Presentation on theme: "ECE 5221 Personal Communication Systems"— Presentation transcript:
1ECE 5221 Personal Communication Systems Prepared by:Dr. Ivica KostanicLecture 6: Link budgets and nominal cell planningSpring 2011
2Outline Vehicle penetration losses Building penetration losses Aggregate fade marginLink budget evaluationExamplesImportant note: Slides present summary of the results. Detailed derivations are given in notes.
3Vehicle penetration losses Many calls are made inside vehiclesMacroscopic propagation model predict “on the street level”Vehicle introduces additional signal lossesThese losses depend onType of vehicleVehicle orientationEnvironmentVehicle losses are variableTypically modeled as normal variable in log domainFor nominal cell planningMean vehicle loss; 6-8dBStandard deviation: 3dBHistogram of vehicle losses
4Building penetration losses Many calls are placed inside buildingsBuildings introduce additional lossesLosses depend on type of building, frequency of operation and environmentTreated as a random variable following normal distributionSome building penetration data from some published sources*:Building Frequency: 900MHz 1900MHzAmeritechContinentalJupiter N/AZurichCompriCitibankWoodfield Corp N/AMarriottNEC600 WoodfieldAverageStd* Garry C. Hess, Handbook of radio-mobile system coverage, Artech House, Inc, 1998Example building penetration measurementsCommonly assumed valuesused in design of RF systems (800/1900 MHz)Building type Average(dB) Std.(dB)Urban CoreUrban 15 8Suburban 10 6
5Cellular system from link budget point of view Link budget analysisUsed to determine maximum allowable path loss that balances two linksImportant: Cellular communication is 2-way – two links need to balanceUsually – mobile power smaller and the link budget is determined by the uplinkTypical process:Calculate uplink budgetAdjust BS power to have balanced linksIn nominal cell planning link budget is used to determine expected cell radiusFor nominal cell planning – three types of usersOn the streetIn vehicleIn buildingCellular system from link budget point of view
6Elements of link budget – Rx Sensitivity Rx sensitivity – minimum RSL required for an RF connection of sufficient qualityCalculated as:Where:kT – PSD of thermal noise ~ 4e-18 mW/HzB – bandwidth of the system expressed in HzF – noise figure expressed in dBS/N – required signal to noise ratio in dBComponents of RxSensExample. Consider technology with bandwidth of 200KHz, Rx noise figure of 7dB and min required S/N ratio of 12dB. Calculate the Rx sensitivity.Note: typically BS receivers have better sensitivity than the MS.
7Cable losses Cellular systems use coaxial cables There is a coaxial cable that connects each o the antennasLosses expressed in xdB/100feetFor a typical tower heights losses of the cables are on the order of 2-5dBStandard 50ohm impedanceThere may be other elements in Tx/Rx path introducing signal loss (duplexers, filters, jumper cables, splitters,…)In link budget analyses – all of the “pluming” losses need to be taken into accountCables on a cell towerCoaxial cablesNote: on the RX link cable losses are sometimes compensated through tower mounted amplifiers
8Omni-directional cell AntennasTwo configurations of antenna systemsOmnidirectionalSectored (usually 3 sectors/site)Nominally – 3 antennas/cellMiddle – transmitEdge – receive A,BTwo receive antennas provide diversity receptionWhen there is space constraint on tower, one of the antennas may duplex TX and RXAntennas are characterized byGain (6-15dB)Horizontal radiation patternVertical radiation patternOmni-directional cellTri-sector cell
9Penetration and body losses Penetration lossesVehicular lossesBuilding lossesSpecified by mean and stdMean added to the radio path lossesIndependence between the path loss and penetration losses is assumedPenetration losses contribute to the model uncertaintyTotal uncertainty-composite standard deviationExample. Consider system in an environment with model uncertainty of 8dB and path loss exponent of Calculate fade margin for in-building coverage assuming standard deviation of penetration losses of 6dB. The reliability requirement is 90%Answers:Composite standard deviation: 10dBZ-score:Fade margin: 7.44dB
10Simple link budget example EnvironmentPath loss exponent: 3.84Model uncertainty: 8dBPenetration lossesMean: 15dBStd: 6dBReliability: 90%Base stationTransmit power: 20WCable losses: 3dBAntenna gain: 9dBBandwidth: 200KHzNoise figure: 5dBRequired S/N: 12dBDiversity gain: 3dBMobileTransmit power: 2WAntenna gain: 0dBBandwidth: 200KHzNoise figure: 8dBRequired S/N: 12dBBody losses: 3dB1. Rx sensitivity at the base2. Rx sensitivity at the mobile
11Simple link budget example (cont.) 3. FM calculations4. Link budget spreadsheetNote: Max allowable path loss is greater for forward link