION OF THE SITE POSITIONS AND ALTITUDES - CONFIRMATION OF LINE OF SIGHT - PATH CLASSIFICATION (OVERLAND PATHS / COASTALLINKS OR OVER THE WATER PATHS) - PROPAGATION CONDITIONS - FREQUENCY INTERFERENCE PROBABILITIES - SOIL INVESTIGATIONS - INFRASTUCTURE IN THE AREA (EX. PRESENCE OF COMMERCIAL POWER; ACCESS ROADS)

SURVEY EQUIPMENTS § § § § § § § § § § § § § § §

MAPS (SCALE OF 1:50,000 OR BETTER) DIGITAL CAMERA BINOCULARS COMPASS ALTIMETERS THERMOMETER SIGNALLING MIRRORS HAND-HELD RADIO COMMUNICATION EQUIPMENT TAPE MEASURE GPS RECEIVER ANTENNA HORNS LOW NOISE AMPLIFIER SPECTRUM ANALYZER PORTABLE PERSONAL COMPUTER CELLULAR PHONE OR WALKIE-TALKIE

SURVEY REPORT §

AFTER THECOMPLETION OF THE FIELD SURVEY, A REPORT IS NORMALLY PREPARED THAT CONTAINS THE FOLLOWING: - SYSTEM DESCRIPTION - SITE DESCRIPTION AND LAYOUT - ANTENNA AND TOWER HEIGHTS - PATH PROFILES - SYSTEM PERFORMANCE CALCULATIONS - FREQUENCY PLANS - PHOTOGRAPHS

DIFFICULT AREAS FOR MICROWAVE LINKS OVER THE WATER PATHS - DUE TO HIGH REFLECTION COEFFICIENT AND PROBABILITY OF DUCTING - SWAMP AND RICE FIELDS - CAUSE STRONG GROUND RFLECTIONS/MULTIPATH FADING. PROPAGATION CONDITIONS VARIES DEPENDING ON THE WEATHER CONDITIONS. CRITICAL PERIOD IS THE RAINY SEASON. - DESERT AREAS - HIGH PROBABILITY OF MULTIPATH FADING AND DUCTING DUE TO LARGE TEM[PERATURE VARIATIONS AND INVERSIONS - HOT AND HUMID COASTAL AREAS

- HIGH DUCTING PROBABILITY PRECIPITATION MICROWAVE SIGNALS ARE VULNERABLE TO PRECIPITATION ABOVE 10 GHz. RAIN, SNOW, ICE PARTICLES MAY ATTENUATE AND SCATTER MICROWAVE SIGNALS. THE ENERGY IS ATTENUATED DUE TO RADIATION (SCATTER) AND ABSORPTION (HEATING). THE ATTENUATION DUE TO ABSORPTION IS LARGER THAN THE ATTENUATION DUE SCATTER FOR WAVELENGTH SMALLER THAN THE DROP SIZE WHILE THE ATTENUATION DUE TO SCATTER IS GREATER THAN THE ATTENUATION DUE ABSORPTION WHEN THE WAVELENGTH IS LARGER THAN THE DROP SIZE. CHARACTERISTICS OF PRECIPITATION §

OROGRAPHIC PRECIPITATION - DETERMINED BY THE TERRAIN IN THE AREA OF INTEREST. FORCED UPLIFT OF MOIST AIR OVER HIGH GROUND GIVES PRECIPITATION WHEN THE DEW POINT IS REACHED. §

CONVECTIONAL PRECIPITATION - HEAVY CLOUDS MAY BUILD UP IN THE AFTERNOON ON A HOT SUMMER DAY DUE TO CONVECTION OF HOT HUMID AIR. THESE MAY RESULT TO INTENSE RAIN(HAIL) WITH THUNDER. §

CYCLONIC PRECIPITATION - CHARACTERIZED BY LARGE SACLE VERTICAL MOTIONS A ASSOCIATED WITH SYPNOTIC FEATURES SUCH AS DEPRESSIONS AND FRONTS - TROPICAL CYCLONE STORMS - IN TROPICAL AREAS, MOVING CIRCULAR STORMS WITH INTENSE CONVECTIVE RAIN MAY OCCUR WITH HEAVY RAIN 5- TO 200 km IN DIAMETER EXTENDED SEVERAL HOURS A DAY (e.g. MONSOON RAIN)

TYPES OF FADING NON-SELECTIVE OR FLAT FADING - ALL COMPONENTS OF THE USEFUL SIGNAL SPECTRUM WILL BE EQUALLY REDUCED. - SELECTIVE FADING - SOME OF THE SPECTRAL COMPONENTS WILL BE REDUCED CAUSING DISTORTION IN THE SPECTRUM AFFECTING DIGITAL RADIO IN THE FOLLOWING WAYS: - REDUCES THE S/N AND INCREASING THE BER - REDUCES THE CARRIER TO INTERFERENCE RATIO AND INCREASING THE BER - DISTORTS THE DIGITAL PULSE WAVEFORM RESULTING IN INTERSYMBOL INTERFERENCE AND INCREASING THE BER - INTRIDUCING CROSSTALK BETWEEN TWO ORTHOGONAL CARRIERS (THE I RAIL AND Q RAIL) AND CONSEQUENTLY INCREASING THE BER REFLECTION POINT CALCULATIONS K = INFINITY H1 H1+H 2

=

D1 D1+D 2

K = 2/3 H1

H2 = D1 D1 D2

- D2

K= 4/3

H D H D = 1 12 2 22 D D 1 2

Where: H1(ft) – elevation of lower antenna above the reflecting surface : H2(ft) – elevation of the higher antenna above the reflecting surface: D1(mi) – distance of lower antenna from the reflection point: D2(mi) – distance of the higher antenna to the reflection point

NON DIVERSITY ANNUAL OUTAGES

ACTUAL FADE R = PROBABILITY RAYLEIGH FADE PROBABILITY FOR THE WORST MONTH:

Rm = a (10-5)(f/4)1.5 Where:

D – path length, miles f – frequency, GHz a = 4 (for vey smooth terrain including overwater) a = 1 (for average terrain with some roughness) a = ¼ (for mountainous, very rough or very dry) OVER A YEAR: Where: areas)

Ryr = b (Rm) b = ½ (Gulf coast or similar hot, humid

b = ¼ (normal interior temperate or northern) b = 1/8 (mountainous or very dry) ACTUAL FADE PROBABILITY:

Undp = ab(1.25 x 10-6)(f1.5)D3(10-FM/10)