How to Design Outdoor Wireless #94802

How to Design Outdoor Wireless

Today isFebruary 2, 2013, I attended a workshopheld byaneducational institution, namedIDN(ID-Networkers)engaged incomputer networking, is locatedin Blok-M Jakarta. The event washeldat2 pmuntil6 pm, withspeakerMrAnsori, HeworksinPTPacificSatelliteNusantaraas"IP NetworkPlanning&MSS" He willgiveshortworkshopabout "How to DesignOutdoor Wireless". Below are thenotes Iquotedfromthis event


Frequency
Frequencyis avibrationspersecond inaelectric that always changing
Unit offrequencyis theHertzabbreviatedHz

FrequencyUnitare:
Kilohertz(kHz)
Megahertz (MHz)
Gigahertz(GHz)
Terahertz(THz)

Electromagnetic Spectrum

Wavelength
The distance betweentwo pointsaresameto onevibration
In awireless system,usually measuredin meters,centimetersormillimeters

Frequency Spectrum and Wavelength

Decibels (dB)‏
From : http://en.wikipedia.org/wiki/Decibel. The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level.

Transmit (Tx) Power Radiohas thepowerto distribute the signalat a particular frequency, poweris calledTransmit(Tx)andis calculated fromtheenergywhich is distributedthroughawidefrequency(bandwidth)
Received (Rx) Sensitivity Allradioshave apoint of no return, which is the statewhere theradiosignalreceivedlessthanthe prescribedRxSensitivityandradioare notable to viewdata. RxSensitivityareactuallyfromthe radiowill varydepending on many factors
Wireless LAN

The deviceused toconnecta computer network(LAN) usingair as thecommunication media. Frequencythatusedis a 2.4GHzor 5GHzfrequencybelonging totheISM(Industrial, ScientificandMedical) andUNII(UnlicensedNationalInformation Infrastructure)

The standardused is802.11x, where xis asubstandard consistingof:
802.112.4 GHz2 Mbps
802.11a5 GHz54 Mbps
2x802.11a5 GHz108 Mbps
802.11b2.4 GHz11 Mbps
2.4 GHz802.11g54Mbps
2.4 GHz802.11n108Mbps

Direct Sequence Spread Spectrum Also known asDirectSequenceCode DivisionMultiple Access(DS-CDMA), DSSSis one wayto spread thedigitalsignalmodulationin the air.
Frequency Hopping Spread SpectrumAlso known asFrequencyHoppingCode DivisionMultiple Access(FH-CDMA), FHSSradioemittedbyboundingbetweenfrequencythat is readily availableand followsaspecific algorithm, eitherat randomor specified.

Channel Assignments

Channel Assignments (cont'd)‏

Outdoor Site Survey1.The installationmust comply with therules ofLineof Sight
2.Requirestoweriftwo pointsare indifferent levels
3.Utilization ofa small powershould really betaken into account
4.Must be able toanticipateReflection,refraction, Diffraction, Interferencethat occurs

Line of SightApplyingLineof Sight(LOS)between theradiotransmitter and receiverantennasare the most important
Thereare twotypes ofLOSthatweshould note:
1.OpticalLOS-the abilityto see each otherfrom placeto place
2.LOSradio-a radioreceiverthe abilityto'see' thesignal emitted

Fresnel ZoneTo determineLineof Sight,FresnelZonetheoryshould be applied. FresnelZoneis a form ofarugby ballin between thetwo pointsthat make up theRFsignal path

Fresnel Zone (cont'd)‏Inthe event of adisruptioninthe firstFresnelZone, will be a lotgoing onthe variousissuesthatwill resultin thedeclineof hisperformance
The main problem is:
1.Reflection
2.Wavesthat propagatebeyond thecurve
3.Multipathfadingoccurs whenthesecondwavearrivesthatcauses a decrease insignalquality4.Refraction
Wave thatmovesdown thecurvemakes an angle, frequencieslessthan10GHzno effect ontherainorfog, at2.4GHz, the damping0:01dB/kmforthe rain150mm/hr

5. Diffraction
Waves propagatearound theinterferencetoward theshadows

Interference

Interferencecomesfrom sources that areintentionalorunintentionalsources



Radio Type

Antenna Type

Outdoor Configuration

Stages ofDesignOutdoor Wireless1. Pre-design:
Determine the number ofuser /topologiesto be created(PTP, PTMP, Mesh)
Considerregulation, Identification ofthe device to beused and howthe number anddeployment ofsubscriber
Considercapacitbandwidthrequirements,any applications thatwill be runningover thewireless network.
Considercost /budget
2. Site survey:PredictiveandphisycalSite Survey
3. MeasurementRF/link budget
4. Determining thelocation ofRadio/tower/repeater
5. Designdocumentation

Site Survey Tools
1. Aplication of predictive site survey :
Google earth, global mapper, radiomobile, dll
2. Compass
3. Binokular
4. GPS
5. RF Measurement tool
Laptop
Netscrumbler
AP/Client set

Global Mapper

1. Advantages
Topologyview/contourof the earth
Graphicalcalculationcleareancefresnel zone
Determiningthe location ofthe antennaheightandfrequency distributiongraphically.
2. Shortage
Do notincludelink budget calculation.