Presentation on theme: "Florida Institute of technologies ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 6: Link budgets and nominal cell planning."— Presentation transcript:
Florida Institute of technologies ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 6: Link budgets and nominal cell planning Spring 2011
Florida Institute of technologies Page 2 Vehicle penetration losses Building penetration losses Aggregate fade margin Link budget evaluation Examples Outline Important note: Slides present summary of the results. Detailed derivations are given in notes.
Florida Institute of technologies Vehicle penetration losses Many calls are made inside vehicles Macroscopic propagation model predict on the street level Vehicle introduces additional signal losses These losses depend on oType of vehicle oVehicle orientation oEnvironment Vehicle losses are variable Typically modeled as normal variable in log domain For nominal cell planning oMean vehicle loss; 6-8dB oStandard deviation: 3dB Page 3 Histogram of vehicle losses
Florida Institute of technologies Building penetration losses Many calls are placed inside buildings Buildings introduce additional losses Losses depend on type of building, frequency of operation and environment Treated as a random variable following normal distribution Page 4 Some building penetration data from some published sources*: BuildingFrequency:900MHz1900MHz Ameritech Continental Jupiter11.7N/A Zurich Compri Citibank Woodfield Corp.12.4N/A Marriott NEC Woodfield Average Std * Garry C. Hess, Handbook of radio-mobile system coverage, Artech House, Inc, 1998 Commonly assumed values used in design of RF systems (800/1900 MHz) Building type Average(dB)Std.(dB) Urban Core2010 Urban158 Suburban106 Example building penetration measurements
Florida Institute of technologies Link budget analysis Used to determine maximum allowable path loss that balances two links Important: Cellular communication is 2-way – two links need to balance Usually – mobile power smaller and the link budget is determined by the uplink oTypical process: Calculate uplink budget Adjust BS power to have balanced links In nominal cell planning link budget is used to determine expected cell radius For nominal cell planning – three types of users oOn the street oIn vehicle oIn building Page 5 Cellular system from link budget point of view
Florida Institute of technologies Elements of link budget – Rx Sensitivity Rx sensitivity – minimum RSL required for an RF connection of sufficient quality Calculated as: Page 6 Where: kT – PSD of thermal noise ~ 4e-18 mW/Hz B – bandwidth of the system expressed in Hz F – noise figure expressed in dB S/N – required signal to noise ratio in dB Components of RxSens Example. 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.
Florida Institute of technologies Cable losses Cellular systems use coaxial cables There is a coaxial cable that connects each o the antennas Losses expressed in xdB/100feet For a typical tower heights losses of the cables are on the order of 2-5dB Standard 50ohm impedance There 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 account Page 7 Cables on a cell tower Coaxial cables Note: on the RX link cable losses are sometimes compensated through tower mounted amplifiers
Florida Institute of technologies Antennas Two configurations of antenna systems oOmnidirectional oSectored (usually 3 sectors/site) Nominally – 3 antennas/cell oMiddle – transmit oEdge – receive A,B oTwo receive antennas provide diversity reception When there is space constraint on tower, one of the antennas may duplex TX and RX Antennas are characterized by oGain (6-15dB) oHorizontal radiation pattern oVertical radiation pattern Page 8 Omni-directional cell Tri-sector cell
Florida Institute of technologies Penetration and body losses Penetration losses oVehicular losses oBuilding losses Specified by mean and std Mean added to the radio path losses Independence between the path loss and penetration losses is assumed Penetration losses contribute to the model uncertainty Total uncertainty-composite standard deviation Page 9 Example. 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: a)Composite standard deviation: 10dB b)Z-score: c)Fade margin: 7.44dB
Florida Institute of technologies Simple link budget example Environment oPath loss exponent: 3.84 oModel uncertainty: 8dB oPenetration losses Mean: 15dB Std: 6dB oReliability: 90% Base station oTransmit power: 20W oCable losses: 3dB oAntenna gain: 9dB oBandwidth: 200KHz oNoise figure: 5dB oRequired S/N: 12dB oDiversity gain: 3dB Mobile oTransmit power: 2W oAntenna gain: 0dB oBandwidth: 200KHz oNoise figure: 8dB oRequired S/N: 12dB oBody losses: 3dB Page Rx sensitivity at the base 2. Rx sensitivity at the mobile
Florida Institute of technologies Page 11 Simple link budget example (cont.) 3. FM calculations 4. Link budget spreadsheet Note: Max allowable path loss is greater for forward link