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//-->Planning Wireless Broadbandan IntroductionSANOG 18Table of ContentsUnits We UsedB vs dBmMore Resources444Link BudgetingWhy budgetWhat is a link budgetWhere is our energyFade MarginsFree Space LossOur FormulaExample - Point to Point LinkHow Can We Improve a LinkAvailability and ReliabilityExample AvailabilityLine of Sight AnalysisFresnel ZonesFresnal Zone Example555566678810101111Planning SoftwareMore Resources1213Designing a Power SystemPower RequirementsHow to find your power requirements141414Storing ElectricityExample - Working Out Our Power UsageExample - Working Out Storage Requirements141515Units We UseUnderstanding our units gives us a much better understanding of what we are dealing with. Many of theunits we use in radio concern energy.UnitJouleWattDecibelShort Form What it IsJWdBEnergyPower. The rate energy is consumed. 1 W = 1 J persecondA logarithmic representation of a unit. Often in radiowe represent Watts or milliWatts in decibels (dBW ordBm)dB vs dBmThe difference between dB and dBm can be confusing and they are often used interchangeably.dBm is an absolute measure, it is directly related to a milliWatt. For example:1 dBm = 1 milliwatt12 dBm = 15.85 mWdB is a ratio measure, so it applies to any absolute power. It’s like multiplying the number. It can be likesaying we lose 5% of the power, or we halve the power. 3dB in loss roughly equal to halving the power.More ResourcesLink BudgetingWhy budgetWe do a link budget for the following reasons:1. To ensure our link will operate at all2. To estimate our link uptimes say on an annual basis3. To understand if we need to change any components (e.g radio, antenna, cables)4. To understand our full radio systemsWhat is a link budgetA link budget is effectively an energy budget. We are seeing ho much energy we lose through our radiosystem. If we lose too much energy the link will not operate or be unreliable. Many things contribute to theloss of energy across the system.• Losses at connectors or lightning arrestors• Losses through cables or waveguides• Losses through the air due to distance• Losses through the air due to atmospheric conditions• Losses due to water in the system (e.g. moisture in cables)We measure our energy in the system in Watts (W). To make life easier we represent watts logarithmicallyas decibels (dB), so decibels relative to a Watt becomes dBW and relative to a milliWatt becomes dBm.Representing values using decibels makes it easier to work with numbers. We can use addition andsubtraction rather than multiplication and division.Where is our energyTaking a very basic outline of a radio system. Energy losses are when the energy goes outside of thesystem. Energy itself cannot be created or destroyed.45673128RadioRadio [ Pobierz całość w formacie PDF ]